Re: bandwidth saving idea

[Oscar Mechanic <oscar@ufomechanic.net>]

On Mon, 2005-07-11 at 15:26 +0200, Eric Leblond wrote: 
> Le lundi 11 juillet 2005 à 14:16 +0100, Oscar Mechanic a écrit :
> > Machine A sends a packet to machine B. As the packet passes through
> > If the same packet is sent again through A it does not send the payload
> > to Machine B but sends the checksum. B sees the checksum finds the
> > payload and replaces the checksum with the payload.
> 
> Well, there's a problem with protocol like TCP, you've got SEQ number
> and other flags in TCP header that are changing even if the datas
> contained in the packet are the same. Thus your compression protocol is
> not efficient. Even a 1000 unit FIFO is useless. Furthermore, your
> protocol is theoritically wrong, as checksum functions are not
> injective.
> 
> You better try to set up an ipsec tunnel with compression between the
> two machines. On protocol other than citrix, this can bring you a good
> compression level (30% or more if I recall correctly some tests I've
> made).
> 
> BR,

Thank you for your response I have looked at ipcomp in detail and find
it a mature and well developed protocol. 

The TCP flags would have to be short sequenced to numeric codes. The
sequence number I will have to think about, as a single packet in the
stream is fine as it would have the same SEQ number. 

Products that work similar to this are already available and as they
most probably already using a BSD or Linux as an RTOS we will just have
to wait forever to see the code.

I do not understand "checksum functions are not injective" my intention
was to hold a name=value list where name is checksum and value is
payload (or reference to payload on disc/FC/RD). 

Regards
Oscar Mechanic