FDDI MAC Protocol

Posted by AJ × 09:27

• As for 802.5 except:

• Station seizes token by aborting token transmission

• Once token captured, one or more data frames transmitted

• New token released as soon as transmission finished (early token release in 802.5)

• Handle two type of traffic

• synchronous-tight transfer delay requirement-voice or video

• asynchronous-greater delay tolerance-data

• TTRT-target token rotation time-all stations agree to operate

• Every station is allotted time S during which it can send the synchronous traffic.

• If the sum of Si times is smaller than TTRT then token will return to every node

in less than 2 TTRT sec.

• and hence meets the delay requirement

• Each station maintains TRT-token rotation timer: measures the time elapsed since

the station last received the token.

• When a station receives the token it calculates THT-token hold time:

THT=TTRT=TRT

• if THT>0 all synchronous and asynchronous traffic is sent

• if THT<0 only synchronous traffic is allowed

All Syllabus