區域網路設備基礎介紹

1. 區域網路設備基礎介紹 Data Communications and Computer Networks: A Business User’s Approach Fifth Edition (Chap 7)

2. Introduction • A local area network is a communication network that interconnects a variety of data communicating devices within a small geographic area and broadcasts data at high data transfer rates with very low error rates • Since the local area network first appeared in the 1970s, its use has become widespread in commercial and academic environments Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

3. Primary Function of Local Area Networks (continued) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

4. Hubs • Hub interconnects two or more workstations into a local area network • When a workstation transmits to a hub, hub immediately resends the data frame out to all connecting links • Can be managed or unmanaged • A managed hub possesses enough processing power that it can be managed from a remote location Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

5. Bridges • A bridge (or bridge-like device) can be used to connect two similar LANs, such as two CSMA/CD LANs • Can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

6. Bridges (continued) • Examines destination address in a frame and either forwards this frame onto next LAN or does not • Examines source address in a frame and places this address in a routing table, to be used for future routing decisions Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

7. Bridges (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

8. Transparent Bridge • A bridge observes each frame that arrives at a port, extracts the source address from the frame, and places that address in the port’s routing table • A transparent bridge is found with CSMA/CD LANs Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

9. Transparent Bridge (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

10. Transparent Bridge (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

11. Switches • A combination of hub and bridge • Can interconnect two or more workstations, but like a bridge, it observes traffic flow and learns • When a frame arrives at a switch, switch examines destination address and forwards frame out the one necessary connection • Workstations that connect to a hub are on a shared segment • Workstations that connect to a switch are on a switched segment Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

12. Switches (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

13. Switches (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

14. Virtual LANs • Virtual LAN (VLAN) – logical subgroup within a LAN that is created via switches and software rather than by manually moving wiring from one network device to another • Even though employees and their actual computer workstations may be scattered throughout the building, LAN switches and VLAN software can be used to create a “network within a network” Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

15. Wired Ethernet • Most common form of LAN today • Star-wired bus is most common topology but bus topology still not totally dead yet • Comes in many forms depending upon medium used and transmission speed and technology Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

16. Wired Ethernet (continued) • Originally, CSMA/CD was 10 Mbps • Then 100 Mbps was introduced • Most NICs sold today are 10/100 Mbps • Then 1000 Mbps (1 Gbps) was introduced • 10 Gbps is now being installed in high-end applications Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

17. Wired Ethernet (continued) • 1000 Mbps introduces a few interesting wrinkles: • Transmission is full-duplex (separate transmit and receive), thus no collisions • Prioritization is possible using 802.1p protocol • Topology can be star or mesh (for trunks) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

18. Wired Ethernet (continued) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

19. Wireless Ethernet • Not really a specific topology • Workstation in a wireless LAN can be anywhere as long as it is within transmitting distance to an access point • Several versions of IEEE 802.11 standard define various forms of wireless LAN connections • Workstations reside within Basic Service Set, while multiple basic service sets create an Extended Service Set Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

20. Wireless Ethernet (continued) • Two basic components necessary: • Client radio • Usually a PC card with an integrated antenna installed in a laptop or workstation • Access point (AP) • An Ethernet port plus a transceiver • AP acts as a bridge between the wired and wireless networks and can perform basic routing functions • Workstations with client radio cards reside within Basic Service Set, while multiple basic service sets create an Extended Service Set Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

21. Wireless Ethernet (continued) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

22. Wireless Ethernet (continued) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

23. Wireless Ethernet (continued) • IEEE 802.11 • Original wireless standard, capable of transmitting data at 2 Mbps • IEEE 802.11b • Second wireless standard, capable of transmitting data at 11 Mbps • In actual tests, 11 Mbps 802.11b devices managed 5.5 Mbps (from a July 2000 test by Network Computing) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

24. Wireless Ethernet (continued) • With directional antennae designed for point-to-point transmission (rare), 802.11b can transmit for more than 10 miles • With an omni-directional antenna on typical AP, range may drop to as little as 100 feet Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

25. Wireless Ethernet (continued) • IEEE 802.11a • One of the more recent standards • Capable of transmitting data at 54 Mbps (theoretical) using the 5-GHz frequency range • IEEE 802.11g • The other recent standard • Also capable of transmitting data at 54 Mbps (theoretical) but using the same frequencies as 802.11b (2.4-GHz) • Is backwards compatible with 802.11b Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

26. Wireless Ethernet (continued) Data Communications and Computer Networks: A Business User's Approach, Fifth Edition

27. Wireless Ethernet (continued) • As we have already seen, IEEE has created the 802.11b, 802.11a, and 802.11g wireless standards • IEEE 802.11n (100 Mbps) will be ratified soon and should start appearing in product form in 2006 (maybe?) • Latest wireless Ethernet is using MIMO technology (multiple input multiple output) • Sender and receiver have multiple antennas for optimum reception Data Communications and Computer Networks: A Business User's Approach, Fifth Edition