1 / 42

Ethernet LAN

Ethernet LAN . 1. LANs. Local Area Networks Limited Geographical Area Single office Single building University campus or industrial park Generally, high speeds Now, most operate at around 10 Mbps 100 Mbps is emerging as the new “base speed” Most Data Traffic is Local. 2.

tamah
Download Presentation

Ethernet LAN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ethernet LAN 1

  2. LANs Local Area Networks Limited Geographical Area Single office Single building University campus or industrial park Generally, high speeds Now, most operate at around 10 Mbps 100 Mbps is emerging as the new “base speed” Most Data Traffic is Local 2

  3. Standards Setting LANs are Subnets (single networks) Subnet technology is Dominated by OSI Standards (true for LANs) IEEE Creates most LAN Standards Institute for Electrical and Electronic Engineers Submits its standards to ISO and ITU-T for ratification IEEE 802 Committee LAN standards are set by the IEEE 802 Standards Committee. 802.3 for Ethernet Standards 802.5 for Token-Ring LAN Standards 802.11 for Radio and Infrared Wireless LANs 3

  4. LANs and OSI Architecture OSI is a 7-layer architecture LAN transmission only uses Layers 1 and 2 Layer 1: Physical Layer Connectors, Media, Electrical signaling Layer 2: Data Link Layer Packaging data into frames Managing transmission over link (error handling, etc.) Access control: when each station may transmit 4

  5. OSI Physical and Data Link Layers Physical Layer (OSI Layer 1) Physical (plugs, media, etc.); Electrical (voltages, timing, etc.) Electrical Signal Station A Station B Transmission Medium (telephone wire, etc.) Connector Plug Connector Plug F4-1 5

  6. OSI Physical and Data Link Layers Data Link Layer (OSI Layer 2) Frame 2 Frame 1 Station A Station B 6

  7. Data Link Layer For point-to-point transmission A point-to-point connection is a data link So is a transmission system shared by multiple devices, only one of which can transmit at a time because of collisions Transmission 7

  8. Data Link Layer First function:Packaging of Data (1s and 0s) PDU at Data Link Layer is called a frame Second Function: Access Control Only one station can transmit at any time If another transmitted, their signals would scramble one another Must control access to (transmission into) the transmission medium 8

  9. Data Link Layer Logical Link Control Layer OSI Data Link Layer (Layer 2) Media Access Control (MAC) Layer OSI Physical Layer (Layer 1) 802.3 10Base-T 802.3 10Base-5 802.3 Other Physical Layer 802.5 Physical Layer 4 Mbps 802.5 Physical Layer 16 Mbps Other Physical Layer OSI Data Link Layer is subdivided into two layers Media access control Logical link control 9

  10. MAC Layer Media Access Control (MAC) Layer Media Access Control 802.3 10Base-T 802.3 10Base-5 802.3 Other Physical Layer 802.5 Physical Layer 4 Mbps 802.5 Physical Layer 16 Mbps Other Physical Layer OSI Physical (Layer 1) MAC layer implements media access control: When a station may transmit Controls the framing of data along the wire 10

  11. Logical Link Control Layer 802.2 Logical Link Control Layer LLC 802.3 Media Access Control (MAC Layer) 802.5 MAC 4 Mbps 802.5 MAC 16 Mbps Other MAC 802.3 10Base-T 802.3 10Base-5 802.3 Other Physical Layer 802.5 Physical Layer 4 Mbps 802.5 Physical Layer 16 Mbps Other Physical Layer OSI Physical (Layer 1) Provides Control Function Begin/end connections between stations Error correction (optional) 11

  12. Simple LAN Using Ethernet 10Base-T RJ-45 jacks 10Base-T Hub (Multiport Repeater) 10Base-T UTP Wiring Bundles: 4 Pairs EIA Category 3, 4, or 5 Unshielded Twisted Pair (UTP) Wiring (4-Pair Bundle) PC Network Interface Card RJ-45 Jack NIC 12

  13. Ethernet 10Base-T (802.3u) Physical Layer Standard 10 Mbps (10 in 10Base-T) Baseband signaling: Injects voltage changes directly into the wires (Base in 10Base-T) Hubs (Multiport Repeaters) Connect the stations together 10Base-T Hub 13

  14. NICs Network Interface Cards Implement Physical Layer Plug and Electrical Signaling Implements the Data Link Layer (data packaging, access control, etc.) LLC (802.2) MAC (802.3 MAC) 14

  15. Wiring Unshielded Twisted Pair (UTP) Twisted several times per foot to reduce interference, T in 10Base- and Unshielded No protection except for plastic coating Distance limitation: 100 meters (attenuation, distortion, noise and interference, crosstalk) -- propagation Categories of UTP Wiring Category 5, 6: The best. Good for 100 Mbps Category 3 and 4: lower. May be OK for 100 Mbps Wiring Plugs: RJ-45 Standard Similar to home (RJ-11) jacks, but wider 15

  16. Physical Layer Transmission in 10Base-T 10Base-T Hub Step 1 Station A Transmits on Upstream Pair (Wires 1&2) Station A Station B Station C F4-4 16

  17. Physical Layer Transmission in 10Base-T 10Base-T Hub Step 2 Hub Repeats (Broadcasts) The Message To All Stations On Downstream Pairs (Wires 3&6) Bus transmission means broadcasting Station A Station B Station C 17

  18. MAC LayerCSMA/CD Media Access Control Controls when stations may transmit If two transmit at once, signals will be scrambled X Collision Collisions will grow rapidly above 30% of line utilization. Keep traffic moderate, or throughput will be affected. 18

  19. CSMA/CD Media Access Control CS: Carrier Sense Each NIC always listens for traffic on the line This lets it recognize messages sent to its address This also lets it know if the line is free CSMA: Carrier Sense Media Access A station may transmit if it hears no traffic on the network 19

  20. CSMA/CD Media Access Control in Ethernet 10Base-T Hub Station A is Transmitting Station B must wait Must Wait Station A Station B Station C 20

  21. CSMA/CD Media Access Control CD: Collision Detection If two stations transmit at once …. Their signals collide, scrambling one another Because each sender listens (senses the carrier), both know that there has been a collision Both stop and wait a random amount of time. 101010 001110 X Collision 21

  22. Layering in 802 Networks InternetLayer TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) Data Link Layer Logical Link Control Layer 802.2 Media Access Control Layer Ethernet 802.3 MAC Layer Standard Non-Ethernet MAC Standards (802.5, 802.11, etc.) Physical Layer 100BASE- TX 1000 BASE- SX … Non-Ethernet Physical Layer Standards (802.11, etc.) 22

  23. 802.3 MAC Layer Frame Preamble In asynchronous transmission, each byte is sent separately, in a 10-bit frame. In 802.3 MAC Layer frames, transmission is synchronous. Many data bytes are sent in each frame of variable length. Frames must be between 64 octets and 1518 octets long, divided into groups of bits called fields. Field lengths are measured in “octets”, eight bits. “Octet” is a synonym for “byte” Start of Frame Delimiter Destination Address Source Address Length Data Pad Frame Check Sequence 23

  24. Error Detection MAC Layer Process Provides error detection Determines that an error exists Does not provide error correction Merely discards the frame No request for retransmission if there is an error Logical Link Control Layer may do error correction Receiving LLC process detects discarded frames Receiving LLC process asks for retransmissions 24

  25. Logical Link Control (LLC) Layer 802.2 can ask for retransmission of lost MAC frames. Optional. Next Higher Layer (Usually Internet) Next Higher Layer (Usually Internet) LLC Frame LLC Layer Process LLC Layer Process LLC frame placed within MAC frame MAC Layer Process MAC Layer Process MAC Frame Station A Station B 25

  26. Ethernet 10Base-T Network with Two Hubs Hub 1 Hub 2 100 m Segment Maximum Station A Transmits to Hub 1 Hub 2 Broadcasts the Message Out All of Its Ports 100 m Segment Maximum 100 m Segment Maximum Hub 1 Transmits Out All Ports, Including the Port to Hub 2 Station C Receives the Message Station A Station B Station C 26

  27. Ethernet 10Base-T LAN with Multiple Hubs Hub 2 Hub 3 Hub 1 UTP Wire UTP Wire UTP Wire UTP Wire Station C Hub 4 Daisy chain, no Loops allowed! UTP Wire Station A Station B Station D Maximum distance between farthest Stations is 4 Hubs/5 100 meter segments 27

  28. Speed and Distance Transmission speed worsens problems Error rates increase because bit periods are smaller and are more likely to be damaged by brief noise spikes and interference High speeds create high-frequency components in the signal that attenuate more rapidly than lower-frequency components In general, as speed increases, maximum distance decreases, although improving technology can lessen the decrease 28

  29. Dealing with Propagation Effects Use High-Quality, High-Cost Media Use media designed for long-distance propagation Optical fiber, coaxial cable Too expensive for runs to many desktops, good for hub-to-hub Use Inexpensive Media to the Desktop Improve the technology (allows 100 Mbps+ on UTP) Accept distance limitations (100 meters for UTP) More popular alternative to desktop because of low cost 29

  30. 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 30

  31. 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 optical fiber standard dominates trunk links todayS means that the standard uses short wavelength light (850 nm) 31 .

  32. Shared media LANs • Limits to Shared Media LANs • FDDI, 100Base-X, 1000Base-SX are all shared media LANs • Only one station can transmit at a time, causing latency • Every station hears every message, so as the number of stations grow, the LAN saturates • 100, 1000 Mbps speed only delays saturation 32

  33. Shared media LANs • Shared Media Networks with Hubs (such as 10Base-T) • Incoming frame arrives through a single port • Hub broadcasts frames out all ports • Congestion on output ports Hub 33

  34. Switched LANs • In a switched network • Incoming frame arrives on a single port • Frame sent out again only on a single port--the one leading to the receiver • No congestion on other ports Switch 34

  35. Switch With a switch, multiple stations may transmit simultaneously: no congestion as traffic grows. Switch Station C Station A Connection 1 A-C Connection 1 A-C Station D Station B Connection 2 B-D Connection 2 B-D 35

  36. Switching in Perspective • Switching is dominant in LANs today • Congestion does not increase as the number of stations grows • Today, switches are no more expensive than 10Base-T or 100Base-X hubs • Read CISCO white paper 36

  37. Switch connections • paths called connections must be pre-defined between stations • a fixed logical data link (logical connection) is established between stations before transmission even begins • during the transmission, all traffic between the stations must pass over that data link • unless a data link has been pre-established, two stations may not communicate at all • only OSI Layer 2 (Data Link Layer) protocols are needed 37

  38. Ethernet Switches • Ethernet Hubs are Half Duplex • Most Ethernet Switches are Full Duplex • No collisions are possible • So two stations can both transmit to each other at the same time (full duplex operation) • Requires full duplex switches • Requires full duplex NICs • Lowest-cost LAN switches • Not standardized, so buyers tend to get locked into a single vendor 38

  39. Data Link Using Multiple Switches Received Signal Original Signal Received Signal Received Signal Regenerated Signal Regenerated Signal Switches regenerate signals before sending them out; this removes propagation effects It therefore allows signals to travel farther 39

  40. Multiswitch Ethernet LAN 40

  41. Hierarchical Ethernet LAN Ethernet switches must be arranged in a hierarchical topology In a hierarchical LAN, there is only one possible path between any hosts 41

  42. Routed LAN with Ethernet Subnets When a routed LAN links multipleEthernet switched networks,individual switched networks are called subnets 42

More Related