i think if were bieng honest there is NO answer to this question... EACH lan is different EACH wan is different and to come up with a hard and fast rule to cover everyone is impossible.. there are so many variables to take into account how many routes are you advertising to how many people how big is the mtu how big is the header how much is taken up with call connection/teardown are you using hub-and-spoke are you using multipoint,NBMA,point-to-point ALL of these factors will be different for every wan you work on... i can`t say " oh 15% will be used in my wan"..this might not be the case... you have to just take each network as it comes... read all the info ...do you maths and go from there >From: "John Neiberger" >Reply-To: "John Neiberger" >To: [EMAIL PROTECTED] >Subject: Re: Theoretical vs. Actual Bandwidth - Refining the Question >[7:10001] >Date: Tue, 26 Jun 2001 16:36:06 -0400 > >Ah, this is one of those cases where I wasn't really answering the >question you were asking. :-) Sorry about that! > >I know I have some information like that around here but I can't find >it at the moment. Perhaps some of the listmembers that are more versed >in network analysis than I could provide some links. If I can find the >links that I've used in the past for this type of information, I'll let >you know. > >Regards, >John > > >>> [EMAIL PROTECTED] 6/26/01 2:04:07 PM >>> >You're comparing apples to oranges. A 10BaseT LAN is a shared medium, >which explains the oft-quoted-but-not-quite-accurate 40% max usage >figure. The theory is that with CSMA/CD, as traffic increases so do >collisions, which forces retransmits. This is exacerbated in a half >duplex environment. > >Dana's Comment - I realize that LAN and WAN environments are different. > I >was just using the 10Mb quote as an example. > >WAN links, such as a T-1, are synchronous (or isochronous or >pleisochronous or some other x-ochronous word that I don't understand) >full duplex connections. This means that frames are travelling boths >directions over the link at the same speed regardless of the amount of >traffic to be carried. In the case of a T-1, if you have 1.536 Mb/s >of >data to send, then go for it. The bandwidth is there if you need it. >For you hair-splitters, I'm purposefully not getting overly detailed. > >Of course, you have to factor in packet headers in your calculations. >Any data you have to send has to be encapsulated first. If you're >using >IP, then any data packets must be encapsulated with a UDP or TCP >header >and then with an IP header. This packet then must be placed inside >whichever datalink frame you're using, whether it's Ethernet, HDLC, >PPP, >or whatever. All of this creates overhead that you have to take into >account when calculating how much bandwidth you actually have >available. > >Dana's Comment - On WAN links, I just was wondering how what percentage >I >should give to headers, framing, signaling, etc. One Cisco SE told me >that >I should calculate 25% to cover those issues. I.E. On a 512K link I >could >only expect 384K of usable bandwidth. I figured that different >technologies should have different percentages - ATM vs. ISDN vs. Frame > >Relay etc. That is what I am looking for is specifics per technology >as >opposed to a general WAN figure. I hope these notes clarify my >question. > >But the moral of the story is that point-to-point WAN links suffer >from >different issues than CSMA/CD networks. > >Dana's comment - John, thanks for your comments. > >Regards, >Dana >CCNP, CCDP _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=10088&t=10088 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
