1. Connecting to Remote Networks © 2004 Cisco Systems, Inc. All rights reserved. Using Circuit Switching in WANs INTRO v2.0—7-1

2. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-2 Outline Overview Circuit-Switched Communication Links Public Switched Telephone Network Integrated Digital Services Network Summary

3. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-3 Circuit Switching

4. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-4 PSTN

5. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-5 PSTN Considerations Advantages Simplicity Availability Cost Disadvantages Low data rates Relatively long connection setup time

6. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-6 ISDN

7. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-7 BRI and PRI

8. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-8 ISDN Considerations Advantages Speed Always-on availability Disadvantages Limited geographic availability Cost

9. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-9 Summary With circuit-switched WAN communication links, a dedicated physical circuit is established, maintained, and terminated through a carrier network for each communication session. The most common type of circuit-switched WAN communications is PSTN (also referred to as POTS). The physical characteristics of the local loop and its connection to the PSTN limit the rate of the signal over the PSTN. The upper limit is around 33 kbps. The rate can be increased to around 56 kbps if the signal is coming directly through a digital connection. ISDN refers to a set of communication protocols proposed by telephone companies to permit telephone networks to carry data, voice, graphics, music, and video. ISDN was developed to permit faster access over existing telephone systems without the additional call setup time.

10. © 2004 Cisco Systems, Inc. All rights reserved. INTRO v2.0—7-10 Summary (Cont.) ISDN offers two types of services: BRI and PRI. The ISDN BRI service, intended for the home and small business users, provides two B channels (128 Kbps) and one D channel (16 Kbps). The BRI B channels carry user data, while the BRI D channel usually carries control and signaling information. The ISDN PRI service, intended for larger installations, delivers 23 B channels and one D channel in North America for a total bit rate of up to 1.544 Mbps (T1).