In this section:

Overview

Point Code EmulationTM (PCE) is an optional Level 4 (L4) software application on the DSC, used to significantly simplify and reduce the risk of switch migration activities.

PCE is a Level 4 (L4) software application that Ribbon offers as an option with the DSC. This application is used to divide a network into two different addressing spaces for the reuse of point codes (PCs). These two addressing spaces are typically referred to as the public network and the private network. PCE can be used for Integrated Services Digital Network (ISDN) User Part (ISUP) and for Transaction Capabilities Application Part (TCAP) messaging.

This application ensures that service providers have the ability to transparently configure and manipulate SS7 nodes without disruption or reconfiguration of the public SS7 network. PCE is similar to network address translation (NAT) on an IP network. Similarly to NAT, PCE allows computers to use one IP address when accessing the Internet and many network elements to appear to the network as one or more shared point codes (PCs).

PCE is a cost effective solution for expanding networks where new PCs are rare and expensive by minimizing the number of direct SS7 links to an STP pair. Nodes within the private network are accessed using trunk-based routing for ISUP traffic and Transaction Identifiers with GTT routing for TCAP traffic.

The benefits of PCE include the following:

  • ability to move and test trunk facilities without disrupting the interconnecting networks, hence, saving both time and money

  • Next-Generation network expansion without requiring additional PCs

  • cost reduction by limiting the number of PCs required to be presented to the PSTN

  • F-link consolidation to reduce port and/or SS7 link exhaustion on existing nodes

The enhanced version of PCE supports a second private Network Appearance (NA) that can be used as a swing-box in a cut-over environment for migration to next-generation solutions and to address the cap-and-grow issue. PCE allows two switches on the private domain to share the same PC, thereby, giving operators the ability to manipulate nodes without disrupting the network.

The DSC supports 1,024 Public Gateways. The Public Gateways are the private network entry point codes that the Public Nodes use as their Destination Point Codes.

Typically, all nodes in the public network that interact with PCE require an associated Public Node UI object. The Non-Member Routeset Support feature allows nodes in the private network (or networks for Enhanced PCE) with cluster, network, or default routeset definitions to respond to TCAP queries from nodes in the public network that are not defined in the PCE as Public Nodes.

For more information about the Non-Member Routeset Support feature, refer to Public Node and General Configuration.

For information about configuring PCE, refer to Configuring the Point Code Emulator.

ISUP Trunk Management

The following figures show an example of the ISUP call flow and the ISUP message sequence for the corresponding network configuration.

Example of PCE Network and Internal Architecture

Example of ISUP Message Sequence

The ISUP message flow for the preceding figure (Figure Example of ISUP Message Sequence) is as follows:

  1. Switch 1 sends a message to the public gateway PC (3.3.3). This is the public representation of the internal switches.

  2. PCE looks up the trunk record on the public side of the trunk mapping table. This process allows PCE to determine that the message must be sent to Switch 2 and that the Circuit Identification Code (CIC) value must be mapped. The OPC has been mapped, however, because the values for Switch 1 and the internal PC in the PC mapping table are identical, the value happens to be the same. This configuration is highly preferred because this arrangement makes troubleshooting easier by eliminating the extra conversion.

  3. Switch 2 responds back to the originator (internal 2.2.2).

  4. PCE again uses its trunk mapping record to look at the Originating Point Code (OPC), Destination Point Code (DPC), and CIC value to determine the appropriate values on the public side.

TCAP Transaction Management

TCAP message handling in PCE is different than the ISUP message handling because there is no CIC value to determine which internal switch to use. TCAP transaction management includes the following two transaction types:

  • TCAP Internally-initiated Transactions

  • TCAP Public-initiated Transactions

TCAP Internally-initiated Transactions

At the heart of the TCAP handling technology is a temporary database used to hold the TCAP transaction IDs, information known about each transaction and how the transaction is distributed across the various CPUs (VMs) on both mates of an STP pair.

The operator is given a flexible set of routing possibilities to handle a new TCAP query or transaction as it crosses PCE. TCAP queries, starting from the private side of PCE (internal-initiated), are added to the database and sent to the public destination. Any subsequent messages on the same TCAP transaction use the same end points as stored in the database.

TCAP Public-initiated Transactions

When PCE receives a public-initiated TCAP query message, PCE processes this message in the order indicated in the following list:

  1. Sends the query directly to an internal node if this option has been declared in the provisioning of the receiving public gateway.

  2. Sends the message to GTT. If there is an entry found in the GTT database for this message, GTT sends the message to the internal node according to the match of the GTT translations and the Called Party Address Global Title (GT). If there is no entry found in the GTT database for this message, GTT returns the MSU for further processing to PCE.

  3. If IS-41 messaging is used, the Billing ID in the messages may be configured to determine the internal destination.

  4. PCE confirms whether ISUP Learning has been enabled. The message may be routed with information that has been recovered by the system having monitored recent ISUP messages.

  5. If the other methods have not routed the message, PCE may be configured to broadcast the message to all internal nodes and await a positive response.

    Note

    If the broadcast is not enabled, the MSU cannot be routed and an SCCP relay error handling is performed.

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