Silver Peak

I received this whitepaper from Silver Peak. I haven’t heard of the company previously and I thought this was an interesting paper and worth posting. I think VoIP quality is a hidden problem the industry needs to do a better job of addressing. This paper is a bit commercial but still worth a read:


Many of you are aware of "server sprawl" – the proliferation of servers and storage in branch and remote offices. This occurs when applications run poorly over the WAN and local servers are required in the branch office to achieve acceptable performance for branch office workers.

Following are unique VoIP challenges that we have seen as companies begin to consolidate branch office servers:

-The Branch Office Problem

-Special VoIP Challenges

-How to Measure VoIP Quality

-Fixing VoIP on the WAN

-Additional Resources

The Branch Office Problem


When most people think of server sprawl, they think about conventional branch office applications, such as email, file and web. Every time a new branch office is opened, a rack of networking equipment is required to support these functions. To combat this, companies have begun to strategically move towards a model of server centralization.

As fixed or declining budgets have intersected with new regulatory standards such as Sarbanes Oxley, the environment has become ripe for this type of change. (More information on the security and compliance issues that come from server sprawl can be found at:

As branch office infrastructure is centralized, applications are subject to the inherent limitations of WAN technology. Originally, compression, QoS and other optimization techniques were sufficient to support basic branch office application needs. The emergence of web acceleration technology gave rise to an alternative solution, caching, which was later extended to address file services and email.

Unfortunately, they are not enough to support today’s complex branch office application needs.

Special VoIP Challenges


Of special interest is the effect that server centralization in the branch office is having on VoIP. According to a recent ComputerWorld survey, VoIP deployments will grow faster in the next 18 months than any other category of enterprise applications. As VoIP (and Video) becomes more prevalent throughout the enterprise, IT staff are being forced to address the unique requirements of delivering voice to branch office and remote users. At the same time, to keep user performance acceptable for the newly centralized applications, they must accelerate other business critical applications over the WAN, which have very different delivery requirements from voice, video, and other real-time applications.

VoIP, for example, is based on UDP, which is highly sensitive to WAN traffic quality – jitter, latency and packet loss. As a result, companies considering VoIP and consolidation projects will require an acceleration platform that is specifically architected to support UDP, including advanced QoS capabilities to minimize jitter, latency, and packet loss.

Sidebar: How to Measure VoIP Quality


Voice quality is measured in the telecom industry using the ‘Mean Opinion Score’, or MOS. The MOS score is a number between 1 and 5 used to quantitatively express the subjective quality of speech in communications systems. A "MOS score" of 4.0 is considered toll quality voice – the quality you would hear on a wired land-line from your local telephone company. A "typical" cell phone call might achieve a MOS score of 3.0 to 3.5, give or take.

Running VoIP with the current generation of IP PBX equipment and a G.711 codec will achieve a MOS score of 4.0 ~ 4.4 on a clean LAN. On a WAN link however, the impact of jitter, latency and packet loss can drop the voice quality to that of an old analog cell phone – a MOS of under 3.0.

Fixing VoIP on the WAN


To maintain toll quality over an impaired WAN, application acceleration devices need to use advanced Quality of Service (QoS) techniques, jitter and latency mitigation, loss mitigation, and real-time data reduction. But the typical network link between the branch office and headquarters is carrying more than VoIP: web traffic, file sharing Citrix and other traffic is mixed in with VoIP traffic.

Here’s the problem: most acceleration products today do not handle all traffic types. Some accelerate only web (HTTP) traffic while others provide packet shaping or file acceleration only. More recent acceleration products accelerate only TCP traffic (VoIP and video are UDP traffic and are either passed through the acceleration appliance, or are ‘stepped on’, which doesn’t do much to improve VoIP quality).

Does voice matter? There is enormous overlap between companies undergoing branch office server centralization initiatives and those implementing VoIP. As many application acceleration platforms ignore VoIP, or hamper voice performance by adding latency and/or jitter, these two initiatives are likely to be on a collision path. Proper planning can ease this transition, as – there are application acceleration solutions that support voice traffic in conjunction with traditional data applications.

Net/net: If you are considering acceleration appliances as a means to reduce server sprawl in the branch office, be sure your vendor can in fact accelerate and manage all traffic types: TCP, UDP, streaming traffic (VoIP and video) and even real time traffic.

Additional Resources


Below are various white papers and resources with additional insights into the VoIP/centralization challenge (no registration required):

Independent VoIP performance report

This test report, completed by Miercom, which shows the effect that WAN latency and jitter can have on VoIP, and how a proper acceleration solution can attain toll quality MOS (note – this report also demonstrates the performance you can expect when accelerating file services, NFS and Citrix)

VoIP application brief

This one describes in more detail unique requirements for delivering VoIP and other traffic types to remote and branch offices.

ComputerWorld Survey

A CIO survey conducted by Computerworld that shows how voice, video, and other real-time applications are the fastest growing traffic in today’s enterprise.

"The Future of Application Delivery"

A whitepaper by industry veteran Robin Layland that addresses different techniques for application acceleration across the WAN, including advanced data reduction techniques, such as "Network Memory."

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