RE: Question about QOS taken from IE LAB 7 posted 06/01/2004
- Subject: RE: Question about QOS taken from IE LAB 7
- From: "Kenneth Wygand" <KWygand@xxxxxxxxxxxxxxxx>
- Date: Tue, 1 Jun 2004 19:38:36 -0400
- Content-class: urn:content-classes:message
- Thread-index: AcRIK1WpziudI6heQeisBauLHPsBtAABLq5p
- Thread-topic: Question about QOS taken from IE LAB 7
I'm not sure I understand all the details of the task you are trying to solve. However, you must make sure you understand the difference between _queuing_ delay and _serialization_ delay... Queuing delay is the delay experienced sitting in the output queue when the Tx ring is full. Serialization delay, however, is the time from the moment the first bit is placed on the line until the final bit is placed on the line of any given packet. Propegation delay is the time it takes an electronic pulse (and thus a bit) to traverse the medium (which is almost the speed of light which is negligible).
Serialization delay is a direct result of the size of the packet and the speed of the link, where serialization_delay_in_seconds = packet_size_in_bits / speed_in_bits_per_second. Ideally you want to keep serialization delay at 10ms, so you set your Bc to be 1/100th of your CIR (or access rate if you are not shaping/policing). So in your case, the CIR is 768000, so your Bc should be 768000/10 = 7680. Of course, you don't want a single packet to take up more than a single Bc, so you fragment all packets down to this size.
If there is any more to your question that I can help you with, please feel free to ask!
From: nobody@xxxxxxxxxxxxxx on behalf of Scott, Tyson C
Sent: Tue 6/1/2004 6:54 PM
Subject: Question about QOS taken from IE LAB 7
Quick question that is plaguing me on this scenario I have
done and I am not sure I understand how Serialization occurs on an
interface when it is done on a per VC basis. Serialization is stating
the amount of time it takes the interface to queue the packet and send
it out I believe. So with multiple classes applied on the interface is
each queue serviced independently or are they all the same.
For example you are asked to minimize the serialization of
VOIP traffic going from Router4 to Router5 and your CIR is 768000. To
minimize this I would set my Bc = 7680 and fragment any packets going
out that are greater than 960 bytes since 7680 bits = 960 bytes. There
is a second VC that goes from Router3 to ROUTER5 but with the second VC
they don't specify that the Bc should be set to a minimum. In the
solutions guide for this question it shows the Bc being set to 48384 but
wouldn't it also need to be set to 7680 and fragment anything above 960
to meet the requirements of TASK 1 or is each queue serviced
independently and I am not understand the term serialization delay?
Please help this is bugging me that I can't answer this question to
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