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:

ISDN4Linux
http://www.isdn4linux.de/
See Asterisk i4l channels
Does not support DID; isdn4linux is known to be the cause of many problems (echo, stability etc)
Is in the process of being superseded by mISDN as of Kernel 2.6
Only seems to support 'Passive' cards
An example of a card only supported by this driver is the Traverse Netjet

CAPI
See Asterisk capi channels
Will support DID on AVM Fritz cards
Will support Hardware fax (Hylafax with capi4hylafax - instead of SpanDSP)
Supposedly better voice quality than ISDN4Linux
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

ZAPHFC
See Asterisk zaphfc
Zaptel BRI interface (A GOOD thing)
Only supports cards using HFC 'Cologne' chipset
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.

mISDN
http://www.isdn4linux.de/mISDN/
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.
Note: may be unstable on SMP machines
not ready for production

Sirrix
optional encryption
4-port BRI card

vISDN
See Asterisk vISDN
native channel for HFC-S chipsets (does not rely on Zaptel)
supports NT-mode
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.

http://www.asteriskguru.com/tutorials/bri.html

4.2. Asterisk and the BRI Cards - types and useful information¶

1. Introduction:¶

Basic rate interface (BRI, 2B+D, 2B1D) is an Integrated Services Digital Network (ISDN) channel consisting of two 64 kbit/s "bearer" (B) channels and one 16 kbit/s "delta" (D) channel. The B channels are used for voice or user dat*a, and the *D channel is used for control and signalling and/or X.25 packet networking. The two B channels can be bonded together giving a total data rate of 128 kbit/s.

2. Different approaches / channel drivers¶

There are 4 ways to get BRI cards to work with asterisk:

1. The first one is by using chan_mISDN (requires mISDN kernel patches)
2. The second one is by using chan_capi (requires "bristuff")
3. The third one is by using chan_modem_i4l (requires i4l) - This is an old and deprecated way of interfacing with the BRI card (not recommended.)
4. The forth one is for sirrix cards only and uses the sirrix channel driver
5. the 5th is ZAPHFC (requires "bristuff"), this is only for cards with the HFC (cologne) chipset - and only those cards sold on junghanns.net (works on others too, but then it needs some minor patching). Please note that using bristuff breaks PRI support, so you cant have both bri and pri in the same server.
6. the 6th is vISDN, only for cards with the HFC (cologne) chipset.

3. Things you should know before starting¶

3.1.: Difference between active and passive cards:¶

Cards can come in different versions: passive, semi-active, active. Active cards handle the D-channel and B-channel protocol in their hardware, whereas (cheaper) Passive cards do this in software.

Active cards usually need a special driver, (although there are some generic drivers available on linux nowadays), passive cards are mostly based on a few popular chipsets, this way one driver will fit many cards.

The big difference is the CPU load the card is causing on the server.
Still 1 or more passive cards could be used in a 386 or 486.
Active cards might also have on board echo cancellation whereas passive cards might or might not be able to do echo cancellation and if they can do it, it has to be done by the driver, taking up a lot of cpu resources of the server.

Another big difference between active and passive ISDN cards is in working on Point to Point (P2P) (see below) configured lines.
A passive card like the AVM Fritz PCI cant' work on P2P configured lines.

There is no real definition for "semi-active" cards, probably they handle the B-channel protocol in hardware with a special DSP, and leave the D-channel for the servers CPU.

3.2.: Difference between NT, NT mode and TE mode.:¶

- NT :
NT is the abbreviation of network terminator. This is the interface between an ISDN user and the ISDN provider. It is a small hardware box to which the user has to connect his ISDN devices via a so called S0 interface. In most European countries, the ISDN provider supplies the NT. A user in North America usually has to buy one, therefore the NT is often integrated into the ISDN card there.

- NT mode :
When multiple devices are connected to the ISDN connection, then all user device behave as slaves, where the network terminator (NT) behaves as master and synchronizes the communication on the S0 bus. The special behavior of the network terminator is called NT mode. User devices are normally not capable of running in NT mode. As a result, user devices can not communicate with each other even when they are connected via a crossed cable. Only some special ISDN cards (HFC chipset) are capable of running in NT mode, and can directly communicate with other ISDN user devices via a crossed cable.

NT mode is only supported by the mISDN, zaphfc, vISDN and the sirrix channel drivers. You will need NT mode if you want to connect your asterisk server to a PBX and the pbx cannot be put into NT mode.

• update: according to a certain pif on #asterisk, chan_capi can do NT mode, and isdn phones can connect to it. *

- TE mode :

TE is the abbreviation for Terminal Equipment, an ISDN telephone is an example of this, although a PBX could also be configured to be in TE mode.

Generally if you need to connect to ISDN phones, the pbx will need to use NT mode, if you want to connect 2 PBX'es, one of them will need to be in TE mode and one in NT mode.

3.3.: Difference between p2p and p2mp mode.¶

Your ISDN interface can be configured either in multi-device (p2mp) mode, or in point-to-point (p2) mode.

• p2mp
  • The multi-device mode is the normal connection mode for private ISDN users or very small business users. The user can attach multiple devices to the ISDN connection. The ISDN provider will assign a small number of fixed telephone numbers (usually up to 10 MSN), if any, to the ISDN connection.

• p2p
  • The point-to-point mode is the normal connection mode for business ISDN users. The user can attach only one single devices to the ISDN connection which will have to handle all calls (typically a PBX will be used). The ISDN provider will assign a range of numbers to the ISDN connection. Any call within this number range will be sent to the user. The ISDN provider will leave assignment of the last digits of the telephone number to the ISDN user. This setup usually allows for additional features, but is also more expensive.

On a P2P line all PBX (private branch exchange, a private telephone network) functionality has to be done by a device on the users side. On a Point to Multipoint (P2MP) line, the network provider manages PBX functionality for the user.

Call your telephone provider to find out how your ISDN line is configured. Your provider can change your line from P2MP to P2P within an hour.

3.3.: MSN number¶

Unlike a normal telephone connection, an ISDN connection can have more than one telephone number - each of these is called an MSN (Multiple Subscriber Number).

This is sometimes also called a DDI or DID.

4. BRI cards known to work with asterisk¶

Currently digium (the main asterisk sponsor) does not make any BRI cards, vendors known to have compatible cards are:

• quadBRI : HFC based 4 port BRI card
• octoBRI : HFC based 8 port BRI card

• fritz! pci (passive single BRI board)
• b1 PCI : 1 port active BRI card, known to work with chan_capi and chan_misdn, be sure to update the firmware here
• c2 : 2 port active BRI card, known to work with chan_capi
• c4 : 4 port active BRI card, known to work with chan_capi

• BN4S0 : HFC based 4 port BRI card, known to work with chan_misdn
• BN8S0 : HFC based 8 port BRI card, known to work with chan_misdn

• PCI4S0: 4 port BRI card

• diva server BRI: active 1 port BRI card, requires kernel module: divadidd, known to work with chan_capi, voice and fax
• Diva Server V-BRI: active 1 port BRI card, requires kernel module: divadidd, known to work with chan_capi, voice only
• Diva Server 4BRI: active 4 port BRI card, requires kernel module: divadidd, known to work with chan_capi, voice and fax
• Diva Server V-4BRI: active 4 port BRI card, requires kernel module: divadidd, known to work with chan_capi, voice only

• gazel 128 usb: 1 port BRI card uses hfc chipset, known to work with chan_misdn. Works on USB, so could be used on a laptop

• Digium B410P: 4 ports BRI card. The B410P features on-board DSP-based echo cancellation and supports TE and NT mode over 4-wire S/T interface.

If you know other BRI cards that are known to work, please let us know by posting a comment to this tutorial.

5. Related tutorials:¶

- Read our tutorial about troubleshooting IRQ problems with asterisk interface cards
- Read our tutorial about the installation of Digium B410P
- Read our tutorial about the installation of AVM B1
- Read our tutorial about how to install chan_mISDN and how to make it working with Asterisk

6. F.A.Q.¶

• Q : Can i install multiple AVM cards in one server?
• A : Only avm active cards (b1, c2 and c4) permit multiple installation straight forward. with fritz! pci you can do the hack described on: this site
  for fritz! usb you can't install more then one. This limitiation is due to avm drivers design, they choose to allow multiple installation only on hi-end boards.

7. References:¶

- BRI on wikipedia
- some ISDN
- bristuff breaks pri support

8. Related Definitions¶

For "Eicon Diva"

http://www.melware.de/de/index.html
http://isdn4linux.org/~armin/divas/
http://www.eicon.com/worldwide/products/WAN/cn4linux.htm
http://www.eisfair.org/fileadmin/doc/node10.html (german)

For AVM:¶

http://www.linux-magazin.de/Artikel/ausgabe/2000/10/Capi/capi.html

http://www.voip-info.org/wiki/index.php?page=zaptelBRI

zaptelBRI ISDN Interface cards¶

junghanns.net makes a quadBRI and octoBRI card for interface with ISDN phones or ISDN lines providing a PSTN connectivity gateway with Asterisk. They also have a single and double E1. (PRI)

Resources: junghanns.net zaptelBRI web site

Currently, they make a quad and octo-port BRI card. The card can operate in TE or NT mode.

Quadbri: In TE mode the card can connect 4 ISDN lines for outgoing and incoming calls. In NT mode the card can connect up to 8 ISDN phones. Switching between modes is done using jumpers at the card. The default is NT mode.

bristuff applications¶

• PickUp: Mostly channel independent; part of bristuff patch
• PickUpChan
• PickDown
• Steal

QuadBRI¶

TE mode information¶

• zaptelBRI TE mode installation

• zaptelBRI TE mode zapata.conf
• zaptelBRI TE mode zaptel.conf

NT mode information¶

• zaptelBRI NT mode installation

Possible installation errors¶

If you load the qozap and zaptel driver, all seems to work. If you then do ztcfg -v, after a few seconds the following error scrolls over the screen and your system does not respond:

kernel: qozap: dropped audio card 1 cardid 0 bytes...

The only solution is a reboot. It could be there's a raid controller in your system, this causes the "incompatibility".
A solution is to change in the qozap.c file the line 'if (qoztmp->clicks > 1) {', change the 1 to 100. Recompile qozap, install it, rmmod if loaded, and try again.

Benchmarking
While we are at the subject anyway I can put some on-topic info here aswell. Recent benchmarks with 6 QuadBRI's on a Pentium-4 2.8Ghz resulted in a almost 100% improvement in load under Linux 2.6(.4) over Linux 2.4(.25). This ofcourse resulted in less (no) quirks in the sound under 2.6 than under 2.4.¶

The loadtest was done looping the BRI's to each other and in such way that we used all 24 BRI's (2 channels) resulting in 48 active channels.

The audio quality was easily monitored in contrary to often proposed "test suites"... Two phones at each end...

HFC-S BRI¶

• Acer ISDN-Surf
• Billion Bipac ISDN
• Billion/Asuscom (Asuscom/Askey)
• Conceptronic ISDN PCI card C128i(r)
• Creatix ISDN-S0/PCI
• D-LINK DMI-128+
• HFC cards from "Conrad Elektronik" (ordering no. 95 50 78)
• Longshine LCS-8051
• Neolec FREEWAY ISDNPCI
• Trust PCI ISDN Modem
• I-tec ISDN-128

Installing the latest version of bri-stuff from the junghanns download page (not linked to currently from the front page) runs smoothly on Fedora 2.6.8-1.521. The Billion card was recommended by my supplier for the UK. The bri-stuff installation scripts download the latest asterisk/zaptel and use a stable release not CVS. I kept getting type errors whilst using the bri-stuff installation scripts and zaphfc wouldn't install: then I realised that I hadn't included the "patch" package within my installation, and bri-stuff was looking for a definition which hadn't been patched in to the code.

Known issues¶

• Sometimes it becomes confused about what channels are in use... after a while show channels shows nothing but dial() says the zap channels are busy... (and they are not since a capi board on the same bus can call)
• In newer Versions, the BRIStuffed Version of Asterisk only works with original Junghanns Cards (4 and 8 Port Cards). Junghanns has implemented a ROM Check of the card to avoid the usage of third party multi BRI Cards (for example, the beroNet Technologies Card).

• In most cases not important: bristuff changes the structure of the uniqueid compared to a stock-asterisk:
  • Stock Asterisk: 1133722648.50
  • Bristuff'ed: asterisk-1685-1131631588.9

http://www.voip-info.org/wiki/view/Asterisk+DID+mISDN