How much is FDDI? 1. FDDI and marking ring media access control standards are close, and there are few benefits: (1) Marker ring protocol under heavy load conditions, so FDDI can obtain the same efficiency. (2) Use similar frame formats, global network network interconnections, and this chapter will discuss this problem in the back network. (3) It is easy to understand the IEEE802.5. It is easy to understand FDDI (4) has accumulated the practice of IEEE802.5, especially the economy of integrated circuit films, for the manufacturing of FDDI systems and components. 2, FDDI technology (1) Data encoding: expressed as 1 with an optical pulse, no light energy is expressed as 0. FDDI adopts a new coding technology called 4b / 5b. Each time the four digits are encoded, each four digits are encoded into five symbols, and the existence of light is not to represent each of the five symbols, each bit is 1 or 0. This encoding increases efficiency by 80%. In order to obtain signal synchronization, a secondary encoding method is used, first press 4B / 5B, then use a non-returned zero system called inverted phase, which is similar to differential encoding. (2) Clock offset: FDDI distributed clock scheme, each station with separate clock and elastic buffer. The data clock entering the site buffer is determined according to the clock of the input signal, but the signal clock output from the buffer is determined according to the clock of the station, this scheme makes the number of repeaters in the ring are not subject to clock offset factors. limits. 3, FDDI frame format: It is understood that the FDDI MAC frame and IEEE 802.5 frame are very similar, and the difference includes: FDDI frame contains the above, it is important to synchronize with the clock at high data rate; it is allowed to use 16 bits in the network 48-bit address, more flexible than IEEE802.5; control frames are also different. 4, the two main differences between the FDDI protocol FDDI and IEEE 802.5: (1) After the FDDI protocol regulates a new marker frame immediately after the send station sends a frame, and IEEE802.5 specifies the front edge of the frame sent. When the send station is sent, a new marker frame is sent. (2) The capacity allocation scheme is different. Both can be used in a single marker, and the equivalent equivalent access to each site is provided, and it can also be assigned to some sites. IEEE 802.5 uses priority and appointment programs. 5. In order to meet the requirements of the two communication types, FDDI defines two types of communication types and asynchronous communication, defining a target tag loop time TTRT, and each site has the same TTRT value.
