The protocol reference model makes reference to three separate planes:

User   Plane: Provides    for    user information    transfer,    along    with associated    controls (e.g, flow control, error control).

Control Plane: Performs call control and connection control functions.

Management Plane: Includes   plane management, which   performs management functions related to a system as a whole and provides coordination between all the planes, and layer management, which performs management functions relating to resources and parameters residing in its protocol entities.

                           

Physical layer: Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission.

ATM layer: Combined with the ATM adaptation layer, the ATM layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell.

ATM adaptation layer (AAL): Combined with the ATM layer, the AAL is roughly analogous to the data link layer of the OSI model. The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads.

ATM Advantages:

  • ATM supports voice, video and data allowing multimedia and mixed services over a single network.
  • 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 (such as DS1, 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

ATM 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