In the past couple of weeks, we have run into a rash of HTU-R's no longer looping up to the 11000 code. We have been using this loop up since at least the 90's and it would loop up 99% of the SMJK's out there. There were a few extremely random ones that use a NYNEX code and just as rare ones that would use the ESF Data Link code.
Then a couple of weeks ago, we suddenly started finding multiple SMJK's that will not loop up with the 11000 and instead use the 16 bit ESF Data Link code. We are not sure why but it is causing issues for the remote testers that don't realize what is happening.
This leads to a couple of questions:
1.) What exactly is the ESF Data Link? I have copies of different SMJK manuals but none really explain what the difference is between the normal code and the ESF Data Link codes. It's not that the in-band codes don't work in ESF as that is normally what we use although sometimes they only accept it as Unframed.
2.) What would make the HTU-R's stop accepting the 5 bit codes and now require the 16 bit codes? It's not a specific carrier either. Different carriers are suddenly affected. I'm wondering if there is equipment in-network that is blocking things but that makes no sense either since it would mean multiple carriers all changed something at the same time. Or maybe it was an equipment patch and multiple carriers installed a patch.
Disclaimer: I don't know the version of the SMJK's as we are one of the major network carriers that test out to the local carriers. Most of the carriers do use Adtrans but I don't know the versions. I'm hoping someone in this group can answer this. I couldn't really find a forum on here that fit. This was the closest I could find.
The answers to your questions can be found in the T1 Testing Standards that all Equipment/Test Set Vendors are required to adhere too. Both In-band 5 bit and 16 bit codes are valid. The only solution is to try the In-band 5 bit code first and it that doesn't work try the 16 bit code. If neither code works the next step is to confirm the NIU/SMJK's Loopback option is Enabled.