WEEK 12(INTERNET INFRASTRUCTURE)

Possibly to most important foundation block of Internet Infrastructure is the Network. Without a network connection no data can pass over the Internet.

The Internet: Computer Network Hierarchy

Every computer that is connected to the Internet is part of a network. For example, you may use a modem to connect to an Internet Service Provider(ISP). When you connect to your ISP, you become part of their network. The ISP may then connect to a larger network and become part of their network. The Internet is simply a network of networks. DNS is an Internet service that translates domain names/hostnames to IP addresses and IP addresses to their associated domain names/host names. DNS helping each visitor refer to the desired website only by typing its alpha-numeric name (domain name) in the browser instead of its real numeric system name (IP address).

Internet Protocol: IP Addresses

A typical IP address might be 216.27.22.162. Every machine on the Internet has a unique identifying number, called an IP Address. The IP stands for Internet Protocol, which is the language that computers use to communicate over the Internet. A typical IP address is make it easier for us humans to remember, IP addresses are normally expressed in decimal format. The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers.

The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Network and Host. The Network section always contains the first octet. It is used to identify the network that a computer belongs to. Host sometimes referred to as Node is identifies the actual computer on the network. The Host section always contains the last octet.

IP address structure and classification

Class A

Class A addresses are assigned to networks with a very large number of hosts. The high-order bit in a class A address is always set to 0. The next seven bits (completing the first octet) complete the network ID. The remaining 24 bits (the last three octets) represent the host ID. This allows for 126 networks and 16,777,214 hosts per network.

Class B

Class B addresses are assigned to medium-sized to large-sized networks. The two high-order bits in a class B address are always set to binary 1 0. The next 14 bits (completing the first two octets) complete the network ID. The remaining 16 bits (last two octets) represent the host ID. This allows for 16,384 networks and 65,534 hosts per network.

Class C

Class C addresses are used for small networks. The three high-order bits in a class C address are set to binary 1 1 0. The next 21 bits (completing the first three octets) complete the network ID. The remaining 8 bits (last octet) represent the host ID. This allows for 2,097,152 networks and 254 hosts per network.

Class D

Class D addresses are reserved for IP multicast addresses. The four high-order bits in a class D address are always set to binary 1 1 1 0. The remaining bits are for the address that interested hosts recognize. Microsoft supports class D addresses for applications to multicast data to multicast-capable hosts on an internetwork.

 Class E

Class E is an experimental address that is reserved for future use. The high-order bits in a class E address are set to 1111.

The network ID cannot begin with the number 127. The number 127 in a class A address is reserved for internal loopback functions. For example, 127.0.0.1 is the common loopback address.

Ø  Loopback means the interface created and designated to test a local port or interface. It routes test messages from their source device back to the source without any processing or modification.

Ø  The loopback IP address is the address used to access itself. A loopback interface is also known as a virtual IP, which does not associate with hardware interface.

Ø  The loopback address is used to test network software without physically installing a Network Interface Card (NIC), and without having to physically connect the machine to a TCP/IP network.

Internet Protocol: Domain Name System

Although people can type address information like http://207.241.148.80/ into their Web browser to visit sites, being able to use proper names like http://www.hotmail.com/ is much more practical. When someone types a site's name into their browser, DNS looks up the corresponding IP address for that site, the data required to make the desired network connections between Web browsers and Web servers.

The DNS organizes its servers into a hierarchy. For the Internet, so-called root name servers reside at the top of the DNS hierarchy. The Internet root name servers manage DNS server information for the Web's top-level domains (like ".com" and ".uk"). Servers at the next lower level of the DNS hierarchy track second-level domain names and addresses (like "yahoo.com").

ISP

Short for Internet Service Provider, it refers to a computer access to the Internet. The service provider usually provides a software package,username and password. You can then log on to the Internet and browse the World Wide Web and send and receive e-mail. ISPs also serve large companies, providing a direct connection from the company's networks to the Internet. ISPs.

An ISP is a company that provides individuals and other companies access to the Internet and other related services such as Web site building and virtual hosting. An ISP has the equipment and the telecommunication line access required to have a point-of-presence on the Internet for the geographic area served. The larger ISPs have their own high-speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers.

HTTP  (Hypertext Transfer Protocol)

HTTP stands for Hypertext Transfer Protocol. It is an TCP/IP based communication protocol which is used to deliver virtually all files and other data, collectively called resources, on the World Wide Web. These resources could be HTML files, image files, query results, or anything else.Every Web server on the Internet conforms to the hypertext transfer protocol (HTTP). The Hypertext Transfer Protocol (HTTP) is an application-level TCP/IP based protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems (internet).

There are three important things about HTTP of which you should be aware:

Ø  HTTP is connectionless: After a request is made, the client disconnects from the server and waits for a response. The server must re-establish the connection after it process the request.

Ø  HTTP is media independent: Any type of data can be sent by HTTP as long as both the client and server know how to handle the data content. How content is handled is determined by the MIME specification.

Ø  HTTP is stateless: This is a direct result of HTTP's being connectionless. The server and client are aware of each other only during a request. Afterwards, each forgets the other. For this reason neither the client nor the browser can retain information between different request across the web pages.

The diagram shows where HTTP Protocol fits in communication:

WEEK 11 (UNBOUND MEDIA)

UNBOUNDED / UN GUIDED MEDIA

Unbounded / Unguided media or wireless media doesn't use any physical connectors between the two devices communicating. Usually the transmission is send through the atmosphere but sometime it can be just across the rule. Wireless media is used when a physical obstruction or distance blocks are used with normal cable media. The three types of wireless media are:

• RADIO WAVES
• MICRO WAVES
• INFRARED WAVES

1. RADIO WAVES:-
It has frequency between 10 K Hz to1 G Hz. Radio waves has the following types.

• Short waves
• VHF (Very High Frequency)
• UHF (Ultra High Frequency)

SHORT WAVES:-

There are different types of antennas used for radio waves. Radio waves transmission can be divided into following categories.

• LOW POWER, SINGLE FREQUENCY.
• HIGH POWER, SINGLE FREQUENCY
• LOW POWER , SINGLE FREQUENCY:-

As the name shows this system transmits from one frequency and has low power out. The normal operating ranges on these devices are 20 to 25 meter.


CHARACTERISTICS LOW POWER , SINGLE FREQUENCY:-

• Low cost
• Simple installation with pre-configured
• 1 M bps to 10 M bps capacity
• High attenuation
• Low immunity to EMI

2. HIGH POWER, SINGLE FREQUENCY:-
This is similar to low power single frequency. These devices can communicate over greater distances.

CHARACTERISTICS HIGH POWER, SINGLE FREQUENCY:-

• Moderate cost
• Easier to install than low power single frequency
• 1 Mbps to 10 Mbps of capacity
• Low attenuation for long distances
• Low immunity to EMI

MICRO WAVES

Micro waves travels at high frequency than radio waves and provide through put as a wireless network media. Micro wave transmission requires the sender to be inside of the receiver.

Microwave is divide b 2 ::

- Terrestial Micro Waves

- Satellitte Micro Waves

1. Terrestrial Micro waves:

Terrestrial Micro waves are used are used to transmit wireless signals across a few miles. Terrestrial system requires that direct parabolic antennas can be pointed to each other. These systems operate in a low Giga Hertz range. two types of antennas are used for terrestrial microwave communication are parabolic dish and horn antenna.

A parabolic dish antenna is good at catching a wide range of signal waves and directing them to a common point. Every wave that is parallel to the line of sight reflects back to the focus on a common point.

a horn antenna looks like a gigantic scoop that broadcasts the assembled signals that are deflected outward in a series of narrow parallel beams by the curve head. signals are received in a manner similar to the parabolic dish antenna and are deflected down into the stem.

DISH ANTENNA

HORN ANTENNA

2. Satellite Micro waves

The main problem with aero wave communication is the curvature of the earth, mountains & other structure often block the line of side. Due to this reason, many repeats are required for long distance which increases the cost of data transmission between the two points. This problem is recommended by using satellites.

Satellite micro wave transmission is used to transmit signals through out the world. These system use satellites in orbit about 50,000 Km above the earth. Satellite dishes are used to send the signals to the satellite where it is again send back down to the receiver satellite. These transmissions also use directional parabolic antenna’ with in line of side.

In satellite communication micro wave signals at 6 GHz is transmitted from a transmitter on the earth through the satellite position in space. By the time signal reaches the satellites becomes weaker due to 50,000 Km distance. The satellite amplifies week signals and transmits it back to the earth at the frequency less than 6 GHz.

. WIRELESS @ Wi-Fi

Ø  transmits computer data over distances using radio waves

Ø  most commonly used is 802.11 b (11MBps)

Ø  802.11 a (54MBps)

Ø  to communicate over the network, computer must be equipped with a Wi-Fi card

Ø  types of Wi-Fi card : Wi-Fi PC Cards, USB Adapter, PCI and ISA Adapter etc.

IEEE (Institute of Electrical and Electronics Engineers).

The IEEE describes itself as "the world's largest technical professional society; promoting the development and application of electro technology and allied sciences for the benefit of humanity, the advancement of the profession, and the well-being of our members." One of the technologies they have developed is known as Ethernet 802 standard which governs local area networks (wired LANs). Ethernet governs the way in which Data Communications are done across the spectrum

Difference Between 3G And 4G

4G - 4G speeds are meant to exceed that of 3G. Current 3G speeds are topped out at 14Mbps downlink and 5.8Mbps uplink. To be able to qualify as a 4G technology, speeds of up to 100Mbps must be reached for a moving user and 1Gbps for a stationary user. So far, these speeds are only reachable with wired LANs.

different:

1. 3G stands for 3rd generation while 4G stands for 4th generation.

2. 3G technologies are in widespread use while 4G compliant technologies are still in the horizon.

3. 4G speeds are much faster compared to 3G.

4. 3G is a mix of circuit and packet switching network while 4G is only a packet switching network.

Cellular phone

is a device that can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile phone operator, allowing access to the public telephone network. By contrast, a cordless telephone is used only within the short range of a single, private base station.

In addition to telephony, modern mobile phones also support a wide variety of other services such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, gaming and photography. Mobile phones that offer these and more general computing capabilities are referred to as smartphones.

Radio frequency (RF)

is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems do exist.

Uplink and downlink

In satellite telecommunication, a downlink is the link from a satellite down to one or more ground stations or receivers, and an uplink is the link from a ground station up to a satellite. Some companies sell uplink and downlink services to television stations, corporations, and to other telecommunication carriers. A company can specialize in providing uplinks, downlinks, or both.

The following table shows the main frequency bands used for satellite links.

Frequency Band	Downlink	Uplink
C	3,700-4,200 Mhz	5,925-6,425 MHz
Ku	11.7-12.2 GHz	14.0-14.5 GHz
Ka	17.7-21.2 GHz	27.5-31.0 GHz

The C band is the most frequently used. The Ka and Ku bands are reserved exclusively for satellite communication but are subject to rain attenuation. Some satellites carry transponders for both C and Ku bands.

WEEK 10(CABLING)

 LAN Techonology Cabling :

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

    b) Several types of cable are commonly used with LANs.

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

Types of Cables :

  

    Unshielded Twiested Pair (UTP) cable

    Shielded Twisted Pair (STP) cable

    Coaxial Cable

    Fiber Optic Cable

    Wireless LANs

Twisted-pair cable :

It comes in two forms which is shielded and unshielded cable. As we know, there are two category of transmission media which is bounded and unbounded media and twisted-pair cable is on the bounded categories same goes to coxial cable and fibre-optic cable.

Bounded

Current : UTP, STP and Coxial Cable

Light : Fibre-optic Cable

 Unshielded Twisted Pair (UTP) cable

             

~ suitable for transmitting both data and voice.

~ consists of two conductors (usually copper).

~ help to eliminate and reduce the impact of noise.

~ cheap, flexible and easy to install.

~ connector : RJ-45 connector.

•     Category 1 : Voice 9wayar Telefon)
•     Category 2 : Data to 4 Mbps (Local Talk)
•     Category 3 : Data to 10 Mbps (Ethernet)
•     Category 4 : Data to 20 Mbps (16 Mbps Token Ring)
•     Catogory 5 : Data to 100 mbps (Fast Ethernet)

 The standard connector for unshielded twisted pair cabling is an RJ-45 connector

Shielded Twisted Pair (STP) cable

             

~ wrapped in a foiled shielding.

~ help provide more reliable datacommunication.

~ prevents and eliminate crosstalk.

~ networj using Token Ring.

~ more expensive.

Coaxial cable

            

 ~   a single copper conductor at its center

 ~ a plastic layer provides insulation

 ~   the metal shield helps to block interference

      (fluorescent light, motors and others)

 ~   Bayone-Neill-Concelman (BNC) connector

 ~ T-connector, barrer connector, terminator

 Fibre Optics

             

 ~ consists of a center glass core surrounded by several layers

 ~ transmit light rather than electronic signals

 ~ eliminate the problem of electrical interference

 ~ transmit signals over much longer distances than coaxial and twisted pair

    carry information at vastly greater speeds.

WEEK 6 (NETWORK TOPOLOGY)

NIC

     A network interface controller (also known as a network interface card, network adapter, LAN adapter and by similar terms) is a computer hardware component that connects a computer to a computer network.

Whereas network interface controllers were commonly implemented on expansion cards that plug into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.

     The network controller implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet, Wi-Fi, or Token Ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP. 

Network TOPOLOGY is divide by 3 ::

(1) Network topology

      - is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes.

(2) Physical topology

     - Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network.

(3) Logical topology

- is the mapping of the flow of data between the nodes.

There are several basic types of topology in networks:

(1) BUS TOPOLOGY

A linear bus topology 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 LocalTalk networks use a linear bus topology.The bus cable carries the transmitted message along the cable. As the message arrives at each workstation, the workstation computer checks the destination address contained in the message to see if it matches it's own. If the address does not match, the workstation does nothing more. If the workstation address matches that contained in the message, the workstation processes the message. The message is transmitted along the cable and is visible to all computers connected to that cable.

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.

(2) STAR TOPOLOGY

A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator. Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions 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 LocalTalk.

Advantages

• Easy to install, and wire.
• Easy to add new workstations
• No disruptions to the network when connecting or removing devices.
• Any non-centralised failure will have very little effect on the network
• Easy to detect faults and to remove parts.
• Centralized control Centralized network/hub monitoring

Disadvantages

• Requires more cable length than a linear topology.
• If the hub or concentrator fails, nodes attached are disabled.
• More expensive than linear bus topologies because of the cost of the concentrators.

(3) STAR-WIRED

A star-wired topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) 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.

(4) TREE TOPOLOGY

A tree topology combines characteristics of linear bus and star topologies.It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantage

• Point-to-point wiring for individual segments.

Disadvantages

• 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 other topologies.

(5) ETHERNET

      Ethernet is the most widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless

ethernet cables

(6) LOCALTALK

     

    LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s.CSMA/CA was implemented as a random multiple access method.

LocalTalk cable adapter

connect directly to the Ethernet and LocalTalk