Product specifications

61
Setup E1 Parameter, Line Code
The G.SHDSL NTU supports two different line codes: HDB3 or AMI.
HDB3 is the most popular and preferred line coding and is also the default setting.
AMI line coding is also selectable.
HDB3
In this line coding, the transmitter substitutes a deliberate bipolar violation when
excessive zeros in the data stream are detected. The receiver recognizes these
special violations and decodes them as zeros. This method enables the network to
minimum pulse density requirements. Unless AMI is required for your application,
HDB3 should be used whenever possible.
AMI
A
lternate Mark Inversion defines a pulse as a “mark,” a binary one as, as opposed to
a zero. In an E1 network connection, signals are transmitted as a sequence of one
and zero. One is sent as pulse, and zero is sent as space, i.e. no pulse. Every other
pulse is inverted from the previous pulse in polarity, so that the signal can be
effectively transmitted. This means, however, that a long sequence of zero in data
stream will cause problems, since the NTU receiving the signal relies on the signal to
recover the 2048kbps clock.