What is ATM?
ATM is a connection oriented high speed switching
architecture, at home in both LANs
and WANs, that was designed for voice and video transmisson. Small packets
(53 bytes) are switched by rapid hardware. It is fast
and scaleable and offers dynamic routing
of data with speeds of upto 622Mbps and 1Gbps
in the not too distant future. ATM hardware is more expensive than ethernet's,
but ATM offers quality of service (QoS) and
LAN emulation.
There are four quality of service categories:
-
Constant bit rate (CBR)
-
Variable bit rate (VBR)
-
less stringent on cell delay and variation than CBR.
-
Available bit rate (ABR)
-
less stringent than VBR, limited data losses during congestion.
-
Unspecified bit rate (UBR)
-
less stringent than UBR, data losses during congestion.
ATM switches at the datalink sublayer of the network access layer of
the TCP/IP protocol suite. With ATM, a network
can behave as a LAN (LAN emulation) when, in reality, it may have many
remote (wide area) segments. ATM makes virtual LANs
possible, the geographical distances involved are transparent to the user
due to the fast transmission speeds. ATM resolves each datalink (MAC) address
into an ATM address by a process known as ATM address
resolution. In essence, ATM adds another layer to the protocol suite.
ATM is being challenged by gigabit ethernet.
Gigabit does not offer QoS, but its implementation is considered less daunting
to those familiar with ethernet. ATM and gigabit need not be seen as competing
technologies. Both have distinct advantages and disadvantages, their development
will continue because they both operate effectively.
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