And to add some more confusion - some CSU/DSUs (Larscom) use a EIA-530 cable. In Europe either X.21 or V.35 are used depending on country and (I think) speed. I am guessing that a EIA-530 carries the same signals as a V.35 but uses a different form factor plug (DB-25).
> -----Original Message----- > From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]] > Sent: Friday, June 21, 2002 2:08 PM > To: [EMAIL PROTECTED] > Subject: Re: serial interface down/down or up/down [7:47101] > > > At 01:42 AM 6/21/02, John Neiberger wrote: > >This isn't quite true. > > I agree. I think the materials Michael was looking at > overgeneralized. > Words like "only" and "always" just don't come into play with > networks > unless you're talking about the speed of light or something. ;-) > > Seriously, this much I know is true: > > The link between the router serial interface and the CSU/DSU > (which Howard > tells me is really a DSU) is V.35. The router acts as DTE. > The CSU/DSU acts > as DCE. (We tend to think of the switch in the provider's > office as being > DCE which is true also, but on the local level, the DSU is > acting as DCE). > > On a V.35 connection, this much I know is true: > > DTE is responsible for DTR and RTS > > DCE is responsible for Data Carrier Detect (CD), DSR, and CTS. > > Numerous things can go wrong to cause the DTE or DCE not to > assert one or > more of these. They have to all be asserted for the > interfaces to be up/x. > > However, are all those things local to the V.35 endpoints and > cabling? Or > could a problem out the other end of the DCE (out the carrier > side of the > CSU/DSU) cause them not to be asserted? Could a > misconfiguration of framing > or encoding on an external CSU/DSU cause a problem that resulted in a > down/down interface? I think from the answers that I'm > getting that the > answer is yes. (or at least flapping and sometimes being down/down ;-) > > Thanks everyone for your help. Don't I come up with some good > ones? ;-) > > Priscilla > > > For example, a DCE router interface will be > >down/down if DTR is not raised by the DTE device. I see this quite > >often at work and faulty cabling is generally not the culprit. It's > >almost always bad hardware in the DTE. > > > >John > > > >Michael L. Williams wrote: > > > According to CCIE exam materials, the *only* time the > serial will show > > > down/down is when there is NO serial cable or a bad serial cable > connected. > > > So even if you have a misconfigured framing method, you > should at least > see > > > up/down..... > > > > > > Mike W. > > > > > > "Bob Timmons" wrote in message > > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > >>I can't say I've ever seen a down/up condition. Up/Down perhaps. > > >> > > >>I'm sure there are exceptions, but it's my belief that > the router doesn't > > >>care about encoding, but rather a layer-1 connection to > the dce/dte > > > > > > device. > > > > > >>If the router can 'talk' to the device on the other end > of the cable, you > > >>should get an up/x condition, where x would depend on the csu/dsu > > > > > > condition > > > > > >>of the line. > > >> > > >>I don't have a csu handy, otherwise I'd check that right > now. I can do > > > > > > that > > > > > >>tomorrow morning (10:30 pm est here), but you may have an > answer prior to > > >>that... > > >> > > >> > > >> > > >>>Hi Priscilla, > > >>> > > >>>I have actually had this scenario (multiple times), but > due to the > > >> > > > Telco's > > > > > >>>misconfiguration. > > >>>Specifically we were expecting b8zs/esf. Unfortunately I > can't confirm > > >>>which was configured incorrectly, but I can confirm that > going through > > >>>all of the different combinations available at the > router you will > > >>>get all combinations on the serial interface (up/up, down/up and > > >> > > >>down/down). > > >> > > >>>I can also confirm, you will not establish connectivity, > regardless. I > > >>>believe > > >>>either b8zs/esf or sf/ami are the only valid > combinations. At least that > > >> > > >>is > > >> > > >>>all I've > > >>>ever worked with. > > >>> > > >>>Hope this helps, > > >>>-TV > > >>> > > >>> > > >>>""Priscilla Oppenheimer"" wrote in message > > >>>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > >>> > > >>>>Hi Group Study, > > >>>> > > >>>>While writing some questions for a practice test, I found myself > > >>>>questioning what I thought was the right answer. Here's > the scenario: > > >>>> > > >>>>A Cisco router serial interface is correctly connected > with a good > > >>> > > > V.35 > > > > > >>>>cable to the data port on the DSU side of a CSU/DSU. > The CSU/DSU has > > >>> > > >>been > > >> > > >>>>misconfigured for the framing method (SF instead of > ESF). The framing > > >>>>doesn't match what the provider is using. (The question > refers to a > > >>> > > >>>CSU/DSU > > >>> > > >>>>that is external to the router, not one that is built into the > > >>> > > > router.) > > > > > >>>>Will the Cisco router serial interface be down/down or up/down? > > >>>> > > >>>>And, would the answer be any different if the question > has to do with > > >>>>misconfiguring the encoding (AMI versus B8ZS)? > > >>>> > > >>>>If you have real-world experience with this, that would > help. I have > > >>> > > >>read > > >> > > >>>>the Cisco documentation and the troubleshooting charts, etc. > > >>>> > > >>>>Thanks > > >>>> > > >>>>Priscilla > > >>>> > > >>>>________________________ > > >>>> > > >>>>Priscilla Oppenheimer > > >>>>http://www.priscilla.com > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=47156&t=47101 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
