The receiver recognizes these special violations and decodes them as zeros. This method enables the network to meet minimum pulse den- sity requirements. Unless AMI is required in your application, HDB3 should be used whenever possible.
•AMI. Alternate Mark Inversion defines a pulse as a "mark,” a binary one, as opposed to a zero. In an E1 network connection, signals are transmitted as a sequence of ones and zeros. Ones are sent as pulses, and zeros are sent as spaces, 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 zeros in the data stream will cause problems, since the NTU receiving the signal relies on the signal to recover the 2.048 Mbps clock.
Note If you must use AMI, you should ensure that the data terminal equipment connected to the unit provides a minimally accept- able pulse density. For this reason, there are advantages to using HDB3 instead. AMI coding does not inherently account for ones density. To meet this requirement, the user should ensure that the data inherently meets pulse density requirements.
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