# Signaling System No.7

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Descriptions

Signaling System Number 7 (SS7) is a sophisticated, integrated signaling protocol designed to increase the efficiency of telephone service delivery. It has become the central nervous system for the delivery of wireline and wireless, and more recently IP services, the latest step in the convergence of communication networks. All networks need signaling to create connections, activate service, and deliver traffic.

SS7 basic functions are as follows:

| MTP (Message Transfer Part)

The Message Transfer Part provides a reliable transfer and delivery of signaling information across signaling networks. It is divided into three levels:

•MTP Level 1 defines the physical, electrical, and functional characteristics for the signaling data link.

•MTP Level 2 provides the reliability aspects of MTP including error monitoring and recovery.

•MTP Level 3 provides the link, route, and traffic management aspects of MTP.

The MTP software and boards support ITU-T, ANSI, and Chinese variants of the protocol, enabling applications to be widely deployed.

MTP provides the means to:

•Interface with the SS7 network

•Detect and correct errors to messages sent on signaling links

•Manage links and routes, thus mitigating failures and congestion within the network should they occur

MTP provides routing services for SCCP and ISUP on a point-to-point basis. In addition, MTP supports TCAP, which depends upon SCCP, as well as the protocols such CAP and GSM MAP that are supported by TCAP.

The UltraWAVE MTP modules support the relevant addressing (point code) scheme required by ITU-T, ANSI, and China. In addition, it supports:

•4 network: National, National Spare, International, International Spare

•14-bit / 24-bit originating point code

•1024 signaling links

•512 linksets

•1024 routing sets (destination point code) per network

•16 links per linkset

| SPC Routing

Signaling Point Code (SPC) in the SS7 network is uniquely identified by a numeric point code. Point codes are carried in signaling messages exchanged between signaling points to identify the origination (Originating Point Code) and destination (Destination Point Code) of each message.

Each signaling point in a signaling network is allocated to a code plan that is unambiguous within a domain (International, International Spare, National, National Spare), in accordance with the Network Indicator (NI).

Signaling points in the same domain are specified to a fixed length, either 14-bit or 24-bit.

Message routing is the process of selecting, for each signaling message to be sent, the signaling linkset to be used. It is based on analysis of the predetermined routing data at the signalling point concerned.

•ACN: The Application Context Name enables the version negotiation for the MAP messages, which make the system more compatible with the other networks by means of flexible message version adjustment. The adjustable version includes Version 1, Version 2 and Version 3.

| Link

Telecommunication network served by a common channel signaling is composed of a number of switching and processing nodes interconnected by transmission links. To communicate using SS7, each of these nodes must act as a signalling point within the SS7 network. In addition, there will be a need to interconnect these signalling points by means of signalling data links, such that SS7 information may be conveyed between them.

•SLC: The selection of outgoing link is based on information in the DPC and Signaling Link Code field. The Signaling Link Code is used to:

-Ensure message sequencing. Any two messages sent with the same SLC will always arrive at the destination in the same order in which they were originally sent.

-Allow equal load sharing of traffic among all available links. In theory, if a user part sends messages at regular intervals and assigns the SLC values in a round-robin fashion, the traffic level should be equal among all links (within the combined linkset) to that destination.

•Sigtran: The Sigtran protocol deliveries traditional switched circuit signaling on IP network, with an emphasis on SS7 over IP.

•M2UA: The M2UA protocol is the layer between SCTP and MTP3 that separates the physical SS7 termination from the actual signaling point within the network. M2UA serves several purposes. The first purpose is to provide a mechanism for the transport of SS7 MTP2 user signaling (e.g., MTP3 messages) over IP using SCTP. The second purpose is to allow remote placement of SS7 link terminations and back haul SS7 traffic to a centralized point in the network.

| Linkset

A number of parallel signaling links constitute a linkset.

| Signaling Gateway

The Signaling Gateway provides interworking between the UltraWAVE MSC and the IP-based network elements. It is implemented as an embedded component of MTP3.

| Flexible Point Codes Function

Each signaling point in the SS7 network is identified with a unique address called a point code. Point codes are carried in signaling messages exchanged between signaling points to identify the source and destination of each message. The point code is a hierarchical address that consists of a network identification which identifies a signaling network. In the ITU definition, there are four signaling networks and each signaling network can have a unique Originating Point Code.

The Flexible Point Codes Function of the UltraWAVE system is an extension of the upper definition; it allows each signaling network to have multiple point codes. That means several Originating Point Codes may exist in the same signaling network. This function is based on the achievement of binding OPCs on linksets and routes.

The UltraWAVE system supports up to 512 linkset, each linkset should be assigned to a signaling network and have an individual OPC. When the OPC of the linkset is ignored, the linkset will take the OPC of its signaling network as an alternative. The OPC of the linkset takes priority over the OPC of its signaling network.

Each linkset has its own route to define a particular destination and its accompany alternate linkset. Just like the linkset, a route should be assigned to a signaling network and have an individual OPC. When the OPC of the route is ignored, the route will take the OPC of its signaling network as an alternative. The OPC of the route takes priority over the OPC of its signaling network.

| SCCP (Signaling Connection Control Point)

Signaling Connection Control Point provides additional routing capabilities via Sub-System Numbers (SSNs). It also offers the capability of routing based on dialed digits or global title translation. UltraWAVE SCCP module supports ITU-T, ETSI, ANSI, Chinese variants of the protocol, enabling applications to be widely deployed.

The UltraWAVE SCCP module provides the means to:

•Route TCAP messages from end-to-end

•Translate from Global Title numbers to point code and subsystem numbers

•Establish and release connections

SCCP provides routing services for TCAP on an end-to-end basis, which supplements the point-to-point routing of MTP. In addition, SCCP translates Global Titles to point codes and subsystem numbers, simplifying routing table maintenance within a network.

| Local Node

Local Node provides subsystem numbers to allow messages to be addressed to specific applications.

| GTT

Global Title Translation is the SS7 equivalent to IP routing. Translation examines the destination address (e.g. the number being called) and deciding how to identify it over the telephone network. This process can include global title analysis, which is the act of looking up the number and finding a result address, and global title modification.

| Network Code

The Network Code table contains the information necessary to identify the intended endpoint for the telephone call.

•CC: The Country Code is a one, two, or three digits number used to identify the country's network.

•NDC: The National Destination Code defines the national calling area or national network to which the subscriber belongs.

•MCC: The Mobile Country Code is a three digit number uniquely identifying a given country. It is utilized within the IMSI (International Mobile Subscriber Identity) and LAI (Location Area Identity).

•MNC: The Mobile Network Code is either a two or three digit number used to uniquely identify a given network from within a specified country. The MNC is used as part of the IMSI and LAI.

•International Prefix: It is a digit or combination of digits used by a subscriber when making an international call. The international prefix is used to indicate that the following digits represent an international number and should be routed to an international gateway.

•National Prefix: It is a digit or combination of digits used by a subscriber when calling a national destination (within the country) other than that of the local area network.

| TCAP (Transaction Capability Application Part)

The Transaction Capabilities Application Part (TCAP) uses the transport services of MTP and SCCP to support transaction based services associated with wireline, wireless, and IP networks. TCAP is used to support Intelligent Network services, mobility services, supplemental services, and short message services (SMS).

TCAP provides the means to:

•Establish end-to-end connections between TCAP user parts

•Handle message dialogs between end-points

TCAP information is embedded in the message service units that flow on the SS7 network. TCAP messages contain both transaction information and component information. It is ideal for applications such as switching and mobility services in which switching elements need to query remote databases in order to authenticate (or locate) a roaming subscriber or to translate a destination number to an actual physical number for intelligent routing.

The UltraWAVE TCAP module offers the following features:

•State machine based on ITU-T model

•Dialogue handling, state event processing, and timing capabilities

•2048 simultaneous transactions per process

•Message parameter validation

•Round-robin routing of inbound dialogs

•Application linkage of multiple SS7 variants to provide gateway functionality

•Load distribution across multiple applications

•Abort/reject message generation

| TUP (Telephone User Part)

The Telephone User Part (TUP) provides the signaling backbone between switching elements for basic call establishment, supervision, and release of circuit switched network connections for telecommunications services. TUP supports analog and digital circuits, and limited call management signaling. Since TUP lacks the support for ISDN services, it is found primarily in older networks that support strictly narrowband voice services.

The UltraWAVE TUP module provides the means to:

•Establish, maintain, and release calls and connections

•Supervise and manage the circuit infrastructure

TUP controls the circuits used to carry voice traffic. In addition, the state of circuits can be verified and managed using TUP. The management of the circuit infrastructure can occur both at the individual circuit level and for groups of circuits.

| ISUP (ISDN User Part)

The ISDN User Part (ISUP) provides the signaling backbone between switching elements for basic and supplementary services for the call establishment, supervision, and release of circuit switched network connections for telecommunications services. ISUP supports analog and digital circuits, as well as call management signaling for data transmission. The UltraWAVE ISUP module supports ITU-T, ANSI, and Chinese variants of the protocol, enabling applications to be widely deployed.

The ISUP module provides the means to:

•Establish, maintain, and release calls and connections

•Supervise and manage the circuit infrastructure

ISUP controls the circuits used to carry either voice or data traffic. In addition, the state of circuits can be verified and managed using ISUP. The management of the circuit infrastructure can occur both at the individual circuit level and for groups of circuits.

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