Those Silly Codes

A reader from Oregon recently wrote: "Some friends and I were on a conference call 'social engineering' our local SCC (Switching Control Center).  We were trying to find out where a call to an unknown exchange was going.  The man at the SCC asked us what the 'silly code' for the originating office was.  We, of course being confused, told him we would check with our supervisor and call back.  What is 'silly code?'  How do I find out what mine is?"

Our technical writers did some investigating and this is what they came up with:

In this instance the word that is pronounced "silly" is actually Common Language Location Identification (CLLI).  Quoting from a Bellcore publication:

"This code set uniquely identifies locations ranging from earth stations, building, poles, manholes, etc.  Codes can be used to identify existing or proposed buildings and can aid long range planners, current planners, equipment engineers, installers and maintenance personnel in their work.  Location codes identify cities, states, and foreign countries as well as buildings and specific entities within buildings."

A CLLI code is an 11-character code used by the telephone companies to identify the location and type of a central office.  The 11-character identifier is broken down as follows:

• Town: 4 Alpha Characters
• State: 2 Alpha Characters
• Building: 2 Alphanumeric
• Building Subdivision: 3 Alphanumeric

Here are some examples of towns:

• RCMD: Richmond, VA
• CHCG: Chicago, IL
• DLLS: Dallas, TX
• DNVR: Denver, CO
• NYCM: New York (NY City Manhattan), NY

States adhere to standard postal abbreviations, with the additions of:

• PR: Puerto Rico
• VI: Virgin Islands
• AB: Alberta, Canada
• BC: British Columbia, Canada
• MB: Manitoba, Canada
• NB: New Brunswick, Canada
• NF: Newfoundland, Canada
• NT: Northwestern Territories, Canada
• NS: Nova Scotia, Canada
• ON: Ontario, Canada
• PE: Prince Edward's Island, Canada
• PQ: Quebec, Canada
• SK: Saskatchewan, Canada
• YT: Yukon, Canada

The building field will always have an "X" in it if the central office in question does not belong to AT&T or a Bell Operating Company (BOC).  The building subdivision of an end office or subscriber-serving central office uses short codes like the following, "x" being numeric:

• MGx: Marker Group, used to represent electromechanical switches such as crossbar.
• CGx: Control Group, used to represent a 1, 1A, 2, 2B, or 3ESS office.
• DSx: Digital Switch, used to represent a 5ESS, DMS-100, or other digital switches.

Small independent phone companies often make their building subdivision codes the exchange code of their central office, such as 921, 423, etc.  AT&T numbers its 4ESS toll switches with a 2-digit numeric followed with a "T".  (Example: 57T, 13T, etc.)

Here are some examples of CLLI codes:

CHVLVAXA921 would be Charlottesville, Virginia, independent telephone company, building A, exchange 921.

DNVRCOZUCG0 would be Denver, Colorado, Zuni Street, 1A ESS machine 0.

CHCGIL0257T would be Chicago, Illinois, building 2, 4ESS number 57.

Note:  In cases where the building subdivision ends in "xxT", the building code may be the number that comes after an error message from that particular 4ESS.

For example, CHCGIL0251T error message might be: "Your call cannot be completed as dialed.  Please check the number and dial again.  312 2T."  They don't say "02."