Signaling System 7
Signaling System 7 (SS7)
Trunk Circuit Identification Codes
Overview
This section describes procedures relating to the installation and maintenance of the Signaling System 7 (SS7) trunks used to interconnect between CLECs (CLEC) and AT&T West. For the purpose of this document, the terms SS7 and Common Channel Signaling (CCS) are interchangeable. A related document, Competitive Local Carrier Operations Handbook - SS7 Signaling Links provides additional information.
SS7 Trunk Considerations
The following points are a starting point for discussion between an CLEC and AT&T West. They are not all inclusive.
- TIMER VALUES - The CLEC and AT&T West switches and STPs have many timers associated with link operation and call setup. Since only parameters and not the actual values are stated in technical references, the CLEC and AT&T West may have different time settings for the same timer. Although there is no requirement that the value of specific timers be the same (see note) in both companies, the sharing of the values will provide each company with additional information for trouble resolution.
Note: The T2 Link Timer is the only known exception and must have different values at each end.
- POINT CODES - If an CLEC and AT&T West are contemplating interconnecting, point code range information must be known well in advance to enable the control center to update the Signal Transfer Point (STP) during the scheduled split mode operation. Point codes include those of the STP, the interconnecting switches and any alias point codes.
- FREQUENCY OF CONTINUITY TESTS - When in-band signaling is used, continuity of the trunk selected is assured by call setup. Continuity testing is also available on SS7 trunks. The switch will automatically send, receive and measure tones placed on the trunk prior to setting up a call. The switch will perform continuity on a trunk at a variable rate of 1 out of n times (where n has a value of 1 to 16). It is this information (the value of n) which should be exchanged with the CLEC. The NOF has agreed that continuity operation tests be performed at a minimum rate of 1 out of 8.
- EMERGENCY COMMUNICATIONS - In the remote event a total SS7 failure is experienced, some means of communication between personnel in interconnecting networks may be required. The CLEC and AT&T West should determine what emergency communications are already available and/or what alternative methods, if any, will be provided.
- AVAILABLE OPTIONAL AUTOMATIC TESTING - Circuit Validation Test Message (CVTM/CVR) verifies that the translations at each end of the trunk will select the same trunk. CVTM/CVR is essential for trunk conversion and should also be performed on a periodic basis.
Trunk Circuit Identification Code (TCIC)
The CLEC will administer and assign the Trunk Circuit Identification Codes (TCICs). Certain switches require that the Common Language Location Identifier (CLLI) trunk number equals the TCIC.
The following represents the TCIC assignment criteria:
- The (TCIC) assignment is a five (5) digit number. Numbers are right justified with leading zeros. The ten thousand digit should always be a zero due to trunk number restrictions in some switches.
- The five (5) digit numbers (00001 - 09996) should be broken down into sub-blocks of 96 numbers (i.e., 00001 - 00096, 00101 - 00196, etc.). Numbers ending in 97, 98, 99 and 00 will not be assigned due to the limitations of some digital switches.
- Sub-blocks of 96 will not be split between groups of trunks with the same CLEC Point Code and AT&T West Point Code. This assures a group will always start with XXXX1 and provides for consecutive numbering.
- The smallest available sub-block will be selected for new groups or augments requiring an additional sub-block. Ascending order of assignments is required for minimizing memory loss in some machines.
- TCIC assignments will not be duplicated on groups between the same point codes. A mechanized assignment process with edits is recommended by the NOF to prevent dual assignments.
- TCIC assignments will be provided on all add, change and disconnect Local Interconnection Service Arrangement (LISA) trunk(s) requests. TCIC numbers should be reused on coordinated disconnect and add activity to assure reassignment of the lower sub-blocks to minimize loss in some machines.
SS7 Tones & Announcements
The LEC may either connect the call to a tone or an announcement and subsequently release the call with a normal cause indicator to the originating LEC, or release the call to the originating LEC with a specific cause indicator for the originating LEC to provide the tone or announcement. CLECs in agreement with the originating LEC and compliance to all applicable SS7 message sequences should recognize specific release cause messages and connect the tone or announcement.
The LEC will return the originating LEC a suitable coded Address Complete Message (ACM) prior to connecting the call to an CLEC tone or announcement. Properly coded release messages will be forwarded to AT&T West at the completion of the tine or announcement application. All response message sequences will need to be within the tolerances defined in timing parameter 'T-IAM' (Timer - Initial Address Message) of ANSI T1.113.
Customized announcements, such as automatic intercept for number changes, would have to be played by the terminating LEC. If there is not total SS7 connectivity in the terminating connection, the terminating LEC may have to play all tones and announcements.
Unbundled SS7
Unbundled SS7 is available to CLECs on a contractual basis only. The terms for ordering Unbundled SS7 are specified in each CLEC's contract with AT&T West.
Note:CLECs who want Unbundled SS7, but do not have a contract, must negotiate a contract with AT&T West.
An CLEC has three options for the purchase of unbundled SS7 in AT&T California.
- According to a contract
- From the Tariff, CPUC 175 - T, Section 6.8.2
- FCC 1, Section 6.8.10
An CLEC has three options for the purchase of unbundled SS7 in AT&T Nevada.
- According to a contract
- PUCN C6-A, Section 6.8.2
- FCC 1, Section 6.8.7
Purchasing Unbundled SS7 According to a Contract
- If an CLEC has a contract specifying the provision of SS7 interconnection, the CLEC must purchase from the contract's terms and conditions.
- If an CLEC does not have a contract specifying the provision of SS7 interconnection, an addendum to the contract may be written.
Purchasing Unbundled SS7 from the Tariff
The CLEC can purchase Unbundled SS7 from the tariff, with several choices available:
- SS7 Signaling Links and the Signal transfer point (STP) port from AT&T West.
- STP port from AT&T West and provide their own SS7 link. When the 'STP port only' option is ordered, Carrier Facility Assignment (CFA) information, as well as other information defined by the Marketing Manager, is required.
- SS7 Link and/or the STP port from a third party (a hub provider).
