Re: PPP & Compression: Useful or Useless?
I am not an expert here but I am pretty sure I am correct about this.
Please flame me if I'm wrong :)
>First off, it was my impression that bsd_comp only affects ppp (TCP?)
>headers. It doesn't do any general data compression (so it wouldn't
>try to compress the jpg data in a packet, just the headers). I had
>heard that it is essentially always a win.
No, the bsd_comp is link compression, it affect all traffic transmitted
over the PPP link. Not all the many things support it. What you are
thinking of is VJ Compression (Van Jacobson) which was the difference
between SLIP and CSLIP and is a standard part of PPP. It compresses a 40
bit header to 8 bits(?) or something similar and is almost always a "Good
Thing'.
>> Note that compression protocols, while improving bandwidth, will
>> always introduce some amount of latency since encoding/decoding
>> takes compute time.
>
>This really depends on how you define latency. Let's say I want to
Well sorta. Latency has a meaning :) Latency is also known as propagation
delay and is a measurement of the *MINIMUM* amount of time that it can ever
take to transfer a packet over a link. Modems have a relatively high
latency and ethernet has a low latency.
It is really easy to confuse latency and bandwidth, they are not the same.
For those that are interested there was quite a good article in TidBits a
while back. You can read them at:
http://www.tidbits.com/tb-issues/TidBITS-367.html#lnk4
http://www.tidbits.com/tb-issues/TidBITS-368.html#lnk4
Adam.
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P.O. Box 5301 Adam Shand (fax) +64 3 477 5463
Dunedin, New Zealand Systems Manager (voice) +64 3 479 0303
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