Site, hub and aggregation switches/routers, edge Ethernet devices
Layer 2 Ethernet or Layer 3 IP backhaul, or a hybrid of the two, require devices at the site, edge, hub and aggregation points in the network.
Native Packet Optical solutions support Carrier Ethernet standards, combining Carrier Ethernet-based cell site demarcation with converged optical Ethernet aggregation.
Layer 3 IP solutions push L3 awareness out to the network edge, and builds IP VPNs over the IP infrastructure.
LTE brings the need for X2 interface support between base stations, establishing control of handover at a local aggregation point, rather than back at the core. That reduces latencies in the network.
There has been a wide industry debate as to L2/L3 in backhaul.
“Some use layer 3 routers at the cell sites, and others are strongly opposed to that and want to keep backhaul as simple as possible by using Ethernet. Many operators want to keep as much of their backhaul processing as possible in layer 2, while recognizing that MPLS, MPLS-TP, pseudowires, etc., have elements of layer 2.5. Many operators believe the principal layer 2 advantages over layer 3 are simpler equipment and operations—hence lower equipment and operations cost for a lower cost-per-bit as network scales to support large capacity growth.” (cf Infonetics, 2011)
“Many operators are reaching the conclusion that the service and networking agility and inter-connectivity that they are going to need is best served with a full featured scalable IP/MPLS infrastructure capable of delivering both Carrier Ethernet services and IP services.
“There’s more to it than that of course – there is a high value IP-Optimized Ethernet transport component required in the network. In many locations at the edge of the network this will be adequate and valuable. The architectural goal that is emerging is a layer 3 IP routed capability using MPLS for constructing traffic engineered, manageable VPNS, overlaid on a solid Ethernet transport infrastructure.” (cf Alcatel-Lucent)
