Frame Relay and ATM are specialised types of access (data) service
which have only recently become available in Australia,(some
capital cities only) from the major suppliers. They provide higher
data rate access, typically from a few Mbps up to 155Mbps for
ATM.
Frame Relay "Committed Information Rates"
Access to a frame relay network is typically available at a "port
speeds" of 2Mbps. The port speed is the rate 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 much less than
the actual port speed, even down to 0bps. 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.
ATM Service
ATM service is commonly used as an "integrated" (data/voice/video)
service connecting multiple sites of larger businesses. A "virtual
circuit" (perhaps of specified "sustained information rate" (SIR))
is configured within the ATM network, terminating at the ISPs POP.
Use of technologies such as this only make sense in terms of an
overal "communications architecture" for an organisation.
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