IMO, you can get away with saying that the distinction between DCE and DTE equipment only applies to WANs, but only because everything on the LAN side would be considered DTE equipment. The pitfall that students get presented with has to do with the labs they do in semester 2. It's the first semester of the Netacad curriculum where they actually configure routers, and they start looking for patterns when they do their cabling, particularly connecting ethernet interfaces and computer NICs. A very common conclusion that they draw is, "Routers and PC's are DTE, so switches and hubs must be DCE. When I plug DTE equipment into DCE equipment, I need to use a patch cable. If I'm going from DTE to DTE, I need a crossover cable."
That will work for 90% of the cabling that they do in semester 2, but there are two side effects that I try to head off. The first one is, uplink ports on hubs and/or switches don't fit nicely into the router/hub = dte/dce view. While it isn't exactly a high-performance networking setup, the majority of my students find themselves in an environment that uses cascading hubs at some point or another, and it doesn't do them any good to know how to configure routers if they botch the wiring of thier hubs. The second, and in my opinion worse, side effect is that the students at some level group hubs, switches, and CSU's together as DCE equipment, and in my experience that causes confusion later on in semester 4 (and semester 6 if I understand Tom correctly; my site isn't a CCNP academy so I wouldn't know) when they actually learn about WAN equipment. Meanwhile I think poor Phil's learning a very harsh lesson: Never ask a question on Groupstudy unless you're prepared for several LONG answers. ;) Cheers, Hal Logan CCAI, CCDP, CCNP+Voice Network Specialist / Adjunct Faculty Computing and Engineering Technology Manatee Community College > -----Original Message----- > From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]] > Sent: Wednesday, January 23, 2002 3:37 PM > To: [EMAIL PROTECTED] > Subject: Re: DTE/DCE definitions ? CCAI woes. [7:32924] > > > It's tempting to say that the terms DTE and DCE only apply to > WANs, but, in > fact, IEEE uses the term DTE to refer to stations, nodes, > hosts that reside > on LANs. When talking about "interconnect" devices, they call > them by their > actual name, such as repeater or bridge. I don't think they > ever use the > term DCE, although IEEE documents don't have indexes, so it's > hard to say > for sure. Argh. > > Does Cisco Networking Academy spell out DCE correctly (per > ITU-T) as Data > Circuit-Terminating Equipment? If so, that might help explain the > difference. In LANs, we have end-to-end virtual circuits > (with TCP, etc.) > The "terminating" devices are the end points themselves. (Make those > students learn a little TCP while you're at it?? ;-) One > really couldn't > claim that a LAN repeater, bridge, switch, or router > terminates a circuit > (with the exception of kludges like local ACK with LLC2.) > Well, I'm getting > beyond Cisco Academy here. ;-) > > With WANs, there is an actual circuit that implements the > user-network > interface between the DTE and DCE. Consider what happens when > you make a > phone call. The local phone switch at the Central Office provides > dial-tone, accepts dialed numbers, etc. That switch makes a > network-network > connection to another switch, which has a local connection to > the called > party. This is how WANs work also. They have a telephony > legacy, after all. > > LANs don't really behave like this, (although you could say that the > initial ARP to find the MAC address of the default gateway is > analogous to > the call setup protocols in WANs.) In general, however, a LAN > device makes > a "call" to another LAN device across the network. The devices in the > middle just act as relays. They don't communicate directly > with the end > devices; they just forward packets between end devices. ARP, > ICMP, and IGMP > are exceptions to this, but I wouldn't mention that right away when > teaching academy students. > > Howard Berkowitz has a "grand unifying theory" that compares > and contrasts > LANs and WANs and uses the terminology in a unifying and > elegant way. See > the first chapter of his book WAN Solutions Guide for a > summarized view of > his grand theory. He may have written it up in a Group Study > response in > the past also. See the archives. > > Hey, how did you get the CCAI gig? You seem very well > qualified for it. > Good luck with it. > > Priscilla > > > > At 07:47 AM 1/23/02, Phil Barker wrote: > >Hi group, > > > >I have just started teaching as a CCAI and was asked > >the following question yesterday in class. > > > >One student pointed out that the Sem 2 curriculum > >states that all devices on the LAN side of a > >connection are DTE's. > > > >I disagree with this statement. > > > >If we take a switch and a PC(DTE), this patches to the > >switch via a straight through cable. I conclude > >therefore that the switch port must be a DCE. (Is this > >safe thinking ?) > > > >If I uplink the switch to a Router(DTE) I use a > >straight through cable. My conclusion again is that > >the Switch port is DCE. > > > >If I link a PC(DTE) directly to a Router port(DTE) I > >use a crossover cable since they are both DTE's. > > > >Can I conclude therefore that an internal switch will > >in general be a DCE just as an ISP acts as DCE to a > >LAN. > > > >Regards, > > > >Phil. > > > >__________________________________________________ > >Do You Yahoo!? > >Everything you'll ever need on one web page > >from News and Sport to Email and Music Charts > >http://uk.my.yahoo.com > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=33095&t=32924 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
