Well, the thing is that according to RFC timers A and B are not related like this.
Both timers are started when the initial INVITE is sent, timer A as T1 and timer B as
64*T1. Timer A is restarted after every retransmission with intervals that double, and
when timer B fires at 64*T1, INVITE was just transmitted for the seventh time. This is
the impression that I get from the RFC.
-Mika
> -----Original Message-----
> From: ext [mailto:[EMAIL PROTECTED]
> Sent: 29 August, 2003 11:33
> To: [EMAIL PROTECTED]; [EMAIL PROTECTED];
> [EMAIL PROTECTED]
> Subject: RE: [Sip-implementors] The seventh INVITE
> transmission - isn't
> itawaste
>
>
> Ah, no.
>
> Read the RFC carefully.
>
> "This process MUST continue so that the request is
> retransmitted with intervals that double after each transmission"
>
> ^^^^^^^^
>
> To me, "double" means multiply by 2.
>
> --> INV
>
> 500 ms = T1
>
> --> INV
>
> 2 x 500 ms (double of the previous one) 2 x T1
>
> --> INV
>
> 2 x 1 ms (double of the previous one) 2 x 2 x T1 (4 x T1)
>
> --> INV
>
> 2 x 2 ms (double of the previous one) 2 x 2 x 2 x T1 (8 x T1)
>
> --> INV
>
> 2 x 4 ms (double of the previous one) 2 x 2 x 2 x 2 x T1 (16 x T1)
>
> --> INV
>
> 2 x 8 ms (double of the previous one) 2 x 2 x 2 x 2 x 2 x T1 (32 x T1)
>
> --> INV
>
> 2 x 16 ms (double of the previous one) 2 x 2 x 2 x 2 x 2 x 2
> x T1 (64 x T1)
>
> Timer B
>
> You waiting 32 seconds before Timer B fires
>
> /Hisham
>
> > -----Original Message-----
> > From: ext Christian Jansson [mailto:[EMAIL PROTECTED]
> > Sent: Wednesday, August 27, 2003 3:54 PM
> > To: Khartabil Hisham (NMP/Helsinki); [EMAIL PROTECTED];
> > [EMAIL PROTECTED]
> > Subject: RE: [Sip-implementors] The seventh INVITE
> > transmission - isn't
> > it awaste
> >
> >
> >
> >
> > > The 7th transmission is 32*T1 (assuming T1 is 500ms, the 7th
> > > transmission occurs 16 seconds before the termination of
> > transaction).
> > >
> > > /Hisham
> >
> >
> > No. The 7th transmission is 32*T1 after the 6th transmission, so in
> > absolute time the 7th transmission is 63*T1 = 31,5s, that is
> > T1 (500ms)
> > before TimerB = 64*T1 fires. Look at the picture below.
> >
> > I also start to wonder why we wait 16s between the 5th and the 6th
> > retransmission but only waits 500ms after that before
> terminating the
> > transaction.
> >
> >
> > -------> INVITE sent for the first time at 0s
> > |
> > | T1 = 500ms
> > |
> > ---> 1st retransmission after T1 = 500ms
> > |
> > | 2*T1 = 1s
> > |
> > ---> 2nd retransmission after 3*T1 = 1,5s
> > |
> > | 4*T1 = 2s
> > |
> > ---> 3rd retransmission after 7*T1 = 3,5s
> > |
> > | 8*T1 = 4s
> > |
> > ---> 4th retransmission after 15*T1 = 7,5s
> > |
> > | 16*T1 = 8s
> > |
> > ---> 5th retransmission after 31*T1 = 15,5s
> > |
> > | 32*T1 = 16s
> > |
> > ---> 6th retransmission after 63*T1 = 31,5s
> > *<--- TimerB Fires at 64*T1 = 32s
> >
> >
> >
> > / Christian Jansson
> >
>
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