Since Asterisk is most famous opensource telephony platforum out there. The main reason of the 
popularity is its integration various telecoms service through telephony modules and hardware. Hence most of the people confuse when they upgrade their Asterisk and they do not find chan_zap module in the Asterisk modules directory. Asterisk wonder what’s wrong with the hardware. They do not know that Digium has changed the zaptel package name with Dahdi. I was reported a lot of questions about Zap and Dahdi difference. Below is a little explain that what is DAHDI? what’s difference between Zaptel and Dahdi and how it will effect your Asterisk infrastructure in future.
DAHDI (Digium Asterisk Hardware Device Interface). But it seems that Astricon’s joke was not entirely a joke: Digium Zaptel development stops and rename it DAHDI (Digium Asterisk Hardware Device Interface). Approximately two years ago, the owner of the trademark has contacted the company and Digium Zaptel advised that the name is actually a brand name. The company produces a phone card and would like to see on demand ‘phone card Zaptel’ not granted would not be associated with their brand name products.
In connection with the situation and to prevent it in the future, the new name will be registered as a brand (like Asterisk). For these purposes, will be released version DAHDI 2.0.0, which would include virtually all the functions of Zaptel 1.4 (except for supporting kernel 2.4 and drivers for older cards torisa and wcusb).
Asterisk 1.6 will be able to use only DAHDI, previous versions will remain compatible with Zaptel 1.4 (Asterisk 1.4 cmozhet used as Zaptel, and DAHDI). After version DAHDI 2.0.0 Issue Zaptel with correction of errors will stop.
The file is replaced by zaptel.conf /etc/dahdi/system.conf and although they are virtually equal on the inside, there is a small detail, the echo canceler that can dynamically load and unload and select independently for each DAHDI channel, and if we have a primary E1 (30 channels of voice) can use an echo canceller for the first 10 channels, another echo canceler for the 10 following another for the last 10. ¿Useful? it is not now, but sure someone will find it. For everything else, is exactly the same. 
Moreover, the file has become zapata.conf /etc/asterisk/chan_dahdi.conf and true, is almost the same inside, the differences are minimal and some quite odd that I leave you to discover
I unplugged the Digium FXO card from one machine where it was working just fine, to other machine now i’m unable to make outbound calls and i see following error on Asterisk console:
[Feb 25 14:54:10] WARNING[3600]: chan_zap.c:1946 zt_call: Unable to start channel: No data available
— Couldn’t call g1/03004556745
— Hungup ‘Zap/1-1′
Kindly suggest any solution. Thanks
I’m installing Asterisk new version 1.6.2.x, and after successful installation when i dial out I get these errors:
Jan 31 16:37:33] WARNING[17666]: channel.c:3986 ast_request: No translator path exists for channel type Dahdi (native 0x4c) to 0×100
[Jan 31 16:37:33] WARNING[17666]: app_dial.c:1745 dial_exec_full: Unable to create channel of type ‘Dahdi’ (cause 58 – Bearer capability not available)
Any body please suggest what to do. Even when i do Dahhdi show channels , it shows just fine .. so dahdi hardware is just fine but this issue is there.
I am using TDM cards by Yeaster instead of Digium. so will dahdi drivers works fot it ? i used dahdi drivers but faced alot of performance issues.. someone can suggest on it, if there are drivers available for yeaster or if there is need to do something in dahdi settings ?
Many thanks
Vishu, can you please list down the problem you are facing with Yeaster hardware?
BTW, why don't you use Digium standard hardware?