Mobile Backhaul over Copper Networks

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1 T E C H N O L O G Y W H I T E P A P E R Mobile Backhaul over Copper Networks High-speed carrier Ethernet and E1/T1 on the same copper line Because mobile customers are demanding more broadband services, mobile operators are currently experiencing exponential growth in the demand for backhaul capacity and a desperate need to significantly reduce their cost per megabit. The challenge is that many cell tower service sites are currently served by copper E1/T1 backhaul facilities, which cannot support today s bandwidth requirements. The fast growing data communication traffic results in increasing packet traffic and high backhaul bandwidth demand. In order to take advantage of the existing copper facilities, what s required is a technology that provides broadband Ethernet services and TDM on the existing copper infrastructure without losing all of the physical timing features of a reliable E1/T1 network. This paper describes the Hybrid Packet/TDM solution a unique technology for transporting Ethernet and TDM over a copper loop while meeting every E1/T1 synchronization specification.

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3 Table of contents 1 Backhaul challenges 2 What is the Hybrid Packet/TDM solution? 3 Introducing the Hybrid Packet/TDM solution 3 Reservation of bandwidth for TDM 3 No BER (Bit Error Rate) multiplication 3 TDM quality synchronization 4 Cost savings 4 Benefits summary of the Hybrid Packet/TDM approach 4 Alcatel-Lucent Hybrid Packet/TDM platform 4 Alcatel-Lucent 1532 Copper Line Access Switch (1532 CLAS) Hybrid Packet/TDM Platform 6 Conclusion 6 Authors

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5 Backhaul challenges E1/T1 has been the gold standard for voice transport and timing, but E1/T1s lack the bandwidth required for current and future broadband data transport demands. Mobile operators moving to 3G and eventually 4G cellular networks are offloading their broadband data onto high-bandwidth Ethernet backhaul. However, in the interim, they are leaving E1/T1s in place for voice services and timing, while they continue to search for a way to get all the bandwidth performance and cost advantages of Ethernet without jeopardizing the benefits and performance of E1/T1s for voice and physical layer timing. Figure 1 below illustrates the growth in data traffic and the reduced revenue per bit. In today s data dominant market, existing E1/T1 leased lines solutions cannot solve this challenge. There are many elegant solutions for the carrier to accomplish this goal when high-speed fiber optics backhaul facilities are available. Unfortunately, a considerable portion of the cell sites are served only by copper E1/ T1 backhaul facilities. Even when upgraded to Ethernet over bonded copper (with considerable more bandwidth than E1/T1s), speeds across these last mile copper facilities are much lower than fiber in the 10 Mb/s to 50 Mb/s range. That means latency, jitter and timing become issues in Ethernet-based setups over last mile copper facilities. Figure 1. Data traffic growth and reduced revenue per bit Voice dominant Traffic Time Data dominant Cellular operator revenue and traffic de-coupled Revenues The Hybrid Packet/TDM (Time Division Multiplexing) solution offers a high quality, highly resilient, immediately synchronized timing mechanism. In addition, it provides fundamental elimination of jitter and bit error multiplication, thus ensuring a synchronization signal that meets E1 and T1 standards. Achieving the most efficient optimization for the backhaul network requires consolidation of TDM voice and broadband data traffic onto a single backhaul facility. The Hybrid Packet/TDM solution does that by handling TDM traffic natively retaining all of the requisite native TDM attributes and physical layer timing that are delivered by E1/T1s. With E1/T1s, loss of a single pair will result in loss of service and cell tower synchronization. By contrast, the Hybrid Packet/TDM solution uses a single transport facility that carries both native TDM traffic as well as native Ethernet, and spreading and prioritizing voice timeslots across the bonded copper pairs, while dynamically allocating the remaining bandwidth for the broadband Ethernet traffic. With the Hybrid Packet/TDM solution, the service provider reaps all the benefits of TDM synchronization, unlike circuit emulation over copper a packet link. There is not the problem of stranding bandwidth through static allocation of traffic streams over specific copper pairs as with TDM backhaul links over dual-bearer mode technologies. Mobile Backhaul over Copper Networks Technology White Paper 1

6 What is the Hybrid Packet/TDM solution? The Hybrid Packet/TDM solution offers flexible, resilient transport of both Ethernet and TDM traffic by delivering native TDM traffic simultaneously with native Ethernet traffic over the same bonded copper connection. The technology lets operators transition their mobile backhaul networks from TDM to Ethernet, while providing their customers the bandwidth they need and line quality they expect. The technology delivers any mix of native TDM and native Ethernet over bonded copper and is an alternative to PWE3 (Pseudowire Emulation Edge to Edge) transport of voice services over the copper access networks. The solution overcomes the limitations of pseudowire on copper access networks by: partitioning a bonded copper connection into bits that carry TDM traffic and bits that carry Ethernet traffic, and by transporting TDM natively rather than bundled in a packet format. Figure 2. Hybrid Packet/TDM solution for mobile backhaul Cell site Native TDM + Native Ethernet + Bonded copper = Native Ethernet + native TDM over bonded copper The Hybrid Packet/TDM solution is not intended as a replacement for pseudowire. It complements and interoperates with a pseudowire solution by extending native TDM transport further into the network in particular over the access network where bandwidth, congestion, and noise can significantly disrupt pseudowire performance. The solution can also complement pseudowire over high-capacity fiber optic transport. It offers a flexible bandwidth multiplier for resilient transport of both Ethernet and TDM traffic over multiple pairs of copper, and delivers the significantly higher bandwidth required for a carrier s typical suite of mobile, DSLAM, Wi-Fi and WiMAX backhaul applications. With this solution, carriers will be able to prioritize and dynamically allocate bandwidth to a changing mix of voice and data traffic on their aggregated backhaul transport facilities. The technology provides a significantly bigger pipe than is available on traditional copper, with enough flexibility, carrying capacity and resiliency to meet service demands now and in the future. The technology is optimized for 2G, 2.5G or 3G on NxE1/T1 TDM and Asynchronous Transfer Mode (ATM)/TDM backhaul networks, enabling a seamless transition to all-ethernet RAN and 4G networks. As carriers evolve their networks from TDM-based 2G networks to all-ethernet 4G, they will require optimized performance and a seamless transition. The Hybrid Packet/TDM solution enables a mobile operator to tune its TDM-versus-Ethernet requirement at any stage of the migration process. 2 Mobile Backhaul over Copper Networks Technology White Paper

7 With the Hybrid Packet/TDM solution, one-hundred percent of the bandwidth on the backhaul facility is available at all times, regardless of the traffic mix currently on the network. Operators can use proven TDM timing and synchronization while also carrying Ethernet traffic natively on the same platform. The ability to handle Ethernet in native format is a key benefit, because capacity allocated to data transport is augmented by reassigning the unused voice bandwidth at any time. Introducing the Hybrid Packet/TDM solution Reservation of bandwidth for TDM The Hybrid Packet/TDM solution partitions a bonded copper connection into bits that carry TDM traffic and bits that carry Ethernet traffic. The TDM bits are reserved and cannot be interfered with by any Ethernet traffic. That means the delay and jitter of the TDM remain constant, regardless of what else is going on in the network. The TDM traffic never has to wait in queue behind other (potentially many and large) frames. With regard to latency and jitter, the absence of the packetization effect results in a first-rate performance and makes the Hybrid Packet/TDM solution superior for transporting TDM in the access copper network. This approach is especially ideal for mobile network backhaul. Mobile networks have strict requirements on latency and jitter for each part of the network because of the cumulative effect of these phenomena, as well as restricted timing budgets. No BER (Bit Error Rate) multiplication The packet/tdm solution does not suffer from BER multiplication. This is because each bit error is separate and does not result in a packet error (caused by the CRC checking on Ethernet packets), which is often the equivalent of thousands of bit errors. On new, high quality optical connections, the multiplicative effect of pseudowire to BER is practically unnoticeable because there are so few bit errors and the speeds are so high. However, in the copper access network, which is already the weak link in the BER chain, the effect can be very noticeable. The native TDM approach described in this document eliminates the packetization of TDM and thus delivers a high quality service. TDM quality synchronization The synchronization and timing recovery aspects of pseudowire are relatively unspecified in the standards and left to the implementations where generally some proprietary form of adaptive or differential timing are used. Both adaptive timing and differential timing have some disadvantages in the copper network and are therefore seen as a common challenge for copper implementations. The quality of the pseudowire synchronization signal is affected by many things, including the availability of a high quality, reliable reference clock and the amount of jitter/latency on the pseudowire stream. The packet/tdm solution overcomes these limitations by using one of the physical copper lines as a timing source or sink. This approach ensures the highest quality clock signal by (i) fundamentally eliminating latency and jitter on the TDM traffic and by (ii) having multiple, high quality reference clocks between devices. With this approach, each copper pair carries a physical layer synchronization signal transporting a Stratum 3 clock. This high quality, highly resilient, immediately synchronized timing mechanism, along with the fundamental elimination of jitter and bit error multiplication, ensures a synchronization signal that can meet T1 and E1 standards. Mobile Backhaul over Copper Networks Technology White Paper 3

8 Cost savings The Hybrid Packet/TDM solution delivers more bandwidth than E1/T1 and lets carriers address a larger market footprint at lower operating expense. The cost synergies of using a single transport facility for all backhaul traffic are realized and there is no need to physically reconfigure the network pairs. Any mix of TDM and Ethernet traffic can be supported on the Hybrid Packet/TDM solution backhaul facility with all of the bandwidth on the backhaul facility available at all times, regardless of traffic mix. The ability of the Hybrid Packet/TDM solution to help carriers control both capital expenses going into a service situation and operational expenses as they continue to serve the growing needs of their backhaul customers is a compelling argument. Because the Hybrid Packet/TDM solution does not put TDM into IP or Ethernet packets, the management costs and headaches from dealing with packetization delays are eliminated. Other solutions, such as dual-bearer systems carry voice traffic on one pair and bond the rest of the pairs to handle the data traffic. In such a case, the logistical and operational considerations are many, resulting in additional costs. The carrier must have adjacent pairs for this to be successful. If the voice pair is moved, resiliency is lost. The juggling is constant as traffic demands change. Benefits summary of the Hybrid Packet/TDM approach With the Hybrid Packet/TDM approach, mobile operators benefit in the following ways: cost synergies of using single transport facility for all backhaul traffic any mix of TDM and Ethernet traffic can be supported optimally 100 percent of bandwidth on the backhaul facility is available at all times, regardless of the traffic mix operators can use proven TDM synchronization while also carrying Ethernet traffic natively specific amounts of bandwidth can be dedicated to voice traffic to maintain service objectives capacity allocated to data is augmented by dynamic reassignment of unused voice bandwidth operators can transition the mobile backhaul network from TDM to Ethernet over time. Alcatel-Lucent Hybrid Packet/TDM platform Alcatel-Lucent 1532 Copper Line Access Switch (1532 CLAS) Hybrid Packet/TDM Platform The Alcatel-Lucent 1532 CLAS is designed according to the Hybrid Packet/TDM technology described in this paper and adds a new dimension to Alcatel-Lucent s broadband product offering. The Alcatel-Lucent 1532 CLAS extends the Alcatel-Lucent Ethernet First Mile (EFM) over copper portfolio so that it also offers an attractive solution for mobile backhaul. Figure 3 illustrates the mobile backhaul application using the Alcatel-Lucent 1532 CLAS Hybrid Packet/TDM platform. 4 Mobile Backhaul over Copper Networks Technology White Paper

9 Figure 3. Mobile backhaul options using the Alcatel-Lucent 1532 CLAS E1/T1 transport over SDH/SONET network 4xE1/T1 Cell site gateway FE RNC/BSC site gateway RNC, BSC 4xE1/T1 DSL with repeaters GE Metro Core 1532 CLAS nxe1s/t1s Base stations 16xE1/T CLAS Native clock transport Native clock and data Clock recovery E1 or T1 is sync source SDH/SONET E1/T1 over Packet network 4xE1/T1 Cell site gateway FE RNC/BSC site gateway RNC, BSC 4xE1/T1 DSL with repeaters GE Metro Core Base stations 16xE1/T CLAS Native clock transport Native clock and data 1532 CLAS Clock recovery nxe1s/t1s TDM PWE3 (data) TDM PWE3 (clock) Primary reference clock (PRC) Tailored for Ethernet business access, the Alcatel-Lucent EMF portfolio consists of the 1531 CLAS and the 1521 CLIP, which is a MEF-certified solution offering high bandwidth Carrier Ethernet services to business customers. The Ethernet part of the 1532 CLAS Hybrid Packet/TDM platform includes the same functionality and services as the 1531 CLAS. A detailed description of the Ethernet functionality offered in these two platforms is thoroughly described in the white paper, Business Access over Twisted Copper using IEEE 802.3ah Native Ethernet. Figure 4. Alcatel-Lucent EFM portfolio for copper networks T1/E1 + Ethernet Ethernet 1532 CLAS 1531 CLAS 2BASE-TL and native TDM 2BASE-TL 1521 CLIP Mobile Backhaul over Copper Networks Technology White Paper 5

10 The Alcatel-Lucent 1532 CLAS is capable of delivering up to 480 Mb/s over the existing copper infrastructure to businesses whose application requirements fall within the bandwidth gap between E1/T1 and T3/STM-1. The 1532 CLAS is packaged in a 2RU chassis with the possibility of being equipped with up to five service plug-in modules in order to enable flexible scaling. It has full-front access, is temperature-hardened and supports an industry-leading density of up to 80 copper pairs. The Alcatel-Lucent 1532 CLAS implements the IEEE standard for Ethernet OAM with extensions for complete remote management via open management interfaces. As a result, the Alcatel-Lucent 1532 CLAS is well positioned for integration into any OSS. Main features of the Alcatel-Lucent 1532 CLAS Supports up to 80 twisted pairs or 80 E1/T1 per Alcatel-Lucent 1532 CLAS Bonding of up to 32 twisted pairs gives maximum capacity of 480 Mb/s per link Native E1/T1 and Ethernet services Ethernet over NxE1/T1 Supports TDM offload at CO and evolves to TDM over packet (SAToP, PWE3) Advanced QoS, multiple Services per EVC, multiple SLAs per customer TDRplus for qualification and maintenance of copper loops Supports repeaters for extended reach of SHDSL Virtual LANs (VLANs), stacked VLANs (Q-in-Q) and tag rewriting Resilient platform supports STP/RSTP, LAGs, storm controls, MAC DB limits per service, provider bridge functionality Carrier-class OAM Conclusion Authors Today s mobile services are exploding as a result of a growing demand for new applications and service content. Core networks have been migrated from traditional TDM-based networks to service-rich IP/MPLS networks ensuring lower CAPEX and lower OPEX. In this context, the majority of 2G/3G base station sites are currently connected via copper, so the new challenge is how to migrate this backhaul network in a cost-effective manner in order to bridge the service gap in the copper network. With the Alcatel-Lucent 1532 CLAS Hybrid Packet/TDM solution, operators can transport both Ethernet and TDM simultaneously and in the same product still meet the synchronization specification for E1/T1. They can transform their networks cost-effectively and efficiently, while meeting the challenge of mobile backhaul in their copper network. For further reference: White Paper: Business Access over Twisted Copper using IEEE 802.3ah Native Ethernet Matt Squire Hatteras Networks Per Hasselstrom Alcatel-Lucent 6 Mobile Backhaul over Copper Networks Technology White Paper

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12 Alcatel, Lucent, Alcatel-Lucent and the Alcatel-Lucent logo are trademarks of Alcatel-Lucent. All other trademarks are the property of their respective owners. The information presented is subject to change without notice. Alcatel-Lucent assumes no responsibility for inaccuracies contained herein. Copyright 2009 Alcatel-Lucent. All rights reserved. CAR (01)