Telecommunications Industry Association
(TIA)
TR-30.3/00-12-881
TR-30.3 Meeting, Scottsdale, AZ, Dec 5-8, 2000
COMMITTEE CONTRIBUTION
Technical Committee TR-30 Meetings
TITLE:
Sources of Crosstalk at the CO
SOURCE:
Conexant
CONTRIBUTOR:
Mounir Ayoub
Conexant
PROJECT:
TR-30:
Office Tel:
Office Fax:
E-mail:
(949) 483-6321
(949) 483-7374
mounir.ayoub@conexant.com
PN4254/PN4255
_______________________________
ABSTRACT
This contribution uses a simplified Central Office model to propose that “Composite CEXT” need not be
considered separately from NEXT in the impairment tables of PN4254 Volume 1.
Copyright Statement
The contributor grants a free, irrevocable license to the Telecommunications Industry Association (TIA)
to incorporate text contained in this contribution and any modifications thereof in creation of a TIA
standards publication; to copyright in name any standards publication even though it may include
portions of this contribution, and at TIA’s sole discretion to permit others to reproduce in whole or in
part the resulting TIA Standards publications.
Purpose
The purpose of this contribution is to show through a simplified Central Office (CO) model that it may
not be necessary to consider “Composite CEXT”, which is currently represented by the “y” factor in the
impairment combination tables of PN4254 Volume 1, separately from NEXT.
Simplified CO Model
The CO model presented in section 5.2.1 of PN4254 Volume 1 Figure 5 is shown below for reference:
Line Sharing
400 ft
Composite
CEXT
100 ft CEXT
IDF
DSLAM
H
P
Test
Access
MDF
X
100 ft
100 ft
100 ft
Line Share
Splitter
Data
100 ft
100 ft
Outside
Plant
Voice
Class 5
Switch
Non Line Sharing
Class 5
Switch
100 ft CEXT
300 ft
Composite
CEXT
Voice
IDF
DSLAM
Splitter
MDF
Data
100 ft
100 ft
100 ft
100 ft
Outside
Plant
Figure 5—Central Office Models
This model above can be abstracted as shown in Figure 1 below to just show the physical relationships
within the CO of the interfering sources and loops:
DSLAM
DUT
SS
CPE
DUT
Other
DSLAM’s
SS
Other
CPE’s
100 ft
CEXT
300 ft
Composite CEXT
(“y factor”)
Central Office
Figure 1
NEXT
Proposal
Based on the model in Figure 1 it is proposed that the crosstalk contributed by the 300 ft of Composite
CEXT be considered simply as part of NEXT. The rationale for this proposal is the following:
 The variety of disturber power spectral density (PSD) masks in the Composite CEXT interfering
bundle is very similar to the variety of PSD masks in the NEXT interfering bundle.
 The value of the NEXT crosstalk in Figure 1 is reduced by the fact that the NEXT coupling only
begins outside the CO and thus the coupling signals are attenuated from having traveled 400 ft
from the DSLAM’s.
 The value of the Composite CEXT signal referred to as the “y” factor in the impairment tables of
PN4254 is based on the length of the Composite CEXT coupling, which is modeled as 300 ft,
and is reduced by the fact that it begins 100 ft away from the CO. Therefore, in the absence of
rigorous expressions to evaluate the values of short-range crosstalk, it is likely that the value of
the “y” factor is approximately equal to the value of the reduction in NEXT caused by the 400 ft
span before NEXT coupling begins.
Conclusion
It is proposed that the Composite CEXT crosstalk factor referred to as the “y” factor in the PN4254
impairment tables be removed based on the assumption that it is roughly equivalent to a reduction factor
of NEXT resulting from the distance between the DSLAM’s and the beginning of NEXT coupling.