Date: Fri, 25 Jun 2004 10:14:18 +1000 From: Tim Robbins <tjr@freebsd.org> To: "Wilkinson, Alex" <alex.wilkinson@dsto.defence.gov.au> Cc: current@freebsd.org Subject: Re: HEADS UP: SACK committed to HEAD Message-ID: <20040625001418.GA12712@cat.robbins.dropbear.id.au> In-Reply-To: <20040624234634.GA15795@squirm.dsto.defence.gov.au> References: <20040623210825.GA19715@elvis.mu.org> <20040624221612.A30E35D08@ptavv.es.net> <20040624234634.GA15795@squirm.dsto.defence.gov.au>
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On Fri, Jun 25, 2004 at 09:16:38AM +0930, Wilkinson, Alex wrote: > erm .... what is SACK ? I'm assuming ACK is 'acknowledgment ? > Quick summary anyone ? >From RFC 2018: TCP may experience poor performance when multiple packets are lost from one window of data. With the limited information available from cumulative acknowledgments, a TCP sender can only learn about a single lost packet per round trip time. An aggressive sender could choose to retransmit packets early, but such retransmitted segments may have already been successfully received. A Selective Acknowledgment (SACK) mechanism, combined with a selective repeat retransmission policy, can help to overcome these limitations. The receiving TCP sends back SACK packets to the sender informing the sender of data that has been received. The sender can then retransmit only the missing data segments. Tim
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