Subject: int serv on shared media LANs...

From: Jon Crowcroft <[email-masked]>
Date: Tue, 26 Sep 95 17:30:32 +0100

we're considering how to deploy CBQ or similar systems on a shared
LAN....the idea is that the LAN is a set of virtual links between
hosts, and you can use RSVP i nthe usual way to request a share of a
virtual link....the problem is not the mechanistic one of how to apply
something like CBQ in ip_output routines insterad of just in
ip_forward routines...or even how to apply RSVP to the setup...

it is how to decide what the flow spec request is mapped onto output
since IP output timing will affect link access timeing

on a token ring, the default is to rely on the "perfect fairness"
under >=100 % load, which will work, but of course for several classes
of traffic flow, may result in severley suboptimal access delays....

for csma/cd, it is a whole lot harder, since the interarrival time pattern
of access requests radically alters the maximum utilisation
(e.g. poisson => ~40% max, so for n machines with some load, you can
figure it out, but of course, multimedia traffic and transaction
traffic are self similar, so you do way worse than 37.7%...of course,
you could do ip to link level output rate limiting or shaping to
approximate poisson....maybe???)

anyone think this is worth pursuing (i.e. using int-serv IP to turn
legacy lans into multimedia multiservice capable beasties)???

cheers
jon

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From: Lixia Zhang <[email-masked]>
Date: Tue, 26 Sep 1995 11:16:58 PDT

> legacy lans into multimedia multiservice capable beasties)???

I hesitated for a second whether I should state the following, perhaps
unpopular, views:

- We already have multimedia on legacy LANs, works just fine most of
  the time.
  "Why fix things that arent broken?" -- Dr. Deering

- of course we can come up with some scheme to do all of the
  guarantees, but it is probably a lot easier to better engineer the
  LANs than to add the complexities, perhaps even cheaper too.

Lixia

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From: [email-masked] (Noel Chiappa)
Date: Thu, 28 Sep 95 12:36:04 -0400

From: John Wroclawski <[email-masked]>

    > the real problem is how to deal with all the legacy hosts

    Turns out you can do resource management on an ethernet by building a
    little scheduler box which kills off pkts

How clever! Of course, if the person is just sending a min-length packet, this
won't help, but it's a cute trick.

    build a distributed algorithm which runs on all of the hosts on the LAN
    and manages the bandwidth allocated to each node. Works great when everyone
    plays along

I believe that Int-Serv talked about doing something like this early on, no?
However, I was talking about legacy (i.e. unmodified) hosts, though, and as
we're painfully aware here in the Internet, there do always seem to be some of
those...

    I imagine the best answer for a majority of current ethernet installations
    is to replace the 10BT hub with a switching one which does resource
    management.

Hmm. This saves the investment in host interface cards, but for installations
which did not previously wire everyone separately to a hub (how funny that
rings and busses both wound up being actually wired as stars in service), this
probably does mean rewiring.

	Noel

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From: [email-masked]
Date: Thu, 28 Sep 95 20:52:05 EDT

*** Reply to note of 09/28/95 05:01                                            
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 From:                                                                         
 Subject:                                                                      
Subject: Re: int serv on shared media LANs...                                  
How much restricting the maximum packet size to 64 bytes at the                
legacy hosts help? Raif                                                        
                                                                               
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -                 
 Raif O. Onvural, Senior Engineer, Manager                                     
 Network Technology Architecture, IBM, BUAA/664, RTP, NC 27709                 
 919-254-4687 Fax: 919-254-5410 e-mail: [email-masked]