Wireless LAN control plane protocol for trusted WLAN access to EPC

3GPP TS 24.244 V14.1.0 (2017-06)
Technical Specification
3rd Generation Partnership Project;
Technical Specification Group Core Network and Terminals;
Wireless LAN control plane protocol for trusted WLAN access to EPC;
Stage 3
(Release 14)
	

The present document has been developed within the 3rd Generation Partnership Project (3GPP TM) and may be further elaborated for the purposes of 3GPP..
The present document has not been subject to any approval process by the 3GPP Organizational Partners and shall not be implemented.
This Specification is provided for future development work within 3GPP only. The Organizational Partners accept no liability for any use of this Specification.
Specifications and Reports for implementation of the 3GPP TM system should be obtained via the 3GPP Organizational Partners' Publications Offices.




Keywords
WLAN, access, LTE


3GPP
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Contents
 TOC \o "1-9" Foreword	 PAGEREF _Toc485387719 \h 6
1	Scope	 PAGEREF _Toc485387720 \h 6
2	References	 PAGEREF _Toc485387721 \h 6
3	Definitions and abbreviations	 PAGEREF _Toc485387722 \h 7
3.1	Definitions	 PAGEREF _Toc485387723 \h 7
3.2	Abbreviations	 PAGEREF _Toc485387724 \h 7
4	General	 PAGEREF _Toc485387725 \h 8
4.1	Overview	 PAGEREF _Toc485387726 \h 8
4.2	Protocol stack	 PAGEREF _Toc485387727 \h 8
4.2.1	General	 PAGEREF _Toc485387728 \h 8
4.2.2	UDP port numbers for WLCP	 PAGEREF _Toc485387729 \h 8
4.2.2.1	General	 PAGEREF _Toc485387730 \h 8
4.2.2.2	UE procedure	 PAGEREF _Toc485387731 \h 9
4.2.2.3	TWAG procedure	 PAGEREF _Toc485387732 \h 9
4.2.3	IP addresses of WLCP message	 PAGEREF _Toc485387733 \h 9
4.2.3.1	General	 PAGEREF _Toc485387734 \h 9
4.2.3.2	UE procedure	 PAGEREF _Toc485387735 \h 9
4.2.3.3	TWAG procedure	 PAGEREF _Toc485387736 \h 9
4.2.4	DTLS usage	 PAGEREF _Toc485387737 \h 10
4.3	WLCP layer states	 PAGEREF _Toc485387738 \h 10
4.3.1	General	 PAGEREF _Toc485387739 \h 10
4.3.2	WLCP layer states in the UE	 PAGEREF _Toc485387740 \h 10
4.3.2.1	PDN CONNECTIVITY NOT ESTABLISHED	 PAGEREF _Toc485387741 \h 10
4.3.2.2	PDN CONNECTIVITY ESTABLISHED	 PAGEREF _Toc485387742 \h 10
4.3.2.3	PROCEDURE TRANSACTION INACTIVE	 PAGEREF _Toc485387743 \h 10
4.3.2.4	PROCEDURE TRANSACTION PENDING	 PAGEREF _Toc485387744 \h 10
4.3.3	WLCP layer states in the TWAG	 PAGEREF _Toc485387745 \h 11
4.3.3.1	PDN CONNECTIVITY NOT ESTABLISHED	 PAGEREF _Toc485387746 \h 11
4.3.3.2	PDN CONNECTIVITY PENDING	 PAGEREF _Toc485387747 \h 11
4.3.3.3	PDN CONNECTIVITY ESTABLISHED	 PAGEREF _Toc485387748 \h 11
4.3.3.4	PDN DISCONNECT PENDING	 PAGEREF _Toc485387749 \h 11
4.3.3.5	PROCEDURE TRANSACTION INACTIVE	 PAGEREF _Toc485387750 \h 12
4.3.3.6	PROCEDURE TRANSACTION PENDING	 PAGEREF _Toc485387751 \h 12
4.4	IP address allocation	 PAGEREF _Toc485387752 \h 12
5	Wireless LAN control plane protocol Procedures	 PAGEREF _Toc485387753 \h 12
5.1	General	 PAGEREF _Toc485387754 \h 12
5.1.1	Overview	 PAGEREF _Toc485387755 \h 12
5.1.2	Services provided by lower layers	 PAGEREF _Toc485387756 \h 12
5.1.3	Principles of address handling for WLCP procedures	 PAGEREF _Toc485387757 \h 12
5.1.4	Abnormal cases in the UE	 PAGEREF _Toc485387758 \h 13
5.1.5	Abnormal cases in the TWAG	 PAGEREF _Toc485387759 \h 13
5.1.6	Handling of APN based congestion control	 PAGEREF _Toc485387760 \h 13
5.2	PDN connectivity establishment procedure	 PAGEREF _Toc485387761 \h 13
5.2.1	General	 PAGEREF _Toc485387762 \h 13
5.2.2	PDN connectivity establishment procedure initiation	 PAGEREF _Toc485387763 \h 14
5.2.3	PDN connectivity establishment procedure accepted by the TWAG	 PAGEREF _Toc485387764 \h 15
5.2.3.1	PDN connectivity establishment accepted by the UE	 PAGEREF _Toc485387765 \h 16
5.2.3.2	PDN connectivity establishment not accepted by the UE	 PAGEREF _Toc485387766 \h 16
5.2.4	PDN connectivity procedure not accepted by the TWAG	 PAGEREF _Toc485387767 \h 16
5.2.5	Abnormal cases in the UE	 PAGEREF _Toc485387768 \h 18
5.2.6	Abnormal cases on the network side	 PAGEREF _Toc485387769 \h 18
5.3	TWAG initiated PDN disconnection procedure	 PAGEREF _Toc485387770 \h 19
5.3.1	General	 PAGEREF _Toc485387771 \h 19
5.3.2	Procedure description	 PAGEREF _Toc485387772 \h 19
5.3.3	Abnormal cases in the UE	 PAGEREF _Toc485387773 \h 20
5.3.4	Abnormal cases in the TWAG	 PAGEREF _Toc485387774 \h 20
5.4	UE requested PDN disconnection procedure	 PAGEREF _Toc485387775 \h 20
5.4.1	General	 PAGEREF _Toc485387776 \h 20
5.4.2	Procedure description	 PAGEREF _Toc485387777 \h 20
5.4.3	Abnormal cases in the UE	 PAGEREF _Toc485387778 \h 21
5.4.4	Abnormal cases in the TWAG	 PAGEREF _Toc485387779 \h 21
5.5	STATUS message	 PAGEREF _Toc485387780 \h 21
5.6	TWAG initiated PDN connectivity modification procedure	 PAGEREF _Toc485387781 \h 22
5.6.1	General	 PAGEREF _Toc485387782 \h 22
5.6.2	Procedure description	 PAGEREF _Toc485387783 \h 22
5.6.3	PDN connectivity modification procedure accepted by the UE	 PAGEREF _Toc485387784 \h 22
5.6.4	PDN connectivity modification procedure not accepted by the UE	 PAGEREF _Toc485387785 \h 22
5.6.5	Abnormal cases in the UE	 PAGEREF _Toc485387786 \h 23
5.6.6	Abnormal cases in the TWAG	 PAGEREF _Toc485387787 \h 23
5.7	UE requested PDN connectivity modification procedure	 PAGEREF _Toc485387788 \h 23
5.7.1	General	 PAGEREF _Toc485387789 \h 23
5.7.2	Procedure description	 PAGEREF _Toc485387790 \h 23
5.7.3	PDN connectivity modification procedure accepted by the network	 PAGEREF _Toc485387791 \h 24
5.7.4	PDN connectivity modification procedure not accepted by the network	 PAGEREF _Toc485387792 \h 24
5.7.5	Abnormal cases in the UE	 PAGEREF _Toc485387793 \h 24
5.7.6	Abnormal cases in the TWAG	 PAGEREF _Toc485387794 \h 25
5.8	PGW initiated local PDN disconnection in the TWAG	 PAGEREF _Toc485387795 \h 25
5.8.1	General	 PAGEREF _Toc485387796 \h 25
5.8.2	Procedure description	 PAGEREF _Toc485387797 \h 25
5.9	Local PDN disconnection in the UE initiated from 3GPP access	 PAGEREF _Toc485387798 \h 25
5.9.1	General	 PAGEREF _Toc485387799 \h 25
5.9.2	Procedure description	 PAGEREF _Toc485387800 \h 25
6	Handling of unknown, unforeseen, and erroneous protocol data	 PAGEREF _Toc485387801 \h 25
6.1	General	 PAGEREF _Toc485387802 \h 25
6.2	Message too short	 PAGEREF _Toc485387803 \h 26
6.3	Unknown or unforeseen procedure transaction identity or PDN connection ID	 PAGEREF _Toc485387804 \h 26
6.3.1	Procedure transaction identity	 PAGEREF _Toc485387805 \h 26
6.3.2	PDN connection ID	 PAGEREF _Toc485387806 \h 26
6.4	Unknown or unforeseen message type	 PAGEREF _Toc485387807 \h 27
6.5	Non-semantical mandatory information element errors	 PAGEREF _Toc485387808 \h 27
6.5.1	Common procedures	 PAGEREF _Toc485387809 \h 27
6.5.2	PDN connection management	 PAGEREF _Toc485387810 \h 28
6.6	Unknown and unforeseen IEs in the non-imperative message part	 PAGEREF _Toc485387811 \h 28
6.6.1	IEIs unknown in the message	 PAGEREF _Toc485387812 \h 28
6.6.2	Out of sequence IEs	 PAGEREF _Toc485387813 \h 28
6.6.3	Repeated IEs	 PAGEREF _Toc485387814 \h 28
6.7	Non-imperative message part errors	 PAGEREF _Toc485387815 \h 28
6.7.1	General	 PAGEREF _Toc485387816 \h 28
6.7.2	Syntactically incorrect optional IEs	 PAGEREF _Toc485387817 \h 29
6.7.3	Conditional IE errors	 PAGEREF _Toc485387818 \h 29
6.8	Messages with semantically incorrect contents	 PAGEREF _Toc485387819 \h 29
7	Message functional definitions and contents	 PAGEREF _Toc485387820 \h 29
7.1	PDN connectivity request	 PAGEREF _Toc485387821 \h 29
7.1.1	Message definition	 PAGEREF _Toc485387822 \h 29
7.1.2	Access point name	 PAGEREF _Toc485387823 \h 30
7.1.3	Protocol configuration options	 PAGEREF _Toc485387824 \h 30
7.1.4	NBIFOM container	 PAGEREF _Toc485387825 \h 30
7.2	PDN connectivity accept	 PAGEREF _Toc485387826 \h 30
7.2.1	Message definition	 PAGEREF _Toc485387827 \h 30
7.2.2	Protocol configuration options	 PAGEREF _Toc485387828 \h 31
7.2.3	Cause	 PAGEREF _Toc485387829 \h 31
7.2.4	NBIFOM container	 PAGEREF _Toc485387830 \h 31
7.3	PDN connectivity reject	 PAGEREF _Toc485387831 \h 31
7.3.1	Message definition	 PAGEREF _Toc485387832 \h 31
7.3.2	Protocol configuration options	 PAGEREF _Toc485387833 \h 32
7.3.3	Tw1 value	 PAGEREF _Toc485387834 \h 32
7.4	PDN disconnect request	 PAGEREF _Toc485387835 \h 32
7.4.1	Message definition	 PAGEREF _Toc485387836 \h 32
7.4.2	Protocol configuration options	 PAGEREF _Toc485387837 \h 32
7.5	PDN disconnect accept	 PAGEREF _Toc485387838 \h 33
7.5.1	Message definition	 PAGEREF _Toc485387839 \h 33
7.5.2	Protocol configuration options	 PAGEREF _Toc485387840 \h 33
7.6	PDN disconnect reject	 PAGEREF _Toc485387841 \h 33
7.6.1	Message definition	 PAGEREF _Toc485387842 \h 33
7.6.2	Protocol configuration options	 PAGEREF _Toc485387843 \h 33
7.7	PDN connectivity complete	 PAGEREF _Toc485387844 \h 34
7.7.1	Message definition	 PAGEREF _Toc485387845 \h 34
7.8	Status message	 PAGEREF _Toc485387846 \h 34
7.8.1	Message definition	 PAGEREF _Toc485387847 \h 34
7.9	PDN modification request	 PAGEREF _Toc485387848 \h 34
7.9.1	Message definition	 PAGEREF _Toc485387849 \h 34
7.9.2	Protocol configuration options	 PAGEREF _Toc485387850 \h 35
7.9.3	NBIFOM container	 PAGEREF _Toc485387851 \h 35
7.10	PDN modification accept	 PAGEREF _Toc485387852 \h 35
7.10.1	Message definition	 PAGEREF _Toc485387853 \h 35
7.10.2	Protocol configuration options	 PAGEREF _Toc485387854 \h 35
7.10.3	NBIFOM container	 PAGEREF _Toc485387855 \h 35
7.11	PDN modification reject	 PAGEREF _Toc485387856 \h 36
7.11.1	Message definition	 PAGEREF _Toc485387857 \h 36
7.11.2	Protocol configuration options	 PAGEREF _Toc485387858 \h 36
7.11.3	NBIFOM container	 PAGEREF _Toc485387859 \h 36
7.12	PDN modification indication	 PAGEREF _Toc485387860 \h 36
7.12.1	Message definition	 PAGEREF _Toc485387861 \h 36
7.12.2	Protocol configuration options	 PAGEREF _Toc485387862 \h 37
7.12.3	NBIFOM container	 PAGEREF _Toc485387863 \h 37
8	General message format and information elements coding	 PAGEREF _Toc485387864 \h 37
8.1	General	 PAGEREF _Toc485387865 \h 37
8.2	Message type	 PAGEREF _Toc485387866 \h 38
8.3	Procedure transaction identity	 PAGEREF _Toc485387867 \h 38
8.4	Request type	 PAGEREF _Toc485387868 \h 39
8.5	PDN type	 PAGEREF _Toc485387869 \h 39
8.6	Access point name	 PAGEREF _Toc485387870 \h 39
8.7	Protocol configuration options	 PAGEREF _Toc485387871 \h 39
8.8	PDN address	 PAGEREF _Toc485387872 \h 39
8.9	PDN connection ID	 PAGEREF _Toc485387873 \h 39
8.10	User plane connection ID	 PAGEREF _Toc485387874 \h 40
8.11	Cause	 PAGEREF _Toc485387875 \h 40
8.12	GPRS timer 3	 PAGEREF _Toc485387876 \h 40
8.13	NBIFOM container	 PAGEREF _Toc485387877 \h 40
9	List of system parameters	 PAGEREF _Toc485387878 \h 41
9.1	Timers	 PAGEREF _Toc485387879 \h 41
Annex A (Informative):	IANA UDP port registration form	 PAGEREF _Toc485387880 \h 43
Annex B (informative):	Change history	 PAGEREF _Toc485387881 \h 45

Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x	the first digit:
1	presented to TSG for information;
2	presented to TSG for approval;
3	or greater indicates TSG approved document under change control.
y	the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc.
z	the third digit is incremented when editorial only changes have been incorporated in the document.
1	Scope
The present document specifies the procedures of the Wireless LAN control plane protocol (WLCP) for trusted WLAN access to EPC which is used between User Equipment (UE) and Trusted WLAN Access Gateway (TWAG) for multi-connection mode as specified in 3GPP TS 23.402 [2].
This document also defines the message format, information elements coding, error handling and system parameters applied by the WLCP protocol.
2	References
The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
-	References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific.
-	For a specific reference, subsequent revisions do not apply.
-	For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]	3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2]	3GPP TS 23.402: "Architecture Enhancements for non-3GPP accesses".
[3]	3GPP TS 24.302: "Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3".
[4]	3GPP TS 24.008: "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3".
[5]	3GPP TS 24.301: "Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3".
[6]	IEEE Std 802-2014: "IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture", 30th June 2014.
[7]	3GPP TS 24.007: "Mobile radio interface signalling layer 3; General aspects".
[8]	IETF RFC 768: "User Datagram Protocol"
[9]	3GPP TS 33.402: "3GPP System Architecture Evolution (SAE); Security aspects of non-3GPP accesses".
[10]	3GPP TS 24.161: "Network-Based IP Flow Mobility (NBIFOM); Stage 3".
[11]	3GPP TS 23.380: "IMS Restoration Procedures".
[12]	3GPP TS 29.274: "Tunnelling Protocol for Control plane (GTPv2-C); Stage 3".
3	Definitions and abbreviations
3.1	Definitions
For the purposes of the present document, the terms and definitions given in 3GPP TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP TR 21.905 [1].
PDN connection for emergency bearer services: A PDN connection which was activated with request type "emergency" or "handover of emergency bearer services".
3.2	Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in 3GPP TR 21.905 [1].
APN	Access Point Name
DTLS	Datagram Transport Layer Security
EAP	Extensible Authentication Protocol
EPC	Evolved Packet Core Network
ID	Identifier
IE	Information Element
IEI	Information Element Identifier 
LSB	Least Significant Bit
MAC	Media Access Control
MSB	Most Significant Bit
NBIFOM	Network-based IP flow mobility
PCO	Protocol Configuration Options
PDN	Packet Data Network
PDN GW	Packet Data Network Gateway
PTI	Procedure Transaction Identity
TWAG	Trusted WLAN Access Gateway
UE	User Equipment
WLAN	Wireless Local Area Network
WLCP	Wireless LAN control plane protocol
4	General
4.1	Overview
WLCP is used between user equipment (UE) and trusted wLAN access gateway (TWAG) for multi-connection mode as specified in 3GPP TS 23.402 [2].
The WLCP comprises procedures for:
-	establishment of PDN connections including initial request and handover from a 3GPP access;
-	requesting the release of a PDN connection by the UE or notifying the UE of the release of a PDN connection; 
-	transport of parameters related to PDN connections, such as APN, PDN type, PCO, handover indication, user-plane MAC address of the TWAG etc.; and
-	IP address allocation.
Generally, WLCP procedures described in the clause 5 can be performed only after the UE has successfully completed the following steps:
-	Authentication and negotiation of the multi-connection mode for the trusted WLAN access as specified in 3GPP TS 24.302 [3]; and
-	Establishment of a DTLS connection with the TWAG, according to subclause 4.2.4.
4.2	Protocol stack
4.2.1	General
The protocol stack of WLCP is shown in figure 4.2.1.
 EMBED Word.Picture.8  
Figure 4.2.1: Protocol stack of WLCP
4.2.2	UDP port numbers for WLCP
4.2.2.1	General
The WLCP messages are transported over UDP layer as specified in IETF RFC 768 [8]. The security is provided by the DTLS layer.
The WLCP UDP Port number is 36411.
4.2.2.2	UE procedure
The UE shall use the WLCP UDP port number as the source UDP port and the destination UDP port of WLCP messages.
4.2.2.3	TWAG procedure
The TWAG shall use the WLCP UDP port number as the source UDP port and the destination UDP port of WLCP messages. 
4.2.3	IP addresses of WLCP message
4.2.3.1	General
The WLCP/DTLS/UDP packet shall be carried via IPv6 with link local addressing scope or IPv4 as specified in 3GPP TS 23.402 [2].
4.2.3.2	UE procedure
The UE receives one or two TWAG control-plane addresses during the EAP authentication and authorization procedure as specified in 3GPP TS 24.302 [3] subclause 6.4.2.6.3.
NOTE:	If two TWAG control-plane addresses are received, one includes an IPv4 address and the other includes an IPv6 link-local address.
If the UE receives one TWAG control-plane address, the UE shall select the TWAG control-plane address. If the UE receives two TWAG control-plane addresses, the UE shall select one of the TWAG control-plane addresses.
The UE shall use the IP address of the selected TWAG control-plane address as the destination IP address of WLCP messages.
The UE shall apply the following procedures to set the source IP address of the WLCP message:
-	if the TWAG IP address for WLCP is an IPv4 address and if the UE supports IPv4, the UE shall obtain an IPv4 address via DHCPv4 to be used as the source IP address for WLCP;
-	if the TWAG IP address for WLCP is an IPv6 link-local address and if the UE supports IPv6, the UE shall use the IPv6 link-local address configured on the WLAN interface as the source IP address for WLCP; and
-	if the TWAG IP addresses for WLCP are an IPv4 address and an IPv6 link-local address, which IP version the UE selects is implementation dependent.
4.2.3.3	TWAG procedure
When the UE initiates a WLCP procedure:
-	the TWAG shall use a TWAG control plane address which was included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA' authentication as described in 3GPP TS 24.302 [3], as the source IP address for WLCP. If two TWAG control plane addresses were included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA' authentication as described in 3GPP TS 24.302 [3], the TWAG shall use the TWAG control plane address of the same IP version as the IP version received from the UE in the WLCP message; and
-	the TWAG shall use the source IP address received from the UE in the WLCP message as the destination IP address for further WLCP message to the UE.
When the TWAG initiates a WLCP procedure:
-	the TWAG shall use a TWAG control plane address which was included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA' authentication as described in 3GPP TS 24.302 [3], as the source IP address for WLCP. If two TWAG control plane addresses were included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA' authentication as described in 3GPP TS 24.302 [3], the TWAG shall use the TWAG control plane address of the same IP version as the IP version received from the UE in the WLCP message; and
-	the TWAG shall use the source IP address received from the UE in the earlier WLCP message as the destination IP address for further WLCP message to the UE.
4.2.4	DTLS usage
The UE and the TWAG shall use DTLS according to 3GPP TS 33.402 [9].
4.3	WLCP layer states
4.3.1	General
In this subclause the possible states of WLCP state machine in the UE and in the TWAG are described. Each PDN connection to EPC is associated with an individual state machine.
4.3.2	WLCP layer states in the UE
4.3.2.1	PDN CONNECTIVITY NOT ESTABLISHED
No PDN connectivity to EPC exists over TWAN (see figure 4.3.2.2.1).
4.3.2.2	PDN CONNECTIVITY ESTABLISHED
The PDN connectivity to EPC is established in the UE (see figure 4.3.2.2.1).
 EMBED Visio.Drawing.11  
Figure 4.3.2.2.1: The WLCP state machine in the UE (overview)
4.3.2.3	PROCEDURE TRANSACTION INACTIVE
No procedure transaction exists (see figure 4.3.2.4.1).
4.3.2.4	PROCEDURE TRANSACTION PENDING
The UE has initiated a procedure transaction towards the TWAG (see figure 4.3.2.4.1).
 EMBED Visio.Drawing.11  
Figure 4.3.2.4.1: The procedure transaction states in the UE (overview)
4.3.3	WLCP layer states in the TWAG
4.3.3.1	PDN CONNECTIVITY NOT ESTABLISHED
No PDN connectivity to EPC exists for the UE (see figure 4.3.3.4.1).
4.3.3.2	PDN CONNECTIVITY PENDING
The TWAG has sent PDN connectivity accept towards the UE (see figure 4.3.3.4.1).
4.3.3.3	PDN CONNECTIVITY ESTABLISHED
The PDN connectivity is established in the TWAG (see figure 4.3.3.4.1).
4.3.3.4	PDN DISCONNECT PENDING
The TWAG has initiated a PDN disconnect towards the UE (see figure 4.3.3.4.1).
 EMBED Visio.Drawing.11  
Figure 4.3.3.4.1: The WLCP states for PDN connectivity handling in the TWAG (overview)
4.3.3.5	PROCEDURE TRANSACTION INACTIVE
No procedure transaction exists.
4.3.3.6	PROCEDURE TRANSACTION PENDING
The TWAG has initiated a procedure transaction towards the UE (see figure 4.3.3.6.1).
 EMBED Visio.Drawing.11  
Figure 4.3.3.6.1: The procedure transaction states in the TWAG (overview)
4.4	IP address allocation
WLCP provides the following functionalities related to IP address allocation for multi-connection mode:
-	requesting PDN type by the UE;
-	allocating IPv4 address to the UE; and
-	allocating IPv6 interface identifier to the UE.
IPv6 network prefix is assigned via stateless address autoconfiguration method as specified in 3GPP TS 23.402 [2].
Deferred IPv4 address allocation is not supported in the current release of this specification.
5	Wireless LAN control plane protocol Procedures
5.1	General
5.1.1	Overview
This clause describes principles and procedures used for Wireless LAN control plane protocol for PDN connectivity handling in the UE and in the TWAG.
Re-transmission of WLCP messages for ensuring reliability of WLCP procedures is supervised by timers.
5.1.2	Services provided by lower layers
Unless explicitly stated otherwise, WLCP procedures can be performed only if the UE has been authenticated and has successfully negotiated the multi-connection mode for trusted WLAN access as specified in 3GPP TS 24.302 [3].
5.1.3	Principles of address handling for WLCP procedures
WLCP procedures use the PTI as address parameter in the WLCP message header. When the UE or the TWAG initiates a WLCP procedure, it shall include a valid PTI value in the message header (see subclause 8.3).
In the response message, the sending entity shall include the PTI value received with the request message.
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Figure 5.1.3.1: Procedure initiated by the UE
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Figure 5.1.3.2: Procedure initiated by the TWAG
5.1.4	Abnormal cases in the UE
No abnormal cases have been identified.
5.1.5	Abnormal cases in the TWAG
The following abnormal cases can be identified:
a)	Failure of EAP-AKA' re-authentication: 
	When the TWAG receives a failure indication of the re-authentication procedure, the TWAG shall initiate TWAG-initiated PDN disconnection procedure.
5.1.6	Handling of APN based congestion control
As specified in subclause 5.2.4, TWAG can reject PDN connection request for an APN from a UE and provide a Tw1 timer value to the UE.
5.2	PDN connectivity establishment procedure
5.2.1	General
The purpose of the PDN connectivity establishment procedure is to establish PDN connectivity between the UE and the EPC. The procedure is used either to establish the first PDN connection or to establish subsequent PDN connections. The procedure can be initiated only after successful EAP authentication and authorization has been completed and multi-connection mode of operation has been negotiated, as specified in 3GPP TS 24.302 [3].
The UE and the TWAG may include a Protocol configuration options IE in PDN connectivity establishment procedure if they wish to exchange (protocol) data (e.g. configuration parameters, error codes or messages/events).
If there is already a PDN connection for emergency bearer services established, the UE shall not request another PDN connection for emergency services.
If the UE attached for emergency services, i.e.received an MCM_RESPONSE with the AT_NOTIFICATION attribute indicating success for an MCM_REQUEST with ATTACHMENT_TYPE item set to "emergency attach" or "emergency handover" as specified in 3GPP TS 24.302 [3]: 
-	the UE shall establish the first PDN connection for emergency services or perform handover of an emergency PDN connection from 3GPP access; and
-	the UE shall not request any additional non-emergency PDN connections so long as the UE is attached for emergency services.
5.2.2	PDN connectivity establishment procedure initiation
The UE requests PDN connectivity establishment by sending a PDN CONNECTIVITY REQUEST message to the TWAG.
In order to request connectivity to a PDN using the default APN, the UE includes the Access point name IE in the PDN CONNECTIVITY REQUEST message according to the following conditions:
-	if use of a PDN using the default APN requires PAP/CHAP, then the UE should include the Access point name IE; and
-	in all other conditions, the UE need not include the Access point name IE.
In order to request connectivity to a non-default APN or to an additional PDN, the UE shall send a PDN CONNECTIVITY REQUEST message to the TWAG including the requested APN.
After sending the PDN CONNECTIVITY REQUEST message the UE shall start timer T3582 and enter the state PROCEDURE TRANSACTION PENDING (see example in figure 5.2.2.1).
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Figure 5.2.2.1: PDN connectivity establishment procedure
The UE shall set the PDN type IE in the PDN CONNECTIVITY REQUEST message to IPv4 if:
-	the UE is only IPv4 capable;
-	the UE is both IPv4 and IPv6 capable, has been allocated an IPv6 address for this APN and received the ESM cause #52 "single address bearers only allowed" and the request type is "initial request" or "emergency"; or
-	the UE is both IPv4 and IPv6 capable, has been allocated an IPv4 address for this APN, received the ESM cause #52 "single address bearers only allowed" and the request type is "handover" or "handover of emergency bearer services", and has not been allocated an IPv6 address for this APN.
The UE shall set the PDN type IE in the PDN CONNECTIVITY REQUEST message to IPv6 if:
-	the UE is only IPv6 capable;
-	the UE is both IPv4 and IPv6 capable, has been allocated an IPv4 address for this APN and received the ESM cause #52 "single address bearers only allowed" and the request type is "initial request" or "emergency"; or
-	the UE is both IPv4 and IPv6 capable, has been allocated an IPv6 address for this APN, received the ESM cause #52 "single address bearers only allowed" and the request type is "handover" or "handover of emergency bearer services", and has not been allocated an IPv4 address for this APN.
The UE shall set the PDN type IE in the PDN CONNECTIVITY REQUEST message to IPv4v6 if:
-	the UE is both IPv4 and IPv6 capable and has not been allocated an IP address for this APN and the request type is "initial request" or "emergency";
-	the UE capability is unknown in the UE (as in the case when the MT and TE are separated and the capability of the TE is not known in the MT); or
-	the UE is both IPv4 and IPv6 capable, has been allocated both IPv4 address and an IPv6 address for this APN and the request type is "handover" or "handover of emergency bearer services".
The UE shall not set the PDN type IE to PDN type value other than IPv4, IPv6 and IPv4v6.
The UE shall set the request type to "initial request" when the UE is establishing a new PDN connectivity. The UE shall set the request type to "handover" when the connectivity to a PDN is to be transferred from a 3GPP access network to the trusted WLAN access network. The UE shall set the request type to "emergency" when the UE is requesting a new PDN connection for emergency bearer services. The UE shall set the request type to "handover of emergency bearer services" when a PDN connection for emergency bearer services is to be transferred from a 3GPP access network to the trusted WLAN access network.
5.2.3	PDN connectivity establishment procedure accepted by the TWAG
Upon receipt of the PDN CONNECTIVITY REQUEST message, the TWAG checks if connectivity with the requested PDN can be established. If no requested APN is included in the PDN CONNECTIVITY REQUEST message and the request type is different from "emergency" and from "handover of emergency bearer services", the TWAG shall use the default APN as the requested APN. If the request type is "emergency" or "handover of emergency bearer services", the TWAG uses the APN configured for emergency bearer services or selects the statically configured PDN GW for unauthenticated UEs, if applicable.
If the requested PDN connection can be established, the TWAG shall send a PDN CONNECTIVITY ACCEPT message towards the UE. The TWAG shall retrieve the PTI from the PDN CONNECTIVITY REQUEST message and include it in the PDN CONNECTIVITY ACCEPT message. If the request type is different from "emergency" and from "handover of emergency bearer services", both the network identifier part and the operator identifier part shall be included in the Access Point Name IE. Additionally, the TWAG shall include:
-	PDN connection ID to identify the PDN connection between the UE and the TWAG; and
-	MAC address of the TWAG to the UE. This MAC address is used by the UE and the TWAG to send the user plane packets for this PDN connection.
If connectivity with the requested PDN is accepted, but with a restriction of IP version (i.e. both an IPv4 address and an IPv6 prefix is requested, but only one particular IP version, or only single IP version bearers are supported/allowed by the network), cause #50 "PDN type IPv4 only allowed", #51 "PDN type IPv6 only allowed" ", or #52 "single address bearers only allowed", respectively, shall be included in the PDN CONNECTIVITY ACCEPT message. Upon sending the message the TWAG shall enter the state PDN CONNECTIVITY PENDING and PROCEDURE TRANSACTION PENDING and start the timer T3585.
If the UE requested PDN type IPv4v6, but the PDN GW configuration or UE subscription dictates the use of IPv4 only or IPv6 only for this APN, the network shall override the PDN type requested by the UE to limit it to a single address PDN type (IPv4 or IPv6). In the PDN CONNECTIVITY ACCEPT message the TWAG shall set the PDN type IE to either "IPv4" or "IPv6" and the ESM cause value to #50 "PDN type IPv4 only allowed", or #51 "PDN type IPv6 only allowed", respectively. The UE shall not subsequently initiate another UE requested PDN connectivity procedure to the same APN to obtain a PDN type different from the one allowed by the network until:
-	a new EAP Authentication procedure is performed (e.g. a new WLAN is selected);
-	the PDN type which is used to access to the APN is changed;
-	the UE is switched off; or
-	the USIM is removed.
If the UE requested PDN type IPv4v6, but the operator uses single addressing per bearer, e.g. due to interworking with nodes of earlier releases, the network shall override the PDN type requested by the UE to a single IP version only. In the PDN CONNECTIVITY ACCEPT message sent to the UE, the TWAG shall set the PDN type IE to either "IPv4" or "IPv6" and the ESM cause value to #52 "single address bearers only allowed". The UE should subsequently request another PDN connection for the other IP version using the PDN connectivity establishment procedure to the same APN with a single address PDN type (IPv4 or IPv6) other than the one already activated.
The TWAG shall set the value of the IP Address IE in the PDN CONNECTIVITY ACCEPT message as follows:
-	If the PDN type IE in the PDN CONNECTIVITY ACCEPT message is set to IPv4 or IPv4v6, the PDN Address IE shall contain an IPv4 address for the UE; and
-	If the PDN type IE in the PDN CONNECTIVITY ACCEPT message is set to IPv6 or IPv4v6, the PDN Address IE shall contain an IPv6 interface identifier.
Upon receipt of the PDN CONNECTIVITY ACCEPT message, the UE shall check the PTI to identify the UE requested PDN connectivity, stop timer T3582 and enter the state PROCEDURE TRANSACTION INACTIVE. The UE should ensure that the PTI assigned to this procedure is not released immediately. The way to achieve this is implementation dependent. While the PTI value is not released, the UE regards any received PDN CONNECTIVITY ACCEPT message with the same PTI value as a network retransmission.
If the UE receives an IPv6 interface identifier in the PDN CONNECTIVITY ACCEPT message, the UE may wait for the Router Advertisement from the network with the IPv6 prefix information or it may send a Router Solicitation if necessary.
5.2.3.1	PDN connectivity establishment accepted by the UE
If the UE accepts the PDN connection the UE shall send a PDN CONNECTIVITY COMPLETE message and enter the state PDN CONNECTION ESTABLISHED. 
Upon receipt of the PDN CONNECTIVITY COMPLETE message, the TWAG shall enter the state PDN CONNECTION ESTABLISHED and stop the timer T3585, if the timer is running (see example in figure 5.2.2.1).
5.2.3.2	PDN connectivity establishment not accepted by the UE
If the UE does not accept the PDN connection the UE shall send a PDN CONNECTIVITY REJECT message and enter the state PDN CONNECTIVITY NOT ESTABLISHED.
The PDN CONNECTIVITY REJECT message contains a cause that typically indicates one of the following cause values:
#31:	request rejected, unspecified; or
#95 – 111:	protocol errors.
Upon receipt of the PDN CONNECTIVITY REJECT message, the TWAG shall enter the state PDN CONNECTIVITY NOT ESTABLISHED and PROCEDURE TRANSACTION INACTIVE and stop the timer T3585, if the timer is running (see example in figure 5.2.2.1).
5.2.4	PDN connectivity procedure not accepted by the TWAG
If connectivity with the requested PDN cannot be accepted by the network, the TWAG shall send a PDN CONNECTIVITY REJECT message to the UE (see example in figure 5.2.4.1). The message shall contain the PTI and a cause value indicating the reason for rejecting the UE-requested PDN connectivity.
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Figure 5.2.4.1: PDN connectivity establishment procedure not accepted by TWAG
The cause IE typically indicates one of the following cause values:
#8:	operator determined barring;
#26:	insufficient resources;
#27:	missing or unknown APN;
#28:	unknown PDN type;
#29:	user authentication failed;
#30:	request rejected by PDN GW;
#31:	request rejected, unspecified;
#32:	service option not supported;
#33:	requested service option not subscribed;
#34:	service option temporarily out of order;
#35:	PTI already in use;
#38:	network failure;
#50:	PDN type IPv4 only allowed;
#51:	PDN type IPv6 only allowed;
#52:	single address bearers only allowed;
#54:	PDN connection does not exist;
#55:	multiple PDN connections for a given APN not allowed;
#95 – 111:	protocol errors;
#113:	Multiple accesses to a PDN connection not allowed;
If the PDN type IE in the PDN CONNECTIVITY REQUEST message is set to a PDN type value other than IPv4, IPv6 and IPv4v6, the TWAG shall set the cause IE to #95 "semantically incorrect message".
If the cause value is #26 "insufficient resources", and the request type is different from "emergency" and from "handover of emergency bearer services", the network may include a value for timer Tw1 in the PDN CONNECTIVITY REJECT message. If the request type is "emergency" or "handover of emergency bearer services", the network shall not include the timer Tw1 in the PDN CONNECTIVITY REJECT message.
Upon receipt of the PDN CONNECTIVITY REJECT message, the UE shall stop timer T3582 and enter the state PROCEDURE TRANSACTION INACTIVE.
If the cause value is #26 "insufficient resources" and the Tw1 value IE is included, the UE shall take different actions depending on the timer value received for timer Tw1:
i)	if the timer value indicates neither zero nor deactivated, the UE shall stop timer Tw1 associated with the corresponding APN, if it is running. The UE shall start timer Tw1 with the value provided in the Tw1 value IE and not send another PDN CONNECTIVITY REQUEST message for the same APN until timer Tw1 expires, the timer Tw1 is stopped or the USIM is removed;
ii)	if the timer value indicates that this timer is deactivated, the UE shall not send another PDN CONNECTIVITY REQUEST message for the same APN until the UE is switched off or the USIM is removed; and
iii)	if the timer value indicates zero, the UE may send another PDN CONNECTIVITY REQUEST message for the same APN;
iv)	if the WLAN radio is disabled when the timer Tw1 is running and if the USIM in the UE remains the same when the WLAN radio is enabled, the UE shall behave as follows when the WLAN radio is enabled:
-	let t1 be the time remaining for Tw1 timeout when the WLAN radio was disabled and let t be the time elapsed since the WLAN radio was disabled until the WLAN radio was enabled. If t1 is greater than t, then the timer shall be restarted with the value t1 – t. If t1 is equal to or less than t, then the timer need not be restarted. If the UE is not capable of determining t, then the UE shall restart the timer with the value t1.
If the cause value is #26 "insufficient resources" and the Tw1 IE is not included, the UE may send a PDN CONNECTIVITY REQUEST message for the same APN. 
5.2.5	Abnormal cases in the UE
The following abnormal cases can be identified:
a)	Expiry of timer T3582:
-	On the first expiry of the timer T3582, the UE shall resend the PDN CONNECTIVITY REQUEST and shall reset and restart timer T3582. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3582, the UE shall abort the procedure, release the PTI allocated for this invocation and enter the state PROCEDURE TRANSACTION INACTIVE;
5.2.6	Abnormal cases on the network side
The following abnormal cases can be identified:
a)	UE initiated PDN connectivity request for an already existing PDN connection:
	If the network receives a PDN CONNECTIVITY REQUEST message with the same combination of APN and PDN type as an already existing PDN connection:
-	if the information elements in the PDN CONNECTIVITY REQUEST message do not differ from the ones received within the previous PDN CONNECTIVITY REQUEST message, and the TWAG has not received the PDN CONNECTIVITY COMPLETE message from UE, the TWAG shall re-send the PDN CONNECTIVITY ACCEPT message and continue the previous procedure; and
-	if one or more information elements in the PDN CONNECTIVITY REQUEST message differ from the ones received within the previous PDN CONNECTIVITY REQUEST message, and multiple PDN connections for a given APN are not allowed, the network may release the existing PDN connection locally without notification to the UE and proceed with the requested PDN connectivity procedure or may reject this PDN connectivity procedure including the cause #55 "multiple PDN connections for a given APN not allowed", in the PDN CONNECTIVITY REJECT message; and
	If the network receives a PDN CONNECTIVITY REQUEST message with request type "emergency" and the TWAG has not received the PDN CONNECTIVITY COMPLETE message from UE for the previous PDN connectivity request for emergency bearer services, the network shall resend the PDN CONNECTIVITY ACCEPT message and continue the previous procedure. If there is already a PDN connection for emergency bearer services existing, the TWAG shall reject the request with ESM cause #55 "multiple PDN connections for a given APN not allowed" or deactivate the existing PDN connection for emergency bearer services locally without notification to the UE and proceed with the requested PDN connectivity procedure.
b)	UE initiated PDN connectivity request with request type "handover" for a PDN connection that does not exist:
	If the network receives a PDN CONNECTIVITY REQUEST message for either a default APN or a specific APN with request type set to "handover" and the TWAG does not have any information about that PDN connection, then TWAG shall reject the PDN connectivity request procedure including the cause #54 "PDN connection does not exist", in the PDN CONNECTIVITY REJECT message.
c)	Expiry of timer T3585:
	On the first expiry of the timer T3585, the TWAG shall resend the PDN CONNECTIVITY ACCEPT message,  reset and restart timer T3585. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3585, the TWAG shall release possibly allocated resources for this activation and shall abort the procedure.
d)	A PDN CONNECTIVITY REQUEST message with request type "handover of emergency bearer services" is received from a UE and the TWAG does not have any information about a P-GW currently providing emergency bearer services for the UE or the TWAG is not configured with an address of a P-GW in the TWAG emergency configuration data:
	TWAG shall reject the PDN connectivity request procedure including the ESM cause #54 "PDN connection does not exist", in the PDN CONNECTIVITY REJECT message.
5.3	TWAG initiated PDN disconnection procedure
5.3.1	General
The purpose of the PDN disconnection procedure is to disconnect the UE from a PDN. With this procedure, all resources associated with this PDN connection are released. 
5.3.2	Procedure description
The TWAG shall initiate the PDN disconnection procedure by sending a PDN DISCONNECT REQUEST message to the UE, start the timer T3595, and enter the state PDN DISCONNECT PENDING and PROCEDURE TRANSACTION PENDING (see example in figure 5.3.2.1). The PDN DISCONNECT REQUEST message contains a cause typically indicating one of the following:
#8:	operator determined barring;
#36:	regular deactivation;
#38:	network failure; or
#39:	reactivation requested.
The TWAG may include a PCO IE in the PDN DISCONNECT REQUEST message (e.g. configuration parameters, error codes or messages/events).
If the UE is not authenticated when the TWAG initiates the PDN disconnection procedure, the TWAG shall locally disconnect the PDN connection towards the UE without any WLCP signalling between the TWAG and the UE.
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Figure 5.3.2.1: PDN disconnect procedure
Upon receipt of the PDN DISCONNECT REQUEST message, the UE shall release all the resources associated with the PDN connection and respond to the TWAG with the PDN DISCONNECT ACCEPT.
Upon sending the PDN DISCONNECT ACCEPT message, the UE shall enter the state PDN CONNECTIVITY NOT ESTABLISHED.
If the PDN DISCONNECT REQUEST message includes cause #39 "reactivation requested" the UE should stop timer Tw1 if it is running for the APN associated with the PDN connection and re-initiate the PDN connectivity procedure for the same APN as the disconnected PDN.
NOTE:	User interaction may be necessary in some cases when the UE cannot re-activate the PDN connection automatically.
Upon receipt of the PDN DISCONNECT ACCEPT message, the TWAG shall enter the states PDN CONNECTIVITY NOT ESTABLISHED and PROCEDURE TRANSACTION INACTIVE and stop the timer T3595.
5.3.3	Abnormal cases in the UE
Apart from the case described in subclause 5.1.3, no abnormal cases have been identified.
5.3.4	Abnormal cases in the TWAG
The following abnormal cases can be identified:
a)	Expiry of timer T3595:
	On the first expiry of the timer T3595, the TWAG shall resend the PDN DISCONNECT REQUEST message and shall reset and restart timer T3595. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3595, the TWAG shall abort the procedure and deactivate the PDN connection locally without any peer-to-peer WLCP signalling between the TWAG and the UE; and
b)	Collision of UE-initiated and TWAG-initiated PDN disconnection procedure:
	When the TWAG receives a PDN DISCONNECT REQUEST message during the TWAG-initiated PDN disconnection procedure the TWAG shall proceed with the PDN disconnection procedure.
5.4	UE requested PDN disconnection procedure
5.4.1	General
The purpose of the UE requested PDN disconnection procedure is for a UE to request disconnection from one PDN. With this procedure, all resources associated with this PDN connection are released.
5.4.2	Procedure description
In order to request PDN disconnection from a PDN, the UE shall send a PDN DISCONNECT REQUEST message to the TWAG, start the timer T3592 and enter the state PROCEDURE TRANSACTION PENDING (see example in figure 5.4.2.1).
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Figure 5.4.2.1: UE requested PDN disconnection procedure
Upon receipt of the PDN DISCONNECT REQUEST message, the TWAG shall release all the resources associated with the PDN connection and respond to the UE with the PDN DISCONNECT ACCEPT message.
Upon receipt of the PDN DISCONNECT ACCEPT message, the UE shall stop the timer T3592, deactivate all resources associated with this PDN connection and enter the states PROCEDURE TRANSACTION INACTIVE and PDN CONNECTIVITY NOT ESTABLISHED.
If the PDN DISCONNECT REQUEST message is not accepted by the network, the TWAG shall send a PDN DISCONNECT REJECT message to the UE. The PDN DISCONNECT REJECT message shall contain the PTI and a cause IE that typically indicates one of the following cause values:
#35:	PTI already in use; and
#95 – 111: protocol errors.
Upon receipt of the PDN DISCONNECT REJECT message, the UE shall stop the timer T3592, enter the state PROCEDURE TRANSACTION INACTIVE and abort the PDN disconnection procedure. Additionally, the UE shall deactivate all resources associated with this PDN connection locally without peer-to-peer signalling between the UE and the TWAG and enter the state PDN CONNECTIVITY NOT ESTABLISHED.
5.4.3	Abnormal cases in the UE
The following abnormal cases can be identified:
a)	Expiry of timer T3592:
	On the first expiry of the timer T3592, the UE shall resend the PDN DISCONNECT REQUEST and shall reset and restart timer T3592. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3592, the UE shall abort the procedure, release all resources associated with this PDN connection locally without peer-to-peer signalling between the UE and the TWAG, release the PTI allocated for this invocation and enter the state PROCEDURE TRANSACTION INACTIVE.
5.4.4	Abnormal cases in the TWAG
The following abnormal cases can be identified:
a)	No PDN connection with the same PTI:
	If the PTI included in the PDN DISCONNECT REQUEST message does not belong to an established PDN connection, the TWAG shall reply with a PDN DISCONNECT REJECT message with cause #54 "PDN connection does not exist";
5.5	STATUS message
The purpose of the sending of the STATUS message is to report at any time certain error conditions detected upon receipt of WLCP protocol data. The STATUS message can be sent by both the TWAG and the UE (see example in figure 5.5.1).
If the WLCP entity of the UE receives a STATUS message the UE shall take different actions depending on the received cause value:
#81		(Invalid PTI value);
	The UE shall abort any ongoing WLCP procedure related to the received PTI value and stop any related timer.
#97		(Message type non-existent or not implemented);
	The UE shall abort any ongoing WLCP procedure related to the PTI and stop any related timer.
On receipt of a STATUS message with any other cause value no state transition and no specific action shall be taken as seen from the WLAN radio interface, i.e. local actions are possible.
If the WLCP entity of the TWAG receives a STATUS message the TWAG shall take different actions depending on the received cause value:
#81		(Invalid PTI value);
	The TWAG shall abort any ongoing WLCP procedure related to the received PTI value and stop any related timer.
#97		(Message type non-existent or not implemented);
	The TWAG shall abort any ongoing WLCP procedure related to the PTI and stop any related timer.
The local actions to be taken by the TWAG on receipt of an STATUS message with any other cause value are implementation dependent.
 EMBED Visio.Drawing.11  
Figure 5.5.1: STATUS message
5.6	TWAG initiated PDN connectivity modification procedure
5.6.1	General
The purpose of the TWAG initiated PDN connectivity modification procedure is for the network to modify the protocol data of the PDN connection (e.g. PCO, routing rule). If this procedure was initiated by a UE requested PDN connectivity modification procedure (see subclause 5.7), the PDN MODIFICATION REQUEST shall contain the procedure transaction identity (PTI) value received by the TWAG in the PDN MODIFICATION INDICATION message.
5.6.2	Procedure description
The TWAG shall initiate the PDN connectivity modification procedure by sending a PDN MODIFICATION REQUEST message to the UE, starting the timer T3586 and enter the state PROCEDURE TRANSACTION PENDING (see example in figure 5.6.2.1).
 EMBED Visio.Drawing.11  
Figure 5.6.2.1: TWAG-initiated PDN connectivity modification procedure
5.6.3	PDN connectivity modification procedure accepted by the UE
Upon receipt of the PDN MODIFICATION REQUEST message, the UE may accept the request from the TWAG by sending a PDN MODIFICATION ACCEPT message to the TWAG. Upon receipt of the PDN MODIFICATION ACCEPT message, the TWAG shall stop the timer T3586.
5.6.4	PDN connectivity modification procedure not accepted by the UE
Upon receipt of the PDN MODIFICATION REQUEST message, the UE may reject the request from the TWAG by sending a PDN MODIFICATION REJECT message to the TWAG.
The PDN MODIFICATION REJECT message contains a cause that typically indicates one of the following cause values:
#31:	request rejected, unspecified; or
#95 – 111:	protocol errors.
5.6.5	Abnormal cases in the UE
Apart from the case described in subclause 5.1.3, no abnormal cases have been identified.
5.6.6	Abnormal cases in the TWAG
The following abnormal cases can be identified:
a)	Expiry of timer T3586:
	On the first expiry of the timer T3586, the TWAG shall resend the PDN MODIFICATION REQUEST and shall reset and restart timer T3586. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3586, the TWAG shall abort the procedure and enter the state PDN CONNECTION ESTABLISHED.
	The TWAG may continue to use the previous configuration of the PDN connectivity or initiate PDN disconnection procedure.
b)	Collision of TWAG initiated PDN connectivity modification procedure and UE requested PDN disconnection procedure:
	When the TWAG receives a PDN DISCONNECT REQUEST message during a TWAG initiated PDN connectivity modification procedure, the TWAG shall terminate the PDN connectivity modification procedure locally and proceed with the PDN disconnect procedure.
5.7	UE requested PDN connectivity modification procedure
5.7.1	General
The purpose of the UE requested PDN connectivity modification procedure is for the UE to request the network to modify the protocol data of the PDN connection (e.g. PCO, routing rule). If accepted by the network, this procedure invokes a TWAG initiated PDN connectivity modification procedure (see subclause 5.6).
5.7.2	Procedure description
In order to request the network to initiate PDN connectivity modification procedure, the UE shall send a PDN MODIFICATION INDICATION message to the TWAG, start timer T3586 and enter the state PDN MODIFICATION PENDING (see example in figure 5.7.2.1).
 EMBED Visio.Drawing.11  
Figure 5.7.2.1: UErequested  PDN connectivity modification procedure
5.7.3	PDN connectivity modification procedure accepted by the network
Upon receipt of the PDN MODIFICATION REQUEST message, the UE shall stop the timer T3586.
5.7.4	PDN connectivity modification procedure not accepted by the network
Upon receipt of the PDN MODIFICATION INDICATION message, the network may reject the request from the UE by sending a PDN MODIFICATION REJECT message to the UE.
The PDN MODIFICATION REJECT message contains a cause that typically indicates one of the following cause values:
#31:	request rejected, unspecified; or
#95 – 111:	protocol errors.
5.7.5	Abnormal cases in the UE
The following abnormal cases can be identified:
a)	Expiry of timer T3586:
	On the first expiry of the timer T3586, the UE shall resend the PDN MODIFICATION INDICATION and shall reset and restart timer T3586. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3586, the UE shall abort the procedure, release the PTI allocated for this activation and enter the state PROCEDURE TRANSACTION INACTIVE.
b)	Unknown PDN connection ID
	Upon receipt of the PDN MODIFICATION REJECT message including ESM cause #43 "invalid EPS bearer identity", the UE shall release the existing PDN connection locally without peer-to-peer signalling between the UE and the TWAG.
c)	Collision of a UE requested PDN connectivity modification procedure and a TWAG initiated PDN disconnection procedure.
	When the UE receives a PDN DISCONNECT REQUEST message during the PDN connectivity modification procedure, and the PDN connection ID indicated in the PDN DISCONNECT REQUEST message is the PDN connection ID the UE indicated in the UE requested PDN connectivity modification procedure, then the UE shall abort the UE requested PDN connectivity modification procedure and proceed with the PDN disconnection procedure.
5.7.6	Abnormal cases in the TWAG
Apart from the case described in subclause 5.1.3, no abnormal cases have been identified.
5.8	PGW initiated local PDN disconnection in the TWAG
5.8.1	General
A PDN connection over trusted WLAN can be released locally in the TWAG, i.e. without any peer-to-peer signalling between the TWAG and the UE, based on the trigger from the PGW. This can happen, for example, during the P-CSCF restoration procedure for NBIFOM PDN connections (see 3GPP TS 23.380 [11]).
5.8.2	Procedure description
Upon receiving a request from PGW to release a PDN connection with cause "local release" (see 3GPP TS 29.274 [12]) the TWAG shall:
-	release all resources associated with this PDN connection over WLAN; and
-	not initiate any peer-to-peer WLCP signalling to the UE.
5.9	Local PDN disconnection in the UE initiated from 3GPP access
5.9.1	General
A PDN connection over trusted WLAN can be released locally in the UE, i.e. without any peer-to-peer signalling between the TWAG and the UE, based on the trigger received via 3GPP access. This can happen, for example, during the P-CSCF restoration procedure for NBIFOM PDN connections (see 3GPP TS 23.380 [11]).
5.9.2	Procedure description
Upon receiving over the 3GPP access:
-	a DEACTIVATE EPS BEARER CONTEXT REQUEST message with the EPS bearer context of a default EPS bearer context and ESM cause #39 "reactivation requested" (see 3GPP TS 24.301 [8]); or
-	a DETACH REQUEST message with the detach type "re-attach required" (see 3GPP TS 24.301 [8])
to release the resources for a PDN connection over the 3GPP access, the UE shall: 
-	release all resources associated with this PDN connection over WLAN; and
-	not initiate any peer-to-peer WLCP signalling to the TWAG.
6	Handling of unknown, unforeseen, and erroneous protocol data
6.1	General
The procedures specified in the present document apply to those messages which pass the checks described in this subclause.
This clause also specifies procedures for the handling of unknown, unforeseen, and erroneous protocol data by the receiving entity. These procedures are called "error handling procedures", but in addition to providing recovery mechanisms for error situations they define a compatibility mechanism for future extensions of the protocols.
Subclauses 6.1 to 6.8 shall be applied in order of precedence, starting with subclause 6.1.
Most error handling procedures are mandatory for the UE.
Detailed error handling procedures in the TWAG are implementation dependent and may vary from PLMN to PLMN. However, when extensions of this protocol are developed, TWAG will be assumed to have the error handling that is indicated in this subclause as mandatory ("shall") and that is indicated as strongly recommended ("should").
Also, the error handling of the TWAG is only considered as mandatory or strongly recommended when certain thresholds for errors are not reached during a dedicated connection.
6.2	Message too short
When the UE receives a WLCP message which is too short to contain a complete message type information element, the UE shall discard the message.
The TWAG shall take the same approach.
6.3	Unknown or unforeseen procedure transaction identity or PDN connection ID
6.3.1	Procedure transaction identity
The following TWAG procedures shall apply for handling an unknown, erroneous, or unforeseen PTI received in a WLCP message:
a)	If the TWAG receives a PDN CONNECTIVITY REQUEST message with a reserved PTI value, the TWAG shall respond with a PDN CONNECTIVITY REJECT message including ESM cause #81 "invalid PTI value";
b)	If the TWAG receives a PDN DISCONNECT REQUEST message with a reserved PTI value, the TWAG shall respond with a PDN DISCONNECT REJECT message including ESM cause #81 "invalid PTI value"; and
c)	If the TWAG receives a WLCP message other than those listed in items a through b above with a reserved PTI value, the TWAG shall ignore the message.
The following UE procedures shall apply for handling an unknown, erroneous, or unforeseen PTI received in a WLCP message:
a)	If the UE receives a PDN CONNECTIVITY REJECT message in which the PTI value is an unassigned or reserved value, or an assigned value that does not match any PTI in use, the UE shall ignore the message;
b)	If the UE receives a PDN DISCONNECT REJECT message in which the PTI value is an unassigned or reserved value, or an assigned value that does not match any PTI in use, the UE shall ignore the message; and
c)	If the UE receives a WLCP message other than those listed in items a through b with a reserved PTI value or an assigned value that does not match any PTI in use, the UE shall ignore the message.
6.3.2	PDN connection ID
The following TWAG procedures shall apply for handling an unknown, erroneous, or unforeseen PDN connection ID received in the header of a WLCP message:
a)	If the TWAG receives a PDN CONNECTIVITY REQUEST message which includes an assigned or reserved PDN connection ID value, the TWAG shall respond with a PDN CONNECTIVITY REJECT message including ESM cause #43 "invalid EPS bearer identity";
b)	If the TWAG receives a PDN DISCONNECT REQUEST message which includes an unassigned or reserved PDN connection ID value, the TWAG shall respond with a PDN DISCONNECT REJECT message including ESM cause #43 "invalid EPS bearer identity"; and
c)	If the TWAG receives a WLCP message other than those listed in items a through b above in which the message includes a reserved PDN connection ID value or an assigned value that does not match an existing PDN connection ID, the TWAG shall ignore the message.
The following UE procedures shall apply for handling an unknown, erroneous, or unforeseen PDN connection ID received in the header of a WLCP message:
a)	If the UE receives a PDN CONNECTIVITY REJECT message which includes an assigned or reserved PDN connection ID value, the UE shall ignore the message;
b)	If the UE receives a PDN DISCONNECT REJECT message which includes an unassigned or reserved PDN connection ID value or an assigned PDN connection ID value which does not match existing PDN connection, the UE shall ignore the message;
c)	If the UE receives a PDN DISCONNECT REQUEST message which includes an unassigned or reserved PDN connection ID value or an assigned PDN connection ID value which does not match existing PDN connection, the UE shall ignore the message; and
d)	If the UE receives a WLCP message other than those listed in items a through c in which the message includes an unassigned or reserved PDN connection ID value or a value that does not match an existing PDN connection ID, the UE shall ignore the message.
6.4	Unknown or unforeseen message type
If UE receives a WLCP message with message type not defined or not implemented, the UE shall return a status message with cause #97 "message type non-existent or not implemented".
If the TWAG receives a WLCP message with message type not defined or not implemented, the TWAG shall ignore the message except that the TWAG should return a status message with cause #97 "message type non-existent or not implemented".
6.5	Non-semantical mandatory information element errors
6.5.1	Common procedures
When on receipt of a message,
-	an "imperative message part" error; or
-	a "missing mandatory IE" error
is diagnosed or when a message containing:
-	a syntactically incorrect mandatory IE;
-	an IE unknown in the message, but encoded as "comprehension required" (see 3GPP TS 24.007 [7]); or
-	an out of sequence IE encoded as "comprehension required" (see 3GPP TS 24.007 [7]) is received,
the UE shall proceed as follows:
	The UE shall return a status message with cause #96 "invalid mandatory information"; and
the TWAG shall proceed as follows:
	The TWAG shall either:
-	try to treat the message (the exact further actions are implementation dependent); or
-	ignore the message except that the TWAG should return a status message with cause #96 "invalid mandatory information".
6.5.2	PDN connection management
The following UE procedures shall apply for handling an error encountered with a mandatory information element in a WLCP message:
a)	If the message is a PDN CONNECTIVITY REQUEST, a PDN CONNECTIVITY REJECT message with ESM cause #96 "invalid mandatory information", shall be returned.
b)	If the message is a PDN DISCONNECT REQUEST, a PDN DISCONNECT ACCEPT message shall be returned. All resources associated with that PDN connection shall be released.
The following TWAG procedures shall apply for handling an error encountered with a mandatory information element in a WLCP message:
a)	If the message is a PDN CONNECTIVITY REQUEST, a PDN CONNECTIVITY REJECT message with ESM cause #96 "invalid mandatory information", shall be returned.
b)	If the message is a PDN DISCONNECT REQUEST, a PDN DISCONNECT REJECT message with ESM cause #96 "invalid mandatory information", shall be returned.
6.6	Unknown and unforeseen IEs in the non-imperative message part
6.6.1	IEIs unknown in the message
The UE shall ignore all IEs unknown in a message which are not encoded as "comprehension required" (see 3GPP TS 24.301 [5]).
The TWAG shall take the same approach.
6.6.2	Out of sequence IEs
The UE shall ignore all out of sequence IEs in a message which are not encoded as "comprehension required" (see 3GPP TS 24.301 [5]).
The TWAG shall take the same approach.
6.6.3	Repeated IEs
If an information element with format V, TV, or TLV is repeated in a message in which repetition of the information element is not specified in clause 7 of the present document, the UE shall handle only the contents of the information element appearing first and shall ignore all subsequent repetitions of the information element. When repetition of information elements is specified, the UE shall handle only the contents of specified repeated information elements. If the limit on repetition of information elements is exceeded, the UE shall handle the contents of information elements appearing first up to the limit of repetitions and shall ignore all subsequent repetitions of the information element.
The TWAG shall follow the same procedures.
6.7	Non-imperative message part errors
6.7.1	General
This category includes:
-	syntactically incorrect optional IEs; and
-	conditional IE errors.
6.7.2	Syntactically incorrect optional IEs
The UE shall treat all optional IEs that are syntactically incorrect in a message as not present in the message.
The TWAG shall take the same approach.
6.7.3	Conditional IE errors
When upon receipt of a WLCP message the UE diagnoses a "missing conditional IE" error or an "unexpected conditional IE" error, or when the UE receives a WLCP message containing at least one syntactically incorrect conditional IE, the UE shall ignore the message and shall return a status message with cause #100 "conditional IE error".
When the TWAG receives a message and diagnoses a "missing conditional IE" error or an "unexpected conditional IE" error or when the TWAG receives a message containing at least one syntactically incorrect conditional IE, the TWAG shall either:
-	try to treat the message (the exact further actions are implementation dependent); or
-	ignore the message except that the TWAG should return a status message with cause #100 "conditional IE error".
6.8	Messages with semantically incorrect contents
When a message with semantically incorrect contents is received, the UE shall perform the foreseen reactions of the procedural part of the present document (i.e. of clauses 5). If however no such reactions are specified, the UE shall ignore the message except that the UE shall return a status message with cause #95 "semantically incorrect message".
The TWAG should follow the same procedure except that a status message is not normally transmitted.
7	Message functional definitions and contents
7.1	PDN connectivity request
7.1.1	Message definition
This message is sent by the UE to the network to initiate establishment of a PDN connection. See table 7.1.1.1.
Message type:	PDN CONNECTIVITY REQUEST
Direction:			UE to network
Table 7.1.1.1: PDN CONNECTIVITY REQUEST message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity request message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

Request type
Request type
8.4
M
V
1/2

PDN type
PDN type
8.5
M
V
1/2
28
Access point name
Access point name
8.6
O
TLV
3-102
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.1.2	Access point name
This IE is included in the message when the UE wishes to request network connectivity as defined by a certain access point name during the PDN connection establishment procedure.
7.1.3	Protocol configuration options
This IE is included in the message when the UE wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the network.
7.1.4	NBIFOM container
This information element is used to transfer information associated with network-based IP flow mobility, see 3GPP TS 24.161 [10].
7.2	PDN connectivity accept
7.2.1	Message definition
This message is sent by the network to the UE to acknowledge activation of a PDN connection. See table 7.2.1.1.
Message type:	PDN CONNECTIVITY ACCEPT
Direction:			network to UE
Table 7.2.1.1: PDN CONNECTIVITY ACCEPT message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity accept message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

Access point name
Access point name
8.6
M
LV
2-101

PDN Address
PDN address
8.8
M
LV
6-14

PDN connection ID

PDN connection ID
8.9
M
V
1

User Plane Connection ID
User Plane Connection ID
8.10
M
V
6
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
58
Cause
Cause
8.11
O
TV
2
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.2.2	Protocol configuration options
This IE is included in the message when the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the UE.
7.2.3	Cause
The network shall include this IE, if the network allocated a PDN address of a PDN type which is different from the PDN type requested by the UE.
7.2.4	NBIFOM container
This information element is used to transfer information associated with network-based IP flow mobility, see 3GPP TS 24.161 [10].
7.3	PDN connectivity reject
7.3.1	Message definition
This message is sent by the network to the UE to reject activation of a PDN connection. See table 7.3.1.1.
Message type:	PDN CONNECTIVITY REJECT
Direction:			network to UE
Table 7.3.1.1: PDN CONNECTIVITY REJECT message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity reject message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

Cause
Cause
8.11
M
V
1
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
37
Tw1 value
GPRS timer 3
8.12
O
TLV
3
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.3.2	Protocol configuration options
This IE is included in the message when the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the UE.
7.3.3	Tw1 value
This IE may be included in the message when the cause is #26 "insufficient resources".
7.4	PDN disconnect request
7.4.1	Message definition
This message is sent by the network or the UE to initiate release of a PDN connection. See table 7.4.1.1.
Message type:	PDN DISCONNECT REQUEST
Direction:			both
Table 7.4.1.1: PDN DISCONNECT REQUEST message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN disconnect request message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID
PDN connection ID
8.9
M
V
1
58
Cause
Cause
8.11
O
TV
2
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253

7.4.2	Protocol configuration options
This IE is included in the message when the UE or the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the peer entity.
7.5	PDN disconnect accept
7.5.1	Message definition
This message is sent by the network or the UE to acknowledge release of a PDN connection. See table 7.5.1.1.
Message type:	PDN DISCONNECT ACCEPT
Direction:			both
Table 7.5.1.1: PDN DISCONNECT ACCEPT message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity accept message identity
Message type8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
V
1/2
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253

7.5.2	Protocol configuration options
This IE is included in the message when the UE or the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the peer entity.
7.6	PDN disconnect reject
7.6.1	Message definition
This message is sent by the network to the UE to reject release of a PDN connection. See table 7.6.1.1.
Message type:	PDN DISCONNECT REJECT
Direction:			network to UE
Table 7.6.1.1: PDN DISCONNECT REJECT message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity reject message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
V
1
58
Cause
Cause
8.11
M
V
1
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253

7.6.2	Protocol configuration options
This IE is included in the message when the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the UE.
7.7	PDN connectivity complete
7.7.1	Message definition
This message is sent by the UE to acknowledge establishment of a PDN connection. See table 7.7.1.1.
Message type:	PDN CONNECTIVITY COMPLETE
Direction:			UE to network
Table 7.7.1.1: PDN CONNECTIVITY COMPLETE message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity complete
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
TV
1

7.8	Status message
7.8.1	Message definition
This message is sent by the network or the UE to report certain error conditions detected upon receipt of WLCP protocol data as specified in subclause 5.5. See table 7.8.1.1.
Message type:	STATUS
Direction:			both
Table 7.8.1.1: STATUS message content
IEI
Information Element
Type/Reference
Presence
Format
Length

Status
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
TV
1

Cause
Cause
8.11
M
V
1

7.9	PDN modification request
7.9.1	Message definition
This message is sent by the network to initiate modification of a PDN connection. See table 7.9.1.1.
Message type:	PDN MODIFICATION REQUEST
Direction:			network to UE
Table 7.9.1.1: PDN MODIFICATION REQUEST message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN modify request message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID
PDN connection ID
8.9
M
V
1
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.9.2	Protocol configuration options
This IE is included in the message when the UE or the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the peer entity.
7.9.3	NBIFOM container
This information element is used to transfer information associated with network-based IP flow mobility, see 3GPP TS 24.161 [10].
7.10	PDN modification accept
7.10.1	Message definition
This message is sent by the UE to acknowledge modification of a PDN connection. See table 7.10.1.1.
Message type:	PDN MODIFICATION ACCEPT
Direction:			UE to network
Table 7.10.1.1: PDN MODIFICATION ACCEPT message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity accept message identity
Message type8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
V
1/2
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.10.2	Protocol configuration options
This IE is included in the message when the UE or the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the peer entity.
7.10.3	NBIFOM container
This information element is used to transfer information associated with network-based IP flow mobility, see 3GPP TS 24.161 [10].
7.11	PDN modification reject
7.11.1	Message definition
This message is sent by the network or the UE to reject to modify a PDN connection. See table 7.11.1.1.
Message type:	PDN MODIFICATION REJECT
Direction:			both
Table 7.11.1.1: PDN MODIFICATION REJECT message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN connectivity reject message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
V
1
58
Cause
Cause
8.11
M
V
1
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.11.2	Protocol configuration options
This IE is included in the message when the UE or the network wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the UE.
7.11.3	NBIFOM container
This information element is used to transfer information associated with network-based IP flow mobility, see 3GPP TS 24.161 [10].
7.12	PDN modification indication
7.12.1	Message definition
This message is sent by the UE to request the network to initiate PDN connection modification procedure. See table 7.12.1.1.
Message type:	PDN MODIFICATION INDICATION
Direction:			UE to network
Table 7.12.1.1: PDN MODIFICATION INDICATION message content
IEI
Information Element
Type/Reference
Presence
Format
Length

PDN modification indication message identity
Message type
8.2
M
V
1

Procedure transaction identity 
Transaction identifier
8.3
M
V
1

PDN connection ID

PDN connection ID
8.9
M
V
1
27
Protocol configuration options
Protocol configuration options
8.7
O
TLV
3-253
33
NBIFOM container
NBIFOM container
8.13
O
TLV
3-257

7.12.2	Protocol configuration options
This IE is included in the message when the UE wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the UE.
7.12.3	NBIFOM container
This information element is used to transfer information associated with network-based IP flow mobility, see 3GPP TS 24.161 [10].
8	General message format and information elements coding
8.1	General
The least significant bit of a field is represented by the lowest numbered bit of the highest numbered octet of the field. When the field extends over more than one octet, the order of bit values progressively decreases as the octet number increases.
Figure 8.1.1 shows an example of a field where the most significant bit of the field is marked MSB and the least significant bit of the field is marked LSB.

7
6
5
4
3
2
1
0

MSB
x
x
x
x
x
x
x
octet 1

x
x
x
x
x
x
x
x


x
x
x
x
x
x
x
LSB
octet N
Figure 8.1.1: Example of bit ordering of a field
Within the protocols defined in the present document, the WLCP message consists of the following parts:
a)	Message type;
b)	Procedure transaction identity;
c)	other information elements, as required.
The organization of a message is illustrated in the example shown in figure 8.1.2.
76543210Message type
octet 1
Procedure transaction identity
octet 2

octet 3
Other information elements as required


octet n
Figure 8.1.2: General message organization example for a WLCP message
Unless specified otherwise in the message descriptions of clause 7, a particular information element shall not be present more than once in a given message.
8.2	Message type
The message type octet is the first octet in a WLCP message. Table 8.2.1 defines the value part of the message type IE used in the WLCP protocol. Bit 6 to 7 are coded as "01" indicating it is a WLCP message.
Table 8.2.1: Message types for WLCP
Bits


76543210 
10------
WLCP messages10000001PDN connectivity request10000010PDN connectivity accept1
10
00
00
00
00
11
01
0PDN connectivity reject
PDN connectivity complete
10000101PDN disconnect request10000110PDN disconnect accept10000111
PDN disconnect reject
10001000PDN modification request10001001PDN modification accept10001010PDN modification reject10001011PDN modification indication
10101000Status
8.3	Procedure transaction identity
The procedure transaction identity (PTI) octet is the second octet in a WLCP message. The PTI allows distinguishing up to 254 different bi-directional messages flows for a given message type. Such a message flow is called a transaction. The procedure transaction identity is released when the procedure is completed. Table 8.3.1 defines the value part of the Procedure transaction identity IE used in the WLCP.
Table 8.3.1: Procedure transaction identity

Bits
76543210
00000000
No procedure transaction identity assigned00000001\to

} Procedure transaction identity value
11111110
/11111111ReservedIn this version of the protocol the sending entity shall not set the PTI to the value 0. Any entity receiving a request with a PTI set to the value 0 shall consider that as a syntactical error (see subclause 6.5.1).

8.4	Request type
See subclause 10.5.6.17 in 3GPP TS 24.008 [4].
8.5	PDN type
See subclause 9.9.4.10 in 3GPP TS 24.301 [5].
8.6	Access point name
See subclause 10.5.6.1 in 3GPP TS 24.008 [4].
8.7	Protocol configuration options
See subclause 10.5.6.3 in 3GPP TS 24.008 [4].
8.8	PDN address
See subclause 9.9.4.9 in 3GPP TS 24.301 [5].
8.9	PDN connection ID 
The purpose of the PDN connection ID is to identify the PDN connection between the UE and the TWAG.
The PDN connection ID information element is coded as shown in figure 8.9.1 and table 8.9.1.
76543210PDN connection ID IEI

octet 1
0
0
0
0
PDN connection ID
octet 2
Spare
value
Figure 8.9.1: PDN connection ID information element
Table 8.9.1: PDN connection ID information element
PDN connection ID (bits 1-4)

3
2
1
0

0
0
0
0

to
Reserved
0
1
0
0






0
1
0
1
PDN connection ID value 5
0
1
1
0
PDN connection ID value 6
0
1
1
1
PDN connection ID value 7
1
0
0
0
PDN connection ID value 8
1
0
0
1
PDN connection ID value 9
1
0
1
0
PDN connection ID value 10
1
0
1
1
PDN connection ID value 11
1
1
0
0
PDN connection ID value 12
1
1
0
1
PDN connection ID value 13
1
1
1
0
PDN connection ID value 14
1
1
1
1
PDN connection ID value 15


8.10	User plane connection ID
The purpose of the user plane connection ID is to identify the user plane for one PDN connection between the UE and the TWAG.
The user plane connection ID value is the MAC address of the TWAG with a length of 6 octets. The MAC address is defined in subclause 8 of IEEE Std 802 [6].
The user plane connection ID information element is coded as shown in figure 8.10.1.
76543210User plane connection ID IEI
octet 1
User plane connection ID value
octet 2



octet 7
Figure 8.10.1: User plane connection ID information element
8.11	Cause
See subclause 9.9.4.4 in 3GPP TS 24.301 [5].
8.12	GPRS timer 3
See subclause 10.5.7.4a in 3GPP TS 24.008 [4].
8.13	NBIFOM container
See subclause 10.5.6.21 in 3GPP TS 24.008 [4].
9	List of system parameters
9.1	Timers
Table 9.1.1: WLCP timers – UE side
TIMER
TIMER VALUE
STATE
CAUSE OF START
NORMAL STOP
ON THE
1st, 2nd, 3rd, 4th EXPIRY (NOTE 1)
T3582
8s
PROCEDURE TRANSACTION PENDING
PDN CONNECTIVITY REQUEST sent
PDN CONNECTIVITY ACCEPT received or PDN CONNECTIVITY REJECT received
Retransmission of the same message
T3592
6s
PROCEDURE TRANSACTION PENDING
PDN DISCONNECT REQUEST sent
PDN DISCONNECT ACCEPT received or PDN DISCONNECT REJECT received
Retransmission of the same message
Tw1
NOTE 2
PDN CONNECTIVITY PENDING or SCM_RESPONSE (defined in 3GPP TS 24.302 [3]) reception
PDN CONNECTIVITY REJECT with a timer value for Tw1 received, SCM_RESPONSE (defined in 3GPP TS 24.302 [3]) with a timer value for Tw1 received 
PDN DISCONNECT REQUEST with cause #39 "reactivation requested"
None
T3586
8s
PROCEDURE TRANSACTION PENDING
PDN MODIFICATION REQUEST sent
PDN MODIFICATION ACCEPT received or PDN MODIFICATION REJECT received
Retransmission of the same message
NOTE 1:	Typically, the procedures are aborted on the fifth expiry of the relevant timer. Exceptions are described in the corresponding procedure description.
NOTE 2:	The value of this timer can be provided by the network operator when a request to activate a PDN connection is rejected by the network with a certain cause or when a request to activate a PDN connection in single-connection mode (defined in 3GPP TS 24.302 [3]) is rejected by the network with a certain cause.

Table 9.1.2: WLCP timers – TWAG side
TIMER
TIMER VALUE
STATE
CAUSE OF START
NORMAL STOP
ON THE
1st, 2nd, 3rd, 4th EXPIRY (NOTE 1)
T3585
8s
PDN CONNECTIVITY PENDING

PROCEDURE TRANSACTION PENDING
PDN CONNECTIVITY ACCEPT sent
PDN CONNECTIVITY COMPLETE received 
or PDN CONNECTIVITY REJECT received 
Retransmission of the same message
T3595
8s
PDN DISCONNECT PENDING

PROCEDURE TRANSACTION PENDING
PDN DISCONNECT REQUEST sent
PDN DISCONNECT ACCEPT received
Retransmission of the same message
T3586
8s
PROCEDURE TRANSACTION PENDING
PDN MODIFICATION REQUEST sent
PDN MODIFICATION ACCEPT received or PDN MODIFICATION REJECT received
Retransmission of the same message
NOTE 1:	Typically, the procedures are aborted on the fifth expiry of the relevant timer. Exceptions are described in the corresponding procedure description.

Annex A (Informative):
IANA UDP port registration form
This annex contains information to be provided to IANA for WLCP UDP port registration. The following information are to be used to register WLCP user port number and service name in the "IANA Service Name and Transport Protocol Port Number Registry" and specifically "Service Name and Transport Protocol Port Number Registry". 
Resources required
Port number and service name
Transport Protocols
UDP
Service Code

Service Name
wlcp
Desired Port Number

Description
Wireless LAN Control plane Protocol (WLCP) is a 3GPP control protocol used by the User Equipment (UE) for access to the Evolved Packet Core via trusted Wireless Local Area Network. It enables the management of the Packet Data Network (PDN) connections between the User Equipment (UE) and the Trusted WLAN Access Gateway (TWAG).
Wireless LAN Control plane Protocol (WLCP) uses UDP as a transport protocol.
Reference
3GPP TS 24.244
Defined TXT keys
N/A
If broadcast/multicast is used, how and what for?
Neither broadcast, nor multicast are used.
If UDP is requested, please explain how traffic is limited, and whether the protocol reacts to congestion.
At maximum a few WLCP messages per seconds are expected in communication between a given User Equipment (UE) and a given Trusted WLAN Access Gateway (TWAG). 
Wireless LAN Control plane Protocol does not support any reaction to congestion.
If UDP is requested, please indicate whether the service is solely for the discovery of hosts supporting this protocol.
Wireless LAN Control plane Protocol is not used solely for discovery of hosts supporting this protocol.
Please explain how your protocol supports versioning.
Wireless LAN Control plane Protocol does not support versioning.
If your request is for more than one transport, please explain in detail how the protocol differs over each transport.
N/A
Please describe how your protocol supports security. Note that presently there is no IETF consensus on when it is appropriate to use a second port for an insecure version of a protocol.
Wireless LAN Control plane Protocol does not support security. It relies on the security mechanisms of the lower layers, including EAP-AKA’ authentication and IEEE 802.1x encryption.
Please explain why a unique port assignment is necessary as opposed to a port in range (49152-65535) or existing port.
An assigned User Port would make network management easier. It is possible that packets containing WLCP messages need to traverse several firewalls of the network operator during the signalling exchange between the User Equipment (UE) and the Trusted WLAN Access Gateway (TWAG). The firewalls of the network operator are configured to discard packets other than those containing the WLCP messages and other than those authorized by the WLCP messages. If a dynamic ephemeral port is used for WLCP messages, the firewall configuration needs to be updated whenever a new port starts being used for WLCP messages in the Trusted WLAN Access Gateway (TWAG).
An assigned User Port would make roaming agreements between network operators easier. If a dynamic port is used, each operator will need to provide the port number used by its TWAG to other operators, then the home operator needs to configure in its AAA sever the list of port numbers (in addition to the IP addresses) of the TWAGs of its roaming partners. If dynamic port is used, the port number can change frequently (while the IP address of the TWAG does not change frequently). Each time the port number changes, the roaming agreement documents needs to be updated. If dynamic port is used, the procedure to update the port numbers on the AAA server can cause a short interruption of the service.
As a general principle, 3GPP protocols use assigned User Ports, e.g. GTP-C uses UDP port number 2123, GTP-U uses UDP port number 2152, S1AP uses SCTP port number 36412, X2AP uses SCTP port number 36422. IKEv2 is an example of an IETF protocol between the terminal and a gateway that uses a well-known port number.
An assigned UDP port number would simplify the UE implementation. The UDP port number management between the application processor (AP) and the cellular modem would be simplified if the UDP port for WLCP could be set as a well-known port number. Specifically, there would be a need for an additional API between the WLCP client in the AP and the modem to identify the WLCP packets if dynamic ports are used.

Please explain the state of development of your protocol.
Protocol Standard definition. No implementation exists yet.
If SCTP is requested, is there an existing TCP and/or UDP service name or port number assignment? If yes, provide the existing service name and port number.
N/A
What specific SCTP capability is used by the application such that a user who has the choice of both TCP (and/or UDP) and SCTP ports for this application would choose SCTP? See  HYPERLINK "http://www.iana.org/go/rfc4960" RFC 4960 section 7.1.
N/A
Please provide any other information that would be helpful in understanding how this protocol differs from existing assigned services
This protocol is between the UE (i.e. mobile device) and the Trusted WLAN Gateway. The UDP ports previously assigned to 3GPP were for protocols between network elements.

Annex B (informative):
Change history
Change history
DateTSG #TSG Doc.CRRevSubject/CommentOldNew2013-10Draft skeleton provided0.0.02013-10CT1#84bisIncludes the following contribution agreed by CT1 at CT1#84bis:
C1-1341450.0.00.1.02013-11CT1#85Includes the following contributions agreed by CT1 at CT#85: C1-134919, C1-134924, C1-135207.0.1.00.2.02014-01CT1#86Includes the following contributions agreed by CT1 at CT#86: C1-140385, C1-140386, C1-130388, C1-140705.0.2.00.3.02014-02CT-63CP-140112Version 1.0.0 created for presentation to plenary for information0.3.01.0.02014-04CT1#86bisIncludes the following contribution agreed by CT1 at CT1#86bis:
C1-140813, C1-141260, C1-141262, C1-141265, C1-141266, C1-141267, C1-141309, C1-141580.1.0.01.1.02014-05CT1#87Includes the following contribution agreed by CT1 at CT1#87:
C1-142127, C1-142128, C1-142129, C1-142519.1.1.01.2.02014-07CT1#88Includes the following contribution agreed by CT1 at CT1#88:
C1-142739, C1-143004, C1-143006, C1-143044, C1-143320, C1-143369.1.2.01.3.02014-09CT-65CP-140631Version 2.0.0 created for presentation to plenary for approval1.3.02.0.02014-09CT-65CP-140718Plenary tdoc revised to include missing cover sheet1.3.02.0.02014-09Post CT-65Version 12.0.0 created after approval at CT-652.0.012.0.02014-12CT-66CP-14084000011WLCP security12.0.012.1.02014-12CT-66CP-14084000031Correct the reference on IPv6 network prefix allocation12.0.012.1.02014-12CT-66CP-1408400004Correct the timer name12.0.012.1.02014-12CT-66CP-1408400005Tx value IE12.0.012.1.02014-12CT-66CP-14084000062Update to reference IEEE 80212.0.012.1.02014-12CT-66CP-14084000071Procedure transaction identity12.0.012.1.02014-12CT-66CP-14084000081Corrections and editorials to WLCP12.0.012.1.02015-03CT-67CP-15006500091UDP port number assigned by IANA for WLCP12.1.012.2.02015-06CT-68CP-15030500101Timer Tw112.2.012.3.02015-06CT-68CP-15030500114Reference to EAP authentication and authorization procedure12.2.012.3.02015-09CT-69CP-15052200151WLCP PDN connectivity modification procedure for P-CSCF restoration12.3.013.0.02015-09CT-69CP-15051900161Switch-on and switch-off terms in the context of WLCP for trusted WLAN access to EPC12.3.013.0.02015-09CT-69CP-15052600171Routing rule and default access delivery during PDN connectivity establishment procedure12.3.013.0.02015-09CT-69CP-15052600181IP flow mobility via WLCP PDN modification procedure12.3.013.0.02015-12CT-70CP-1507010019Cleanup of TWAG-initiatd PDN connectivity modification procedure13.0.013.1.02015-12CT-70CP-1507100020Correction of IP address handling during handover to TWAN13.0.013.1.02015-12CT-70CP-1507060021Correction for the UE-initiated PDN connectivity modification procedure13.0.013.1.02015-12CT-70CP-15069600221UE backoff Handling for trusted WLAN access to EPC using WLCP13.0.013.1.02015-12CT-70CP-1507060024NBIFOM container correction13.0.013.1.02015-12CT-70CP-15070600251Editor’s Note on the definition of T358613.0.013.1.02015-12CT-70CP-1507060026Multiple accesses to a PDN connection not allowed for MCM13.0.013.1.02015-12CT-70CP-1507060027PDN modification message type13.0.013.1.02016-03CT-71CP-16008200301Add cause value to WLCP13.1.013.2.02016-03CT-71CP-16007800311UE requested PDN connectivity modification procedure13.1.013.2.02016-06CT-72CP-16032500332PDN connectivity modification procedure13.2.013.3.02016-06CT-72CP-1603250034Correct the direction of PDN modification accept message13.2.013.3.02016-06CT-72CP-16032500351Adding NBIFOM container IE to PDN CONNECTIVITY REJECT message content13.2.013.3.02016-06CT-72CP-16032500361Local release of NBIFOM PDN connection for trusted WLAN13.2.013.3.0
Change history
DateMeetingTDocCRRevCatSubject/CommentNew version2016-09CT#73CP-16050700324Fnon-IP PDN type not applicable in WLCP13.4.02016-12CT#74CP-16079800372BNew emergency PDN connection in TWAN/MCM and handover of emergency PDN connection from 3GPP access to TWAN/MCM14.0.02016-12CT#74CP-16079800393BAdditional PDN connection not allowed via trusted WLAN in MCM when using emergency service14.0.02017-06CT#76CP-1710920040FCorrection to the NBIFOM container IE14.1.0








 STYLEREF ZA 3GPP TS 24.244 V14.1.0 (2017-06)
 PAGE 5
 STYLEREF ZGSM Release 14


3GPP