Chapter6 - LAN Hardware


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Chapter6 - LAN Hardware

  1. 1. Introduction Necessary to connect LAN to LAN or WAN LAN to LAN connections are often performed with bridge-like device. LAN to WAN connections are usually performed with router. Third device, switch, can be used to interconnect segments of LAN.
  2. 2. Local Area Network Hardware <ul><li>Focus on hardware technology </li></ul><ul><li>Transition from shared media network architectures to hardware based switched network architectures </li></ul>
  3. 3. Why Interconnect To connect one division with another. To connect two LANs with different protocols. To connect LAN to Internet. To break LAN into segments to relieve traffic congestion. To provide security between different users.
  4. 4. LAN Requirements <ul><li>LAN requires following components  </li></ul><ul><ul><li>Central wiring concentrator (Hub) </li></ul></ul><ul><ul><li>Media - cable or wireless </li></ul></ul><ul><ul><li>NIC - internal or external </li></ul></ul><ul><ul><li>Other – switch, repeater, etc. </li></ul></ul><ul><li>NIC drivers - programs that interface between NIC and NOS. </li></ul>
  5. 5. LAN Architecture
  6. 6. Implications of LAN Technology Choices <ul><li>Choosing particular technology in one LAN technology category has significant implications/limitations on available technology choices in other LAN technology categories </li></ul>
  7. 7. Implications of LAN Technology Choices
  8. 8. Media Sharing vs. Switched <ul><li>Client/server systems and distributed computing has put increasing demands on LAN infrastructure with demands for amount of data traffic to be transferred </li></ul><ul><li>One solution to bandwidth problem is to offer higher speed shared media network architectures </li></ul>
  9. 9. Media Sharing vs. Switched cont’d <ul><li>LAN switches resolve one at time limitation of shared-media LAN architectures by offering attached workstations access to switching matrix that provided point-to-point connections between any two ports. </li></ul><ul><li>Each port on LAN switch is dedicated LAN segment with dedicated bandwidth </li></ul>
  10. 10. Media Sharing vs. Switched cont’d <ul><li>Limiting factor in switch-based LAN architecture is number of simultaneous point-to-point connections that switch can support. </li></ul><ul><li>Coming slide contrasts differences in wiring center functionality between media sharing and switch based LAN architecture. </li></ul>
  11. 11. Switched LAN Architectures vs. Media-Sharing LAN Architectures Wiring Center Functionality
  12. 12. Building Bandwidth Hierarchy with Switched LAN Architecture
  13. 13. Workstation Connected to LAN
  14. 15. ADVANTAGES of SWITCHED LAN ARCHITECTURES <ul><li>Switched LAN architecture only change wiring center technology and manner in which workstations set up point to point communication to each other. </li></ul><ul><li>Installing LAN switch is often easiest alternative chosen when network bandwidth demands exceed current supply. </li></ul>
  15. 16. Implementation Scenarios for Switched LAN Architectures <ul><li>Stand-alone workgroup/departmental LAN switches </li></ul><ul><li>Backbone attached workgroup/departmental LAN switches </li></ul><ul><li>Backbone/data center switches </li></ul><ul><ul><li>Switches offer switched connectivity to other workgroup switches, media sharing hubs, and corporate servers that must be accessed by multiple departments/groups </li></ul></ul>
  16. 17. Implementation Scenarios for Switched LAN Architectures
  17. 18. Network Interface Card <ul><li>NIC - Physical link between client and server PC and media of network </li></ul><ul><li>NIC have ability to adhere to access methodology (CSMA/CD or token passing) of network architecture </li></ul><ul><li>Software rules, implemented by NIC, control access to shared network media and are known as media access control (MAC) protocols </li></ul>
  18. 19. Network Interface Card, cont’d <ul><li>NIC cards determine network architecture and constituent protocols more than any other component </li></ul><ul><li>NIC act like mediator or translator </li></ul><ul><ul><li>Has demands of client/server PC </li></ul></ul><ul><ul><li>Has network architecture with rules for accessing network media or LAN switch. </li></ul></ul>
  19. 20. Technology Analysis <ul><li>Bus into which network adapter card allows different types of cards to be attached in pathway leading to CPU and RAM memory. </li></ul><ul><li>PCI bus offers clocking signaling and low CPU utilization and seems to be bus of choice for high performance NICs. </li></ul>
  20. 21. Technology Analysis, cont’d <ul><li>Important choice related to bus architecture is that network adapter card chosen is compatible with installed bus and takes advantage of data transfer capability bus may offer. </li></ul><ul><li>Key job of NIC is to transfer data between local PC and shared network media. </li></ul>
  21. 22. Technology Analysis, cont’d <ul><li>Hardware related network adapter characteristics that bare on data transfer efficiency are </li></ul><ul><ul><li>Amount of on board memory </li></ul></ul><ul><ul><li>Processing power of onboard CPU contained on network adapter card </li></ul></ul>
  22. 23. Technology Analysis, cont’d <ul><li>Coming figure summarizes NIC to PC memory data transfer techniques. </li></ul><ul><li>Techniques are: </li></ul><ul><ul><li>Programmed I/O </li></ul></ul><ul><ul><li>Direct Memory Access (DMA) </li></ul></ul><ul><ul><li>Shared memory </li></ul></ul><ul><ul><li>Bus mastering DMA </li></ul></ul>
  23. 24. Network Interface Cards Data Transfer Methods
  24. 25. Technology Analysis, cont’d <ul><li>Only bus mastering DMA data transfer technique leaves system CPU alone to process other applications </li></ul><ul><li>In bus mastering DMA, CPU on network adapter card manages movement of data directly into PC’s RAM without interrupting system CPU by taking control of PC’s expansion bus </li></ul>
  25. 26. Technology Analysis, cont’d <ul><li>Bus mastering DMA on adapter cards requires expansion bus in PC to support being “mastered” by CPU on network adapter card. </li></ul><ul><li>CPU and operating system must have capability to relinquish control of expansion bus for bus mastering network adapter cards to function correctly </li></ul>
  26. 27. Technology Analysis, cont’d <ul><li>NIC must be properly configured to interact successfully with that computer </li></ul><ul><li>NIC configuration issues: </li></ul><ul><ul><li>IRQ (Interrupt request) – IRQ must not be used by other device and must be supported by NIC </li></ul></ul><ul><ul><li>Base I/O port address – defines memory location through which data will flow between NIC and CPU </li></ul></ul>
  27. 28. Technology Analysis, cont’d <ul><ul><li>Base Memory Address – Some NICs require base memory address to indicate starting location in computer’s memory to be used by NIC as buffer memory </li></ul></ul>
  28. 29. Technology Analysis, cont’d <ul><li>NIC must worry about hardware compatibility in two directions </li></ul><ul><ul><li>NIC must be compatible with expansion bus into which it will be inserted </li></ul></ul><ul><ul><li>NIC must be compatible with media of network architecture </li></ul></ul><ul><li>Some NICs come with interfaces for more than one media type. </li></ul><ul><li>Jumpers on NIC enable one media type or another </li></ul>
  29. 30. Ethernet Media Interfaces
  30. 31. Technology Analysis, cont’d <ul><li>Possible for NIC to be connected externally to PC via PC’s parallel port </li></ul><ul><li>USB NICs communicate with PC at speeds greater than 12 Mbps </li></ul><ul><ul><li>Actual USB performance depends on number of devices sharing bus </li></ul></ul>
  31. 32. Network Interface Card Trends <ul><li>Dual speed cards – 10/100 Ethernet cards feature auto sensing, automatically determine whether traffic is being transmitted and received at 10 or 100 Mbps through single media interface card. </li></ul><ul><li>Integrated or on board NICs – Build Ethernet NIC onto motherboard </li></ul><ul><li>Multiport NICS – Ability of PCI bus allows multiport NICs to be manufactured on single card. </li></ul>
  32. 33. Network Interface Card Trends, cont’d <ul><li>On-NIC virus protection and security – Some NICS now offer encryption, virus protection, or both </li></ul><ul><li>   Integrated repeater modules – allow up to seven additional devices to be cascaded from NIC and attached to network via single 10BaseT hub port. </li></ul><ul><li>   Full duplex mode – Some Ethernet NICs have full duplex capability that can be enabled. </li></ul>
  33. 34. Network Interface Card Trends, cont’d <ul><li>  Performance improvements – Mfg of Ethernet NICs implemented fast packet forwarding technology </li></ul><ul><li>Next packet of information is forwarded as soon as start of frame is detected rather than waiting for previous frame to be totally on network media before beginning transmission of next packet. </li></ul>
  34. 35. NIC Drivers <ul><li>Interoperability depends on compatibility between NIC and NOS installed in given computer, and is delivered by network interface card drivers </li></ul><ul><li>It was to an adapter card vendor ‘s advantage to ship drivers for as many operating systems as possible . </li></ul>
  35. 36. Approaches for NIC Drivers <ul><li>Supply drivers that could interact successfully with either NetBIOS or TCP/IP. </li></ul><ul><li>Emulate adapter interface specifications of market leading network interface cards for which drivers are most commonly available. </li></ul>
  36. 37. Multiprotocol NIC Drivers <ul><li>By allowing adapter card vendors to develop one file called IPX.COM which was linked with Novell file called IPX.OBJ through process known as WSGEN, unique drivers could be more easily created and updated. </li></ul>
  37. 38. Network Driver Interface Specification (NDIS) <ul><li>NDIS - driver specification offering standard commands for communication between NDIS compliant NOS protocol stacks (NDIS protected driver) and NDIS compliant network adapter card drivers (NDIS MAC drivers). </li></ul><ul><li>NDIS specifies binding operation managed by protocol manager </li></ul><ul><li>NDIS specifies standard commands for communication between protocol manager program and protocol or MAC drivers. </li></ul>
  38. 39. Open Datalink Interface (ODI) <ul><li>ODI allows users to load several protocol stacks simultaneously for operation with single network adapter card and supports independent development with subsequent linking of protocol drivers and adapter drivers. </li></ul>
  39. 40. PCMCIA Drivers <ul><li>When NICs are PCMCIA based, two levels of driver software are required: </li></ul><ul><ul><li>Drivers to interface to OS and NOS. </li></ul></ul><ul><ul><li>Drivers to interface PCMCIA controller to PCMCIA card and on client software drivers. </li></ul></ul>
  40. 41. PCMCIA Drivers, cont’d <ul><li>PCMCIA version 2.1 has Card and Socket Service (CSS) driver specifications. </li></ul><ul><li>CSS is split into two logical sub layers: </li></ul><ul><li>1. Card services sub layer is hardware independent and interfaces to NOS driver software. </li></ul><ul><li>2. Socket services sub layer is written specifically for type of PCMCIA controller included in laptop. </li></ul>
  41. 42. PCMCIA Drivers, cont’d <ul><li>If compatible card and socket service (CSS) drivers are not available for particular PC card/controller combination or if amount of memory CSS drivers requires is unacceptable, then lower level drivers known as direct enablers must be configured and installed. </li></ul>
  42. 43. LAN Wiring Centers <ul><li>Most common network physical topology employed today is star topology </li></ul><ul><li>Token ring wiring centers are known as MAUs (Multistation Access Units) </li></ul><ul><li>Wiring centers for other networks are known as hubs. </li></ul><ul><li>Hubs and MAUs are multiport digital signal repeaters </li></ul>
  43. 44. Hubs <ul><li>Active central element of star layout. </li></ul><ul><li>When single station transmits, hub repeats signal on outgoing line to each station. </li></ul><ul><li>Physically star; logically bus. </li></ul><ul><li>Hubs can be cascaded in hierarchical configuration. </li></ul>
  44. 45. Types of Wiring Center Categories Management Hubs Enterprise Hubs Multistation Access Units Stackable Hubs Hubs Repeaters
  45. 46. Wiring Center Categories <ul><li>Wiring centers can be separated into three broad categories. </li></ul><ul><li>1. Stand-alone hubs - Offers limited number of ports of particular type of network architecture and media. </li></ul><ul><li>2. Stackable hubs - add expandability and manageability. Stackable hubs can be linked together to form one larger virtual hub of single type of network architecture and media. </li></ul>
  46. 47. Wiring Center Categories, cont’d <ul><li>3. Enterprise hubs - modular by design and offer chassis based architecture to which variety of different modules can be inserted. </li></ul>
  47. 48. Major Categories of Hubs
  48. 49. Wiring Center Functional Comparison
  49. 50. Repeater <ul><li>Repeater - repeats each bit of digital data that it receives. </li></ul><ul><li>Repeating action cleans up digital signal by retiming and regenerating signal before passing this repeated data from one attached device or LAN segment to next. </li></ul>
  50. 51. Hub <ul><li>Hubs - are subnet of repeaters that allow attachment of single devices rather than LAN segments to each hub port. </li></ul><ul><li>Terms hub and concentrator or intelligent concentrator are often used interchangeably. </li></ul>
  51. 52. Hubs, cont’d Hub interconnects two or more workstations into local area network. When workstation transmits, hub resends data frame out all connecting links. Hub can be managed or unmanaged. managed hub possesses enough processing power that it can be managed from remote location.
  52. 53. Multistation Access Unit (MAU) <ul><li>MAU (Multistation Access Unit) is IBM’s name for token ring hub . </li></ul><ul><li>MAUs offer varying degrees of management capability. </li></ul><ul><li>Active management MAUs – send alerts to management consoles regarding malfunctioning token ring adapters and forcibly remove misbehaving adapters from ring. </li></ul>
  53. 54. Enterprise Hubs <ul><li>Hub allows concentrator to mix cards </li></ul><ul><li>Cards could be added for connections with Ethernet modules, Token ring adapters, PCs, workstations with FDDI adapters, or dumb asynchronous terminals </li></ul><ul><li>Additional modules available for some concentrators may allow data traffic to travel to other local LANs via bridge or router add-on modules </li></ul>
  54. 55. Enterprise Hubs, cont’d <ul><li>Local network traffic travels through single enterprise hub; ideal location for security modules to be added for either encryption or authorization functionality </li></ul>
  55. 56. Hub Management <ul><li>Hub - ideal place for installation of management software to monitor and manage network traffic </li></ul><ul><li>In stackable and enterprise hubs, two layers of management software may be found </li></ul><ul><ul><li>1. Software is supplied by hub vendor. Allows monitoring and management of hub. </li></ul></ul><ul><ul><li>2. Hubs - capable of sharing MIS with enterprise network management systems. </li></ul></ul>
  56. 57. Hub Management, cont’d <ul><li>Standards that govern network management communication is part of TCP/IP family of protocols, more correctly known as Internet suite of protocols. </li></ul><ul><li>Network management information is formatted according to simple network management protocol (SNMP) </li></ul>
  57. 58. Standards-Based Network Management Communications Protocols
  58. 59. LAN Switches <ul><li>LAN switch - seeks to overcome this “one at time” broadcast scheme, which can lead to data collisions, retransmissions, and reduced throughput between high bandwidth demanding devices </li></ul><ul><li>Switched LAN Architectures vs. Media-Sharing LAN Architectures Wiring Center Functionality </li></ul>
  59. 60. LAN Switches, cont’d <ul><li>Many high-end LAN switches support ATM (Asynchronous Transfer Mode), which is type of switching that not only allow previously mentioned LAN architectures to be switched extremely quickly, but also allows similarly quick switching of voice, video, and image traffic </li></ul>
  60. 61. Switches, cont’d Switch is combination of hub and bridge. It can interconnect two or more workstations, but like bridge, it observes traffic flow and learns. When frame arrives at switch, switch examines destination address and forwards frame out one necessary connection.
  61. 62. Switches, cont’d <ul><li>Workstations that connect to hub are on shared segment. </li></ul><ul><li>Workstations that connect to switch are on switched segment. </li></ul>
  62. 64. Switches, cont’d Backplane of switch is fast enough to support multiple data transfers at one time. Switch that employs cut-through architecture is passing on frame before entire frame has arrived at switch.
  63. 65. Switches, cont’d <ul><li>Multiple workstations connected to switch use dedicated segments. Very efficient way to isolate heavy users from network. </li></ul><ul><li>Switch can allow simultaneous access to multiple servers, or multiple simultaneous connections to single server. </li></ul>
  64. 66.
  65. 68.
  66. 69.
  67. 70. Full Duplex Switches Full duplex switch allows for simultaneous transmission and reception of data to and from workstation. Full duplex connection helps to eliminate collisions. To support full duplex connection to switch, two sets of wires are necessary - one for receive operation and one for transmit operation.
  68. 71.
  69. 72. Types of Switches – Cut Through Switch <ul><li>Cut through switches - read only address information in MAC layer head before beginning processing. </li></ul><ul><li>After reading destination address, switch consults an address look up table to determine which port on switch this frame should be forwarded to. </li></ul><ul><li>Once address look up is completed, point-to-point connection is created and frame is immediately forwarded. </li></ul>
  70. 73. Types of Switches - Store and Forward <ul><li>Store and Forward switches – read entire frame into shared memory area in switch. </li></ul><ul><li>Contents of transmitted Frame Check Sequence (FCS) field is read and compared to locally recalculated frame check sequence. </li></ul><ul><li>If results match, switch consults address look up table, builds appropriate point-to-point connection, and forwards frame. </li></ul>
  71. 74. Types of Switches - Error free cut through switches <ul><li>Error free cut through switches – read both addresses and frame check sequences for every frame. </li></ul><ul><li>Frames are forwarded immediately to destination nodes in an identical fashion to cut through switches. </li></ul>
  72. 75. Types of Switches - Error free cut through switches, cont’d <ul><li>Should bad frames be forwarded, error free cut through switch is able to reconfigure those individual ports producing bad frames to use store and forward switching. </li></ul><ul><li>As errors diminish to preset thresholds, port is set back to cut through switching for higher performance throughput. </li></ul>
  73. 76. Ethernet Hubs and Switches <ul><li>Shared medium hubs </li></ul><ul><li>Switched LAN hubs </li></ul>x
  74. 77. Advantages of Switched Hubs <ul><li>No modifications needed to workstations when replacing shared-medium hub </li></ul><ul><li>Each device has dedicated capacity equivalent to entire LAN </li></ul><ul><li>Easy to attach additional devices to network </li></ul>
  75. 78. Types of Switched Hubs <ul><li>Store and forward switch </li></ul><ul><ul><li>Accepts frame on input line </li></ul></ul><ul><ul><li>Buffers it briefly </li></ul></ul><ul><ul><li>Routes it to appropriate output line </li></ul></ul><ul><li>Cut-through switch </li></ul><ul><ul><li>Begins repeating frame as soon as it recognizes destination MAC address </li></ul></ul><ul><ul><li>Higher throughput, increased chance of error </li></ul></ul>
  76. 79. Layer 3 Switches <ul><li>Problems With Layer 2 Switches </li></ul><ul><ul><li>Broadcast overload </li></ul></ul><ul><ul><li>Lack of multiple links </li></ul></ul><ul><ul><li>Can be solved with subnetworks connected by routers </li></ul></ul><ul><li>Layer 3 switches implement packet-forwarding logic of router in hardware. </li></ul>
  77. 80. More on Switches <ul><li>Circuit-switched </li></ul><ul><li>Packet-switched </li></ul>
  78. 81. Circuit-Switching <ul><li>Definition: Communication in which dedicated communications path is established between two devices through one or more intermediate switching nodes </li></ul><ul><li>Dominant in both voice and data communications today </li></ul><ul><ul><li>e.g. PSTN is circuit-switched network </li></ul></ul><ul><li>Relatively inefficient (100% dedication even without 100% utilization) </li></ul>
  79. 82. Circuit-Switching Stages <ul><li>Circuit establishment </li></ul><ul><li>Transfer of information </li></ul><ul><ul><li>point-to-point from endpoints to node </li></ul></ul><ul><ul><li>internal switching/multiplexing among nodes </li></ul></ul><ul><li>Circuit disconnect </li></ul>
  80. 83. Circuit Establishment <ul><li>Station requests connection from node </li></ul><ul><li>Node determines best route, sends message to next link </li></ul><ul><li>Each subsequent node continues establishment of path </li></ul><ul><li>Once nodes have established connection, test message is sent to determine if receiver is ready/able to accept message </li></ul>
  81. 84. Information Transfer <ul><li>Point-to-point transfer from source to node </li></ul><ul><li>Internal switching and multiplexed transfer from node to node </li></ul><ul><li>Point-to-point transfer from node to receiver </li></ul><ul><li>Usually full-duplex connection throughout </li></ul>
  82. 85. Circuit Disconnect <ul><li>When transfer is complete, one station initiates termination </li></ul><ul><li>Signals must be propagated to all nodes used in transit in order to free up resources </li></ul>
  83. 86. Public Switched Telephone Network (PSTN) <ul><li>Subscribers </li></ul><ul><li>Local loop </li></ul><ul><ul><li>Connects subscriber to local telco exchange </li></ul></ul><ul><li>Exchanges </li></ul><ul><ul><li>Telco switching centers </li></ul></ul><ul><ul><li>Also known as end office </li></ul></ul><ul><li>Trunks </li></ul><ul><ul><li>Connections between exchanges </li></ul></ul><ul><ul><li>Carry multiple voice circuits using FDM or synchronous TDM </li></ul></ul><ul><ul><li>Managed by IXCs (inter-exchange carriers) </li></ul></ul>
  84. 87. Digital Circuit-Switching Node
  85. 88. Circuit Switching Node: Digital Switch <ul><li>Provides transparent signal path between any pair of attached devices </li></ul><ul><li>Typically full-duplex </li></ul>
  86. 89. Circuit-Switching Node: Network Interface <ul><li>Provides hardware and functions to connect digital devices to switch </li></ul><ul><li>Analog devices can be connected if interface includes CODEC functions </li></ul><ul><li>Typically full-duplex </li></ul>
  87. 90. Circuit-Switching Node: Control Unit <ul><li>Establishes on-demand connections </li></ul><ul><li>Maintains connection while needed </li></ul><ul><li>Breaks down connection on completion </li></ul>
  88. 91. Blocking/Nonblocking Networks <ul><li>Blocking: network is unable to connect two stations because all possible paths are already in use </li></ul><ul><li>Nonblocking: permits all possible connection requests because any two stations can be connected </li></ul>
  89. 92. Switching Techniques <ul><li>Space-Division Switching </li></ul><ul><ul><li>Developed for analog environment, but has been carried over into digital communication </li></ul></ul><ul><ul><li>Requires separate physical paths for each signal connection </li></ul></ul><ul><li>Time-Division Switching </li></ul><ul><ul><li>Used in digital transmission </li></ul></ul><ul><ul><li>Utilizes multiplexing to place all signals onto common transmission path </li></ul></ul><ul><ul><li>Bus must have higher data rate than individual I/O lines </li></ul></ul>
  90. 93. Routing in Circuit-Switched Networks <ul><li>Requires balancing efficiency and resiliency </li></ul><ul><li>Traditional circuit-switched model is hierarchical, sometimes supplemented with peer-to-peer trunks </li></ul><ul><li>Newer circuit-switched networks are dynamically routed: all nodes are peer-to-peer, making routing more complex </li></ul>
  91. 94. Alternate Routing <ul><li>Possible routes between two end offices are predefined </li></ul><ul><li>Originating switch selects best route for each call </li></ul><ul><li>Routing paths can be fixed (1 route) or dynamic (multiple routes, selected based on current and historical traffic) </li></ul>
  92. 95. Control Signaling <ul><li>Manage establishment, maintenance, and termination of signal paths </li></ul><ul><li>Includes signaling from subscriber to network, and signals within network </li></ul><ul><li>In-channel signaling uses same channel for control signals and calls </li></ul><ul><li>Common-channel signaling uses independent channels for controls (SS7) </li></ul>
  93. 96. ISDN <ul><li>1st generation: narrowband ISDN </li></ul><ul><ul><li>Basic Rate Interface (BRI) </li></ul></ul><ul><ul><li>Two 64Kbps bearer channels + 16Kbps data channel (2B+D) = 144 Kbps </li></ul></ul><ul><ul><li>Circuit-switched </li></ul></ul><ul><li>2nd generation: broadband ISDN (B-ISDN) </li></ul><ul><ul><li>Primary Rate Interface (PRI) </li></ul></ul><ul><ul><li>Twenty-three 64Kbps bearer channels + 64 data channel (23B+D) = 1.536 Mbps </li></ul></ul><ul><ul><li>Packet-switched network </li></ul></ul><ul><ul><li>Development effort led to ATM/cell relay </li></ul></ul>
  94. 97. Packet-Switching Networks <ul><li>Includes X.25, ISDN, ATM and frame-relay technologies </li></ul><ul><li>Data is broken into packets, each of which can be routed separately </li></ul><ul><li>Advantages: better line efficiency, signals can always be routed, prioritization option </li></ul><ul><li>Disadvantages: transmission delay in nodes, variable delays can cause jitter, extra overhead for packet addresses </li></ul>
  95. 98. Packet-Switching Techniques <ul><li>Datagram </li></ul><ul><ul><li>each packet treated independently and referred to as datagram </li></ul></ul><ul><ul><li>packets may take different routes, arrive out of sequence </li></ul></ul><ul><li>Virtual Circuit </li></ul><ul><ul><li>preplanned route established for all packets </li></ul></ul><ul><ul><li>similar to circuit switching, but circuit is not dedicated </li></ul></ul>
  96. 99. Packet-Switched Routing <ul><li>Adaptive routing changes based on network conditions </li></ul><ul><li>Factors influencing routing are failure and congestion </li></ul><ul><li>Nodes must exchange information on network status </li></ul><ul><li>Tradeoff between quality and amount of overhead </li></ul>
  97. 100. Packet-Switched Congestion Control <ul><li>When line utilization is >80%, queue length grows too quickly </li></ul><ul><li>Congestion control limits queue length to avoid throughput problems </li></ul><ul><li>Status information exchanged among nodes </li></ul><ul><li>Control signals regulate data flow using interface protocols (usually X.25) </li></ul>
  98. 101. X.25 Interface Standard <ul><li>ITU-T standard for interface between host and packet-switched network </li></ul><ul><li>Physical level handles physical connection between host and link to node </li></ul><ul><ul><li>Technically X.21, but other standards can be substituted, including RS-232 </li></ul></ul><ul><li>Link level provides for reliable data transfer </li></ul><ul><ul><li>Uses LAPB, which is subset of HDLC </li></ul></ul><ul><li>Packet level provides virtual circuits between subscribers </li></ul>
  99. 102. Virtual-Circuit Service <ul><li>External virtual circuit: logical connection between two stations on network </li></ul><ul><li>Internal virtual circuit: specific preplanned route through network </li></ul><ul><li>X.25 usually has 1:1 relationship between external and internal circuits </li></ul><ul><li>In some cases, X.25 can be implemented as packet-switched network </li></ul>
  100. 103. Bridges <ul><li>Allow connections between LANs and WANs </li></ul><ul><li>Operates at Layer 2 (Data Link Layer) of OSI </li></ul><ul><li>Used between networks using identical physical and link layer protocols </li></ul><ul><li>Provide number of advantages </li></ul><ul><ul><li>Reliability: Creates self-contained units </li></ul></ul><ul><ul><li>Performance: Less contention </li></ul></ul><ul><ul><li>Security: Not all data broadcast to all users </li></ul></ul><ul><ul><li>Geography: Allows long-distance links </li></ul></ul>
  101. 104. Bridge Functions <ul><li>Read all frames from each network </li></ul><ul><li>Accept frames from sender on one network that are addressed to receiver on other network </li></ul><ul><li>Retransmit frames from sender using MAC protocol for receiver </li></ul><ul><li>Must have some routing information stored in order to know which frames to pass </li></ul>
  102. 105. Bridges Bridge (or bridge-like device) can be used to connect two similar LANs, such as two CSMA/CD LANs. Bridge can connect two closely similar LANs, such as CSMA/CD LAN and token ring LAN.
  103. 106. Bridges, cont’d <ul><li>Bridge examines destination address in frame and either forwards this frame onto next LAN or does not. </li></ul><ul><li>Bridge examines source address in frame and places this address in routing table, to be used for future routing decisions. </li></ul>
  104. 107. Bridge Interconnecting
  105. 108. Bridge – Similar LANs
  106. 109. Bridge Operation
  107. 110. Transparent Bridges Transparent bridge does not need programming but observes all traffic and builds routing tables from this observation. This observation is called backward learning. Each bridge has two connections (ports) and there is routing table associated with each port.
  108. 111. Transparent Bridges, cont’d <ul><li>Bridge observes each frame that arrives at port, extracts source address from frame, and places that address in port’s routing table. </li></ul><ul><li>Transparent bridge is CSMA/CD LANs. </li></ul>
  109. 112. Bridge – CSMA/CD LANs
  110. 113. Transparent Bridge Transparent bridge can also convert one frame format to another. Note that some people/manufacturers call bridge such as this gateway or sometimes router. Bridge removes headers and trailers from one frame format and inserts (encapsulates) headers and trailers for second frame format.
  111. 114. Data Frame – CSMA/CD to Token
  112. 115. Source-Routing Bridge Source-routing bridge used with token ring networks. Source-routing bridges do not learn from watching tables. When workstation wants to send frame, it must know exact path of network / bridge …
  113. 116. Source-Routing Bridge, cont’d <ul><li>If workstation does not know exact path, it sends out discovery frame. </li></ul><ul><li>Discovery frame makes its way to final destination, as it returns, it records path. </li></ul>
  114. 117.
  115. 118. Remote Bridge Remote bridge is capable of passing data frame from LAN to LAN when LANs are separated by long distance and there is WAN connecting two LANs. Remote bridge takes frame before it leaves first LAN and encapsulates WAN headers and trailers. When packet arrives at destination remote bridge, bridge removes WAN headers and trailers leaving original frame.
  116. 119. LAN with Frame Relay Network
  117. 120. Routers Device that connects LAN to WAN or WAN to WAN. Router accepts an outgoing packet, removes any LAN headers and trailers, and encapsulates necessary WAN headers and trailers.
  118. 121. Routers, cont’d Because router has to make WAN routing decisions, router has to dig down into network layer of packet to retrieve network destination address. Routers operate at third layer, or OSI network layer, of packet. Routers often incorporate firewall functions.
  119. 122. Asynchronous Transfer Mode <ul><li>Connection oriented switched transmission methodology </li></ul><ul><li>ATM characteristics is capability of delivering variety of traffic over both local and wide area networks </li></ul><ul><li>ATM has fixed length 53-byte cell </li></ul><ul><li>Uniform length allows timed, dependable delivery for streaming traffic (voice, video), and simplifies troubleshooting, administration, setup, and design </li></ul>
  120. 123. Migration Strategies to ATM <ul><li>IP over ATM – Known as classical IP, adapts CP/IP protocol stack to employ ATM services as native transport protocol directly </li></ul><ul><li>LAN emulation - allows all current upper layer LAN protocols to be transported by ATM services in an unmodified fashion. Provides translation between ATM addressing scheme and scheme native to particular emulated LAN. </li></ul>
  121. 124. Migration Strategies to ATM, cont’d <ul><li>Multi-Protocol Over ATM (MPOA), provides support for multiple local area network protocols running on top of ATM cell switched network </li></ul>
  122. 125. ATM Implementation