(ATM) Asynchronous Transfer Mode

      The first ATM Assembly standardized was released in 1992. Different ATM Facility working groups are work defining additional standards required to enable ATM to cater a communications potentiality for the comprehensive potentiality of LAN and WAN transmission schemes it is organized to hold. This normalisation labor will likely remain in validity for a extensive punctuation due to the umbrella organisation content of the technol-ogy, which was formed to reinforcement expression, aggregation, and video on both local and wide area networks. The concept of ATM is that its connection oriented network technology. The connections are not tangible end-to-end connections similar with  telephone networks, but they are virtual connections. This agency that, equal with telephony connections, a connectedness must be falsification before any collection can be transferred between the end-points of the transportation. After the connexion has been used and is no someone requisite, it is terminated. ATM connections have properties which describe the kind of traffic carried over the connection and the way it is treated by the network. These properties like Traffic Descriptors are negotiated at connection setup time between the calling party, the ATM network and the called party.

  Because ATM is designed to be easily implemented by hardware rather than software, faster processing and switch speeds are possible. The specified bit rates are either 155.520 Mbps or 622.080 Mbps. Speeds on ATM networks can reach 10 Gbps. Along with Synchronous Optical Network (SONET) and several other technologies, ATM is a key component of broadband ISDN .

   When we say Asynchronous Transfer Mode, it is a technology that has the potential of revolutionizing data communications and telecommunications. Based on the emerging standards for Broadband Integrated Services Digital Networks, ATM offers the economically sound "bandwidth on demand" features of packet-switching technology at the high speeds required for today's LAN and WAN networks -- and tomorrow's.

     ATM is a cell-relay technology that divides upper-level data units into 53-byte cells for transmission over the physical medium. It operates independently of the type of transmission being generated at the upper layers AND of the type and speed of the physical-layer medium below it. This allows the ATM technology to transport all kinds of transmissions like:

Data

                 

Video

Voice

  Recognizing the differences between voice and data transportation requirements, ATM is designed to adapt to the time sensitivity of different applications.
ATM Protocol

   In the ATM protocol domain the socket interface provides an application with direct access to an ATM virtual connection. The ATM protocol is offered as a new address family, AF_ATM. Each Protocol Data Unit to be transmitted over the connection is handed directly to the ATM adaptation layer for segmentation into ATM cells and subsequent transmission. Similarly, received PDUs are handed up to the socket layer by the adaptation layer on completion of reassembly. Draft standards for ATM UNI signalling 3 provide a mechanism for the selection of the ATM adaptation layer and Quality of Service to be used for an ATM connection. However, there is no mechanism in the socket interface to permit an application to specify these parameters to the connect system call in a clean manner. Consequently, for this implementation all ATM connections make use of AAL5, and a default ``best-effort'' QoS specification is used. Additionally the ATM code provides logical interfaces to the IP code within the system and will set up tunnels over the ATM network to carry IP traffic to its destination. In this case the upper layer for the ATM protocol is a logical interface engine rather than the socket code.

The configuration of Ethernet and ATM combined

• Ethernet−attached end systems may communicate with other Ethernet−attached end systems through bridges across the ATM network in a backbone−type configuration.
• ATM−attached end systems may communicate with ATM−attached servers and both may communicate with Ethernet−attached end systems via the bridges.

Asynchronous Transfer Mode Advantages:
-ATM supports voice, video and data allowing multimedia and mixed services over a
single network.
-High evolution potential, works with existing, legacy technologies
-Provides the best multiple service support
-Supports delay close to that of dedicated services
-Supports the broadest range of burstiness, delay tolerance and loss performance through the implementation of multiple QoS classes
-Provides the capability to support both connection-oriented and connectionless traffic using AALs
-Able to use all common physical transmission paths like SONET.
-Cable can be twisted-pair, coaxial or fiber-optic
-Ability to connect LAN to WAN
-Legacy LAN emulation
-Efficient bandwidth use by statistical multiplexing
-Scalability
-Higher aggregate bandwidth
-High speed Mbps and possibly Gbps

Asynchronous Transfer Mode 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
-Presently the applications that can benefit from ATM such as multimedia are rare

Multiprotocol on ATM

    Multiprotocol on ATM or MPOA is the efficient transfer of inter−subnet unicast data in a

LAN Emulation LANE environment. MPOA integrates LANE and Next Hop Resolution Protocols, also known as Next Hop Routing Protocols, to preserve the benefits of LANE while enabling intersubnet, internetwork layer protocol communication over ATM Virtual Circuit Connections without requiring routers in the data path. MPOA provides a framework for effectively synthesizing bridging

and routing with ATM in an environment of diverse protocols, network technologies, and IEEE 802.1

virtual LANs. This is designed to provide a unified paradigm for overlaying internetwork

layer protocols on ATM. MPOA is capable of using both routing and bridging information to locate

the optimal exit from the ATM cloud.

     Multiprotocol on ATM  enables the physical separation of internetwork layer route calculation and forwarding, a technique known as virtual routing. This separation provides a number of key benefits:
- It enables efficient intersubnet communication.
-It increases manageability by decreasing the number of devices that must be configured to
perform internetwork layer route calculation.
-It increases scalability by reducing the number of devices participating in internetwork layer
route calculation.
-It reduces the complexity of edge devices by eliminating the need to perform internetwork
layer route calculation.
    Multiprotocol on ATM  provides MPOA Clients and MPOA Servers, and defines the protocols that are required for MPCs and MPSs to communicate. MPCs issue queries for shortcut ATM addresses and receive replies from the MPS using these protocols. MPOA also ensures interoperability with
the existing infrastructure of routers. MPOs also make use of routers that run standard internetwork
layer routing protocols, such as Open Shortest Path First, providing a smooth integration
with existing networks.

Combining the ATM and DSL at the local loop

  These devices make it possible for the local exchange provider or the competitive DSL provider to

use the existing facilities and still satisfy the needs of voice and data over the existing local loop.

Using voice over the DSL circuit enables up to 16 simultaneous VoIP calls and Internet access to

simultaneously run over the bandwidth on the single cable pair.

Reference:

            http://technet.microsoft.com/en-us/library/bb726929.aspx

            http://margo.student.utwente.nl/simon/finished/thesis/thesis2/node26.html

            Daniel Minoli and Mark Raymond, “Technology Overview: Asynchronous Transfer Mode                                                                          

            (ATM)”,   http://www.be.datapro.com, 1997.