Re: QoS - Calculating path latency

Well, it does not matter if the cable is 1 mt or 30km, because
that time is taken into consideration by propagation delay.

But tx serialization takes exactly the same time that rx
"deserialization" takes, and once you do the "time shift", they can overlap.

If you are able to see that the distance is not an issue, then you
should see that one bit out the tx buffer happens at the same "shifted"
time that the same bit enters the rx buffer.

Your sentence about not being able to start receiving until you end
transmitting is not true. It depends on which time is greater:
serialization or propagation...

-Carlos

Dave Serra @ 12/01/2013 17:06 -0300 dixit:
> hmmmm....I suppose on 10Gig links of short distances in a store and
> forward switch this might happen and it most certainly does happen on a
> LAN where R2 is a cut-through switch as R2 can be bringing a packet in
> while R1 is still serializing the tail end of it but lets assume that
> these are long (from california to NY) links of 56k. In this scenario
> R2 can not bring the packet into the router (what I am calling
> 'serialization delay'. maybe I should call it 'input-serialization
> delay' for better clarity) until R1 has finished serializing the packet
> and it reaches R2.
> Make a small loan, Make a big difference - Kiva.org
> *From:* Carlos G Mendioroz <tron_at_huapi.ba.ar>
> *To:* Dave Serra <maybeedave_at_yahoo.com>
> *Cc:* "ccielab_at_groupstudy.com" <ccielab_at_groupstudy.com>
> *Sent:* Saturday, January 12, 2013 2:58 PM
> *Subject:* Re: QoS - Calculating path latency
>
> Hey Dave,
> it might be that the R2 read serialization happens exactly as (during)
> R1 write serialization ? Then, they do not add up, but only one of them
> is used to account them both.
>
> -Carlos
>
>
> Dave Serra @ 12/01/2013 16:41 -0300 dixit:
> > I have a question. I've been reading Wendell Odom's cisco press book
> 'Cisco
> > QoS, Exam Certification Guide'. In it he calculates total latency
> for the
> > path as processing delay, serialization delay, propagation delay,
> etc... My
> > question is why do we calculate serialization delay only as the packet is
> > leaving the interface and being placed on the wire and not ALSO when the
> > packet is being received by the remote router. Surly there is some
> delay to
> > take an incoming packet off of the wire and store the bytes in memory
> prior to
> > processing it. So in other words, in the network as
> PC1-->R1-->R2-->PC2 why
> > are we not including the delay to get the packet off of the wire and into
> > R2. ie, assume packet is already in R1--> processing delay, seralization
> > delay of R1, propagation delay to reach R2 and then serialization
> delay again
> > to get the packet into R2 for its processing?
> >
> > BTW, I know I grossly
> > missquoted Odom by only including processing delay, serialization delay,
> > propagation delay, etc... He has a lot more delay types in his book. My
> > question really only focuses on the packet that is in R1 and getting
> into R2
> > so I omitted the others.
> >
> > I appreciate anyone's feedback.
> >
> > Thanks guys.
> > Make a small loan, Make a big difference - Kiva.org
> >
> >
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> >
> >
>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>> LW7
> EQI Argentina
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net