HP 200 Series Services And Applications page 282

Linking Up with Frame Relay
History
Ports and PVCs
Two important Frame Relay access characteristics are port speed and
committed information rate (CIR). These characteristics govern the rate at
which data may be transmitted into the network.
Port speed is the maximum rate at which data will be
Port Speed
accepted by the boundary Frame Relay switch to which a router is
connected. This is the aggregate rate at which data can be transmitted to
the network on all PVCs. Note that the port speed is frequently lower
than the speed of the physical access link.
Committed information rate is the
Committed Information Rate
speed at which data is guaranteed to be accepted by the network on an
individual PVC. The sum of the CIRs for all PVCs subscribed to is
typically equal to the port speed. This is a general rule; it varies
depending on the switches and software used to provide the Frame
Relay networking service.
History
The motivations for Frame Relay began with X.25. The X.25 recommenda-
tion was released in 1974 by the CCITT. X.25 was widely accepted and
implemented worldwide by the early 1980s. X.25 allowed a user to
communicate with any other X.25 user worldwide simply by knowing the
other party's X.121 address. (X.121 is a global data communication
addressing standard.) In addition, X.25 pricing was usage based. X.25 was
ideal for companies with many locations and with low to moderate
communication requirements. X.25 could be implemented quickly, especially
in situations that required international communications, and the costs were
low when compared to private leased lines.
In the mid-1980s, many companies' communications requirements were in-
creasing as a result of more powerful processors, more capable networking
software, and new applications that required more bandwidth. It was becom-
ing clear that X.25 would not be able to provide the throughput for future
networking requirements.
Data communications standards committees were aware of these problems.
New standards were being developed—the overall objective of which was to
integrate both voice and data into one high-speed digital network. These
standards—called ISDN (Integrated Services Digital Network)—are the
basis upon which Frame Relay was defined.
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