Chapter 6 Data Communications. Q1: What is a computer network? Q2: What are the components of a LAN?...

Chapter 6

Data Communications

Q1: What is a computer network?Q2: What are the components of a LAN?Q3: What are the alternatives for a WAN?Q4: How does encryption work?Q5: What is the purpose of a firewall?Q6: What is a VPN and why is it important?

Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall

Study Questions

6-2

• Network– Collection of computers – Communicate with one another over transmission

media• Basic types of Network Topologies

– Local Area Network (LAN)– Wide Area Network (WAN)– Internet

6-3

Q1: What Is a Computer Network?


• Computers connected on single company site

• Usually located in small area, such as a home, office building, or group of buildings

• Connects two to several hundred computers

• Company/Enterprise owned resources

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LAN (Local Area Network)


• Connects computers across metropolitan, state, regional, national areas

• Uses communication networks from vendors– Licensed by government

• FCC (Federal Communications Commission)

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WAN (Wide Area Network)


• Global network of networks• Public and private network of networks

– Intranets - within an Enterprise– Extranets – connects Intranets of customers,

suppliers and partners through secure connections

• Uses a variety of communication methods and conventions

• Protocol: a set of standard rules for data representation, signaling, authentication, and error detection required to send information

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Internet


Network Protocols: The OSI Architecture

6-7Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall

Application LayerApplication Layer

Presentation LayerPresentation Layer

Session LayerSession Layer

Transport LayerTransport Layer

Network LayerNetwork Layer

Data Link LayerData Link Layer

Physical LayerPhysical Layer

SevenLayers ofthe OSICommunicationsArchitecture

1. Client

2. TC Interfaces

3. Media

4. Server

5. TC Software

Q2: What Are the Components of a LAN?


Client

TC Interface

MediaServer

TC Software

Basic Network Model

Telecommunication Interface• Switch

– Connects devices on a network• Router

– Connects multiple networks and directs/distributes messages

– Provided NAT (Network Address Translation)• Network interface card (NIC)

– Hardware that connects each device’s circuitry to the cable (Firmware for communications)

Q2: What Are the Components of a LAN? (cont’d)


Media• Wired

– UTP (unshielded twisted pair cable)– Optical fiber cable– Coaxial Cable

• Wireless– Wi-Fi (Wireless Fidelity – Wi-Fi Alliance)

Q2: What Are the Components of a LAN? (cont’d)


• World’s most popular protocol for LANs

• 10/100/1000 Mbps Ethernet

• Ethernet protocol specifies hardware characteristics, cables, and how messages are packaged and processed

– MAC (media access control) subset of the Data Link level + Physical Layers

– MAC Address is assigned by the NIC manufacturer.

IEEE 802.3 Protocol(Institute of Electrical and Electronics Engineers)


1. Connect to an Internet service provider (ISP)2. Network of Leased Lines3. Public Switched Data Networks4. Wireless Networks (WiMax)5. Virtual Private Network (VPN)

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Q3: What Are the Alternatives for a WAN?


• Internet service provider (ISP)– A company that provides customers

access to the Internet– Provides legitimate Internet address (Public)– Serves as gateway to Internet

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Q3: What Are the Alternatives for a WAN? (cont’d)


1. Dial-up Modems2. DSL Modems3. Cable Modems

• Modem – a device to produce a signal that can be transmitted easily and decoded to reproduce the original digital data (Modulates/Demodulates)

• Bandwidth – measure of capacity or throughput– Narrowband – less than 256 kbps speed (56K Max)– Broadband – more than 256 kbps speed

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Connecting the Personal Computer to an ISP: Modems


– Converts signals between analog and digital so computers can communicate over a regular telephone line (POTS)

– Maximum transmission speed of 56 kbps (53 kbps really)

– Modulation standards – V.34, V.90, V.92 specify how digital signals are converted to analog (Physical Layer)

1. Dial-up Modems


Digital Subscriber Line (DSL)– Operates over telephone lines separate from

voice, 256 kbps+– Always on connection– ISDN (Integrated Services Data Network) Hybrid

or (Integrated Services Digital Network)

– Download and upload speeds may differ– Asymmetric digital subscriber lines (ADSL)– Symmetrical digital subscriber lines (SDSL)

– Distance Limitation of 2 miles (2km)

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2. DSL Modems


• Use cable television lines– High-capacity optical fiber cable– Does not interfere with television transmission– Hundreds of subscribers connected at each

substation• Performance can vary based on number

connected– Symmetric and Asymmetric options are available

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3. Cable Modems


• Point to Point communication services (24x7x365)

• Router or network switch connects sites

• Leased line alternatives– T1 line (1.544 Mbps), T3 line (44.736 Mbps), OC-768 (40

Gbps)– Monthly connection and maintenance costs expensive– Provide low cost per bit transmitted for high traffic

networks

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Networks of Leased Lines


WAN Using Leased Lines


• Shared communications network• Time leased on network (Pay for Use)• Basis for the birth of the Internet (X.25 Protocol)• Each site leases line to connect to PSDN network

at access point• Point of presence (POP)

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Public Switched Data Network (PSDN)


WAN Using PSDN


• Frame relay– Process traffic at 56 kbps to 40 Mbps– Best application is data– Lower cost than ATM– PVC (Permanent Virtual Circuit)– CIR (Committed Information Rate}

• Asynchronous transfer mode (ATM)– Process speeds from 1 to 156 Mbps– A connection based protocol – Support video, voice and data communication

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PSDN Protocols


• WiMax - Worldwide Interoperability for Microwave Access

• A standards-based technology for wireless broadband access.

• Last-mile problem—getting broadband access into homes, small businesses and mobile clients

• WiMax Forum CertifiedTM systems to have capacity of 40 Mbps per channel, for fixed, nomadic, portable, and mobile applications

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Wireless Networks (WiMax)


Types of Access to a WiMax Network


Source: Table 1, “Types of Access to a WiMax Network,” from Fixed, Nomadic, Portable, and Mobile Applications for 802.16–2004 and 802.16e WiMax Networks, prepared by Senza Fili Consulting on behalf of the WiMax Forum.© 2005 WiMax Forum, www.wimaxforum.org/technology/downloads(accessed June 2008).

Figure 6-13

6-25

Criteria for Comparing WANs


Q4: How does encryption work?Q5: What is the purpose of a firewall?Q6: What is a VPN and why is it important?

Data CommunicationsClass II


• Encryption– Process of transforming clear text into coded text

– Used for secure storage or communication

– Uses algorithms• DES (Data Encryption Standard)• 3DES (Triple DES)• AES (Advanced Encryption Standard)

• Key– Used to encrypt data

– Algorithm applies key to produce coded message• Symmetric encryption – same key encrypts and decrypts• Asymmetric encryption – different keys are used

– Key used to decrypt message

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Q4: How Does Encryption Work?


• Public key/private key cryptography– Public key used to encrypt messages– Public key sent to other party to encode messages to be sent

back– Decrypted with private key– Complex and slow

– Asymmetric public key encryption

• HTTPS uses secure socket layer (SSL, a.k.a. TLS) protocol to encrypt data

– Fast, secure

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Q4: How Does Encryption Work? (cont’d)


Figure 6-14

Q4: How Does Encryption Work? (cont’d)


SCOTS - Security

• Computer device that prevents unauthorized network access• May be special-purpose computer or program on a general-purpose

computer• Organizations may have multiple firewalls

– Perimeter firewalls sit outside organizational network– Internal firewalls are inside network– Packet-filtering firewalls examine each part of a message (source

address, destination address, and other bytes) before allowing message to pass

– May filter both incoming and outgoing messages

• Access control list (ACL) encodes rules stating which IP addresses are allowed into or prohibited from the network

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Q5: What Is the Purpose of a Firewall?


Virtual private network– Uses Internet or private switched network to

create appearance of point-to-point private network

– Client and server have point-to-point connection called tunnel

• Private pathway over shared network

– Secure, encrypted communications• VPN client software encrypts data and receiving VPN

server decrypts it • Users and their keys must be registered with VPN server

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Q6: What Is a VPN, and Why Is It Important?


Remote Access Using VPN: Actual Connections


• Dee and salespeople use thin client computers– Dee creates blog entries on Web pages using Movable

Type– Salespeople use pages served by Movable Type

• Client computers contain VPN client software– Interact with VPN server via Internet– Secure, private connections– Firewalls stop traffic not addressed to VPN server– Salespeople know how to use VPN

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How Does the Knowledge in This Chapter Help Dee and You?


• IT department cannot schedule resources to setup blog server in timely fashion– Will not allow outside person to do setup

• Would then have access to system

• Consultant can create server on unprotected test server– Can be copied onto network server after acceptance– Requires some internal IT labor– Consultant could include Trojan horse virus or malware

• Install only software from known sources• Code should not reside on production server

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How Does the Knowledge in This Chapter Help Dee and You? (cont’d)


Q1: What is a computer network?Q2: What are the components of a LAN?Q3: What are the alternatives for a WAN?Q4: How does encryption work?Q5: What is the purpose of a firewall?Q6: What is a VPN and why is it important?

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Chapter 6

Data Communications

Chapter 6 Data Communications. Q1: What is a computer network? Q2: What are the components of a LAN?...

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