Connectionless service

Description

A connectionless service is a communication paradigm in which data is transferred between service users without the need for a pre-established end-to-end connection or call setup procedure. In the context of 3GPP, this concept is fundamental to packet-switched (PS) domains and IP-based services. Unlike connection-oriented services, where a dedicated path or virtual circuit is established before data transfer (e.g., in circuit-switched telephony), connectionless service allows each data unit—typically a packet or datagram—to be routed independently through the network based on the destination address contained in the packet header. This means that no prior signaling is required to set up a connection, and the network does not maintain state information about the communication session.

In 3GPP networks, connectionless service is primarily realized through the General Packet Radio Service (GPRS) and its evolved packet core (EPC) and 5G core (5GC) counterparts. The User Plane (UP) functions, such as the Serving Gateway (SGW) and Packet Data Network Gateway (PGW) in EPC, or the User Plane Function (UPF) in 5GC, forward packets based on routing information without establishing a dedicated connection for each communication. This is in contrast to connection-oriented services like those in the circuit-switched domain, where a dedicated radio resource and core network path are reserved for the duration of a call. The connectionless nature is inherent to the IP protocol, which is the foundation of modern mobile broadband, IoT, and mission-critical services.

The key components enabling connectionless service in 3GPP include the packet data network (PDN) connection or PDU session, which provides the logical association between the User Equipment (UE) and a data network. However, within this session, individual packets are forwarded independently. The UE is assigned an IP address, and the network uses this address to route packets to and from the UE. The core network elements, such as the SGSN/GGSN in GPRS/UMTS or the MME/SGW/PGW in LTE, and the AMF/SMF/UPF in 5G, manage the mobility and session context but do not establish per-communication connections. The radio access network (RAN) also supports connectionless transmission at the radio link control (RLC) layer in unacknowledged mode (UM) for certain services, where data is transmitted without an established RLC connection.

Connectionless service is essential for many 3GPP services, including IP multimedia subsystem (IMS) services like voice over IP (VoIP) and video calling, where the underlying transport is packet-based. It also supports machine-type communication (MTC) and IoT applications, where devices may send small data packets infrequently without the overhead of connection setup. In 5G, the concept is further enhanced with features like control plane and user plane separation (CUPS) and network slicing, allowing tailored connectionless service characteristics for different use cases. The service is defined in 3GPP TS 21.905 (Vocabulary for 3GPP Specifications) and TS 22.060 (General Packet Radio Service (GPRS); Service description; Stage 1), which outline the requirements and definitions.

Overall, connectionless service is a cornerstone of modern mobile networks, enabling efficient, scalable, and flexible data communication. Its simplicity and alignment with IP protocols have made it the dominant mode of operation for data services in 3GPP systems, from GPRS to 5G and beyond.

Purpose & Motivation

The connectionless service exists to provide efficient, scalable data transfer without the overhead of establishing and maintaining dedicated connections. In early mobile networks, circuit-switched connections were used for voice and data, requiring a call setup that reserved resources for the entire duration, which was inefficient for bursty data traffic. The introduction of GPRS in 3GPP Release 4 brought packet-switched capabilities, leveraging the connectionless nature of IP to allow multiple users to share network resources dynamically. This solved the problem of resource underutilization and enabled always-on connectivity, where users could send and receive data without a lengthy setup procedure.

The motivation for connectionless service also stems from the need to support a wide range of applications with varying traffic patterns. For example, web browsing, email, and instant messaging generate sporadic packets, and establishing a connection for each would be wasteful. Connectionless service allows these applications to operate seamlessly, with the network routing each packet independently. Furthermore, as mobile networks evolved towards all-IP architectures in LTE and 5G, connectionless service became the default mode for data transport, supporting high-speed broadband, low-latency communications, and massive IoT deployments. It addresses the limitations of connection-oriented approaches by reducing signaling overhead, improving scalability, and simplifying network design.