Subject: Asymmetric, thin and long (satellite) links

From: Markus Buchhorn <[email-masked]>
Date: Thu, 02 Sep 1999 15:16:59 +1000

Hi All 

I've had a question from a colleague in Australia facing an interesting
problem. Due to the high-expense of cable under the Pacific it appears that
one ISP is suggesting (or has in fact set it up) to put http downstream
traffic over a satellite link, nationally and internationally. This would
mean that requests go over terrestrial lines and responses come back over
satellite (to be reinjected onto terrestrial links locally).

http may not be the only traffic to face this modification, but it would
certainly be the highest impact. (ftp and email would cover a lot, then
there's the various multimedia streaming/realtime protocols, DNS, ICQ?, ...)

Besides the obvious impact of increased rtt's, or bandwidth*delay products,
(you can't go under the Pacific for less than 200ms rtt, or to geosynch and
back for much under 500ms) what other issues leap to mind, regarding tcp
performance on assymetric services and very-long/thin pipes? Malcolm asked
if there are any "classic" papers that cover this. I don't know of any
(although I'm looking at RFC2488 and its excellent references to start
with) but I see that the PILC charter has a couple of milestone documents
due about now:

 May 99 Submit Internet-Draft on long-thin networks (based on
draft-montenegro-pilc-ltn-01.txt) submitted to the IESG for publication.

 Jun 99 Draft on asymmetric network paths.

neither of which I can find online yet - so somebody here is presumably
working on this as I type :-) 

[oh - just found the first one at
http://mirror.aarnet.edu.au/ietf/internet-drafts/draft-montenegro-pilc-ltn-0
2.txt - sorry]

From Malcolm:
>[on Monday 6 Sep] we want to
>discuss issues of routing web traffic over satellite circuits.  (It would
seem
>that currently XXXXXXXX is routing our http traffic over satellite,
perhaps in
>one direction only)
>
>I have a feeling that there are a few classic papers about the problems of
>using tcp over satellite circuits, and the disadvantages of running tcp over
>asymmetric paths.

Any help, comments, advice, references, brickbats or bouquets appreciated !
By Monday would be great :-), but any time thereafter too would be very
useful. 

Thanks !

Cheers,
	Markus

Markus Buchhorn,  Advanced Computational Systems CRC     | Ph: +61 2 62798810
email: [email-masked], snail: ACSys, RSISE Bldg,|Fax: +61 2 62798602
Australian National University, Canberra 0200, Australia |Mobile: 0417 281429

---

From: "Barry Raveendran Greene" <[email-masked]>
Date: Wed, 1 Sep 1999 23:17:32 -0700

Hello Markus,

This is actually common now. Cuts the RTT satellite latency in half. Add
some redirection tools into the systems (policy based routing, L4 switches,
or equivalent) and you can push http over satellite and all other traffic
over the terrestrial link - keeping the terrestrial links free for latency
sensitive applications/services.

Better yet, stick WWW Caches on both ends of the hybrid
satellite/terrestrial backbone. It increases the "goodput" by locking up
http persistent connections between the two cache clusters. This is done by
one Asian ISP that I know of with many other looking into the WWW Cache/PEP
technique.

For some config details on how it's done on a Cisco, check out:

http://www.cisco.com/public/cons/isp/documents/Trans-Oceanic_Systems-BGP.pdf

of for some pictures (Power Point Presentation on a Trans-Oceanic Backbone
Seminar):

http://www.cisco.com/public/cons/isp/documents/Trans-OceanicInternetBackbone
sv1.zip

Barry

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On
> Behalf Of Markus Buchhorn
> Sent: Wednesday, September 01, 1999 10:17 PM
> To: [email-masked]; [email-masked]
> Cc: [email-masked]; [email-masked]; [email-masked]
> Subject: Asymmetric, thin and long (satellite) links
>
>
>
> Hi All
>
2.txt - sorry]

seem
perhaps in

Thanks !

Cheers,
	Markus

Markus Buchhorn,  Advanced Computational Systems CRC     | Ph: +61 2
62798810
email: [email-masked], snail: ACSys, RSISE Bldg,|Fax: +61 2
62798602
Australian National University, Canberra 0200, Australia |Mobile: 0417
281429