Table of Contents
- About the Authors
- Icons Used in This Book
- Command Syntax Conventions
- Part I. Introductions and Overviews
- Chapter 1. The Evolution of Signaling
- Chapter 2. Standards
- Chapter 3. The Role of SS7
- Chapter 4. SS7 Network Architecture and Protocols Introduction
- Chapter 5. The Public Switched Telephone Network (PSTN)
- Part II. Protocols Found in the Traditional SS7/C7 Stack
- Chapter 6. Message Transfer Part 2 (MTP2)
- Chapter 7. Message Transfer Part 3 (MTP3)
- Chapter 8. ISDN User Part (ISUP)
- Chapter 9. Signaling Connection Control Part (SCCP)
- Chapter 10. Transaction Capabilities Application Part (TCAP)
- Part III. Service-oriented Protocols
- Chapter 11. Intelligent Networks (IN)
- Chapter 12. Cellular Networks
- Chapter 13. GSM and ANSI-41 Mobile Application Part (MAP)
- Part IV. SS7/C7 Over IP
- Chapter 14. SS7 in the Converged World
- Part V. Supplementary Topics
- Chapter 15. SS7 Security and Monitoring
- Chapter 16. SS7 Testing
- Part VI. Appendixes
- Appendix A. MTP Messages (ANSI/ETSI/ITU)
- Appendix B. ISUP Messages (ANSI/UK/ETSI/ITU-T)
- Appendix C. SCCP Messages (ANSI/ETSI/ITU-T)
- Appendix D. TCAP Messages and Components
- Appendix E. ITU-T Q.931 Messages
- Appendix F. GSM and ANSI MAP Operations
- Appendix G. MTP Timers in ITU-T/ETSI/ANSI Applications
- Appendix H. ISUP Timers for ANSI/ETSI/ITU-T Applications
- Appendix I. GSM Mobile Country Codes (MCC) and Mobile Network Codes (MNC)
- Appendix J. ITU and ANSI Protocol Comparison
- Appendix K. SS7 Standards
- Appendix L. Tektronix Supporting Traffic
- Appendix M. Cause Values
As discussed in Chapter 4, "SS7 Network Architecture and Protocols Introduction," each node is uniquely identified by a Point Code. A national Point Code identifies a node within a national network, and an International Signaling Point Code (ISPC) identifies a node within the international network. An International Switching Center (ISC) is identified by both a national and international Point Code. All nodes that are part of the international signaling network use the ITU-T ISPC globally. However, national point codes are based on either the ITU national format or the ANSI format (North America). The structure for international and national Point Codes is discussed in the sections on ITU-T and ANSI, later in this chapter.
Each MSU contains both an Originating Point Code (OPC) and a Destination Point Code (DPC). The DPC is used for identifying the message's destination, and the OPC is used for identifying which node originated the message. As mentioned in the previous section and further discussed in the section "Signaling Message Handling," the DPC is the key entity for routing messages within a network. The OPC identifies which node originated the message.
The identity of the originator is needed for the message to be processed for the correct node. The received OPC can also be used to determine how to populate the DPC when formulating response messages. Because Point Codes are an integral part of MTP3, this chapter discusses them in various contexts, such as network hierarchy, message format, and Signaling Message Handling.
ITU-T International and National Point Codes
ITU-T defines Point Codes for both national and international networks. The international Point Code is based on a hierarchical structure that contains the following three fields:
- Signaling Point
As shown in Figure 7-1, the ITU-T has defined six major geographical zones that represent the major areas of the world. A Zone number that forms the first part of the Point Code represents each geographical zone.
Figure 7-1 ITU-T World Zone Map
Each zone is further divided into an Area or Network based on a specific geographical area within the zone, or as designated by a particular network within the zone. Together, the Zone and Area/Network form the Signaling Area/Network Code (SANC). ITU-T Q.708 lists the SANC codes for each geographical zone. For example, Figure 7-2 shows the SANC designations for the United Kingdom area. The SANC codes are administered by the ITU. ITU operational bulletins publish updates to the numbering assignments after the publication of Q.708.
Figure 7-2 UK Network/Area Point Code Numbers
The Signaling Point identifies the individual signaling node represented by the Point Code.
ITU-T National Point Codes do not have a standardized scheme for defining hierarchy. Each Point Code is a single identifier that designates a specific node.
ANSI National Point Codes
For national Point Codes, ANSI uses a hierarchical scheme similar to that defined by the ITU-T for international signaling. The ANSI Point Code is comprised of three identifiers:
The Network identifier represents the highest layer of the SS7 signaling hierarchy and is allocated to telecommunications companies that have large networks.
For example, each of the major operating companies in the U.S. (Verizon, Southwestern Bell, Bellsouth, and Qwest) is allocated one or more Network identifier codes, which identify all messages associated with their network. Smaller, independent operating companies share Network Identifiers, in which case they must use the remaining octets of the Point Code to discriminate between them. Within a network, the Cluster is used to group nodes in a meaningful way for the network operator. If an operating company owns a Network Identifier, it can administer the Cluster assignments in any manner of its choice. Clusters are often used to identify a geographical region within the operator's network; the Member identifies the individual signaling node within a cluster. Figure 7-3 shows the address hierarchy of ANSI networks.
Figure 7-3 Address Hierarchy of ANSI Networks
For the purpose of Point Code allocation, networks are divided into three categories:
- Large Networks
- Small Networks
- CCS Groups
Assignable Point Code Network IDs are numbered 1–254. Network ID 0 is not used, and Network ID 255 is reserved for future use. Point Codes for large networks are assigned in descending order, beginning with Network ID 254.
Point Codes for small networks are assigned in ascending order from the point codes within the Network ID range of 1–4. Each small network is assigned a cluster ID, along with all of the Point Code members within that cluster. A small network operator may be assigned multiple clusters if the network is large enough to warrant the number of Point Codes.
Network ID 5 is used for CCS groups. These groups are blocks of Point Codes belonging to a set of signaling points that are commonly owned but do not have any STPs in the network. These are the smallest category of networks. Point Codes within a cluster may be shared by several different networks depending on the size of the CCS groups. Telcordia administers ANSI Point Codes.
Network ID 6 is reserved for use in ANSI-41 (Mobile Networks) and CCS groups outside of North America.