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

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

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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