Re: LINK, 2.5g3g and CDMA2000

[Gorry Fairhurst <[e-mail]>]

> Please provide your feedback.
> --Farid
> 
> -----------------------------------
> 1. Disabling Van Jacobson TCP/IP Header Compression
> 
> Van Jacobson TCP/IP header compression (VJC) algorithm [35] is
> negotiated between peer PPP layers. In CDMA2000 networks it could be
> implemented between the Mobile Terminal Equipment, such as laptop computer,
> and the Packet Data Serving Node. The algorithm was designed to increases
> application layer throughput by reducing packetization overhead. In the
> absence of TCP segment errors, for MTU=1000 Bytes, enabling VJC increases
> throughput by about 4%.


"enabling VJC increases throughput by about 4%" - but you can only quote
numbers for packets with a specific TCP segment size. MTU =/= segment size.

> However, experiments have shown that in the presence
> of TCP segment errors,

"errors" is a bad term - I suggest you say "packet loss", if you mean loss.

> VJC is not desirable because it does not allow TCP to
> take advantage of Fast Retransmit Fast Recovery mechanism [n4].

When the loss occurs on the link using VJC - loss of a TCP data segment
could occur elsewhere along the forward path, and then FR/FR would work.

> VJC
> algorithm transmits not the TCP/IP headers but only the changes in the
> headers of consecutive segments. Therefore, a segment error

"error" should be "loss a TCP segment on the VJC link"

> causes the
> transmitting and receiving TCP sequence numbers to go out of synch. When a
> TCP segment is lost, none of the following segment will go through until RTO
> expires.

"go through" should be "will be forwarded by the link"

Suggest you refer to "draft-ietf-pilc-link-design"

> It is recommended to disable VJC algorithm unless TCP segment errors
> are very low.


I agree with Lloyd, it seems foolish at this stage not to also mention
ROHC for TCP, which is planning to address these issues directly.

Gorry Fairhurst