ASYNCHRONOUS TRANSFER MODE networks are true multi-service networks with the potential to offer broad band services. This transfer mode is considered to be the ground on which BISDN is built. Public ATM network implementation will mainly be used as broadband backbone networks to support leased lines, IP traffic, transit telephony etc, since a common network infrastructure for provision of multiple services is a very cost effective solution.This paper is mainly highlighted by the transmission and switching information in a network. Switching combines the aspects of ‘time division multiplexing’ and ‘packet switching’.
One problem with other protocols which implement virtual connections is that some time slots are wasted if no data is being transmitted. ATM avoids this by dynamically allocating bandwidth for traffic on demand. This means greater utilization of bandwidth and better capacity to handle heavy load situations. When an ATM connection is requested, details concerning the connection are specified which allow decisions to be made concerning the route and handling of the data to be made. Typical details are the type of traffic [video requires higher priority], destination, peak and average bandwidth requirements [which the network can use to estimate resources and cost structures], a cost factor [which allows the network to chose a route which fits within the cost structure] and other parameters.
ATM is a technique used in BISDN’s (Broad band integrated services digital network) BISDN is a typical ITU term denoting that ATM based networks should be embedded into the ISDN environment. ISDN refers to a new form of network which integrates voice, data and image in a digitized form. The ISDN connection is digital end-to-end.
We shall look at two common protocols used in Serial data communications, the first is known as Asynchronous, the second as Synchronous. In asynchronous serial transmission, each character is packaged in an envelope, and sent across a single wire, bit by bit, to a receiver. Because no signal lines are used to convey clock (timing) information, this method groups data together into a sequence of bits (five - eight), then prefixes them with a start bit and appends the data with a stop bit. It’s important to realize that the receiver and sender are re-synchronized each time a character arrives. This method of transmission is suitable for slow speeds less than about 32000 bits per second. The signal that is sent does not contain any information that can be used to validate if it was received without modification. This means that this method does not contain error detection information, and is susceptible to errors.
In addition, for every character that is sent, additional two bits are also sent.. The asynchronous protocol evolved early in the history of telecommunications. It became popular with the invention of the early tele-typewriters that were used to send telegrams around the world .synchronous systems send data bytes between the sender and receiver. Each data byte is preceeded with a start bit, and suffixed with a stop bit. These extra bits server to synchronize the receiver with the sender. Transmission of these extra bits (2 per byte) reduce data throughput. Synchronization is achieved for each character only. When the sender has no data to transmit, the line is idle and the sender and receiver are NOT in synchronization. Asynchronous protocols are suited for low speed data communications
After initializing the receiver in correction mode .when a single bit error is detected, it is corrected or else the cell is discarded. The above receiver operation has been chosen to take into account the error characteristics of fiber based transmission systems. One problem with other protocols which implement virtual connections is that some time slots are wasted if no data is being transmitted. ATM avoids this by dynamically allocating bandwidth for traffic on demand. This means greater utilization of bandwidth and better capacity to handle heavy load situations. When an ATM connection is requested, details concerning the connection are specified which allow decisions to be made concerning the route and handling of the data to be made. Typical details are the type of traffic [video requires higher priority], destination, peak and average bandwidth requirements [which the network can use to estimate resources and cost structures], a cost factor [which allows the network to chose a route which fits within the cost structure] and other parameters. When designing the architecture of the internetwork, it is important to take into account the communications requirements. This is not just an issue of total traffic, but also of instantaneous demand and user response requirements. ATM technologies will enable the use of the same lines for voice, data, or video communications without preallocating exclusive portions of the network to each application.ATM layer operation and maintenance functions are monitoring of virtual path and virtual channel availability and performance monitoring at the VP and VC levels
The data exchange interface is defined by the ATM Forum for connecting non ATM capable devices to an ATM network. The frame based user to network interface (FUNI) was defined for ATM for access rates of nX64kbits. The DXI allows data terminal equipment (DTE) such as a router to be connected via data circuit terminating equipment (DCE) to an ATM switch. The DXI header contains fields to carry cell loss priority (CLP) and congestion notification (CN) information. The transfer of cells through an ATM network is supported by the generation of the cells through packetizer, multiplexing and switching of cells this is illustrated clearly in ATM switching.
The ATM originally invented by researches as a hybrid switching technique combining the merits of channel and packet switching for optimized for real time systems.ITU-T originally defined two options for the user network interface, one on pure cell multiplexing and other on SDH(synchronous digital hierarchy.
Datelcircuits are justly elated to Leased lines. Here the multiplexing takes place by the time interval between each Channel, hence it is known as Time division multiplexing. This process is also known a bus switching technique.TMD comes under central memory switching element .the interconnection network can be realized by a high speed TDM bus. A multiplexor is a device which shares a communications link between a number of users. It does this by time or frequency division. It is costly to provide a single circuit for each device (terminal) It is costly to provide a single circuit for each device (terminal). Imagine having 200 remote terminals, and supplying 200 physical lines for each terminal.
Rather than provide a separate circuit for each device, the multiplexer combines each low speed circuit onto a single high speed link. The cost of the single high speed link is less than the required number of low speed links.
In time division, the communications link is subdivided in terms of time. Each sub-circuit is given the channel for a limited amount of time, before it is switched over to the next user, and so on.
Here it can be seen that each sub-channel occupies the entire bandwidth of the channel, but only for a portion of the time. In frequency division multiplexing, each sub-channel is separated by frequency (each channel is allocated part of the bandwidth of the channel).
The speed or bandwidth of the main link is the sum of the individual channel speeds or bandwidth. It can be though of as a many to one device. The use of ATM cell packetize in a customer networks is to convert non ATM signals to the ATM cell format this will arise especially during the introductory phase of ATM networks .to this end the terminals have to be provided with the network clock via access line.
Actually ATM is a hybrid switching technique combining the merits of channel and packet switching optimized for real time systems. The multiplexer combines each low speed circuit onto a single high speed link. In TMD each channel is given certain time before shifting to another user.
Introduction
The asynchronous transfer mode is considered to be the ground on which BISDN is to be built. ATM is the transfer mode for implementing BISDN.The term transfer comprises both transmission and switching aspects, so a transfer mode is a specific way of transmitting and switching information in a network. The service of an ATM network is the transport and routing that is multiplexing, transmission and switching of ATM cells.ATM implementations serve as back bone networks mainly for data communication .the merit of an ATM back bone network for the network operator is that a common, unique network infrastructure can be deployed flexibly to support all the existing and future services.One problem with other protocols which implement virtual connections is that some time slots are wasted if no data is being transmitted. ATM avoids this by dynamically allocating bandwidth for traffic on demand. This means greater utilization of bandwidth and better capacity to handle heavy load situations. When an ATM connection is requested, details concerning the connection are specified which allow decisions to be made concerning the route and handling of the data to be made. Typical details are the type of traffic [video requires higher priority], destination, peak and average bandwidth requirements [which the network can use to estimate resources and cost structures], a cost factor [which allows the network to chose a route which fits within the cost structure] and other parameters.
ATM is a technique used in BISDN’s (Broad band integrated services digital network) BISDN is a typical ITU term denoting that ATM based networks should be embedded into the ISDN environment. ISDN refers to a new form of network which integrates voice, data and image in a digitized form. The ISDN connection is digital end-to-end.
Asynchronous Systems
Asynchronous systems send data bytes between the sender and receiver by packaging the data in an envelope. This envelope helps transport the character across the transmission link that separates the sender and receiver. The transmitter creates the envelope, and the receiver uses the envelope to extract the data. Each character (data byte) the sender transmits is preceded with a start bit, and suffixed with a stop bit. These extra bits serve to synchronize the receiver with the sender. This section briefly discusses the differences between two different methods of Serial transmission, namely, asynchronous and synchronous. A protocol establishes a means of communicating between two systems. As long as the sender and receiver each use the same protocol, information can be reliably exchanged between them.We shall look at two common protocols used in Serial data communications, the first is known as Asynchronous, the second as Synchronous. In asynchronous serial transmission, each character is packaged in an envelope, and sent across a single wire, bit by bit, to a receiver. Because no signal lines are used to convey clock (timing) information, this method groups data together into a sequence of bits (five - eight), then prefixes them with a start bit and appends the data with a stop bit. It’s important to realize that the receiver and sender are re-synchronized each time a character arrives. This method of transmission is suitable for slow speeds less than about 32000 bits per second. The signal that is sent does not contain any information that can be used to validate if it was received without modification. This means that this method does not contain error detection information, and is susceptible to errors.
In addition, for every character that is sent, additional two bits are also sent.. The asynchronous protocol evolved early in the history of telecommunications. It became popular with the invention of the early tele-typewriters that were used to send telegrams around the world .synchronous systems send data bytes between the sender and receiver. Each data byte is preceeded with a start bit, and suffixed with a stop bit. These extra bits server to synchronize the receiver with the sender. Transmission of these extra bits (2 per byte) reduce data throughput. Synchronization is achieved for each character only. When the sender has no data to transmit, the line is idle and the sender and receiver are NOT in synchronization. Asynchronous protocols are suited for low speed data communications
ATM Transmission
ATM breaks data into small chunks of fixed size cells (48 bytes of data plus a 5 byte overhead). ATM is designed for handling large amounts of data across long distances using a high speed backbone approach. ATM cell header error control is a physical layer function. Every ATM cell transmitter calculates the HEC value across the first four octets of cell header.HEC code is capable of correcting single bit error codes.After initializing the receiver in correction mode .when a single bit error is detected, it is corrected or else the cell is discarded. The above receiver operation has been chosen to take into account the error characteristics of fiber based transmission systems. One problem with other protocols which implement virtual connections is that some time slots are wasted if no data is being transmitted. ATM avoids this by dynamically allocating bandwidth for traffic on demand. This means greater utilization of bandwidth and better capacity to handle heavy load situations. When an ATM connection is requested, details concerning the connection are specified which allow decisions to be made concerning the route and handling of the data to be made. Typical details are the type of traffic [video requires higher priority], destination, peak and average bandwidth requirements [which the network can use to estimate resources and cost structures], a cost factor [which allows the network to chose a route which fits within the cost structure] and other parameters. When designing the architecture of the internetwork, it is important to take into account the communications requirements. This is not just an issue of total traffic, but also of instantaneous demand and user response requirements. ATM technologies will enable the use of the same lines for voice, data, or video communications without preallocating exclusive portions of the network to each application.ATM layer operation and maintenance functions are monitoring of virtual path and virtual channel availability and performance monitoring at the VP and VC levels
The data exchange interface is defined by the ATM Forum for connecting non ATM capable devices to an ATM network. The frame based user to network interface (FUNI) was defined for ATM for access rates of nX64kbits. The DXI allows data terminal equipment (DTE) such as a router to be connected via data circuit terminating equipment (DCE) to an ATM switch. The DXI header contains fields to carry cell loss priority (CLP) and congestion notification (CN) information. The transfer of cells through an ATM network is supported by the generation of the cells through packetizer, multiplexing and switching of cells this is illustrated clearly in ATM switching.
The ATM originally invented by researches as a hybrid switching technique combining the merits of channel and packet switching for optimized for real time systems.ITU-T originally defined two options for the user network interface, one on pure cell multiplexing and other on SDH(synchronous digital hierarchy.
Switching techniques
Rather than allocating a dedicated virtual circuit for the duration of each call, data is assembled into small packets and statistically multiplexed according to their traffic characteristics.ATM also provides automatic protection switching (APS) Connection is made to the public communications carrier packet network. This is a special network which connects users which send data grouped in packets. Packet technology is suited to medium speed, medium volume data requirements. It offers cheaper cost than the datel circuit, but for large volumes, is more expensive than the leased circuit. Special hardware and software is required to packetize the data before transmission, and depacketize the data on arrival. Packet switched circuits exist for the duration of the call.Datelcircuits are justly elated to Leased lines. Here the multiplexing takes place by the time interval between each Channel, hence it is known as Time division multiplexing. This process is also known a bus switching technique.TMD comes under central memory switching element .the interconnection network can be realized by a high speed TDM bus. A multiplexor is a device which shares a communications link between a number of users. It does this by time or frequency division. It is costly to provide a single circuit for each device (terminal) It is costly to provide a single circuit for each device (terminal). Imagine having 200 remote terminals, and supplying 200 physical lines for each terminal.
Rather than provide a separate circuit for each device, the multiplexer combines each low speed circuit onto a single high speed link. The cost of the single high speed link is less than the required number of low speed links.
In time division, the communications link is subdivided in terms of time. Each sub-circuit is given the channel for a limited amount of time, before it is switched over to the next user, and so on.
Here it can be seen that each sub-channel occupies the entire bandwidth of the channel, but only for a portion of the time. In frequency division multiplexing, each sub-channel is separated by frequency (each channel is allocated part of the bandwidth of the channel).
The speed or bandwidth of the main link is the sum of the individual channel speeds or bandwidth. It can be though of as a many to one device. The use of ATM cell packetize in a customer networks is to convert non ATM signals to the ATM cell format this will arise especially during the introductory phase of ATM networks .to this end the terminals have to be provided with the network clock via access line.
Summary:
ASYNCHRONOUS TRANSFER MODE networks are true multi-service networks with the potential to offer broad band services. Asynchronous systems send data bytes between the sender and receiver by packaging the data in an envelope, another interesting thing related to ATM network implementation is the architectural concept for virtual path and virtual channel, since Leased line services would then be realized via the VP network and switched connections.Actually ATM is a hybrid switching technique combining the merits of channel and packet switching optimized for real time systems. The multiplexer combines each low speed circuit onto a single high speed link. In TMD each channel is given certain time before shifting to another user.
References:
- Concepts, protocols, applications, (Third edition) Jonathan B.Kudsen.
- Network principles And Concepts, (Fifth edition), Microsoft press
- Switching networks, J.F.Kurose.
Technical Paper on ATM Networks
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