North American Network Operators Group

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RE: Satellite latency

  • From: David Luyer
  • Date: Wed Mar 06 00:57:53 2002

Tony Rall wrote:
> > Specifically made for satellite networks:
> > ip tcp window-size 750000
> I don't understand the benefit of this on a router.  Except for 
> connections where the router itself is an endpoint (telnet to the
> for example), the router has no need to even be aware of window size.
> Perhaps the router's window size comes into play if the router is 
> performing advanced functions such as NAT or IPSEC?

I don't expect the router would do anything in the NAT case, but a
proxy used to work magic in the satellite days in Australia (before
Cross).  A SOCKS proxy would do the same but be far more intrusive.

Basically a customer accessing a US web site ends up looking like this
hops deliberately missed):

DIAL CUSTOMER (customer tcp stack)
 medium latency hop (modem)
 layer 4 switch or router with WCCP or policy routing
PROXY FARM (good tcp stack with good window sizes)
 high latency hop (satellite)
 US internet
US WEBSITE (server tcp stack)

Often the server TCP stack and the customer TCP stack may be dodgy and
even unable to directly communicate, but the good TCP stack in the
middle can
communicate to both of the dodgy TCP stacks at either end as well as
a good window size to receive from the server and splitting the latency
half on each TCP connection leg as to a direct connection.

David Luyer                                     Phone:   +61 3 9674 7525
Network Development Manager    P A C I F I C    Fax:     +61 3 9699 8693
Pacific Internet (Australia)  I N T E R N E T   Mobile:  +61 4 1111 BYTE                      NASDAQ:  PCNTF