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1 Chapter 8-10 Local Area Networks (LANs)
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Comparison 4e and 5e Ch 7, 4eCh 8, 5e Ch 10, Forouzan Ch 8, 4eCh 14, 5e Ch 13, Forouzan Ch 9, 4eCh 13, 5e Ch 14, Forouzan Ch 10, 4eCh 15, 5e Ch 14, Forouzan 2
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3 Classification Terminology Network technologies classified into three broad categories Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) LAN and WAN most widely deployed
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4 The Local Area Network (LAN) Engineering classification Extremely popular (most networks are LANs) Many LAN technologies exist
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5 Key Features of a LAN High throughput Relatively low cost Limited to short distance Often rely on shared media
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6 Scientific Justification For Local Area Networks A computer is more likely to communicate with computers that are nearby than with computers that are distant Known as the locality principle
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7 Topology Mathematical term Roughly interpreted as “geometry for curved surfaces”
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8 Network Topology Specifies general “shape” of a network Handful of broad categories Often applied to LAN Primarily refers to interconnections Hides details of actual devices
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Fully connected mesh topology (for five devices)
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10 Bus Topology Shared medium forms main interconnect Each computer has a connection to the medium
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11 Ring Topology No central facility Connections go directly from one computer to another
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12 Star Topology Central component of network known as hub Each computer has separate connection to hub
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13 Example Bus Network: Ethernet Most popular LAN Widely used IEEE standard 802.3 Several generations Same frame format Different data rates Different wiring schemes
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14 Shared Medium in a LAN Shared medium used for all transmissions Only one station transmits at any time Stations “take turns” using medium Media Access Control ( MAC ) policy ensures fairness
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15 Illustration of Ethernet Transmission Only one station transmits at any time Signal propagates across entire cable All stations receive transmission CSMA/CD media access scheme
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16 CSMA/CD Paradigm Multiple Access ( MA ) Multiple computers attach to shared media Each uses same access algorithm Carrier Sense ( CS ) Wait until medium idle Begin to transmit frame Simultaneous transmission possible
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17 CSMA/CD Paradigm (continued) Two simultaneous transmissions Interfere with one another Called collision CSMA plus Collision Detection (CD) Listen to medium during transmission Detect whether another station’s signal interferes Back off from interference and try again
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18 Backoff After Collision When collision occurs Wait random time t1, 0 < t1 < d Use CSMA and try again If second collision occurs Wait random time t2, 0 < t2 < 2*d Double range for each successive collision Called exponential backoff
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19 Media Access on a Wireless Net Limited range Not all stations receive all transmissions Cannot use CSMA/CD Example in diagram Maximum transmission distance is d Stations 1 and 3 do not receive each other’s transmissions
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20 CSMA/CA Used on wireless networks Both sides send small message followed by data transmission “ X is about to send to Y ” “ Y is about to receive from X ” Data from sent from X to Y Purpose: inform all stations in range of X or Y before transmission Known as Collision Avoidance (CA)
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21 Identifying a Destination All stations on shared-media LAN receive all transmissions To allow sender to specify destination Each station assigned unique number Known as station’s address Each frame contains address of intended recipient
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22 Assignment of physical address The stations may get their address in different ways: Static Configurable Dynamic
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23 Ethernet Addressing Standardized by IEEE Each station assigned by unique 48-bit address e.g. 00:30:65:52:2E:96 in hexadecimal form Address assigned when network interface card ( NIC ) manufactured (In most cases)
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24 Ethernet Address Recognition Each frame contains destination address All stations receive a transmission Station discards any frame addresses to another station Important: interface hardware, not software, checks address
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25 Possible Destinations Packet can be sent to: Single destination ( unicast ) All stations on network ( broadcast ) Subset of stations ( multicast ) Address used to distinguish
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26 Advantages of Address Alternatives Unicast Efficient for interaction between two computers Broadcast Efficient for transmitting to all computers Multicast Efficient for transmitting to a subset of computers
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27 Broadcast on Ethernet All 1 s address specifies broadcast (FF:FF:FF:FF:FF:FF in hexcode) Sender Places broadcast address in frame Transmits one copy on shared network All stations receive copy Receiver always accepts frame that contains this address
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28 Multicast Half of addresses reserved for multicast Network interface card Always accepts unicast and broadcast Can accept zero or more multicast addresses Software Determines multicast address to accept Informs network interface card
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29 Promiscuous Mode Designed for testing / debugging Allows interface to accept all packets Available on most interface hardware
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30 Identifying Frame Contents Integer type field tells recipient the type of data being carried Two possibilities Self-identifying or explicit type (hardware record type) Implicit type (application sending data must handle type)
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31 Conceptual Frame Format Header Contains address and type information Layout fixed Payload Contains data being sent
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32 Illustration Of Ethernet Frame Sender places Sender’s address in source Recipient’s address in destination Type of data in frame type Cyclic redundancy check in CRC
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Figure 14.3 Minimum and maximum length
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34 Example Ethernet Types
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35 When Network Hardware Does Not Include Types Sending and receiving computers must agree To only send one type of data To put type information in first few octets of payload Most systems need type information
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36 Illustration of Type Information Added to Data In practice Type information small compared to data carried Format of type information standardized
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37 A Standard For Type Information Defined by IEEE Used when hardware does not include type field Called LLC / SNAP header Logical Link Control SubNetwork Attachment Point
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38 Demultiplexing On Type Network interface hardware Receives copy of each transmitted frame Examines address and either discards or accepts Passes accepted frame to system software Network device software Examines frame type Passes frame to correct software module
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39 Network Analyzer Device used for testing and maintenance Listens in promiscuous mode Produces Summaries (e.g., % of broadcast frames) Specific items (e.g., frames from a given address)
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40 Bus Topology Any user with a Network Analyzer can read all packets!
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41 Star Topology Star Topology and Bus Topology are equal fom security point!
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42 Ethernet Wiring Three schemes Correspond to three generations All use same frame format
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43 Original Ethernet Wiring Used heavy coaxial cable Formal name 10Base5 Called thicknet
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44 Second Generation Ethernet Wiring Used thinner coaxial cable Formal name 10Base2 Called thinnet
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45 Modern Ethernet Wiring Uses a hub Formal name 10Base-T Called twisted pair Ethernet
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46 Ethernet Wiring In An Office
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47 A Note About Ethernet Topology Apparently Original Ethernet used bus topology Modern Ethernet uses star topology In fact, modern Ethernet is Physical star Logical bus Called star-shaped bus
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48 Higher Speed Ethernets Fast Ethernet Operates at 100 Mbps Formally 100Base-T Two wiring standards 10/100 Ethernet devices available Gigabit Ethernet Operates at 1000 Mbps (1 Gbps) Slightly more expensive
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49 Another LAN Using Bus Topology LocalTalk Developed by Apple Corp. 1984 Simple to use Slow by current standards (230,4 kbps)
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50 Illustration Of LocalTalk Transceiver required per station Transceiver terminates cable
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51 Ring Topology Second most popular LAN topology Bits flow in single direction Several technologies exist
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52 Token Passing Used with ring topology Guarantees fair access Token Special (reserved) message Small (a few bits)
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53 Token Passing Paradigm Station Waits for the token to arrive Transmits one packet around ring Transmits token around ring When no station has data to send Token circulates continuously
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54 Token Passing Ring Transmission Station waits for token before sending Signal travels around entire ring Sender receives its own transmission
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55 Strengths of Token Ring Approach Easy detection of Broken ring Hardware failures Interference
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56 Weaknesses of Token Ring Approach Broken wire disables entire ring Point-to-point wiring Awkward in office environment Difficult to add / move stations
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57 Token Passing Ring Technologies ProNet-10 Operated at 10 Mbps IBM Token Ring Originally operated at 4 Mbps Later version operated at 16 Mbps Fiber Distributed Data Interconnect (FDDI) Operated at 100 Mbps
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58 FDDI Terminology FDDI Uses optical fibers High reliability Immune to interference CDDI FDDI over copper Same frame format Same data rate Less noise immunity
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59 FDDI Hub Technology Part of FDDI standard Stations attach to hub Same frame format and data rate as FDDI Called star-shaped ring
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60 FDDI Failure Recovery Uses two rings Automatic failure recovery Terminology Dual-attached Counter rotating Self healing
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61 Illustration of FDDI Failure Recovery
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62 Another Example of a Physical Star Topology Asynchronous Transfer Mode (ATM) Designed by telephone companies Intended to accommodate Voice Video Data
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63 ATM Building block known as ATM switch Each station connects to switch Switches can be interconnected
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64 Details of ATM Connection Full-duplex connections Two fibers required
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65 ATM Characteristics High data rates (e.g. 155 Mbps) Fixed size packets Called cells Important for voice Cell size is 53 octets 48 octets of data 5 octets of header
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66 Summary Local Area Networks Designed for short distance Use shared media Many technologies exist Topology refers to general shape Bus Ring Star
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67 Summary (continued) Address Unique number assigned to station Put in frame header Recognized by hardware Address forms Unicast Broadcast Multicast
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68 Summary (continued) Type information Describes data in frame Set by sender Examined by receiver Frame format Header contains address and type information Payload contains data being sent
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69 Summary (continued) LAN technologies Ethernet (bus) IBM Token Ring FDDI (ring) ATM (star)
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70 Summary (continued) Wiring and topology Can distinguish Logical topology Physical topology (wiring) Hub allows Star-shaped bus Star-shaped ring
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Figure 14.1 Three generations of Ethernet
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Figure 14.5 Unicast and multicast addresses
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Figure 14.6 Physical layer
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Figure 14.7 PLS
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Figure 14.8 AUI
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Figure 14.9 MAU (transceiver)
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Figure 14.10 Categories of traditional Ethernet
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Figure 14.11 Connection of a station to the medium using 10Base5
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Figure 14.12 Connection of stations to the medium using 10Base2
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Figure 14.13 Connection of stations to the medium using 10Base-T
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Figure 14.14 Connection of stations to the medium using 10Base-FL
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Figure 14.15 Sharing bandwidth
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Figure 14.16 A network with and without a bridge
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Figure 14.17 Collision domains in a nonbridged and bridged network
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Figure 14.18 Switched Ethernet
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Figure 14.19 Full-duplex switched Ethernet
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14.2 Fast Ethernet MAC Sublayer Physical Layer Physical Layer Implementation
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Figure 14.20 Fast Ethernet physical layer
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Figure 14.21 MII
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Figure 14.22 Fast Ethernet implementations
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Figure 14.23 100Base-TX implementation
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Figure 14.24 Encoding and decoding in 100Base-TX
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Figure 14.25 100Base-FX implementation
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Figure 14.26 Encoding and decoding in 100Base-FX
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Figure 14.27 100Base-T4 implementation
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Figure 14.28 Using four wires in 100Base- T4
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14.3 Gigabit Ethernet MAC Sublayer Physical Layer Physical Layer Implementation
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Figure 14.29 Physical layer in Gigabit Ethernet
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Figure 14.30 Gigabit Ethernet implementations
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Figure 14.31 1000Base-X implementation
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Figure 14.32 Encoding in 1000Base-X
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Figure 14.33 1000Base-T implementation
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