Wireshark-users: Re: [Wireshark-users] Question on InternetPerformanceTroubleshooting

From: "Small, James" <JSmall@xxxxxxxxxxxx>
Date: Fri, 2 Mar 2007 17:01:09 -0500

Steve,

I believe the 3 T1 are multiplexed using multilink PPP using an Adtran
router if I remember correctly.

Is there any way to tell if this PPP bundle is causing out of order
packets or other issues?

Thanks,
  --Jim

> > One off the wall idea - the site had two T1's (3.0 Mbps) multiplexed
> > via PPP before.  The problems seem to start close to around when
they
> > added a third T1 (again via PPP) for a total of approx 4.5Mbps.  Is
> > there any chance that this could cause issues - seems to be a pretty
> > standard provider setup...
> 
> How are the three T1s load-balanced?  Multilink PPP or just using
three
> paths that the routers see between each other?  When there are just
> three paths seen between the routers, the routers will often cache
which
> destination goes over which circuit so the packets are transmitted
> across the same circuit in proper order for each destination on the
> other end.  Multilink PPP sends the packets in more of a round-robin
> fashion, where one of the packets could get caught behind a larger
> packet on say the first T1 while two other packets from the same
session
> make it across the other two T1s quickly.  This would cause
out-of-order
> packets.  Although that case is usually confined to slower speed links
> (< 768Kbps) and is called serialization delay.