February 15, 2020
Amitraj
What is ATM ?
Asynchronous transfer mode (ATM) is a switching technique used by telecommunication networks that uses asynchronous time-division multiplexing to encode data into small, fixed-sized cells. This is different from Ethernet or internet, which use variable packet sizes for data or frames. ATM is the core protocol used over the synchronous optical network (SONET) backbone of the integrated digital services network (ISDN).
-> B-ISDN is the low-level MAC(Media Access control) protocol for transferring the actual data.
ATM was designed with an aim to provide:-
1. High speed data rate.
2. Low error rate between two or more switching centers.
3. Digital voice and videos.
4. Low operating cost.
Features of ATM:-
1. Flexibility and versatility of voice, videos and images can be transmitted simultaneously over a single or integrated corporate network.
2. Higher transmission capability.
3. It provides support for virtual networks.
ATM Bit Rates:-
ATM supports four different types of bit rate:
1. Constant bit rate (CBR)
CBR traffic is derived from the source, where the information is transmitted at a constant rate.
Example: Telephonic speech without silencer.
2. Variable Bit Rate (VBR)
Variable traffic is derived from a variable source.
Example: Compressed voice or video with silence suppression.
3. Available Bit Rate (ABR)
When a carrier has allocated the necessary bandwidth on the links to carry CBR traffic and minimum VBR is guaranteed.
The ABR is the mechanism to share the remaining bandwidth fairly between the links.
4. Unspecified Bit Rate (UBR)
1. In UBR, there is no guarantee about the bandwidth traffic delay and loss. The control of flow in UBR can be provided from the end device.
2. The protocol which performs the operation of braking frames into the cells is known as ATM Adaptation Layer (AAL).
3. Cells carrying speech and video must be received in the order they were sent. This is known as preserving data integrity and it is a function of ATM layer.
4. Any link which preserves the order of data entering and leaving is known as channel.
5. In ATM protocols, an end-to end connection is established before traffic and starts to flow. Then ,the traffic follows the same path through the network to achieve a true quality of service.
6. The connection-less services are implemented with the help of AAL.
ATM Architecture -
1. Physical Layer -
This layer corresponds to physical layer of OSI model. At this layer, the cells are converted into bit streams and transmitted over the physical medium. This layer has two sub layers: PMD sub layer (Physical Medium Dependent) and TC (Transmission Convergence) sub layer.
2. ATM layer -
-> ATM layer provides the routing information to the data cells.
-> ATM interfaces with the AAL and the Physical layer.
-> Functions of ATM layer are under the network management, signaling and OAM protocol.
3. ATM Adaptation Layer -
-> AAL provides the flexibility of a single communication process to carry the multiple types of traffic such as data, voice, video and multimedia.
-> AAL is divided into two major parts.
-> Upper part of the AAL is called as the convergence sublayer. Its task is to provide the interface to the application. The lower part of the AAL is called as the segmentation and reassembly (SAR) sublayer. It can add headers and trailers to the data units given to it by the convergence sublayer to form cell payloads.
Asynchronous transfer mode (ATM) is a switching technique used by telecommunication networks that uses asynchronous time-division multiplexing to encode data into small, fixed-sized cells. This is different from Ethernet or internet, which use variable packet sizes for data or frames. ATM is the core protocol used over the synchronous optical network (SONET) backbone of the integrated digital services network (ISDN).
-> B-ISDN is the low-level MAC(Media Access control) protocol for transferring the actual data.
ATM was designed with an aim to provide:-
1. High speed data rate.
2. Low error rate between two or more switching centers.
3. Digital voice and videos.
4. Low operating cost.
Features of ATM:-
1. Flexibility and versatility of voice, videos and images can be transmitted simultaneously over a single or integrated corporate network.
2. Higher transmission capability.
3. It provides support for virtual networks.
ATM Bit Rates:-
ATM supports four different types of bit rate:
1. Constant bit rate (CBR)
CBR traffic is derived from the source, where the information is transmitted at a constant rate.
Example: Telephonic speech without silencer.
2. Variable Bit Rate (VBR)
Variable traffic is derived from a variable source.
Example: Compressed voice or video with silence suppression.
3. Available Bit Rate (ABR)
When a carrier has allocated the necessary bandwidth on the links to carry CBR traffic and minimum VBR is guaranteed.
The ABR is the mechanism to share the remaining bandwidth fairly between the links.
4. Unspecified Bit Rate (UBR)
1. In UBR, there is no guarantee about the bandwidth traffic delay and loss. The control of flow in UBR can be provided from the end device.
2. The protocol which performs the operation of braking frames into the cells is known as ATM Adaptation Layer (AAL).
3. Cells carrying speech and video must be received in the order they were sent. This is known as preserving data integrity and it is a function of ATM layer.
4. Any link which preserves the order of data entering and leaving is known as channel.
5. In ATM protocols, an end-to end connection is established before traffic and starts to flow. Then ,the traffic follows the same path through the network to achieve a true quality of service.
6. The connection-less services are implemented with the help of AAL.
ATM Architecture -
1. Physical Layer -
This layer corresponds to physical layer of OSI model. At this layer, the cells are converted into bit streams and transmitted over the physical medium. This layer has two sub layers: PMD sub layer (Physical Medium Dependent) and TC (Transmission Convergence) sub layer.
2. ATM layer -
-> ATM layer provides the routing information to the data cells.
-> ATM interfaces with the AAL and the Physical layer.
-> Functions of ATM layer are under the network management, signaling and OAM protocol.
3. ATM Adaptation Layer -
-> AAL provides the flexibility of a single communication process to carry the multiple types of traffic such as data, voice, video and multimedia.
-> AAL is divided into two major parts.
-> Upper part of the AAL is called as the convergence sublayer. Its task is to provide the interface to the application. The lower part of the AAL is called as the segmentation and reassembly (SAR) sublayer. It can add headers and trailers to the data units given to it by the convergence sublayer to form cell payloads.
