1. DATA COMMUNICATION
Lecture-31

2. Recap of Lecture 30 Time Division Multiplexing Asynchronous TDM
Inverse Multiplexing
The Telephone System

3. Overview of Lecture 31 The Telephone System Analog Services
Digital Services
Fiber To The Curb (FTTC)

4. Telephone System
North American telephone system includes many common carriers
Local companies and long-distance providers

5. Telephone System

6. Telephone Services Analog services: Analog network and FDM
Digital services: Digital network and TDM
For now, both types of services are available

7. Telephone Services

8. Analog Services Switched service and leased services
Sensitive to noise and other forms of interference

9. Analog Services

10. Analog Switched Service
The familiar dial-up service
Local loop: Two-wire connection between the subscriber’s handset and the network
The network is called PSTN (Public Switched Telephone Network)

11. Analog Switched Service

12. Analog Leased Service
Offers a dedicated line, that is permanently connected to another customer
The connection still passes through the PSTN, but no dialing is needed

13. Analog Leased Service

14. AT&T’s Analog Hierarchy

15. Digital Services Less sensitive than analog services to noise
Less expensive than analog services

16. Digital Services

17. Switched/56 Service Switched digital service - data rate up to 56 Kbps
Subscribers need DSU instead of modem

18. Switched/56 Service DSU (Digital Service Unit)
Changes the subscriber’s rate to 56 Kbps
Encodes the data in the format used in the network

19. Switched/56 Service

20. Digital Data Service
Digital leased line with a maximum data rate of 64 Kbps
DDS also requires the use of a DSU

21. Digital Data Service

22. DS Hierarchy

23. T Lines Telephone companies use T lines to implement the DS services
DS-0 is not actually offered as a service

24. T Lines Service Line Rate(Mbps) Voice channels
DS T
DS-2 T
DS-3 T
DS T

25. Summary The Telephone System Analog Services Digital Services
Fiber To The Curb (FTTC)

26. Suggested Reading
Section 8.5, “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan