thotsaphon Sun, 04/26/2009 - 06:33

Hi Sam,


What is the FORWARD DELAY in stp and what is the dafault time for that.


Default : 15 s

Excerpt from a cisco document


forward delay


The movement of a port into the listening state indicates that there is a change in the active STP topology and that a port will go from blocking to forwarding. So the listening and learning periods during which the forward delay runs must cover this consecutive period:


*


Time from when the first bridge port enters the listening state (and stays there through the subsequent reconfiguration) to when the last bridge in the bridged LAN hears of the change in the active topology


In addition, you need to count the same delay that you use to calculate max age (message age overestimate and BPDU propagation delay).

*


Time for the last bridge to stop forwarding frames that are received on the previous topology (maximum transmission halt delay), until the last frame that is forwarded on the previous topology disappears (maximum frame lifetime)


This amount of time is necessary in order to be sure that you do not get duplicated frames.


Therefore, twice the time of the forward delay (listening time + learning time) contains all these parameters. The formula is:


2 x forward delay

= end-to-end_BPDU_propagation_delay + Message_age_overestimate +

Maximum_frame_lifetime + Maximum_transmission_halt_delay

= 14 + 6 + 7.5 + 1 = 28.5


forward_delay

= 28.5 /2

= 15 (rounded)



http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094954.shtml


Default : 15 s

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Can anyone also confirm..what are the codec used in VoIP.


It depends. You can use G.729 , G.711 etc.


http://www.tech-faq.com/voip-codec.shtml




HTH,

Toshi




netbeginner Sun, 04/26/2009 - 06:41

Thanks Toshi....


for VoIP codec question --> is there only 2 codec for VoIP.

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