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

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?

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

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

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

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

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

Frame Headers and Format Payload is not fixed in size Preamble – 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 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 for interoperability LLC specifies that a type field follows Logical link control / Subnetwork attachment point OUI – Organizationally unique identifier

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

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)

Chapter 10 LAN Wiring, Physical Topology & Interface Hardware

Topics 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 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 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 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 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 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 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 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

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

Any Questions ?