Subject: CL vs. CIR

From: "Michael W. Patrick" <[email-masked]>
Date: Tue, 10 Jun 1997 18:16:47 -0400

Please pardon the following "newbie" questions.  They basically have
to do with my not understanding the difference between Controlled Load
and a Committed Information Rate service.  

1) Whatever happened to Committed Rate (CR) service?
   Why was draft-ietf-intserv-commit-rate-svc-00.txt allowed to
    expire?  
    I remember from the "Differentiated Services" BOF in Memphis that
    major customers seemed to want a "best effort with floor" service,
    i.e. a minimum guaranteed rate through the Internet.  
    Is CL intended to serve this need?

2) What are the  differences between the controlled load (CL) service at a
    traffic rate "r" and a "Committed Rate" (CR) service with requested
    rate R equal to the traffic rate r? (Call this R=r CR service 
    Committed Information Rate "CIR" service, a la Frame Relay).
    I can think of two:
        a) CL's explicit requirement to clear above-r bursts.
        b) CR's silence on non-conforming traffic handling,
           but I would think the same problems and solutions 
           for non-conforming traffic with CL would apply for CR.
    Any others? 
    Can anyone think of any cases where CL would admit a
    flow that CIR wouldn't?  CIR could use the same statistical
    criteria as CL for "overbooking". 
    
3)  Would it be inaccurate to assert that the main "value" of CL 
    is the committment of the network to provide a "minimum" bandwidth
    of the token rate r? Is CL the same as "best effort with minimum"?
    Is anyone else having trouble explaining the value of "controlled
    load"  service to customers who just want a CIR?  

4) Is there a technical difference between the statements
    A) "Service X provides little or no average packet queueing delay over 
        all timescales significantly larger than the 'burst time'";
        [CL draft]
        and
    B) "Service X at each network element should ensure that packets
       do not experience delays at a network element that are 
       significantly in excess of what they would experience from a 
       dedicated transmission facility operating at the committed
        rate."
        [CR draft]
    
5)  Was the description of CL's "end to end behavior" intended to mean
    unloaded best effort on the full-speed -physical- links of the
    network element, or on -"virtual"- links of rate at or near the
    traffic rate r?
    
    I would think that the aggregate loading of CL traffic on a full-speed link
    can be high (say 50-75%), and that this would involve average delays
    that are significantly higher than "unloaded best effort conditions". 
    Suppose a network element admits CL flows to fill, say, rho=75% capacity
    on a WAN link. With M/M/1 assumptions, that puts the average wait time
    at (rho/(1-rho)) = 3 service times. I'm not sure I'd call that "unloaded
    best effort service" over the -full- link, but I would call it
    "unloaded best effort service" with a virtual link of rate r.

6)  Has anyone published a study of 2-priority vs. WFQ implementations
    of CL?

Sorry if I'm rehashing old issues. I'm still reading the 4 MB mail
archive :-).
    
-mike
------------------------------------------------------------------------
Michael W. Patrick  Motorola ISG/NSD               20 Cabot Rd, MS M4-30
[email-masked]  (508) 261-5707              Mansfield MA 02048