This Tutorial covers the fundamentals of Signaling System Seven (SS7) telecommunication standards. It provides descriptions and examples of SS7 network components, architecture, and basic network operations. It will prepare you with the necessary knowledge to:

• Define the components of an SS7 network
• Create a diagram of a generic SS7 network setup
• Define each layer within an SS7 protocol stack
• Differentiate various types of signaling units
• Use the fields of a signaling unit to identify its type
• Recall categories of a signaling network management function in response to phrases that describe that functions' purpose
• Recall criteria for establishing a signaling link and keeping it in service
• Determine whether a signaling unit was transmitted and received without error
• Predict how MTP Level 3 selects a link for an outbound message from SCCP
• Predict how SCCP's class of service will affect delivery of MSUs to remote points
• Describe components of TCAP messages
• Recall the purpose of messages used by originating and destination points during ISUP call control

HISTORY AND BACKGROUND

Before learning about Signaling System Seven (SS7), which is used throughout the world for today's telecommunications, it is helpful to briefly review the history behind SS7. The following is an overview of how telephone networks operated in the past, and how the SS7 network has changed them. This section of the SS7 Tutorial addresses the advantages and opportunities SS7, with its "out-of-band signaling", has created for the telecommunications industry.

Common Channel Signaling 

In the original Public Switched Telephone Network (PSTN), switches resided at local phone offices. These switches sent analog signaling information and voice for subscribers over the same physical connection. This basic type of common channel call control (setup and teardown of telephone calls) was all that the technology could support - until the digital era began.

Signal & Voice Split

As the digital age began to emerge and new means of communication grew in popularity, a need for "out-of-band signaling" arose. That meant that the analog connections once used for voice and signaling would now be dedicated to carrying voice only, and separate digital connections would be dedicated to signaling. This required the addition of specialized equipment to relay information to various end points across the network. Therefore, the out-of-band signaling that is characteristic of SS7 provided new connections and signal relay equipment that could handle all signaling messages between end points in the communication network.

Intelligent Networks

As networks became more "intelligent", databases were added to accommodate new types of communication services. With signaling messages (via the relay points), switches could now "talk to" databases, providing a greater array of sophisticated communication services.

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