two questions:1 relationship between dummynet and wireshark 2 how to add latency for each packet to be sent

[Luigi Rizzo]

On Thu, Nov 25, 2010 at 03:31:16PM +0000, nangergong wrote:
> Hi, all:
> 
> 1  relationship between dummynet and wireshark
> 
> I have a question on the relationship between dummynet and wireshark. Does
> wireshark capture packets before dummynet starts working or after? Which of
> the following charts is right?
> 
> (1)
>       send packets
> capture                                   add pkt loss, delay..
> A------------------> wireshark -------------------->
> dummynet--------------------------->
> 
>                                                                 add pkt
> loss,delay...                      capture
> network----------------->dummynet ------------------------->
> wireshark-------------> B
> 
> or
> 
> (2)
>       send packets                              add delay,loss
>                            capture
> A------------------> dummynet -------------------->
> wireshakr--------------------------->
> 
>                                                                 add pkt
> loss,delay...                      capture
> network----------------->dummynet ------------------------->
> wireshark-------------> B
> 
> At first, I think (1) is right, and I did a test using "ping". However
> during my following test, it seems that (2) is the fact:
> 
> I have two machines, A and B. When I play music on A, the RTP packets flow
> from A to B.  I added a pipe with packet loss and bandwidth limitation,
> which regulates the flow from A to B. Then I captured packets on A using
> wireshark. If the chart (1) is right, then the packets I captured on A
> should be the same to the music I played on A, however, this is not the
> truth.
> 
> 2 how to add latency for each packet to be sent
> 
>   I want to vary the delays(latencies) for different packets. So, is there a
> way to add latency for for each packet to be sent. For example, bind one
> pipe to one packet. Thank you!

hi,
wireshark is closest to the wire so it will intercept
incoming traffic before dummynet, and outgoing traffic
after dummynet.
As for binding pipes to packets, you can only do it if
those packets carry metadata (i.e. 5-tuple, length,
flags...) that ipfw can match and distinguish one packet
from another. Usually, though, this is not the case for
packets from the same flow.

cheers
luigi