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The X2 is a new type of interface introduced by the LTE Radio Access Network.
It connects neighbouring eNodeBs in a peer to peer fashion to assist handover and provide a means for rapid co-ordination of radio resources.
This paper considers in detail the functions that are performed over the X2 in order to derive performance requirements for the transport networks which will need to carry it.
X2 does not require a significant bandwidth. RAN Vendors expect that traffic levels will be only a few percent of the main „S1‟ backhaul interface.
Latency requirements, on the other hand, are more challenging.
X2 delay for user traffic is additional to that on the S1, so should be as small as possible.
Furthermore, interference co-ordination features proposed for future releases of LTE-Advanced are highly sensitive to small delays.
The paper goes on to consider the impact of different last mile backhaul topologies on X2 connectivity and latency.
The hub-and-spoke topology achieved with point-to-multipoint (PMP) microwave provides a lower and more consistent latency than achieved with the tree-topologies resulting from point-to-point (PTP) networks.
Finally, it shows that VectaStar point-to-multipoint microwave backhaul from Cambridge Broadband Networks is well suited to the transport of LTE X2 traffic.