[e2e] Reordering in routers

[Ghanwani, Anoop]

As far as I know, under normal circumstances most routers do not 
reorder packets.  I think Juniper routers had a problem with reordering,

but the general design practice (as far as I know) is that reordering 
is a no-no.

See
http://www.lightreading.com/document.asp?doc_id=4009&page_number=8
for an interesting discussion on this subject.

-Anoop

> -----Original Message-----
> From: abhijit [mailto:abhijit at engr.colostate.edu] 
> Sent: Friday, August 08, 2003 2:45 PM
> To: end2end-interest at postel.org
> Subject: [e2e] Reordering in routers
> 
> 
> Hi all,
> I am studying the packet-reordering problem over the Internet 
> from the point 
> of view of the routers being a reason of reordering.
> 
> In the paper by "Packet Reordering is Not Pathological 
> Network Behavior" by 
> Bennet, Partridge, and Shectman, the router queuing structure 
> was said to be 
> the reason behind the reordering observed at MAE-east. The 
> DEC gigaswitch used 
> at MAE-east point used hunt groups i.e. collection of ports 
> together acting as 
> input ports that caused the packets getting distributed and 
> hence reordered.
> 
> I am studying queuing architectures and queuing disciplines 
> of present 
> routers. But I do not find any routers with parallel input 
> queuing sothat 
> incoming packets are distributed over a number of queues 
> before getting 
> processed. It will be great if anybody can give me 
> information or pointers 
> over this problem, especially:
> 1. Are the internal structure issues i.e. queuing 
> architectures (input, output 
> queues, VOQ, VIQ etc), disciplines (packet scheduling or 
> buffer management 
> schemes) responsible or can be responsible for reordering?
> 2. Or the external reasons such as route flapping, multi-path 
> routing, 
> parallel links between two routers, etc. are more responsible 
> for reordering 
> happening in the present Internet?
> 
> I appreciate any information shared on this problem.
> Regards,
> Abhijit
> 
>