Chapter 9Chapter 9

Hardware Addressing & Frame Type Identification

EE 526 Presentationby Ryan Star

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)

Chapter 10Chapter 10

LAN Wiring, Physical Topology & Interface Hardware

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

Any Questions ?Any Questions ?