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CN_KCS-603 Week: 2
UNIT-
ISP: Internet Service Provider
ISP stands for Internet Service Provider. It is a company that provides access to the internet
and similar services such as Website designing and virtual hosting. For example, when you
connect to the Internet, the connection between your Internet-enabled device and the internet
is executed through a specific transmission technology that involves the transfer of
information packets through an Internet Protocol route.
Data is transmitted through different technologies, including cable modem, dial-up, DSL, high
speed interconnects. Accordingly, based on the method of data transmission, the Internet access
provided by ISPs can be divided into many types, some of which are as follows:
Dial-up Internet access:
It is the oldest technology to provide Internet access by modem to modem connection using
telephone lines. In this method, the user's computer is connected to a modem with a telephone
line. This method has become outdated today due to slow connection speed. However, in remote
areas, this method can be used where the broadband network is not available.
DSL:
DSL, which stands for 'digital subscriber line' is an advanced version of the dial-up Internet
access method. It uses high frequency to execute a connection over the telephone network and
allows the internet and the phone connection to run on the same telephone line. This method
offers an Asymmetric Digital Subscriber (ADSL), where the upload speed is less than the
download speed, and a Symmetric Digital Subscriber Line (SDSL), which offers equal upload
and download speeds. Out of these two, ADSL is more popular among users and is popularly
known as DSL.
Wireless Broadband (WiBB):
It is a modern broadband technology for Internet access. It allows high-speed wireless internet
within a large area. To use this technology, you are required to place a dish on the top of your
house and point it to the transmitter of your Wireless Internet Service Provider (WISP).
Wi-Fi Internet:
It is the short form for "wireless fidelity," which is a wireless networking technology that
provides wireless high-speed Internet connections using radio waves. To use the internet, you
are required to be within the range of wi-fi network. It is commonly used in public places such
as hotels, airports, restaurants to provide internet access to customers.
ISDN:
It is a short form of Integrated Services Digital Network. It is a telephone system network which
integrates a high-quality digital transmission of voice and data over the same standard phone
line. It offers a fast upstream and downstream Internet connection speed and allows both voice
calls and data transfer.
Organization of the Internet
The Internet, an autonomous, interconnected network, loosely structured international
cooperation, facilitates host-to - host communication, voluntarily following transparent
protocols and procedures set out in the Internet standards. There also are a number of
disconnected Internet sites that do not connect to the Internet, but use Internet standards , for
example, interconnected network sets. (The 1602 RFC).
Nobody owns the internet or actually regulates it. Alternatively, Internet engagement is the
result of voluntary Internet involvement. To addition to complying with these requirements,
many internet providers already allow public access to their networks.
The digital Web consists of these providers' mutual interconnection and cooperation. Roughly
300 service providers are currently interconnected with the Internet (beginning in 1996).
1. Internet Society (ISOC)
The Internet Society (ISOC) is a professional organization that is concerned with the
development and advancement of the Internet worldwide, its use and its financial, political and
technological issues. The approval of the IAB nominations from the candidates sent by the
Nominating Committee of the IAB is the responsibility of ISOC Trustees. (RFC 1718).
2. Internet Architecture Board (IAB)
The ISOC is a technical advisory committee of the Internet Architecture Board ( IAB). It is
chartered to control the internet infrastructure and protocols and to serve as an body through
which IESG decisions can be appealed in the form of the Internet standard procedure. The IAB
is responsible for the approval of IESG appointments by the candidates submitted by the IETF
committee of nominations. (RFC 1718)
3. Internet Engineering Steering Group (IESG)
Transmission Medium:
A transmission medium can be broadly defined as anything that can carry information from a source to a destination.
Classes of transmission media
Guided Media:
Guided media, which are those that provide a medium from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.
Twisted-Pair Cable: A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together. One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference.
Unshielded Versus Shielded Twisted-Pair Cable The most common twisted-pair cable used in communications is referred to as unshielded twisted-pair (UTP). STP cable has a metal foil or braided mesh covering that encases each pair of insulated conductors. Although metal casing improves the quality of cable by preventing the penetration of noise or crosstalk, it is bulkier and more expensive.
The most common UTP connector is RJ45 (RJ stands for registered jack) Applications Twisted-pair cables are used in telephone lines to provide voice and data channels. Local-area networks, such as l0Base-T and l00Base-T, also use twisted-pair cables.
Coaxial Cable Coaxial cable (or coax) carries signals of higher frequency ranges than those in twisted pair cable. coax has a central core conductor of solid or stranded wire (usuallycopper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two. The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit.This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover.
The most common type of connector used today is the Bayone-Neill-Concelman (BNe), connector.
Applications
When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna sends waves that can be received by any receiving antenna. The omni directional property has a disadvantage, too. The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signals using the same frequency or band.
Omni directional Antenna
Radio waves use omnidirectional antennas that send out signals in all directions. Based on the wavelength, strength, and the purpose of transmission, we can have several types of antennas. Figure shows an omnidirectional antenna.
Applications
o The Omni directional characteristics of radio waves make them useful for multicasting, in which there is one sender but many receivers. o AM and FM radio, television, maritime radio, cordless phones, and paging are examples of multicasting.
Microwaves
Electromagnetic waves having frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional. The sending and receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas Unidirectional Antenna Microwaves need unidirectional antennas that send out signals in one direction. Two types of antennas are used for microwave communications: the parabolic dish and the horn.
Applications:
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.
Infrared
Infrared waves, with frequencies from 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm), can be used for short-range communication.
Infrared waves, having high frequencies, cannot penetrate walls. This advantageous characteristic prevents interference between one system and another; a shortrange communication system in one room cannot be affected by another system in the next room.
When we use our infrared remote control, we do not interfere with the use of the remote by our neighbours.
Infrared signals are useless for long-range communication.
In addition, we cannot use infrared waves outside a building because the sun's rays contain infrared waves that can interfere with the communication.
Applications:
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
1. Physical Layer
It is the bottom-most or the first layer of the OSI Model It comprises the raw data which is further transmitted to the higher layers of the structure Preparing the physical devices in the network and accepting the received data for transmission The termination of connection between two nodes of a network also takes place at this stage This layer converts the digital bits into electrical, radio, or optical signals.
The functions of the physical layer are :
- Bit synchronization: The physical layer provides the synchronization of the bits by providing a clock. This clock controls both sender and receiver thus providing synchronization at bit level.
- Bit rate control: The Physical layer also defines the transmission rate i.e. the number of bits sent per second.
- Physical topologies: Physical layer specifies the way in which the different, devices/nodes are arranged in a network i.e. bus, star, or mesh topology.
- Transmission mode: Physical layer also defines the way in which the data flows between the two connected devices. The various transmission modes possible are Simplex, half- duplex and full-duplex.
- Hub, Repeater, Modem, Cables are Physical Layer devices. ** Network Layer, Data Link Layer, and Physical Layer are also known as Lower Layers or Hardware Layers. 2. Data Link Layer
The data link layer is responsible for the node-to-node delivery of the message. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer. When a packet arrives in a network, it is the responsibility of DLL to transmit it to the Host using its MAC address. Data Link Layer is divided into two sublayers:
- Logical Link Control (LLC)
- Media Access Control (MAC) The packet received from the Network layer is further divided into frames depending on the frame size of NIC (Network Interface Card). DLL also encapsulates Sender and Receiver’s MAC address in the header.
The Receiver’s MAC address is obtained by placing an ARP(Address Resolution Protocol) request onto the wire asking “Who has that IP address?” and the destination host will reply with its MAC address.
The functions of the Data Link layer are:
- Framing: Framing is a function of the data link layer. It provides a way for a sender to transmit a set of bits that are meaningful to the receiver. This can be accomplished by attaching special bit patterns to the beginning and end of the frame.
- Physical addressing: After creating frames, the Data link layer adds physical addresses (MAC address) of the sender and/or receiver in the header of each frame.
- Error control: Data link layer provides the mechanism of error control in which it detects and retransmits damaged or lost frames.
- Flow Control: The data rate must be constant on both sides else the data may get corrupted thus; flow control coordinates the amount of data that can be sent before receiving acknowledgement.
- Access control: When a single communication channel is shared by multiple devices, the MAC sub-layer of the data link layer helps to determine which device has control over the channel at a given time. * Packet in Data Link layer is referred to as Frame. ** Data Link layer is handled by the NIC (Network Interface Card) and device drivers of host machines. *** Switch & Bridge are Data Link Layer devices. 3. Network Layer
The network layer works for the transmission of data from one host to the other located in different networks. It also takes care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available. The sender & receiver’s IP addresses are placed in the header by the network layer. The functions of the Network layer are :
- Routing: The network layer protocols determine which route is suitable from source to destination. This function of the network layer is known as routing.
- Logical Addressing: In order to identify each device on internetwork uniquely, the network layer defines an addressing scheme. The sender & receiver’s IP addresses are placed in the header by the network layer. Such an address distinguishes each device uniquely and universally. * Segment in Network layer is referred to as Packet.
source after a packet or group of packets is received. This type of transmission is reliable and secure.
- Connectionless service: It is a one-phase process and includes Data Transfer. In this type of transmission, the receiver does not acknowledge receipt of a packet. This approach allows for much faster communication between devices. Connection-oriented service is more reliable than connectionless Service. * Data in the Transport Layer is called as Segments. ** Transport layer is operated by the Operating System. It is a part of the OS and communicates with the Application Layer by making system calls. Transport Layer is called as Heart of OSI model. 5. Session Layer (Layer 5) :
This layer is responsible for the establishment of connection, maintenance of sessions, authentication, and also ensures security. The functions of the session layer are :
- Session establishment, maintenance, and termination: The layer allows the two processes to establish, use and terminate a connection.
- Synchronization: This layer allows a process to add checkpoints which are considered synchronization points into the data. These synchronization points help to identify the error so that the data is re-synchronized properly, and ends of the messages are not cut prematurely and data loss is avoided.
- Dialog Controller: The session layer allows two systems to start communication with each other in half-duplex or full-duplex. **All the below 3 layers(including Session Layer) are integrated as a single layer in the TCP/IP model as “Application Layer”. **Implementation of these 3 layers is done by the network application itself. These are also known as Upper Layers or Software Layers. SCENARIO: Let’s consider a scenario where a user wants to send a message through some Messenger application running in his browser. The “Messenger” here acts as the application layer which provides the user with an interface to create the data. This message or so-called Data is compressed, encrypted (if any secure data), and converted into bits (0’s and 1’s) so that it can be transmitted.
6. Presentation Layer (Layer 6) :
The presentation layer is also called the Translation layer. The data from the application layer is extracted here and manipulated as per the required format to transmit over the network.
The functions of the presentation layer are :
- Translation: For example, ASCII to EBCDIC.
- Encryption/ Decryption: Data encryption translates the data into another form or code. The encrypted data is known as the ciphertext and the decrypted data is known as plain text. A key value is used for encrypting as well as decrypting data.
- Compression: Reduces the number of bits that need to be transmitted on the network. 7. Application Layer (Layer 7) : At the very top of the OSI Reference Model stack of layers, we find the Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network. This layer also serves as a window for the application services to access the network and for displaying the received information to the user. Ex: Application – Browsers, Skype Messenger, etc. **Application Layer is also called Desktop Layer.
The functions of the Application layer are :
- Network Virtual Terminal
- FTAM-File transfer access and management
- Mail Services
- Directory Services
- ARP – stands for Address Resolution Protocol. Its job is to find the hardware address of a host from a known IP address. ARP has several types: Reverse ARP, Proxy ARP, Gratuitous ARP and Inverse ARP. 3. Host-to-Host Layer –
This layer is analogous to the transport layer of the OSI model. It is responsible for end-to-end communication and error-free delivery of data. It shields the upper-layer applications from the complexities of data. The two main protocols present in this layer are :
- Transmission Control Protocol (TCP) – It is known to provide reliable and error-free communication between end systems. It performs sequencing and segmentation of data. It also has acknowledgment feature and controls the flow of the data through flow control mechanism. It is a very effective protocol but has a lot of overhead due to such features. Increased overhead leads to increased cost.
- User Datagram Protocol (UDP) – On the other hand does not provide any such features. It is the go-to protocol if your application does not require reliable transport as it is very cost- effective. Unlike TCP, which is connection-oriented protocol, UDP is connectionless. 4. Application Layer –
This layer performs the functions of top three layers of the OSI model: Application, Presentation and Session Layer. It is responsible for node-to-node communication and controls user-interface specifications. Some of the protocols present in this layer are: HTTP, HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS, X Window, LPD. Have a look at Protocols in Application Layer for some information about these protocols. Protocols other than those present in the linked article are :
- HTTP and HTTPS – HTTP stands for Hypertext transfer protocol. It is used by the World Wide Web to manage communications between web browsers and servers. HTTPS stands for HTTP-Secure. It is a combination of HTTP with SSL(Secure Socket Layer). It is efficient in cases where the browser need to fill out forms, sign in, authenticate and carry out bank transactions.
- SSH – SSH stands for Secure Shell. It is a terminal emulations software similar to Telnet. The reason SSH is more preferred is because of its ability to maintain the encrypted connection. It sets up a secure session over a TCP/IP connection.
3. NTP – NTP stands for Network Time Protocol. It is used to synchronize the clocks on
our computer to one standard time source. It is very useful in situations like bank transactions. Assume the following situation without the presence of NTP. Suppose you carry out a transaction, where your computer reads the time at 2:30 PM while the server records it at 2:28 PM. The server can crash very badly if it’s out of sync.
