Patton electronic 2720/I Series user manual System Configuration

3.2.2 System Configuration

The default System Configuration menu looks like this:

The System Configuration options are described below:

aLine Format: ESF (default)

Options: ESF, D4, UNFRAMED

D4: This is an older, but widely used, line format that does not provide FDL, so network interface performance cannot be monitored so easily. AT&T TR 62411 contains the specifica- tions for this format and the ESF. D4 is also known as Superframe format. According to TR 62411, “The Superframe format…consists of 12 frames of 193 bits each for a total of 2316 bits. Each 193 bit frame consists of 192 bits preceded by one framing bit….the framing bit is time shared to both synchronize the terminal equipment and to identify the signal- ing frames.” (Sec. 4.1.1)

ESF: This stands for Extended Superframe Format, a line format developed by AT&T. AT&T Technical Reference 54016 (TR 54016) defines the ESF, a format which is commonly used to allow monitoring of the network interface performance over the Facility Data Link (FDL). AT&T TR 62411 says, “the Extended Superframe Format “extends” the DS1 superframe structure from 12 to 24 frames…for a total of 4632 bits. It redefines the 8 kb/s channel previously used exclusively for terminal and robbed bit signaling synchronization.” The ESF provides a 4 kb/s data link, called the FDL, which allows for in-service monitoring and fast troubleshooting. Certain net- work services require the ESF.

UNFRAMED:This is a special mode that allows you to achieve the maximum possible data rate of 1.544 Mb/s (million bits per second) by using the framing bits for data transmission. There is no signaling or FDL. This is commonly used for campus connections, and by the Federal government and the military. This format is not to be used when connecting to a public car- rier’s network without its permission. This provides one chan- nel at a rate of 1.544 Mb/s. In addition, this format can be used with external clocking.

bLine Coding: B8ZS (default)

Options: AMI, B8ZS, B7ZS.

AMI: Alternate Mark Inversion defines a pulse as a “mark”, a binary one, as opposed to a zero. In a T1 (DS1) network con- nection, 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 CSU/DSU receiving the signal relies on the signal to recover the 1.544 Mb/s clock. To get around this problem, one method is to limit the data rate per channel (known as a DS0, because it is a 64 kb/s portion of the DS1 frame or super- frame) to 56 kb/s and forcing a pulse in the last data bit to ensure a minimum pulse density in the signal. If you must use AMI with a DS0 data rate of 64 kb/s, you should ensure that the data terminal equipment connected to the unit provides a minimally acceptable pulse density. For this reason, there are advantages to using B8ZS instead.

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