WAN Optimization Glossary

Acceleration Techniques

A series of algorithms that automatically tune TCP to overcome the limitations of TCP in handling high latency data links or links with loss, like those seen in satellite and wireless networks. Satellite data links inherently have a long round trip delay (more than 500ms) which the standard implementation of TCP interprets as congestion causing the sender to slow down the data transmission to prevent overwhelming the network. Satellite links without TCP acceleration limit each sender or connection to small part of the actual available bandwidth. TCP acceleration tricks the sender, by splitting the connection (sometimes called spoofing), into believing that it is not going over the long delay path. The algorithms take care of managing the connection over the long delay path independently of the sender and receiver, which results in transmission speeds close to the available bandwidth on the link.

More on TCP acceleration on Wikipedia.

A variety of methods of TCP acceleration to mitigate the performance impact of degraded TCP performance caused by adverse link characteristics. These link degradation environments are found in satellite, wireless LANs, and cellular data. The loss and delay in cellular networks which are back hauled over satellite can have a particularly negative impact on performance. A strong TCP accelerator can overcome this limitation.

IETF RFC 3135 has a list of typical PEP algorithm implementations. Section 5 of this RFC has a case study of PEP in a VSAT environment.

A type of PEP defined in 2006 specifically for satellite communications, commonly pronounces “skips.” An open-source, TCP variant, SCPS is an extension to TCP to support high-speed and keep up bandwidth efficiencies during high round-trip times, channel asymmetry, packet loss, and other environmental impacts on satellite communications. In addition to use in the WAN, SCPS also enhances performance in terrestrial wireless environments which experience performance issues due to the environment interfering with their transmissions.

SCPS-TP (TP=Transport Protocol) is the only specification in the suite of space protocols in use today. The other protocols defined are SCPS-SP security layer, SCPS-FP file transfer, and SCPS-NP network protocol).

Read the Space Communications Protocol Standard document for more details.

Caching Techniques

A compression technology, operating at the transport layer of the IP protocol stack, that builds a catalog of data patterns that have passed through the network with the goal of replacing repeated patterns with a token. A copy of the byte patterns stored on the remote caching appliance are served to the user when duplicate data is requested. This helps reduce the amount of traffic over the constrained network resource.

Since it operates at the byte level, all applications benefit from byte caching. It is also sometimes called dictionary compression, network sequence caching or transparent data reduction.

Most modern browsers have a cache that stores a copy of the web pages and images on a computer, tablet, or smart phone. This Web cache is only available to the local user. In WAN optimization, the web cache is on an appliance which becomes part of network at the remote location that stores web pages and images the first time viewed. This appliance serves up the web pages or images from the local cache to any users on that local network. Note: In satellite WANs the local network could be as large as an entire city being serviced by one satellite link.

This WAN optimization technique not only reduces the amount of traffic going over the network, it also improves the remote users experience with an increase in performance.

Additional details on web caching techniques are on Wikipedia.

Compression Techniques

Techniques and algorithms that create a more efficient representation of data patterns for WAN optimization. Depending on the requirements of the user and the data, this technique is either lossless or lossy . Lossless compression is the removal of the redundant information by replacing with pointers, typically used on data. Lossy compression reduces the amount of data by discarding unnecessary information, typically used on images. Lossy compression is particularly useful in reducing bandwidth from websites transmitted over satellite, often eliminating 35% or more of the traffic required without it.

More information on data compression is found on Wikipedia.

A data compression technique that eliminates the transfer of repeating data. Prior to data entering the WAN small pointers, that represent the original data, replace repeating byte patterns in the transmission stream.The pointer is replaced with the original data when the data leaves the WAN. This technique works at the byte level, making it ideal for WAN optimization on wireless and satellite networks. Increased performance and/or reduced cost are the two benefits from this technique.

Wikipedia has more information on data deduplication.

ROHC replaced compressed real-time protocol (cRTP) as the preferred method of compacting the headers for header compression. cRTP, as the name suggests, operates only on Internet real-time protocols, like voice. ROHC compresses the headers for IP, UDP, UDP-Lite, RFP, and TCP headers. Headers make up 40 bytes (for IPv4) and 60 bytes (IPv6) and can account for up to 60% of all traffic sent. There are significant advantages to removing these headers on a constrained link such as satellite. Data makes it to the correct destination by placing a compression appliance at both ends of the link, one takes off the headers and replaces with a tag, the other replaces the tag with the original header.

Basic details of Robust Header Compression implementation are found on Wikipedia.

Traffic Shaping Techniques

Traffic shaping controls data flow for specific applications based on the policies established by the network administrators. Used on contended links to give applications the network characteristics they need. Typical uses of traffic shaping are to guarantee performance and increase bandwidth and reduce latency from congestion for high priority packets and reduce bandwidth for low priority applications. Guaranteed bandwidth for real-time applications can also be reserved.

Some WAN optimization appliances are able to traffic shape with granularity far beyond traditional network devices. Such as shaping traffic on a per user AND per application basis simultaneously.

Read a good overview of traffic shaping (also known as packet shaping) techniques on Wikipedia.

A WAN Optimization technique that combines multiple smaller packets into a single larger packet before being transmitted. primarily used in bandwidth constrained networks (like satellite) to improve the efficiency and speed of delivery of the packets by filling up the data path more effectively.

The article Packets per Second Stressing your Modem? has a detailed explanation of packet coalescing.