Signaling System 7

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Signaling System 7 (SS7)
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Chapter Thirty One Objectives

• Describe the signaling systems
• Define the role signaling plays in a network
• Discuss the benefits of out-of-band signaling
• Compare the different types of circuits used in
  SS7
• Describe at least one type of call flow through
  the network using signaling system 7

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Signaling System 7

• Making a call over the PSTN
• Off hook
• Dial some digits
• Talk to someone anywhere in the world
• Network figures out where to route the call
• Set up call instantly
• Tear down the call as quickly
• Behind the scene is the backbone of signaling
  systems
• Subsecond call setup and teardown
• Evolution of signaling systems
• Common Channel Interoffice Signaling System
  Number 7
• Save time and money on the network
• Introduce new features and functions in an
  intelligent network

4
Signaling System 7

• Pre-SS7
• Per-trunk signaling (PTS)
• Tones or multiple frequencies
• Trunk provides monitoring and supervision
• Systems not ISDN-compatible use PTS

5
Signaling System 7 An Introduction

• SS6 mid-1960s, evolved to SS7
• Success of SS6 protocol uses messages to request
  services from other entities on the network
• Format started as 2,400 bps, upgraded to 4,800
  bps, data packets
• Placing 12 signal units (28 bits each) assembled
  data packets into a data block
• Similar to that used in SS7 today
• North America uses 56 kbps, world 64 Kbps
• Use of full DS-1 data link still being considered
  in North American marketplace

6
Signaling System 7 Purposes

• Purpose of SS7 Network
• access remote data bases, look up and translate
  information from 800 and 900 calls
• marry various stored program-controlled systems
  in the world
• 1 second call set up and tear down
• integration of supervision, monitoring, billing
  systems
• enable introduction of additional features and
  capabilities

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Signaling System 7 Out-of-Band Signaling

• out-of-band signaling does not take place in the
  talk path
• original out-of-band signals used in 4-KHz
  voice-grade channel 3,500 and 3,700 Hz
• out-of-band signal evolved to a separate digital
  channel (signaling link) a la ISDN D channel

8
Signaling System 7 Why Out-of-Band?

• Advantages over in-band signaling
• enables transport of more data at higher speeds
  (56 Kbps than MF)
• enables signaling at any time in the entire
  duration of the call
• enables signaling to network elements to which no
  direct trunk connection is available

9
Signaling System 7 Architecture

• associated signaling
• non-associated signaling
• quasi-associated signaling
• components of SS7 network

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Signaling System 7 Architectural Beginnings
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