Point-to-point

Description

Point-to-point (P2P) is a fundamental communication configuration value defined in 3GPP TS 21.905, the vocabulary specification for 3GPP. It describes a service attribute called "communication configuration" that specifies the number of network terminations involved in a communication session. When set to point-to-point, the communication involves exactly two network terminations, establishing a direct one-to-one relationship between them.

In the context of 3GPP networks, a network termination represents an endpoint of a communication path. This could be a user equipment (UE), a server, or any other addressable entity within the network. The point-to-point configuration is the simplest form of communication topology, as opposed to point-to-multipoint or multipoint configurations where more than two terminations are involved.

The point-to-point attribute is used in service descriptions and capability negotiations. It helps define the nature of a service and ensures that network resources are allocated appropriately. For example, a voice call between two parties is a classic point-to-point service, where each party is a network termination. The network must establish a dedicated bearer or connection between these two endpoints to carry the voice traffic.

From an architectural perspective, point-to-point communication can be realized through various bearer types depending on the access technology. In GSM/UMTS, a point-to-point PDP context or bearer is established between the UE and the GGSN, effectively creating a point-to-point tunnel. In LTE, an EPS bearer provides a point-to-point connection between the UE and the P-GW. In 5G, a PDU session can be of type IPv4, IPv6, or Ethernet, and it typically provides point-to-point connectivity between the UE and a data network (DN), although the DN itself may be a multipoint network.

The point-to-point configuration is also relevant in the context of multicast and broadcast services. For instance, in MBMS (Multimedia Broadcast Multicast Service), a distinction is made between point-to-point and point-to-multipoint delivery. When only a few users are interested in a service, the network may choose to deliver it via point-to-point bearers to each user individually, rather than using a broadcast bearer. This decision is based on the number of users and radio resource efficiency.

In summary, point-to-point is a basic service attribute that defines a two-party communication. It is a building block for many services and is used in network design, resource allocation, and service description. Its simplicity makes it a universal concept across all 3GPP generations, from Rel-4 through Rel-19 and beyond.

Purpose & Motivation

The point-to-point communication configuration exists to provide a clear, standardized way to describe the topology of a communication service. In the early days of 3GPP, as networks evolved from circuit-switched to packet-switched, there was a need to categorize services based on how many parties were involved. This categorization helps in service definition, capability negotiation, and resource management. By specifying that a service is point-to-point, the network can allocate dedicated resources and apply appropriate QoS and security policies tailored for a two-party session.

Before the formal definition of this attribute, service descriptions were often ad-hoc and lacked a common vocabulary. The introduction of point-to-point as a value of the "communication configuration" attribute in TS 21.905 provided a consistent terminology that could be used across specifications and vendor implementations. This is particularly important in interoperability scenarios, where different networks and devices must agree on the nature of a service to establish it correctly.

Moreover, the point-to-point concept addresses the need to distinguish between unicast and multicast/broadcast communications. While multicast and broadcast are efficient for delivering content to many users simultaneously, point-to-point is necessary for personalized, bidirectional communication such as voice calls, video calls, and interactive data sessions. The attribute allows the network to choose the appropriate delivery method based on the service requirements and the number of users.