Hi Arjuna, By my reading of RFC 4342, it seems to be talking about the *initial* sending rate -- that would be before you know what the RTT is. Is this confusion over initial sending rate of 1 packet/second instead of 1 packet/RTT? They're functionally equivalent -- as soon as you get feedback from the receiver you're next rate is 2 packets/RTT (per RFC3448). For CCID 3, the initial rate is up to 4 packets per second or RTT -- however you wish to look at it -- and after feedback it's up to 8 packets/RTT. Tom P. > -----Original Message----- > From: Arjuna Sathiaseelan [mailto:arjuna.sathiaseelan@xxxxxxxxx] > Sent: Wednesday, August 16, 2006 10:17 AM > To: Phelan, Tom > Cc: 'dccp' working group; Gorry Fairhurst > Subject: Re: CCID 3 - Slow Starting with One packet per second.. > > Hi Tom, > Thanks for your reply :). Yes it does, but I thought it was only > after it has got a RTT sample (which is got by setting the rate to one > packet per SECOND, sending that packet and when the feedback is > received) and then setting to 2 or 4 packets per RTT? RFC 4342 says: > > "[RFC3448], Section 4, specifies an initial sending rate of one packet > per round-trip time (RTT) as follows: The sender initializes the > allowed sending rate to one packet per second. As soon as a feedback > packet is received from the receiver, the sender has a measurement of > the round-trip time and then sets the initial allowed sending rate to > one packet per RTT. However, while the initial TCP window used to be > one segment, [RFC2581] allows an initial TCP window of two segments, > and [RFC3390] allows an initial TCP window of three or four segments > (up to 4380 bytes). [RFC3390] gives an upper bound on the initial > window of min(4*MSS, max(2*MSS, 4380 bytes)). > > Therefore, in contrast to [RFC3448], the initial CCID 3 sending rate > is allowed to be at least two packets per RTT, and at most four > packets per RTT, depending on the packet size. The initial rate is > only allowed to be three or four packets per RTT when, in terms of > segment size, that translates to at most 4380 bytes per RTT." > > Am I confused? :) > > Regds > Arjuna > > On 8/16/06, Phelan, Tom <tphelan@xxxxxxxxxxxx> wrote: > > Hi Arjuna, > > > > CCID3 allows an initial sending rate of at least two and up to four > > packets depending on the packet size (up to 4380 bytes in the initial > > burst of three or four packets). > > > > Tom P. > > > > > -----Original Message----- > > > From: Arjuna Sathiaseelan [mailto:arjuna.sathiaseelan@xxxxxxxxx] > > > Sent: Wednesday, August 16, 2006 5:27 AM > > > To: 'dccp' working group > > > Cc: Gorry Fairhurst > > > Subject: CCID 3 - Slow Starting with One packet per second.. > > > > > > Dear All, > > > I presume that CCID 3 is still following RFC 3448's slow start > > > behaviour of 1 packet per second during the start of the connection, > > > and when the ACK is received for that packet, the INITIAL ALLOWED > > > SENDING RATE is set to 2 packets to 4 packets per RTT appropriately. > > > > > > Now my question is do we still need to follow TFRC's way of starting > > > with one packet per second to determine the RTT estimate? Since, DCCP > > > has its initial three way handshake similar to TCP, can CCID3 use the > > > handshake to determine the RTT and start with an initial allowed > > > sending rate set to 3 or 4 packets accordingly? > > > > > > Based on this paper, using the SYN/ACK, RTT could be accurately > > measured. > > > http://www.acm.org/sigs/sigcomm/ccr/archive/2002/jul02/ccr-2002-3- > > > jiang.pdf > > > > > > I guess starting with one packet per second , induces an additional > > > RTT's worth of delay which may not be good for certain applications > > > such as VoIP running over a satellite network.. > > > > > > Correct me if I am wrong..thanks > > > > > > -- > > > Regards, > > > Arjuna > > > > > > Postdoctoral Researcher > > > Engineering Research Lab, > > > Department of Engineering, > > > University of Aberdeen > > > > > > > -- > Regards, > Arjuna > > Postdoctoral Researcher > Engineering Research Lab, > Department of Engineering, > University of Aberdeen
