Re: [PCN] Concensus questions from Thursday's PCN meeting

["Geib, Ruediger" <[e-mail]>]

Hi Georgios,

on the configuration and operation of ECMP you may want to read 
the documentation provided by backbone router vendors or 
other publications.

Regards,

Rudiger 

| -----Original Message-----
| From: Georgios Karagiannis [mailto:[e-mail]] 
| Sent: Tuesday, March 18, 2008 11:43 AM
| To: Geib, Rüdiger
| Cc: [e-mail]
| Subject: RE: [PCN] Concensus questions from Thursday's PCN meeting
| 
| Hi Ruediger
| 
| What is not realistic?
| Is it not realistic to use ECMP routing?
| Is it not realistic that one path fails and its traffic is 
| rerouted to another path?
| 
| Best regards,
| Georgios
| 
| 
| 
|  
| 
| > -----Original Message-----
| > From: Geib, Ruediger [mailto:[e-mail]]
| > Sent: dinsdag 18 maart 2008 11:36
| > To: [e-mail]
| > Cc: [e-mail]
| > Subject: RE: [PCN] Concensus questions from Thursday's PCN meeting
| > 
| > Hi Georgios
| > 
| > see in line.
| > 
| > Regards, Rudiger
| > 
| > | -----Original Message-----
| > | From: Georgios Karagiannis [mailto:[e-mail]]
| > | Sent: Tuesday, March 18, 2008 11:17 AM
| > | To: Geib, Rüdiger
| > | Cc: [e-mail]
| > | Subject: RE: [PCN] Concensus questions from Thursday's PCN meeting
| > | 
| > | Hi Ruediger
| > | 
| > | The problem that I have explained it does not have to do 
| with slow 
| > | reaction time but it has to do with complete collapse of the PCN 
| > | domain operation.
| > | This occurs when the admission control/flow termination 
| triggers at 
| > | the egress are not activated when they should be activated.
| > | 
| > | 
| > | Here is a more concrete example:
| > | 
| > | When ECMP routing is used, it means that flows that are 
| associated 
| > | with the same ingress-egress-aggregate can follow different paths.
| > | Assume that there are 5 such paths that are carrying flows
| > associated
| > | with the same ingress-egress-aggregate.
| > | 
| > | Consider now that one of the 5 paths fails and it is
| > rerouted to one
| > | of the other paths.
| > | Assume that path1 is becoming congested and the other 3 remaining 
| > | paths are not congested.
| > | I am also assuming in this case that the thresholds are well 
| > | configured.
| > 
| > This is not realistic.
| > 
| > 
| > | The egress will calculate CLE in the following way:
| > | CLE = marked_1 /(unmarked_1 + unmarked_2 + unmarked_3 + 
| unmarked_4 +
| > | marked_1)
| > | 
| > | I think that typcially the above calculated CLE will not
| > reach 1% when
| > | marked packets are preferentially dropped.
| > | This problem is due to the fact that ECMP routing is used 
| and flows 
| > | that are not participating at the congestion are
| > contributing to the
| > | calculation of the CLE. The flows that are not passing through 
| > | congested nodes will actually forward unmarked packets to
| > the egress
| > | node.
| > | 
| > | When marked packets are preferentially dropped than marked_1 can 
| > | easily be smaller than 1% * (unmarked_1 + unmarked_2 +
| > | unmarked_3 + unmarled_4 + marked_1). 
| > | In this case the admission control situation is not 
| triggered and a 
| > | complete collapse of the PCN domain operation can occur!
| > | 
| > | Thus:
| > | If no ECMP routing would have been used than for the same 
| situation 
| > | CLE = marked_1/unmarked_1 + marked_1), which can go easily
| > to 1%, if
| > | the C-A-R is well configured.
| > | 
| > | But when ECMP routing is used and the above scenario is
| > applied then
| > | CLE = marked_1 /(unmarked_1 + unmarked_2 +
| > | unmarked_3 + unmarled_4 + marked_1), which probaly will not
| > reach 1%
| > | when marked packets are preferentially dropped, since
| > marked_1 can be
| > | smaller than 1% * (unmarked_1 +
| > | unmarked_2 + unmarked_3 + unmarled_4 +
| > | marked_1)
| > | 
| > | I hope that you now understand the problem!
| > | 
| > | Best regards,
| > | Georgios
| > | 
| > | > -----Original Message-----
| > | > From: Geib, Ruediger [mailto:[e-mail]]
| > | > Sent: dinsdag 18 maart 2008 8:30
| > | > To: [e-mail]
| > | > Cc: [e-mail]
| > | > Subject: RE: [PCN] Concensus questions from Thursday's 
| PCN meeting
| > | > 
| > | > Hi Georgios,
| > | > 
| > | > in the situation you describe, packet losses occur. This
| > | will result
| > | > in bad press, as the customers using PCN based services
| > | were promised
| > | > another type of service.
| > | > 
| > | > In this situation it doesn't matter whether or not ECMP
| > is deployed
| > | > and it also doesn't matter whether termination is fair or
| > not. The
| > | > important event is: packet losses occur (in one of your 
| examples 
| > | > several routers drop packets). The drops are the only
| > | relevant issue.
| > | > Whether service resumes after 5 seconds due to extremly well 
| > | > engineered termination or after 10 seconds after a
| > | sufficient number
| > | > of customers hang up is not important.
| > | > I can't recall having read anytime in the news "Major
| > | network outage -
| > | > but termination was fair." I can only recall having seen
| > the first
| > | > part.
| > | > 
| > | > I'm sure you're happy in adapting your example, as you 
| do all the 
| > | > time. I'm having work to do, but maybe someone else is
| > | interested in
| > | > continuing discusion. I think, I've made my point.
| > | > 
| > | > Regards,
| > | > 
| > | > Rudiger
| > | > 
| > | > | -----Original Message-----
| > | > | From: Georgios Karagiannis [mailto:[e-mail]]
| > | > | Sent: Monday, March 17, 2008 5:36 PM
| > | > | To: Geib, Rüdiger
| > | > | Cc: [e-mail]
| > | > | Subject: RE: [PCN] Concensus questions from Thursday's
| > PCN meeting
| > | > | 
| > | > | Hi Ruediger
| > | > | 
| > | > | Please note that what I have described holds also for the
| > | situation
| > | > | that the routers are well configured, but a catastrophic
| > | > event occur
| > | > | and at the same time ECMP routing is used.
| > | > | 
| > | > | Best regards,
| > | > | Georgios
| > | > | 
| > | > | 
| > | > | > -----Original Message-----
| > | > | > From: Geib, Ruediger [mailto:[e-mail]]
| > | > | > Sent: maandag 17 maart 2008 17:10
| > | > | > To: [e-mail]
| > | > | > Cc: [e-mail]
| > | > | > Subject: RE: [PCN] Concensus questions from Thursday's
| > | PCN meeting
| > | > | > 
| > | > | > Hi Georgios,
| > | > | > 
| > | > | > what I say is if PCN decides to deal with catastrophic
| > | events in
| > | > | > combination with misconfigured routers, then it will end up 
| > | > | > standardising solutions for academic problems.
| > | > | > 
| > | > | > Regards,
| > | > | > 
| > | > | > Rudiger
| > | > | > 
| > | > | > 
| > | > | > | -----Original Message-----
| > | > | > | From: Georgios Karagiannis [mailto:[e-mail]]
| > | > | > | Sent: Monday, March 17, 2008 4:38 PM
| > | > | > | To: Geib, Rüdiger
| > | > | > | Cc: [e-mail]
| > | > | > | Subject: RE: [PCN] Concensus questions from Thursday's
| > | > PCN meeting
| > | > | > | 
| > | > | > | Hi Ruediger
| > | > | > | 
| > | > | > | I do not understand what you try to say. Please note
| > | that flow
| > | > | > | termination is used for the below explained reason, see
| > | > | below text
| > | > | > | taken from the PCN architecture draft:
| > | > | > | 
| > | > | > | o  The termination mechanism complements admission
| > | control.  It
| > | > | > |       allows the network to recover from sudden
| > | > | unexpected surges of
| > | > | > |       PCN-traffic on some links, thus restoring QoS to
| > | > | the remaining
| > | > | > |       flows.  Such scenarios are expected to be
| > rare but not
| > | > | > | impossible.
| > | > | > |       They can be caused by large network failures that
| > | > | > redirect lots
| > | > | > | of
| > | > | > |       admitted PCN-traffic to other links, or by
| > | > | malfunction of the
| > | > | > |       measurement-based admission control in the presence
| > | > | > of admitted
| > | > | > |       flows that send for a while with an atypically low
| > | > | > rate and then
| > | > | > |       increase their rates in a correlated way.
| > | > | > | 
| > | > | > | Best regards,
| > | > | > | Georgios
| > | > | > | 
| > | > | > |  
| > | > | > | 
| > | > | > | > -----Original Message-----
| > | > | > | > From: Geib, Ruediger 
| [mailto:[e-mail]]
| > | > | > | > Sent: maandag 17 maart 2008 16:32
| > | > | > | > To: [e-mail]
| > | > | > | > Cc: [e-mail]
| > | > | > | > Subject: RE: [PCN] Concensus questions from Thursday's
| > | > | PCN meeting
| > | > | > | > 
| > | > | > | > Hi Georgios,
| > | > | > | > 
| > | > | > | > QoS on redundant links means, that one link is able to
| > | > | > | carry the QoS
| > | > | > | > traffic of the other. This may not hold for non QoS
| > | > | > | traffic. This is,
| > | > | > | > what typical carrier backbones providing QoS are
| > | > engineered for
| > | > | > | > (commonly known as traffic engineering).
| > | > | > | > 
| > | > | > | > Should a misconfiguration occur, things may go wrong. 
| > | > | > | > Operational staff corrects this a soon as the
| > | > | misconfiguration is
| > | > | > | > identified.
| > | > | > | > 
| > | > | > | > The engineering of carrier backbones is often done with
| > | > | automated
| > | > | > | > tools, leaving little room for human errors.
| > | > | > | > However maintenance work may result in humanne system
| > | > | > | interference. I
| > | > | > | > doubt that Telekom's engineering department is 
| willing to
| > | > | > | accept extra
| > | > | > | > protocol and router complexitiy to deal with operator
| > | > | > configuration
| > | > | > | > errors. While I time and again hear of the worst
| > | > | > | misconfigs, I can't
| > | > | > | > recall that my colleagues try to adapt standardisation
| > | > | afterwards.
| > | > | > | > 
| > | > | > | > Regards,
| > | > | > | > 
| > | > | > | > Rudiger
| > | > | > | > 
| > | > | > | > | -----Original Message-----
| > | > | > | > | From: Georgios Karagiannis
| > [mailto:[e-mail]]
| > | > | > | > | Sent: Monday, March 17, 2008 3:34 PM
| > | > | > | > | To: Geib, Rüdiger
| > | > | > | > | Cc: [e-mail]
| > | > | > | > | Subject: RE: [PCN] Concensus questions from Thursday's
| > | > | > PCN meeting
| > | > | > | > | 
| > | > | > | > | Hi Ruediger
| > | > | > | > | 
| > | > | > | > | Please note that typical IP networks (thus not
| > | > | MPLS/GMPLS based
| > | > | > | > | domains) can recover from failures by using rerouting.
| > | > | > | > | Or do you know another standardized mechanism in
| > | typical IP
| > | > | > | > networks
| > | > | > | > | (thus not MPLS/GMPLS based) that can provide
| > another kind
| > | > | > | > of recovery
| > | > | > | > | from failures.
| > | > | > | > | 
| > | > | > | > | Furthermore, I will just explain the example again
| > | > | with maximum
| > | > | > | > | capacity of
| > | > | > | > | pathh2 being equal
| > | > | > | > | to maximum capacity of path1 = C.
| > | > | > | > | Please explain what you do not understand in
| > this example!
| > | > | > | > | 
| > | > | > | > | Here are the assumptions:
| > | > | > | > | * In the PCN domain we assume that ECMP routing
| > | is possible!
| > | > | > | > | * ingress-eggress-aggregate can contain flows that are
| > | > | > | > passing through
| > | > | > | > | one path or more paths (when ECMP routing is used).
| > | > | > | > | 
| > | > | > | > | * routers are currently dropping packets 
| randomly. Thus
| > | > | > | marked and
| > | > | > | > | unmarked packets will be
| > | > | > | > |   dropped randomly
| > | > | > | > | 
| > | > | > | > | * When excess rate measurements are used, the
| > | triggering of
| > | > | > | > admission
| > | > | > | > | control and flow
| > | > | > | > |   termination are done at the egress by using
| > the CLE. One
| > | > | > | > example of
| > | > | > | > | this trigger is:
| > | > | > | > |   CLE > 1%. Note that CLE = marked/(unmarked 
| + marked). 
| > | > | > | This means
| > | > | > | > | that if this trigger is not activated while a severe
| > | > | > | > |   congestion occurs in the PCN domain, then the
| > operation
| > | > | > | > of the PCN
| > | > | > | > | domain will completely collapse.
| > | > | > | > | 
| > | > | > | > | 
| > | > | > | > | My statement is:
| > | > | > | > | If the routers do not preferentially drop 
| marked packets
| > | > | > | > then the PCN
| > | > | > | > | domain operation, even in corner case and
| > misconfiguration
| > | > | > | > situations,
| > | > | > | > | is more robust and more stable than in the
| > situation that
| > | > | > | > the router
| > | > | > | > | is preferentially dropping marked packets.
| > | > | > | > | 
| > | > | > | > | The below example show such a corner case!
| > | > | > | > | 
| > | > | > | > | 
| > | > | > | > | I will describe two situations:
| > | > | > | > | 
| > | > | > | > | Situation 1:
| > | > | > | > | Consider that an ingress-egress-aggregate due to ECMP
| > | > | > routing it
| > | > | > | > | includes flows that are passing from at least 
| two paths.
| > | > | > | > | Assume that path1 supports a maximum bandwidth
| > | > capacity of C. 
| > | > | > | > | Now consider that the maximum bandwdith capacity of
| > | > | path2 is C.
| > | > | > | > | Consider also that both paths are fully utilized.
| > | > | > | > | 
| > | > | > | > | Consider that preferentially marked packets are
| > | dropped and
| > | > | > | > that path2
| > | > | > | > | fails.
| > | > | > | > | Now assume that all (maximum) traffic passing through
| > | > | > | path2 will be
| > | > | > | > | rerouted through path1.
| > | > | > | > | If a bottleneck router located in path1, say Rbott, is
| > | > | > | > misconfigured
| > | > | > | > | (i.e., from the point of view of having wrongly
| > too high
| > | > | > | > | configured-admissible-rate value), or even if 
| it is well
| > | > | > | > configured,
| > | > | > | > | then it can be possible that CLE measured at 
| the egress
| > | > | > | > cannot reach
| > | > | > | > | 1%.
| > | > | > | > | Note that
| > | > | > | > | CLE = marked packets/ (marked packets +
| > unmarked packets).
| > | > | > | > | This is because Rbott will just allow an 
| excess rate to
| > | > | > | > pass through
| > | > | > | > | that is
| > | > | > | > | 
| > | > | > | > | equal to: C - configured-admissible-rate. The rest of
| > | > | > the marked
| > | > | > | > | packets, so the rest of the excess rate, will 
| be dropped
| > | > | > | by Rbott,
| > | > | > | > | since this router is preferentially dropping
| > | marked packets.
| > | > | > | > | Furthermore, note that due to the ECMP routing
| > | > flows that are
| > | > | > | > | belonging to the same 
| ingress-egress-aggregate and that
| > | > | > | are passing
| > | > | > | > | through another path,
| > | > | > | > | 
| > | > | > | > | than path1, which is not congested, will 
| forward traffic
| > | > | > | > towards the
| > | > | > | > | egress node that will be unmarked.
| > | > | > | > | This will mean that the CLE > 1% will not be 
| triggered,
| > | > | > | > this will mean
| > | > | > | > | that the flow termination will not be 
| triggered and that
| > | > | > | > the operation
| > | > | > | > | of the PCN domain will collapse completely.
| > | > | > | > | 
| > | > | > | > | 
| > | > | > | > | Situation 2:
| > | > | > | > | Now consider that the router just operates as
| > | > | > currently, i.e., no
| > | > | > | > | preferential drop, randomly dropping marked and
| > | > | > unmarked packets.
| > | > | > | > | Consider also that the two paths described in
| > Situation 1
| > | > | > | above are
| > | > | > | > | used, ECMP routing is used, and that they are fully
| > | > utilized.
| > | > | > | > | Assume also that path2 fails and that the path2
| > traffic is
| > | > | > | > rerouted on
| > | > | > | > | path1.
| > | > | > | > | Now the CLE value will have a higher probability of
| > | > | > reaching the
| > | > | > | > | triggering value of 1%.
| > | > | > | > | 
| > | > | > | > | This is because the routers in path1 will 
| drop randomly
| > | > | > | marked and
| > | > | > | > | unmarked packets.
| > | > | > | > | It is more certain that in this case the CLE
| > will reach 1%
| > | > | > | > due to the
| > | > | > | > | following reason.
| > | > | > | > | In this example it is assumed that the maximum
| > | > | > bandwidth capacity
| > | > | > | > | supported by path2 is C.
| > | > | > | > | This means that after rerouting the traffic from
| > | path2 into
| > | > | > | > path1, the
| > | > | > | > | ratio between marked packets and unmarked packets that
| > | > | > | are passing
| > | > | > | > | thorugh path1 can be equal or higher than 100%.
| > | > | > | > | Note that the routers in path1 will mark the 
| excess rate
| > | > | > | > above C, thus
| > | > | > | > | 1*C (i.e., the rerouted traffic from path2) as marked.
| > | > | > | > | The above observation holds also for the 
| situation that
| > | > | > | the routers
| > | > | > | > | are preferentially dropping unmarked packets.
| > | > | > | > | 
| > | > | > | > | Thus when routers are preferentially dropping marked
| > | > | > packets the
| > | > | > | > | robustness of the PCN domain operation is
| > | decreasing and in
| > | > | > | > some cases
| > | > | > | > | it severely decreases, which could cause the complete
| > | > | > | > collapse of the
| > | > | > | > | PCN domain operation.
| > | > | > | > | 
| > | > | > | > | Best regards,
| > | > | > | > | Georgios
| > | > | > | > | 
| > | > | > | > | 
| > | > | > | > |  
| > | > | > | > | 
| > | > | > | > | > -----Original Message-----
| > | > | > | > | > From: Geib, Ruediger
| > | [mailto:[e-mail]]
| > | > | > | > | > Sent: maandag 17 maart 2008 15:26
| > | > | > | > | > To: [e-mail]
| > | > | > | > | > Cc: [e-mail]
| > | > | > | > | > Subject: RE: [PCN] Concensus questions from 
| Thursday's
| > | > | > | PCN meeting
| > | > | > | > | > 
| > | > | > | > | > Hi Georgios,
| > | > | > | > | > 
| > | > | > | > | > Unfortunately you missed my point.
| > | > | > | > | > 
| > | > | > | > | > No such thing as you describe has been, is or
| > | will for the
| > | > | > | > | foreseeable
| > | > | > | > | > future be engineered in the IP backbone of 
| the company
| > | > | > | > I'm working
| > | > | > | > | > for.
| > | > | > | > | > 
| > | > | > | > | > My expectation on the backbone of any 
| carrier offering
| > | > | > | > | transport QoS
| > | > | > | > | > is, that it is engineered to survive 
| probable failures
| > | > | > | > (like single
| > | > | > | > | > link losses) without impact on the 
| performance of QoS
| > | > | > | > | traffic. This is
| > | > | > | > | > where we should start from, if we discuss PCN. 
| > | From there
| > | > | > | > | on, PCN is
| > | > | > | > | > able to add value.
| > | > | > | > | > 
| > | > | > | > | > Links without traffic engineering followed by
| > | > | > | > misconfigured routers
| > | > | > | > | > aren't the arguments which will convince
| > either product
| > | > | > | > | management or
| > | > | > | > | > backbone engineering of the company I work for to
| > | > | deploy PCN.
| > | > | > | > | > 
| > | > | > | > | > As a general comment: I don't regard PCN as 
| a plug and
| > | > | > | > play toy for
| > | > | > | > | > the operational equivalent of a 'script
| > | kiddie'. If others
| > | > | > | > | share that
| > | > | > | > | > view and our documents don't state that, we
| > | > should add text.
| > | > | > | > | > 
| > | > | > | > | > Regards,
| > | > | > | > | > 
| > | > | > | > | > Rudiger
| > | > | > | > | > 
| > | > | > | > | > | -----Original Message-----
| > | > | > | > | > | From: Georgios Karagiannis
| > | > [mailto:[e-mail]]
| > | > | > | > | > | Sent: Monday, March 17, 2008 2:49 PM
| > | > | > | > | > | To: Geib, Rüdiger
| > | > | > | > | > | Cc: [e-mail]
| > | > | > | > | > | Subject: RE: [PCN] Concensus questions from
| > Thursday's
| > | > | > | > PCN meeting
| > | > | > | > | > | 
| > | > | > | > | > | Hi Ruediger
| > | > | > | > | > | 
| > | > | > | > | > | You missed my point!
| > | > | > | > | > | The explanation applies to all types of 
| IP networks.
| > | > | > | > | > | Please note that the problem occurs also when
| > | path2 and
| > | > | > | > path1 use
| > | > | > | > | > | exactly the same maximum capacity, say C!
| > | > | > | > | > | 
| > | > | > | > | > | In this case, if pathh2 fails then path1 will see
| > | > | an excess
| > | > | > | > | > rate equal
| > | > | > | > | > | to at least C.
| > | > | > | > | > | The rest of the explanation is identical to
| > | the one used
| > | > | > | > | during my
| > | > | > | > | > | previous example!
| > | > | > | > | > | 
| > | > | > | > | > | 
| > | > | > | > | > | 
| > | > | > | > | > | Best regards,
| > | > | > | > | > | Georgios
| > | > | > | > | > | 
| > | > | > | > | > | 
| > | > | > | > | > | 
| > | > | > | > | > |  
| > | > | > | > | > | 
| > | > | > | > | > | > -----Original Message-----
| > | > | > | > | > | > From: Geib, Ruediger
| > | > | [mailto:[e-mail]]
| > | > | > | > | > | > Sent: maandag 17 maart 2008 14:34
| > | > | > | > | > | > To: [e-mail]
| > | > | > | > | > | > Cc: [e-mail]
| > | > | > | > | > | > Subject: RE: [PCN] Concensus questions from
| > | Thursday's
| > | > | > | > | PCN meeting
| > | > | > | > | > | > 
| > | > | > | > | > | > Hi Georgios,
| > | > | > | > | > | > 
| > | > | > | > | > | > What you describe isn't backbone traffic
| > | engineering. 
| > | > | > | > What you
| > | > | > | > | > | > describe may happen in corporate VPNs, where a
| > | > | DSL access
| > | > | > | > | > | is used to
| > | > | > | > | > | > back up a WAN Fast Ethernet access or the
| > | > like. I don't
| > | > | > | > | > | object to have
| > | > | > | > | > | > standards on PCN for VPNs, but I'm not
| > | > | interested in this
| > | > | > | > | > issue for
| > | > | > | > | > | > now.
| > | > | > | > | > | > 
| > | > | > | > | > | > If you know any carrier who's operating his
| > | > | network with a
| > | > | > | > | > | > 16:1 load balancing for QoS traffic on any
| > | > | particular link
| > | > | > | > | > | set, please
| > | > | > | > | > | > publish the name, we are all interested in
| > | hearing it.
| > | > | > | > | > | > 
| > | > | > | > | > | > Regards,
| > | > | > | > | > | > 
| > | > | > | > | > | > Rudiger
| > | > | > | > | > | > 
| > | > | > | > | > | >  
| > | > | > | > | > | > 
| > | > | > | > | > | > | -----Original Message-----
| > | > | > | > | > | > | From: Georgios Karagiannis
| > | > | > [mailto:[e-mail]]
| > | > | > | > | > | > | Sent: Monday, March 17, 2008 11:03 AM
| > | > | > | > | > | > | To: Geib, Rüdiger
| > | > | > | > | > | > | Cc: [e-mail]
| > | > | > | > | > | > | Subject: RE: [PCN] Concensus questions from
| > | > Thursday's
| > | > | > | > | > PCN meeting
| > | > | > | > | > | > | 
| > | > | > | > | > | > | Hi Ruediger
| > | > | > | > | > | > | 
| > | > | > | > | > | > | I will try to explain this more clearly.
| > | > | > | > | > | > | Here are the assumptions:
| > | > | > | > | > | > | * In the PCN domain we assume that 
| ECMP routing
| > | > | > | is possible!
| > | > | > | > | > | > | * ingress-eggress-aggregate can contain
| > | > flows that are
| > | > | > | > | > | > passing through
| > | > | > | > | > | > | one path or more paths (when ECMP routing
| > | is used).
| > | > | > | > | > | > | 
| > | > | > | > | > | > | * routers are currently dropping packets
| > | > | randomly. Thus
| > | > | > | > | > | marked and
| > | > | > | > | > | > | unmarked packets will be
| > | > | > | > | > | > |   dropped randomly
| > | > | > | > | > | > | 
| > | > | > | > | > | > | * When excess rate measurements are used, the
| > | > | > | triggering of
| > | > | > | > | > | > admission
| > | > | > | > | > | > | control and flow
| > | > | > | > | > | > |   termination are done at the egress by using
| > | > | > the CLE. One
| > | > | > | > | > | > example of
| > | > | > | > | > | > | this trigger is:
| > | > | > | > | > | > |   CLE > 1%. Note that CLE = marked/(unmarked
| > | > | + marked). 
| > | > | > | > | > | This means
| > | > | > | > | > | > | that if this trigger is not activated
| > | while a severe
| > | > | > | > | > | > |   congestion occurs in the PCN 
| domain, then the
| > | > | > operation
| > | > | > | > | > | > of the PCN
| > | > | > | > | > | > | domain will completely collapse.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | My statement is:
| > | > | > | > | > | > | If the routers do not preferentially drop
| > | > | marked packets
| > | > | > | > | > | > then the PCN
| > | > | > | > | > | > | domain operation, even in corner case and
| > | > | > misconfiguration
| > | > | > | > | > | > situations,
| > | > | > | > | > | > | is more robust and more stable than in the
| > | > | > situation that
| > | > | > | > | > | > the router
| > | > | > | > | > | > | is preferentially dropping marked packets.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | The below example show such a corner case!
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | I will describe two situations:
| > | > | > | > | > | > | 
| > | > | > | > | > | > | Situation 1:
| > | > | > | > | > | > | Consider that an ingress-egress-aggregate
| > | > due to ECMP
| > | > | > | > | > routing it
| > | > | > | > | > | > | includes flows that are passing from at least
| > | > | two paths.
| > | > | > | > | > | > | Assume that path1 supports a maximum bandwidth
| > | > | > | > capacity of C. 
| > | > | > | > | > | > | Now consider
| > | > | > | > | > | > | that the maximum bandwdith capacity of
| > | > path2 is 15*C.
| > | > | > | > | > | > | Consider also that both paths are fully
| > utilized.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | Consider that preferentially marked 
| packets are
| > | > | > | dropped and
| > | > | > | > | > | > that path2
| > | > | > | > | > | > | fails.
| > | > | > | > | > | > | Now assume that all (maximum) traffic
| > | > passing through
| > | > | > | > | > | path2 will be
| > | > | > | > | > | > | rerouted through path1.
| > | > | > | > | > | > | If a bottleneck router located in path1,
| > | > say Rbott, is
| > | > | > | > | > | > misconfigured
| > | > | > | > | > | > | (i.e., from the point of view of 
| having wrongly
| > | > | > too high
| > | > | > | > | > | > | configured-admissible-rate value), or even if
| > | > | it is well
| > | > | > | > | > | > configured,
| > | > | > | > | > | > | then it can be possible that CLE measured at
| > | > | the egress
| > | > | > | > | > | > cannot reach
| > | > | > | > | > | > | 1%.
| > | > | > | > | > | > | Note that
| > | > | > | > | > | > | CLE = marked packets/ (marked packets +
| > | > | > unmarked packets).
| > | > | > | > | > | > | This is because Rbott will just allow an
| > | > | excess rate to
| > | > | > | > | > | > pass through
| > | > | > | > | > | > | that is
| > | > | > | > | > | > | 
| > | > | > | > | > | > | equal to: C - configured-admissible-rate. 
| > | > The rest of
| > | > | > | > | > the marked
| > | > | > | > | > | > | packets, so the rest of the excess rate, will
| > | > | be dropped
| > | > | > | > | > | by Rbott,
| > | > | > | > | > | > | since this router is preferentially dropping
| > | > | > | marked packets.
| > | > | > | > | > | > | Furthermore, note that due to the ECMP routing
| > | > | > | > flows that are
| > | > | > | > | > | > | belonging to the same
| > | > | ingress-egress-aggregate and that
| > | > | > | > | > | are passing
| > | > | > | > | > | > | through another path,
| > | > | > | > | > | > | 
| > | > | > | > | > | > | than path1, which is not congested, will
| > | > | forward traffic
| > | > | > | > | > | > towards the
| > | > | > | > | > | > | egress node that will be unmarked.
| > | > | > | > | > | > | This will mean that the CLE > 1% will not be
| > | > | triggered,
| > | > | > | > | > | > this will mean
| > | > | > | > | > | > | that the flow termination will not be
| > | > | triggered and that
| > | > | > | > | > | > the operation
| > | > | > | > | > | > | of the PCN domain will collapse completely.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | Situation 2:
| > | > | > | > | > | > | Now consider that the router just operates as
| > | > | > | > | > currently, i.e., no
| > | > | > | > | > | > | preferential drop, randomly dropping 
| marked and
| > | > | > | > | > unmarked packets.
| > | > | > | > | > | > | Consider also that the two paths described in
| > | > | > Situation 1
| > | > | > | > | > | above are
| > | > | > | > | > | > | used, ECMP routing is used, and that they
| > | are fully
| > | > | > | > utilized.
| > | > | > | > | > | > | Assume also that path2 fails and that 
| the path2
| > | > | > traffic is
| > | > | > | > | > | > rerouted on
| > | > | > | > | > | > | path1.
| > | > | > | > | > | > | Now the CLE value will have a higher
| > | probability of
| > | > | > | > | > reaching the
| > | > | > | > | > | > | triggering value of 1%.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | This is because the routers in path1 will
| > | > | drop randomly
| > | > | > | > | > | marked and
| > | > | > | > | > | > | unmarked packets.
| > | > | > | > | > | > | It is more certain that in this case the CLE
| > | > | > will reach 1%
| > | > | > | > | > | > due to the
| > | > | > | > | > | > | following reason.
| > | > | > | > | > | > | In this example it is assumed that the maximum
| > | > | > | > | > bandwidth capacity
| > | > | > | > | > | > | supported by path2 is 15*C.
| > | > | > | > | > | > | This means that after rerouting the 
| traffic from
| > | > | > | path2 into
| > | > | > | > | > | > path1, the
| > | > | > | > | > | > | ratio between marked packets and unmarked
| > | > packets that
| > | > | > | > | > | are passing
| > | > | > | > | > | > | thorugh path1 can be equal or higher than 16.
| > | > | > | > | > | > | Note that the routers in path1 will mark the
| > | > | excess rate
| > | > | > | > | > | > above C, thus
| > | > | > | > | > | > | 16 * C (i.e., the rerouted traffic from path2)
| > | > | > as marked.
| > | > | > | > | > | > | The above observation holds also for the
| > | > | situation that
| > | > | > | > | > | the routers
| > | > | > | > | > | > | are preferentially dropping unmarked packets.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | Thus when routers are preferentially
| > | dropping marked
| > | > | > | > | > packets the
| > | > | > | > | > | > | robustness of the PCN domain operation is
| > | > | > | decreasing and in
| > | > | > | > | > | > some cases
| > | > | > | > | > | > | it severely decreases, which could cause
| > | > the complete
| > | > | > | > | > | > collapse of the
| > | > | > | > | > | > | PCN domain operation.
| > | > | > | > | > | > | 
| > | > | > | > | > | > | Best regards,
| > | > | > | > | > | > | Georgios
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | 
| > | > | > | > | > | > | > -----Original Message-----
| > | > | > | > | > | > | > From: Geib, Ruediger
| > | > | > | [mailto:[e-mail]]
| > | > | > | > | > | > | > Sent: maandag 17 maart 2008 9:42
| > | > | > | > | > | > | > To: [e-mail]
| > | > | > | > | > | > | > Cc: [e-mail]
| > | > | > | > | > | > | > Subject: RE: [PCN] Concensus questions from
| > | > | Thursday's
| > | > | > | > | > | PCN meeting
| > | > | > | > | > | > | > 
| > | > | > | > | > | > | > Hi Georgios,
| > | > | > | > | > | > | > 
| > | > | > | > | > | > | > PCN is designed for deployment in traffic
| > | > engineered
| > | > | > | > | > networks. 
| > | > | > | > | > | > | > Please decribe, how to engineer a high
| > | performance
| > | > | > | > | > | > carrier backbone
| > | > | > | > | > | > | > and then review the assumptions your
| > discussion
| > | > | > | > is based on.
| > | > | > | > | > | > | > 
| > | > | > | > | > | > | > Regards,
| > | > | > | > | > | > | > 
| > | > | > | > | > | > | > Rudiger
| > | > | > | > | > | > | > 
| > | > | > | > | > | > | > | -----Original Message-----
| > | > | > | > | > | > | > | From: Georgios Karagiannis
| > | > | > | > [mailto:[e-mail]]
| > | > | > | > | > | > | > | Sent: Monday, March 17, 2008 9:34 AM
| > | > | > | > | > | > | > | To: Geib, Rüdiger
| > | > | > | > | > | > | > | Cc: [e-mail]
| > | > | > | > | > | > | > | Subject: RE: [PCN] Concensus 
| questions from
| > | > | > Thursday's
| > | > | > | > | > | > PCN meeting
| > | > | > | > | > | > | > | 
| > | > | > | > | > | > | > | Hi Ruediger
| > | > | > | > | > | > | > | 
| > | > | > | > | > | > | > | What do you mean?
| > | > | > | > | > | > | > | Do you mean that you do not want 
| to discuss
| > | > | > | corner cases
| > | > | > | > | > | > | > (ECMP related
| > | > | > | > | > | > | > | cases) that could collapse the PCN domain 
| > | > | > | > | > | > | > | operation?
| > | > | > | > | > | > | > | What I am saying is that if the
| > routers do not
| > | > | > | > | > | > | preferentially drop
| > | > | > | > | > | > | > | marked packets then the PCN domain
| > | operation is
| > | > | > | > | more robust
| > | > | > | > | > | > | > and more
| > | > | > | > | > | > | > | stable than in the situation that the
| > | router is
| > | > | > | > | > | preferentially
| > | > | > | > | > | > | > | dropping marked packets.
| > | > | > | > | > | > | > | 
| > | > | > | > | > | > | > | Are you saying that this statement is
| > | not right?
| > | > | > | > | > | > | > | 
| > | > | > | > | > | > | > | 
| > | > | > | > | > | > | > | Best regards, Georgios
| > | > | > | > | > | > | > |  
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