Features of E1 and T1

E1 and T1 are characterized by the following:

• Signaling modes

• Fax function

• Protocols and standards

E1/T1 interfaces support these types of signaling:

• DSS1/QSIG user signaling—Adopted on the D channel between ISDN user and network interface (UNI). It comprises a data link layer protocol and a Layer 3 protocol used for basic call control.

• ITU-T R2 signaling—Includes digital line signaling and interregister signaling. Digital line signaling is transmitted in TS16 (ABCD bits) of E1 trunk. It conveys status information about E1 trunks to describe whether the trunks are occupied, released, or blocked. Interregister signaling conveys information about address, language and discriminating digits for internal calls, echo suppressor, caller properties and callee properties in multi-frequency compelled approach (forward and backward) in each timeslot.

• Digital E&M signaling—Similar to R2 signaling. It transmits E (recEive) and M (transMit) call control signals similar to analog E&M signaling in TS16, alignment signals in TS0, and voice signals in other timeslots. In digital E&M signaling, when an E1 trunk detects and sends connection signaling, it looks at the signal in TS16. Digital E&M signaling provides three start modes, immediate, wink, and delay, to adapt to different devices for more reliable connection.

• Digital LGS—Digital loop start signaling is used between telephones and switches to identify the off-hook/on-hook state, while ground-start signaling is used between switches. They differ in that the two parties in conversation must check grounding state before closing the line in the ground-start approach.

The FAX function is available on E1/T1 voice interfaces to set up fax channels and transmit/receive fax data.

E1/T1 voice supports SIP and recommendations in the ITU-T H.323 framework, and G.711, G.729, and G.723.1 Annex A (5.3K and 6.3K) in ITU standards.