If you have a WAN, then one very important concern should be latency. Latency, in this case, is the time that a package of information takes to reach the other end of the slow link. This package of information could be a DNS query, ping, file, or a transaction in a client/server application. Notice that the package of information has not fully arrived at the destination until all bits have arrived. It is often tempting to assume that the only variable here is the bandwidth. It seems logical that the fatter the pipe, the quicker the information package will arrive at its destination. For a large file, latency doesn't play much of a part; however, in the case of small packages like a DNS query, ping, or a transaction, latency can kill your performance. It is very important to distinguish between bandwidth and latency.
Bandwidth is the capacity of the link to transfer quantities of information in a given amount of time. A 128k link can transfer roughly 13 k bytes of information in one second. This can vary depending on compression and other factors. For a 13 meg file, the total time to transfer the file across the link would be 1000 seconds. This doesn't vary that much between different kinds of slow links: frame, ppp, ISDN, etc. This gets interesting, though, when you consider that there are many packages of information that are relatively small. Different slow links have different latency characteristics. Further, as these slow links get loaded down with many different kinds of network traffic, latency can go up quickly.
- ping
- traceroute ( Uses ping command )
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