2.4 Packet Based Backhaul Networks

The previous sections discuss many drivers strongly pushing existing MBH networks to change, and new MBH networks to be different; they will be based on packet technologies and networking. In a fully packet-based MBH network there are no more PDH and SDH/Sonet nor ATM equipment, but it consists of packet switches and routers (layer 2 and 3 devices) connected directly to each other by physical (layer 1) connections, for example by optical fiber or microwave links. Packet networks and networking will be discussed more in Chapter 04 and technologies and equipment used in Chapter 05; below are some general observations.

2.4.1 Physical Network and Topology

Network basic structure and topology will often look quite similar to that of the earlier MBH networks (see section 2.2), as the basic economics of the physical network (layer 1) optimization do not change much – physical links are still shared as much as possible for several base station sites and the un-shared final links to base station sites are kept as short as possible.

The nodes used in the traffic merging and concentration points are obviously different in the packet-based MBH networks – they are, for example, Ethernet switches and IP/MPLS routers, i.e. layer 2 and layer 3 devices in packet networking terminology; some examples on possible (access) network solutions are presented in Chapter 10.

In general access tiers are more often implemented based on layer 2 solutions (e.g. Ethernet switching) while in backbone tiers more often layer 3 or IP/MPLS solutions are used; in the aggregation tier both solutions can be feasible. In each individual case selection of the packet technology to be applied is made based on economic comparisons in that environment and network topology, with expected traffic profiles and traffic growth.

2.4.2 Logical Network and Protocol Layers

Logical structure and protocols used in the MBH packet networks are discussed more in Chapter 04. However, it may be worth noting already here that even if a MBH network is based on packet technology, it is a MBH internal solution and separate from the packet technology used for the end-user traffic. This may be best seen looking on a simplified protocol picture in Figure 2.9: the end-user IP traffic is tunneled over the MBH network and remains a few protocol layers above the transport IP and transport L2/L1 protocols. Therefore, for example, the IP addresses used in the MBH network are its internal issue, and have no relation to the end-user traffic and addresses used in that.

Figure 2.9 Relation of end-user IP and transport IP in a packet-based MBH network (just the principle, here LTE user plane protocols used as an example).