Chapter 12
Transport
12.1 Introduction
Radio Transport, also known as Mobile Backhaul, refers to solutions for transferring data between base stations and the core network. As air interface data rates and capacities are increasing with LTE, the requirements on the transport network are also increasing. Transport solutions may cause a substantial part of network operating expenses and in some cases the transport network may be the bottleneck from an end-to-end point of view. So, transport optimization may be even more important than air-interface capacity optimization. The transport network can utilize a number of different physical media. Globally, more than 50% of the base stations are connected using microwave radio technology. Fiber, today, constitutes only a small part of transport connections but the share is increasing, especially in urban areas with high LTE capacity requirements. In turn, the share of solutions based on copper lines for connecting macro base stations is decreasing. However, advanced DSL technologies will have their position mainly for connecting femto base stations. Whereas the Radio Network Layer (RNL) is being specified by 3GPP, as shown in Chapter 3 with the presentation of the protocol stacks for different interfaces, the Transport Network Layer (TNL) for LTE is nowhere defined consistently. Mostly reference is made to protocols outside 3GPP. Several standardization bodies are contributing, among them IETF (Internet Engineering Task ...
