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. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition2 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

3. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition3 Primary Function of Local Area Networks (continued)

4. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition4 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

5. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition5 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

6. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition6 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

7. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition7 Bridges (continued)

8. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition8 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

9. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition9 Transparent Bridge (continued)

10. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition10 Transparent Bridge (continued)

11. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition11 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

12. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition12 Switches (continued)

13. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition13 Switches (continued)

14. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition14 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”

15. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition15 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

16. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition16 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

17. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition17 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)

18. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition18 Wired Ethernet (continued)

19. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition19 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

20. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition20 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

21. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition21 Wireless Ethernet (continued)

22. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition22 Wireless Ethernet (continued)

23. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition23 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)

24. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition24 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

25. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition25 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

26. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition26 Wireless Ethernet (continued)

27. Data Communications and Computer Networks: A Business User's Approach, Fifth Edition27 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