In TIA-568 Standard For Premises Cabling Systems
As of January 2011 but subject to change in the standards committees.
The terminology in TIA-568-C.0, Generic Telecommunications Cabling For Customer Premises, has changed to a more generic (i.e. not traditional telecom) nomenclature. Current plans are to revise the other T568/T569/T570 documents to this nomenclature in the future.
Unfortunately, all this can be confusing, so we'll present the TIA wording and explain our interpretation in CAPS and give you a diagram of our explanation.
The traditional terms for the location of the ends of the cabling or interconnections have been changed to "connection points."
Distributor C: Initial or central connection point in a hierarchical star topology. EQUIPMENT ROOM OR MAIN CROSS CONNECT
Distributor B: Intermediate connection point between Distributor A and Distributor C in a hierarchical star topology. AN OPTIONAL SECOND PATCH IN EQUIPMENT OR TELECOM ROOM OR MEDIA CONVERTER AND/OR REPEATER
Distributor A: Intermediate connection point between Distributor C and Equipment Outlet in a hierarchical star topology. HORIZONTAL CROSS CONNECT, e.g. TELECOM ROOM or ZONE MUTOA
Equipment Outlet: Final connection point in a hierarchical star topology. WORK AREA OUTLET
In a typical commercial building, Distributor C would be the main cross-connect, Distributor A would be the horizontal cross-connect, and Equipment Outlet would be the telecommunications outlet (TO. ) Distributor B is optional and not often used.
Connecting these points are "cabling subsystems" defined as:
Cabling Subsystem 2 or 3: Cabling between either Distributor A and Distributor C or Distributor B and Distributor C. BACKBONE
Cabling Subsystem 2: Cabling between Distributor A and Distributor B. CROSS CONNECT
Cabling Subsystem 1: Cabling between Distributor A and Equipment Outlet. HORIZONTAL
In addition, some of the definintions have changed:
Centralized cabling, Fiber optics with a direct connection from the equipment to user is defined as: A cabling configuration from Distributor C to a centralized cross-connect using pull through cables, an interconnect, or splice at Distributor A.
Consolidation point: A connection facility within Cabling Subsystem 1 for interconnection of cables extending from building pathways to the equipment outlet.
These drawings illustrate some of the options within the standard architecture.
Below is the "traditional" view of TIA-568 architecture:
Distributor B is optional and can be used for a connection, e.g. fiber splices, or media converters:
In fact, no intermediate connections are required, e.g. centralized fiber:
Premises Cabling Website Contents
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Overview of Premises Cabling and Standards