EXFO CableSHARK P3 VF/DSL Cable Qualifier - Manual (Page 50)

VF / DSL Cable Qualifier
38
5.5 Industry Standard Test Loops
ADSL, HDSL, and ISDN modems are generally designed to operate on Industry Standard Test Loops. It is
quite possible to have a real local loop, which is shorter (distance) than one of the various test loops (see
Appendix A - Ideal Cable Results) and not have error free transmission.
This is usually caused by:
1. Bridge taps,
2. Load coils,
3. Uneven pair twisting
4. Bad
splices,
5. Water in cable, etc.
Please note that ISDN U Interface devices are designed to work on the sixteen test loops as designated by
ANSI T1.601-1995. HDSL modems are designed to work on Customer Service Area (CSA) test loops and
ADSL modems are designed to work on ANSI T1.413 test loops (see Appendix A).
Also note that Rate adaptive Asymmetric Digital Subscriber Line (R-ADSL) operates at a lower speed when
confronted with a local loop which is longer than one of the standard test loops, has a bridge tap longer than
those of the standard test loops or cables which are impaired with noise or other anomalies.
ISDN, HDSL, and ADSL (plus all other types of DSL) will not connect on local loops which have load coils.
5.6 Bandwidth Requirements
The various DSL technologies need different bandwidths on the line to operate a full potential. The
CableSHARK will help identify if a particular DSL is supported.
•
ISDN requires approximately 200 kHz of bandwidth in order to operate.
• HDSL requires approximately 400 kHz of bandwidth in order to operate.
• G.SHDSL requires approximately 1 MHz of bandwidth in order to operate.
• ADSL requires approximately 1.1 MHz of bandwidth in order to operate.
• ADSL2 requires approximately 1.1 MHz of bandwidth in order to operate.
• ADSL2+ requires approximately 2.2 MHz of bandwidth in order to operate.