Asynchronous transfer mode (ATM) is a high [629699]

ATM

Asynchronous transfer mode (ATM) is a high
bandwidth, low-delay, connection-oriented
switching and multiplexing technique. ATM
technology is based on the switching of small
fixed-length packets of data called cells. In ATM,
all data is transferred in 53-byte cells. Each cell
has a 5-byte header that identifies the cell’s
route through the network and 48 bytes that
contain user data (called the payload).

ATM service categories

constant bit rate ( CBR)—The CBR service category
supports real time applications that require tightly
constrained delay and delay variation.
These applications include voice and video applications.
The consistent availability of a fixed quantity of
bandwidth is appropriate for CBR service. Cells that the
network delays beyond the value for CTD are of
significantly reduced value to the application.

real time variable bit rate ( RT-VBR)—The RT-VBR
service category also supports for real time applications
that require tightly constrained delay and delay
variation.Theseapplications include voice and video
applications. The network expects sources to transmit
at a rate that varies with time. Standards describe this
source as bursty. Cells that the network delays beyond
the value for CTD are of significantly reduced value to
the application. Real-time VBR service can support
statistical multiplexing of real time sources.

non-real time variable bit rate ( NRT-VBR)—The NRT-
VBR service category supports non-real time
applications that have burstytraffic characteristics and
that standards characterize in terms of a PCR, SCR,
and MBS. For cells that the network transfers within
the traffic contract, the application expects a low cell
loss ratio. For all connections, the application expects a
limit to the mean cell transfer delay. Non-real time
VBR service support statistical multiplexing of
connections.

unspecified bit rate ( UBR)—The UBR service category
supports nonrealtime applications. The network
expects UBR sources to be bursty. UBR service supports
a high degree of statistical multiplexing among
sources. UBR service does not specify traffic related
service guarantees, and does not define numerical
commitments with respect to cell loss ratio or cell
transfer delay.

Signaling

ATM Traffic Descriptors

Multiservice Switch nodes support four ATM
connection types:
• “Permanent virtual channels and paths”
• “Soft permanent virtual channels and paths”
• “Switched connections”
• “Virtual path terminators”