/mcpThe default dial peer that is used inbound on the termination gateway and default parameters do not match with the outbound dial peer on the origination gateway. ○ Incorrect Compand Type The companding type for the US is µ-law; for Europe and Asia, it is a-law. You can issue the show voice call command to see which value is currently configured. If on a BRI or E1 port, the companding type on the router does not match the one on the connected device, and calls sometimes fail and sometimes connect, but the voice becomes heavily distorted so that the person becomes unrecognizable and a high low-pitch noise level appears. In Cisco IOS Software Release 12.2(3), the compand-type command is not on on the BRI ports, and the companding type is the default value. For more information about this bug, see Cisco bug ID CSCdv00152 and Cisco bug ID CSCdv01861. • Other basic connectivity problems not related to dial peers include these: Cisco IOS Software incompatibilities on gateway pairs. Again, it is not always required that Cisco IOS Software releases match, but it is recommended to check releases when problems occur. • Compressed Real-Time Transport Protocol (cRTP). There are several known problems associated with cRTP. Fixes are available for these problems, and it makes sense to disable cRTP when problems occur to check whether a Cisco IOS Software upgrade is an appropriate course of action. • On Cisco AS5300 voice gateways, ensure that the VCWare and Cisco IOS Software are compatible. • 3. Fax connectivity problems across the PSTN. If voice calls work in both directions but fax calls fail in at least one direction, check that normal faxes between these two machines works across the PSTN. In other words, ensure that the fax machines successfully transmit faxes to each other with the PSTN without traversing the VoX network. If they do not, the fax machines can have problems that need to be addressed before you consider fax relay problems. 4. 3. Check for SLIPs and Other Errors on Digital Interfaces If there are any T1 or E1 digital connections used by the routers that perform fax relay, make sure that they are error free. Fax relay is very sensitive to errors on digital interfaces, especially slips. The errors is not noticeable on voice calls but they can cause faxes to fail. show controller T1(E1) 1/0 Command