Nortel Networks CTA 500dm - Manual (Page 81)

Appendix 81
P0873832 Issue 05 CTA 500 dm On Line Guide
other authentication protocol is selected, the CTA 500dm will not be
able to use MP and the call must be redialed using PPP.
Link Assumptions
For PPP and MP, it is assumed that the links are CRC-16 with
Maximum Receive Units (MRU) less than 1750 bytes.
For MP, it is assumed that call back is not required and that both
links can be identically conÞgured.
Bearer Capabilities
The use of ISDN and digital networks allows a user to select a
number of different bearer capabilities and data rates. Using a bearer
capability gives the network information about how it should treat
the call. In general, data cannot be sent over one of the voice bearer
capabilities (3.1 kHz audio and speech). However, in some cases,
especially on local calls, it may be possible to support 56 kbit/s and
even 64 kbit/s data rates over voice calls. The CTA 500dm supports
this capability.
To do this, your ISP must set up special dial-in phone numbers. Ask
your ISP about this feature if you are using CTA 500dm where data
calls are more expensive than voice calls.