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4.3. E1/T1 Cards 1. Introduction Most of the E1 and T1 cards supported by asterisk are capable of carrying both voice and data. For now, we only have tutorials on how to do the audio part, the data tutorials might be available later. So what is this E1 or T1 all about ?

1.1. E1 / T1 E1 is a physical layer protocol, like ethernet. It defines a 2Mbps link between two endpoints. T1 is similar to E1. It is used in North America and is 1.544Mbps A more in depth difference between the two can be found here A J1 card is the Japanse version of a T1. (the tiny differences between T1 and J1 can be found here Both T1 and E1 can be used to transmit data or voice, or a mixture of both. For example: if an E1 is reserved for voice channels only, the 2mbit will be split into 32 64Kbps telephone channels. 30 of these channels can carry one telephone conversation each, and 2 carry signalling and timing information. A t1 could carry 24 telephone channels, each of which can carry a telephone conversation. Please note that in the states, its a common practice for carriers to offer fractional T1s, these have only some of the 24 channels provisoned. Lets have a look at the supported audio operating modes:

1.2.: Supported Audio Modes on E1/T1:

There are a number of protocols which can run on top of E1. These protocols are grouped into 3 big subgroups, CAS, CCS, RBS. (a detailed difference between these subgroups can be found here) Lets have a closer look on these subgroups:

a) CAS signalling CAS stands for Channel Associated Signalling. Examples are FXS loop start and E&M wink start. These protocols provide information such as the number that was called, and what state the call is in. They're limited in what information they can carry, and are slow to set up. With this kind of signalling, a set of bits is used to replicate opening and closing the circuit (as if picking up the telephone receiver and pulsing digits on a rotary phone), or using

tone signalling which is passed through on the voice circuits themselves CAS is the original signaling system used by E1. In CAS, channel 16 is reserved for signaling. In recent years, the term RBS has been replaced by CAS which is now used to refer to bits that are associated with a specific channel whether it is in the T1 or E1 format. Different subprotocols are:

- E&M

- Wink (this might be only RBS, if you know this for sure, please leave a comment.) - Feature Group B - Feature Group D

- FXO & FXS: this seems to only use CAS on E1's

- Ground Start - Loop Start - Loop Start with Disconnect Detect

b) CCS signalling Common Channel signalling: A more recent kind of signalling, which resolves the problems associated with CAS signalling. In this kind of signalling, short messages are sent over the signalling channel, with more information about the call, including caller ID, type of transmission required, etc. etc. CCS is used by either T1 or E1 and refers to a system that does not use a specific bit structure for signaling. Instead, all or part of a channel is used to pass messages between two systems to indicate how a channel is being used. CCS is used by either T1 or E1 and refers to a system that does not use a specific bit structure for signaling. Instead, all or part of a channel is used to pass messages between two systems to indicate how a channel is being used. This type of system is commonly found in ISDN which uses a D channel to pass messages. ISDN signalling and ss7 signalling are a subgroup of CCS signalling. - ISDN (PRI CPE & PRI NET) ISDN uses one channel (called the D channel) for signalling call information. On E1, this is one of the 2 signalling channels, leaving 30 channels for voice (called B channels). On T1, there aren't any spare signalling channels, so one of the voice channels is used, leaving 23 B channels for voice. A PRI (Primary Rate ISDN) is simply an E1 or T1 with ISDN on top of it. ISDN gives fast, reliable call setup and hangup detection, and detailed information about the call. In the UK, PRI is also called ISDN30. An important extension to ISDN is Q.SIG, which provides extra signalling information that is used when connecting PBX systems. Currently, asterisk has limited support for Q.SIG, it can make and receive calls and retrieve some of the extra information.

- On E1, EuroISDN is the standard for ISDN signalling. - On T1, there are different standards from different providers: - NI1 - NI2 - 4ESS (AT&T) - 5ESS (Lucent) - DMS100

- SS7 c) RBS: Robbed Bit Signalling RBS is the original signaling system used by T1 and provides either 2 or 4 signaling bits per channel depending on the multiframe format. In recent years, the term RBS has been replaced by CAS which is now used to refer to bits that are associated with a specific channel whether it is in the T1 or E1 format.

- E&M

- Wink - Feature Group B - Feature Group D

- FXO & FXS: this seems to only use RBS on T1's

- Ground Start - Loop Start - Loop Start with Disconnect Detect

1.3. Framing AMI, B8ZS, and HDB3 are different types of line coding used in T1 and E1 communications systems. AMI stands for alternate mark inversion and is used in both T1 and E1 systems. B8ZS stands for Bipolar with 8 Zeros Substitution and is used in T1 systems while HDB3 stands for High-Density Bipolar 3 and is used in E1 systems. - HDB3: High-Density Bipolar 3 -> E1 only - AMI: Aternate Mark Inversion -> E1 and T1, the T1 version exists with both ESF (extended super frame) and SF (super frame) - B8ZS: Bipolar with 8 Zeros Substitution -> T1 only, exists with both ESF (extended super frame) and SF (super frame)

1.4. What signalling and framing should i ask my carrier?

1.5. Timing or clock sources A T1/E1 connection needs a timing device on one of both ends. A T1/E1 line can be clocked internally or can be clocked by the telco. See more about this in the zaptel E1/T1 howto.

2. Asterisk Compatible E1/T1 cards 2.1 available cards Digium: -

TE110p: 1 port T1/E1 for use in 3.3 or 5 volt pci slots. TE205p: 2 port T1/E1 for use in 5 volt pci slots TE210p: 2 port T1/E1 for use in 3.3 volt pci slots TE405p: 4 port T1/E1 for use in 5 volt pci slots TE410p: 4 port T1/E1 for use in 3.3 volt pci slots TE406p: 2nd generation 4 port T1/E1 for use in 5 volt pci slots, with hardware DTMF recognition and echo cancellation. (now discontinued, but still supported) TE411p: 2nd generation 4 port T1/E1 for use in 3.3 volt pci slots, with hardware DTMF recognition and echo cancellation. (now discontinued, but still supported) TE407p: 3rd generation 4 port T1/E1 for use in 5 volt pci slots, with octasic hardware DTMF recognition and echo cancellation. TE412p: 3rd generation 4 port T1/E1 for use in 3.3 volt pci slots, with octasic hardware DTMF recognition and echo cancellation.

- Tormenta 2: Discontinued cards based on the open source project zapatatelephony These cards were known as: Wildcard T100P, T400P, E100P, E400P

intel

- Dialogic D/41JCT-LS: quad t1/e1 board, requires additional (paid) drivers from digium to make it work.

sangoma

- A101: One port T1/E1 card

- A102 :Two port T1/E1 card - A104: Four port T1/E1 card

varion

- V400P-E: 4 port E1 card, based on the open source zapata telephony project. These are the same cards as the discontinued digium cards. - V400P-T: 4 port E1 card, based on the open source zapata telephony project. These are the same cards as the discontinued digium cards.

Eikon - none public available yet.

2.1 What card should you pick ? I recommend against using cards based on the tormenta project, they are way older and take up a lot more cpu. (and their development seems stalled). The newest digium cards (TE406p and TE411p) as well as the latest firmware versions of the te405p and te410p are optimized for speed. Only the digium TE406p and the digiun TE411p have hardware echo cancellation, causing a big difference in cpu usage. But this comes at a slightly higher cost. If you need the 40% speed gain with on board echo cancellers, go for these cards, otherwise go for the cheaper te410p or te405p. (or the 1 or 2 port versions). It is said on the mailinglists that the hardware echo canceller also has better quality than the echo cancellation done in software. (I can confirm nor deny this claim - it's based on a single source).

3. Asterisk E1/T1 channel drivers There are two ways to get the E1/T1 cards to work: First one is chan_zap (requires the zaptel kernel modules), this is recommended for all digium + sangoma cards. The second one is chan_mISDN (requires the mISDN kernel patches) This is probably only usefull for eicon cards. chan_misdn is written for BRI cards, but also supports some E1/T1 cards.

4. Building, installing and configuring asterisk with E1/T1 cards

We will only discuss using chan_zap for now (its the only recommended thing to do). First read up on more details for your card,

- TE405 / TE410p tutorial - the other cards are coming soon then read the general tutorial on chan_zap.

Base Transceiver Station

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