Compression Overview

The Xpress feature is Packeteer’s application traffic acceleration option that includes advanced compression technologies to allow you to increase the virtual size of WAN bandwidth and improve application performance. By integrating compression technologies with traffic management, PacketWise ensures that the increased virtual WAN pipe is not consumed by aggressive, non-mission critical applications that burst to consume any bandwidth given to them. In addition, the effective throughput of the mission critical traffic can also increase, providing a double benefit. Traffic management protects mission critical traffic, contains recreational and unsanctioned traffic, and smoothes peaks in bursty traffic, while Xpress provides greater throughput and network capacity.

PacketShaper Xpress works by identifying other Xpress units on the network, creating compression tunnels between the units, and sending compressed data through the tunnels. A tunnel is automatically set up when traffic is sent through a PacketShaper Xpress to a host on the other side of an Xpress unit. No manual configuration is required.

Xpress does not attempt to compress all traffic. Because PacketShaper is application intelligent, it is able to identify each traffic flow and compress only the flows that are likely to achieve useful gains. Previously compressed traffic (such as images, zipped attachments, and streaming media) and encrypted data are examples of non-compressible traffic. The ability to apply appropriate compression algorithms to different applications is built into the Xpress compression engine. With this design, PacketWise can choose, for each application, the appropriate algorithm that will yield the best compression ratio, with minimal latency.

There are several things to keep in mind regarding compression. First, a packet’s uncompressed data size is used for all calculations relating to flows and their policies (such as the guaranteed rate). Second, PacketShaper uses the compressed data size for calculating how much data can fit in a partition. For example, if you create a 150K partition, Xpress will allow 150K of compressed data in the partition (which could be 300K of uncompressed data, assuming a 2:1 compression ratio). Third, the standard measurement variables measure the actual data (compressed and uncompressed) that passes through the link. Measurement variables specific to compression are available, allowing you to analyze the effectiveness of compression on your link. For a list of these variables, see Compression Measurement Variables.

To enhance the efficiency of the Xpress feature, you can define hosts that can use the compression facility with the (setup compression hosts CLI command. When this functionality is used, the specified hosts are the only ones allowed to use the compression tunnel. If a host is not on the list of allowed hosts, the data will not be sent through the tunnel; it will be sent through the normal mechanism. A similar command is available to restrict the PacketShaper units that can be a tunnel partner (setup compression partners). By defining lists of compression hosts and/or partners, you can improve efficiency because the unit needn’t spend time looking for hosts and partners. There are also commands to override the default algorithms used for specific traffic classes (class compress on) and to disable compression for a class (class compress off).

Getting Started

As soon as compression is enabled and compressible traffic goes through your PacketShaper, Xpress will automatically create compression tunnels with other compression-enabled units that are detected on the network. Xpress creates tunnels and compresses data when the following conditions are true:

• Compression is enabled.
  
  
• The flow is destined for a host on the other side of a compression-enabled PacketShaper Xpress or is received from a host on the other side of a compression-enabled PacketShaper Xpress.
  
  
• The flow belongs to a compressible service. Services that are unlikely to achieve useful gains from compression are not compressed. Voice Over IP and encrypted data are examples of traffic that are not compressed.
  
  
• The two Xpress units are configured outside port to outside port. (illustration)

To see how compression is working on your link, you can look at compression reports. The report tab offers a Compression Summary, the Statistics:Reports page has compression reports for links, partitions, and classes, and the top ten tab offers views for Top Ten - Compression Bytes Saved and Top Ten - Compression % Bytes Saved.

Requirements and Limitations

• Xpress acceleration is available on the following PacketShaper models: 1550, 2500, 6500, and 8500. It is not available on the Packeteer 1500 or 4500 series.
  
  
• Xpress is available as an upgrade to PacketSeeker 1550 and 2500 models.
  
  
• There are special memory requirements for Xpress; for a list of requirements for each Packeteer series, see Check Memory.
  
  
• To use Xpress on existing PacketShaper or PacketSeeker units, you need to purchase an Xpress compression software key from Packeteer, and install it onto each unit. The banner in the browser user interface will say “PacketShaper Xpress” after the key is installed. After the compression key is installed on PacketSeeker, the banner will say “PacketSeeker with Xpress option.”
  
  
• You cannot use Xpress with Packeteer's direct standby feature.
  
  
• Xpress compression tunnels cannot be set up when the PacketShaper Xpress unit sits on a VLAN trunk and a router in the data path requires a VLAN header. This is because the PacketShaper unit on the trunk does not add its own VLAN header. Consequently, you will not be able to use the compression feature in this situation.
  
  
• If Xpress is deployed in a Virtual Private Network (VPN), the (private) address space on both sides of the VPN tunnel between the Xpress units needs to be separate and unique in order to allow the two Xpress units to set up a compression tunnel.
  
  
• Only packets with unicast destination addresses are sent through the compression tunnel; multicast packets are not sent through the tunnel.

See also:

Configure Compression

Assess Compression Results

Accelerate Traffic — Enabling and Tuning Compression

Compression Troubleshooting

Compression Algorithms and Dictionaries

Compression Notes