hybrid microwave for smooth network evolution

WHITE PAPER

SEPTEMBER 2010

HYBRID MICROWAVE FOR SMOOTH NETWORK EVOLUTION

EXECUTIVE SUMMARY

Fourth Generation Hybrid or Dual Ethernet/TDM microwave systems provide comprehensive transmission of both native

TDM and native Ethernet/IP traffic for smooth evolution of existing 2G/3G mobile backhaul networks to enable the

introduction of next-generation 4G/LTE mobile broadband.

This white paper builds on Aviat Networks’ previous April 2010 white paper titled “What is Packet Microwave?” and

provides market data from recent Industry Analyst reports that demonstrates the significant and continuing role of TDM

in mobile backhaul networks and some of the prevailing concerns of operators in introducing Ethernet/IP backhaul

services.

2 AVIAT NETWORKS SEPTEMBER 2010

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HYBRID MICROWAVE FOR NEXT GENERATION NETWORK EVOLUTION

INTRODUCTION

The growth of next-generation broadband services and the pressure to reduce network operational costs,

increase flexibility and boost backhaul capacity is driving operators around the world to plan the migration

of their backhaul networks from traditional circuit-switched time division multiplexed (TDM) over to all-

packet-based Ethernet/IP.

However, the pace of this migration will differ with the individual operators circumstances, including their

CAPEX constraints, legacy installed base and the volume of TDM traffic that needs continued support. The

fact is that TDM still dominates most mobile backhaul networks and, as shown in Figure 1, is not going

away anytime soon. Operators must remain focused on preserving the voice-based traffic that is reliant on

reliable and stable TDM networks to preserve existing revenues and minimize customer churn that can

result from network disruptions and a complicated transition to Ethernet/IP.

Figure 1: The migration from existing TDM backhaul networks to Ethernet/IP has only just started.

TDM backhaul, whether low-speed PDH connections in the last mile or high-speed SDH/SONET in the

metro and core, is subject to significant sunk investment by operators and is well understood. In contrast,

moving from essentially a Layer 1 transport technology to Layer 2 or 3 Ethernet/IP is a complicated step,

and many operators will need to develop the skills and resources to execute this migration with a minimum

of risk and expense.

Heavy Reading recently reported1 that many operators have had significant difficulty scaling their Ethernet

backhaul deployments due to a number of factors, ranging from the need to optimize TDM and introduce

IP/Ethernet backhaul without succumbing to sharp spikes in CAPEX or OPEX; sub-optimal performance of

the chosen architecture or technologies; and generating the operational processes to rapidly turn up

Ethernet backhaul service at thousands of cell sites.

1Heavy Reading's Ethernet Backhaul Quarterly Market Tracker, August 2010.


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MOVING FROM TDM TO ETHERNET/IP

Given that this migration from TDM to Ethernet/IP must happen over the long term, operators can

essentially take three paths:

1. IP Network Overlay. With this approach, the existing legacy TDM network is preserved and a new

Ethernet/IP network is deployed in parallel. Legacy voice traffic stays on the TDM network, while

all next generation data services are supported on the new IP network. This represents the lowest

risk migration solution, but has higher cost implications, as the operator essentially has to build

and maintain two networks instead of just one.

2. Hybrid Network. In a hybrid or dual network approach, new Ethernet traffic is introduced side-by-

side over the same backhaul infrastructure as the existing TDM services. Both types of traffic are

preserved in their native form. Hybrid networks provide the advantage of balancing low risk with

low migration costs. Existing TDM backhaul links can be upgraded to hybrid, providing continuity

of high quality TDM transport while also enabling introduction of new IP backhaul services on the

same homogeneous network.

3. All-IP Network. This involves moving straight to an all-IP network, removing and replacing legacy

TDM systems with new all-IP links and shifting native TDM traffic over to be transported over IP

using circuit emulation techniques such as Pseudowires (PWE). While representing the most

future-proof solution (building the network you need tomorrow, today), moving to all-IP in one step

represents a potentially risky leap, involving dependency on technologies that are still in their

infancy and are largely unproven in mass deployments.

Several recent Industry reports found that the most common approach is to move from TDM to hybrid.

Infonetics found2 that Operators report that they are turning up an increasing proportion of Ethernet

connections using hybrid equipment, while EJL Wireless Research also revealed3 that PDH technology has

quickly given way to Hybrid TDM/Ethernet-based solutions.

‘Operators report that they are turning up an increasing proportion of Ethernet connections using hybrid equipment.’

Infonetics

TDM SYNCHRONIZATION STILL FAVORED

Another key consideration in the migration to all-packet backhaul networks is that new standardized

synchronization schemes have not yet matured to the point where most operators will be confident to

replace their trusted and reliable TDM synchronization.

2Infonetics Report on Microwave Equipment. Quarterly Worldwide and Regional Market Size, Share, and

Forecasts, March 1, 2010.

3EJL Wireless Research, 6th Edition Global Digital PTP Radio Market Analysis and Forecast, 2009-2014,

July 2010.


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As a result, EJL Wireless found that there is still a preference for TDM's synchronization capabilities to

support growing voice-only mobile traffic, though this is changing. Heavy Reading also states that leaving at

least one T1/E1 at the cell site remains by far the preferred solution for synchronization of Ethernet

backhaul and will continue to remain the single most popular solution through to the end of 2012.

Of course, this approach is supported inherently by Hybrid microwave systems. Aviat Networks has

developed an improved method of maintaining TDM synchronization with its unique Distributed Sync

solution. With Distributed Sync, instead of having to maintain a dedicated E1/T1 circuit for every base

station back to the synchronization source, a single omnibus E1/T1 can be utilized to provide TDM timing to

a complete sub-network of base stations, reducing the demand on backhaul capacity that would otherwise

be needed.

MARKET FORECASTS

Heavy Reading forecasts that by the end

of 2011 TDM backhaul will still be present

at 93 percent of the world’s cell sites.

Further, the publication predicts that TDM

will be the exclusive backhaul technology

deployed at 86 percent of the world’s cell

sites.

Even by the end of 2013, 66 percent of

cell sites will still have exclusively TDM

backhaul. Heavy Reading explains that

this is due, in part, to operator anxiety

about putting voice over Ethernet in the

backhaul.

Another explanation is that in many

markets operators simply do not want to

discard the capacity in which they have

already invested. In this case, operators

may deploy Ethernet microwave in

parallel to their old TDM microwave,

keeping the latter in place for voice.

Figure 2: Ethernet Microwave Sites by Implementation, Heavy Reading's Ethernet Backhaul Quarterly Market Tracker, August 2010.

Alternatively, if spare capacity is available, carry the new IP traffic over the existing TDM legacy link using

an encapsulation method, such as ML-PPP.

‘Most of the known deployments in Africa, South America, Europe, and parts of Asia consist of this hybrid model, with operators preferring to carry their voice and low-speed data natively over TDM rather than invest in Pseudowire emulation for legacy services.’

Heavy Reading


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According to Heavy Reading’s estimates, there were only 65,000 cell sites (out of more than 2 million sites

worldwide) in live service with Ethernet backhaul at the end of 2009. Of these, at least two thirds are hybrid

deployments in which T1/E1s are still used for voice traffic. Even in the small number of “pure Ethernet”

backhaul links, some retain a T1/E1 just for synchronization.

Heavy Reading also expects the hybrid TDM/Ethernet model to account for 85 percent of live Ethernet

microwave sites by the end of 2010 and 51 percent by the end of 2013. Worldwide, most operators prefer

to carry their voice and low-speed data natively over TDM rather than invest in Pseudowire emulation for

legacy services. Compared with maintaining legacy traffic on native TDM, Pseudowires are a complex

solution where significant TDM traffic remains, causing scalability and management issues, as well as

potential additional latency and wasting valuable backhaul bandwidth.

HYBRID MIGRATION TO ALL-PACKET BACKHAUL

The benefit of hybrid microwave solutions is that as TDM transport needs decline and eventually (one day!)

disappears, the capacity allocated to this traffic can be reassigned over to Ethernet/IP, as demands for data

transport grow. Bandwidth can be re-allocated through software control, without on-site intervention, without

additional CAPEX, and even without affecting other TDM or IP traffic on the link.

As EJL Wireless states, “Hybrid radio offers future proofing in both capacity as well as in transport

technologies. It is becoming a ‘catch all’ all-in-one radio solution for the industry.” This ability of hybrid

microwave systems to support the gradual migration of backhaul networks, as well as their eventual

transformation to all-IP, gives this approach a huge advantage over competing IP-only solutions, which

force an operator to switch TDM traffic over Pseudowires immediately.

‘Hybrid radio offers future proofing in both capacity as well as in transport technologies. It is becoming a "catch all" all-in-one radio solution for the industry.’

EJL Wireless

Infonetics also noted in its recent report that dual Ethernet/TDM microwave is hybrid equipment that can

operate native TDM and native Ethernet links, enabling operators to keep legacy TDM microwave for 5 to

10 years, transition to a combination of both, and gradually deploy more Ethernet. Some hybrid multi-mode

solutions can operate as an all-IP system by configuration.

Indeed, Hybrid microwave systems, like Eclipse Packet Node from Aviat Networks, can be simply

configured for all-packet transport, with all the Ethernet features operators expect from an IP-only platform.

This includes Adaptive Modulation, co-channel operation using XPIC, integrated Layer 2 Ethernet

Switching, QoS, traffic prioritization, control and monitoring, and support for synchronization over packet

networks. With Hybrid, you still get a first-class Ethernet/IP transport solution, but with the benefit of

continued smooth support for TDM.


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CONCLUSION

There is no one-size-fits-all solution that meets the needs of all these operators, which takes into account

the technologies they have deployed in their network and their desired pace to migrate to all-IP. Many

microwave solutions force operators to make a risky leap to all-IP, because they do not provide continued

support for native TDM.

Recent industry reports have shown that Hybrid microwave solutions continue to be the favored backhaul

solution for operators around the world, and that they offer the ”best of both worlds” when it comes to

maintaining legacy TDM while also introducing new high-speed IP, with a minimum of cost, complexity and

risk.

REPORTS CITED IN THIS PAPER

1. Heavy Reading's Ethernet Backhaul Quarterly Market Tracker, August 2010.

2. Infonetics Report on Microwave Equipment. Quarterly Worldwide and Regional Market Size,

Share, and Forecasts, March 1, 2010.

3. EJL Wireless Research, 6th Edition Global Digital PTP Radio Market Analysis and Forecast, 2009-

2014, July 2010.

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