Wireshark-users: Re: [Wireshark-users] Question on Internet PerformanceTroubleshooting

From: Stephen Fisher <stephentfisher@xxxxxxxxx>
Date: Fri, 2 Mar 2007 13:43:58 -0800

On Fri, Mar 02, 2007 at 04:24:01PM -0500, Small, James wrote:

> 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.


Steve