04-10-2012, 10:52 AM
Asynchronous Transfer Mode
Atm-intro.ppt (Size: 1.78 MB / Downloads: 86)
Need for Network Convergence
PSTN sometimes used as a data network backbone – but since it is circuit switched (voice optimized) not very WAN efficient
Delay sensitive traffic such as voice not possible on data networks since there is no guarantee of QoS
Types of Traffic and demand on a communication channel
Voice
Its generation is asynchronous (a speaker may speak anytime)
Its transmission must be synchronous (once the message starts, it must flow continuously as it is spoken)
The bandwidth required for a voice conversation in digital communication is relatively small and constant (64K)
The signals may contain a high degree of error and the information can still be retrieved correctly
Video
The generation is synchronous (continuous)
Its transmission is synchronous. The bandwidth required is variable and it could range from under 64 Kbps to several Mbps in the same session.
Error control should be tight - otherwise the wrong information on the monitor may trigger severe wrongful actions
Data
Its generation could be either asynchronous (text) or synchronous (telemetry)
Its transmission in general can be asynchronous (data typically can wait patiently in buffers)
The information is extremely error-sensitive, so extreme caution must be exercised in transmission and error control must be very tight.
How can we combine voice , data and video on the same link?
Fixed and relatively short packets
Delays associated with each packet are going to be short and fixed – predictable transmission
If Voice and Video can be given priority handling – then mixing is possible without any diminishing in quality
Introduction
ATM – Asynchronous Transfer Mode
It is a high speed, connection – oriented switching and multiplexing technology capable of transmitting voice, video and data and interconnecting LAN’s
ATM is asynchronous because information streams can be sent independently without the need of a common clock
Features and Benefits of ATM
Convergence of Voice , Video and Data on one network
High speed switching at hardware level
Bandwidth on demand
Predefined and guaranteed QoS and CoS
Superior Management features
Scalability in network size and speed
Ease of integration with other technologies
Important terms relevant to ATM
Quality of Service (QoS) :A broadly used term that refers to the performance attributes of an end-to-end connection. A QoS definition for data would address attributes such as error rates, lost packet rates, throughput, and delay
Class of Service (CoS) :It is a way of managing traffic in a network by grouping similar types of traffic together and treating each type as a class with its own level of service priority
Fast Packet Switching :A packet switching technique that increases the throughput by eliminating overhead. Overhead reduction is accomplished by allocating flow control and error correction functions to either the user applications or the network nodes that interface with the user. Cell relay is an implementation of this.
Cells and Cell relay
A Cell is a formatted packet that uses a fixed length data unit
Cell relay is the process of moving these cells through switching elements
Fixed size cells can be switched at a very high speed and add predictability to data transmissions
Variable length frames produce unpredictable patterns and performances as the buffer time cannot be determined
Cell tax – overhead imposed by ATM cells which can cut into amount of data that can be transferred
Fundamental ATM Operations Concept
A virtual or logical connection is established
ATM forms a packet of fixed length – 53 octets ( 5 octet header and 48 octet information field )
Cells are placed in a queue, on reaching ATM switch
Cells are then multiplexed asynchronously with other cells for transmission
Switch adapts the incoming bit rate to match the transmit channel bit rate
Switch inserts dummy cells to meet the aggregate bit stream rate of 155.52 Mbps
Atm-intro.ppt (Size: 1.78 MB / Downloads: 86)
Need for Network Convergence
PSTN sometimes used as a data network backbone – but since it is circuit switched (voice optimized) not very WAN efficient
Delay sensitive traffic such as voice not possible on data networks since there is no guarantee of QoS
Types of Traffic and demand on a communication channel
Voice
Its generation is asynchronous (a speaker may speak anytime)
Its transmission must be synchronous (once the message starts, it must flow continuously as it is spoken)
The bandwidth required for a voice conversation in digital communication is relatively small and constant (64K)
The signals may contain a high degree of error and the information can still be retrieved correctly
Video
The generation is synchronous (continuous)
Its transmission is synchronous. The bandwidth required is variable and it could range from under 64 Kbps to several Mbps in the same session.
Error control should be tight - otherwise the wrong information on the monitor may trigger severe wrongful actions
Data
Its generation could be either asynchronous (text) or synchronous (telemetry)
Its transmission in general can be asynchronous (data typically can wait patiently in buffers)
The information is extremely error-sensitive, so extreme caution must be exercised in transmission and error control must be very tight.
How can we combine voice , data and video on the same link?
Fixed and relatively short packets
Delays associated with each packet are going to be short and fixed – predictable transmission
If Voice and Video can be given priority handling – then mixing is possible without any diminishing in quality
Introduction
ATM – Asynchronous Transfer Mode
It is a high speed, connection – oriented switching and multiplexing technology capable of transmitting voice, video and data and interconnecting LAN’s
ATM is asynchronous because information streams can be sent independently without the need of a common clock
Features and Benefits of ATM
Convergence of Voice , Video and Data on one network
High speed switching at hardware level
Bandwidth on demand
Predefined and guaranteed QoS and CoS
Superior Management features
Scalability in network size and speed
Ease of integration with other technologies
Important terms relevant to ATM
Quality of Service (QoS) :A broadly used term that refers to the performance attributes of an end-to-end connection. A QoS definition for data would address attributes such as error rates, lost packet rates, throughput, and delay
Class of Service (CoS) :It is a way of managing traffic in a network by grouping similar types of traffic together and treating each type as a class with its own level of service priority
Fast Packet Switching :A packet switching technique that increases the throughput by eliminating overhead. Overhead reduction is accomplished by allocating flow control and error correction functions to either the user applications or the network nodes that interface with the user. Cell relay is an implementation of this.
Cells and Cell relay
A Cell is a formatted packet that uses a fixed length data unit
Cell relay is the process of moving these cells through switching elements
Fixed size cells can be switched at a very high speed and add predictability to data transmissions
Variable length frames produce unpredictable patterns and performances as the buffer time cannot be determined
Cell tax – overhead imposed by ATM cells which can cut into amount of data that can be transferred
Fundamental ATM Operations Concept
A virtual or logical connection is established
ATM forms a packet of fixed length – 53 octets ( 5 octet header and 48 octet information field )
Cells are placed in a queue, on reaching ATM switch
Cells are then multiplexed asynchronously with other cells for transmission
Switch adapts the incoming bit rate to match the transmit channel bit rate
Switch inserts dummy cells to meet the aggregate bit stream rate of 155.52 Mbps