1. Chapter 6 High-Speed LANs1 Chapter 6 High-Speed LANs

2. Chapter 6 High-Speed LANs2 Introduction Fast Ethernet and Gigabit Ethernet High-speed Wireless LANs

3. Chapter 6 High-Speed LANs3 Table 6.1 Fast Ethernet Gigabit Ethernet Fibre Channel Wireless LAN Data Rate100 Mbps1 Gbps, 10 Gbps 100 Mbps – 3.2 Gbps 1 Mbps – 54 Mbps Transmission Media UTP, STP, optical fibre UTP, shielded cable, optical fibre Optical fibre, coaxial cable, STP 2.4 GHz, 5 GHz, microwave Access Method CSMA/CDCSMASwitchedCSMA/CA Polling Supporting Standard IEEE 802.3 Fibre Channel Association IEEE 802.11 Characteristics of some High-Speed LANs

4. Chapter 6 High-Speed LANs4 Emergence of High-Speed LANs 2 Significant trends Computing power of PCs continues to grow rapidly Network computing Examples of requirements Centralized server farms Power workgroups High-speed local backbone

5. Chapter 6 High-Speed LANs5 Classical Ethernet Bus topology LAN 10 Mbps CSMA/CD medium access control protocol 2 problems: A transmission from any station can be received by all stations How to regulate transmission?

6. Chapter 6 High-Speed LANs6 Solution to First Problem Data transmitted in blocks called frames: User data Frame header containing unique address of destination station

7. Chapter 6 High-Speed LANs7 Figure 6.1

8. Chapter 6 High-Speed LANs8 CSMA/CD Carrier Sense Multiple Access/ Carrier Detection 1. If the medium is idle, transmit. 2. If the medium is busy, continue to listen until the channel is idle, then transmit immediately. 3. If a collision is detected during transmission, immediately cease transmitting. 4. After a collision, wait a random amount of time, then attempt to transmit again (repeat from step 1).

9. Chapter 6 High-Speed LANs9 Figure 6.2

10. Chapter 6 High-Speed LANs10 Figure 6.3

11. Chapter 6 High-Speed LANs11 Medium Options at 10Mbps 10Base5 10 Mbps 50-ohm coaxial cable bus Maximum segment length 500 meters 10Base-T Twisted pair, maximum length 100 meters Star topology (hub or multipoint repeater at central point)

12. Chapter 6 High-Speed LANs12 Hubs and Switches Hub Transmission from a station received by central hub and retransmitted on all outgoing lines Only one transmission at a time Layer 2 Switch Incoming frame switched to one outgoing line Many transmissions at same time

13. Chapter 6 High-Speed LANs13 Figure 6.5

14. Chapter 6 High-Speed LANs14 Bridge Frame handling done in software Analyze and forward one frame at a time Store-and-forward Layer 2 Switch Frame handling done in hardware Multiple data paths and can handle multiple frames at a time Can do cut-through

15. Chapter 6 High-Speed LANs15 Layer 2 Switches Flat address space Broadcast storm Only one path between any 2 devices Solution 1: subnetworks connected by routers Solution 2: layer 3 switching, packet- forwarding logic in hardware

16. Chapter 6 High-Speed LANs16 Figure 6.6

17. Chapter 6 High-Speed LANs17 Figure 6.7

18. Chapter 6 High-Speed LANs18 Figure 6.8

19. Chapter 6 High-Speed LANs19 Figure 6.9

20. Chapter 6 High-Speed LANs20 Figure 6.10

21. Chapter 6 High-Speed LANs21 Figure 6.11

22. Chapter 6 High-Speed LANs22 Benefits of 10 Gbps Ethernet over ATM No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells Network is Ethernet, end to end IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM Wide variety of standard optical interfaces for 10 Gbps Ethernet

23. Chapter 6 High-Speed LANs23 Wireless LAN Forming LAN without wires has taken off big time License-free operation Specified as IEEE 802.11 Started with link rate: 1 Mbps  54 Mbps Different PHYs available 802.11b, a, g Quality of service is being introduced thru 802.11e  4 classes Mesh networks are formed for broader coverage

24. Chapter 6 High-Speed LANs24 IEEE 802.11 Wireless LAN 802.11b 2.4-2.5 GHz unlicensed radio spectrum up to 11 Mbps widely deployed, using base stations 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-2.5 GHz range up to 54 Mbps All use CSMA/CA for MAC protocol All have infrastructure and ad-hoc network versions

25. Chapter 6 High-Speed LANs25 Infrastructure Approach Wireless host communicates with an access point Basic Service Set (BSS) (a.k.a. “ cell ” ) contains: wireless stations one access point (AP) BSSs combined to form a distribution system (DS) McGraw-Hill © The McGraw-Hill Companies, Inc., 2004

26. Chapter 6 High-Speed LANs26 Ad Hoc Approach No AP! Wireless stations communicate with each other Typical usage: “ laptop ” meeting in conference room, car interconnection of “ personal ” devices battlefield IETF MANET (Mobile Ad hoc Networks) working group looks into this approach Special needs such wireless routing, security

27. Chapter 6 High-Speed LANs27 Two medium access control schemes o Distributed Coordination Function - DCF o Point Coordination Function - PCF IEEE802.11 MAC Layer Point Coordination Function Distributed Coordination Function Contention Free Services Contention Services

28. Chapter 6 High-Speed LANs28 IEEE 802.11: MAC protocol Collision if 2 or more nodes transmit at same time as the wireless channel is shared CSMA makes sense: get all the bandwidth if you ’ re the only one transmitting shouldn ’ t cause a collision if you sense another transmission Thus, it uses CSMA with collision avoidance (CSMA/CA) Not CD because detecting collision is difficult in wireless environment Two-handshaking used

29. Chapter 6 High-Speed LANs29 o Basic access method o Contention based, distributed protocol  DCF uses CSMA/CA and a random backoff time following a busy medium condition  Uses RTS/CTS extension  to combat the hidden terminal problem  to reduce the BW wastage due to packet collision DCF

30. Chapter 6 High-Speed LANs30 PCF  Contention free, centralised access protocol  Channel access is controlled using polling  Point coordinator will switch the access mode between DCF and PCF  Unpopular with vendors, mostly not used!

31. Chapter 6 High-Speed LANs31 Latest Developments 802.11 has no QoS support; 802.11e MAC introduced in 2005 Supports 4 classes uses soft resource reservation and backoff manipulation 802.11s taskforce working on extending 802.11 hotspots to larger wireless networks Courtesy of Sensors Mag

32. Chapter 6 High-Speed LANs32 Summary Wired networks has become really fast Everything is Ethernet End to end is Ethernet Wireless networks supplementing wired nets for mobility Next: How to design and test networks without actually deploying them? Simulate!