Friday, February 10, 2012

Asynchronous Transfer Mode (ATM)


ATM

Asynchronous Transfer Mode (ATM) is a technology that has the potential of revolutionizing data communications and telecommunications. Based on the emerging standards for Broadband Integrated Services Digital Networks (B-ISDN), 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 (e.g, data, voice, video, etc.) in a single integrated data stream over any medium, ranging from existing T1/E1 lines, to SONET OC-3 at speeds of 155 Mbps, and beyond.



Evolution 


Asynchronous Transfer Mode (ATM) represents a relatively recently developed communications technology designed to overcome the constraints associated with traditional, and for the most part separate, voice and data networks. ATM has its roots in the work of a CCITT (now known as ITU-T) study group formed to develop broadband ISDN standards during the mid-1980s. In 1988, a cell switching technology was chosen as the foundation for broadband ISDN, and in 1991, the ATM Forum was founded.



ATM Standards


The following are some of the basic ATM standards documents available from the International Telecommunications Union (ITU).
  • ITU-T I.361 - Defines the ATM Layer functions.
  • ITU-T I.363 - Defines the ATM Adaptation Layer protocols.
  • ITU-T I.610 - Defines the ATM Operation and Maintenance (OAM) functions.


Architecture 


ATM is based on the switching of 53-byte cells, in which each cell consists of a 5-byte header and a payload of 48 bytes of information. The figure illustrates the format of the ATM cell, including the explosion of its 5-byte header to indicate the fields carried in the header.





The ATM Protocol Reference Model


Three layers in the ATM architecture form the basis for the ATM Protocol Reference model, illustrated in Figure below. Those layers are the Physical layer, the ATM layer, and the ATM Adaptation layer.






Using Cells and Virtual Circuits for Traffic Engineering


Another key ATM concept involves the traffic contract. When an ATM circuit is set up each switch on the circuit is informed of the traffic class of the connection. The performance of ATM is often expressed in the form of OC (Optical Carrier) levels, written as "OC-xxx." Performance levels as high as 10 Gbps (OC-192) are technically feasible with ATM. More common performance levels for ATM are 155 Mbps (OC-3) and 622 Mbps (OC-12).

ATM traffic contracts form part of the mechanism by which "quality of service" (QoS) is ensured. There are four basic types (and several variants) which each have a set of parameters describing the connection.

1. CBR - Constant bit rate: a Peak Cell Rate (PCR) is specified, which is constant. 

2. VBR - Variable bit rate: an average cell rate is specified, which can peak at a certain level for a maximum interval before being problematic. 

3. ABR - Available bit rate: a minimum guaranteed rate is specified. 

4. UBR - Unspecified bit rate: traffic is allocated to all remaining transmission capacity. 

VBR has real-time and non-real-time variants, and serves for "bursty" traffic. Non-real-time is sometimes abbreviated to vbr-nrt. Most traffic classes also introduce the concept of Cell Delay Variation Tolerance (CDVT), which defines the "clumping" of cells in time. To maintain traffic contracts, networks usually use "shaping", a combination of queuing and marking of cells. "Traffic policing" generally enforces traffic contracts.












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13 comments:

  1. kingFebruary 10, 2012 at 8:29 AM

    ATM is very useful and has been the stepping stone for other networks to emerge tnx for that info keep it up

    ReplyDelete
  2. alvin.lastimosoFebruary 10, 2012 at 8:46 AM

    ATM would be very helpful in offering sound features of packet-switching technology at the high speed that is needed for the present networks and for the future use..Thank you..

    KUDOS!!

    ReplyDelete
  3. PAULFebruary 10, 2012 at 8:59 AM

    ATM technology transports all kinds of transmissions (e.g, data, voice, video, etc.) in a single integrated data stream over any medium, ranging from existing T1/E1 lines, to SONET OC-3 at speeds of 155 Mbps, and beyond. this gives us more helpful way to transport data fast.

    ReplyDelete
  4. RhoneilLuayon(Gothic)February 10, 2012 at 9:56 AM

    ATM is designed to be easily implemented by hardware (rather than software), faster processing and switch speeds are possible.

    ReplyDelete
  5. Matt DiestroFebruary 10, 2012 at 10:21 AM

    ATM has five vertical markets fo equipment sales, which are carrier switches, ISP switches, enterprise WAN switches, ATM WAN access, and ATM LAN. thanks for the info neil.

    ReplyDelete
  6. coi28February 10, 2012 at 3:54 PM

    DSL is advantageous over analog modems is improved.. that includes faster and less error with the DSL is connected to the local loop with two modems for data transmission..

    ReplyDelete
  7. NitropipFebruary 10, 2012 at 4:38 PM

    ATM improves the data rate by lessening the traffic. thanks a lot

    ReplyDelete
  8. chingFebruary 10, 2012 at 5:03 PM

    Which main factors do i need to consider when designing an ATM network?

    ReplyDelete
    Replies
    1. NeilVincentFebruary 10, 2012 at 10:07 PM

      hi ching.. if you want to design atm network.. you should understand WAN network devices, what equipment is needed, and cell technology. You have also to understand what components are needed, the protocol layers used for communicating with the ATM, and what transmission methods are used. You should know how to put together simple LAN and WAN networks and should have the work experience and educational background to design an ATM network. And simply you should seek professional help from domain experts, vendors, and network architects.

      Delete
  9. arnel o.February 10, 2012 at 6:21 PM

    I've learned a lot about ATM..
    nice post pal... keep it up ;)

    ReplyDelete
  10. christine saladagaFebruary 10, 2012 at 7:57 PM

    In your ATM Protocol Reference Model, can you define each of the following:Physical layer,ATM layer, and the ATM Adaptation layer.

    Thanks for the info. keep it up

    ReplyDelete
    Replies
    1. NeilVincentFebruary 11, 2012 at 5:39 AM

      The Physical Layer is responsible for the electrical or optical transmission and receipt along the physical media between two devices. ATM layer is placed above the Physical Layer. The responsibility of ATM layer is to handle multiplexing and switching and maintains the Quality of Service (QoS). And The ATM Adaptation layer (AAL's) adapts user traffic into cell-format.

      Delete
  11. Jed PalazueloFebruary 10, 2012 at 9:01 PM

    nice post neil. it help me understand more about ATM. specially on how the ATM was capable of handling different types of data.

    ReplyDelete

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