Mobile Backhaul

4.6 IP and Transport Layer Protocols

For the terrestrial transport, both 3G and LTE specifications define an IP based protocol stack for the logical interfaces; Iub, Iur, Iu-cs, Iu-ps for the 3G, and S1 and X2 for the LTE. For 2G, A and Gb have been standardized also for IP transport as discussed in Chapter 03. 2G Abis interface does not have a standardized IP alternative.

Base stations and other radio network elements (controllers) are basically hosts with an IP stack.² RNC, even if it has all logical interfaces based on IP, is not a router that routes IP packets between its ports. Instead, it terminates the radio network layer and the transport protocol stacks. For another logical interface a new IP packet is created (after the radio network processing).

UDP is used as the upper layer protocol in the user plane, SCTP in the control plane. The intermediate transport network may use Ethernet in the access, IP or MPLS for the aggregation, or a combination of those. At IP, routes may be learned by a routing protocol, or static routes may be configured.

Details of how mobile elements obtain their IP addresses and what is the addressing structure, is not defined in 3GPP. Networking and transport standards are not in the scope of 3GPP.

Since the mobile network elements must be able to interface standard compliant packet networks, it can be assumed that the mobile network elements need to comply with the relevant IETF, IEEE and other standards bodies' definitions, even when these are ...