Basic WAN acceleration techniques
Application delivery optimization (ADO) is the design and deployment of networks and systems to guarantee appropriate, effective application delivery in the mobile and distributed world. WAN optimization is a cornerstone technology in the ADO toolkit. The trick is selecting the right optimization tools to solve your organization's particular application performance problems.
The basic techniques available to WAN optimizers are as follows:
WAN application acceleration technique for large file transfers/backupsCompression, caching and deduplication improve network performance by reducing the amount of traffic sent over the wire. Some optimizers accomplish this using standard file compression techniques, the same kinds that go into compressing a file on a server. Others use some variation on the data dictionary, by cataloging bit patterns in the input, sending each pattern through only the first time it is seen, and subsequently sending an index to that pattern any time it recurs.
When WAN managers should use compression, caching and deduplication: This helps most if performance issues center around moving large files from place to place: backing up or replicating data from one location to another or moving large streams of bulky text data, such as XML-formatted messages flowing among elements in a service-oriented architecture, or EDI or HL7 data.
WAN application acceleration technique for bulky protocols
Protocol accelerators compensate for the shortcomings in applications' network protocols. Many network applications have
Accelerators can cheat chatty protocols, faking answers at each end to speed up operations. They can also monkey with TCP flow control for more intelligent ramping of transmission speeds, up or down.
When WAN managers should use protocol accelerators: Most (but not all) TCP-based protocols can benefit from acceleration via improved flow controls. Among those that are only moderately or slightly improved are RDP and SSH. TCP accelerators do nothing for UDP-based protocols, such as those used for VoIP and video conferencing, but some appliances can help such traffic in other ways. Many older LAN protocols, such as Microsoft's pre-Vista standard for file server traffic, called Server Message Blocks (SMB), aka the common Internet file system (CIFS), are classically chatty and greatly accelerable.
WAN application acceleration technique for lossy WAN links, voice, video and remote desktops
Traffic conditioning tries to make up for some of the weaknesses in the network, remediating packet loss, for example. It can also make up for applications sending small amounts of data in packets with large overhead. UDP applications, which do not do TCP-style flow control, are especially vulnerable to loss.
Traffic conditioners can repackage small, high-overhead packets into larger, lower-overhead ones or employ error correction techniques to allow lost packets to be reconstructed rather than retransmitted.
When WAN managers should use traffic conditioners: Use traffic conditioning when you have lossy WAN links, especially if you need to send real-time traffic streams over them: Voice, video and remote desktops hate re-transmits!
WAN application acceleration technique for real-time protocols
Traffic shaping is aimed at making sure an organization has some control over how it consumes bandwidth; traffic shaping guarantees that certain applications, devices or users get (or don't get) bandwidth. It can involve quality of service (QoS) settings, manipulating traffic flow rates, queuing (parking packets in buffers, or queues, to await delivery after higher-priority packets), and connection-closing (sending a "close" packet to one or both ends of a stream to shut it down).
When WAN managers should use traffic shaping: Traffic shaping can make the biggest difference when real-time protocols such as VoIP, video conferencing and virtual desktops are suffering. It can also help make sure sanctioned traffic has priority over recreational traffic.
When to use WAN application acceleration in general
Most application performance problems over WANs can be remedied, or at least mitigated, through judicious deployment of WAN optimization tools. Different solutions have differing strengths, be they in compression, acceleration, conditioning or shaping. It is critical to do proof-of-concept deployments to diagnose application delivery problems and test various solutions for the underlying protocol or network problems at the root of the performance issues.
About the author
John Burke is principal research analyst with Nemertes Research. With nearly two decades of technology experience, he has worked at all levels of IT, including end-user support specialist, programmer, system administrator, database specialist, network administrator, network architect and systems architect. He has worked at Johns Hopkins University, the College of St. Catherine, and the University of St. Thomas.
This was first published in July 2010