Would creating a loopback plug for the CSU side help to test if the problem is on the carriers side? In other words, if a up/up (looped) condition is maintained with a loppback plug...could one assume that it is not a local problem but the problem of the service provider? Dain. ""Priscilla Oppenheimer"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Here's the conclusion, since a few people have wondered about it. By the > way, the question had to do with an external CSU/DSU. > > According to Cisco documentation, a down/down serial interface means the > router interface cannot determine that CD has been asserted. As mentioned > earlier, a CSU/DSU acts more like a DSU than a CSU and presents a > synchronous signal to the router. The CSU/DSU must assert Data Carrier > Detect (DCD or CD), Data Set Ready (DSR), and Clear to Send (CTS). The > router, which is playing the DTE role, must assert Data Terminal Ready > (DTR) and Request to Send (RTS). For all these control leads to be > asserted, and for the router to recognize that they are asserted, the > router and CSU/DSU hardware must be operational, and the cabling must be > properly constructed. > > However, even if all hardware checks out, there are still cases when the > interface may be down/down or flapping between up/up, up/down, and > down/down. For example, some CSU/DSUs won't assert CD if the link to the > carrier is having problems. In these cases, check the CSU/DSU > configuration. Make sure the right clocking, framing, and encoding are > configured. If they are correctly configured, then call the service > provider and work with the provider to isolate the problem. > > Priscilla > > At 03:42 PM 6/22/02, Kevin Cullimore wrote: > >Some wrap-up comments: > > > >Challenged by the incompleteness of the cisco-press materials, I attempted > >to produce a complete taxonomy mapping configurations/conditions to > >interface/line up/down states. An unimaginably short attention-span cut that > >short, but I realized that maybe a superset of that information, up/down > >states AND the serial indicators shown at the bottom of the show interface > >command. That project ended similarly, but I believe that working in the > >other direction might be easier, wherein you tackle the task of categorizing > >the large set of circumstances responsible for the four interface states by > >examining the entirety of the output for both interface & controller show > >commands per misconfiguration, and gradually developing a profile for the > >entirety of the show output, allowing patterns to emerege that might render > >the first line of the show interface command somewhat intelligible. > > > >A real possibility is that the case of the integrated csu/dsu serial > >interface might have to be treated seperately from the the one involving a > >mere serial interface, due to the lack of interaction with an external > >device for those functions. > > > >The two references that dramatically increased my understanding of layer 1 > >operations are the paradyne 3160 manual and uyless s black's Physical Layer > >Interfaces and Protocols book. > > > > > >----- Original Message ----- > >From: "Priscilla Oppenheimer" > >To: > >Sent: 21 June 2002 8:02 pm > >Subject: Re: serial interface down/down or up/down [7:47101] > > > > > > > At 07:17 PM 6/21/02, Chuck wrote: > > > >""Priscilla Oppenheimer"" wrote in message > > > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > I guess the question is too hard for a practice test if NOBODY can > >answer > > > > > it!? > > > > > > > > > > > > >CL: surprise surprise we all THINK we know the answer byt realy we don't > >;-> > > > > > > My messages arrived asynchronously, when I meant for them to arrive > > > isochronously. ;-) Seriously, they arrived out of order. Despite all the > > > confusion, I do feel like I have an answer now. Thanks to everyone who > > > answered. > > > > > > Priscilla > > > > > > > > > > > > > > Here's the thing: Cisco says that a down/down interface means the > >router > > > > > interface is not sensing a Carrier Detect signal (that is, the CD is > >not > > > > > active). > > > > > > > > > > Now, from my studies of V.35 I know that data carrier detect (DCD or > >CD) > > > > > comes from the DCE side of the V.35 link, carried on pin 8, yadda, > >yadda. > > > > > It comes from the data interface on the DSU side of the CSU/DSU. > > > > > > > > > > If the router is correctly connected to the CSU/DSU, will it see CD > or > > > >does > > > > > the answer depend on whether the CSU/DSU is also correctly talking to > >the > > > > > telco? > > > > > > > > > > Does "carrier detect" mean literally what it sounds like it means? > >Would > > > > > the CSU/DSU not assert CD if there was a problem on the telco side? > >And > > > > > hence the router wouldn't see CD and would say the interface was > > > >down/down. > > > > > > > > > > > > >CL: in my old dial up to the BBS days, I always interpreted "carrier" as > > > >essentially a completed telephone call. I've carried that "idea" into > the > >T1 > > > >world I live in now. however, I think we all know the problem with Frame > >or > > > >ATM, where the line is up ( i.e. there is carrier ) because of LMI or > the > > > >ATM equivalent signalling, so dial backup doesn't kick in, even though > >end > > > >to end is down. > > > > > > > > > > > > > Not something I can easily test. Maybe I better simplify the > question. > > > ;-) > > > > > > > > > > > > >CL: personally, I enjoy getting into the nitty gritty of how things > >really > > > >work. Not that I need to, or that it is necessary, even in the > >certification > > > >quest. It just serves to broaden the perspective. It never hurts to > > > >understand things a bit better. > > > > > > > > > > > > > Priscilla > > > > > > > > > > At 06:34 PM 6/20/02, Priscilla Oppenheimer wrote: > > > > > >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 > > > ________________________ > > > > > > Priscilla Oppenheimer > > > http://www.priscilla.com > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com
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