SS7 Software Architecture

Excel uses the PPL environment to implement the Excel SS7 stack. This feature makes the stack modular and easy to customize. The SS7 software consists of the following modules:

Each signaling stack must include MTP, L3P, and at least one user part. Selection of a specific module automatically uses the associated default PPL components.

Excel implements BT IUP, a variant of L3P TUP. See TUP, BT IUP & SSUTR2, for an example configuration file and call flows for the BT IUP configuration. See SS7 PPL Information and the SS7 Signaling Stack Configure 0x5C for additional data on BT IUP.

Call control, circuit supervision, and maintenance can be managed using either the ISDN User Part (ISUP) or Telephone User Part (TUP) interfaces. The call control user part for a CIC is configured with the SS7 CIC Configure message.

The figures on the following pages show how the SS7 Signaling Stack integrates into the Excel platform architecture. Default protocol component sets for each module are stored as part of system software and do not require downloading. Selection of a specific module automatically uses the associated PPL components.

L3P is an interface between Layer 3 Call Control (ISUP/TUP) and Layer 4 Call Control on the Matrix Controller, and Layer 5 (the host application). It also manages application-specific variants for call control.

Formats the presentation of SS7 data to and from the host and manages call control.

Manages signaling links and formats presentations of SS7 signaling link control to and from the host.

L3P TUP is an interface between Layer 3 (TUP), Layer 4 Call Control on the Matrix Controller, and Layer 5 (the host). L3P TUP formats information from Layer 3 into the programmed format for the host and host formatted information for Layer 3. It also manages application-specific variants for call control.

Integrated Services Digital Network User Part (ISUP) is the protocol for voice and non-voice services. ISUP includes the following PPL components:

CPC manages the call processing portion of ISUP. It manages both incoming and outgoing call setup and tear down.

SPRC acts as an ISUP message router. It validates and routes incoming ISUP messages to the correct ISUP state machine. It also sends outgoing messages to MTP.

A collection of state machines that manage circuit maintenance, such as group blocking/unblocking and circuit reset.

SPRC validates and routes incoming TUP messages to the correct TUP state machine. It also sends outgoing messages to MTP.

Standard	Component
ANSI	BLR, BLS, CCI, CRI, CGRR, CGRS, CRR, CRS, GBUR, GBUS, UCIC
ITU-TS	BLR, BLS, CCI, CGRR, CGRS, CRCR, CRR, CRS, HGBR, HGBS, HLB, HRB, MGBR, MGBS

Message Transfer Part (MTP) is responsible for end-to-end reliable delivery of messages generated by its local user part (for example, ISUP). The MTP module comprises the MTP2 and MTP3 layers. MTP includes protocols and procedures to handle network failures and to dynamically reconfigure signaling resources to prevent message loss or duplication and out-of-sequence delivery.

Signaling Connection Control Part (SCCP) provides both connectionless and connection-oriented network services above MTP Level 3. Transaction Capabilities Application Part (TCAP) provides transaction and remote operation capabilities to a large variety of applications distributed over the CSP and service centers in the network. Excel’s SCCP/TCAP development supports the following connectionless services:

See Programmable Protocol Language.

See Signaling System Number Seven.

See Integrated Services Digital Network User Part.

See Transaction Capability Application Part.

See Message Transfer Part.

Setting up, monitoring, and tearing down calls.

See Integrated Services Digital Network.

See Circuit Identification Codes.

Protocol layer of the CSP.

Call processing layer of the CSP.

Application layer of the CSP.

ISDN. Network architecture based on digital transmission, switching, and common channel signaling. Basic configurations include 2B+D called a Basic Rate Interface, and 23+D called a Primary Rate Interface. Outside North America, PRI is 30B+D.

American National Standards Institute. ANSI administers and coordinates the U.S. voluntary standardization and conformity assessment system for the
telecommunications industry. More details on these standards may be
viewed at www.ansi.org.

International Telecommunications Union (UN)

MTP. Message Transfer Part of the SS7 signaling protocol.

Message Transfer Part level 2 - data link level

Message Transfer Part level 3 - network level

SCCP. The signaling connection and control part of the SS7 signaling protocol. For example, performs Global Title Translations (GTT), Subsystem Management.

TCAP. The transaction capabilities application part of the SS7 protocol. It is the top layer of the SS7 stack, equivalent to Layer 7 of the OSI model.

The condition of a component at a given instant. The current "context" of a PPL object, such as Idle, Seizing, Answered. In PPL files, a State is represented by a circle.