Distribution Frames in Advanced Digital Telephone Exchange System
5.36.1 Main Distribution Frame (MDF)
The MDF shall be compatible with the specified digital switching system and protect the switching equipment from all abnormal electrical effects originated in the outside plant.
The MDF shall be designed to provide compatibility with the assignment system recommended for use with the specified switching equipment; convenient access for the placement and removal of jumpers; and a rapid, dependable means of securing reliable jumper connections. The necessary terminal blocks required to accommodate subscriber lines and trunks shall be provided.
The MDF shall be of the miniature type, vertical, or an equivalent high- density protector frame with a separate cross-connect frame. The Vertical to Horizontal ratio for the MDF must be 1.6.
Vibration-resistant test shoe connectors shall be included to permit the connection of line-testing devices. Insertion of the test shoe connectors shall isolate the subscriber lines from the exchange equipment.
The following miscellaneous circuits (a), ground bus (b), and tip cables (c), shall be included with the MDF:
a) Miscellaneous Circuits
Means of extending external network circuits to test desks, fault-monitoring/locating equipment, and auxiliary test equipment. Any other circuits normally required at the MDF to implement standard features of MDF, Centralized Operation and Maintenance (COM) centers, and exchange equipment.
b) Ground Bus
MDFs shall be equipped with ground bus bars having the conductivity of a number 6 AWG copper conductor, or greater.
c) Tip Cables
Each terminal group on the MDF shall have a factory-assembled tip cable. Connectors shall be installed to the tip cables for connection to the entrance cable in the cable vault. Tip cables shall have the size of a number 24 AWG copper wire, individually insulated with polyethylene, and with a polyvinyl chloride outer jacket. Tip cables shall contain cable pairs in multiples of 25 pair-binder groups. Tip cables shall also have an 8-millimeter aluminum jacket between the core and outer jacket with a coating that provides bonding to the outer jacket. A suitable wrapper shall be used over the cable core to provide insulation between the insulated conductors of the core and the shield. The metal shield shall be connected to the main frame bus at the MDF. Tip cables shall have a certain number of meters in length depending on each individual side’s requirements. Refer to SAES-T-903, SAES-T-920, and SAES-T-938.
With each MDF, the following shall be included:
1. A double quantity of jumper wire needed to place the exchange in full service.
2. A set of jumper wire dispensers.
3. Special tools required for jumper connections.
4. A full set of test equipment.
5.36.2 Digital Distribution Frame (DDF)
All DDFs required for terminating digital interoffice trunks shall be provided complete with frames, jack panels, patching cords, and all necessary accessories as required.
5.36.3 Intermediate Distribution Frame (IDF)
All IDFs to be located at each exchange room to terminate all voice-grade circuits for miscellaneous use, if required, shall be provided complete with frames, terminal blocks, and jumper wires.