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E1 Frame Formats
Framing is the way E1 equipment formats bits on the E1 line for encoding digital voice.
Selecting the method of framing is a major E1 network design issue. There are two
options for E1 frame formatting:
• CRC4 (16 Frame)
• FAS (2 Frame)
E1 Line Coding
Line coding is the method the E1 Daughter Card uses to maintain a sufficient density of
ones in the bit stream, which is required for clock synchronization. HDB3 is the line
coding method used for E1 transmission.
• AMI (Alternate Mark Inversion) inverts, or changes the polarity of, successive ones
(marks) to maintain ones density.
• HDB3 (High Density Bipolar Order 3) is transparent (not confused with data). It
relies on the transmission of both positive and negative pulses. It is based on AMI,
but extends this method by inserting violation codes whenever 4 or more 0s occur
consecutively. This and similar (more complex) codes have replaced AMI in modern
distribution networks.
Signaling Options
The signaling option defines how the E1 Daughter Card signals the telco switch when
starting ("seizing") the phone line or trunk line.
• R2 Digital
• R2 MF
R2 MF signaling is used outside the United States, mostly in Europe and the Far East.
A sequence of tones initiated at the central office (PTT) is exchanged back and forth
between the PTT and the subscriber, generally at an R2 MF of 4 to 4.5 tones per second.
Although this tone rate work successfully in most instances, some countries require
tone exchange rates of up to 8 transactions per second. If the central office sends a tone
and is not answered fast enough with a return tone, the call is terminated. The delay
introduced by asking the application for each new tone limits the rate of signaling.
DNIS digits
The DNIS (Dialed Number Identification Service) digits option describes the number of
DNIS digits to be received from the CO. For example, when you dial a number, you
generally dial seven digits. Therefore, seven is the number of DNIS digits you would
receive from the switch. In general, this option should be left at the default value of 0 to
use automatic mode. You need to enter a DNIS digits value only if your telco switch
does not support automatic mode.
CommPlete Communications Server
5 E1 Daughter Card
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