Core Signaling Transfer Point

Overview

When configured as a Signaling Transfer Point (STP) node, the DSC offers standard features and many additional features that are expected of a full-scale industry-leading STP. Standard STP functions, including Gateway Screening (GWS) and Global Title Translation (GTT), are further enhanced to support flexible routing and reporting. At the same time, these platforms offer extended capabilities and features such as Signaling Gateway (SG) MTP Level 3 (MTP3) User Adaptation Layer (M3UA), Signaling Connection Control Part (SCCP) User Adaptation Layer (SUA), and Point Code Emulation^TM (PCE). The DSC offers the flexibility to interface with traditional SS7 Time Division Multiplex (TDM), Asynchronous Transfer Mode (ATM), and next-generation (IP-SIGTRAN) networks while providing the ability to incorporate applications into a single platform.

The DSC supports the following routing mechanisms:

• full PC routing
  
  
• cluster routing
  
  
• network routing
  
  
• default routing
  
  
• multiple PCs
  
  
• Gateway Screening (GWS)
  
  
• national spare
  
  
• advanced managed routing (routing based on incoming linkset)

The DSC supports up to 32 Network Appearances (NAs). The system may be partitioned into separate virtual STPs, each having its own PC identity and each assigned its own protocol variant, routing rules, and timers. For detailed information about the supported routesets and routes, refer to Capacity and Performance. The system is designed for both American Standards Institute (ANSI) and International Telecommunications Union-Telecommunication Standardization Sector (ITU) network protocols that can be assigned to any of the NAs. The system can also support Nippon Telegraph and Telephone (NTT) and Telecommunication Technology Committee (TTC) for Japan and China SS7 variants.

For detailed information about configuring a DSC as a core STP, refer to the appropriate chapters in the SS7 Application Guide 1 and SS7 Application Guide 2. 

MTP3 Routing

MTP3 provides the routing functionality to transport signaling messages through the SS7 network to the requested node. Each network element in the SS7 network has a unique address or point code (PC). Message routing is performed according to this address. A distinction is made between a Signaling Transfer Point (STP) that only performs MTP3 message routing functions and a Signaling End Point (SEP) that uses MTP3 to communicate with other SEPs (that is, telecommunication switches). MTP3 is also responsible for network management. When the availability of MTP2 data links change, MTP3 establishes alternative links as required and propagates information about route availability through the network.

For information about MTP3 Routing, refer to the SS7 Application Guide 1 and The MTP3 User Interface.

Local PC

The Local Point Code (LPC) refers to the MTP3 address of a network element on an SS7 network. All signaling links and linksets defined in a network element are locally terminated using this PC. Typically, an LPC may not be shared between two nodes in one network, because addressing conflicts may result. The Ribbon STP and SG may be configured with up to 32 Network Appearances (NAs). Each NA can be represented as an individual or virtual STP or SG. Each NA has one LPC, but may have many virtual nodes each with its own PC.

For more information about LPC, refer to Configuring Basic NA Attributes.

Virtual PC

The Virtual Point Code (VPC) typically refers to an application. VPC is a PC that can be shared on both nodes of a mated pair configuration. In this configuration, if the STP is out-of-service, the other nodes still have access to this application. The other nodes use the VPC in their routeset definitions. VPC is a standard SS7 concept, used as VNodes at the MTP3.

For more information about VPC, refer to Configuring a VNode.

SLS Manipulation

The Signaling Links Selection (SLS) is an attribute in the MTP3 user interface in the DSC Web UI. This attribute can be used in reference to the algorithm that an SS7 node uses for selection of the appropriate signaling link to use for communication with an adjacent SS7 node. Factors such as load balancing and link availability are used to determine the appropriate link.

The DSC allows the following SLS provisioning:

• setting the SLS size and rotation
   
• configuring the SLS ignore bit
  
  
• configuring the SLS linkset select bit

For more information about SLS, refer to Configuring Additional NA Attributes.