1. Database Administration - GWS User's Guide
  2. Gateway Screening (GWS) Overview
  3. Introduction

Introduction

This chapter provides an overview of the gateway screening feature and procedures for provisioning these items in the database:

  • GLS cards
  • Gateway screening stop action sets
  • The threshold for gateway screening activity
  • Setting the maximum number of gateway screening rejected messages

The gateway screening tables are loaded onto Link Interface Modules (LIMs) or service modules. Service modules can be any of these cards:

  • EAGLE-Service Module 4 GB (E5-SM4G or E5-SM8G-B cards)

The use of the service modules in the EAGLE is dependent on the combination of global title translation features that are being used in the EAGLE. for more information on the global title translation features, go to Database Administration - GTT User's Guide.

The gateway screening tables provide screening of MTP (LIMs) and SCCP (service modules) messages.

MTP Screening consists of the following items:

  • Allowed Originating Point Code (OPC)
  • Blocked Originating Point Code (BLKOPC)
  • Allowed Signaling Information Octet (SIO)
  • Allowed Destination Point Code (DPC)
  • Blocked Destination Point Code (BLKDPC)
  • Allowed Affected Destination Field (DESTFLD)
  • Allowed ISUP Message Type (ISUP) - ISUP and TUP messages can be screened by the allowed ISUP message type screen.

SCCP Screening consists of the following items:

  • Allowed Calling Party Address (CGPA)
  • Allowed Translation Type (TT)
  • Allowed Called Party Address (CDPA)
  • Allowed Affected Point Code (AFTPC).

The procedures shown in this manual use a variety of commands. If more information than what is shown in these procedures is needed, go to Commands User's Guide to find the required information.

The EAGLE's role in the SS7 network is to provide SS7 message transport between originating and destination signaling points. EAGLEs that route messages to and from other networks also perform gateway screening. The screening process results in a message being accepted into the network or rejected. The criteria for message screening depends on the type of message received by the EAGLE, and the contents of the EAGLE screening tables.

Gateway screening functions on the EAGLE reside within the LIM and the service modules and are defined using screening tables or screen sets which contain a set of rules. Each screen set is uniquely identified by a screen set name. Each rule in the screen set is identified by a screening reference name. Each screening reference belongs to a specific category, which indicates the criteria that is used to either accept or reject an incoming MSU. For example, the category blkopc rejects all MSUs with the OPCs specified in the screening reference. The screening parameters (point codes, routing indicator, subsystem number, etc.) are used to match information in the SS7 message. The screening data is defined by the attributes discussed in the Gateway Screening Attributes section.

Each group of screening references is referred to as a screen set and is identified by a particular screen set name (scrn). The screen set is applied to a particular linkset. This allows the capability, for example, for specific OPCs with particular SIOs and DPCs to be allowed into the network.

With the SEAS interface, the screen set function is performed by a gateway linkset. A gateway linkset combines the functions of a gateway screening screen set and an SS7 linkset specifying the gwsa=on and scrn parameters. Like an EAGLE gateway screening screen set, a gateway linkset defines the screening references that are to be used to screen the messages on the linkset. It also defines the linkset whose messages are to be screened. A gateway linkset can only be configured from a SEAS terminal and not from an EAGLE terminal. The linkset attributes of a gateway linkset can be displayed on an EAGLE terminal with the rtrv-ls command. A gateway linkset is shown by the entry SEAS in the SCRN field of the rtrv-ls command output. The gateway screening portion of the gateway linkset can only be displayed on the SEAS interface.

There are two basic functions, allow and block. In an allowed screen (for example, allowed DPC), if a match is found and the next screening function identifier (nsfi) is equal to anything but stop, the next screening reference (nsr) is identified and the screening process continues to the next screen identified by the nsfi and nsr parameters. If the next screening function identifier is stop, the message is processed and no further screening takes place. If no match is found, the message is rejected.

In a blocked screen (for example, blocked DPC), if a match is found and the next screening function identifier is fail, the message is rejected and no further screening takes place. If no match is found and the next screening function identifier is equal to anything but stop, the next screening reference is identified and the screening process continues to the next screen identified by the nsfi and nsr parameters. If the next screening function identifier is equal to stop, the message is processed and no further screening takes place.

When the screening process stops, other actions can be assigned to the screen set. These actions, called gateway screening stop actions, define the actions the EAGLE can perform on the MSU that passes gateway screening. For more information on configuring gateway screening stop actions, go to the Configuring Gateway Screening Stop Action Sets procedure. The EAGLE currently uses these gateways screening stop actions.

  • COPY – copy the MSU for the STPLAN feature
  • RDCT – redirect the MSU for the DTA feature
  • CNCF – convert the PIP parameter with the GN parameter or the GN parameter with the PIP parameter in the ISUPIAM message for the Calling Name Conversion Facility feature.
  • TLNP – ISUPIAMs that pass gateway screening are processed either by the ISUPNP with EPAP feature (if the ISUPNP with EPAP feature is enabled and turned on) or by the Triggerless LNP feature (if the Triggerless LNP feature is turned on).
  • TINP – ISUP IAMs that pass gateway screening are intercepted by the Triggerless ISUP based Number Portability (TINP) feature and converted to include the routing number (RN) if the call is to a ported number. This gateway screening stop action can be specified only if the TINP feature is enabled.

The allowed OPC and DPC screens are useful in the gateway screening process when specifying particular sets of point codes that are allowed to send messages to another network or receive messages from another network. The blocked OPC and DPC screens are useful in the gateway screening process specifying particular sets of point codes that are not allowed to send SS7 messages to another network or receive SS7 messages from another network.