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BRI (Basic Rate Interface)
BRI is an ISDN access method, typically used for home and small offices.
Consists of two 64Kps digital channels and one 16Kbps digital signalling and control channel.
Often referred to as 2B+D
Support for BRI in Asterisk is bewildering and highly dependant upon the driver (and thus chipset) in your BRI modem. Asterisk supports the following drivers / channels for BRI:
Starting with Asterisk 1.6 libpri also includes BRI support, therefore providing an alternative to mISDN
Driver independant BRI PCI and PCIe cards. Runs on Linux and Windows.
Very easy to setup compared to Passive cards. berofix solves the
traditional VoIP to TDM issues like Echo and Fax and it is even modular.
See Asterisk capi channels and chan-capi.org
Will support DID on AVM Fritz cards
Will support Hardware fax (Hylafax with capi4hylafax - instead of SpanDSP)
Supports Eicon/Dialog active cards and their fax features, as well as native conferencing
With Q.SIG support; on BRI cards can be shared (!) amoung several applications (e.g. Asterisk and HylaFax)
Can be used together with remote CAPI/ CAPI-over-TCP clients/servers
Works quite stable; echo cancellation is limited; no noticeable quality impact switching BRI;
NT-mode does not work (for me on HFC+mISDN-CAPI)
chan_capi with Fritz is stable enough for production
DAHDI B410P wcb4xxp
B410P native DAHDI driver (wcb4xxp).
New as of 2008-10-28 !
Experimental, but is included in 1.2.x stable branch of Asterisk.
It allows both PTP and PTMP on cards having mISDN drivers (Fritz!, Cologne HFC chipsets etc)
stability is good and improving (Mar 2006). See asterisk/doc/README.misdn for instructions.
See Asterisk zaphfc and the new Asterisk vzaphfc module
Zaptel BRI interface (A GOOD thing)
Only supports cards using HFC 'Cologne' chipset, also external ones connected thru USB
(note: I was unable to find anything about the USB support in zaphfc  )
Works quite stable; signalling is limited to 2 channels on BRI; can be combined with chan_capi;
requires CAPI (n.a. for all cards).
Some features caused kernel deep freeze (call forwarding from ISDN-phone menu), but didn't check for some time.
See Asterisk i4l channels
mISDN is the successor of isdn4linux
4-port BRI card
Sangoma create their first BRI card A500 in 2007, using the ISDN-BRICKS stack from NetBricks
See Asterisk vISDN
native channel for HFC-S chipsets (does not rely on Zaptel)
Looks very promising; needs some patches for recent kernels; no more updates for some months (developer is working on vGSM-stack)
choppy sound on incoming ISDN (sound is ok on same hardware with zaphfc)
not ready for production
Single and quad BRI cards are available.
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