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Chapter 5

Ethernet Basic, Coaxial Cable Based Ethernet Technologies (10Base5 and 10Base2). Chapter 5. Ethernet: A family of network technologies (standards) Logical bus topology Bus physical topology: The “older” Ethernet: Star physical topology: The “newer” Ethernet (“ Star Bus topology”).

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Chapter 5

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  1. Ethernet Basic, Coaxial Cable Based Ethernet Technologies (10Base5 and 10Base2) Chapter 5

  2. Ethernet: • A family of network technologies (standards) • Logicalbus topology • Busphysical topology: The “older” Ethernet: • Starphysical topology: The “newer” Ethernet (“Star Bus topology”) What is the Ethernet?

  3. Ethernet: • Ethernet frame • CSMA/CD as the network access method/media access control, i.e., a method to determine which computer in the network can access the wire (in the network) at a given moment What is the Ethernet?

  4. Ethernet in the OSI 7 layer model

  5. Ethernet frame • Created, sent, received, read, and destroyed by Ethernet NIC • The advantages of using frame: • Frame defines the maximum data size, and therefore, large data must be broken into smaller pieces. This provides two benefits: • Benefit 1:Preventing one computer from monopolizingthe shared wire in the network (distributing the network use among all computers in the network more evenly) • Benefit 2:Whenever data is corrupted during transmission, the sending computer only has to retransmit one (or few) frame(s) that contains the corrupted data Ethernet Frame

  6. Seven major parts in Ethernet frame: • Part 1: Preamble • 64 bits of alternating 1s and 0s and ends with 11 • Functions: • Enabling the receiving NIC to recognize the beginning of a frame • Giving time to the receiving NIC to realize a coming of a frame and therefore, can make all necessary preparations to receive the frame properly Ethernet Frame

  7. Seven major parts in Ethernet frame: • Part 2 and 3: Receiver/destination MAC address and Sender MAC Address • Whenever a computer in a network (NODE) sends a frame to the network, the frame will be sent to EVERY OTHER NODE in the network • Whenever a computer (NIC) receives a frame, it will first examine the destination MAC address • If the destination MAC address in a frame is the same as the computer’s (NIC’s) MAC address, the computer (NIC) will process the frame further • If different, the computer (NIC) will destroy the frame • A program/software called SNIFFER can enable NIC to run in PROMISCUOUS MODE to processALL frames it receives, regardless of their destination MAC addresses • http://support.microsoft.com/kb/812953 • http://www.tamos.com/htmlhelp/monitoring/monitoringusinghubs.htm Ethernet Frame

  8. Sniffer, Promiscuous Mode Frame For Computer 3 Computer 1 Computer 2 Computer 3 Computer 4 Computer 5 Computer 6 Destroy the Frame Process the Frame NOT the Intended Receiver, BUT Process the Frame if Running Sniffer Destroy the Frame Destroy the Frame

  9. Seven major parts in Ethernet frame: • Part 4: Length • Information about the number of BYTES of DATA inside the frame • Minimum number of bytes of data: 46 bytes • Maximum number of bytes of data: 1500 bytes • Part 5: Data • Data that is received from the upper layer of the OSI seven-layer model (Network Layer): PACKET • Minimum number of bytes of data: 46 bytes • Maximum number of bytes of data: 1500 bytes Ethernet Frame

  10. Seven major parts in Ethernet frame: • Part 6: Pad • Minimum number of bytes of data: 46 bytes • If the data size is less than 46 bytes, the sender will add more bytes in this part (PAD) to bring the data up to the minimum 46 bytes • Part 7: Frame Check Sequence • Error Detection Information (CRC for the Ethernet) • To detect data transmission error that causes data modification during the transmission Ethernet Frame

  11. Ethernet Frame FCS (Frame Check Sequence) : IEEE 802.3 version of CRC

  12. Carrier Sense Multiple Access (CSMA)/Collision Detection (CD) • Network access method (media access control) • Carrier Sense: • Every computer in the network must first examine (sense) the BUS/SEGMENT before sending a frame • If the computer detects traffic in the BUS/SEGMENT, it will wait for a moment, and then reexamine (resense) the BUS/SEGMENT • If the computer detects no traffic, it will send the frame to the BUS/SEGMENT CSMA/CD

  13. Multiple Access: • All computers in a network have equal access to the wire (no computer has greater access (priority) to access the wire) • Collision Detection: • When two or more computers are sending frames to a BUS/SEGMENT simultaneously, a collision occurs, and all frames will be corrupted/damaged/lost (the transmission is wasted) • During a frame transmission (after sending a frame to a BUS/SEGMENT), the sender’s NIC will always monitor (listen to) the BUS/SEGMENT • If the sender’s NIC detects another frame being transmitted in the BUS/SEGMENT, it recognizes that its frame has been corrupted by collision with another frame CSMA/CD

  14. Collision Domain: • A segment/part in a network in which there will be collision if two or more computers in this segment/part both transmit frames simultaneously • Collisions can significantly slow down the network. Why? Because every time there is a collision, the sender will automatically retransmit the frame (the original transmission is wasted) • A SWITCH or BRIDGE (i.e., a two-port switch) can divide a network into multiple collision domains Collision Domain

  15. Switch Computer A For Computer B Switch Computer B Accept the message

  16. Bridge Computer 1 Computer 2 Computer 3 Computer 4 Computer 5 Computer 6 Switch (Bridge) to Break a Network in Multiple Collision Domains Frame For Computer 3 Collision domain 1 Collision domain 2

  17. FAQ: • Can I break a network into multiple “collision domains” by using a Router? • Yes, you can • So, why do I use Switch instead of a Router? • Switch is cheaper (although the price of Router continues going down) • Switch is easier to install (e.g., no (not much) configuration is needed) Collision Domain

  18. Ethernet is a family of network technologies that use the same bus logical topology, the Ethernet frame, the same network access method (CSMA/CD) • Three classes of Ethernet technology • Coaxial Cable Based Ethernet (Use Coaxial Cable) • Thick Ethernet (Thicknet) = 10Base5 • Thin Ethernet (Thinnet) = 10Base2 • UTP Based Ethernet (Use UTP/Unshielded Twisted Pair cable) • 10BaseT • 100BaseTX • Fiber-Optic Cable Based Ethernet (Use Fiber-Optic cable) • 100BaseFX Ethernet technologies

  19. Thick Ethernet (Thicknet) = 10Base5 Thin Ethernet (Thinnet) = 10Base2 The oldest Ethernet technologies Using coaxial cable as the bus cable Physical Bus and Logical Bus topology (“OLD”) Coaxial Cable Based Ethernet

  20. Thick Ethernet • Thick Ethernet (Thicknet) • RG-8 coaxial cable as the BUS (SEGMENT) • Each computer is connected to the RG-8 BUS CABLE (SEGMENT) by using Attachment Unit Interface (AUI) cable and TRANSCEIVER • AUI cable is also known as Transceiver cable (Transceiver Drop cable)

  21. Thick Ethernet

  22. Thick Ethernet

  23. 10Base5 (Thick Ethernet, Thicknet) • Thick Ethernet (Thicknet) is also known as 10Base5: • 10: Data transmission speed/rate/bandwidth/throughput: 10 Mbps • Base: Baseband: A single cable can carry only one signal • 5: a BUS/SEGMENT cannot be longer than 500 meters (without repeater)

  24. Bits versus Bytes • 1 Byte contains 8 bits • 1 B = 8 b • A single character is represented by 8 bit code (1 Byte code) • B is used to measure storage capacity (B, MB, GB) • b is used to measure data transmission speed/rate (bps, mbps)

  25. Baseband versus Broadband • Baseband: • A single cable can carry only onesignal at any time (a single channel in a single cable at any time) • Broadband: • A single cable can carry multiplesignals at any time (multiple channels in a single cable at any time)

  26. 10Base5 • How to build a 10Base5 network? • Step 1: Install 10Base5 NICs in ALL computers in the network • Step 2: Create an RG-8 BUS/SEGMENT (installing TERMINATORS at the two ends of an RG-8 cable) • Step 3: To connect a 10Base5 NIC to the BUS/SEGMENT, • Install a TRANSCEIVER in the BUS/SEGMENT • Use AUI cable to connect the NIC to the TRANSCEIVER

  27. 10Base5 • Things to remember during installation: • TRANSCEIVER must be installed at any one of the 2.5-meter intervals along the RG-8 BUS/SEGMENT • AUI cable can be up to 50 meters • The BUS/SEGMENT (without repeater) can be up to 500 meters • Up to 100 computers can be attached to a BUS/SEGMENT (without repeater)

  28. 10Base5 Bus length: Maximum 500 meters Multiples of 2.5 meters Multiples of 2.5 meters  50 meters  50 meters  50 meters

  29. Thin Ethernet • Thin Ethernet (Thinnet) • RG-58 bus cable • Computers are connected to the RG-58 bus cable by using BNC (“Bayonet-Neill-Concelman”) Connectors

  30. 10Base2 BNC Connector BNC T-Connector

  31. 10Base2

  32. 10Base2 (Thin Ethernet, Thinnet) • Thin Ethernet (Thinnet) is also known as 10Base2 • 10Base2: • 10: data transmission speed/rate/throughput/bandwidth: 10 Mbps • Base: Baseband method • 2: the BUS/SEGMENT cannot be longer than 185 meters

  33. 10Base2 versus 10Base5 • Advantages of 10Base2: • Cheaper to install: RG-58 cable is cheaper than RG-8 cable; no need for Transceiver and AUI cable • Easier to install: • Computers must be installed at least0.5 meters apart, but they do not have to be spaced at specific intervals as required by 10Base5; no need to install Transceiver and AUI cable • Disadvantage of 10Base2: • Maximum 30 computers/NICs per BUS/SEGMENT • Maximum coverage only 185 meters

  34. Bus and Repeater • ATTENUATION refers to a reduction in the strength of a signal • The longer the distance the signal has traveled, the weaker the signal becomes • Repeater can regenerate the original signal

  35. Ethernet’s 5-4-3 Rule: • 5: Maximum of 5 bus cables/segments • 1 segment 10Base5 = RG-8 bus cable, max 500 meters • 1 segment 10Base2 = RG-58 bus cable, max 185 meters • 4: Maximum of 4repeaters • 3: Only 3 segments (out of maximum of 5) can have computers attached (maximum of 3 populated segments) How Many Repeaters can be Used in an Ethernet Network?

  36. The 5-4-3 rule in 10Base5 network 5 bus cables (segments) - 4 repeaters - 3 bus cables (segments) with computers connected How Many Repeaters can be Used in an Ethernet Network?

  37. How Many Repeaters can be Used in an Ethernet Network? The 5-4-3 rule in 10Base2 network 5 bus cables (segments) - 4 repeaters - 3 bus cables (segments) with computers connected

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