round trip delay in RTCP packets

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How to calculate the round trip delay in a RTCP packets using Ethereal for
windows?

According to H.225, in a RTCP frame and RTP informations, we can calculate
round trip delay with the formula " delay=A - LSR - DLSR".

Parameters A and DLSR are easily find in a Ethereal rtcp frame :

1) A is the time the rtcp frame arrived since the begining of the call.

2) DLSR in seconds, is the number informed in dlsr positions divided by
65536.

3) But is hard to understand the big number in "Last SR time stamp" . How
to find LSR in seconds? According to H.225, LSR is the middle 32 ou 64 of
last NTP time stamp.

Please see the capture below of a Voip call:

(Embedded image moved to file: pic11647.pcx)



(Embedded image moved to file: pic17432.jpg)


Alfredo Guimarães Menezes
Furnas Centrais Elétricas SA
DET.T Depto de Engenharia de Telecomunicações
Divisão de Engenharia de Telefonia e Sistemas Auxiliares
Rua Real Grandeza 219 sala 308 Bloco B
Botafogo Rio de Janeiro  RJ Brasil CEP 22281-900
Tel  (21)2528-5770/4909
Fax (21)2528-2186
email: [email protected]


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