Transcript 30003023.ppt

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
TR30.3/00-03-023
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 inband 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-
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
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
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
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
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.
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
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 can be affected in both directions (upstream and
downstream) by Robbed Bit Signals
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
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
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
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
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