Increasingly, telecom operators are using a technique called router off-load to help reduce CapEx and OpEx in their core networks. But what is it? How does it work? And is it for everyone?

What is router off-load, and why is it needed?

There’s no way around it. Core network traffic is rising, and it shows no signs of slowing down anytime soon. What’s really troubling, however, is that traffic is growing faster than revenues, driving down revenue per bit. Operators find themselves between the proverbial rock and a hard place. They have to find a way to cope with growing traffic volume and, at the same time, reduce the cost of operating their networks. That’s no easy task.

Typical core network configuration
(source: Innovation Observatory)

Throwing more routers at the problem won’t help. Routers are expensive network elements, and they use up a great deal of space and power, adding to OpEx.

Adding high-rate interfaces to existing routers isn’t the best solution, either. With this approach, there is the risk of paying upfront for capacity that may never be needed.

One strategy that is showing promise in helping operators deal with the challenge of reducing core network costs is router off-load.

Taking the Bypass
Router off-load (also referred to as router bypass) is a technique that enables operators to add capacity without adding routers. It follows the principle of performing transport in the most cost-effective layer. With off-load, traffic that would normally pass through routers on its way to other destinations (transit traffic) is instead identified and handed off to more cost-efficient network layers -- Layer 1 or Layer 0 -- for transport.

The strategy is attractive because it utilizes lower cost optical and optical transport network (OTN) switching equipment, saving CapEx by avoiding expensive investments in additional router capacity and lowering OpEx through decreased space and power requirements.

Of course, there is always some cost associated with transporting network traffic, even in the lower layers. Still, when benchmarked in terms of dollar per Gbps of capacity, optical and OTN switching equipment costs less than router equipment.

Although router off-load isn’t going to solve all the cost challenges operators may face, it does offer a viable solution for reducing core network costs.

OTN-switched router off-load architecture
(source: Innovation Observatory)

How It Works
First, it’s important to establish that not all traffic is suitable for router off-load. Off-load is appropriate only in scenarios where routers act as intermediary points through which traffic is transiting: where traffic is simply passing through a PoP to get to another PoP elsewhere.

That said, traffic that is eligible to bypass a router can be switched in one of two ways:
1. Using OTN cross-connects at Layer 1
2. At the optical layer using ROADMs (reconfigurable optical add-drop multiplexers)

Before delving into how these two approaches work, let’s look at a classic core network configuration. In this typical architecture, all traffic that flows through a PoP is processed by a router -- even if it is just transit traffic flowing through the PoP on its way to another PoP. Obviously, this is inefficient because an expensive resource, the router, is being used to handle traffic unnecessarily.

Now, let’s look at the 2 off-load scenarios.
Off-Load Scenario 1: OTN cross-connects at Layer 1. In this scenario, OTN cross-connects are used to bypass the routers. Transit traffic is not passed up the layers to the routers, but rather is managed using the cross-connects, which take on the control plane duties of the router.

Off-Load Scenario 2: Optical bypass. In this type of configuration, optical cross-connects are used to bypass the routers. Transit traffic never leaves the optical domain but is instead forwarded in the proper direction using ROADMs, which then switch the traffic at the fiber or lambda levels. (Note that some deployments may omit the OTN switch between the ROADM and router.)

Both approaches offer the potential to reduce costs because they perform transport in the most cost-effective layers. The choice of which is more appropriate will depend upon an operator’s existing architecture.

Is It Right for Every Operator?
The question of whether router off-load can benefit all operators is not an uncomplicated one.

Many experts in the field have evaluated the potential of router bypass using a wide range of models, and they have arrived at different conclusions. Likewise, numerous texts have been published either supporting or challenging the validity of off-load strategies. This is not surprising given the complexity of networks today.

Wavelength-switched optical router off-load architecture  
(source: Innovation Observatory)

No Two Networks Alike
What is clear is this: No two networks are alike, so understandably there is no simple formula for determining the degree of savings that is possible. Many factors need to be taken into consideration, and the economics will vary for each operator because every network will have a unique optimal configuration based on its starting point, topology, and traffic mix.

As a general rule of thumb, though, the architectural changes brought about by router off-load could result in significant cost reductions for most operators.

Consider, for example, the analysis produced by research firm Innovation Observatory (http://innovationobservatory.com/). Their analysis suggests -- as far as the cost of expansion capacity is concerned (operators will not want to throw away router capacity they have already bought) -- that savings in the range of 20 to 40 percent are realistic. Some proponents of off-load have put this number a bit higher, at 40 to 60 percent. And even critics have conceded that the use of OTN in combination with routers is cheaper than routers alone.

Given the potential it holds as a cost-reduction strategy, all operators with large networks should at least explore router off-load as a way to cost-effectively cope with growing transit traffic.

Some final thoughts about the subject: In order to remain profitable today, operators must find ways to push down the cost of delivering each bit of data while squeezing out increased efficiencies from their networks. Router off-load is a solution that enables them to do just that.

Resources: Router Off-Load Strategies: When is Router Off-Load an Attractive Option? A whitepaper by Innovation Observatory. For more information, visit http://innovationobservatory.com/content/router-load-strategies-new-whit.... October 2011. Whitepaper sponsored by ECI Telecom.

Jimmy Mizrahi is Product Manager at ECI Telecom for the NG packet-optical product lines. He has more than 10 years of experience in the telecom market in the areas of product management, product marketing, strategic marketing, and business planning. For more information, please email jimmy.mizrahi@ecitele.com or visit www.ecitele.com.

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