So, what’s changing with LTE and LTE-Advanced?
Well, the name backhaul has actually been a pretty accurate moniker to date. The majority of traffic has historically flowed from the cell sites to the mobile radio node controllers and vice versa. However, LTE and LTE-A represent a major transition for operators as they plan their backhaul strategy. There are many implications of LTE and LTE-A overall, but, just considering the backhaul aspects, 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. Previous generations of mobile could, and did, leverage IP for backhaul but often could get by in an essentially connection-oriented approach using point-to-point tunnels such as pseudo wires over a packet infrastructure. Of course the network must continue to emulate point to point capabilities for earlier radio generations as needed at the same time supporting layer 3 routing services to optimally address new base station inter-communication interfaces introduced by LTE. Let's take a quick look at a few LTE and LTE-A features as examples of where the challenges come from – with some of the attributes in the backhaul network to meet these challenges:
- There is the X2 interface - the e Node B basestation inter-connection interface – supporting local traffic between co-operating groups of base stations to support features such as network configuration, handover, and algorithms to increase RAN optimization. IP virtual private networks can provide manageable connectivity here.
- Accurate phase synchronization through the network will be required for: location based services, interference mitigation mechanisms, handovers, Coordinated Multipoint and multimedia broadcast, also time-division duplexed TD-LTE. Accurate phase synchronization delivery through an IP network has been made possible by developments in protocols such as IEEE1588, a protocol that can support the phase and time of day requirements for these capabilities securely and efficiently.
- Multimedia Broadcast can leverage IP Multicast in the backhaul infrastructure to make its operation more efficient, removing unnecessary load on the network, by only replicating multimedia broadcast packets where they are required in the network.
So, in backhaul, a good recipe for success would seem to be: IP for strategic flexibility, MPLS for scalable, manageable traffic engineering, all on a solid IP-Optimized Ethernet transport layer. All of which can leverage any network media across copper fiber and microwave. LTE and LTE-Advanced are technologies that are really all about delivering a better user experience, with efficient resource usage also of course, operator surveys indicate this to be true. Creating a backhaul capability to augment and support the capabilities of LTE and LTE-A greatly assists in pursuing that goal. For a little more insight into some of the detail I have glossed over here – take a look at the application note 'Backhaul Considerations For LTE And LTE-Advanced' and other relevant information on our mobile backhaul solutions page. To contact the author or request additional information, please send an email to firstname.lastname@example.org.
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