Path: utzoo!utgpu!watserv1!watmath!att!rutgers!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!sdd.hp.com!hplabs!hpda!hpcupt1!hprnd!pat
From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.dcom.lans
Subject: Re: Re: "real-time" over a lan: token ring vs ethernet vs ?
Message-ID: <2230110@hprnd.HP.COM>
Date: 31 Aug 90 17:18:23 GMT
References: <19300@well.sf.ca.us>
Organization: HP Roseville Networks Division
Lines: 31

|> 
|> Also, it was mentioned that "the token is believed to be lost" when a new
|> station inserts and clicks in its MAU relay, thus causing longish delay.
|> This is not what the protocol specifies; the Initialisation Phase merely
|> causes the new station to exchange special MAC frames with designated
|> Server nodes on the ring. At any rate, there should be no loss of token
|> *theoretically*.
|> -- 
From IEEE 802.5:

  7.4.2 Insertion/Bypass Transfer Timing.  The insertion/bypass mechanism
  shall break the existing circuit before establishing the new circuit.
  The maximum time that the ring trunk circuit is open shall not exceed
  5 ms.

and

  6.4 Symbol Timing ....

    (2) Whenever a station is inserted into the ring or loses phase
  lock with the upstream station, it shall, upon receipt of a signal
  which is within specification from the upstream station (re)aquire
  phase lock within 1.5 ms.
    (3) .....

So it looks to me like station insertion causes at least a 6.5 ms break
in the network, perhaps longer since all the stations between the
inserting station and the master lose and reaquire lock.  During
that time packets or the token can be lost.

Pat Thaler