17. Network fddi, main characteristics

FDDI(Fiber Distributed Data Interface ) was developed in the 1980s. Standards for fiber distributed data interface networks were defined by the American National Standards Institute (ANSI), to provide for a high-speed networking architecture that could be used for LANs and MANs

FDDI was designed to be a reliable architecture that could handle high-traffic mission-critical networking implementations.  FDDI runs on fiber optic cable, using pulses of light to transmit data form one station to another. A related architecture, called CDDI for Copper Distributed Data Interface, can use copper cable in the same configuration as a FDDI network.

FDDI's topology is a dual ring. It can be implemented as a physical ring, or it can be a star-wired ring. In the star configuration, the computers connect to a FDDI concentrator, which is a special type of hub.

How it works: FDDI uses two rings, one of which is designated as the primary and the other as the secondary ring. The second ring provides fault tolerance, so that if the primary ring fails, data has an alternate path to take. This makes FDDI a highly reliable architecture. Traffic flows in opposite directions on the two rings.

Computers (referred to as "stations") on the FDDI network are classed as type A or B. Class A stations are physically connected to both rings; class B stations are connected to only one ring.

FDDI uses a token passing access control method. All the computers on the network monitor the token-passing activity.

topology	ring
transfer rate	100Мбит/с
access method	Token-passing
Transmission medium	Twisted pair and fiber optic
collision	no

18. Atm technology

Asynchronous transfer mode (ATM) is a method of transmitting data using fixed length (53 bytes) data units, called cells, over circuits that can support not only traditional data requirements, but also voice and video. Since it operates at the MAC sublayer of the data link layer of the OSI model, which is above the physical layer, it can convert any type of packet into these fixed-length cells. Unlike other packet switching, ATM cells arrive at the destination point in the correct sequence.

• ATM is a high-speed data transmission technology that can be used for LANs and WANs. Primarily because of its bandwidth and quality of service capabilities, ATM could form the basis of a unified network. ATM is connection-oriented. Cell switching has many advantages over frame switching. ATM requires special ATM switches and interfaces to connect ATM switches to one another and to LANs. ATM is scalable. As an ATM network grows, more bandwidth can be added to handle more traffic.

ATM is independent of the transmission medium, though the medium can limit how fast ATM can operate. It is possible but still rare to have an all-ATM LAN. It is more common to connect an Ethernet network to an ATM backbone. LAN Emulation (LANE) specifies a way to do this. MPOA defines how to run IP and other Layer 3 transmission protocols over ATM. It enhances LANE, especially in the use of VLANs. But, ATM is still quite expensive and networks must have ATM devices that are interoperable. This requires new equipment

topology	creations of networks with frame switching
transfer rate	25 Mbps to 2.46 Gbps
access method	Cell switching
Transmission medium	Fiber optic
collision	no