Girish Mahajan (Editor)

Circuit ID

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A circuit ID is a company-specific identifier assigned to a data or voice network between two locations, usually local telephone exchanges. The circuit is then leased to a customer by that ID. A subscriber having an issue with a circuit contacts the Controlling Local Exchange Carrier (Controlling LEC) telecommunications provider to provide this circuit ID for action on the designated circuit.


Telecom Circuit ID formats

The LEC circuit IDs are based on Telcordia Technologies' Common Language Coding. At one time, the abbreviations were meaningful (for example, HC for high capacity) but the complexity of the business no longer allows for it.


  • A Prefix: 3-5 Alphanumeric characters. Required.
  • B Facility Type: 2–6 Alphanumeric characters. Required.
  • C A CLLI Code: 8 or 11 alphanumeric characters. This is a Required Field.
  • D Z CLLI Code: 8 or 11 alphanumeric characters. This is a Required Field.
  • Example:

  • HN101/T3U/MPLSMNDT000/GLVYMNORIII is an unframed T3 circuit between two locations in Minnesota.
  • Serial Number format: AA/BBCC/DDDDDD/EEE/FF/G prefix/service code - service code modifier/serial number/suffix/company identifier/segment name

  • A Prefix: 1–2 alphanumeric characters. Optional. They may or may not be based on LATA
  • B Service Code: 2 Characters. Required. The type of service this circuit is providing.
  • C Service Code Modifier: 2 Characters. Required. Modifies the service code, often used for different billing options.
  • D Serial Number: 1–6 digits. Required.
  • E Suffix: 3 character suffix to the serial number. May be required, but rarely used.
  • F Company Code: 2–4 alphabetic characters (NW, MS, PN, GTEW, NRLD, UDMN, FROT) Required, identifies the Controlling LEC.
  • G Segment: 1–3 alphanumeric characters. Optional for point to point, but usually found with multi-point DS0 circuits.
  • Example:

  • 32/HFGS/012345/NW is a T3 Circuit by Qwest
  • 73/HCGS/123456/000/NE is a T1 Circuit by New England Telephone
  • 44/AQDU/987654/000/G4 is a HDSL Circuit by G4 Telecom
  • Telephone Number Format: AA/BBBB/CCC/DDD/EEEE/FF/G

  • A Prefix: Alphanumeric characters. Required if it exists.
  • B Service Code & Modifier: 2–4 alphabetic characters. Required for non-DSL numbered circuits.
  • C NPA: 3 digits. This is a required field.
  • D NXX: 3 digits. This is a required field.
  • E Line: 4 digits. This is a required field.
  • ? Extension: 1–5 alphanumeric characters. This is an optional field.
  • F For states: AZ, CO, ID, MT, NM, UT, WY, alphas not accepted; convert D1 to 0001, D2 to 0002, etc.
  • G Segment: 1–3 alphanumeric characters. This is an rarely used optional field.
  • Circuit Designations in the United Kingdom

    Each carrier (Public Telecomms Operator) in the UK has its own form of designation. The Post Office/BT system is described here from the original term ‘Engineering Circuit Designation’. Other PTOs have their own scheme and would be suitable for inclusion.

    The Post Office or BT system historically used PW and R, optionally followed by a Region and/or Area code, followed by a number of digits between 4 and 6 for rented, analogue private lines. A Region code might have been LR for London Region or ER for Eastern Region, and for an Area L/NW for North West London or CB for Cambridge. In all but the rarest instances these must have been migrated to AX by the Analogue Upgrade project to digitise as much as possible for FDM Offload, (no) dc path uniformity and remote access in maintenance.

    Between 2 locations then:

  • AX nnnnnn designates an analogue (2w or 4w) presented link.
  • KX nnnnnn designates a digitally presented link up to 64 kbit/s.
  • NX nnnnnn designates a digitally presented link from 128 up to 1,024 kbit/s.
  • MX nnnnnn designates a digitally presented link from 2 Mbit/s upwards
  • Each of the prefixes may have an addition making MX/GB, KX/INT for example.

    There are many specialist designations covering bearers for other purposes, for example for IP and bearers provided for other PTOs. One common other use has been IMUK and IMGB for the 2 Mbit/s link from the public exchange to a customer location for the delivery of ISDN30 in the earlier DASS and more recent I.421 format.

    The trend has been that the local UK area suffixes are no longer used though legacy lines with these may still be in place.

    International Circuit Designations for Correspondent IPLCs

    These were known as CCITT, now ITU-T, designations. In the interests of international recognition, a protocol with recognisable town names has been used.

    The format is: <Earliest alphabetical town or city> – <second alphabetical town or city> <Type> <Serial>

    Towns and cities have abbreviations accepted by the 2 corresponding PTOs and the CCITT/ITU-T.

    Examples are:

  • AMS = Amsterdam
  • BS = Bristol
  • DSSD = Düsseldorf
  • FFTM = Frankfurt-am-Main
  • KOB = Copenhagen
  • L = London
  • MDD = Madrid
  • PS = Paris
  • Original CCITT Leased Circuit Types were:


    P = Audio circuit (however transmitted over distance) presented as Audio for voice

    FP = Audio circuit (however transmitted over distance) presented as Audio for Fax modem

    DP = Audio circuit (however transmitted over distance) presented as Audio for Data modem

    XP = Audio circuit (however transmitted over distance) presented as Audio and switched by customer for alternate use by Voice or Data modem

    L – PS P4 was the fourth analogue line between Paris and London normally used for voice transmission at that time. DSSD-L XP2 was the fourth analogue line between Düsseldorf and London alternately used for voice and data at that time.


    NP became the Type designator for most correspondent International digital links.

    BS – MDD NP12 and KOB – PS NP34 would have been typical uses of the scheme for links between Bristol & Madrid and Copenhagen & Paris.


    The choice of letters in designating major town and cities could be seen to reflect a short form of the name in the language of the country and also to disambiguate with similarly named locations. København being the Danish home version of Copenhagen attracted KOB as the abbreviation. FFTO was the designation for Frankfurt-an-der-Oder, where there was the clear need to disambiguate references from FFTM.

    The serial or the numbered occurrence of a link between two PTOs between 2 cities was usually the next free number in the system, but the CCITT allowed for the re-use of old serial numbers after a period of 6 months. A customer ordering 3 links could be allocated DP23, DP24 and then DP6 between 2 major cities. (DP6 had been ceased over 6 months earlier).

    It can be considered that the serial or last number of the type of correspondent link between two places made the link unique but did lead to problems, for example when a major PTO in one country was setting up links in correspondent relations with more than one PTO in another country.

    The development was away from correspondent IPC links to a situation where one facilities provider could provide the link over the international part and sometimes as afar as the distant end customer. This was the result of liberalisation and competition in home and overseas markets. In some cases the facilities provider would carry the link to their PoP in the distant country and then rent a national or local tail from the PTO in that country. That would attract a designation particular to that area and not reflect its international connection significance.


    Circuit ID Wikipedia

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