CAPI versus TAPI
Herbert Feichtinger
in Europe. My comments on CAPI are therefore biased and reflect my personal
meaning, not necessary the company's view.
CAPI is a software interface for European ISDN hardware. It is required by
German Telecom to get approval and therefore every manufacturer entering
the European market must include it in the box. The specs are available:
www.capi.org
CAPI is available in several flavors, 16 bit / 32 bit and now has a
supplement offering voice functions.
CAPI is 100% modelled for ISDN features offered by European telcos.
It is available for MS-Windows, Unix flavors (including Linux), MS-DOS,
BeOS, MacOS...
CAPI is available for ISDN, GSM (digital cellular), ATM, CableTV.
CAPI offes data and fax and includes a special file transfer protocol named
Eurofile. CAPI became successful, because
a) German Telekom insisted on it
b) t-online, the ISP subsidiary of German Telecom enforces it
c) home banking in Germany is based on it
d) customers saved a lot of money using the 64 kpbs compared to analog
modems
e) ISDN was the only way to get callerID, DID, ....
See www.megasoft.co.at for a list of available TAPI drivers for ISDN
hardware !
I have made a comparison of CAPI versus TAPI for telephony:
www.megasoft.co.at
and can translate it if somebody needs.
Here are the main issues:
1) CAPI still is vendor specific. You can install only one API flavour on a
PC. So no mix and match of ISDN hardware. And vendor specific also means
vendor specific added function calls.
2) CAPI is made for data transmission, voice was not in the picture. Voice
was added last year, yet not implemented widely.
3) CAPI features do not match TAPI features and vice versa. So creating a
TSP on top of CAPI, as most German vendors currently try, limits this TSP to
CAPI functionality. Only very few vendors implement CAPI and TAPI on an
equal basis. But then: which subsystem should get an incoming call?
4) CAPI is specified by Germans, TAPI is open to contributions by everybody.
5) CAPI only has two layers: Hardware and CAPI. There is nothing like the
concept of a TSP driver as in TAPI..
6) CAPI handles call control AND media stream (at least transparent). With
TAPI nobody knows how to handle remote WAV in W2K....
7) There is no activity like the TAPI Bakeoff with CAPI. Let the customer
find out what works...
8) TAPI uses 16 bit characters, CAPI 8 bit characters. I don't know how CAPI
is used in China, yet it is...
9) TAPI is integrated with Windows, CAPI is on top of it. Therefore CAPI is
not linked with the Windows Security Model, Acrive Directory,...
10) CAPI uses call types like data / voice/ fax (at least in general, in
practice this doesn't work with analog callers)
11) CAPI does not offer "hands-off" (but I have never seen any TAPI app that
uses this feature..)
12) CAPI has no speakerphone concept
13) ISDN uses a bus structure. However there is no spec that allows one
device on the bus to control another one. So a PC with an ISDN board cannot
establish and transfer a call to an ISDN phone on the same bus.
For the customer, TAPI with ISDN / CAPI hardware is still a mess. This has
several reasons
1) Microsoft was left out of the CAPI game and doesn't like it.
2) All German ISDN vendors fight against each other as much as they fight
against Microsoft.
3) Available TSPs for CAPI hardware are all limited. Media stream is almost
never supported!
Now let's look at available products:
1) ISDN boards and ISDN USB adapters
The largest manufacturer is AVM. They have a nice TSP for their "Fritz!"
products for Win9x and Win NT. NOT for Windows2000!
AVM's CAPI is included with Windows2000.
AVM's TSP only supports phonecalls using the PC soundboard.
Diehl/Eicon and Teles probably nr. 2 and 3 in the market do not offer
TSPs.
2) ISDN phones
All new ISDN phones have RS.232 or USB and offer a TSP for Call control;
no media stream handling. Only two TSPs for Win NT I know of.
usually only 1st party stuff.
2) ISDN small scale PBX
TSPs for 1st and 3rd party are usually included for free. Those written
by MegaSoft work with Windows2000.
3) ISDN large scale PBX
TSPs available for a few of them. Quality sometimes lousy (that means
stability as well as number of TAPI functions included). Usually very
expensive!
What does this mean altogether?
1) If you need TAPI Call control, you find many ISDN products with proven
TSPs.
2) If you need media stream, you have to
a) develop for CAPI or
b) buy much more expensive ISDN stuff from Dialogic, Rhetorex and the
like which are no-names in Europe's consumer markets or
c) hope that VoIP will take off (yawn!, not as long as there is no flat
rate in Europe).
Remember that this still doesn't make your CTI product useful in Europe. The
different numbering schemes, dialing rules, tariff structures etc. all are
big barriers...
Comments please!
Herbert Feichtinger