Re: QoS - Calculating path latency

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
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________________________________
 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
>
>
> Blogs and organic
groups at http://www.ccie.net/
>
>
Received on Sat Jan 12 2013 - 12:06:21 ART