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Chapter 9

Chapter 9. Hardware Addressing & Frame Type Identification. EE 526 Presentation by Ryan Star. Topics To Be Covered. LAN Hardware Addressing Packet Filtering Physical Address Format Broadcasting & Multicasting Packet Type Identification Frame Headers and Format Network Analyzers.

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Chapter 9

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  1. Chapter 9 Hardware Addressing & Frame Type Identification EE 526 Presentation by Ryan Star

  2. Topics To Be Covered • LAN Hardware Addressing • Packet Filtering • Physical Address Format • Broadcasting & Multicasting • Packet Type Identification • Frame Headers and Format • Network Analyzers

  3. Introduction – Local Area Network • LAN technology is used to communicate over short distances • Most LANs are shared networks with a physical path to all computers • Shared - any signal sent reaches all attached stations • Most communication does not involve all stations, but rather just a pair of computers • At a given station the network interface hardware detects the signal and extracts the frame • How does the correct pair of computers find each other across this shared medium?

  4. LAN Hardware Addressing • Physical Address, Hardware Address or MAC Address (media access control address) • All transmitted frames contain a fixed header • Source field and destination field • These fields contain the sender and recipient addresses • The NIC (network interface card) at each station accepts or rejects traffic • Easy reply to sender

  5. Packet Filtering • Independent processing = Powerful • CPU and NIC physically separate hardware • NIC handles all frame transmission: size checking , frame sending and receiving • NIC performs CRC checks without bothering CPU • Addressing allows the NIC to filter only the correct packets or frames to the CPU and operating system • Frames received for other destinations get discarded

  6. Physical Address Format Three main types of Addressing: • Static - 48 bit, IEEE assigns to hardware manufacturer • Configurable - manual with switches or electronic with EPROMs (erasable programmable ROM) • Dynamic - Automatic at boot up. Random. Advantages: • Static - unique and permanent • Dynamic - smaller, but may conflict often • Configurable - best of both - small and permanent

  7. Broadcasting & Multicasting • Application sends message to all stations • Broadcast – uses physical or reserved broadcast address • Inefficient – bothers CPU • Multicast – additional multicast address • Application passes address to NIC • More efficient – doesn’t bother CPU

  8. Packet Type Identification • Addressing alone does not tell what’s in the frame, example - images or ASCII (text) • Two types of frame identification • Explicit Frame Type : Hardware designers specify how and where ID bits are used • Implicit Frame Type : Hardware does not include frame type fields, only data • Explicit frame types are self identifying by their frame type field • Implicit frame types must agree before hand on the frame type or use data space to create a custom type field

  9. Frame Headers and Format • Payload is not fixed in size • Preamble – 10101 for synchronization • Standard broadcast addresses are all 1s • Multicast addresses begin with 1 • Hexadecimal examples of frame types • Standards guarantee device interoperability

  10. Non Self-Identifying Frames • Computer pair must agree on format before transmission or …. • Use part of the data field for type identification • Problem – Different organizations have different standards • IEEE standardized with 802.2 for interoperability • LLC specifies that a type field follows • Logical link control / Subnetwork attachment point • OUI – Organizationally unique identifier

  11. Network Analyzers • Device to monitor and report statistics • Usually a laptop with a NIC • NIC put in promiscuous mode • Accepts all frames without address check • Applications - sometimes called a sniffer. • Used to debug addressing errors • Used to organize and track traffic flow

  12. Summary • LAN Hardware Addresses (Source & sink Addressing) • Packet Filtering (NIC is a traffic cop) • Physical Address Format (static, config, dynamic) • Broadcasting & Multicasting (CPU usage or not) • Packet Type Identification (Implicit or explicit) • Frame Headers and Format (Header & payload) • Network Analyzers (Task monitor)

  13. Chapter 10 LAN Wiring, Physical Topology & Interface Hardware

  14. Topics To Be Covered • LAN & Computer Speeds • Network Interface Hardware • Thick Ethernet Wiring • Connection Multiplexing • Thin Ethernet Wiring • Twisted Pair Ethernet • Wiring Scheme Decisions

  15. LAN & Computer Speeds • Each network technology has a data rate • A CPU also has a computation rate • Usually the network is faster than the CPU • As faster CPUs are invented they become more in line with the speed of the LANs. • Typically many different CPU speeds are present on any LAN • Example FDDI speed 100Mbs & CPU speed of 800MHz can’t process all the instructions for each bit received

  16. Network Interface Hardware • If CPUs can’t process at LAN rates how does it function? • Network interface cards (NICs) handle all transmission • NICs are design for specific LAN speeds • Most NICs contain DMA direct memory access • DMA can TX or RX bits from memory w/o the CPU • The NIC only informs the CPU after it’s verified a frame has been correctly delivered or received.

  17. Thick Ethernet Wiring • Thicknet or 10Base5 • Large coax cable • AUI (attachment unit interface) cable • Thicknet NIC only handles digital aspects • Transceiver – handles analog signaling • Coax must be terminated to cancel reflections

  18. Connection Multiplexing • Thicknet wiring is inconvenient • Transceivers must be a certain distance apart • Connection multiplexers clean up wiring • Act as a transceiver for all computers but only connects to one real transceiver • Connects to multiple stations in one easy location • Performs all transceiver functions

  19. Thin Ethernet Wiring • Thinner, flexible coax cable • Called Thinnet or 10Base2 • Costs less - transceiver is built into NIC • No transceivers, no AUI cables, but still needs termination because it shares the same electrical properties as thicknet • Attaches with a BNC type connector • What does BNC stand for? Hint: military

  20. Twisted Pair Ethernet • 10BaseT - commonly called Ethernet • Connects to a hub with RJ45 (registration jack) connectors • Hub - like connection multiplexing • Physically a star but logically a bus • NIC hides LAN devices so that all work together • No termination is required

  21. Wiring Scheme Decisions • Transceivers vs. BNC & hubs • Cost – wiring, spacing, conduits, # of computers, current set up. • Perhaps all three • Mac’s Localtalk – like Thicknet with thin wire and close transceivers • Multiple connector NIC • Wireless & Fiber Optics

  22. Summary • LAN & Computer Speeds • Network Interface Hardware • Thick Ethernet Wiring • Connection Multiplexing • Thin Ethernet Wiring • Twisted Pair Ethernet • Wiring Scheme Decisions

  23. Any Questions ?

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