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Frame Relay "Committed Information Rates"
Access to a frame relay network is generally available at "port
speeds" of 64 kbps, up to 1.984 Mbps -- obviously related to ISDN
line speeds. The port speed is the rate, in bps, of the
point-to-point physical link between a user's premises and the
frame relay service.
Internally, the frame relay network is engineered on the basis
that not all nodes will continuously attempt to transmit at their
full port speed all of the time. In fact, each port is only
guaranteed reliable service at an agreed "Committed
Information Rate" (CIR). This is typically less than half
of the actual port speed in bps.
The charge for a frame relay PVC is mainly based on the agreed
CIR, and to a lesser extent on the actual port speed. To minimise
the cost, some providers even allow a CIR of 0 bps.
It is possible for a frame relay user to transmit up to the port
speed -- in other words, continuously. However, the network is
engineered so that reliable frame delivery becomes less and less
probable as the average offered data rate rises above the CIR:
ultimately, the network is permitted to drop frames.
Useful links
Telstra Bigpond
Direct
NSFNET
history
Ameritech's Chicago
NAP
Google
Links to Internet History pages
Another bit of NSFNET
history
The aus.net.access newsgroup
sometimes has interesting discussions about Internet access in
Australia.
The tutorial for this lecture is Tutorial
#14.
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Copyright © 2001 by
Philip Scott, La Trobe
University.
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