1. Network Operations & administration CS 4592 Lecture 18 Instructor: Ibrahim Tariq

2. 2 Taxonomy of Multiple-Access Protocols

3. 12.3 12-3 CHANNELIZATION Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations. In this section, we discuss three channelization protocols. Frequency-Division Multiple Access (FDMA) Time-Division Multiple Access (TDMA) Code-Division Multiple Access (CDMA) Topics discussed in this section:

4. 12.4 Figure 12.21 Frequency-division multiple access (FDMA)

5. 12.5 In FDMA, the available bandwidth of the common channel is divided into bands that are separated by guard bands. Note

6. 12.6 Time-division multiple access (TDMA)

7. 12.7 In TDMA, the bandwidth is just one channel that is timeshared between different stations. Note

8. 12.8 In CDMA, one channel carries all transmissions simultaneously. Note

9. 12.9 Simple idea of communication with code

10. 12.10 Figure 12.24 Chip sequences

11. 12.11 Figure 12.25 Data representation in CDMA

12. 12.12 Figure 12.26 Sharing channel in CDMA

13. 12.13 Figure 12.27 Digital signal created by four stations in CDMA

14. 12.14 Figure 12.28 Decoding of the composite signal for one in CDMA

15. 12.15 12-2 CONTROLLED ACCESS In controlled access, the stations consult one another to find which station has the right to send. A station cannot send unless it has been authorized by other stations. We discuss three popular controlled-access methods. Reservation Polling Token Passing Topics discussed in this section:

16. Reservation Station needs to make a reservation before sending data Time is divided into intervals In each interval reservation frame goes before data telling which station has to send data

17. 12.17 Figure 12.18 Reservation access method

18. Polling Works with topologies in which one device is designated as primary station and others are secondary stations All data is communicated through Primary station If primary device has to send data is alerts secondary by Sending SELECT function Primary device if not sending continues to Poll each device NAK is send is secondary device does not want to send data

19. 12.19 POLLING Select and poll functions in polling access method

20. Token Passing Works in any topology if Logical ring is created Special packet called a token is circulated through the ring. The possession of token gives the station the right to access the channel and send its data If no data to send token is passed to next logical station in ring

21. 12.21 Figure 12.20 Logical ring and physical topology in token-passing access method