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Chapter 6

Chapter 6. High-Speed LANs. Introduction. Fast Ethernet and Gigabit Ethernet High-speed Wireless LANs. Table 6.1. Characteristics of some High-Speed LANs. Emergence of High-Speed LANs. 2 Significant trends Computing power of PCs continues to grow rapidly Network computing

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Chapter 6

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

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

  3. Table 6.1 Characteristics of some High-Speed LANs Chapter 6 High-Speed LANs

  4. 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 Chapter 6 High-Speed LANs

  5. 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? Chapter 6 High-Speed LANs

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

  7. Figure 6.1 Chapter 6 High-Speed LANs

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

  9. Figure 6.2 Chapter 6 High-Speed LANs

  10. Figure 6.3 Chapter 6 High-Speed LANs

  11. Medium Options at 10Mbps • <data rate> <signaling method> <max length> • 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) Chapter 6 High-Speed LANs

  12. 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 Chapter 6 High-Speed LANs

  13. Figure 6.5 Chapter 6 High-Speed LANs

  14. 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 Chapter 6 High-Speed LANs

  15. 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 Chapter 6 High-Speed LANs

  16. Figure 6.6 Chapter 6 High-Speed LANs

  17. Figure 6.7 Chapter 6 High-Speed LANs

  18. Figure 6.8 Chapter 6 High-Speed LANs

  19. Figure 6.9 Chapter 6 High-Speed LANs

  20. Figure 6.10 Chapter 6 High-Speed LANs

  21. Figure 6.11 Chapter 6 High-Speed LANs

  22. 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 Chapter 6 High-Speed LANs

  23. 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 Chapter 6 High-Speed LANs

  24. 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 IEEE 802.11 Wireless LAN • All use CSMA/CA for MAC protocol • All have infrastructure and ad-hoc network versions Chapter 6 High-Speed LANs

  25. 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) Chapter 6 High-Speed LANs McGraw-Hill • The McGraw-Hill Companies, Inc., 2004

  26. 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 Chapter 6 High-Speed LANs

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

  28. 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 Chapter 6 High-Speed LANs

  29. DCF • Basic access method • 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 Chapter 6 High-Speed LANs

  30. 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! Chapter 6 High-Speed LANs

  31. 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 Chapter 6 High-Speed LANs

  32. 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! Chapter 6 High-Speed LANs

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