Layer One and Two LAN Networking

Wires and connectionsStation to station packet transmission

OSI:Open SystemsInterconnectionReference Model

LAN

Application

Presentation

Session

Transport

Network

Data Link

Physical

©”A Guide to Networking Essentials”, 1998, Course Technology.

OSI Reference Model

Open Systems Interconnection (OSI)

International StandardWritten to be a manufacturing

standard, but never builtUsed as a vocabulary short handApplies to all extensions of networks

OSI Reference Model

7. Application layer6. Presentation layer5. Session layer

UserPrograms

4. Transport layer3. Network layer

WAN

2. Data link layer1. Physical layer

LAN

OSI Layer 1

Local Area Network protocolsPhysical layer:

standards for physical connections (e.g. plugs and connectors)

Responsible for getting bits from one location to another.

Medium Connectors Representation of signals

Media

Twisted Pair Copper Wireshielded vs unshieldedplenum vs PVC

Coaxial Copper Cablethinnet and thicknet

Fibersingle mode and multi-mode

MicrowaveInfrared, Radio

Unshielded Twisted Pairs

Cheapest alternative for LAN cablingAlready exists in most officesAdapts to star wiring and hub systemsTrend in modern LAN installationsNew technologies adapt to itShielded cable used where electronic

interference a problem

Cat 5 Twisted Pair Wiring

Twisted Pair SignalsReverse phases to cancel noise

LINE 1 +

LINE 2 -

Cable categories

Cable Type UseLevel 1 Voice & low speed dataLevel 2 Data to 4 MbpsCategory 3 LAN to 10 MbpsCategory 4 LAN to 20 MbpsCategory 5 LAN to 100 Mbps

Twisted Pair Connectors

Wiring Pairs blue, white-blue orange, white-orange green, white-green brown, white-brown

RJ-11 and RJ-45D connectors

RJ-45 (Registered Jack 45): 8 wires for Ethernet

RJ-11 (4 or 6 wire versions) for telephones

Unshielded Twisted Pairs

Phones use 1 pair10BaseT uses 2 pairs of Category 5

copper100BaseT uses 2 pairs of Category 5

copper100BaseFX uses multimode fiber

10BaseT Ethernet Wiring

Fiber Optic Cables

Longer distancesHigh data rate requirementsHigh interference situationsHigh security situationsConnections more difficult than with

UTP

Fiber Optic

8/125 micron

62.5/125 micron

SingleMode

MultimodeLED

Laser

Up to 50 miles

Up to 2000 meters

Fiber-optic Connectors

Wireless

InfraredRadio

Microwave Radio Frequency

Spread Spectrum & Wi-Fi (IEEE 802.11)

Wireless security

Wireless LAN Access

Local Area Networks

Layer 2

"Gentlemen! Start — your — laptops!"

Copyright 1998 Doug Adams

Local Area Networks

Networks that move data from station to station using a common set of layer 1 and layer 2 protocols. Common broadcast domain Local ownership Common operating system Machine ID addressing

Application

Presentation

Session

Transport

Network

Data Link

Physical

©”A Guide to Networking Essentials”, 1998, Course Technology.

OSI Reference Model

Data Link - Layer 2

2. Data link layer:

protocols for error free transmission from station to station The data link is responsible for node to node validity and integrity of the transmission. The transmitted bits are divided into frames; for example, an Ethernet, Token Ring or FDDI frame in local area networks. Layers 1 and 2 are required for every type of communications.

Data Link - Layer 2 functions

Media access Gain access to the network

Data delineation Start &stop characters,delimiters, frame formats

Error control Trailers: e.g. cycleredundancy checks (CRC)

Addressing MAC addresses (48 bitpermanent device ID’s)

Transparency Special codes in data notinterpreted as delineation

Code independence ASCII, EBCDIC or anyother code accepted

Data Link Sub-layers

Media Access Control (MAC) Standards for addressing and

locating nodesLogical Link Control (LLC)

Standards for communication with higher layers

LAN Operating Protocols

Ethernetopen standard, cheap, most common

Token RingIBM proprietary, high quality, expensive

Others

Network Interface Cards

Build, send out and accept framesUsually a daughter board on PCMust match LAN and CPURequire drivers to operate

Network Interface Cards (NIC)

EthernetCarrier Sense Multiple Access/Collision Detection

HeaderBodyTrailer

Listen before transmitContention accessRetransmit on collision

Ethernet:CSMA/CD (IEEE 802.3)

Carrier Sense Multiple Access with Collision Detection Compare channel voltage to reference

level Any node can transmit if channel free Collision detection during transmission

JammingRandom back off

Slot time and minimum packet size

Manchester Encoding(self-clocking bit stream)

0 1 0High-to-Low = 0Low-to-High = 1

Switch voltage ateach time point

Ethernet Packets

SynchronizationData transparencyMAC addressesMinimum lengthError checkAlternate Ethernet packet formats

Ethernet Packet Structure

Section Length Contents

Preamble 7 bytes 10101010 (7X)

Start Frame Delimiter

1 byte 10101011

Destination 6 bytes MAC destination

Source 6 bytes MAC source

Length 2 bytes Number of bytes in data field

Data 46 – 1500 bytes

Message

Check Sequence

4 bytes Cyclical redundancy check field

Administration

AcknowledgementsAddress announcements

(identification)Slot timeCard streamingHub access10BaseT, 100BaseT, Gigabit Ethernet

10BaseT Specifications(Twisted Pair Ethernet)

100 m to hub1024 stations per network10 mbpsUTPStar/bus

LAN Logical/Physical Topologies

Bus

Ring

Star

Network Logical Topologies

Topologies are determined by the technologies that run the network

Bus:Ethernet

Ring:Token ringSONET, FDDI

Star:MainframeSwitched Ethernet

Ethernet: Physical Star, Logical Bus

LAN with hubs

Hubs or Switches

Switches (Layer 2)

Route packets to destination nodes based on MAC addresses Limit traffic on unused branches Provide additional security Connect 10Mb and 100Mb branches

Operate in firmware

Switch (CISCO Catalyst 1928)

Ethernet Switching

Token Ring (IEEE 802.5)

Allocated access via electronic tokenPriority access reservationConfirmed packet deliveryMultiple monitor functions

Token Ring

Token Ring

Message

CRC HeaderBody

HeaderBody

HeaderBodyToken accessEqual accessCollision avoidance

CRC

CRC

Empty Token Structure

Block Use Bytes

Starting Delimiter Begin Token 1

Access Control PriorityTokenMonitorReservation

1

Ending Delimiter End Token 1

Dataframe Token Structure

Bytes

Start delimiter 1 Code violations

Access control 1 Priority, Token,Monitor, Reservation

Frame control 1 Logical Link or MAC

Destination address 6

Source address 6

Data To 4,500

Frame check sequence 4 Error detection

Ending delimiter 1 Code violations

Frame Status 1 Address recognized,Copied?

Topology: Logical or Physical?

Bus

Ring

Star

Network Topologies

Topologies are determined by the technologies that run the network

Bus:Ethernet

Ring:Token ringSONET, FDDI

Star:MainframeSwitched Ethernet