[c-nsp] ppp multiclass

[Bruce Pinsky]

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Gary Roberton wrote:
| Hello All
|
| This question was floated around a few days ago but I am still unsure
| of a resolution.
|
| We are using two 256k DSL links bonded together using ppp multilink
| and running voice traffic across this.  The problem lies in the fact
| that;
|
| voice packet 1 travels physically along link 1
| voice packet 2 travels physically along link 2
| voice packet 3 travels physically along link 1
|
| If anything happens to packet 2 the receiving router gets 1 and 3,
| obviously not good.  We have therefore used the ppp multilink
| multiclass statement.  This puts sequence numbers on the voice
| packets/fragments and the receiving router will dynamically create a
| buffer to reorder anything that is received out of order before
| forwarding onto the LAN.  This should smooth out any variance in delay
| between the two physical links.
|
| The problem is that the receiving router waits up to 1000 ms for any
| late fragments.  This is too long as it will introduce an unacceptable
| delay to packets that are slightly late.  Shown here;
|
| Virtual-Access5, bundle name is <removed>
| Bundle up for 6d16h, 63/255 load, 2 receive classes, 2 transmit classes
| Receive buffer limit 24384 bytes per class, frag timeout 1000 ms
| Dialer interface is Dialer0
| Receive Class 0:
|   3/724 fragments/bytes in reassembly list
|   1 lost fragments, 5397672 reordered
|   0/0 discarded fragments/bytes, 0 lost received
|   0xEDB5DD received sequence
| Receive Class 1:
|   0/0 fragments/bytes in reassembly list
|   0 lost fragments, 0 reordered
|   0/0 discarded fragments/bytes, 0 lost received
|   0x0 received sequence
| Transmit Class 0:
|   0x5A981B sent sequence
| Transmit Class 1:
|   0x313F82 sent sequence
| Member links: 2 (max not set, min not set)
|   Vi3, since 6d16h, 640 weight, 632 frag size
|   Vi4, since 6d16h, 640 weight, 632 frag size
|
| Someone here suggested that we try the ppp multilink slippage command
| but this sets a minimum time to wait for delayed packets.  Does anyone
| know how we can reduce the time the receiving router will wait
| (perhaps 50 ms) so that we can cover up slight differences between our
| physical links without introducing too much delay.
|

The command you want is "ppp timeout multilink lost-fragment <x>", however,
the minimum value is 1 sec (1000 msec).

I've filed an enhancement request CSCsa75457 requesting granularity of
milliseconds that can be tracked on CCO via the bug toolkit .

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bep

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