INTRODUCTIONTo

NETWORK BASICS

Why Use Networks?

• Network: group of computers and other devices that are connected

by some type of transmission media

• Advantages of using networks over standalone computers:

• Networks enable multiple users to share the network’s resources (devices

and data)

• Networks allow you to manage, or administer, resources on multiple

computers from a central location

Types of Networks: Peer-to-peer Networks

• Every computer can communicate directly with every other computer

• By default, no computer has more authority than another

• Every computer is capable of sending and receiving information to

and from every other computer

Peer-to-peer Networks (cont’d)

Example of a Windows XP Professional Workgroup

Client/Server Networks

• Server: central computer used to facilitate communication and resource

sharing between other computers on the network (called clients)

• Client/server network: uses a server to enable clients to share data, data

storage space, and devices

• To function as a server, a computer must be running a network operating

system (NOS)

• Most of the concepts on the Network+ exam pertain to client/server

networks

Client/Server Networks (continued)

• Advantages of using client/server networks over peer-to-peer networks:

• User logon accounts and passwords can be assigned in one place

• Access to multiple shared resources can be centrally granted to a single user or

groups of users

• Problems can be tracked, diagnosed, and often fixed from one location

• Servers are optimized to handle heavy processing loads and dedicated to handling

requests from clients, enabling faster response time

• Because of their efficient processing and larger disk storage, servers can connect

more than a handful of computers on a network

Client/Server Networks

Microsoft Windows 2000 Domain

LANs, MANs, and WANs

• Local area network (LAN): confined to a relatively small space, such as a

building or an office

• Metropolitan area network (MAN): larger than a LAN; connects clients and

servers from multiple buildings

• Wide area network (WAN): connects two or more geographically distinct

LANs or MANs

LANs, MANs, and WAN

A simple WAN

Elements Common to Client/Server Networks

• Client

• Server

• Workstation

• Network interface card (NIC)

• NOS

• Host

• Node

• Connectivity device

Elements Common to Client/Server Networks

• Segment

• Backbone

• Topology

• Protocol

• Data packets

• Addressing

• Transmission media

Topology

Transmission media

How Networks Are Used

• Network services: functions provided by a network• File services

• Capability of a server to share data files, applications, and disk storage space

• File server• Print services: used to share printers across a network• Communications services

• Allow remote users to connect to the network• Remote access server (also known as communications server or

access server)• Mail services

• Coordinate the storage and transfer of e-mail between users on a network

• Mail server

How Networks Are Used Cont..

• Internet services• Supplying Web pages, file transfer capabilities, Internet addressing

schemes, security filters, and a means for directly logging on to other computers on the Internet

• Web server• Management services: centrally administer management tasks on

the network• Traffic monitoring and control• Load balancing• Hardware diagnosis and failure alert• Asset management• License tracking• Security auditing• Software distribution• Address management• Backup and restoration of data

Networking Standards Organizations

• Standards: documented agreements containing technical

specifications or other precise criteria stipulating how particular

products or services should be designed or performed

• Define minimum acceptable performance

• Many different organizations have evolved to oversee computer

industry’s standards

ANSI

• American National Standards Institute (ANSI)

• Composed of more than a thousand representatives from

industry and government

• Represents United States in setting international standards

• ANSI standards documents available:

• ANSI’s Web site (www.ansi.org)

• At university or public libraries

EIA and TIA

• Electronic Industries Alliance (EIA): Trade organization composed

of representatives from electronics manufacturing firms across US

• Sets standards for its members

• Helps write ANSI standards

• Lobbies for legislation favorable to growth of computer and electronics

industries

• Telecommunications Industry Association (TIA): Focuses on

standards for information technology (IT), wireless, satellite, fiber

optics, and telephone equipment

IEEE

• Institute of Electrical and Electronics Engineers

• International society composed of engineering professionals

• Goals are to promote development and education in electrical

engineering and computer science

• IEEE technical papers and standards are highly respected in the

networking profession

• Can purchase IEEE documents online from IEEE’s Web site

(www.ieee.org)

ISO

• International Organization for Standardization

• Collection of organization standards representing 146 countries

• Goal is to establish international technological standards to

facilitate global exchange of information and barrier-free trade

• Fewer than 300 of ISO’s more than 14,250 standards apply to

computer-related products and functions

ITU

• International Telecommunication Union

• Regulates international telecommunications:

• Radio and TV frequencies

• Satellite and telephony specifications

• Networking infrastructure

• Tariffs applied to global communications

• Typically, documents pertain more to global telecommunications issues

than to industry technical specifications

ISOC

• Internet Society

• Professional membership society that helps to establish technical

standards for the Internet

• Oversees groups with specific missions:

• Internet Architecture Board (IAB): Technical advisory group of researchers

and professionals

• Interested in overseeing Internet’s design and management

• Internet Engineering Task Force (IETF): Sets standards for how systems

communicate over the Internet

• How protocols operate and interact

IANA and ICANN

• Internet Protocol (IP) addresses: Addresses used to identify

computers on the Internet and other TCP/IP-based networks

• Internet Assigned Numbers Authority (IANA): Used to keep

records of available and reserved IP addresses and determines

how addresses were doled out

• In 1997, coordinated efforts with three Regional Internet Registries

(RIRs)

• Not-for-profit agency that manages distribution of IP addresses to

private and public entities

IANA and ICANN (continued)

• In late 1990s U.S. Department of Commerce (DOC) overhauled IP

addressing and domain name management

• Internet Corporation for Assigned Names and Numbers (ICANN):

Ultimately responsible for IP addressing and domain name

management

• IANA still performs system administration

• Individuals and businesses lease addresses from Internet Service

Provider (ISP)

• Business providing access to Internet and other services

The OSI Model

• Open Systems Interconnection (OSI) Model: divides network

communications into seven layers:

• Physical, Data Link, Network, Transport, Session, Presentation,

and Application

• Protocols perform services unique to layer

• Protocols interact with protocols in layers directly above and below

• Protocol: set of instructions to perform a function or group of functions

• Written by a programmer

The OSI Model (continued)

• Theoretical representation of what happens between two nodes

communicating on a network

• Does not prescribe type of hardware or software that should support each layer

• Does not describe how software programs interact with other software programs or

how software programs interact with humans

• Each layer communicates with same layer from one computer to another

• Model is imperfect

The OSI Model

Application Layer

• Services facilitate communication between software and lower-

layer network services

• Helps software applications negotiate formatting, procedural, security,

synchronization, and other requirements with network

• Hypertext Transfer Protocol (HTTP): formats and sends requests

from client’s browser to server

• Also formats and sends Web server’s response back to client’s browser

• Application program interface (API): set of routines that make up

part of a software application

Presentation Layer

•Protocols accept Application layer data and format it

• So that one type of application and host can understand

data from another type of application and host

• e.g., translation and conversion between graphics file

types

•Manages data encryption and decryption

Session Layer

• Protocols coordinate and maintain communications between two network nodes

• Establish and maintain communications link for duration of session

• Keep communication secure

• Synchronize dialogue between two nodes

• Determine if communications have been cut off

• Determine where to restart transmission

• Terminate communications

• Sets terms of communication• Decides which node will communicate first

• Decides how long a node can communicate

• Monitors identification of session participants• Ensures that only authorized nodes have access

Transport Layer

• Protocols accept data from Session layer and manage end-to-

end delivery of data

• Ensure data transferred reliably, in correct sequence, and without

errors

• Protocols also handle flow control

• Gauging appropriate rate of transmission based on how fast recipient

can accept data

• Transmission Control Protocol (TCP): Takes care of reliably

transmitting HTTP requests from client to server and vice versa

Transport Layer (continued)

• Connection-oriented protocols: ensure that data arrives

exactly as it was sent

• Establish connection before transmitting data

• TCP is connection-oriented

• Client’s TCP protocol first sends synchronization (SYN) packet

request to server

• Server responds with synchronization-acknowledgment (SYN-ACK)

packet

• Client responds with own acknowledgment (ACK)

Transport Layer (continued)

• Acknowledgments also used to ensure that data was

properly delivered

• For every data unit sent, connection-oriented protocol expects

acknowledgment from recipient

• If no acknowledgment, data retransmitted

• Connection-oriented protocols use a checksum

• Unique character string allowing receiving node to determine

if arriving data unit exactly matches data unit sent by source

Transport Layer (continued)

• Connectionless protocols do not establish connection before transmitting • No effort to ensure data delivered error-free

• Transport layer protocols break large data units received from Session layer into smaller segments (segmentation)

• Maximum transmission unit (MTU): largest data unit a given network will carry

• Reassembly: process of reconstructing segmented data units

• Sequencing: method of identifying segments that belong to same group of subdivided data

• Indicates where unit of data begins

• Indicates order in which groups of data were issued

• Transport layer protocols of two nodes must synchronize timing and agree on starting point for the transmission

Transport Layer

Network Layer

• Primary functions of protocols:• Translate network addresses into physical counterparts• Decide how to route data from sender to receiver

• Each node has two types of addresses:• Network address: follows hierarchical addressing scheme

• Can be assigned through OS software• Network layer addresses, logical addresses, or virtual addresses

• Physical address• Network layer protocols accept Transport layer segments and add logical

addressing information in network header• Network layer handles routing

• Determining best network path

• IP: Network layer protocol that underlies most Internet traffic• Fragmentation: Network layer protocol subdivides segments it receives from

Transport layer into smaller packets

Data Link Layer•Protocols divide received data into distinct frames •Can then be transmitted by Physical layer

•Frame: structured package for moving data •Raw data•“payload” •Sender’s and receiver’s network addresses•Error checking and control information

•Error checking accomplished by 4-byte Frame Check Sequence (FCS).•Ensures data at destination exactly matches data issued from source

•When source node transmits data, performs Cyclic Redundancy Check (CRC) to get FCS

•Destination node’s Data Link layer services unscramble FCS via same CRC algorithm

•Data Link layer divided into two sub-layers:•Logical Link Control

•Media Access Control

Data Link Layer

• Logical Link Control (LLC) sublayer:

• Provides interface to Network layer protocols

• Manages flow control

• Issues requests for transmission for data that has suffered errors

• Media Access Control (MAC) sublayer:

• Manages access to physical layer

• Appends destination computer’s physical address onto data frame (MAC address, Data

Link layer address, or hardware address)

• MAC addresses contain two parts:

• Block ID: six-character sequence unique to vendor

• Device ID: six-character sequence based on NIC’s model and manufacture date

Physical Layer

• Protocols accept frames from Data Link layer and generate voltage to

transmit signals

• When receiving data, protocols detect voltage and accept signals

• Protocols also set data transmission rate and monitor data error rates

• Cannot perform error correction

• NICs operate at both Physical layer and Data Link layer

• Network administrators mostly concerned with bottom four layers of

OSI Model

Applying the OSI Model

Communication Between Two Systems

Data transformation through the OSI Model

Frame Specifications

• The two major categories of frame types:

• Ethernet

• Four types of Ethernet frames

• Most popular form characterized by unique way in which devices

share a common transmission channel (described in IEEE 802.3

standard)

• Token Ring: relies on direct links between nodes and a ring topology

• Nodes pass around tokens (control frames that indicate to

network when a node is about to transmit data)

IEEE Networking Specifications

IEEE 802 standards

Transmission Direction: Simplex, Half-Duplex, and Duplex

• Simplex transmission: signals may travel in only one direction

• Half-duplex transmission: signals may travel in both directions over a

medium

• Only one direction at a time

• Full-duplex or duplex: signals free to travel in both directions over a

medium simultaneously

• Used on data networks

• Channel: distinct communication path between nodes

• May be separated logically or physically

Throughput and Bandwidth

• Throughput: measure

of amount of data

transmitted during

given time period

• Bandwidth: difference

between highest and

lowest frequencies that

a medium can transmitPoint-to-point versus broadcast transmission

Baseband and Broadband

• Baseband: digital signals sent through direct current (DC)

pulses applied to a wire

• Requires exclusive use of wire’s capacity

• Baseband systems can transmit one signal at a time

• Ethernet

• Broadband: signals modulated as radiofrequency (RF)

analog waves that use different frequency ranges

• Does not encode information as digital pulses

Network Architecture Terminology

• Network protocols

• OS protocols (eg, NetBEUI, TCP/IP)

• Hardware protocols (eg, Ethernet,Token Ring)

• Data transmission

• Packets, datagrams, or frames

Ethernet Variations,Distinguished by Speed

Ethernet Cable Types

Ethernet Cable Types (continued)

Ethernet Topology

• Bus topology

• Connects each node in a line

• Has no central connection point

• Star topology

• Connects all nodes to a centralized hub

• More popular; easier to maintain

• Patch cables and crossover cables

Bus and Star Topologies

Ethernet Hub Broadcasting aData Packet

A Hub

Star Bus Topology

Repeaters

• Amplify signals on a network

• Help overcome limitations on length of cables that can be used; signals can travel

farther Two kinds Amplifier repeater

• Signal-regenerating repeater (used by Ethernet)

Repeaters (continued)

Wireless LANs

Use radio waves or infrared light to connect computers or devices Wireless

NIC includes antenna to send and receive Signals Standards 1999 IEEE

802.11b (Wi-Fi or AirPort) Bluetooth Slower than wired networks Security is

an issue.

Wireless LANs (continued)

Token Ring

• Physical star; logical ring

• Data packet is preceded by a token

• Transmits data at 4 Mbps or 16 Mbps

• Uses a centralized device called a MAU

• (Multistation Access Unit)

• Uses UTP or STP cables (two twisted pairs)

• lUses RJ-45 or UDC connectors

FDDI

• Uses tokens; structured as a ring, but does not

• require a centralized hub

• Multiple nodes can have data on the ring at the same time

• Provides data transfer at 100 Mbps

Used as:

• Network technology for a large LAN

• Backbone network to connect several LANs

Now NICs Work

• Plug into motherboard expansion slot

• Provide port(s) on back of card for connection to network Manage

communication and hardware network

• protocol for the PC

Network Cards

Network Cards

• Send and receive data:

• To and from system bus in parallel

• To and from network in series

• Use a transceiver for signal conversion

• Identified by a MAC address

• Require an IRQ and an I/O address range

• May be PnP; legacy cards can use jumpers or DIP switches

Ethernet Combo Card

Considerations When Selecting

a Network Card

Speed and type of network Type of cable (shielded twisted-pair, coaxial, or

fiber-optic) Type of slot (PCI or ISA)

Segmenting a Network

• Communication on a local network uses MAC

• address of NIC to identify the destination computer;

• Other computers discard the packet because it is not addressed to them Bridges and

switches

• Reduce traffic on each segment and improve

• network performance More intelligent than hubs

How Bridges Work

Bridges and Switches

Bridges and Switches (continued)

Bridges Send broadcast messages; not good for large Networks Effective at

separating high-volume areas on a LAN

Best for connecting LANs that do not communicate outside their immediate

network

Bridges and Switches (continued)

Switches Send a packet only to network segment for which it is destined Both

keep source and destination MAC addresses in routing tables and learn new

addresses

Bridges Compared withSwitches

How Computers Find EachOther on a LAN

• Checks NetBIOS name cache

• Queries WINS server, if it has its IP address

• Sends broadcast message to all computers on LAN asking for IP address of computer

with broadcasted NetBIOS name

• Checks LMHosts file

• If IP address still not discovered, computer assumes network is using DNS and checks

Hosts file

• Queries DNS server, if it has its IP address

Installing a Network Card and

Connecting to a Network

• Physically install the card and device drivers

• Configure the NIC using Windows so it has

• appropriate addresses on the network and

• correct network protocols

• Give the computer a name

• Test the NIC to verify that PC can access

• resources on the network

Installing a NIC Using Windows2000/XP

Network Drive Maps

Using NFS client/software, network drive map makes one PC (client) appear to have new

hard drive when that hard drive space is actually on another host computer (server) Use

Windows Explorer to map a network drive

Results of Drive Mapping

Symptoms of NIC Problems

• Cannot make connection to network

• My Network Places or Network Neighborhood does not show other computers on

network Error message appears during installation of NIC drivers

• Device Manager shows yellow exclamation point or red X beside name of NIC No

lights on NIC

Troubleshooting NetworkConnections

Check the following:

• Cabling and ports for PC

• NIC itself

• BIOS

• Device drivers

• Troubleshooting tools

• Ping (TCP/IP utility)

• Ipconfig (Windows NT/2000/XP)

• Winipcfg (Windows 9x)

Connecting Networks withRouters

• Use IP addresses to determine path by which to send a packet;

• Tables détermine most efficient available route Stateless devices - concerned about

destination address;

• Unconcerned about data Transmit data packet to remote network only if routable

protocol was used to produce data packet

Connecting Networks withRouters (continued)

Brouter

• Functions both as a bridge and a router

• As a router Routes routable protocols (TCP/IP and IPX/SPX packets)uAs a bridge

• Forwards packets that are not routable (NetBEUI)

• packets) to other local networks

Connecting Networks withBandwidth Technologies

• Bandwidth: measure of data capacity

• Greater bandwidth = faster communication

• Common bandwidth technologies

• Regular telephone lines

• Cable modem

• ISDN (Integrated Services Digital Network)

• DSL (Digital Subscriber Line)

• Satellite access

• Wireless access

Bandwidth Technologies

Bandwidth Technologies

Bandwidth Technologies

Summary

• How local networks are built

• How bridges and switches can segment large local Networks

• How routers connect networks

• Technologies used to connect PCs and networks to the Internet Supporting PCs that

are connected to a network

• How computers are identified over a network

• How to share computer resources over a network

• How to troubleshoot a network connection

Wireless Transmission

• Networks that transmit signals through the atmosphere via infrared or RF waves are known as wireless networks or wireless LANs (WLANs).

Wireless transmission and reception

The wireless spectrum

Antennas

• Radiation pattern describes relative strength over three-dimensional area of all electromagnetic energy the antenna sends or receives

• Directional antenna issues wireless signals along a single direction

• Omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions

• Range: geographical area an antenna or wireless system can reach

Signal Propagation

Signal Degradation

• Fading: change in signal strength resulting from

electromagnetic energy being scattered, reflected, or

diffracted after being issued by transmitter

• Wireless signals experience attenuation

• May be amplified and repeated

• Interference is significant problem for wireless

communications

• Atmosphere saturated with electromagnetic waves

Narrowband, Broadband, and Spread Spectrum Signals

• Narrowband: transmitter concentrates signal energy at single frequency or

in very small range of frequencies

• Broadband: uses relatively wide band of wireless spectrum

• Offers higher throughputs

• Spread spectrum: use of multiple frequencies to transmit a signal

• Frequency hopping spread spectrum (FHSS)

• Direct sequence spread spectrum (DSSS)

Wireless LAN (WLAN) Architecture

An ad-hoc WLAN

An infrastructure WLAN

Wireless LAN Architecture

Wireless LAN interconnection

Summary

• Types of Networks:• LAN, MAN, WAN

• Network Considerations • Network Components • Networking Models • What Is the OSI Model?

• Physical Layer • Data Link Layer• Network Layer • Transport Layer • Session Layer • Presentation Layer • Application Layer

• Types of Cables and connectors• LAN, WAN, MAN, WLAN Architechture

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