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JUNOSe 11.1.x Physical Layer Configuration Guide
line modules that support MDL and FDL, see ERX Module Guide, Appendix A, Module
Protocol Support.
You can use MDL and FDL messages to determine the status of a link and to display
statistics for the remote end of a connection. MDL and FDL messages do not interfere
with other data transmitted over the link.
MDL Standards
You can configure channelized T3 interfaces to send MDL messages that comply
with ANSI T1.107a-1990 Standard for Telecommunications Digital Hierarchy –
Supplement to Formats Specification (August 1990). MDL messages identify a
particular link by sharing common codes for data such as the equipment identifier,
line identifier, frame identifier, and unit.
FDL Standards
Similarly, you can configure T1 channels to send FDL messages that comply with
either or both of the following standards:
Timeout of Received MDL and FDL Messages
When a line module receives an MDL or FDL message string, it stores the strings for
a period of 10 seconds after the last message was received. If the line module does
not receive another message of any type containing the same string within 10
seconds, it erases the local copy of the message.
Most MDL and FDL message strings are common to all three types of messages that
can be transmitted: path identifications, idle signals, and test signals. Certain message
strings, however, are unique to a particular message type. Table 9 on page 111 briefly
describes each MDL/FDL message string and indicates, with a checkmark ( ), the
types of messages in which it can be sent.
110
Overview
ANSI T1.403-1989 Standard for Telecommunications Network and Customer
Installation Interfaces – DS1 Metallic Interface – Robbed-bit Signaling State
Definitions (1989)
FDL messages that comply with the ANSI standard identify a particular link by
sharing common codes for data such as the equipment identifier, line identifier,
frame identifier, and unit.
AT&T Technical Reference 54016 Requirements for Interfacing Digital Terminal
Equipment to Services Employing the Extended Superframe Format (September
1989)
FDL messages that comply with the AT&T standard identify a particular link by
sharing performance data and do not use common codes for data such as the
equipment identifier, line identifier, frame identifier, and unit.
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