ATM Network has star topology. ATM network is based on one or more switches, which are an integral part of the communication structure.
The high transfer rate and extremely low probability of errors in the fiber-optic systems highlights the task of creating high-performance switching systems based on standard ATM.
The simplest example of such a network - a switch that provides packet switching, and multiple terminal devices.
ATM - a method of transferring information between devices on the network in small packages fixed length, called cells (cells). Fixing the size of a cell has some significant advantages over the package of variable length.
• First, fixed length cells require minimal processing operations routing switches. This allows maximum simplify designs exchanges at high switching speeds.
• Secondly, all processing of cells, compared with the processing of packets of variable length is much easier because there is no need for calculating the length of the cell.
• Third, in the case of packets of variable length long packet data transmission could delay the issuance of in-line packages with speech or video that would lead to distortion.
The model has four ATM structure. There are several levels:
- User (User Layer) - includes levels, ranging from network and above (IPX / SPX or TCP / IP);
- Adaptation (ATM Adaptation Layer - AAL);
- ATM (ATM Layer);
- Physical (Physical Layer).
The user level ensures that messages to be sent to the ATM network and appropriately transformed.
The level of adaptation (AAL) provides access custom applications to the ATM switching devices. This standard forms the standard ATM cells and transmit them to transmit them to a standard ATM for further processing.
The physical level provides the cells through a variety of switching environment. This level consists of two sub - sub conversion transmission implementing various protocols for the transfer of personal lines and sub adapt to the environment peredachi.4
ATM terminal device - a network connecting to switches through an interface called UNI - the user interface to the network. UNI can be an interface between the workstation, PC, PBX, router, or with everything «black box» and ATM switches.