Re: [dcp] sequence numbers on resend
Mark Handley <mjh@icir.org> Wed, 08 May 2002 16:58 UTC
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From: Mark Handley <mjh@icir.org>
X-Organisation: ICIR
To: "Patrick R. McManus" <mcmanus@ducksong.com>
cc: Eddie Kohler <kohler@icir.org>, dcp@ietf.org
Subject: Re: [dcp] sequence numbers on resend
In-reply-to: Your message of "Wed, 08 May 2002 12:39:16 EDT." <20020508163916.GA1532@ducksong.com>
Date: Wed, 08 May 2002 09:58:45 -0700
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>t0: xmit A->B Req SN=0 with data >t3: xmit A->B Req SN=1 with data > >t5: rcv A->B Req SN=1 with data >t5: xmit B->A Resp SN=0 ack=1 vector=0,192 >t6: rcv A->B Req SN=0 with data (dropped as we're in APP-ACCEPT) > >t7: rcv B->A Resp SN=0 ack=1 vector=0,192 >however new ack vectors at times > 6 will still represent >sn=0 as unreceived (which is untrue) and will impinge on A's cwnd for >a while. How does the receiver even know that sn=0 was sent? The ack vector it sends at t5 wouldn't cover 0 because the request ISN was 1. However the sender knows it was sent, and should act accordingly. >if A retransmits with the same isn (because it's the same data he is >only expecting one ack bit for) this problem goes away. The flipside is that if you send with the same ISN, in the same scenario, you also can't tell if the first packet was lost or not. The sender MUST assume it was lost (it sent two SYNs, got one ACK). So the problem is very similar, but there's less information if you don't increment ISN for the sender to go on. If you want to solve this corner-case problem correctly, I think you need to increment the ISN, and in this case back off the start of the ack-vector to 0 when you get the delayed request at t6 (you don't completely ignore it - it just doesn't cause a state-machine transition). Cheers, Mark _______________________________________________ dcp mailing list dcp@ietf.org https://www1.ietf.org/mailman/listinfo/dcp
- [dcp] Protocol Version number Alex Audu
- [dcp] Comments and Question Re: DCP drafts Patrick R. McManus
- Re: [dcp] Comments and Question Re: DCP drafts Eddie Kohler
- Re: [dcp] rcp-response packet reserved bits Eddie Kohler
- Re: [dcp] sequence numbers on resend Eddie Kohler
- Re: [dcp] sequence numbers on resend Mark Handley
- Re: [dcp] sequence numbers on resend Patrick R. McManus
- Re: [dcp] sequence numbers on resend Eddie Kohler
- Re: [dcp] sequence numbers on resend Patrick R. McManus
- Re: [dcp] sequence numbers on resend Mark Handley
- Re: [dcp] Protocol Version number Mark Handley