Subject: [Tsvwg] Eifel draft and usage of time-stamps.

From: "sanjay kaniyar" <[email-masked]>
Date: Mon, 31 Dec 2001 14:53:29 -0800

I have seen the spurious retransmission problem occur in my experiments with 
GPRS networks. The frequency of occurrence seems to be quite small though, 
about once or twice during the transmission of a 500 K Bytes file with an 
MSS of 1500 bytes. Ofcourse, I agree that this frequency could vary with 
different networks. In this case, however, incurring 12 bytes of overhead in 
every segment and acknowledgemnt seems quite a bit.

Since it is not necessary to timestamp every segment and acknowledgement 
when timestamp option is enabled on a connection, we could do it only when 
it is necessary. It is the sender which determines when this is necessary, 
and the following approach is backwards compatible in the sense that a 
sender taking this approach would work properly with a receiver adhering to 
the traditional time-stamping approach and vice-versa.

Sender-TCP would put a timestamp in a segment if:
(a) PAWS protection is necessary for the connection.
(b) An RTT measurement using timestamps is desired, and one such measurement 
is in progress. We consider a measurement to be in progress if sender has 
sent a timestamp after it started a measurement and it is not yet echoed 
back.
(c) Retransmission of a segment upon timeout.

Receiver-TCP would put a timestamp (or echo what it got) in an ack if:
(a) no more than 3 acks have been sent after any segment with a timestamp 
was received.

An Eifel-TCP-Sender would consider an acknowledgement received after a 
timeout to be for the original segment if (a) the acknowledgemet does not 
contain a timestamp or (b) the echoed timestamp is less than the timestamp 
sent in the retransmitted segment.

Thanks,
Sanjay

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