The 13 bytes for MLP mentioned on pg 1-15 has been subject for many debates on this list. Everybody has there own conclusion. Mine is that in the lab I would treat the 13 bytes as including the FR header and hence this is the value that I would use. I think if you use the codec calculator tool it will show 11 bytes as the correct value for MLPoFR. -- Vik Malhi CCIE #13890, CCSI #31584 Senior Technical Instructor - IPexpert, Inc.
Telephone: +1.810.326.1444 Fax: +1.810.454.0130 Mailto: vma...@ipexpert.com Join our free online support and peer group communities: http://www.IPexpert.com/communities IPexpert - The Global Leader in Self-Study, Classroom-Based, Video-On-Demand and Audio Certification Training Tools for the Cisco CCIE R&S Lab, CCIE Security Lab, CCIE Service Provider Lab , CCIE Voice Lab and CCIE Storage Lab Certifications. > From: Davide Fantin <fand...@gmail.com> > Date: Sun, 22 Feb 2009 16:23:25 +0100 > To: OSL Group <ccie_voice@onlinestudylist.com> > Cc: Mark Snow <ms...@ipexpert.com> > Subject: [OSL | CCIE_Voice] Re: Fw: Compressed voice call bw calculation > > Hi Mark and all, > > I am new in this list and was reading this interesting thread. > > I am a bit puzzled here about the MLP header size you used, 4 to 6 bytes. > The SRND at page 1-15 states it's 17 bytes "Multilink PPP (MLP) adds > 13 bytes of Layer 2 overhead". > So I would conclude that MLP over FR gives 17 (13 + 4) or 19 (13+6) > bytes whether you consider FR with 4 or 6 bytes. With these values you > come up with: > > 17 L2 > 40 IP+UDP+RTP > 20 Payload > ---------------------- > 77 bytes ==> (x8bit/bytes x50 pps) 30,8 kbps > with cRTP: 29 bytes ==> 15,6 kbps > > > 19 L2 > 40 IP+UDP+RTP > 20 Payload > ---------------------- > 79 bytes ==> 31,6 kbps > with cRTP: 41 bytes ==> 16.4 kbps > > > 1) This is quite a different range that the one you calculated. So I > am confused about MLP size, could you please comment? > > 2) Also, I'd like some one to confirm the calculation I normally do > for FR with FRF.12 I come out with these values: > > 8 L2 FR+FRF.12 > 40 IP+UDP+RTP > 20 Payload > ---------------------- > 68 bytes ==> (x8bit/bytes x50 pps) 27,2 kbps > > with cRTP: 30 bytes ==> 12 kbps > > > Thanks. > > Regards, > > Davide > >> Message: 2 >> Date: Tue, 10 Feb 2009 21:22:58 -0500 >> From: Mark Snow <ms...@ipexpert.com> >> Subject: Re: [OSL | CCIE_Voice] Fw: Fw: Compressed voice call bw >> calculation >> To: Cliff McGlamry <cl...@mcglamry.net> >> Cc: ccie_voice@onlinestudylist.com >> Message-ID: <859151d2-aa80-46fd-a146-1f1e251c5...@ipexpert.com> >> Content-Type: text/plain; charset=WINDOWS-1252; format=flowed; >> delsp=yes >> >> You are all correct that this has been kicked around a number of >> times. I have looked at the RFC, along with other peoples thoughts and >> without trying to "dumb down" anything, have come to this simple >> conclusion that I think should be considered: >> >> Whether you are looking at FR as being 4 bytes or 6 (depending on >> which headers (and FCS trailer) you are counting due to which you >> think the QoS scheduler may be taking in to account), and whether you >> are looking at MLPPP (by itself - without FR) as 4bytes or 6 (again >> depending on which publication you read) - the important thing is that >> they all come out to within 10% of each other and therefore all would >> be acceptable answers in the CCIE V lab according to the proctors. >> >> Here are a few "ideas" I have heard of header sizes with calculations, >> all figured with and without cRTP: >> >> 5 mp >> 4 fr >> 20 payload >> 40 ip/udp/rtp >> -- >> 69 bytes >> x 8 bits x 50pps >> 27.6kbps >> 12.4 with cRTP >> >> >> >> 6 mp >> 4 fr >> 20 payload >> 40 ip/udp/rtp >> -- >> 70 >> x 8 bits x 50pps >> 28kbps >> 12.8 with cRTP >> >> >> >> 6 mp >> 6 fr >> 20 payload >> 40 ip/udp/rtp >> -- >> 72 >> x 8 bits x 50pps >> 28.8kbps >> 13.6 with cRTP >> >> >> >> 7 mp >> 6 fr >> 20 payload >> 40 ip/udp/rtp >> -- >> 73 >> x 8 bits x 50pps >> 29.2kbps >> 14 with cRTP >> >> >> If we call the median 28k then 10% variation gives us a range from >> 25.2kbps up to 30.8kbps -- in which all of the below calcs fall into >> that range. >> >> >> BTW - at the end of the day - in the real lab you have the QoS SRND, >> which states 13 bytes for MLPPP. >> I would rely on that to be where they are basing their grading on, >> since that is what they put on your candidate desktop. >> >> >> IMHO, >> >> -- >> Mark Snow
