atm by rahul rk(9986510206)
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An ATM Primer
ATM can be described as having several key
attributes that makes it effective in supporting diverse,
high speed applications:
Cell Relay Technology,
High Speed Interfaces,
Highly Flexible Connectivity,
Multiple Service Classes,
Logical Functional Distinctions,
Quality of Service Standards, and
Comprehensive Management Structure.
Cell Relay
ATM is a cell relay technology, which is based onthe segmentation of an incoming data stream into a
series of small, fixed-length (53 octets) data units.
These units are called cells. As illustrated below, data,
voice and video traffic is all broken into cells and trans-
ported across the network by interleaving the combined
stream of cells onto the transmission media.ATM is
officially defined by the International
Telecommunication Union-Telecom Sector. ATM isalso standardized by the American National Standards
Institute (ANSI).
TrafficSources Interface Device
Interleaved Cells
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User and Network Interfaces
Presently, as illustrated below, there are three inter-
face standards for use with public ATM networks.
User-Network Interface (UNI)
Network- Network Node Interface (NNI)
Broadband-Inter Carrier Interface (B-ICI) (ATM
Forum only)
The UNI is the standard interface between
customer premises equipment (CPE) and public ATM
network service. By complying with this standard, users
are assured that premises equipments such as PBX,
routers, hubs, ATM Data Service Units (DSUs), andATM switches, are compatible with public ATM
network service. The basic interface between two ATM
switches is specified by the NNI standard. The NNI
standard provides for additional flows of management
data beyond what is available with the UNI standard.
The interface between two public ATM networks is
defined by the Broadband Inter Carrier Interface (B-
ICl) specification. Based on the NNI standard, the B-
ICI specification provides the exchange of
management, configuration, and performance data
that is needed when connecting public networks. The
B-ICI will allow end-to-end management of the inter-
connected networks.
UN I NN I B-ICI
Device ATM Switch Public ATM Public ATM
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Virtual Paths and Connections
Virtual Connections allow multiple connections to
be defined simultaneously across a single network
facility, with each connection having flexible
bandwidth. In addition to virtual connections (VCs),
ATM defines a higher level of system-to-system
connectivity. These are called Virtual Paths (VP). A VC
is used to connect individual end systems through the
network. A VP is simply a logical collection, or
bundle of multiple VCs, as shown above. The prede-
fined VP assigned between end systems provides a
tunnel over which VCs destined for the remote loca-
tion can be routed. IN a VP tunnel configuration, noneof the Virtual Channels are switched by the network,
only Virtual Paths.
Virtual Paths allow users to provision their own
end-to-end VCs among locations that are connected
with predetermined VPs. This can be accomplished
without interacting with the ATM Service provider,allowing a quick response to end user needs. In addi-
tion, both permanent and switched VCs may be
included in existing permanent VPs, so that users can
efficiently load balance traffic flow between the two
locations. A single port may support both VPs and VCs
of differing service classes. VCs and VPs support a
Virtual Path (VP)
Virtual Connections
- Permanent - PVC- Switched - SVC
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Center, for example, maintains full responsibility for
the operation and maintenance of the ATM services.
This includes all access facilities and their customer
premises equipment (CPE).
With these services, they are able to provide early
identification and resolution of network issues as theyoccur and deliver high quality customer service.
The Broadband Operations Center
The Broadband Operations Center includes
responsibility for:
ATM Service monitoring for seven days a week
for 24 hours a day,
Coordination of all physical and logical aspects of
the ATM service,
Monitoring network circuits and switches,
Real time performance and fault monitoring of all
access and interoffice trunk facilities,
Proactive monitoring of selected switch parame-
ters and tables to allow for early identification of
potential problems,
Assigning all VP and VC addressing for ATM
switch and CPE,
Performing Modifications to switch routing tables;
providing routing and configuration control,
Optimizing throughput by modifying switch para-
meters and settings, and
Monitoring and analyzing network performance.
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called a VCC. A VCC is a specific instance of a SVC
or PVC. A VCC may traverse one end-to-end VPC or
several sequential VPCs.
Virtu al Ch an nel Iden tifier (VCI)The 16-bit
number in an ATM cell header identifying the specific
virtual channel on which the cell is traversing on the
current physical circuit.
Virt ua l Circuit (VC)(1) A portion of a virtual path
or a virtual channel used to establish a virtual connec-
tion between two end nodes. (2) Logical channels estab-
lished as a result of the call initiation procedure to a
network address that exists for a period of time.
Virtu al Path Conn ection (VPC)Virtual paths in
two or more sequential physical circuits can be concate-
nated to create a logical connection, called a VPC.
VPCs must be pre-configured. All cells traversing VCs
in a VPC are routed the same way.
Virtua l Path Identifier/ Virtua l Chan nel
Iden tifier (VPI/ VCI)Combined, these fields iden-
tify a connection in the ATM network.
Virtual Path Link (VPL)Between switches, may
carry many connections (ATM).
Virtu al Tribu tar y (VT)A payload structure that
specifies where and how a sub-STS-1 signal will fit into
an STS-1 SPE.
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NOTES
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Produced and Published by
One Apple Hill, Suite 216, Natick, MA 01760
Tel: (508) 651-1155 Fax: (508) 651-1171 E-mail: [email protected]
http://www.techguide.com
This Technology Guide is one
of a series of guides, publishedby ATG, designed to put complex
communications and netw orking
technology concepts into practica l
and understandable terms.
Each guide provides objective,
non-biased information to assist in
the internal education, evaluation
and decision making process.
This Technology Guide, as w ell
as the other communications and
netw orking technology guides
in the series, are available
on ATGs Web Site.