Many thanks for that Priscilla! I was pushing the limits of terminology almost (hopefully just almost) to the point of clouding the issue more than clarifying it.
I wonder if you, and others, would comment on ppp as a character-oriented protocol. I did a search on the internet and found some university teaching papers that characterize synchronous ppp as character-oriented while at the same time acknowleging the fact that it is based on the bit-synchronous HDLC frame format. I guess the LCP is the culprit? This is purely acedemic of course but interesting nonetheless. It seems kind of a hybrid to me. An out-of-band but yet sorta in-band character-oriented aspect that advances to purely (in my opinion) bit-synchronous operation (to include the HDLC flag). Regards, Scott Priscilla Oppenheimer wrote: > > Nice job on bit-serial. > > The question of whether WANs are reliable and > connection-oriented requires > more explanation. I acknowledge Howard Berkowitz for teaching > me this new > way of looking at the question. > > To understand PPP, ISDN, Frame Relay, X.25, and probably many > other WAN > protocols, it helps to recognize that these protocols have > control and > management planes that carry signaling and overhead > information. The > control and management planes are separate from the user plane > that carries > user data. > > Think of the ordinary 7-layer model as the front (main plane). > Now think of > the model as being 3-dimensional, with a control plane and > management plane > in addition to the user plane in front. > > The behavior of the control and management planes may be quite > different > than the behavior in the user plane. In fact, the control plane > is probably > connection-oriented and reliable, whereas the user plane is not. > > The control plane handles call setup. Think of what happens > when you make a > telephone call. (Because WAN protocols have a telephone network > legacy, it > makes sense to use a telephone example.) When you lift the > handset off the > cradle of your telephone, the switch at the telephone company's > local > office senses that your telephone has gone off hook, provides > dial tone, > and accepts the numbers that you dial. This happens in the > control plane. > The interconnected switches that permit national and > international calls > also communicate with each other in the management plane, using > complicated > routing and administrative protocols such as Signaling System 7 > (SS7). The > user plane sends the actual telephone conversation. > > This division of tasks also occurs in both LAN and WAN > networks, although > one difference is that the control plane protocols for WANs are > often quite > complex. (In LAN environments, people don't pay much attention > to the > control plane, although both ARP and IGMP could be considered > control plane > functions.) Control plane protocols in the WAN world include > LCP in PPP, > LAPD in ISDN, LAPF in Frame Relay, and LAPB in X.25. > > NOTE > See the first chapter of Howard Berkowitz's "WAN Survival > Guide" (John > Wiley & Sons, 2001) for an elegant explanation of the different > OSI planes > and their functions. > > Priscilla > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=34701&t=34629 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
