RE: Question about QOS taken from IE LAB 7

From: Kenneth Wygand (KWygand@customonline.com)
Date: Tue Jun 01 2004 - 21:06:18 GMT-3

Scott,
 
Yes I believe you are correct in your assumption. Maybe if we are wrong, someone can tell us otherwise.
 
Thanks,
Ken

        -----Original Message-----
        From: Scott, Tyson C [mailto:tyson.scott@hp.com]
        Sent: Tue 6/1/2004 7:47 PM
        To: Kenneth Wygand
        Cc:
        Subject: RE: Question about QOS taken from IE LAB 7
        
        

        Kenneth,

                  What you have stated is my understanding of Serialization. You confirmed what I thought but I have one more question.

                  So if serialization is the amount of time it takes for a packet to be transmitted out of the interface on to the line if you have multiple PVCbs coming out of the interface wouldnbt you want all of the PVCbs be < or equal to the maximum serialization delay you want on the interface.

         

        For this example I have two PVCbs and the interface rate is 1536. I want to split that between the two VCbs. So if I set the Bc on the mission critical to be 7680 and max fram size to coincide at 960 bytes would that also mean I would want to set the same on the second VC because if I have it at something greater than 7680 (Both CIRbs being equal to each other) I am going to cause serialization delay for the Critical RTP packets going out the mission critical circuit. Is this a correct understanding?

         

        Regards,

         

        Tyson Scott

        Agilent Problem Management Team

        Managed Network Services

        Phone: 313-583-5812

        Pager: 877-997-0811

         

        -----Original Message-----
        From: Kenneth Wygand [mailto:KWygand@customonline.com]
        Sent: Tuesday, June 01, 2004 7:39 PM
        To: Scott, Tyson C; ccielab@groupstudy.com
        Subject: RE: Question about QOS taken from IE LAB 7

         

        Scott,

         

        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!

         

        Thanks!

        Ken

                -----Original Message-----
                From: nobody@groupstudy.com on behalf of Scott, Tyson C
                Sent: Tue 6/1/2004 6:54 PM
                To: ccielab@groupstudy.com
                Cc:
                Subject: Question about QOS taken from IE LAB 7

                Group,
                
                          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
                myself?
                
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