Lecture 7LANS & WLANS

Tonga Institute of Higher EducationIT 141: Information Systems

Encoding and Decoding

The data has to be encoded before being sent.

For computers, this means they must be encoded into binary.

We have already seen one type of encoding, it is called ASCII. Characters are encoded into binary in ASCII

NETWORK CLASSIFICATIONS

- 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.

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. – I EEE 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 are configured with Ethernet technology and use compatible Wi-Fi standards in applications that require wireless access.

Network Devices 1. node – A single device connected to a network is

called a node 2. Modem – uses phone lines to transmit data over a

network 3. Network Interface Card (NIC) – a peripheral to

connect to a local area network with Ethernet cable. 4. Hub/Switch – a device that connects nodes on a

network together (hub slow, switch fast) 5. Router – connects two different networks together

(like a local network and the internet) 6. Repeater – amplifies signals on a network so that

they don’t lose data to noise 7. Network-attached storage (NAS) – a storage

device that directly connects to a network

Network Devices

8. 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 Print server – handles jobs sent to network printers

Can a network function without a server? – yes. Files and applications can be shared among workstation operating in PEER-TO-PEER MODE. They can use popular file sharing systems such as Gnutella, Kazaa and BitTorrent to operate in peer to peer mode.

Network Devices

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

Network Physical Topology physical topology is the arrangement of devices in a network 1) Star topology 2) Bus topology 3) Ring 4) Mesh 5)Tree topology

1. Star topology – a disadvantage with wireless networks. Advantage is if any link fail, it doesn’t affect the rest of network2. Ring topology – minimizes cabling but failure of one device can take down the whole network3. Bus topology – work best with a limited number of devices. If backbone cable fails, the entire network becomes useless4. Mesh topology – Advantage: if several links fail, data can follow alternative functioning links to reach destination. Used for wireless.5. Tree topology – blend of star and bus networks. Excellent flexibility for expansion. Many of today’s school and business networks are based on tree topologies.

Bridge – a device that can connect two similar networks Gateway – any device or software code used to join two networks, even if those networks use different protocols or address ranges

Network Links

What connects the nodes of a network?“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)

Bandwidth Bandwidth the word describe how much data can

be transmitted over a network link over a certain amount of time (transmission capacity of a communications channel) 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)

If the network is slow your "bandwidth" is small. To get a faster speed you may need to purchase a higher speed to obtain more bandwidth.

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)

Communications Protocol

Protocol – a set of rules for interacting and negotiating. Communications protocol – set of rules for efficiently

transmitting data from one network node to another (process called handshaking)

Commonly used to describe how computers send data over a network link

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

TCP/IP and Network Protocols

The most popular communications protocol is called TCP/IP (transmission control protocol / Internet protocol)

It is used for transferring websites and email because it is able to safely send data without error.

All computers that use TCP/IP know how to communicate with each other, even if they use different operating systems or are located in different countries.

All modern networks use TCP/IP to transmit most data. Other protocols commonly used are

UDP – for sending data quickly without checking for errors

ICMP – for checking connections between computers

How is data sent through a network

When data is transmitted (sent) it is usually sent by electromagnetic signals

This means the data will take different forms depending on the transmitter and receiver. For example, electronic voltages, radio waves, light waves or phone tones.

To get the Internet in Tonga, think about all the different connections. Ethernet cables, satellites, underwater cables,

phone lines

Sending Data

How does data travel over a network?

- 1948, Claude Shannon published an article describing the communications system model applicable to networks of all types including today’s computer networks

- Data transmitted over a network usually takes the form of an electromagnetic signal. Digital signals are transmitted as bits using limited set of frequencies. Analog signals can assume any value within a specified range of frequencies

- What about corrupted signals?- Correcting errors is one of the responsibilities of protocols

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.

Circuit switching Packet switching

Why packets?

Why break up data into small parts? When people designed networks, they

realized if data pieces were smaller it would be easier to manage. If one packet was lost it could be easily resent.

If a big file was sent all at once and there was an error in the data, you’d have to send the whole big data file again

With packets you just send small little pieces of data

Network Addresses

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.

Address: Physical Address (network address, MAC

address) Logical Address (IP address) Domain Name

How do devices get a network address

MAC addresses: Unique number assigned to a network interface card when it is made. Used for network security

IP addresses: a series of numbers used to identify a network device. (e.g. 204.127.129.1) It is separated into 4 sections by periods. Each section is called an octet, because in binary it is represented by 8 bits. It can be assigned by ISPs or system managers. 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)

Dynamic and Static IPs If your IP address does not ever change, it is

static. Usually servers and websites will have static

IP addresses because other computers always need to know where to find them

A dynamic IP address will change every time you connect to the internet. Usually, if you connect to the internet through a modem, you will have a dynamic IP

If you have a dynamic IP, you can’t have a server on your computer

Physical Addresses

A physical address is built into the hardware of a network interface card (NIC). This address may also be called the MAC address.

Every NIC has a unique physical address. No other device will share the same address.

The Logical Address - IP Addresses

Besides the physical address, a computer needs a logical address that is used by the operating system and software in order to connect to other computers.

IP addresses are the way that computers know where to send data. Every computer on a network has a different IP address

The IP address is a series of numbers like 192.168.0.2

Each number can range from 0-255, which means each part is 8 bits (2^8 = 256). Since there are 4 parts, each IP address uses 32 bits.

How many IP addresses can be used on the internet? Just over 4 billion.

Domain Names

Computers may be able to remember and use IP addresses easily, but people have trouble remembering long numbers

Domain names were invented so people have an easier time remembering the location of a server

A domain name will “map” an IP address to a name

Our domain name is tihe.org and our IP address is 209.58.72.33.

Domain names will end in an extension that indicates something called the ‘top-level’ domain. Example: .org, .to., .net

Wired Networks

Wired network – 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 –

Powerline network – uses premises electrical wiring to form the infrastructure for a LAN

ETHERNET: Wired Link 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 [Carrier Sense Multiple Access with Collision Detection]. It takes care 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

EHTERNET 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

Routers

Routers are similar to hubs in that they connect networks together, but routers are used to connect different networks together.

Most of the time, you will use a router to connect your network to the Internet.

It is a special device that determines where the data should go on your network. Either to the internet (or another network) or stay inside your LAN

ROUTER

HUB

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

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

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

POPULAR TECHNOLOGY FOR WIRELESS NETWORKS

1. Wi-fi2. Bluetooch3. Wireless USB (WUSB)4. Wireless HD (WiHD)

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

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