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ATM Concept
In the ATM-based networks, all forms
of user traffic are segmented into uniform data units of small size
and routed through the switching nodes and transmission links of the
network. The users would have bandwidth on demand, and the
underlying network would be based upon a single switching and
multiplexing principle. This capability has been viewed as
especially important for multimedia services, where a given call may
contain voice, data, and video information.
ATM opens the
telecommunications information-transfer modes not only to circuit
switching but also to packet switching and statistical multiplexing
i.e. ATM supports all of these schemes. ATM is a virtual
connection-oriented bearer technique based on the use of fixed size,
small packets called cells (53-byte packets-5 byte cell header and
48-byte payload). Cells are switched across the ATM transport
network. The cell header provides control information on a per-link
basis, including two logical connection identifiers (VPI and VCI);
the type of cell payload (OAM&P or user cells); and the HEC
sequence. Prior to sending data, an ATM end-to-end connection should
be set up either on
The
connection-oriented nature of ATM provides for resource reservation
capability transmission link by transmission link, from end user to
end user, and throughout all the switching nodes on the connection
path. Resource reservation is executed at connection set up, though
the re-negotiation of the terms of an active connection contract is
possible. If at any intermediate link of any available
source-destination path the network is not able to offer the
requested resources (for example, a given dedicated bandwidth to the
end-to-end connection), the connection request is refused and the
network access is blocked.
Like packet
switching for data (e.g., X.25, frame relay, transmission control
protocol [TCP]/Internet protocol [IP]), ATM integrates the
multiplexing and switching functions, is well suited for bursty
traffic (in contrast to circuit switching), and allows
communications between devices that operate at different speeds.
Unlike packet switching based on best effort IP traffic, ATM is
designed for high-performance multimedia networking. ATM technology
has been implemented in a very broad range of networking devices:
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PC,
workstation, and server network interface cards
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switched-Ethernet and token-ring workgroup hubs
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workgroup and campus ATM switches
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ATM
enterprise network switches
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ATM
multiplexers
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ATM–edge switches
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ATM–backbone switches
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