Re: draft-ietf-pilc-2.5g3g-04.txt (TCP performance over CDMA2000 1X networks)Hi Farid,
Could you please describe which TCP and simulator has been used in your experiments? Also what is the latency of the link with and without SCH?
I would say that spurious RTOs are unlikely due to bandwidth oscillation if TCP uses default MSS of 536 Bytes and follows RFC2988 by implementing the minimum RTO of 1 sec. I assume that FCH can be used for transmission while SCH is being allocated. Then, in about half of the cases, the receiver has a delayed ACK outstanding and will send it out when the del. ack. timer experies. This ACK will restart the retransmit timer at the sender. In another half of the cases, the default MSS size is transmitted in less than half a second over 9.6 or 14.4 kbps link. That leaves another half a second to deliver an ACK which will restart the retransmit timer.
Andrei
----- Original Message -----
From: Farid Khafizov
To: 'pilc@grc.nasa.gov'
Cc: Mehmet Yavuz ; Farid Khafizov
Sent: Monday, November 19, 2001 8:14 PM
Subject: Re: draft-ietf-pilc-2.5g3g-04.txt (TCP performance over CDMA2000 1X networks)
We would like to bring our findings related to improving TCP performance over CDMA2000 1x (a.k.a., 1XRTT) networks
to the attention of this forum. Our results are based on simulations and lab measurements for FTP sessions.
We believe that our results are generally applicable to W-CDMA and, possibly, GPRS networks as well.
However, since we didn't simulate those networks, we can't claim that with absolute certainty.
Our hope is that the discussions on this email list will help to better identify
TCP performance improvement techniques which are applicable to all 3G wireless data networks.
Our view on 3g wireless links is that three factors make them different from other links:
- 3g wireless links are links with Errors (rfc3155 covers that part)
- 3g wireless links experience (some) bandwidth asymmetry (asymmetry ID covers that part)
- 3g wireless links experience "bandwidth oscillation" (see below)
In some cases bandwidth oscillation proved to be the most significant single factor
causing throughput degradation. (For more details please see the document).
We believe that effects of bandwidth oscillation will have to be addressed
in 3G wireless data ID because they will be present in any system which does
scheduling of RF resources.
We put our observations/recommendations in a document which was submitted
to IETF last week and can be accessed at
http://www.geocities.com/tsg_p/draft-khafizov-pilc-cdma2000-00.txt
We apologize for some typos left in the document.
--Farid
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