Tonga Institute of Higher Education IT 141 Lecture 6: LANS and WLANS

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Network Classifications

• Classified according to size and geographic scope PAN (personal area network) – within a range of 30 feet (10 meters) NAN (neighborhood area network) – within a limited geographical area, usually over several buildings LAN (local area network) – connects personal computers within a very limited geographical area MAN (metropolitan area network) – public high-speed network capable of voice and data transmission within a range of about 80 km WAN (wide area network) – covers a large geographical area usually consists of several smaller networks

We will focus on LAN because you are most likely to encounter this type of network.

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LAN standards

    It ranges from simple households to large businesses LAN standards – LAN technologies are standardized by the Institute of Electrical and Electronic Engineers (IEEE). E.g. – IEEE 802.3 is sometimes used to refer to a network standard in articles and advertisements Popular LAN standards – ARCnet, Token Ring, FDDI WERE POPULAR. Today, most LANS configured with Ethernet technology and use compatible Wi-Fi standards in applications that require wireless access.

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NETWORK DEVICES

• • • • • •

node

– A single device connected to a network

Workstation

a network – personal computers connected to

Modem

– uses phone lines to transmit data over a network

Network Interface Card (NIC)

– network circuitry required to connect a computer to a LAN

Networked peripheral

– any device that has network circuitry to directly connect to a network

Network attached storage (NAS)-

that directly connects to a network storage device 4

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CLIENTS, SERVERS, AND PEERS

•

Servers

– a computer that provides services for other computers on a network called clients E.g.

– Application server – run application software for network workstations – File server – stores files and supplies them to workstations on request 6

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CLIENTS, SERVERS, AND PEERS

 

Workgroup (Peer-to-Peer)

  A workgroup is a group of computer connected by a LAN, but not sharing similar information, like usernames and passwords.

This is commonly used in networks with less than five computers where each user has their own computer

Domain (Client-Server)

  A domain allows all computers to be a part of a group that shares usernames, passwords and various settings.

This allows a user to log into any computer on a network with the same password, as well as using the same settings 8

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Interconnecting various networks

• •

Bridge

– device that connects two similar networks

Gateways

– device or software code used to join two networks that use different topologies. Term for any device or software to join two networks, even if they use different protocols or address range.

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NETWORK LINKS

• • •

“communications channel” or link

: physical path or a frequency for signal transmissions Data in a network with

wired links

travels from one device to another over CABLES (E.g. – Ethernet, HomePNA, HomePlug) Networks without wires transport data through the air or

wireless network technologies

(E.g. – Wi-fi, Bluetooth) 11

BANDWIDTH

   

Bandwidth

channel) - how much data can be transmitted over a network link over a certain amount of time (transmission capacity of a communications  E.g. Coaxial cable brings more than 100 channels of cable TV, and has a higher bandwidth than your home telephone line.

56Kbps (dial-up), 10Mbps (cable TV), 100Mbps (computer lab) Network is slow your "bandwidth" is small. If something has a lot of bandwidth it is called

broadband

(Ethernet networks, cable TV) If it has little bandwidth, it is called

narrowband

(phone lines, infrared ) 12

COMMUNICATIONS PROTOCOLS

• • • •

Protocol

– a set of rules for interacting and negotiating.

Communications protocol

node to another – set of rules for efficiently transmitting data from one network

Handshaking

– process where a protocol helps two network devices communicate

TCP/IP

– best known communications protocol 13

COMMUNICATIONS PROTOCOLS

• Protocols are responsible for the following aspects of network communications: – Dividing messages into packets – Attaching addresses to packets – Initiating transmission – Regulating the flow of data – Checking for transmission errors – Acknowledging receipt of transmitted data 14

DATA TRAVELLING OVER A NETWORK

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COMMUNICATIONS PROTOCOLS

• • • • Digital signals are transmitted as bits using limited set of frequencies Analog signals can assume any value within a specified range of frequencies.

Digital equipment is sensitive to only two frequencies that represents 1s and 0s. If there are errors, protocols usually correct these 16

PACKETS

• • • Most communication protocols will divide data into small pieces, called packets, when sending over a network link

Packets

– parcel of data that is sent across a computer network Each packet contains – address of its sender, destination address, a sequence number, some data. At destination, packets rearrange themselves into original message according to sequence numbers.

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SENDING MESSAGES

• • Circuit switching – technology used by communications networks, such as the telephone system Packet switching – technology, which divides a message into several packets that can be routed independently to their destination. Every packet has destination addresses that communication protocols use 19

ADDRESS

• • • Every node on a network has at least one address so that other nodes know how to send data to it. A node may have other addresses depending on the protocols it uses.

Two commonly used Addresses: – Physical Address (network address, MAC address) – Logical Address (IP address) 20

IP ADDRESSES

• • Assigned IP addresses are semi-permanent and stay the same every time you boot your computer. (

Static IP addresses

) It can also be obtained through DHCP (Dynamic Host Configuration Protocol). This protocol was designed to distribute IP addresses automatically. The next time you boot, you will be assigned with a different IP address. (

Dynamic IP addresses

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Packets reaching destination

• Packets might not travel directly to their destination. When it reaches its destination, it is checked for errors one last time and then the packets are reassembled into their original configuration.

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WIRED NETWORKS

• • • • • • Uses cables to connect devices. Advantages – fast, secure, simple to configure.

Disadvantages – devices connected have limited mobility. Running cables can be a problem with some building codes. Drilling can also be a problem Examples– Ethernet, HomePNA, HomePlug technologies Home PNA – uses telephone wires and coaxial cables Powerline network – uses premises electrical wiring to form the infrastructure for a LAN 23

   

ETHERNET

Ethernet

– simultaneously broadcasts data packets to all network devices. A pack is accepted by the device to which it is addressed Ethernet relies on

CSMA/CD

with Collision Detection]. [Carrier Sense Multiple Access  Takes care of network devices transmitting packets at the same time  It detects collision, deletes the colliding signals, resets network and prepares to retransmit data

How fast?

Original carried data over a coaxial cable bus topology at 10 Mbps. Today, up to 40 or 100 Gbps Ethernet is popular because it is easy to understand, available almost everywhere, allows flexibility in network, and compatible with Wi-Fi networks 24

ETHERNET EQUIPMENT

• • • • • Two or more Ethernet-ready computers (look for an Ethernet port, and determine it’s speed. If the computer doesn’t have one, install an Ethernet adapter, or Ethernet card/NIC) An Ethernet router (hub – device that links two or more nodes of a wired network. Switch – sends data only to the devices specified as the destination. Router – ship data from one network to another) Surge strip or UPS Network Cables for each computer Internet access device such as cable modem or DSL modem and corresponding cables 25

NETWORK DEVICES

• • • •

Network device/appliance

– electronic device that broadcasts network data, boosts signals, or routes data to its destination

Hub/Switch

– a device that connects nodes on a network together (hub slow, switch fast)

Router

– connects two different networks together (like a local network and the internet)

Repeater

– amplifies signals on a network so that they don’t lose data to noise 26

Types of Links/Cables

Twisted Pair cable – 4 copper wires twisted around each other. These are what are used for phone lines and Ethernet cables. They will end in a RJ-45 plug for Ethernet, or RJ-11 for a phone line Coax Cable – one wire that is surrounded by insulators to reduce data loss. Used for cable television and modems sometimes Fiber optic – A bundle of extremely small glass tubes. They do not use electric signals like the other cables, but use lasers instead. They are very fast and expensive 27

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• • • • • •

Wireless Networks/Cable-less

Does not use cables or wires

USES

1. Radio – Uses what is called RF signals (radio waves). Sent and received with a transceiver (a transmitter and receiver combined) 2. Microwaves – These can carry a lot of data, but need a direct line of sight to work well Because radio and micro waves cannot bend to go around the curve of the earth, satellites are used in space to transmit signals around the globe 3. Infrared light – uses light waves to transmit data. Only good for very short distances with clear line of sight 29

Wireless networks

• • Advantages – Mobility – – No unsightly cables Power spikes are much less likely to run through cables to damage workstations Disadvantages – Was more expensive in the past – Speed – Range – Licensing – security 30

POPULAR TECHNOLOGY FOR WIRELESS NETWORKS

1. Wi-Fi 2. Bluetooth 3. Wireless USB (WUSB) 4. Wireless HD (WiHD) 31

Bluetooth

• • • • • • • Short-range wireless network technology Bluetooth networks automatically forms when two or more Bluetooth devices come within range of each other.

Piconet – a Bluetooth network Operates at the unlicensed 2.4GHz frequency Not for a collection of workstation but for mouse, keyboard or printer to computer connection For PAN Speed: Bluetooth 2.1 – 3 Mbps, range of 3 to 3000 feet. Bluetooth 3 – operates in the 6 to 9 GHz frequency range, peak speeds of 480 Mbps 32

Wi-Fi

• • • Set of wireless networking technologies defined by IEEE 802.11 standards that are COMPATIBLE with Ethernet.

Transmits data as radio waves over 2.4 GHz or 5.8 GHz frequencies Speed and range can be improved with various technologies including MIMO (multiple-input multiple-output) 33

Wi-Fi Standards

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WIRELESS SETUP

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WIRELESS SETUP

• • • • Check the computer’s if it has wireless capability If not, you can add a Wi-Fi adapter and plug it into a PC slot or USB port Wireless ad-hoc network: devices broadcasts directly to each other Wireless infrastructure network: there a wireless access point (wireless router) 36

WIRELESS SETUP

• • • • • • • • • Set up the router Connec to the router with a computer Configure router Access the router setup utility Create a new router password Enter a SSID for the network Activate WEP, WPA or PSK and create and encryption key Set up the wireless workstations Connect an Internet access device 37

Security through Encryption

• • • • LAN jacking – hackers interception signals driving through wireless enabled premises Pinpoint wireless access point Can see hackers in the list of clients accessing your network Preventing interception is difficult, but encrypting makes data useless to intruders 38

WIRELESS ENCRYPTION

• • • • WEP (Wired Equivalent Privacy) WPA (Wi-Fi Protected Access), WPA2 making sure that packets have not been intercepted . PSK (pre-shared key) a type of WPA, and PSK2 To activate, use the router configuration utiliteis to select and encryption protocol, and create a wireless network key Basis for scrambling and unscrambling. Key is similar to password.

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ENCRYPTION

- Transforms a message in such a way that its content are hidden from unauthorized readers - Can be used to - Scramble data over wired or wireless networks to prevent intrusions - Security credit card numbers and other personal information transferred from shoppers’ computers to e-commerce sites - Encrypting computer databases - Scrambling email contents to maintain privacy 40

How encryption works

• • • • Original message (plaintext/cleartext) Is encrypted to ciphertext. Converting ciphertext to plaintext is decryption.

Uses cryptographic algorithm and key Cryptographic algorithm: way for encrypting or decrypting a message Eg. Do not trust Brutus (see next slide) encrypted to GRQRWWUXVWEUXWXV 41

ENCRYPTION

The algorithm for Caeser’s encryption technique was to offset letters of the alphabet.

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Weak & Strong encryption

• • • • • • • Weak encryption: Caeser’s simple substitution key Strong encryption: very difficult to break – E.g. Advanced Encryption Standard (AES) used for WPA2 Breaking encryption methods uses expensive, specialized, code-breaking computers 32-bit key, 4.2 billion numbers, 40-bit key, 1 trillion numbers.

There is 56-bit and 64-bit 128-bit and 256-bit takes a long time to decrypt Most encryption uses 128-bit 43

Public key encryption

• • Symmetic key encryption: KEY used to encrypt a message is also used to decrypt Public key encryption: uses one KEY to encrypt a message, but ANOTHER KEY to decrypt the message 44

Public Key encryption

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