|
Void frames are also used by stations using Frame Content Independent
Stripping (also known as Bridge strip mode). This includes most DEC
equipment. After transmitting its frames, a station will transmit 1
void frame, and then give up the token. It will strip frames based
on a count of the number of frames it transmitted, and will stop
stripping when the count = 0, or, the void frame is seen.
|
| Hi,
Void frames are used for frames stripping. There are 2 ways to strip
frames, one is to check the source address, this method is called Source
Address Match (SAM), the other method is called Frame Content Independent
Stripping (FCIS). FDDI station such as bridges need to use FCIS otherwise
it would have to cache all the source addresses of the nodes connected on
its ports. Digital calls FCIS "Bridge Stripping", one of the screens of
the DECswitch displays this.
If using FCIS, when transmitting,the number of frames transmitted is
counted, then at the end,it transmits a void frame followed by the token.
When this data comes around the ring back to the station that transmitted
it will strip an equal number of frames from the ring, and it will stop
stripping when:
1. Frames stripped = frames transmitted
2. The void frame is received.
3. When it receives the token
It gets more complicated when frames are lost, maybe somebody else wants
to adventure in that...
Paul Savoie
MCS Support,Canada
|