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Ethernet and Wireless Local Area Networks

Ethernet and Wireless Local Area Networks

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Ethernet and Wireless Local Area Networks

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  1. Ethernet and WirelessLocal Area Networks

  2. History of Ethernet Standards • Ethernet • The dominant wired LAN technology today • Only “competitor” is wireless LANs (which actually are supplementary) • The IEEE 802 Committee • LAN standards development is done primarily by the Institute for Electrical and Electronics Engineers (IEEE) • IEEE created the 802 LAN/MAN Standards Committee for LAN standards (the 802 Committee)

  3. History of Ethernet Standards • The 802 Committee creates working groups for specific types of standards • 802.1 for general standards • 802.3 for Ethernet standards • The terms 802.3 and Ethernet are interchangeable • 802.11 for wireless LAN standards • 802.16 for WiMax wireless metropolitan area network standards

  4. Ethernet Physical Layer Standards UTP Physical Layer Standards Speed Maximum Run Length Medium Required 10BASE-T 10 Mbps 100 meters 4-pair Category 3 or higher 100BASE-TX 100 Mbps 100 meters 4-pair Category 5 or higher 1000BASE-T (Gigabit Ethernet) 1,000 Mbps 100 meters 4-pair Category 5 or higher 100BASE-TX dominates access links today. Although 1000BASE-T is growing in access links today

  5. Ethernet Physical Layer Standards Fiber Physical Layer Standards Speed Maximum Run Length Medium 850 nm light (inexpensive) Multimode fiber 1000BASE-SX 1 Gbps 220 m 62.5 microns 160 MHz-km 1000BASE-SX 1 Gbps 275 m 62.5 200 1000BASE-SX 1 Gbps 500 m 50 400 1000BASE-SX 1 Gbps 550 m 50 500 The 1000BASE-SX standard dominates trunk links today. Carriers use 1310 and 1550 nm light and single-mode fiber.

  6. Gigabit Ethernet • 10 Gbps Ethernet usage is small but growing • Several 10 Gbps 10GBASE-x fiber standards are defined, but none is dominant • Copper is cheaper than fiber but cannot go as far • 100 Gbps has been selected as the next Ethernet speed • Chosen over 40 Gbps • 100 Gbps Ethernet standards development is just getting underway

  7. Data Link Using Multiple Switches Received Signal Received Signal Original Signal Received Signal Regenerated Signal Regenerated Signal 62.5/125 Multimode Fiber UTP UTP 100BASE-TX (100 m maximum) Physical Link 1000BASE-SX (220 m maximum) Physical Link 100BASE-TX (100 m maximum) Physical Link Each trunk line along the way has a distance limit

  8. Multi-Switch Ethernet LAN Architecture Switch 2 (root switch) Port 7 on Switch 2 to Port 4 on Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Switch 1 Switch 3 C3-2D-55-3B-A9-4F Switch 2, Port 5 B2-CD-13-5B-E4-65 Switch 1, Port 7 A1-44-D5-1F-AA-4C Switch 1, Port 2 D4-55-C4-B6-9F Switch 3, Port 2 E5-BB-47-21-D3-56 Switch 3, Port 6

  9. Single Point of Failure in a Switch Hierarchy Switch Fails Switch 2 No Communication No Communication C3-2D-55-3B-A9-4F Switch 1 Switch 3 B2-CD-13-5B-E4-65 D4-47-55-C4-B6-9F A1-44-D5-1F-AA-4C E5-BB-47-21-D3-56

  10. Hierarchy Implications • Single possible path between stations. • Makes switching tables very simple because there is only one possible row for each address. Find the row, send the frame out the indicated port. Very fast, so minimizes switching cost. • Creates the potential for single points of failure. • Low cost is responsible for Ethernet’s LAN dominance. PortStation 2 A1-44-D5-1F-AA-4C 7 B2-CD-13-5B-E4-65 5 E5-BB-47-21-D3-56

  11. Switch Operation in Ethernet • Today, Switches Dominate in Ethernet • A frame comes in one port • The switch looks up the frame’s destination MAC address in the switching table • The switch sends the frame out a single port • Only two ports are tied up • Other conversations can take place on other port pairs simultaneously

  12. Ethernet 802.3 10Base2 • Ethernet 10Base2 NIC To Next Station T-Connector to Link NIC to next segments

  13. Ethernet 802.3 10Base2 • Ethernet 10Base2 To next station T-connector BNC connector

  14. Server broadcast Client C Client B Client A Server D Server E Virtual LAN with Ethernet Switches Server broadcasting without VLANS Frame is Broadcast Goes to all other stations Creates congestion

  15. Virtual LAN with Ethernet Switches Server multicasting with VLANS With VLANs, broadcasts go to a server’s VLAN clients; less latency Multicasting (some), not Broadcasting (all) Server broadcast NO NO Client C on VLAN1 Client B on VLAN2 Client A on VLAN1 Server D on VLAN2 Server E on VLAN1

  16. Handling Momentary Traffic Peaks with Overprovisioning and Priority Momentary traffic peak:Congestion and latency Traffic Momentary traffic peak: Congestion and latency Network capacity Momentary traffic peaks usually last fraction of a second; They occasionally exceed the network’s capacity. When they do, frames will be delayed, even dropped. Time

  17. Handling Momentary Traffic Peaks with Overprovisioning and Priority Overprovisioned traffic capacity in Ethernet Traffic Overprovisioned network capacity Momentary peak: No congestion Overprovisioning: Build high capacity than will rarely if ever be exceeded. This wastes capacity. But cheaper than using priority. Time

  18. Handling Momentary Traffic Peaks with Overprovisioning and Priority Priority in Ethernet Traffic Momentary peak High-priority traffic goes Low-priority waits Network capacity Priority: During momentary peaks, give priority to traffic that is intolerant of delay, such as voice. No need to overprovision, but expensive to implement. Ongoing management is very expensive. Time

  19. Routed LAN with Ethernet Subnets If a routed LAN links multiple Ethernet switched networks, the switched networks are called subnets

  20. Wireless LANs

  21. Local Wireless Technologies • 802.11 Wireless LANs (Wi-Fi) • Today, mostly speeds of tens of megabits per second with distances of 30 to 100 meters or more • Can serve many users in a home or office • Increasingly,100 Mbps to 600 Mbps with 802.11n • Organizations can provide coverage throughout a building or a university campus by installing many access points

  22. 802.11 Wireless LANs (WLANs) Wireless hosts connect by radio to access points Transmission speed: up to 300 Mbps but usually 10 Mbps to 100 Mbps. Distances between station and access point: 300 to 100 meters.

  23. Wireless Access Points and NICs

  24. Typical 802.11 Wireless LAN Operation with Wireless Access Points 802.11 uses a different frame format than 802.3 The access point translates between the two frame formats However, the packet goes all the way between the two hosts

  25. Hosts and Access Points Transmit in a Single Channel The access point and all the hosts it servers transmit in a single channel If two devices transmit at the same time, their signals will collide, becoming unreasonable Media access control (MAC) methods govern when a device may transmit; It only lets one device transmit at a time

  26. Media Access Control (MAC) • MAC methods govern when devices transmit so that only one station or the access point can transmit at a time • To control access (transmission), two methods can be used • CSMA/CA+ACK (mandatory) • RTS/CTS (optional unless 802.11b and g stations share an 802.11g access point)

  27. CSMA/CA+ACK in 802.11 Wireless LANs • CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) • Sender listens for traffic • 1. If there is traffic, waits • 2. If there is no traffic: • 2a. If there has been no traffic for less than the critical time value, waits a random amount of time, then returns to Step 1. • 2b, If there has been no traffic for more than the critical value for time, sends without waiting • This avoids collision that would result if hosts could transmit as soon as one host finishes transmitting

  28. CSMA/CA + ACK in 802.11 Wireless LANs • ACK (Acknowledgement) • Receiver immediately sends back an acknowledgement; no waiting because ACKs have highest priority. • If sender does not receive the acknowledgement, retransmits the frame using CSMA/CA. • 802.11 with CSMA/CA+ACK is a reliable protocol!

  29. Request to Send/Clear to Send

  30. Specific 802.11 Wireless LAN Standards

  31. Specific 802.11 Wireless LAN Standards

  32. Specific 802.11 Wireless LAN Standards • 802.11g • Most popular 802.11 standard today • 54 Mbps rated speed with much slower throughput • Generally sufficient for Web browsing • Inexpensive • All access points support it

  33. 802.11n • Under development • Rated speeds of 100 Mbps to 600 Mbps • Will operate in both the 2.4 GHz and 5 GHz bands • May use twice current bandwidth per channel (~20 MHz) to roughly double speed • Currently a draft standard • A bit of overkill for most users

  34. Bluetooth Personal Area Networks (PANs) • Bluetooth is standardized by a consortium • Connect devices on or near a single user’s desk • PC, Printer, PDA, Laptop, Cellphone • Connect devices on or near a single user’s body • Laptop, Printer, PDA, Cellphone • The goal is cable elimination

  35. Bluetooth PANs • There may be multiple PANs in an area • May overlap • PANs are called piconets

  36. Bluetooth PAN Operation Notebook master File synchronization Client PC slave Printing Printer slave Note: Printer is in both piconets; Slave has two masters. Piconet 1 Call through company phone System Cellphone master Telephone slave Piconet 2

  37. 802.11 versus Bluetooth PANs 802.11 Bluetooth Focus Large WLANs Personal Area Network Speed 11 Mbps to 54 Mbps In both directions 722 kbps with back channel of 56 kbps. May increase. Distance 100 meters for 802.11b (but shorter in reality) Even shorter of 802.11a 10 meters. May increase Number of devices in an area Only 10 piconets, each with 8 devices maximum Limited in practice only by bandwidth and traffic

  38. 802.11 versus Bluetooth PANs 802.11 Bluetooth Scalability Good through having multiple access points Poor (but may get access points) Cost Probably higher Probably Lower Battery Drain Higher Lower Profiles No Yes Profiles allow specific products to work together. Different profiles for printing, cordless telephones, headsets, etc. Must be implemented on both master and slave.

  39. Bluetooth PANS • Trends • Bluetooth Alliance is enhancing Bluetooth • The next version of Bluetooth is likely to grow to use ultrawideband transmission • This should raise speed to 100 Mbps (or more) • Transmission distance will remain limited to 10 meters • Good for distributing television within a house

  40. Emerging Local Wireless Technologies In mesh wireless networks, the access points do all routing There is no need for a wired network The 802.11s standard for mesh networking is under development This P2P networking needs high density of devices

  41. Emerging Local Wireless Technologies Can be focused electronically to give better reception

  42. Emerging Local Wireless Technologies • Ultrawideband (UWB) • Uses channels that are several gigahertz wide • Each UWB channel spans multiple frequency bands • Low power per hertz to avoid interference with other services • Wide bandwidth gives very high speeds • But limited to short distance and ideal for video networking at home • Wireless USB provides 480 Mbps up to 3 meters, 110 Mbps up to 10 meters

  43. Emerging Local Wireless Technologies • ZigBee for almost-always-off sensor networks • Very low speeds (250 kbps maximum) • Very long battery life (months or years) • At the other end of the performance spectrum from UWB

  44. Emerging Local Wireless Technologies • RFID (Radio Frequency Identification) Tags • Like UPC tags but readable remotely • In most cases, the radio signal from the reader provides power for the RFID tag • The RFID tag uses this power to send information about itself • Battery-operated RFID tags can send farther and send more information • 30-500 KHz, short distances, for supermarket scanning and inventory control • 850-950 MHz, large distances, higher speed, for automated toll collection

  45. Emerging Local Wireless Technologies • Software-Defined Radio • Can implement multiple wireless protocols • No need to have separate radio circuits for each protocol • Reduces the cost of multi-protocol devices