INTRODUCTION TO ATM
(ATM) is an international telecommunication Union-Telecommunication standards section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells, ATM networks are connection-oriented.ATM is an evolving technology designed for high speed transfer of voice, video and data through public and private network in a cost effective manner
NEED AND ROLE OF ATM IN INTERNET WORKS
Today 90% of computing power resides on desktops, and that power is growing exponentially. Distributed applications are increasingly bandwidth hungry. In the LAN band width is free and connectivity is limited. In the WAN band width has been the overriding cost and delay sensitive traffic such as voice, has remained separate from data.ATM has emerged has one of the technologies for integrating LANs and WANs. ATM can support any traffic type in separate or mixed streams, delay or non-delay sensitive traffic .ATM can also scale from low to high speeds. It has been adopted by the industry equipment vendors, from LAN to private branch exchange (PBX) with ATM network designers can integrate LANs and WANs, support emerging applications with economy in the enterprise, and support legacy protocols with added efficiency.
ATM DEVICES AND THE NETWORK ENVIRONMENT
ATM is a cell-switching and multiplexing technology this combines the benefits Of circuit switching (guaranteed capacity and constant transmission delay)with those of packet switching(flexibility and efficiency for intermittent traffic). It provides scalable bandwidth from a new megabits per second (mbps) to many gigabits per second (Gbps). Because of its asynchronous nature, ATM is more efficient than synchronous technologies station has much data to send, it can send only when its time slot comes up, even if all time slots are empty. However, if as station has nothing to transmit when its time slot comes up. The time slot is sent empty and is wasted. Because ATM is asynchronous, timeslots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell.
ATM DEVICES
An ATM network is made up of an ATM switch and ATM endpoints. An ATM switch is well defined. It accepts the incoming cell from an ATM endpoint or another ATM switch. It then reads and updates the cell header information and quickly switches the cell to an output interface toward its destination. An ATM endpoint (or end system) contains an ATM network interface adapter. Examples of ATM endpoints are workstations, routers, digital service units (DSU), LAN switches, and video coder-decoder (CODEC)
STRUCTURE OF ATM NETWORK
ATM is based the concept of two end-points devices communicating by means of intermediate switches. An ATM network is made up of series of switches and end-points devices. The end point devices can be ATN- attached end stations, ATM-attached end points, ATM attached servers, or ATM-attached routers.
STRUCTURE OF ATM NETWORK
ATM is based the concept of two end-points devices communicating by means of intermediate switches. An ATM network is made up of series of switches and end-points devices. The end point devices can be ATN- attached end stations, ATM-attached end points, ATM attached servers, or ATM-attached routers.
- User-to-User interface (UNI)
- Network-to-Network interface (NNI)
The UNI connection is made up of an end-point device and a private or public ATM switch. The NNI is the connection between two ATM switches. The UNI and NNI connections can be carried by different physical conditions. In addition to the UNI and NNI protocols, the ATM forum has defined a set of LAN Emulation (LANE) standards and a private Network to Network interface (PNNI) phase 0 protocols. LANE is a technology network designers can use to integrate legacy LAN such as Ethernet and Token Ring with ATM attached devices. Most LANE networks consist of multiple ATM switches and typically the PNNI protocol.
GENERAL OPERATION OF AN ATM NETWORK
Because ATM is connection oriented, a connection must be established .Between two end points before any data transfer can occur. This connection is accomplished through a signaling protocol as shown in figure.
As figure shows, for router A to connect to Router B the following must occur. Router A sends a signaling request packet to its directly connected ATM switch (ATM switch 1)
As figure shows, for router A to connect to Router B the following must occur. Router A sends a signaling request packet to its directly connected ATM switch (ATM switch 1)
- ATM switch 1 resembles the signaling packet from Router A, and then examines it.
- If ATM switch 1 has an entry for Router B ATM address in its switch table and it can accommodate the QoS requested for the connection, it set up the connection and forwards the request to the next switch(ATN switch along path 2)
- Every switch along the path to router B reassembles and examines the signaling packet, and then forwards it to the next switch if the QoS parameter can be supported. Each switch also sets up the virtual connection as the signaling packet is forwarded.
- If any switch along the path cannot accommodate the requested QoS parameters, the request is rejected and a rejection message is sent back to Router A.
- When the signaling packet arrives at Router B, router B reassembles it and evaluates the packet. If Router B can support the requested QoS, it responds with an accept message. As the accept message is propagated back to Router A, the switches set up a virtual circuit.
- Router A receives accept message from its directly connected ATM switch (ATM switch 1) as well as the virtual path identifier (VPI) and virtual channel identifier (VCI) others that it should use for cells sent to Router B.
ATM FUNCTIONAL LAYER
Just as an Open System Interconnection (OSI) reference model describes how to computers communicate over a network, the ATM protocol model describes how to end systems communicate through ATM switches. The ATM protocol model consists of the following three functional layers
- ATM Physical layer
- ATM layer
- ATM adaptation layer
ATM SWITCHING OPERATION
The basic operation of an ATM switch is straightforward. The cell is received across a link on known VCI or VPI value. The switch looks up the connection value in a local translation table to determine the outgoing port (or ports) of the connection and the new VPI/VCI value of the connection on that link. The switch then retransmits the cell on that outgoing link with the appropriate connection identifiers. Because all VCI and VPI have only local significance across a particular link, these values are remapped, as necessary, at each switch.
DIFFERENT TYPES OF ATM SWITCHES
Even though all ATM switches perform cell relay, ATM switches differ manually in the following ways:
1. Variety of interfaces and services that are supported
2. Redundancy
3. Depth of ATM internetworking software
4. Sophistication of traffic management mechanism
Just as there are routers and LAN switches available at various price/performance points with different levels of functionality, ATM switches can be segmented into the following four distinct types that reflect the needs of particular applications and markets.
1. Workgroup ATM switches
2. Campus ATM switches
3. Enterprise ATM switches
4. Multiservice access switches
DIFFERENT TYPES OF ATM SWITCHES
Even though all ATM switches perform cell relay, ATM switches differ manually in the following ways:
1. Variety of interfaces and services that are supported
2. Redundancy
3. Depth of ATM internetworking software
4. Sophistication of traffic management mechanism
Just as there are routers and LAN switches available at various price/performance points with different levels of functionality, ATM switches can be segmented into the following four distinct types that reflect the needs of particular applications and markets.
1. Workgroup ATM switches
2. Campus ATM switches
3. Enterprise ATM switches
4. Multiservice access switches
ATM SIGNALING AND CONNECTION ESTABLISHMENT
When an ATM device wants to establish a connection with another ATM device, it sends a signaling-request packet to it is directly connected ATM switch. This request contains the ATM address of the desired ATN endpoint, as well as any QoS parameters required for the connection. ATM signaling protocols vary by the type of ATM link, which can be either UNI signals or NNI signals. UNI is used between an ATM end system across ATM UNI, and NNI across NNI links.
THE ATM CONNECTION-ESTABLISHMENT PROCESS
ATM signaling uses the one-pass method of connection setup that is used in all modern telecommunication networks, such as the telephone network. An ATM connection setup proceeds in the following manner. First, the source endpoints send, a connection-signaling request. The connection request is prorogated through the network. As a result, connections are set up through the network. The connection request reaches the final destination, which either or rejects the connection request.
LAN EMULATION
LAN Emulation (LANE) is a standard defined by the ATM forum that gives to station attached via ATM the same capabilities that they normally obtain from legacy LAN, such as Ethernet and Token ring. As the name suggests, the function of the LANE protocol is to emulate a LAN on top of ATM network. The LANE protocol defines a service interface for higher-layer (that is. Network layer) protocols that is identical to that of existing LAN. Data sent across the ATM network is encapsulated in the appropriate LAN MAC packet format. Simply put. The LANE protocols make an ATM network look and behave like an ETHERNET LAN.
LAN EMULATION
LAN Emulation (LANE) is a standard defined by the ATM forum that gives to station attached via ATM the same capabilities that they normally obtain from legacy LAN, such as Ethernet and Token ring. As the name suggests, the function of the LANE protocol is to emulate a LAN on top of ATM network. The LANE protocol defines a service interface for higher-layer (that is. Network layer) protocols that is identical to that of existing LAN. Data sent across the ATM network is encapsulated in the appropriate LAN MAC packet format. Simply put. The LANE protocols make an ATM network look and behave like an ETHERNET LAN.
BENEFITS OF ATM
Distributed Architecture of ATM
Intelligent ATM minimizes the effect of failure with distributed architecture when there is no single point of failure faults can be localized and have little or no effect on overall network performance intelligent routing supports this approach by instantly redirecting traffic around problem areas.
Fault HandlingEvery network management platform should include intelligent features that include the time it takes to identify and resolve network problems and keep downtime to a minimum .For example alarm correlation provides a quick way to provide meaningful information about the root causes and automated responses solve problem faster.
Intelligent ATM minimizes the effect of failure with distributed architecture when there is no single point of failure faults can be localized and have little or no effect on overall network performance intelligent routing supports this approach by instantly redirecting traffic around problem areas.
Fault HandlingEvery network management platform should include intelligent features that include the time it takes to identify and resolve network problems and keep downtime to a minimum .For example alarm correlation provides a quick way to provide meaningful information about the root causes and automated responses solve problem faster.
In Service Upgrade
Network availability should not be interrupted by hardware and a software replacement in-service upgrade enables the network to continue operating throughout making this activity.
Network availability should not be interrupted by hardware and a software replacement in-service upgrade enables the network to continue operating throughout making this activity.
Redundancy
Redundancy is important for preventing downtime but it must be provided cost effectively that means matching the level of redundancy with the equipment role in the network one to one redundancy is the system closest to the core for lesser the one to n redundancy may be more cost effective this balance approach provides optimum availability for the price.
Redundancy is important for preventing downtime but it must be provided cost effectively that means matching the level of redundancy with the equipment role in the network one to one redundancy is the system closest to the core for lesser the one to n redundancy may be more cost effective this balance approach provides optimum availability for the price.
LEGACY ACCESS TO ATM
Adaptation
Network interworking adopts flows to ATM carries across ATM network adapts it back in its original format this provides the benefit of consolidated ATM back pond while allowing non ATM services to be provisioned to end to end bases service interworking adopts non ATM services to ATM and allowing and delivers it in an ATM format for carrier this provision non ATM sites to communicate with an ATM hub site.
Network interworking adopts flows to ATM carries across ATM network adapts it back in its original format this provides the benefit of consolidated ATM back pond while allowing non ATM services to be provisioned to end to end bases service interworking adopts non ATM services to ATM and allowing and delivers it in an ATM format for carrier this provision non ATM sites to communicate with an ATM hub site.
Efficiency
Intelligent ATM makes efficient use of network resources with traffic consideration of ATM switch port traffic aggregation and physical port
Leverage.
Intelligent ATM makes efficient use of network resources with traffic consideration of ATM switch port traffic aggregation and physical port
Leverage.
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