Data Compression

Data compression has become a standard feature of most bridges and routers, as well as modems. In its simplest implementation, compression capitalizes on the redundancies that are found in the data. The algorithm detects repeating characters or strings of characters and represents them as a symbol or token. At the receiving end, the process works in reverse in order to restore the original data.

The compression ratio tends to differ by application. The compression ratio can be as high as 6-to-1 when the traffic consists of heavy-duty file transfers. The compression ratio is less than 4-to-1 when the traffic consists of mostly database queries. When there are only keep-alive signals or sporadic query traffic on a T1 line, the compression ratio can dip below 2-to-1.

Encrypted data exhibits little or no compression because the encryption process expands the data and uses more bandwidth. If data expansion is detected and compression is withheld until the encrypted data is completely transmitted, however, the need for more bandwidth can be avoided. The use of data compression is particularly advantageous in the following situations:

• When data traffic is increasing due to the addition or expansion of LANs and associated data-intensive, bursty traffic
• When LAN and legacy traffic are contending for the same limited bandwidth
• When reducing or limiting the number of 56Kbps/64Kbps lines is desirable in order to reduce operational costs
• When lowering the Committed Information Rate (CIR) for Frame Relay services or sending fewer packets over an X.25 network can...