Subject: Re: IEEE802.1 Looking for Guidance

From: Craig Partridge <[email-masked]>
Date: Tue, 05 Jul 94 13:59:43 -0700

I think the assumptions behind this have to be clarified

    in the backbone, we have routers connected by pt-pt links (or
    underlying VCs from isdn, smds or atm) and we think we can do the
    resource reservation in the IP boxes _only_

    .....

    however, i heard mention at the last IETF in the RSVP meeting
    of a mapping onto shared media LANs that do provide some mechanisms
    for resource allocation...

    the use of the 2 levels of priority in 100basevg springs to mind for
    instance...

[I've added int-serv since we're into integrated services issues]

Jon:
    
    Another way to think of this topic is that the point-to-point links
provide a perfect service guarantee:

    * when the IP layer hands a packet to the p-2-p MAC layer it gets
    sent immediately

while multiaccess LANs provide a different service:

    * when the IP layer hands a packet to the MAC layer, the packet is
    transmitted when the MAC transmission rules permit

the game is to find a service model that allows us to map between IP's
service model and the various MAC models.  Mapping to p-2-p is trivial
because by the p-2-p rules, anything IP does is, by definition, the p-2-p
link's behaviour (unless the link is shared with other protocols).  The
LAN case is trickier.

Craig