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PC PeripheralsPC Peripherals for for TechniciansTechnicians

Chapter 5 Chapter 5 LAN OverviewLAN Overview

Systems Manufacturing Training Systems Manufacturing Training and Employee Developmentand Employee Development

Copyright © 1998 Intel Corp.Copyright © 1998 Intel Corp.

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Local Area Network Local Area Network OverviewOverview

OBJECTIVES: At the end of this section, the student will be able to do the following:

Discuss the architecture of Local Area Networks Describe Ethernet Standards and Topologies. Discuss Ethernet operation and Ethernet LAN Media. Describe 100 Mbps Fast Ethernet. Explain the functions of a Network Interface Card. List common devices used for extending LANs.

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Introduction to Local Area Networks

EMail

Network OS

AdapterDrivers

Network Interface

Card

EMail

Network OS

Adapter

Drivers

Network Interface

Card

TheNetwork

My PC

Your PC

A Network is a collection of independent computers that communicate with one another over a shared network medium

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Introduction to Local Area Networks A Network is a way of connecting a bunch of

computers (nodes, clients, workstations, or servers) and peripherals together.Allows sharing of Peripherals, Applications, and Data.

» E-mail, Web browsing, and sharing a printer or disk drive.

Ethernet is the most widely used network protocol and is the focus of this chapter.

Stations are generally connected to the Network through an intelligent interface known as a Network Interface Card (NIC), Network Adapter Card, LAN Adapter, or Ethernet Card.The NIC provides a physical connection between the

network cable and the computer’s internal bus.

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Introduction to Local Area Networks Local Area Networks (LANs) encompass Computers,

Workstations, Peripherals, Cabling and Software.» LANs are networks confined to a moderate sized geographic

area (typically 0.1 to 1 km) such as a campus, building, floor, or a room.

» LANs may link hundreds of computers used by thousands of users.

LANs can be interconnected to form larger networks called Wide Area Networks (WANs).A Wide Area Network is the connecting of multiple LANs

that are geographically separated (100 km to 10,000 km). A WAN connects the different LANs using

telecommunications services including phone lines and satellite links.

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Introduction to Local Area Networks A SERVER is a device on a network that manages

network resources. Servers are often dedicated--they perform no other tasks

besides their server tasks. » Computers connected to the server are called “clients”.

The most common types of servers are file servers, print servers, mail servers, database servers, and communication gateway servers.

» A file server is a computer dedicated to network accessible file storage.

> Any user on the network can access files on the server.> Can be thought of as a remote hard disk

» A print server is a computer that manages one or more printers.

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Introduction to Local Area Networks

Routing

Application

Presentation

Session

Transport

Network

Data Link(MAC)

Physical

Application

Presentation

Session

Transport

Network

Data Link(MAC)

Physical

PC #1 PC #2

Network Interface Cards are part of Layers 1 & 2

The rest is software!

SOFTWARE

HARDWARE

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6

5

4

3

2

1

7 Layered Model of Computer Networks

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Introduction to Local Area Networks 7 Layered Model of Computer Networks (Cont.)

Upper Layers (3-7): Software» Provide user oriented services (email, file transfer, etc.),

maintains & terminates connections, and provides address translation, text compression & encryption when necessary.

Data Link - Layer 2: Hardware» Applies protocol which makes layer 1 appear as error free

point to point link to layer 3 (e.g ENET, Token Ring).> MAC (Medial Access Control) & LLC (Logical Link Control)

Physical -Layer 1: Hardware» Deals with transmission of raw bits - converts digital signals

to electrical signals the network can understand.

» Specifies hardware, cable, connectors, signaling speed.

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Introduction to Local Area Networks Network Interface Cards (NICs) provide the physical

connection between the network cable and the computer's internal bus (More NIC details later in chapter).A software Device Driver enables the NIC in a computer to:

» Encode data from the operating system for transmission by the Ethernet card through the network.

» Decode received packets and send them to the O/S.

NetworkCable

PC

TransceiverPacket

FormationData Packets

(Serial)Encode/Decode

Buffer(FIFO)

Data Bits(1’s/0’s

ParallelData`

Network Interface Card (NIC)

NIC/CableInterface

PC/NICInterface

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Introduction to Local Area Networks

Devices on a baseband network, such as Ethernet, use the entire frequency spectrum, so that only one transmission can take place at a time.An analogy is a single phone line: Only one person can talk at a

time--if more than one person wants to talk everyone has to take turns.

1 1 1 1

0 0 0 0

1 1 1 1

0 0 0 0

HOST PCNETWORK

INTERFACE CARD

NETWORKMEDIA

FULL CAPACITY OFNETWORK MEDIA

Baseband

Baseband vs. Broadband Signaling

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Introduction to Local Area Networks

Broadband uses only a portion of the spectrum for each transmission, so that multiple channels can share the same medium using frequency division multiplexing.One of several “Channels” on Network Media.

» The signals need to be multiplexed onto a carrier frequency.A broadband example is a television signal over the cable line.

1 1 1 1

0 0 0 0 1 1 1 10 0 0 0

NETWORKINTERFACE

CARD

Modulator/Demodulator

NETWORKMEDIAHOST PC

Broadband

Baseband vs. Broadband Signaling

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Ethernet Standards & TopologiesEthernet is the most widely used LAN technologyEthernet is the most widely used LAN technology

» Ethernet is a type of network cabling and signaling specifications (OSI Model layers 1 [physical] & 2 [data link])

IEEE 802.3 - “Ethernet”: All Ethernet equipment since 1985 is built according to this standard.

» 10BASE-5 Thick coax

» 10BASE-2 Thin coax - “Cheapernet”

» 10BASE-T Twisted Pair Ethernet - “TPE”

» 10BASE-FL Fiber Optic Link

» Note: IEEE 802.3u known as 100BASE-xx presented later.

IEEE 802.5--Token Ring is an alternative LAN standard .» A special bit pattern, called a token, passes around -- if a

station wants to transmit, it has to wait until it gets the token.

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Ethernet Standards & Topologies

IEEE identifiers include three pieces of information. First item, "10", stands for the media speed of 10-Mbps.

» Data Rate: 1, 10, or 100 Megabits per second

BASE/BROAD: Baseband vs. Broadband signaling.3rd part is a rough indication of segment type or length.

» For thick coax the "5" indicates the 500 meter maximum length allowed for individual segments of thick coaxial cable.

» For thin coax the "2" is rounded up from the 185 meter maximum length for individual thin coaxial segments.

» The "T' and "F" stand for "twisted-pair" and "fiber optic," and indicate the cable type--they do not imply a specific length.

802.3 Naming Conventions: Example: 10BASE-5

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Ethernet Standards & Topologies

A bus topology consists of nodes linked together in series with each node connected to a long cable or bus.

» All stations connect in a single row to the same segment.

The BUS is the simplest (and the traditional) topology.» Standard Ethernet (10BASE5) & Thin Ethernet (10BASE2),

both based on coaxial cable systems, use the bus.

» A cable break will cause the segment to be inoperable.

Both ends of a segment should be terminated .

BUS TOPOLOGYBUS TOPOLOGY Thin Ethernet

Thick Etherne

t

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Ethernet Standards & TopologiesSTAR TOPOLOGYSTAR TOPOLOGY

In a star topology, all attached nodes (workstations) are wired directly to a

central hub, which establishes and maintains connections between them.

The Star topology is used for twisted-pair cabling (10BASE-T Ethernet), fiberoptic links, & Fast Ethernet.The advantage of a star topology is that it is easy to

isolate a problem node. » Point to Point--dedicated line between two endpoints.

The disadvantage is that if the hub fails, the entire system is compromised.

Twisted Pair Ethernet (TPE)

hub

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Basic Operation of an Ethernet LAN Individual computers are generally connected to the

LAN through an intelligent interface unit, the NIC.» The NIC implements CSMA/CD in Layer 2 (MAC).

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) allows many stations to share a single common media and resolve contention (collisions).

» Multiple stations access a medium (Multiple Access) by listening until no signals are detected (Carrier Sense).

» Then they transmit and check to see if more than one signal is present (Collision Detection).

» If the sending station detects the collision, it sends a jam signal to insure that all nodes are aware of the collision.

» If there is a collision, each station attempts to retransmit after a preset delay, which varies for each station.

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Basic Operation of an Ethernet LAN The data is sent in packets (each station listens to all

the transmissions, picking up those addressed to it).

A block of data is called a "frame" which includes address fields, a variable size data field, and an error checking field (64-1518 bytes total).

» The preamble is a string of alternating 1’s and 0’s used to "lock on" to the sending station's encoded clock signal.

» A frame contains a Destination Address & Source Address.> A unique 6-byte ENET address is pre-assigned to each

Ethernet card when it is manufactured (AKA: Ethernet address, physical address, hardware address, or MAC address).

Preamble CRCDataDA SA Type/Length

00 AA 00 12 34 56

Ethernet Address

Company number Address

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Basic Operation of an Ethernet LAN The physical layer hardware monitors (receives) every

frame transmitted across the media (cable), picking up those packets addressed to it. Devices look for their own MAC address in each packet

to determine whether they should capture it or not. If the Destination Address (first 6 bytes of frame)

matches the address of this station, the frame is stored and passed up to the higher layers of protocol .

» If the address does not match, the frame is ignored.

The NIC asserts an interrupt to instruct the processor to read the data.

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ETHERNET LAN MEDIA The Communication Channel, Transmission Medium,

or the LAN Medium defines the nature of the physical path along which the data must travel.

There are three major types of media in use today: Coaxial cable

» Thickwire for 10BASE5 networks.

» Thin coax for 10BASE2 networks.

Twisted pair cable (the most popular Ethernet cabling)» Unshielded twisted pair (UTP) for 10BASE-T networks.

» Many newer buildings are already wired with 10BASE-T.

Fiber optic cable. » 10BASE-FL or Fiber-Optic Inter-repeater Link (FOIRL)

networks.

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ETHERNET LAN MEDIA

Thick Ethernet (10 Base-5) is the oldest form of Ethernet and is laid out in a bus topology.The most common coax cables used are RG-8 and RG-11 (50 ohm) Devices attach to the backbone via a Medium Attachment Unit

(MAU), also known as the transceiver.Both ends of segment should be terminated with a 50-ohm resistor. Today, the most common use for 10 Base-5 is as a "backbone" used

to connect together multiple 10 Base-T Hubs.

Standard Ethernet (Coax) 10BASE5--ThickwireStandard Ethernet (Coax) 10BASE5--Thickwire

PC with adapter (NIC)

Coax cable 500m max.

MAU--100 max per segment

AUI cable-- 50m max PC PC

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ETHERNET LAN MEDIA

10 Base-2, Thin Ethernet, or "Cheapernet" uses an RG-58A/U (50 ohm) coaxial cable & is wired in a bus topology.Each device is connected to the bus through a BNC "T" adapter, and

each end of the bus must have a 50 Ohm terminator attached.

» Any unused connection must have a 50 ohm terminator.Typically devices use Ethernet NICs with built-in BNC transceivers.

coax cable185m max

BNC T-ConnectorMAU--(PC with Adapter)30 max per segment

Thin Ethernet (Coax) 10BASE2--CheapernetThin Ethernet (Coax) 10BASE2--Cheapernet

PC PC PC

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ETHERNET LAN MEDIA

Workstations are connected to a central concentrator ("hub") in a STAR configuration.

10Base-T uses 2 pairs of Twisted wires in a star topology which are terminated in an 8-pin RJ-45 connectorAn RJ-45 connector looks like a large telephone-style connector.

Continued on next page

Standard Ethernet (Coax) 10BASE T Hub

RJ-45

MAU - PC Adapter

Twisted Pair Ethernet (10BASE-T)Twisted Pair Ethernet (10BASE-T)

100m Max

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ETHERNET LAN MEDIA

Cable is Unshielded Twisted Pair (UTP) ~standard telephone wire (many buildings already wired with UTP).Uses 2 pairs of wires: One for transmit data, other for receive data.

» Note: A small transformer couples the data from the network to the LAN section and prevents damages caused by improper power wiring, lightning strikes, power surges, etc.

TX+

TX-

RJ45Connector

RX+

RX-

1

2

3

6

Transmitdata

Recievedata

Magnetics(Transformer)

Twisted Pair Ethernet (10BASE-T) Cont.Twisted Pair Ethernet (10BASE-T) Cont.

Continued on next page

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ETHERNET LAN MEDIA

10 Base-T utilizes CAT 3 (or higher) 100 ohm UTP cable.One difference between the categories of UTP is the

tightness of the twisting of the copper pairs. » Category 1 Voice Only (Telephone Wire)

» Category 2 Data to 4 Mbps (LocalTalk)

» Category 3 Data to 10 Mbps (Ethernet)

» Category 4 Data to 20 Mbps (Token Ring)

» Category 5 Data to 100 Mbps (Fast Ethernet)

The two wires in each pair must be twisted together for the entire length of the segment to reduce susceptibility to interference from adjacent pairs & the environment.

» Shielded twisted pair (STP) is suitable for environments with electrical interference (e.g. factory floor)

Twisted Pair Ethernet (10BASE-T) Cont.Twisted Pair Ethernet (10BASE-T) Cont.

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ETHERNET LAN MEDIA

FOIRL (Fiber Optic InterRepeater Link) and the more recent 10BASE-FL differ only in how far each will transmit FOIRL is 1 km (0.6 miles); for 10BASE-FL it is 2 km (1.2 miles).

Fiber optic transmission requires conversion of the electrical signals to light by a light source (e.g. LED/Laser) incorporated in an external Fiber Optic MAU.

Fiber-optic cable is more expensive, but it is often used for situations where electronic emissions (EMI), security, and environmental hazards (e.g. lightning) are a concern.

PVC Jacket

Sleeve

Sleeve

PVC Jacket

LightSource

Fiberoptic EthernetFiberoptic Ethernet (FOIRL, 10BASE-FL) (FOIRL, 10BASE-FL)

10 Base-FL is wired in a star topology, is half-duplex, & supports transmission speeds from 200-1000 Mbits/sec.

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ETHERNET LAN MEDIA Wireless LANsWireless LANs typically use high frequency radio

signals or infrared light beams to communicate.Each workstation and file server has some sort of

transceiver/antenna to send and receive data as if they were physically connected.

» Longer distance communications can also take place through cellular telephone technology or by satellite.

Wireless networks allows laptops & remote computers to connect to the LAN and are also used in older buildings where it may be difficult to install cables. Wireless LANs currently are expensive, susceptible to

errors from electrical interference, and provide poor security unless encrypted.

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100 Mbits/sec "Fast Ethernet" Fast Ethernet (IEEE 802.3u - June 1995) transports

data at 100 Mbps over either UTP or fiber-optic cable.Fast Ethernet is an extension of 10BASE-T Ethernet &

retains the CSMA/CD protocol of 10 Mbps Ethernet. » Uses star topology and doesn't support coaxial cabling.

There are three types of Fast Ethernet: » 100BASE-TX--a two-pair system for data grade Cat 5 UTP.

> Uses one pair of high quality wires for transmission and the other pair for collision detection and receive.

» 100BASE-FX for use with multimode fiber-optic cable.

» 100BASE-T4 utilizes 4 pairs of wires with the relatively slow Category 3 UTP cable.

> "Demultiplexing" slows down each byte enough that the signal won't overrun the slower Category 3 UTP cable.

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Fast Ethernet Optional FeaturesFull Duplex provides bi-directional communication and

delivers up to 100 Mbps in each direction (200 Mbps).» The full duplex mode of operation requires that each end of

the link only connects to a single device.> Can be used in a server connection, where the wiring is

dedicated and bi-directional operation is useful.

» Full-duplex communication is implemented by disabling the collision detection function.

Auto-Negotiation allows devices to exchange information about their abilities & to perform automatic configuration to achieve the best possible mode of operation.

» Auto-Negotiation detects the various modes that exist in the device on the other end of the wire and automatically switches to the correct technology--10Base-T, 100Base-TX, 100Base-T4, or Half/Full Duplex mode.

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Network Interface Card Functions The Network Interface Card (NIC) provides the physical

connection between the network and the PC.The NIC takes the transmit data from the PC, puts it into the

appropriate format, and sends the serialized transmit data over the media to another LAN interface card.

The NIC also receives the data, puts it into a form the PC understands, and places data & status in shared memory for the CPU to read.

NetworkCable

PC

TransceiverPacket

FormationData Packets

(Serial)Encode/Decode

Buffer(FIFO)

Data Bits(1’s/0’s

ParallelData`

Network Interface Card (NIC)

NIC/CableInterface

PC/NICInterface

30

Network Interface Card Functions

The NIC functions to get data from the memory of one PC to the memory of another PC can be broken into tasks:

» 1 - PC/NIC communications> The CPU & NIC communicate via shared host PC memory to

move data between the Host PC & the LAN Coprocessor.

» 2 - Packet formation (Transmit sequence example)> Data is formatted into packets & converted from parallel-serial.

» 3 - Encoding/decoding > Manchester encoding is used to combine the clock and data.

» 4 - Transmission/reception> NIC accesses the cable using the CSMA/CD protocol.

NetworkCable

PC

TransceiverPacket

FormationData Packets

(Serial)Encode/Decode

Buffer(FIFO)

Data Bits(1’s/0’sParallel

Data`

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Network Interface Card Functions 1 - The CPU & the NIC communicate via shared memory to

move Data between the Host PC & the LAN CoprocessorThe CPU places commands and transmit data in shared memory in

the host PC and notifies the NIC that data is available.

» Either Programmed I/O, DMA, or Bus Master DMA is used to transfer the data between the NIC & PC main memory, depending on NIC architecture, bus type (ISA, PCI, etc), & the Network O/S.

The NIC also receives packets from the physical layer, places data & status in shared memory, and notifies the CPU that data is available using the IRQ line.

Shared Memory

CPULAN

configstatus

commandsRx BufferTx Buffer

LAN Data

Coprocessor

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Network Interface Card Functions 2 - Packet formation: Data is sent as packets and

converted from parallel-serial.» A packet has three sections: header (synch information,

destination address, & source address), data, and trailer.> Each NIC is identified by a unique 12 digit (6-byte) hex

address which is usually stored in an EEPROM or FLASH on the NIC.

» The trailer includes a CRC calculated by the sending NIC.

A transmit and receive buffer (FIFO) hold data moving into and out of the NIC (e.g. 3Kbytes; ~2 packets).

» Data often moves into or out of the card faster than it can be processed by the NIC.

The NIC performs parallel-serial conversion & vice versa.» The packets must be converted to serial form to be sent

over the cable one bit at a time.

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Network Interface Card Functions 3 - Encoding/decoding

Once a packet is formed and changed from parallel to serial, it is encoded using Manchester encoding to combine the clock & data into one serial data stream.

With Manchester encoding, the encoded data has a transition at the center of each data bit.

» A change from negative to positive represents a 1.

» A change from positive to negative represents a 0.

Actual Data

ManchesterEncoded Data

BIT CELL

“1”

“1”

“0” “1”

“1”“0”

“0” “0”

“0” “0”

“0”“1”

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Network Interface Card Functions 4 - Transmission/reception: Before data can be sent

the NIC accesses the cable using CSMA/CD protocol.Ethernet uses the CSMA/CD protocol as a means for

many stations to share a single common media and resolve contention (collisions).

» The entire protocol for the access method, all the circuitry and firmware, resides on the Network Interface Card.

The Medium Attachment Unit (MAU), also known as the transceiver, performs the task of transmitting the frames onto the cable and receiving them from it.

» The transceiver can either be external or on-board the NIC.> Many NICs contain a built-in 10BASE-T or 10BASE2

transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver.

Continued on next page

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Network Interface Card Functions 4 - Transmission/reception (cont.):

At the receiving end, a transceiver is waiting to accept the signal and begin the whole process in reverse:

» Decoding the signal, Serial-Parallel conversion, and depacketizing to a PC-readable data format.

» When the NIC receives the data it asserts an interrupt request line, and an Interrupt Service Routine (ISR) instructs processor to read the data.

Note: An optional “Boot Rom” may be used to connect to a server to download the O/S at boot time.A Boot Rom enables diskless workstations to remote

boot an operating system at startup.» The Prom or Flash chip contains the instructions necessary

to access a disk image on the server.

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Extending LANs Bridges, Routers, and Gateways are Internetworking

devices that provide communications between local area network (LAN) segments.

» Internetworking refers to linking individual LANs together.

Geographically distant company sites can be tied together in the enterprise-wide internetwork.

Workgroup LANs on different floors or in separate buildings can be linked together so that all of the computing systems at that site are interconnected.

» Internetworking provides network connectivity for more people, or extends coverage to a larger area.

» Internetworking is also used to segment LANs to maintain performance by reducing the number of users per segment.

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Extending LANs - HUBS A HUB takes an ENET packet transmitted to it by one

station, & repeats it to all of the other ports of the hub.Hubs are generally associated with 10BASE-T Ethernet

networks and are necessary in star topologies.» If the hub is attached to a backbone, then all computers at

the end of the twisted pair segments can communicate with all the hosts on the backbone.

Passive hubs are simple splitters or combiners that group workstations into a single segment.

» Requires no power and does no processing of traffic.

Active hubs contain circuitry, include a repeater function, and are capable of supporting many more connections.

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Extending LANs - Bridges Bridges connect LANs & forward or filter data packets

based on the destination address--forward if not local.Bridges operate at the data link level (a layer 2 relay)

» Bridges know the addresses of all computers on each side of the network.

» If a packet's destination is on the same segment (usually referring to a physical length of wire), it is not forwarded.

» If it is destined for a station on another LAN, it is connected to a different bridge port and forwarded to that port.

Bridges are transparent to client & server workstations.Bridges normally connect similar LANs that use the same

protocol but may have different types of cabling (e.g. Ethernet Coax to Ethernet 10BaseT)

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Extending LANs - Routers A Router is an OSI layer 3 device.

Routers are more complex and typically more expensive than bridges, and are often PC based.

» Bridging occurs at a lower level (more a hardware function) whereas routing occurs at a higher level where the software component can perform more complex path analysis.

Routers communicate with each other and share information that allows them to determine the best route.

» A router maintains a list of all stations & determines the optimal routing paths (which cable to send out information).

> Routers know the addresses of computers, bridges, and other routers on the network.

» A router can convert from different access methods (CSMA/CD, Token Ring, etc).

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Extending LANs - Gateways A Gateway is a protocol converter between dissimilar

networks.Gateways are complex and relatively slow and can

connect dissimilar networks that differ in all details. » Gateways can translate all protocol levels from the Physical

layer up through the Applications layer of the OSI model.

» Can convert a TCP/IP packet to a Netware IPX packet.

Gateways capabilities can include:» Terminal emulation - So a PC can act like an IBM 3270

mainframe terminal.

» File transfer - A Novell user could download a file from a Unix machine.

» Mail - Exchanging messages between users on different e-mail systems.

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REVIEW & SUMMARYWE HAVE DISCUSSED THE FOLLOWING:

The architecture of Local Area Networks.A Network is a collection of computers that communicate

with one another over a shared network medium.NICs provide the physical connection between the

network cable and the computer's internal bus. Ethernet Standards and Topologies.

Ethernet is the most widely used type of network cabling and signaling specification.

The BUS is the simplest (and the traditional) topology.The Star topology is used for twisted-pair cabling

(10BASE-T Ethernet), fiberoptic links, & Fast Ethernet.

42

REVIEW & SUMMARY Ethernet operation and Ethernet LAN Media.

CSMA/CD allows many stations to share a single common media and resolve contention (collisions)

» The data is sent in packets and each station listens to all the transmissions, picking up those addressed to it.

» If the Destination Address matches this station, the frame is stored and passed up to the higher layers of protocol .

There are three major types of media in use today: » Coax cable--Thickwire (10BASE5) & Thin coax (10BASE2);

Twisted pair cable (the most popular); and Fiber optic cable.

100 Mbps Fast Ethernet.Fast Ethernet is an extension of 10BASE-T Ethernet,

uses star topology and doesn't support coaxial cabling.

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REVIEW & SUMMARY The functions of a Network Interface Card.

NIC functions can be broken into tasks:» 1 - PC/NIC communications (via shared host PC memory)

» 2 - Packet formation and conversion from parallel-serial.

» 3 - Manchester encoding to combine the clock and data.

» 4 - Transmission/reception--access cable using CSMA/CD.

Common devices used for extending LANs.» HUB repeats packet to all of the other ports of the hub.

» Bridges connect LANs and forward if not local.

» Routers are more complex than bridges, are often PC based, and determine the optimal routing paths.

» A Gateway is a protocol converter between dissimilar networks (more complex than a Bridge or Router).

End of Chapter 5-1