Day 8 - Wednesday, 30 May 2012

Hi everyone. Today is the last class for this subject. The topic for today's lesson is Internet Infrastructure.

The Internet: 

Computer Network Hierarchy

1. From a single computer to LAN

2. From LAN to ISP

3. From ISP to WWW

Internet Service Provider (ISP)

A regional or national access provider. 

A regional ISP usually provides Internet access to a specific geographic area. 

A national ISP is a business that provides Internet access in cities and towns nation wide.

In order to connect with Internet, you need to have:

1. computer

2. web browser

3. internet access

How Data and Information Travel the Internet

Computers connected to the Internet work together to transfer data and information around the world using servers and clients and various wired and wireless transmission media. 

On the Internet, computer is a client that can access data, information, and services on a variety of servers. The inner structure of the Internet works much like a transportation system. Several main transmission media carry the heaviest amount of traffic on the Internet. These major carriers of network traffic are known collectively as the Internet Backbone.

Internet Addresses

The Internet relies on an addressing system to send data and information to a computer at a specific destination. 

An IP address, short for Internet Protocol address, is a number that uniquely identifies each computer or device connected to the Internet.

The IP address usually consists of four groups of numbers, each separated by a period. The number in each group is between 0 and 255. 

For example, 72.14.207.99 are an IP address. In general, the first portion of each IP address identifies the network and the last portion identifies the specific computer. 

These all-numeric IP addresses are difficult to remember and use. Thus, the Internet supports the use of a text name that represents one or more IP addresses. A domain name is the text version of an IP address.

IP address ----> 72.14.207.99

Domain name ----> www.google. com

Domain Name System (DNS)

The method that the Internet uses to store domain names and their corresponding IP addresses. When you specify a domain name, a DNS server translates the domain name to its associated IP address so that data and information can be routed to the correct computer.

Web Browser

A web browser, or Browser, is application software that allows users to access and view Web pages or access Web 2.0 programs. 

That is all for this last entry. Thank you for reading my entry.

Day 7 - Wednesday, 9 May 2012

Hi everyone. The topic for this entry is WIRELESS TECHNOLOGY.

NETWORK COMMUNICATION STANDARDS

Today's networks connect terminals, devices, and computers from many different manufacturers across many types of networks, such as wide area, local area, and wireless. 

A network standard defines guidelines that specify the way computers access the medium to which they are attached.

Wi-Fi

Computers and devices that have the appropriate wireless capability can communicate via radio waves with other computers or devices using Wi-Fi (wireless fidelity), which identifies any network based on the 802.11 standards.

Develop by IEEE, 802.11 is a series of network standards that specifies how two wireless devices communicate over the air with each other.

BLUETOOTH 

Bluetooth is a network standard, specially a protocol, that defines how two Bluetooth devices use short-range radio waves to transmit data. The data transfers between devices at a rate of up to 3 Mbps. 

Bluetooth devices often must be within about 10 meters (about 33 feet) but can be extended to 100 meters with additional equipment in order to communicate with each other.

A Bluetooth device contains a small chip that allows it to communicate with other Bluetooth devices. Examples of Bluetooth - enabled devices can include desktop computers, notebook computers, handheld computers, smart phones, headsets, keyboards, mouse devices, microphones, digital cameras, GPS receivers and printers. 

INFRARED 

Some computers and devices use the IrDA standard to transmit data wirelessly to each other via infrared (Ir) light waves. The devices transfer data at rates from 115 Kbps (thousand bits per second) to 4 Mbps between their IrDA ports.

Infrared requires a line-of-sight transmission; that is, the sending device and the receiving device must be in line with each other so that nothing obstructs the path of the infrared light wave. 

BROADBAND

The term broadband refers to a telecommunications signal or device of greater bandwidth. A broadband signalling method is one that includes or handles a relatively wide range of frequencies. The wider the bandwidth of a channel, the greater the information- carrying capacity, given the same channel quality.

Broadband system usually use a different radio frequency modulated by the data signal for each band. The total bandwidth of the medium is larger than the bandwidth of any channel. In data communications, a 56 k modem will transmit a data rate of 56 kilo bits per second over 1 4 kilo hertz wide telephone line.

Broadband media transmit multiple signals simultaneously. In many cases, download transfer rates of broadband are faster than its upload transfer rates. Home and business users today opt for broadband Internet access because of the fast transfer rate.

That is all for this entry. Thank you for spending your time to read.

   

Day 6 - Wednesday, 2 May 2012

Hi everyone. The topic for this week lesson is regarding to WIRELESS TECHNOLOGY. Wireless is also known as Unbounded or Unguided Media.

Wireless networking technologies range from global voice and data networks, which allows users to establish wireless connections across long distances, to infrared light and radio frequency technologies that are optimized for short-range wireless connections.

Wireless connection

Wireless signals are used to send signal through the air between devices instead of using a physical cable.

Wireless network most commonly used to refer to a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a computer network.

Wireless telecommunication networks are generally implemented with some type of information transmission system that uses electromagnetic waves.

Wireless communication involves:

1. Radio frequency communication

2. Microwave communication

3. Infrared (IR) short-range communication 

TERRESTRIAL MICROWAVE

- require line-of-sight transmission and reception

two types of antennas:

parabolic dish and horn

- works like a funnel (catching a wide range of waves and directing to a common point called focus).

HORN

- looks like gigantic scoop.

- outgoing transmission are broadcast up a stem and deflected outward in series.

- broadcast up and deflected outward in a series of a narrow parallel beams by the scooped shape of the beam.

SATELLITE 

- same principle as terrestrial microwave.

- single bounce.

- satellite acting as a super tall antenna and repeater.

- capability= any location on earth no matter how remote.

- high quality(very clear) communication without requiring a huge investment.

- same speed as the earth.

- geosynchronous satellite = orbit speed is based on distance from planet.

- up link = transmission from earth to satellite

- down link = transmission from satellite to earth

- minimum 3 satellites to provide full global transmission.

Wi-Fi

- the underlying technology of wireless local area network (WLAN).

- based on the IEEE 802.11 specifications.

- used for mobile computing devices, such as laptops, in LANs, increasingly used for more services, including internet and VoIP phone access, gaming and basic connectivity of consumer electronics.

- frequency 2.4 GHz

- range 100-300 feet (indoor) 300-900 feet(outdoor)

3G

3G networks are in between standard. 3G is seen more as pre4G instead of a standard of its own. The advantage of 3G networks have over 2G networks speed. 3G networks are built to handle the needs of today's wireless users. This standard of wireless networks increase the speed of internet browsing, picture and video messaging, and handheld GPS use.

4G

4G (Beyond 3G) is like the other generations in that its advantages lies in promised increased speed in data transmission. There is  currently no formal definition for 4G, but there are objectives. One of these objectives is for 4G to become a fully IP-based system, much like modern computer network. The supposed speeds for 4G will be between 100 Mbit/s and 1 Gbit/s.

CELLULAR PHONE

One of the most interesting things about a cell phone is that it is really a radio. An extremely sophisticates radio, but a radio nonetheless. A good way to understand the sophistication of a cell phone is to compare it to a CB radio or a walkie-talkie. A CB radio is a simplex device. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cell phone is a duplex device, so it uses one frequency for talking and a second, separate frequency for listening. A CB radio has 40 channels. A cell phone can communicate on 1,664 channels. Cell phones also operate within cells and they can switch cells as they move around. Cells gives cell phones incredible range. Someone using a cell phone, on the other hand, can drive clear across a city and maintain a conversation the entire time. Cells are what give a cell phone its incredible range.

(http://peacecraft.tripod.com/infomining/cellphon.htm)

RADIO FREQUENCY

A radio wave is an electromagnetic wave propagated by an antenna. Radio waves have different frequencies and by turning a radio receiver to a specific frequency you can pick up a specific signal. 

BLUETOOTH

- An industrial specification for wireless personal area networks (PANs).

- Designed for very short range <10m.

- Connect and exchange information between devices such as mobile phones, laptops, PCs, printers, digital cameras and video game consoles over a secure, globally unlicensed short-range radio frequency. 

- Frequency 2.4 GHz.

- Data speed up to 3Mbps.

That is all from me for this week.

Thank you for reading my entry.

Day 5 - Wednesday, 25 April 2012

Hi everyone. How are you guys? I hope you guys are doing fine.

The topic for today's class is CABLING.

Cable is the medium through which information usually moves from one network device to another. Several types of cable are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. 

CABLING

GUIDED = BOUNDED

UNBOUNDED = UNGUIDED

Types of Cables

1) Twisted-Pair Cable

A twisted pair consists of two insulated copper wires, typically about 1 mm thickness. The wires are twisted together in a helical shape. The purpose of twisting the wires is to reduce electrical interference from similar pairs that are close by.

Twisted pair wires are commonly used in local telephone communication and for digital data transmission over short distances up to 1 km. When many twisted pairs run in parallel for a substantial distance, such as all the wires coming from a multistory apartment building to the telephone exchange, they are bundled together and placed in a protective sheath. The pairs in these bundles would interfere with one another if they are not twisted.

Unshielded Twisted Pair (UTP) Cable

Advantages of Twisted-Pair Wire

• Being the oldest method of data transmission, trained manpower to repair and service this media of communications are easily available. 
• In a telephone system, signals can travel several kilometers without amplification when twisted pair wires are used.
• These media can be used for both analog and digital data transmission. The bandwidth depends on the thickness of the wire and the distance traveled, but several megabits per second can be achieved for a few kilometers in may cases.
• It is the least expensive media for transmission for short distances.
• If a portion of a twisted-pair cable is damaged, the entire network is not shut down as it may be the case with coaxial cable.

Disadvantages of UTP Cable

• Easily pick up noise signals which results in higher error rates when the line length exceeds 100 meters.
• Being this in size, it is likely to break easily.
• It can support 19,200 bps up to 50 feet on RS-232 port.

Shielded Twisted Pair (STP) Cable

Shielded Twisted Pair (STP) has a grounded outer copper shield around the bundle of twisted pairs or around each pair.This provide added protection against Electromagnetic Interference (EMI). 

Unshielded Twisted Pair (UTP) does not have a grounded copper shield. UTP cables are easier to work with and are less expensive than shielded cables.

Shielded wire is used in an electricity noisy environment to limit the effects of noise absorption. Twisted-pair wiring is more commonly used for LAN media.

The unique thing about twisted pair network cabling is the fact that the wires are twisted. This is done because we run an electrical current through a piece of copper wiring, Electromagnetic Interference and cross talk around the wires.  That can be a problem when we have a second wire in close proximity because it can absorb the signal from the first wire. In that case the data on wires can get corrupted. 

2) Coaxial Cable

A coaxial cable is one that consists of two conductors that share a common axis. The inner conductor is typically a straight wire,either solid or stranded and the outer conductor is typically a shield that might be braided or a foil. Coaxial cable is a cable type used to carry radio signals, video signals, measurement signals and data signals. Most common coaxial cable impedances in use in various applications are 50 ohms and 75 ohms.

Advantages of Coaxial Cable

• It has better shield against electromagnetic interference than twisted pair cable, so it can span longer distance a t higher data bits per second (bps).
• It can be used for both analog and digital data transmissions. For analog g data transmission, 75-ohm broadband coaxial is used and for digital transmission, 50 - ohm base band cable is used.
• It is inexpensive as compared to twisted pair wires and UTP cables but easy to handle. 

3) Fiber Optic Cable

Optic Fiber is the newest form of bounded media. This media is superior in data handling and security characteristics. The fiber optic cable transmits light signals rather than electrical signals. It is far more efficient that the other network transmission media. Each fiber has an inner core of glass or plastic that conducts light. There are two types of light sources for which fiber cables are available. These sources of light are:

a. Light Emitting Diodes (LEDs)

b. Light Amplification by Stimulated Emission Radiation (Lasers) 

Below figure shows the principle of operation of the fiber optic system. The system basically consists of fiber optic cables that are made of tiny threads of glass or plastics. In a single- mode fiber, the core is 8 to 10 microns ( about the size of hair). In multimode, the core is about 50 microns on diameter. 

Advantages of Fiber Optic Cable

• It can handle much higher bandwidth than copper. Due to the low attenuation, repeaters are needed only about every 30 km on fiber lines, versus about every 5 km for copper. 
• Fiber is not affected by power surges, electromagnetic interference, or power failure. Nor is it affected by corrosive chemicals in the air, making it ideal for factory environments where electrical interference is very high. 
• Fiber is lighter than copper. One thousand twisted pairs copper cables of 1 km long weigh 800 kg. But fibers have only 100 kg.
• Fibers do not leak light and are quite difficult to tap. This gives them excellent security against potential wire-tappers.

Disadvantages of Fiber Optic Cable

• Fiber is an unfamiliar technology requiring skills which may not be easily available. 
• Since optical transmission is inherently unidirectional, two-way communication requires either two fiber cables or two frequency bands on one fiber.
• Fiber interfaces cost more than electrical interfaces.

4) Wireless LANs

 A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection. The IEEE 802.11 standards use the Ethernet Protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing and include an encryption method, the Wired Equivalent Privacy Algorithm. 

That is all for this week. Thank you for reading my entry.

Day 4 - Wednesday, 4 April 2012

Hi everyone. The topic for today's class is TOPOLOGY.

Network Topology is the study of the arrangement or mapping of the elements (links,nodes) of a network. It is divided into two which are the physical (real) andlogical (virtual) interconnections between nodes.

PHYSICAL TOPOLOGY

The physical layout of devices on a network.

The way that the devices on a network are arranged and how they communicate with each other.

The workstations are connected to the network through the actual cables that transmit data.

The physical structure of the network.

LOGICAL TOPOLOGY

The mapping of the flow of data between the nodes in the network determines the logical topology of the network.

The way that the signals act on the network media.

The way that the data passes through the network from one device to the next without regard to the physical in interconnection of the devices.

CLASSIFICATION OF PHYSICAL TOPOLOGY

Linear bus

Star

Star- Wired Ring

Tree

FDDI

Mesh

LINEAR BUS

consists of a main run of cable with a terminator at each end.

all nodes ( file server, workstations and peripherals) are connected to the linear cable.

Ethernet and Local Talk networks use a linear bus topology.

Advantages of a Linear Bus Topology:

Easy to connect a computer or peripheral to a linear bus.

Requires less cable length than a star topology.

Disadvantages:

Entire network shuts down if there is a break in the main cable.

A faulty cable or workstation will take the entire LAN down.

Terminators are required at both ends of the backbone cable.

Difficult to identify the problem if the entire network shuts down.

Not meant to be used as a stand- alone solution in a large building.

Summary:

Advantages of Linear Bus

Easy to install

Costs are usually low

Easy to add systems to network

Great for small networks

Disadvantages of Linear Bus

Out-of-date technology

If cable breaks, whole network is down

Can be difficult to troubleshoot

Unmanageable in a large network

RING

each of the systems is connected to its respective neighbor forming a ring.

the main difference between the bus and the ring is that the ring topology does not require termination. Because the systems are connected all together in a loop.

there is no beginning and end point as there is with the bus topology.

this configuration is seen in Fiber Distributes Data Interface (FDDI) networks.

Advantages of RING:

easy to install

costs are usually low

easy to add systems to network

great for small networks

Disadvantages of RING:

out-of-date technology

if cable breaks, whole network is down

can be difficult to troubleshoot

unmanageable in a large network

STAR

A star topology is designed with each node (file server, workstations and peripherals) connected directly to a central network hub or connector.

Data on a star network passes through the hub manages and controls all function of the network.

It also acts as a repeater for the data flow.

This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

The protocols used with star configurations are usually Ethernet or Local Talk.

Advantages of Star:

easy to install and wire

easy to add new workstations

no disruptions to the network when connecting or removing devices

any non-centralized failure will have very little effect on the network

easy to detect faults and to remove parts.

centralized control

centralized network/hub monitoring

Disadvantages of Star:

Requires more cable length than a linear topology.

If the hub or connector fails, nodes attached are disabled.

More expensive than linear bus topology because of the cost of the hub.

STAR-WIRED

A star wired topology may appear (externally) to be the same as a star topology.

Internally, the Multistation Access Unit (MAU) of a star wired ring contains wiring that allows information to pass from one device to another in a circle or ring.

The Token Ring protocol uses a star-wired topology.

TREE

A Tree (hybrid) topology combines characteristics of linear bus and star topology.

It consists of groups of star-configured workstations connected to a linear bus backbones cable.

Tree topology allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantages of Tree:

Point-to-point writing for individual segments.

Disadvantages of Tree:

Overall length of each segment is limited by the type of cabling used.

If the backbone line breaks, the entire segment goes down.

More difficult to configure and wire than the other topology.

FDDI

100 mbps

Normally implemented over fiber optic (fast-Ethernet, UTP)

Dual redundancy built in by use of primary and secondary ring.

Automatic by passing and isolation of faulty nodes.

LAN PROTOCOLS

ETHERNET

TOKEN RING

FDDI

GIGABIT ETHERNET

PROTOCOL

A protocol is a set of rules that governs the communications between computers on a network.

These rules include guidelines that regulate the following characteristics of a network:

- access method

- allowed physical topology

- cables of cabling

- speed of data transfer

Logical topology are bound to network protocols and describe how data is moved across the network.

The Ethernet protocol is a common logical bus topology protocol.

Local Talk is a common logical bus or star topology protocol.

Token Ring is a common logical ring topology protocol.

CABLING

Cable is the medium through which information usually moves from one network device to another.

Several types of cable are commonly used with LANs.

In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types.

TYPES OF CABLES

Non-shielded Twisted Pair (UTP) Cable

Shielded Twisted Pair (UTP) Cable

Coaxial Cable

Fiber Optic Cable

Wireless LANs

That is all for this week lesson. Thank you.