- Copper cables with traditional E1/T1 services
- Copper cables with DSL services
- Point-to-multipoint Passive Optical Networks (PON)
- Point-to-point active Ethernet
- Point-to-point Fixed Microwave wireless
Operators will use several or all of these techniques in order to meet in-time installation and reduce operational expenses. The decision is made on a case by case basis and depends on availability and costs. As a result, mobile backhaul systems need to be flexibly supporting all of the above technologies while maintaining a unified management system and insulating the operator from operational impact generated by different technologies.
The number of cell sites connected over T1/E1 leased lines is still significant, in particular in the US, but as data services take the front stage, operators need to increase available bandwidth to these sites. The simplest and fastest way to do so, albeit incurring higher expenses, is to use bonded T1/E1 access using MLPPP and GFP-VCAT for Ethernet encapsulation and Inverse Multiplexing ATM (IMA) for ATM payloads used for 3G.
Mobile Backhaul over DSL
DSL lines are very attractive and cost effective solution, particularly in urban and suburban areas, where DSL has been widely deployed. There are three DSL technologies that can be used to that end: G.SHDSL, ADLS2+ and VDSL. The technologies differ in supported bandwidth and reach. G.SHDSL serves the longest reach, but delivers only 2.5 Mbps per wire pair. VDSL2 can deliver up to 50 Mbps over a distance of 1 km.
In order to support data rates required by 4G (LTE) networks, DSL- based equipment has to deliver a high bandwidth of 500 Mbps and higher per cell base. To that end, mobile backhaul equipment needs to implement EFM bonding of a number of pairs using ITU-T G.998.2.
Mobile Backhaul over PON
Point-to-Multipoint (P2MP) fiber technologies – EPON and GPON – are deployed today by many wireline Service Providers and are starting to take over DSL as the preferred technology for broadband access delivery. As PON systems become increasingly present in metro and sub-urban areas, the use of PON as the mobile backhaul transport technology of choice will increase. There are several reasons for that. PON technology, contrary to DSL, does not require a trade-off between distance and throughput and can deliver 100 Mbps to a distance of 20 km with no difficulty. Since PON is a technology addressing the residential market, high volumes and service price pressure should meet a low cost of service, i.e. OpEx.
While GPON systems use precise PRC derived 8 kHz timing, EPON system can support the required timing/synchronization signal using Ethernet synchronization protocols, SynchE or 1588v2.
Mobile Backhaul over Optical Ethernet
This method is the most straightforward and based on standard Ethernet interfaces. The down side of using this method is a need for a fiber network that may be costly to deploy.
Mobile Backhaul over Fixed Microwave
Widely used in Europe and other parts of the world, microwave point-to-point (P2P) radio provides a number of benefits that make it ideally suited for next-generation backhaul applications. Microwave cellular backhaul has several inherent advantages: low acquisition cost (CapEx) as it does not require costly civil engineering work for infrastructure, low operational cost (OpEx) as it doesn’t require leasing transmission capacity from fixed wireline operators, short deployment time and long reach.
Use of microwave P2P for mobile backhaul does not come without a price, however. First of all, in order to deploy a mobile backhaul based on microwave links, the operator must obtain a necessary spectrum. This can be difficult in certain countries. Second, microwave links’ capacity is susceptible to weather conditions and available bandwidth can fluctuate widely with time of day and rain. To address this problem, microwave based systems must be able to implement a number of traffic management profiles, to interact with the radio front end and receive indication of the link quality and to switch between several traffic management profiles based on these indications.
Mobile Backhaul over Free Space Optics
Free Space Optics (FSO) is a transport technology similar to Fixed Microwave. It relies on transmission over the air by optical systems using high power lasers. FSO presents the same benefits as microwave, i.e. low acquisition costs due to low infrastructure investment. FSO also suffers from similar problems like fixed microwave links, although FSO links are affected by fog and not by rain, like microwave. Several vendors have created dual mode systems with FSO and microwave acting as a back for one another.
Mobile Backhaul Network Elements
The industry consensus is that the emerging mobile backhaul network should be based on a Layer 2 packet network. This network must support efficient transport of 4G mobile services – data and voice – and at the same time to guarantee a seamless migration from the current 2G and 3G networks. To that end, network elements in a mobile backhaul network have to support:
- Hierarchical Traffic Management
- Carrier grade Ethernet OAM
- Synchronization – SyncE and 1588v2
- Pseudowire (PWE3) for TDM, ATM, and PPP
In order to support mobile backhaul services universally, network elements have to support a variety of transport technologies:
- Optical transport
- Fixed wireless
- DSL with Ethernet bonding
- T1/E1 with bonding
Any mobile backhaul network requires two types of network elements: Cell Tower Gateway and Network Edge Aggregator.
Cell Tower Gateway (CTG)
Cell Tower Gateway (CTG) is located at a cell tower and connects a number of base stations to the all-packet, Ethernet mobile backhaul network. Its function is to connect base stations of different generations – 2G, 3G, 4G to the all-packet RAN. To that end, CTG includes pseudowire (PWE3) interworking functions for interconnecting PDH and ATM payloads serving 2G and 3G base stations. CTG is required to serve as termination point for CGE OAM packets to support network management functionality. It also implements a local Stratum 3 clock derived from SyncE or 1588v2 slave function.
CTG is required to support all technologies available in RAN – PDH, DSL, PON, fixed microwave links and P2P optical Ethernet. This capability can be achieved by a modular design, where CTG Layer 2 functionality is independent of RAN PHY technology, and only PHY related sub-assembly is network related.
To accommodate future growth, CTG should have data throughput capability of 10 Gbps.
For a modular cell tower gateway design Ethernity’s ENET solution can be splitted to a chipset solution where a pure Carrier Ethernet solution together with jitter buffer, reordering engine and synchronization is located on a main board, and a companion FPGA that holds Ingress and Egress TDM silos is located at on a TDM module through Giga Ethernet interface or G.999.1 channelized Gigabit interface.
Network Edge Aggregator (NEA)
Network Edge Aggregator is the second network element in RAN. Its function is to connect and multiplex services from a number of base stations, to groom signals from different mobile generations and direct them to an appropriate radio controller.
NEA grooms PDH and ATM payloads serving 2G and 3G networks, aggregates them in a higher order signal, e.g. DS3, OC3/STM1, and connects with appropriate network controllers. It also generates a synchronization clock for subtended CGTs based on PRC traceable clock input from BITS, GPS or received from a Master clock using 1588v2, SyncE or from a PDH/Sonet-SDH signal.
NEA throughput depends on the number of served CTGs and can scale from 40 Gbps to 200 Gbps. It will use different RAN technologies to connect to subtended CTGs.
NEA can be implemented in a multiservice access platform that embodies IP-DSLAM and GPON/EPON OLT functionality on the same chassis and delivers residential broadband wireline services and mobile backhaul simultaneously.
Ethernity’s Mobile Backhaul Solution– ENET3800 and ENET4200 Access Processors
Ethernity’s access processors provide the best solution for designing efficient and cost effective Cell Tower Gateways and Network Edge Aggregators.
ENET3800PW is optimized for CTGs and NEA Sonet/SDH line cards, and ENET4200 provides an optimal solution for high port count NEA line cards and Network Interface/Switching Cards.
The design of ENET3800 and ENET4200 is based on Ethernity’s proprietary architecture and implemented on state-of-the-art FPGAs. The fragment based architecture requires a single memory access per packet and results in efficient use of FPGA resources, providing a cost effective solution.
ENET3800 family scales from 2 Gbps up to 12 Gbps throughput. The devices are optimized for mobile backhaul CGT and NEA applications and incorporate:
- Versatile classification rules
- Per-flow and per-port policing and metering
- 4-level hierarchical scheduling
- EFM bonding
- Support for SyncE and 1588v2
- CGE OAM hardware processors
- PWE3 for SAToP/CESoPSN, ATM and PPP traffic
ENET3800 and ENET4200 families are based on hardware configurable devices. All packet processing and inter-working functions are implemented in hardware and deliver deterministic performance at all speeds. ENET Access Processors are configurable and not programmable and as such do not require the major software effort required by network processors. The both families use identical APIs to reduce software development required by system designers.
Using ENET3800 and ENET4200 families, Telecommunication Equipment Manufacturers (TEMs) can design a cost effective solution for the next generation of mobile backhaul networks in a record time. Implemented on FPGA, Ethernity’s solutions can evolve with the emergence of new protocols and also integrate proprietary functions to create even more cost effective offerings.