VICTOR LOPEZ FUTURE-PROOFING
Future-proofing front-haul and back-haul networks
T here is a great interest of the industrial and academic communities in the development of the next generation of cellular communications, referred as 5G networks. In this way several key forums, such as ITU, 3GPP, IEEE and IETF, are working on the standardization of the different components to have a complete solution for 2020. In fact, Europe has an important program from the 5G Infrastructure Public Private Partnership, which is under the Horizon2020 Framework Programme. The technologies and requirements of the 5G solutions are not specifically outlined, but there are some indicators of the technical objectives of a 5G solution. As an example, the ITU-R WP5D has defined a peak data rate of 20Gbps and the radio interface latency as 1ms. There are new technologies that must handle these indicators in the Radio Access Network (like small cells, offering massive multiplexing, flexible resource sharing, etc.). However, these requirements will be extended to the front-haul and back-haul networks to some extent. Nowadays, network operators start separating their Remote Radio Unit (RRU) and their Baseband Unit (BBU) in order to maximize investments in the radio equipment. The front-haul deployments are based on microwave technologies (e-band) or fibre deployments. The operator generally selects fibre in urban areas, where there is an important amount of clients, or when microwave technologies cannot fulfill the requirements. LIMITATIONS OF CPRI Current fibre deployments do not use any optical technology, but just so-called grey interfaces. Right now, the Common Public Radio Interface (CPRI) is used to interface the RRUs and the BBU. However, it has some limitations and a high bandwidth, which can limit the centralization of BBUs on a larger scale. When the number of RRUs increases, the operator must deploy optical transmission to reach the BBU site. There is an initiative to improve such interface called “Next Generation Fronthaul Interface” (NGFI). As there is room for improvement on the CPRI, the operator must consider which is a future-proof deployed not only current requirements, but also the ones for 5G networks. On the other hand, current back- haul networks are deployed using IP/ MPLS equipment on top of ring physical topologies. This physical infrastructure
Although the emerging 5G network protocol is not yet precisely specified, its various iterations currently under development are showing great potential to meet the needs of rapid growth in bandwidth demand.
VÍCTOR LÓPEZ
Several industry forums are working on the standardization of 5G technology to produce a complete solution by 2020.
of adding/dropping signals at the fibre topology. There are some limitations to this solution: the number of passive filters and the distances. When the number of hops is high or the distances are significant, the only solution is to deploy CWDM or DWDM technology with amplification. In this way, the distance is a limiting factor due to the latency restriction of the services. This parameter may discard some technologies like OTN for front-haul or long-haul links to reach remote areas. PACKET OPTICAL OPTION Some transport equipment vendors are proposing packet-optical solutions. This equipment has not only the transponders for CWDM/DWDM, but also a packet matrix that enables the aggregation of traffic at the transport equipment. This may end up with a reduction on the number of ports at the routers, as the traffic is by-passed and aggregated at the transport layer. A drawback of this approach is that the network operation is more complex. Instead of using L3 services from the edge, the transport equipment and the routers must be jointly configured. To sum up, there are several optical technologies that can cope with the requirements of current network operator needs. However, the operator must remember that today’s deployments are our future legacy networks. The evolution of 5G and CPRI technologies are crucial for the architectural decisions of future-proof optical solutions.
is based on ring ducts from the SDH deployment, where the number of fibres was limited. The IP/MPLS equipment evolved from 1G to 10G technologies, but now they must migrate from 10G interfaces to 100G. Such evolution must consider not only the packet layer, but also the underlying infrastructure with its limitations. structured by the cascading of routers to aggregate the traffic. At the lower part of the hierarchy, the traffic from different base stations (BS) and from the DSLAMs and OLTs is aggregated until the IP edge is reached. At the packet level, the operator may consider changing the 10G rings into 10G stars or 100G rings. However, the deployment of optical technologies allows creating logical stars even when the fiber is deployed forming ring structures, using in a more efficient way the deployed fiber plant. Both network segments (front-haul and back-haul) have similar problems as the operator may decide whether to deploy optical technologies and when. The initial point at both network segments is that the operator has dark fiber deployments, but there is a need for extra capacity due to CPRI limitations or traffic increment in the end users. Typically, the distances are lower than 40km and a cost-effective solution is required. The best solution for both scenarios, it is to use coloured interfaces at the router equipment, using simple passive filters for the sake AGGREGATION The packet equipment is typically
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| ISSUE 7 | Q3 2016
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