18-07-2012, 11:15 AM
ATM
[attachment=27891]
Introduction
Asynchronous Transfer Mode (ATM) is a standard switching technique designed to unify telecommunication and computer networks.
ATM uses asynchronous time-division multiplexing and it encodes data into small, fixed-sized cells
ATM provides data link layer services that run over a wide range of OSI physical Layer links.
Introduction
ATM is a cell-relay technology that divides upper-level data units into 53-byte cells for transmission over the physical medium.
ATM is Connection oriented switching technology
Consist upon 53-byte cells.
ATM supports different types of services via ATM adaptation layers (AAL).
Speeds on ATM networks can reach 10 Gbps.
Architecture
ATM operates with a layered structure that is similar to the OSI 7-layered model.
ATM only addresses the functionality of the two lowest layers of the OSI model: the physical layer (Layer 1) and the data link layer (Layer 2).
In ATM, the functionality of the two lower OSI layers are handled by three layers.
These layers are ATM Adaption Layer,ATM Layer and Physical Layer.
Physical Layer:
The Physical Layer defines the medium for transmission, any medium-dependent parameters (e.g., rate, quality of service required), and framing used to find the data contained within the medium.
ATM Layer:
The ATM Layer provides the basic 53-byte cell format, by defining the 5-byte ATM header for each 48-byte payload segment
ATM Adaption Layer(AAL):
The ATM Adaptation Layer (AAL) adapts the higher-level data into formats compatible with the ATM Layer requirements, i.e., this layer segments the data and adds appropriate error control information as necessary.
Several AAL protocols have been defined for specific types of data.
These are AAL 1,AAL 2,AAL 3/4 and AAL 5
AAL1
AAL1, a connection-oriented service, is suitable for handling constant bit rate sources (CBR), such as voice and videoconferencing.
AAL1 requires timing synchronization between the source and the destination.
Most important task is to synchronize the bytes on the ATM cell.
AAL2
Traffic type has timing requirements like CBR but tends to be bursty in nature. This is called variable bit rate (VBR) traffic.
The AAL2 process uses 44 bytes of the cell payload for user data and reserves 4 bytes of the payload to support the AAL2 processes.
AAL3/4
AAL3/4 supports both connection-oriented and connectionless data.
An AAL 3/4 PDU (Protocol Data Unit) header consists of Type, Sequence Number, and Multiplexing Identifier fields.
AAL5
AAL5 is the primary AAL for data and supports both connection-oriented and connectionless data.
AAL5 also is known as the simple and efficient adaptation layer (SEAL)
For all cells except the last, a bit in
The Payload Type (PT) field is set to 0 to indicate that the cell is not the last cell in a series that represents a single frame.
For the last cell, the bit in the PT field is set to 1.
ATM cells
Each individual ATM cell consists of a 5-byte cell header and 48 bytes of information encapsulated within its payload. The ATM network uses the header to support the virtual path and the virtual channel routing, and to perform a quick error check for corrupted cells.
Cell Header
Generic Flow Control (GFC):
The GFC field of the header is only defined across the UNI. It is intended to control the traffic flow across the UNI
Payload Type Identifier (PTI):
Bit 3 is set to 1 to indicate that congestion was experienced by a data cell in transmission and is only valid when bit 4 is set to 0.
Bit 2 is used by AAL 5 to identify the data as Type 0 (beginning of message, continuation of message; bit = 0) or Type 1 (end of message, single-cell message; bit = 1) when bit 4 is set to 0. It may also be used for management functions when bit 4 is set to 1
ATM Devices
ATM Switches: An ATM switch is responsible for cell transit through an ATM network. It can reads and updates the cell header information and quickly switches the cell to an output interface toward its destination.
ATM Endpoints: An ATM endpoint (or end system) contains an ATM network interface adapter.
Benefits
High-speed communication
Connection-oriented service, similar to traditional telephony
Fast, hardware-based switching
A single, universal, interoperable network transport
A single network connection that can reliably mix voice, video, and data
Flexible and efficient allocation of network bandwidth
Applications
ATM technology is implemented in backbone, enterprise, and edge switches as well as hubs, routers, bridges, multiplexers, servers, server farms, and NICs (Network Interface Cards) in high-end Internet appliances.
Edge devices at the boundary of an ATM network convert non-ATM traffic streams into standard ATM cells.
ATM technology supports network configurations that include DANs (Desk Area Networks), LANs, MANs (Metropolitan Area Networks), WANs (Wide Area Networks), and GANs (Global Area Networks
Advantages
ATM supports voice, video and data allowing multimedia and mixed services over a single network.
High evolution potential, works with existing technologies
Provides the best multiple service support
Supports delay close to that of dedicated services
Able to use all common physical transmission paths like SONET.
Ability to connect LAN to WAN
High speed Mbps and possibly Gbps
Disadvantages
Flexible to efficiency’s expense, at present, for any one application it is usually possible to find a more optimized technology
Cost, although it will decrease with time
New customer premises hardware and software are required
Competition from other technologies -100 Mbps FDDI, 100 Mbps Ethernet and fast Ethernet.
[attachment=27891]
Introduction
Asynchronous Transfer Mode (ATM) is a standard switching technique designed to unify telecommunication and computer networks.
ATM uses asynchronous time-division multiplexing and it encodes data into small, fixed-sized cells
ATM provides data link layer services that run over a wide range of OSI physical Layer links.
Introduction
ATM is a cell-relay technology that divides upper-level data units into 53-byte cells for transmission over the physical medium.
ATM is Connection oriented switching technology
Consist upon 53-byte cells.
ATM supports different types of services via ATM adaptation layers (AAL).
Speeds on ATM networks can reach 10 Gbps.
Architecture
ATM operates with a layered structure that is similar to the OSI 7-layered model.
ATM only addresses the functionality of the two lowest layers of the OSI model: the physical layer (Layer 1) and the data link layer (Layer 2).
In ATM, the functionality of the two lower OSI layers are handled by three layers.
These layers are ATM Adaption Layer,ATM Layer and Physical Layer.
Physical Layer:
The Physical Layer defines the medium for transmission, any medium-dependent parameters (e.g., rate, quality of service required), and framing used to find the data contained within the medium.
ATM Layer:
The ATM Layer provides the basic 53-byte cell format, by defining the 5-byte ATM header for each 48-byte payload segment
ATM Adaption Layer(AAL):
The ATM Adaptation Layer (AAL) adapts the higher-level data into formats compatible with the ATM Layer requirements, i.e., this layer segments the data and adds appropriate error control information as necessary.
Several AAL protocols have been defined for specific types of data.
These are AAL 1,AAL 2,AAL 3/4 and AAL 5
AAL1
AAL1, a connection-oriented service, is suitable for handling constant bit rate sources (CBR), such as voice and videoconferencing.
AAL1 requires timing synchronization between the source and the destination.
Most important task is to synchronize the bytes on the ATM cell.
AAL2
Traffic type has timing requirements like CBR but tends to be bursty in nature. This is called variable bit rate (VBR) traffic.
The AAL2 process uses 44 bytes of the cell payload for user data and reserves 4 bytes of the payload to support the AAL2 processes.
AAL3/4
AAL3/4 supports both connection-oriented and connectionless data.
An AAL 3/4 PDU (Protocol Data Unit) header consists of Type, Sequence Number, and Multiplexing Identifier fields.
AAL5
AAL5 is the primary AAL for data and supports both connection-oriented and connectionless data.
AAL5 also is known as the simple and efficient adaptation layer (SEAL)
For all cells except the last, a bit in
The Payload Type (PT) field is set to 0 to indicate that the cell is not the last cell in a series that represents a single frame.
For the last cell, the bit in the PT field is set to 1.
ATM cells
Each individual ATM cell consists of a 5-byte cell header and 48 bytes of information encapsulated within its payload. The ATM network uses the header to support the virtual path and the virtual channel routing, and to perform a quick error check for corrupted cells.
Cell Header
Generic Flow Control (GFC):
The GFC field of the header is only defined across the UNI. It is intended to control the traffic flow across the UNI
Payload Type Identifier (PTI):
Bit 3 is set to 1 to indicate that congestion was experienced by a data cell in transmission and is only valid when bit 4 is set to 0.
Bit 2 is used by AAL 5 to identify the data as Type 0 (beginning of message, continuation of message; bit = 0) or Type 1 (end of message, single-cell message; bit = 1) when bit 4 is set to 0. It may also be used for management functions when bit 4 is set to 1
ATM Devices
ATM Switches: An ATM switch is responsible for cell transit through an ATM network. It can reads and updates the cell header information and quickly switches the cell to an output interface toward its destination.
ATM Endpoints: An ATM endpoint (or end system) contains an ATM network interface adapter.
Benefits
High-speed communication
Connection-oriented service, similar to traditional telephony
Fast, hardware-based switching
A single, universal, interoperable network transport
A single network connection that can reliably mix voice, video, and data
Flexible and efficient allocation of network bandwidth
Applications
ATM technology is implemented in backbone, enterprise, and edge switches as well as hubs, routers, bridges, multiplexers, servers, server farms, and NICs (Network Interface Cards) in high-end Internet appliances.
Edge devices at the boundary of an ATM network convert non-ATM traffic streams into standard ATM cells.
ATM technology supports network configurations that include DANs (Desk Area Networks), LANs, MANs (Metropolitan Area Networks), WANs (Wide Area Networks), and GANs (Global Area Networks
Advantages
ATM supports voice, video and data allowing multimedia and mixed services over a single network.
High evolution potential, works with existing technologies
Provides the best multiple service support
Supports delay close to that of dedicated services
Able to use all common physical transmission paths like SONET.
Ability to connect LAN to WAN
High speed Mbps and possibly Gbps
Disadvantages
Flexible to efficiency’s expense, at present, for any one application it is usually possible to find a more optimized technology
Cost, although it will decrease with time
New customer premises hardware and software are required
Competition from other technologies -100 Mbps FDDI, 100 Mbps Ethernet and fast Ethernet.