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WAN optimization speeds up branch office applications

Have you ever noticed that there just never seems to be enough WAN bandwidth? These application acceleration techniques can help.

Have you ever noticed that there just never seems to be enough WAN bandwidth? It's a problem that's been with us for awhile.

Back in the '90s, dedicated point products emerged to help address this nagging issue, using a combination of compression and Quality of Service (QoS) to get more out of limited WAN links.

Those technologies are still important today, allowing IT administrators to guarantee bandwidth for critical applications while controlling the effects of other traffic. With WAN optimization, enterprises can get more out of their congested WAN links, saving money by delaying the purchase of additional bandwidth.

However, WAN optimization point products only provide short term gains when used in isolation. Furthermore, they don't address latency issues across the WAN, which have a significant impact on application performance – particularly when dealing with real-time applications like voice over IP (VoIP) and transactional applications like Citrix.

In addition, even when WAN bandwidth is doubled, it's still significantly smaller than the throughput provided on a LAN. As a result, link optimization is often not enough to ensure LAN-like performance when delivering applications across a WAN.

While compression and QoS are vital, they must be included with other application acceleration techniques to provide a comprehensive solution for application delivery. Newer application delivery solutions, for example, will combine all of the following bandwidth management and application acceleration techniques:

  • Data reduction: This a technique whereby appliances inspect all incoming and outgoing WAN traffic and store a local instance of information in an application independent data store. Outbound WAN packets are examined to see if a match exists in the local instance at the destination location. If a match exists, then the repetitive information is not sent across the WAN and instructions are sent to deliver the data locally. If the data has been modified, only the delta is transmitted across the WAN, maximizing bandwidth utilization and application performance. Data reduction dramatically improves WAN utilization and improves application response time by enabling information to be delivered locally whenever possible.

  • Compression: State of the art cross-flow data compression and header compression increase bandwidth utilization across the WAN.

  • Quality of Service (QoS) : Advanced queuing and scheduling, policy based decisions, and application tagging are used for traffic classification and enforcement. This enables real-time traffic, such as voice, and business critical applications, such as CRM and ERP, to be deployed alongside Web, email and other applications.

  • Latency mitigation: TCP acceleration techniques, such as the dynamic adjustment of window and transaction sizes and selective acknowledgements, can improve latency across the WAN. Protocol specific acceleration, such as CIFS read-aheads and write-behinds, can also be quite useful. But, avoid solutions that rely heavily on protocol-specific modifications as these are often difficult to deploy and are short lived as the applications themselves continue to evolve.

  • Loss mitigation: Forward Error Correction (FEC) is a technology that is well known for its ability to correct bit errors at the physical-layer. However, this technology can also be adapted to operate on packets at the network-layer to improve application performance across WANs that have high loss characteristics. Packet-level FEC is used to reconstitute lost packets at the far end of a WAN link, avoiding delays that come with multiple-round-trip retransmissions. This enables WANs to easily recover from packet loss due to a variety of network layer conditions, such as queue overflows and constrained bandwidth links. Some acceleration solutions dynamically adjust the FEC overhead in response to changing link conditions for maximum effectiveness in environments with high packet loss.
  • It is important to look for an acceleration solution that addresses the full gambit of application delivery needs. In addition to optimizing WAN bandwidth and ensuring proper handling of business critical applications, it must dramatically reduce perceived application response time, while enabling centralized control of branch office infrastructure. This is the only way to transition from a tactical to a strategic approach to application delivery, going beyond the short term gains that come with bandwidth band-aids.

    Dr. Hughes founded Silver Peak Systems in 2004 and previously held senior architect positions with Cisco Systems, Stratacom, Blueleaf and Nortel. Dr. Hughes has a PhD in packet network optimization.
    This was last published in February 2006

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