January 2008 | Volume 11/ Number 1
Wireless Backhaul is Booming
By: Richard “Zippy” Grigonis
As the world’s populace becomes more mobile, wireless backhaul – the link between a carrier’s cell site (base station at the cell tower) and its mobile switching facility and thence to the PSTN – suddenly becomes a big issue. In times past, telecom service providers (TEMs) in the wireless world could get by with some T-1s connecting base stations to a core network. Today, however, wireless operators spend about half of the operational costs – more than $3 billion – for leasing T1/E1 lines from Local Exchange Carriers. Moreover, with the rise of mobile video, multimedia and data over such 3G and 4G technologies as W-CDMA (Wideband CDMA), HSDPA (High-Speed Downlink Packet Access), and HSUPA (High Speed Uplink Packet Access), bandwidth considerations are focusing carriers to come up with more scalable, or just outright high bandwidth backhaul schemes, involving both wireline and wireless technologies (Optical fiber, improved ways of sending IP over copper, microwave and Ethernet over copper or fiber), or else just leasing bandwidth from wholesale providers and opportunistic alternative carriers who target this increasingly lucrative market.
A recent ABI Research study predicts that North America will adopt Ethernet as the primary wireless backhaul transport, while Asia Pacific will use more microwave, and South America will continue to use the increasingly primitive-looking (not to mention expensive and low bandwidth) T-1 spans.
The first cost-effective reaction to deal with the increasing bandwidth needs of wireless backhaul is to get copper to carry more information, just like the way DSL revolutionized the delivery of high bandwidth Internet access to the home over ordinary copper “last mile” phone lines. In the case of Pseudowire technology, telecom services are transported over IP-based networks
Pseudowire Teaches Old Copper New Tricks
As its name implies, pseudowire is the emulation of a native service over a PSN (Packet Switched Network). The native service may be anything from ATM, Frame Relay, Ethernet, TDM, or SONET/SDH, while the PSN may be MPLS, IP (either IPv4 or IPv6), or L2TPv3. Thus, conventional voice and TDM traffic can be carried over packet networks without having to buy new equipment.
Axerra Networks (http://www.axerra.com) bills itself as “The Pseudo-Wire Company” and is in fact a leading provider of circuit emulation solutions. Their Axerra AXN Pseudo-Wire solution is a full-service alternative to TDM access for mobile wireless operators’ growing backhaul bandwidth needs for both voice and data services in packet-based Radio Access Networks (RANs), including those operators providing CDMA and EV-DO as well as GSM and UMTS services. Less expensive packet access networks can now replace TDM backhaul for voice and wireless services for mobile wireless operators, cable MSOs, competitive access providers, and incumbent carriers. Indeed, any packet access network (carrier Ethernet, cable HFC, xDSL, EPON/GPON, broadband wireless such as WiMAX) can become a full-service alternative to TDM access.
RAD Data Communications (http://www.rad.com) is also a major provider of packet network backhaul solutions. Their ACE-3x00 series of multiservice aggregation units simultaneously support TDM and ATM over packet-switched networks (Ethernet, IP or MPLS), and are Psudowire-enabled. For example, RAD’s ACE-3400 RAN backhaul multiservice aggregation unit and ACE-3402 RAN backhaul multiservice aggregation unit multiplex multiple E1/T1/J1 lines to ensure the most economical allocation of backhauling resources and the delivery of 2G and 3G services. Several ATM/TDM services can be aggregated onto a single network interface (IMA, STM-1/OC-3 or Gigabit Ethernet).
Pseudowire capabilities can also be founding RAD’s Airmux-200, a carrier-class, point-to-point and multi point-to-point wireless broadband multiplexer that connects E1/T1 and Ethernet networks over a wireless link. Compliant with FCC, CAN/CSA and ETSI regulations for license-exempt transmission, the Airmux-200 wireless multiplexer combines legacy TDM and Ethernet services for transmission over 2.3 GHz to 2.7 GHz and 4.9 GHz to 5.95 GHz bands. The unit has a total air data rate of 48 Mbps, with a theoretical maximum transmission distance of up to 80 kilometers (50 miles). Transmission is encrypted to ensure security.
Finally, RAD’s LA-130 DSL cell-site gateway is a small 1U high unit, that takes a novel approach in aggregating four E1 lines, delivering 2G and 3G cellular backhaul traffic over the existing DSL infrastructure. It uses pseudowire emulation so that carriers can provision ATM and TDM services over IP DSLAMs and packet-switched networks. The LA-130 even allows “grooming” of several fractional E1 UNI, several IMA links, or E1 TDM (CES) into a single IMA network interface, over four SHDSL pairs, thus reducing cellular backhaul expenses.
Fiber to the Rescue?
In the U.S., Verizon (http://www.verizon.com) has a wholesale division, Verizon Partner Solutions (http://www.verizon.com/wholesale), that is now heavily involved with selling bandwidth for wireless backhaul. Like the companies mentioned previously, one of their approaches to serve this market is a TDM-based pseudowire solution they call the Verizon Packet Access Service. However, their initial method to stake a claim in this market is their fiber-based ETAG (Ethernet Transport and Aggregation) backhaul service, which should be available by the time you read this. What’s so interesting about Verizon’s ETAG is that, just as the RAD system mentioned earlier uses (or “re-uses”) existing DSL lines, Verizon’s ETAG is going use an Ethernet-based pseudowire system running over the existing (and growing) FiOS FTTP (Fiber-to-the-Premise) BPON and GPON infrastructure that by 2011 will be passing more than 18 million home and business premises – not to mention cell towers and base stations. Thus wireless backhaul services can be added to the fiber network deployed for fiOS.
A Piece of the Pie
Cable operators have also noticed the skyrocketing wireless broadband market, and, noting that many of their HFC plats are near wireless base stations, have been attempting to enter the market. In such cases backhaul is generally implemented using something on the order of a SONET/SDH in the access network with ring termination centralized at the headend. Ciena Corporation (http://www.ciena.com) champions such a system, since they say it minimizes cost by reducing the number of T1/E1 cross-connect points and ring nodes while providing integrated transport for 2G/2.5G and 3G services. Ciena’s SONET/SDH micro-MSPP supports T1/E1, DS3, 10/100baseT and GbE client interfaces with OC-3/12/48 or STM-1/4/16 network ports. Several nodes can be connected in a ring or point-to-point architecture to an aggegration node, either at the closest d-hub or centralized at the headend or primary hub. In either scenario, the SONET/SDH line signals can be transparently multiplexed using G.709 digital wrapper technology onto a common wavelength with VOD and CMTS traffic back to a headend MSPP node. There, the MSPP can groom the DS1/E1 traffic to channelized OC-n/STM-n ports and Ethernet traffic from all the cell sites to FE/GbE ports for handoff to the appropriate wireless operator.
Wireless Transport for Wireless Backhaul
The idea of using point-to-point wireless broadband to serve as a backhaul scheme for wireless services goes back to the early days when people were talking about deploying WiMAX as a backhaul solution for WiFi hotspots and meshes. This has actually been done by the Waltham, Massachusetts-based company TowerStream (http://www.towerstream.com) which back in 2003 extended its WiMAX-like wireless T1-level service to the five boroughs of New York City and Northern New Jersey, in the process providing wireless backhaul to 802.11 hotspots.
TowerStream’s network uses 802.16-class base stations from Aperto Networks (http://www.aperto.com), laid out in a self-healing wireless ring wherein towers connect to point-to-point unlicensed and licensed links. Each point on the ring can act as an Internet point of presence (POP). Customers connect directly to the ring via an eight-inch dish installed outside their buildings. To connect the Aperto equipment to the 802.11 WiFi hotspots, TowerStream uses 10/100 Ethernet.
TowerStream has also used the AirPair 50 and AirPair 100 transceivers from DragonWave (http://www.dragonwave.com) as a backhaul solution to provide high capacity connectivity from multi-point sites. The AirPair 100 supports traditional TDM services through DragonWave’s APX-104/108E modules. AirPair solutions can provide native Ethernet backhaul with less than a 0.5ms delay, making them suitable for supporting such services as Voice and Video-over-IP. TowerStream can increase AirPair throughput to 200 Mbps via remote software commands, making the whole system quite scalable.
Of course, microwave point-to-point communications goes back a long way, to 1947 in fact, when the first microwave line was deployed between the headquarters of AT&T’s Long Lines Department at 32 Avenue of the Americas and the New England Telephone and Telegraph’s Bowdoin Square building via seven relay stations. On August 17, 1951 the first telephone call traveled over AT&T’s then-new microwave backbone route, at the time the longest microwave system in the world, a chain of 107 microwave towers spaced about 30 miles apart and stretching coast-to-coast across America. It was built over a period of three years at a cost of $40 million. Just like today’s microwave backbones, the system could carry TV signals too.
Today, FiberTower Corporation (http://www.fibertower.com), founded in 2000, has targeted the wireless carrier backhaul and access transport market with an interesting hybrid microwave (24 GHz and 39 GHz bands)/SONET network solution. FiberTower has a presence in 12 major markets, works with six of the leading cellular carriers, and has partnerships with the biggest U.S. tower operators.
Wireless backhaul will continue to be a booming opportunity for many years to come. Expect a continuous stream of ingenious solutions for backhauling ever-increasing bandwidths from the world’s wireless services players. IT
Richard Grigonis is Executive Editor of TMC’s IP Communications Group.
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