Download ATM: Architecture

ATM CELL STRUCTURE
By:EZHANDIN ANUAR
IMRANDIN
WET010026
ATM cell structure
ATM architecture is a fixed length "cell.“
An ATM cell is a short, fixed length block of data
that contains a short header with addressing
information, followed by the upper layer traffic,
or "payload."
Figure 1 - ATM Cell Structure (UNI Format)
The cell structure, shown in Figure 1, is 53 bytes
long, with a 5 bytes header, followed by 48 bytes
of payload.
The information contained in the header of each
cell is used to identify the circuit (in the context)
of the local link, carries local flow control
information, and includes error detection to
prevent cells from being mis-routed.
The remaining 48 bytes are routed through the
network to the destination using the circuit.
Figure 2 - ATM Cell Header Structure
The header is composed of six elements,
each detailed in Figure 2:
 GFC – Generic Glow Control
 VPI – Virtual Path Identifier
 VCI – Virtual Channel Identifier
 PTI – Payload Type Indicator
 CLP – Cell Loss Priority
 HEC – Header Error Check
Generic Flow Control
4 bit
Support the connection of ATM Networks
 Negotiate multiplexing and flow control among the cells
of various ATM connections
Virtual Path Identifier
8 bit
Defines the virtual path for this particular cell
Discovered during the connection setup process for
SVC and manually configured for PVC
Virtual Channel Identifier
16 bit
Defines the virtual channel within the specified
virtual path for this particular cell
Also discovered during the connection setup
process for SVC and manually configured for PVC
Payload Type Indicator
3 bit
1st bit indicates the type of ATM cell that follows
2nd bit indicates whether the cell experienced
congestion in its journey from source to destination
3rd bit indicates the last cell in a block ATM cells
Cell Loss Priority
1 bit
Used as a priority indicator
Header Error Check
8 bit
Allows to correct a single bit error or to detect
multi bit errors in the 1st 4 bytes of the ATM
header
ATM Network
Architecture
By: Mohd Zaki Bin Sirat
wet010082
• All connections are point to point
• Switched based traffic
• 2 network architecture
– Private Networks
– Public Networks
• Private Networks
– Concern with end-user connections
– Provide bridging services to other types
of networks – frame relay, voice
subsystems
– Permit the use of lower speed short haul
interconnects oftenly
– Interface between the components –
Private User Network Interface (UNI)
• Public Networks
– Great for the usage of lower speed
short haul interconnections (useful in
LAN environments)
– Interfaces between the switches –
Network Node Interface (NNI)
• 3 types of NNI
– NNI-ISSI
» Connects switches in the same Local Area
Transport Area (LATA)
– NNI-ICI
» Connects ATM networks of different
carriers (Inter Carrier)
– Private NNI
» Permits the connection of different switches
in private network
• Interfaces between Public and
Private Network – Public UNI
Protocol Reference
Model
By Farah Hazwani Zulkafli
WET020031
ATM architecture
Function of the Layers
adaptation layer:
• adaptation layer: only at edge of ATM network
– “adapts” upper layers (IP or native ATM
applications) to ATM layer below
– AAL present only in end systems, not in
switches
– It has two sub layer
• Convergence sub layer
• segmentation and reassembly sub layer
– Types of AAL( segmentation and reassembly
sub layer:• AAL 1 and 2 designed for applications that
need guaranteed bit rate (e.g., voice, video)
• AAL 3/4 designed for packet data
(connect/less)
• AAL 5 is an alternate “simple” std. for
packet data
ATM layer
• ATM layer: “network” layer
– The ATM Layer is responsible for the
transport of 53 byte cells across an ATM
network
– Multiplex logical channels within a physical
channel
The ATM Layer can provide a variety of services
for cells from an ATM virtual connection:
1. Constant Bit Rate (CBR)
2. Variable Bit Rate (VBR)
3. Available Bit Rate (ABR)
4. Unspecified Bit Rate (UBR)
5. Guarantees Frame Rate (GFR)
Physical layer
1. Physical Medium
– Interfaces to media
– Transmits & receives bits
2. Transmission Convergence
– Takes cells delivered by ATM layer
– Fits these into transmission multiplex
What is Protocol Reference
Model?
• More to the ATM standards than the ATM
cell format alone.
• Specifications exist to describe acceptable
physical signaling, call control, and upper layer
payload formats.
ATM Protocol
Architecture
the hierarchy of protocols
involved in ATM. Mapping
roughly to layers 1 and 2
of the OSI model, ATM is
broken into 3 distinct
layers. At the bottom,
several classes of physical
layers have been adapted
to support the different
types of ATM applications.
ATM Protocol
Architecture
The ATM layer provides
the cell-switching and
routing services.
Application services rely
on the ATM Adaptation
Layer (AAL) that serves
two purposes, to provide a
common framework for
the segmentation and
reassembly of larger data
sets into the ATM cells
and to provide service
specific mechanisms for
the transport of different
types of data.
ATM Protocol
Architecture
Four different classes of
traffic are supported by
the AAL ranging from
straight circuit switched
data through packet mode
applications. Many of the
early implementations of
ATM have been focused
on the packet mode
services, often as a
backbone for Frame Relay
services.
ATM Protocol
Architecture
Typically, the AAL should
be viewed as an internal,
software interface to
bridge end-user services
over ATM. There is
typically a good bit of work
required to bind other
protocols to the ATM
stack.
ATM connection
By AQILAH ANUAR
WET020010
ATM Connections
Two levels of ATM connections:
1. virtual path connections
2. virtual channel connections
Virtual Channel Connections




VCC is a Full duplex virtual circuit
with logical connection between
source and destination – can be PVC or
SVC
It represent a single network
connection data flow between source
and destination.
The ATM standards define this as a
unidirectional connection between 2
end-points on the network
 Virtual Path Connection
 A virtual path is used to carry one or
more virtual channels through the
network. It is represented as a bundle
of channels between the two end-points.
 A single virtual path supports multiple
virtual channels (analogy – highway =
VPC, lane = VCC)
Advantages of using virtual paths
1.
2.
3.
4.
simplified network architecture
increased network performance and
reliability
reduced processing and short connection
setup time
flexible network services
Traffic Flow Through The
Network
• As can be seen in the figure, each virtual
path contains one or more virtual channels.
• These values are established when the
actual Virtual Channel Connections (VCC)
are established. The number of Paths and
Channels over a single link are limited by
the ATM cell format
Call
Establishment
Using VPs
ATM cell Formats
By Haryani Othman
WET020044
ATM cell format
•Divided into 2:
•1-UNI(User-to Network Interface)
•Used for communication between ATM endpoints
and ATM switches in private ATM networks
•2-NNI(Network-to Network Interface)
•Used for communication between ATM switches
•ATM transmits, switches and multiplexes
information in fixed-length cells.
• The length of cell is 53 bytes,
containing:Header
5 bytes
Data (payload)
48 bytes
53 bytes
• ATM cell header contains
information about destination,
type, and priority of cell.