Subject: Re: draft-bmwg-ospfconv-term-00.:P2P Converge Time

From: "Manral, Vishwas" <[email-masked]>
Date: Mon, 10 Jun 2002 08:17:45 -0400

Hi Mitchell,

Apologies for the delayed reply(I have been away from my mail for some time
now) and thanks for the comment.

I guess the point you are trying to make is that although the DR election
itself could cause a delay in the broadcast case, there are certain other
factors involved.

However in the context of the discussion, what we have tried to say is that
all other things being the same(as we have put it as "of the same speed"),
because on a broadcast network if routers were comming up symultaneously
they would have to wait for the Waiting interval before electing a DR, it
would take a longer time. Also the flooding takes place via the DR/BDR and
that causes additional delay. Maybe we will try and modify the text to make
the fact clearer.

Besides I would like to know of any other point you you would like to
comment on(not agree on) within the draft.

Thanks,
Vishwas

-----Original Message-----
From: Erblichs [mailto:[email-masked]]
Sent: Friday, June 07, 2002 12:07 AM
To: [email-masked]
Subject: draft-bmwg-ospfconv-term-00.:P2P Converge Time

Group,

        I have a few items that I don't necessarily agree
        with here, but the one item that I feel most
        strongly with is..

        5. Definition
        Point-to-Point links
        Discussion      "will take lesser time to converge than
                        a broadcast link"

        Yes, I do agree that a DR election, mainly due to the
        initial wait time, can become a large part in the time
        to converge.

        Given that if point-to-point links are substituted for
        broadcast links, I feel that the above statement becomes
        false..

        Note: adjacencies = adjs

        Why,,

        The fewer number of adjs
        allows a fewer number of database description packets to
        be exchanged, a fewer number of master/slave negotiations,
        etc. As each additional adj is formed, there is a higher
         probability that additional SPF calculations will need
        to be performed.

        In addition, additional flooding due to additional adjs
        will slow the converge process. Also with the additional
        load, the router may identify a overload condition, and
        even temporally reject some of these point-to-point adj
        formations..

        I am unsure whether a single slow router to inform the
        DR or BDR of its links vs informing all of the adjs of
        its links, will adversely effect the MA vs the P2P link
        topology more. In my mind there are just too many variables.

        In addition, the statement does not implicitly or explicitly
        imply whether the routing topology has changed and thus
        the BDR is being elected as the DR.

        THUS, I would consider a different wording to be on the
        order of ... (Please note that I have not mentioned
        Ethernet (shared-meda) type links where collisions with
        exponential backoff may play a role OR....) To keep it
        simple.

        A point-to-point link network topology makes the tradeoff
        of additional adjacencies formations vs the overhead of
        the required multi-access DR/ BDR election. Given a small
        number of adjacencies in a point-to-point environment, it
        can be more efficent than a multi-access topology if the
        links between the DR and DRothers are constantly changing
        OR that the election wait-time requirement is a large
        part of the convergence time.

        Thanks,
                Mitchell Erblich

---

From: Erblichs <[email-masked]>
Date: Mon, 10 Jun 2002 12:29:19 -0700

A)

5. Definitions

 Hello Interval

"and point-to-point networks" -> and non-Demand Circuit point-to-point
networks.

OR

"and point-to-point networks". + Exceptions of some point-to-point
circuits are demand point to point circuits, which would be the
successful of hello supression negotiation..

On the assumption that RFC 1793 Hello suppression is employed.

B) 5. Definitions

Shortest Path First Time

ADD... Some implimentations may force a interval between
successive SPF calculations. If it exists, then this additional time
value should be subtracted from the total time.

C) Meaning of Convergence

I would suggest..

A network is termed converged at one point in time when all of the
following has occured.

* all adjacencies that are to be formed have proceeded to full
  state.
* all retransmission lists are empty
* all recieved update, req LSAs have been processed
* All MAXAGE LSAs within the link state databases have been removed
* the link state databases are synchronized, exceptions are opaque LSAs
* all routers within an area have completed their SPF calculations
  and have inserted the results into their respective routing tables

D) New item....

6.3 Types of Network Events

* SPF events / triggers

Time the various types of events/triggers that would cause a
SPF calculation to occur.

Mitchell Erblich
==========================