E1 is a the European equivalent of a T1 but runs at 2.048Mbps and has 32 x 64Kbps channels DS0s where 30 is used for voice and two are used for syncronization and signaling.

Alarms that can occur on an E1:

• YELLOW: remote alarm indication (RAI): The RAI (remote alarm indication) signal indicates loss of layer 1 capability at the user-network interface. RAI propagates towards the network if layer 1 capability is lost in the direction of the user, and RAI propagates toward the user if layer 1 capability is lost in the direction of the network.

• BLUE: alarm indication signal (AIS): The AIS (alarm indication signal) is used to indicate loss of layer 1 capability in the ET-to-TE direction on the network side of the user-network interface. A characteristic of AIS is that its presence indicates that the timing provided to the TE may not be the network clock. AIS is non-framed and coded as all binary ONEs.

• RED: Loss of signal (LOS): The equipment shall assume "loss of signal" when the incoming signal amplitude is, for a time duration of at least 1 ms, more than 20 dB below the nominal amplitude. The equipment shall react within 12 ms by issuing AIS.

Although E1s don't use the terms YELLOW, BLUE, RED, they are for comparisons with T1.

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See also

• DSx Digital Signal X
• ISDN
• PRI
• E1 @ wikipedia