RE: [RPRWG] RE: Evaluation of timeToLive alternatives
Necdet,
In that case, with the information that we currently
have in the RPR MAC header, there is no way for us
to avoid duplication and incorrect learning per the
example that I provided (when doing wrapping). The
only way out is to add some kind of identification of
the node that was responsible for putting the frame
on the ring. This will allow it to reliably remove the
frame from the ring if it makes its way back to the
node.
If you can think of a better solution to guarantee
that frames will be reliably removed under all
circumstances even when wrapping, please share it
with the group.
-Anoop
> -----Original Message-----
> From: Necdet Uzun [mailto:nuzun@xxxxxxxxx]
> Sent: Thursday, June 27, 2002 6:03 PM
> To: Anoop Ghanwani
> Cc: 'Mike Takefman'; David V. James; stds-802-17@xxxxxxxx
> Subject: Re: [RPRWG] RE: Evaluation of timeToLive alternatives
>
>
> Anoop,
>
> I am not saying that wrapping does not work with bridging.
> What I am saying
> that you can not require the same set of features that are
> composed for
> bridging when steering is used as a protection mechanism from an
> implementation that uses wrapping for the protection mechanism.
>
> Bridging should consider steering and wrapping separately as
> they may have
> different set of requirements and issues. Solution to a
> packet duplication
> problem may be different for steering than wrapping..
>
> Thanks.
>
> Necdet
>
> Anoop Ghanwani wrote:
>
> > Necdet,
> >
> > I wasn't aware that wrapping was not intended to
> > work for bridged frames. All the folks in the BAH group
> > have been busy scratching their heads for about 4 months
> > now worrying about how to make this stuff work with both
> > wrapping and steering. Poor fellas (me included!).
> >
> > -Anoop
> >
> > > -----Original Message-----
> > > From: Necdet Uzun [mailto:nuzun@xxxxxxxxx]
> > > Sent: Thursday, June 27, 2002 4:34 PM
> > > To: Anoop Ghanwani
> > > Cc: 'Mike Takefman'; David V. James; stds-802-17@xxxxxxxx
> > > Subject: Re: [RPRWG] RE: Evaluation of timeToLive alternatives
> > >
> > >
> > > Anoop,
> > >
> > > We do have a do not wrap bit in the packet header. If a
> > > packet is bridged
> > > packet it should set the WE bit right (i.e., do not WRAP).
> > >
> > > Thanks.
> > >
> > > Necdet
> > >
> > > Anoop Ghanwani wrote:
> > >
> > > > Mike,
> > > >
> > > > Based on the flooding analysis that was presented
> > > > at the last meeting, source stripping is required
> > > > regardless of whether one does basic or enhanced
> > > > bridging.
> > > >
> > > > Consider the following bridging example. Without
> > > > source-stripping, if we're doing wrapping, and a node
> > > > on the ring dies, the packet will be able to make its
> > > > way back to the source with a valid TTL (because one
> > > > of the nodes that would have decremented TTL has
> > > > disappeared). If we don't have the source address
> > > > (or some other way to identify the source) in the
> > > > frame, then the source will pick up that frame as a
> > > > regular bridged frame, and will learn the source
> > > > address of the frame as being on the ring, which is
> > > > incorrect.
> > > >
> > > > If we're serious about any kind of bridging, I think
> > > > we will need a way to explicitly identify at least
> > > > the source node (even if we don't care about
> > > > explicitly identifying the destination node).
> > > >
> > > > -Anoop
> > > >
> > > > > -----Original Message-----
> > > > > From: Mike Takefman [mailto:tak@xxxxxxxxx]
> > > > > Sent: Thursday, June 27, 2002 1:09 PM
> > > > > To: David V. James
> > > > > Cc: Anoop Ghanwani; stds-802-17@xxxxxxxx
> > > > > Subject: Re: Evaluation of timeToLive alternatives
> > > > >
> > > > >
> > > > > David,
> > > > >
> > > > > I hate to give a legalistic response, but here it goes.
> > > > >
> > > > > You are assuming facts not in evidence, specifically
> > > > > that enhanced bridging and not basic bridging is
> > > > > supported. I am a proponent of basic bridging.
> > > > >
> > > > > This algorithm does not work for basic bridging
> > > > > and hence is flawed. To be clear, the reason it
> > > > > does not work is that the the SA of a basic bridge
> > > > > is not present in the frame.
> > > > >
> > > > > That being said, I will look at the algorithms
> > > > > intent and evaluate it once the WG makes a decision
> > > > > to support enhanced bridging.
> > > > >
> > > > > As a side note: Its the Canada Day Long weekend coming
> > > > > up, so reponse times will be even slower, and the
> > > > > US long weekend is following so we might have to discuss
> > > > > futher in a restaurant in Vancouver.
> > > > >
> > > > > cheers,
> > > > >
> > > > > mike
> > > > >
> > > > > "David V. James" wrote:
> > > > > >
> > > > > > Mike,
> > > > > >
> > > > > > I can see two ways of performing timeToLive timeouts,
> > > > > > listed below:
> > > > > > 1) Source-specified.
> > > > > > a) Before being sent, the source sets:
> > > > > > frame.timeToLive=dataBase.hopsToDestination
> > > > > > b) Special frame-dependent/topology-dependent
> > > > > > stuff happens at the wrap point to prevent
> > > > > > the estimate in (a) from becoming incorrect.
> > > > > > c) Potential multidrop endpoints check and
> > > > > > discardframes based on:
> > > > > > frame.timeToLive==1
> > > > > > No error is logged.
> > > > > > d) Potential duplicates are discarded based on:
> > > > > > frame.timeToLive==0
> > > > > > An error is logged.
> > > > > > 2) Destination-specified.
> > > > > > a) Before being sent, the source sets:
> > > > > > frame.timeToLive=255
> > > > > > b) Potential multidrop endpoints check and
> > > > > > discard frames based on:
> > > > > > frame.DSID=myState.DSID
> > > > > > c) Potential duplicates are discarded based on:
> > > > > > frame.timeToLive>database.hopsfFromSource&&
> > > > > > frame.timeToLive!=
> > > > > > database.hopsFromSource+database.stationsOnRing
> > > > > >
> > > > > > I believe that the option (2) has several benefits:
> > > > > > i) The timeToLive field is processed in all frames.
> > > > > > ii) The timeToLive always means distance-from-source.
> > > > > > iii) Error logs are accurate, since timeToLive frames
> > > > > > are never discarded during steady-state operations.
> > > > > >
> > > > > > Can you comments on your perception of these conclusions?
> > > > > >
> > > > > > DVJ
> > > > > >
> > > > > > David V. James, PhD
> > > > > > Chief Architect
> > > > > > Network Processing Solutions
> > > > > > Data Communications Division
> > > > > > Cypress Semiconductor, Bldg #3
> > > > > > 3901 North First Street
> > > > > > San Jose, CA 95134-1599
> > > > > > Work: +1.408.545.7560
> > > > > > Cell: +1.650.954.6906
> > > > > > Fax: +1.408.456.1962
> > > > > > Work: djz@xxxxxxxxxxx
> > > > > > Base: dvj@xxxxxxxxxxxx
> > > > > >
> > > > > > >>-----Original Message-----
> > > > > > >>From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> > > > > > >>[mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]On Behalf Of
> > > > > Mike Takefman
> > > > > > >>Sent: Monday, June 24, 2002 8:17 PM
> > > > > > >>To: djz@xxxxxxxxxxx
> > > > > > >>Cc: Anoop Ghanwani; stds-802-17@xxxxxxxx
> > > > > > >>Subject: Re: [RPRWG] control TTL (the 255-station and
> > > > > 2000-km issue)
> > > > > > >>
> > > > > > >>
> > > > > > >>
> > > > > > >>That is a fair request David, and I will do
> > > > > > >>my best to accomdate it.
> > > > > > >>
> > > > > > >>Consider instead a host on your ring. Are you
> > > > > > >>suggesting that hosts have to behave as
> > > > > > >>bridges do in terms of learning the mappings
> > > > > > >>of MAC addresses to bridge IDs?
> > > > > > >>
> > > > > > >>If so, I believe you are placing an overly
> > > > > > >>large burden on hosts, one that no other 802
> > > > > > >>standard has done.
> > > > > > >>
> > > > > > >>Either way, the scenario I pointed out for bridges
> > > > > > >>(that you deflected by pointing out that I was
> > > > > > >>assuming a different scenario (which is fair
> > > > > > >>on your part)) is back. A bridge flooding a non local
> > > > > > >>packet for the first time, a host inserting a packet
> > > > > > >>that is off ring, but does not know which bridge
> > > > > > >>it exits (which in my world happens for every host
> > > > > > >>packet). If that station goes off the ring, ttl
> > > > > > >>will be the only mechanism to stop the double
> > > > > > >>delivery.
> > > > > > >>
> > > > > > >>Don't get me wrong, I do like your slick trick,
> > > > > > >>but your solution is to change the frame format
> > > > > > >>and add new features, whereas I am working to
> > > > > > >>fix the currently approved text.
> > > > > > >>
> > > > > > >>cheers,
> > > > > > >>
> > > > > > >>mike
> > > > > > >>
> > > > > > >>
> > > > > > >>
> > > > > > >>David James wrote:
> > > > > > >>>
> > > > > > >>> Mike,
> > > > > > >>>
> > > > > > >>> I believe part of the problem is that you claiming
> > > > > > >>> something that is not documented does not fail.
> > > > > > >>> Its hard to argue, as the definition can change
> > > > > > >>> whenever a failure is illustrated.
> > > > > > >>>
> > > > > > >>> Perhaps you should document the TTL stripping
> > > > > > >>> protocols with some background text and illustrations?
> > > > > > >>> And, clearly define the synchronizatoin points
> > > > > > >>> with Discovery, that are often implied.
> > > > > > >>>
> > > > > > >>> In my comments to D0.3 I have done this for
> DSID scoping.
> > > > > > >>> While this was much easier (since it doesn't have
> > > > > > >>> all of TTL stripping exceptions and problems), I believe
> > > > > > >>> its only fair to ask for you to do the same.
> > > > > > >>>
> > > > > > >>> Then, we will be able to analysize a problem,
> > > > > > >>> without the problem statement constantly changing.
> > > > > > >>>
> > > > > > >>> Even after that, there is the basic problem that:
> > > > > > >>> 1) Bidirectional flooding is required for performance.
> > > > > > >>> 2) A single-stations failure of (1) generates a
> duplicate
> > > > > > >>> 3) An multi-station failure of DSID stripping
> > > > > > >>> generates no duplicates.
> > > > > > >>>
> > > > > > >>> Remember, 2/3 is the failure scenario you mentioned
> > > > > > >>> in previous email. Having agreed, I'm a bit surprized
> > > > > > >>> this no longer appears to be a concern to you, just
> > > > > > >>> because the repercussions of that statement changed...
> > > > > > >>>
> > > > > > >>> DVJ
> > > > > > >>>
> > > > > > >>> David V. James, PhD
> > > > > > >>> Chief Architect
> > > > > > >>> Network Processing Solutions
> > > > > > >>> Data Communications Division
> > > > > > >>> Cypress Semiconductor, Bldg #3
> > > > > > >>> 3901 North First Street
> > > > > > >>> San Jose, CA 95134-1599
> > > > > > >>> Work: +1.408.545.7560
> > > > > > >>> Cell: +1.650.954.6906
> > > > > > >>> Fax: +1.408.456.1962
> > > > > > >>> Work: djz@xxxxxxxxxxx
> > > > > > >>> Base: dvj@xxxxxxxxxxxx
> > > > > > >>>
> > > > > > >>> > -----Original Message-----
> > > > > > >>> > From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> > > > > > >>> >
> [mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]On Behalf Of
> > > > > > >>Mike Takefman
> > > > > > >>> > Sent: Monday, June 24, 2002 1:31 PM
> > > > > > >>> > To: Anoop Ghanwani
> > > > > > >>> > Cc: 'djz@xxxxxxxxxxx '; 'stds-802-17@xxxxxxxx '
> > > > > > >>> > Subject: Re: [RPRWG] control TTL (the 255-station and
> > > > > 2000-km issue)
> > > > > > >>> >
> > > > > > >>> >
> > > > > > >>> >
> > > > > > >>> > Anoop,
> > > > > > >>> >
> > > > > > >>> > For a protection hierarchy to work all nodes
> > > > > > >>> > need to know about all failures.
> > > > > > >>> >
> > > > > > >>> > I agree with your comment that this needs to be
> > > > > > >>> > clearly documented as part of the standard.
> > > > > > >>> > Futhermore, if the WG decides to accept this
> > > > > > >>> > TTL decrement algorithm it must be documented
> > > > > > >>> > properly.
> > > > > > >>> >
> > > > > > >>> > With regard to your last question / comment.
> > > > > > >>> > In wrapping, the adjacent nodes can react
> immediately if
> > > > > > >>> > they have the highest priority failure. Thereby
> > > > > > >>> > wrapping will have quicker reaction times to
> > > > > > >>> > steering. The need to broadcast in the wrapping
> > > > > > >>> > case is to support the hierarchy. If no hierarchy
> > > > > > >>> > was supported, then the decision could be completely
> > > > > > >>> > local. In this case I would still argue that a
> > > > > > >>> > broadcast of the event was useful for 2 reasons.
> > > > > > >>> > 1) The same algorithm supports steering which is
> > > > > > >>> > the default mode
> > > > > > >>> > 2) The packets that are trapped on the wrong ring
> > > > > > >>> > will get killed.
> > > > > > >>> >
> > > > > > >>> > cheers,
> > > > > > >>> >
> > > > > > >>> > mike
> > > > > > >>> >
> > > > > > >>> >
> > > > > > >>> > Anoop Ghanwani wrote:
> > > > > > >>> > >
> > > > > > >>> > >
> > > > > > >>> > > Mike,
> > > > > > >>> > >
> > > > > > >>> > > I was trying to say that when a node "unwraps" due
> > > > > > >>> > > to the ring healing, it can't throw away packets
> > > > > > >>> > > forever because the ring might wrap at some other
> > > > > > >>> > > place making it valid for this node to see packets
> > > > > > >>> > > with the wrap bit set. Therefore a node would have
> > > > > > >>> > > to set some kind of timer (on the order of RTT) and
> > > > > > >>> > > only throw away packets for that duration.
> > > > > > >>> > >
> > > > > > >>> > > The above discussion was trying to solve the problem
> > > > > > >>> > > where all nodes do not know about protection events;
> > > > > > >>> > > only those adjacent to the fault do. If
> all nodes do
> > > > > > >>> > > know about protection events, the solution
> you mention
> > > > > > >>> > > should work, but it does need to be
> documented in the
> > > > > > >>> > > spec.
> > > > > > >>> > >
> > > > > > >>> > > [Off topic discussion]
> > > > > > >>> > > To me, it seemed like the main argument for
> > > doing wrapping
> > > > > > >>> > > is that only nodes adjacent to the fault need
> > > to know about
> > > > > > >>> > > it and react to it. If all nodes do need
> to know about
> > > > > > >>> > > a protection event, then it it probably
> more efficient
> > > > > > >>> > > for them to use steering.
> > > > > > >>> > >
> > > > > > >>> > > -Anoop
> > > > > > >>> > >
> > > > > > >>> > > -----Original Message-----
> > > > > > >>> > > From: Mike Takefman
> > > > > > >>> > > To: Anoop Ghanwani
> > > > > > >>> > > Cc: djz@xxxxxxxxxxx; stds-802-17@xxxxxxxx
> > > > > > >>> > > Sent: 6/24/02 12:07 AM
> > > > > > >>> > > Subject: Re: [RPRWG] control TTL (the 255-station
> > > > > and 2000-km issue)
> > > > > > >>> > >
> > > > > > >>> > > Anoop,
> > > > > > >>> > >
> > > > > > >>> > > wrapping nodes always communicate with every other
> > > > > > >>> > > node anyway. This is necessary for protection
> > > > > > >>> > > heirarchy to work. Also, given the broadcast
> > > > > > >>> > > nature of messages to make steering work in under
> > > > > > >>> > > 50 ms, I have no concern over all nodes knowing
> > > > > > >>> > > that all protection events are done and the ringlets
> > > > > > >>> > > are healed.
> > > > > > >>> > >
> > > > > > >>> > > If one waits for the ringlets to be healed
> > > > > > >>> > > and then killing the packet life is fine. Or
> > > > > > >>> > > maybe I did not understand your comment.
> > > > > > >>> > >
> > > > > > >>> > > mike
> > > > > > >>> > >
> > > > > > >>> > > Anoop Ghanwani wrote:
> > > > > > >>> > > >
> > > > > > >>> > > > > > The problem with (3), which you seem
> to advocate,
> > > > > > >>> > > > > > is the time gap between the wrap
> action and the
> > > > > > >>> > > > > > the distribution/settling of the wrap state
> > > > > information
> > > > > > >>> > > > > > in other stations. During this time
> > > difference, any
> > > > > > >>> > > > > > and all TTL-strip based frames will
> be discarded.
> > > > > > >>> > > > >
> > > > > > >>> > > > > A good point david, in response please consider
> > > > > the following
> > > > > > >>> > > > >
> > > > > > >>> > > > > Never decrement when on the wrong ring.
> > > Once the wrap
> > > > > > >>> > > > > state is left, kill the packet if the ring id
> > > > > > >>> > > > > is wrong. THus going into wrap does not
> cause the
> > > > > > >>> > > > > packets to be prematurely lost. When
> leaving wrap
> > > > > > >>> > > > > the packets will be killed once everyone knows
> > > > > > >>> > > > > the wrap is over.
> > > > > > >>> > > >
> > > > > > >>> > > > Mike,
> > > > > > >>> > > >
> > > > > > >>> > > > Does everyone on the ring know when a
> wrap has occured
> > > > > > >>> > > > and when it heals? I thought wrapping was a
> > > local issue
> > > > > > >>> > > > and only nodes adjacent to the fault know
> about it.
> > > > > > >>> > > > In that case, if the node at which wrapping occurs
> > > > > > >>> > > > detects a heal, and for some reason doesn't
> > > pull a wrap
> > > > > > >>> > > > packet off, it will continue to circulate forever.
> > > > > > >>> > > > The node can't be dropping wrapped packets forever
> > > > > > >>> > > > because the wrap could occur somewhere else at
> > > > > > >>> > > > which time it would be a legal packet for
> > > pass-through.
> > > > > > >>> > > >
> > > > > > >>> > > > -Anoop
> > > > > > >>> > >
> > > > > > >>> > > --
> > > > > > >>> > > Michael Takefman tak@xxxxxxxxx
> > > > > > >>> > > Manager of Engineering, Cisco Systems
> > > > > > >>> > > Chair IEEE 802.17 Stds WG
> > > > > > >>> > > 2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> > > > > > >>> > > voice: 613-254-3399 fax: 613-254-4867
> > > > > > >>> >
> > > > > > >>> > --
> > > > > > >>> > Michael Takefman tak@xxxxxxxxx
> > > > > > >>> > Manager of Engineering, Cisco Systems
> > > > > > >>> > Chair IEEE 802.17 Stds WG
> > > > > > >>> > 2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> > > > > > >>> > voice: 613-254-3399 fax: 613-254-4867
> > > > > > >>> >
> > > > > > >>
> > > > > > >>--
> > > > > > >>Michael Takefman tak@xxxxxxxxx
> > > > > > >>Manager of Engineering, Cisco Systems
> > > > > > >>Chair IEEE 802.17 Stds WG
> > > > > > >>2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> > > > > > >>voice: 613-254-3399 fax: 613-254-4867
> > > > >
> > > > > --
> > > > > Michael Takefman tak@xxxxxxxxx
> > > > > Manager of Engineering, Cisco Systems
> > > > > Chair IEEE 802.17 Stds WG
> > > > > 2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> > > > > voice: 613-254-3399 fax: 613-254-4867
> > > > >
> > >
>