Sprint Frame Relay 1

[bugmn99]

I've got a question for anyone who normally deals with a Frame Relay provider (ours is Sprint).

We're experiencing an issue with our East-West coast frame relay link frame relay circuit. As per procedure, I submitted a ticket with Sprint to take the circuit for testing. My question is, what exactly would be entailed in the testing they do on a frame relay circuit? When they do test, it normally means shceduling downtime as the circuit is unavailable. Any idea what sort of testing would cause this?

 

[lgarner]

In my experience, it depends on whether they'll be doing intrusive testing. If so, they'll loop the CSU or smartjack on site and watch for errors. That will take the link down.

 

[jeter]

I work for Sprint and the above comment is correct. Sprint will run intrusive to look for errors on the span. What problems are you having that Sprint is looking at the circuit?

“Reserve your right to think, for even to think wrongly is better than not to think at all”

CCNA,CCNP,CIPT, Network+
Tek-TIP Member 19,650

 

[bugmn99]

We're seeing the interface going up and down every few minutes, as well as a ton of CRC and other errors. This is at a remote site so I'm not able to go physically check out the CSU/DSU.

I've heard them mention a smartjack before, lgarner. What is that?

 

[robertjo24]

The "Smart Jack" is the interfacing device that supplies the T1 to your equipment. This "box" allows the Telco to remotely loop back the T1 interface so they can run pattern tests to look for errors.
If they run intrusive tests and report no errors, request that they conduct passive monitoring. If they then see errors, they can call you to request the circuit for intrusive test durting the time of the fault.
If they say they cannot find any problems, which happens more often that we would like to see, request they dispatch the Telco to test head to head from the site.
This requires that a Telco tech be on site, and actually plug in a test fixture in the physical jack on the smart jack.
We have seen issues with the older line interface units, (smart jacks) where they remotely loop for testing and find no errors, but start incrementing errors upon release. It turns out to be faulty physical connections on the card or wiring in the case of the unit.
I would also check the cabling between the smart jack and your CSU/DSU.
Here are a couple questions:
Do you have an extended demark or is your router near the smart jack?
Do you run routers with integrated or external CSU/DSU's?
What type of cable are you using to interconnect the T1 to your equipment?
How long is the cable run, and who installed it?

 

[bugmn99]

I do know that we use an external CSU/DSU. I'm not entirely sure about the demark, although I get the feeling that the smart jack is close by, just by hearing people describe the area out there. Out of curiousity, what difference would there be in troubleshooting an extended demark?

The specs on the cable are something I'd probably have to dig for. I'm still learning where we keep these things - I'm fairly new here ;-) (Of course, the great thing about being new is that you do tend to dig for things like that and then all the old-timers are like 'Wow, I didn't even know we had that. That would've helped us a few months ago!')

 

[robertjo24]

Extended demarks can be an issue if the smart jack and the telco demark are separated by end user owned in house/in plant cabling. If there is an issue with faulty wiring, it will show up as errors when they loop the unit. Also, if the cabling is owned by you, the telco will nearly always point to your cabling as the issue. If the CSU/DSU is separated by a long distance from the smart jack, you can also induce problems on the cable.
You can cause problems by running the cables too close to fluorescent lighting, unshielded power, or VFD’s (variable frequency drives). We had a particular nasty network issue with a tech running an unshielded comm. cable too close to the VFD cabling.

As far as the cable between the smart jack and the CSU/DSU, I would look at the length and condition of this cable. If the CSU/DSU is relatively close to the smart jack, there is no reason why you cannot use a standard Cat5e patch cord to connect the two. If they are separated by a greater distance, you may have a custom made cable. If the cable runs near to and parallel with any power cables, I would consider moving/rerouting it.

As far as the separate CSU/DSU goes, the telco can loop your CSU/DSU, but it only tests it so far. I would check the interconnect cable between the CSU/DSU and make sure it is tight and not twisted tightly, or run adjacent to power. If this all looks good, I would consider swapping out the CSU/DSU.

I personally never had a router with an external CSU/DSU show up with a bad serial interface on the router, it is usually the external equipment facing the telco. Sometimes you can take a hit on the T1 and it will mess with the CSU/DSU.