Quantifying Data Traffic

Data traffic usually consists of short, bursty transactions from a few milliseconds duration to several seconds, depending on the data transmission rate (i.e., the number of bits per second). This is particularly true on local area networks (LANs). As the data rate slows down, such as we might find on a wide area network (WAN), transaction time increases,

Offered traffic (in erlangs)

Figure 4.6 Group efficiency increases with size.

Offered traffic (in erlangs)

Figure 4.6 Group efficiency increases with size.

6Carrier systems are frequency-division multiplex systems introduced in Section 4.5.

possibly to a minute or so. For these reasons, it is dangerous to apply speech telephony traffic theory and practice to the data environment.

There is an exception here—that is, when a data protocol specifies a permanent virtual circuit (PVC). This is a circuit that is set up in advance for one or several data transactions. One group of traffic engineers has proposed the milli-erlang for LAN and PVC applications. We think this idea bears merit.

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