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
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.
B8ZS: Bipolar violations occur when consecutive pulses are of the same polarity. In B8ZS, or Bipolar Eight Zero Substitution, bipolar violations are introduced deliberately to indicate that eight zeros have been transmitted. This special encoding is recognized by the receiver and decoded correctly. See AT&T TR62411 Section 4.2.2 for a detailed description of B8ZS. This enables information to be sent over a T1 connection without any constraints on the data’s pulse density. This is the most acceptable way to accomplish 64 kb/s on each DS0 channel.
B7ZS: This stands for Bipolar Seven Zero Substitution. Instead of introducing bipolar violations, this method substitutes a one for a zero in bit 7 (out of 8) of a DS0 channel when the data in that channel are all zeros. This is a special form of AMI and is compatible only with special equipment. For most applica- tions, AMI or B8ZS will suffice.
cDS0 Line Rate: 64kbps (default)
Options: 64kbps, 56kbps
64kbps: Also known as Clear Channel, this takes full advantage of the available bandwidth in a DS0 channel. Implementing it usually requires B8ZS line coding. In certain cases, special equipment may implement Clear Channel using AMI or B7ZS. Consult the equipment manual for compatibility. Your carrier will advise you on whether to use 64 or 56 kb/s. Campus applications may not have such restrictions, enabling you to use 64kbps. In Unframed format, the 24 DS0s and the fram- ing bits are combined to provide 1.544Mb/s for your use.
56kbps: This uses only the first seven bits of the DS0, limiting the data rate per DS0 channel to 56 kb/s. Your carrier will advise you on whether to use 64 or 56 kb/s. This is not available when using the Unframed format.
17 | 18 |
