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:

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 In recent years, the term RBS has been replaced by CAS which is now used to refer to bits that are associated with a specific channel whether it is in the T1 or E1 format.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:

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.




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.

- 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)

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.

- 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

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

- A101: One port T1/E1 card
- A102 :Two port T1/E1 card
- A104: Four port T1/E1 card

- 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.