Backhaul Challenges and Strategies

By: Stephen Las Marias, Editor
( 1 Nov 2008 )

The exponential growth of mobile traffic has been generating business for wireless operators. However, when it comes to the network equipment side, one major issue arises: the current-highly congested wireless backhaul network—the link from the base station back to the central office, which has been experiencing drastic increase in bandwidth demand driven by high-end consumer devices that are now able to surf the Internet, download mobile videos and music, and provide access to emails, among others. The existing backhaul networks are no longer efficient, and mobile operators now need more bandwidth than ever, while keeping in mind their existing infrastructures.

"Traffic on mobile backhaul networks will grow approximately 32 percent annually due to the adoption of mobile broadband services worldwide," says Idris Vasi, Senior Vice President for Global Strategic Sales and Alliances, Ordyn Technologies. With that, he says mobile operators today are challenged to grow backhaul capacity quickly, flexibly and economically, to support rapid growth in bandwidth-intensive mobile data services.

Michael Murphy, Head of Technology, Nokia Siemens Networks (NSN) APAC, agrees. "The biggest technical challenge is to carry increasingly large amounts of data traffic. From a practical perspective, this cannot be done using E1 links anymore, so operators have to look at potentially costly fiber or Ethernet alternatives," says Murphy. Speaking specifically about the High Speed Packet Access (HSPA) protocol, Murphy cites the growth in bandwidth of HSPA from just about 1.8Mbps in around the year 2004 toward 42Mbps in 2009—theoretical speeds—per sector, as one factor. "In practice, this could mean 50Mbps of traffic for 3G from a single three-sector BTS, and obviously much higher for LTE [Long Term Evolution]. This simply cannot practically be carried on E1s, and that is the driver for change," he says.

"When you add data services, traffic will increase. I think the prediction is that the amount of traffic being transported will increase multiple times. Some say 10, some say 20, sometimes a hundred times more—a lot more, that's the bottom line. The existing infrastructure will be challenged to support that, so expanding the capacity of the backhaul infrastructure will be important. However, it is not easy to predict where or which part of the network, how quickly, how much—so we see that as a challenge. And then, coming behind that is the challenge of the cost of that backhaul solution versus the incremental revenues they may see from data or not see from data. Those are the biggest challenges," comments Shaun McFall, Vice President, Marketing, Harris Stratex Networks Inc.

According to Nadine Manjaro, senior analyst at market research firm ABI Research, in order for mobile operators to deliver the expected bandwidth of 3G and newer technologies, they should focus on their backhaul networks, especially with the emergence of next-generation networks and service. "Backhaul is a major contributor to network performance and cost, and operators should design their networks to meet peak traffic demand, not just average usage levels," says Manjaro.

T1s/E1s are still considered the dominant cellular backhaul technology as operators simply cannot afford to start over again due to the huge investments they have made in these legacy architectures. "With more than $20 million spent in 2007 on leased lines to backhaul wireless services, mobile operators are feeling the pain of expensive backhaul costs, which for larger operators, can amount to hundreds of millions of dollars per year," says Ordyn's Vasi. "At the same time, these mobile operators need to upgrade their bandwidth capabilities to support new, advanced multimedia applications, such as delivering video content with enough quality to make it a viable and profitable service." He adds that while packet-based backhaul networks are being deployed in a lot of instances, the issue of timing/synchronization has stopped mobile operators from entirely replacing their existing TDM network, leading to hybrid network architectures.

For his part, Aviv Ronai, Chief Marketing Officer of Ceragon Networks Inc., says the major challenge is how to survive the migration from TDM to IP. "Everyone understands the end-game, maybe not in 18 months but in a few years, will be all-IP. In the interim period, the coming four, five or six years, we will see a lot of coexistence between TDM and IP over the same network. Sometimes it is because, for example, operators have two different base stations on the same site: one legacy, one 3G or 3.5G. So one needs TDM connectivity, one would require IP connectivity. In terms of services, sometimes carrier would rather have voice services over TDM, and the data services over Ethernet. So how to manage these changes, I think, will be the major issue and challenge for backhaul."

HYBRID SOLUTIONS AND STRATEGIES
Service providers who have selected WiMAX as their underlying technology will need higher-capacity backhaul to ensure continuous delivery of rich media services across high-speed data networks. The same is the case for cellular operators that are planning for network migration due to increasing 3G backhaul requirement. These operators have been evaluating alternative backhaul solutions for some time, and cost and future-proofing emerge to be among the key considerations when it comes to new wireless backhaul design.

"Operators should be focused on solutions that will meet their performance requirements with the minimum CAPEX [capital expenditure] and OPEX [operating expenditure]," Manjaro explains.

There are different approaches, according to Ronai of Ceragon. "We took the approach of supporting the native Ethernet and native TDM side-by-side over the same radio. Other players in the market chose to do different things, like all TDM radio and the Ethernet over TDM; or only pure Ethernet radio, and then map the TDM over the Ethernet. We thought the best of both worlds will be to support the native TDM and native Ethernet," says Ronai. According to him, one solution is the Ethernet microwave.

"Operators now are looking at how they can lower their CAPEX and OPEX associated with supporting the cost of capacity needs. So in this regard, I think the shift to Ethernet microwave also addresses those two issues, because it is more flexible in terms of capacity, with a moderated additional cost but not as expensive as it would be when you are trying do it using E1s," Ronai explains.

According to Ordyn, its SDH Radio and IPRadio are alternative technologies that can meet the backhaul challenge, especially in emerging market countries where fiber deployment is minimal. Ordyn's SDH Radio and IP-Radio—cell site aggregation products—flexibly aggregate packet-based and TDM traffic to provide optimized bandwidth backhaul capabilities over a common transport layer.

Meanwhile, Murphy says solving this requires solving both the connectivity to the BTS and the longer-haul transmission systems that carry the traffic to its destination. "The 3G BTS already installed in the field can be connected in an inexpensive way by using existing copper connection—SHDSL. bis/bonded or VDSL2. This could be realized in a shorter timeframe without too much civil work, for example, digging up roads."

When it comes to LTE, which will require bandwidths over 100Mbps per BTS, Murphy notes that fiber is the best solution. To drive down cost, one strategy is Carrier Ethernet. "We believe Ethernet switches are inherently cheaper than IP routers at the same capacity levels, and that connection-oriented Ethernet protocols like VLAN or MPLS-TP are inherently easier to manage than MPLS and all its attendant supporting protocols. Putting it more simply, a Carrier Ethernet network reduces capex and opex," says Murphy. "That being said, you must do IP routing at some point, and that is why we say use Carrier Ethernet everywhere except where you must route. Being more general, by having virtually all alternatives for operators, the operator has a suite of options to choose from, and optimize decisions for each area of their network."

"Ethernet- and IP-based networks are pretty much everywhere, they are running over existing infrastructure. I think, specific to mobile backhaul there are one or two technical questions on if it is whole Ethernet, how you preserve synchronization and timing, or GSM and all the base stations. There are a number of possible solutions, but I don't think that they are all fully deployable at this time. In most cases, the solution is to preserve somewhere where TDM transport and synchronization is not an issue. But the long term goal for these operators is to run on all-Ethernet or all-IP networks, and that will have to be solved by then. But we probably have two or three years to figure that out," says McFall. "You can probably get more out of the same backhaul infrastructure with Ethernet architecture than you can with TDM, in the long run. I think we are still always away from happy to do that, but that's the general trend."

Vasi of Ordyn points out that a staged evolution strategy will eventually reduce the complexity and cost of the transport/backhaul network significantly. He adds that mobile WiMAX, as a 4G technology, is designed to meet the requirements necessary for the delivery of broadband data services as well as voice, and that with the new technologies employed in mobile WiMAX, such as scalable OFDMA, MIMO, etc., it will eventually result in lower equipment complexity and simpler mobility management when it comes to the all-IP core network.

According to NSN's Murphy, there are no different needs in WiMAX and LTE, except that they are IP-only systems, and LTE has higher peak bandwidths. "3G still uses circuit switching for voice, so there are separate voice and data links in 3G. In WiMAX and LTE, there are no circuit-switching, only IP," he says. He adds that voice is inherently delay sensitive and many IP networks are not designed suitably to carry voice at the quality levels expected, so operators need to consider that in their whole network plan. "For example, is it possible to have six hops in an end-to-end connection or do they need to limit it to two or three? This consideration is a must in LTE, which of course carries voice; and in WiMAX, when it is used for commercial voice. That being said, there are all-IP solutions in 3G coming soon as well, so this might be an issue in 3G depending on if the operator deploys it or not," explains Murphy.

Once the operator decided to support higher bandwidth pipes, Murphy says the next question is how that traffic will be routed. "Using Carrier Ethernet, SDH, or IP/MPLS routers? This is a topic of some debate now, each with its pros and cons. Strictly speaking, routing with IP/MPLS routers may not be required at the edges of the network, Ethernet is cheaper. This then brings up the question of where to use Carrier Ethernet, and where to use IP/MPLS routers. Our view is to use Carrier Ethernet everywhere except where IP routing is required, and that is usually in the core area of the transmission network," explains Murphy.


You can reach Stephen Las Marias at stephen.lasmarias@rbi-asia.com.