Jack Douglass Chairman TIA TR30.3 2/22/00 T1E1.2/2000-029 T1E1.1/200-024

1. Operation of V.90 modems Over Cable Telephony/HFC (Hybrid Fiber Coax) Circuits that use T1 403.2 and GR-303 Signaling Jack Douglass Chairman TIA TR30.3 2/22/00 T1E1.2/2000-029 T1E1.1/200-024

2. Problem Description • A large percentage (estimated 90%) of legacy V.90 modems, when operating over some Cable Telephony/ HFC (Hybrid Fiber Coax) circuits that use in-band T1 403.2 and GR-303 Signaling have the following problems: • Fallback to V.34 mode • Fallback to low speed V.90 • Have significantly reduced throughput (even if a high connect speed is reported) • Problem also occurs on standard telephone line IDLC circuits that use in-band GR303 signaling

3. Problem Description(Continued) • Millions of V.90 client modems in the field are not optimized to operate over these circuits • Some V.90 client modems have been designed to handle this situation • Not all Cable Telephony and GR303 IDLC circuits have these problems, because some of the equipment manufacturers have recognized the problems and found solutions to them

4. Reason for the Problem • 0101 RBS Pattern • Many of the Cable Telephony circuits use a 0101 Robbed Bit Signaling (RBS) patterns for the ABCD bits to indicate Loop Current Feed (LCF) as specified in GR303 and T1 403.2 • Most V.90 client modems are optimized for operation with RBS patterns of 0000 or 1111 and don’t operate well over circuits with 0101 RBS patterns

5. Reason for the Problem (Continued) • Multi-Frame Alignment is not always used • Many of the Cable Telephony circuits don’t synchronize robbed bits, which results in up to 5 robbed bits being seen by the modem • All V.90 modems connect at lower speeds and have lower throughput when more bits are robbed

6. Reason for the Problem (Continued) • Fixed-loss plan is not always followed, which results in a high receive signal level • Typically modems are not optimized to operate over circuits with high receive levels since standard telephone lines have local loops, which attenuate the signal • V.90 modems operate better over the Cable Telephony circuits if there is a fixed loss of at least 6 dB in the downstream direction

7. Number of Reported Problems on Cable Telephony Lines • Some Cable companies are experiencing as many 50 reported problems/2500 installed lines • This number would be much larger if it were not for the following: • Many of the lines are used just for telephone service • Many of the users don’t report the problem to the Cable Telephony company • Many of the problems are reported to the ISP or modem manufacture instead of the cable company • Many of the users don’t know that they have a problem.

8. The problem doesn’t occur on most standard telephone lines • A large embedded base of standard telephone line IDLC circuits pass an RBS pattern of “1s” to the CODEC, because they are designed to TR08 • Standard telephone lines that don’t use IDLC circuits, typically pass RBS patterns of “0s” or “1s” to the CODEC, since the robbed bits come from the trunking part of the network

9. Steps that modem companies are taking to resolve the problem. • Investigating ways of optimizing the operation of V.90 modems when 0101 RBS patterns are encountered • Investigating ways of upgrading legacy V.90 client modems that are in the field • Many of the modems have limited memory • Many of the users are not technical enough to upgrade the modems themselves • Investigating ways to optimize the operation of future V.92 modems • V.92 is a new bi-directional PCM modem Recommendation being considered by the ITU • V.92 canbe affected in both directions (upstream and downstream) by Robbed Bit Signals

10. Steps that Cable companies are taking to resolve the problem • Sending technicians to the field to upgrade their customer’s modems • In extreme cases, they are replacing the existing legacy V.90 modems with newer modems that are more optimized to operate over these circuits

11. Other Options for Improving V.90 Performance on GR-303 and T1 403.2 Circuits • Providing Remote Data Terminal (RDT) signaling through a separate channel • Eliminates the RBS issues for that link • Provides the modem with a clear channel • Yields the best V.90 performance • Adding all 1s “Bit-Stuffing” into the downstream RBS signaling at the RDT • This will significantly improve the performance of legacy V.90 modems

12. Other Options for Improving V.90 Performance on GR-303 and T1 403.2 Circuits (Continued) • Synchronize the RBS patterns as they pass through the network for this application • Improves V.90 performance by limiting the number of frames containing robbed bits • Multi-Frame Alignment is specified by some operating companies • Inform the field about the possible problems and possible solutions to this problem

13. Other Options for Improving V.90 Performance on GR-303 and T1 403.2 Circuits (Continued) • Change RBS pattern from 0101 to 1111 or 0000 • Very difficult because this would require upgrading equipment in the field, modifying GR-303, and T1 403.2 • Partition the CO Switch and IDLC circuits to use 0000 or 1111 instead of 0101 for LCF signaling • This would cause administrative difficulty • Other methods that you recommend

14. Request for Assistance to Resolve this problem • TIA TR30 is open to any assistance, questions, comments or recommendations concerning this issue • Thank you for considering this issue and for working with TIA TR30 to help resolve it Finding a solution to this problem is in the interest of our common customers