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Topics To Be CoveredTopics To Be Covered
LAN Hardware AddressingPacket FilteringPhysical Address FormatBroadcasting & MulticastingPacket Type IdentificationFrame Headers and FormatNetwork Analyzers
Introduction – Local Area NetworkIntroduction – 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?
LAN Hardware AddressingLAN 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
Packet FilteringPacket 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
Physical Address FormatPhysical Address FormatThree 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
Broadcasting & MulticastingBroadcasting & Multicasting
Application sends message to all stationsBroadcast – uses physical or reserved
broadcast addressInefficient – bothers CPUMulticast – additional multicast addressApplication passes address to NICMore efficient – doesn’t bother CPU
Packet Type IdentificationPacket 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
Frame Headers and FormatFrame 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
Non Self-Identifying FramesNon 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
Network Network AnalyzersAnalyzers 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
SummarySummary 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)
Topics To Be CoveredTopics To Be Covered
LAN & Computer Speeds Network Interface
Hardware Thick Ethernet Wiring Connection Multiplexing Thin Ethernet Wiring Twisted Pair Ethernet Wiring Scheme Decisions
LAN & Computer SpeedsLAN & 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
Network Interface HardwareNetwork 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.
Thick Ethernet WiringThick 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
Connection MultiplexingConnection 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
Thin Ethernet WiringThin 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
Twisted Pair EthernetTwisted 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
Wiring Scheme DecisionsWiring 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
SummarySummary
LAN & Computer Speeds Network Interface Hardware Thick Ethernet Wiring Connection Multiplexing Thin Ethernet Wiring Twisted Pair Ethernet Wiring Scheme Decisions