Data Communication and Network- Network Layer onward all layers

Data Communication and Network- Network Layer onward all layers

1. Network Layer of OSI Model Mr. C. P. Divate Department of Computer Engineering

2. Switching techniques in Computer Network In large networks, there can be multiple paths from sender to receiver . The switching technique will decide the best route for data transmission. Switching technique is used to connect the systems for making one-to-one communication .

3. Switching techniques in Computer Network Classification Of Switching Techniques

4. Switching techniques in Computer Network 1) Circuit Switching Circuit switching is a switching technique that establishes a dedicated path between sender and receiver. In the Circuit Switching Technique, once the connection is established then the dedicated path will remain to exist until the connection is terminated. Circuit switching in a network operates in a similar way as the telephone works. A complete end-to-end path must exist before the communication takes place.

5. Switching techniques in Computer Network 1) Circuit Switching In case of circuit switching technique, when any user wants to send the data, voice, video, a request signal is sent to the receiver then the receiver sends back the acknowledgment to ensure the availability of the dedicated path. After receiving the acknowledgment, dedicated path transfers the data. Circuit switching is used in public telephone network. It is used for voice transmission. Fixed data can be transferred at a time in circuit switching technology.

6. Switching techniques in Computer Network 1) Circuit Switching Communication through circuit switching has 3 phases: Circuit establishment Data transfer Circuit Disconnect

7. Switching techniques in Computer Network 1) Circuit Switching Circuit Switching can use either of the two technologies : Space Division Switches Time Division Switches

8. 1) Circuit Switching

9. Time Division Switches: Time slot Interchange (TSI) 1) Circuit Switching

10. Switching techniques in Computer Network 1) Circuit Switching Time Division Multiplexing(TDM) : works in two modes i ) Synchronous TDM ii) Asynchronous TDM

11. Switching techniques in Computer Network 1) Circuit Switching 2) Space Division Switches : Space Division Switches can be categorized in two ways: Crossbar Switch 2) Multistage Switch

12. Switching techniques in Computer Network 1) Circuit Switching 2) Space Division Switches : i ) Crossbar Switch Space Division Switching is a circuit switching technology in which a single transmission path is accomplished in a switch by using a physically separate set of crosspoints . Space Division Switching can be achieved by using crossbar switch . A crossbar switch is a metallic crosspoint or semiconductor gate that can be enabled or disabled by a control unit. The Crossbar switch is made by using the semiconductor. Space Division Switching has high speed, high capacity, and non-blocking switches. The Crossbar switch is a switch that has n input lines and n output lines. The crossbar switch has n2 intersection points known as crosspoints .

13. Switching techniques in Computer Network 1) Circuit Switching 2) Space Division Switches : ii ) Multistage Switch Multistage Switch is made by splitting the crossbar switch into the smaller units and then interconnecting them. It reduces the number of crosspoints . If one path fails, then there will be an availability of another path.

14. Switching techniques in Computer Network 1) Circuit Switching 2) Space Division Switches : ii) Multistage Switch

15. Switching techniques in Computer Network 1) Circuit Switching Advantages Of Circuit Switching In the case of Circuit Switching technique, the communication channel is dedicated. It has fixed bandwidth .

16. Switching techniques in Computer Network 1) Circuit Switching Disadvantages Of Circuit Switching Once the dedicated path is established, the only delay occurs in the speed of data transmission. It takes a long time to establish a connection approx 10 seconds during which no data can be transmitted. It is more expensive than other switching techniques as a dedicated path is required for each connection. It is inefficient to use because once the path is established and no data is transferred, then the capacity of the path is wasted. In this case, the connection is dedicated therefore no other data can be transferred even if the channel is free.

17. Switching techniques in Computer Network 2) Message Switching Message Switching is a switching technique in which a message is transferred as a complete unit and routed through intermediate nodes at which it is stored and forwarded. In Message Switching technique, there is no establishment of a dedicated path between the sender and receiver. The destination address is appended to the message. Message Switching provides a dynamic routing as the message is routed through the intermediate nodes based on the information available in the message . Each and every node stores the entire message and then forward it to the next node. This type of network is known as store and forward network.

18. Switching techniques in Computer Network 2) Message Switching Advantages Of Message Switching Data channels are shared among the communicating devices that improve the efficiency of using available bandwidth. Traffic congestion can be reduced because the message is temporarily stored in the nodes. Message priority can be used to manage the network. The size of the message which is sent over the network can be varied. Therefore, it supports the data of unlimited size . Disadvantages Of Message Switching The message switches must be equipped with sufficient storage to enable them to store the messages until the message is forwarded. The Long delay can occur due to the storing and forwarding facility provided by the message switching technique.

19. Switching techniques in Computer Network 3 ) Packet Switching The packet switching is a switching technique in which the message is sent in one go, but it is divided into smaller pieces, and they are sent individually. The message splits into smaller pieces known as packets and packets are given a unique number to identify their order at the receiving end. Every packet contains some information in its headers such as source address, destination address and sequence number .

20. Switching techniques in Computer Network 3 ) Packet Switching Packets will travel across the network, taking the shortest path as possible. All the packets are reassembled at the receiving end in correct order. If any packet is missing or corrupted, then the message will be sent to resend the message. If the correct order of the packets is reached, then the acknowledgment message will be sent.

21. Switching techniques in Computer Network 3) Packet Switching There are two approaches to Packet Switching: 1) Datagram Packet switching 2) Virtual Circuit Switching

22. Switching techniques in Computer Network 3) Packet Switching 1) Datagram Packet switching It is a packet switching technology in which packet is known as a datagram, is considered as an independent entity . Each packet contains the information about the destination and switch uses this information to forward the packet to the correct destination. The packets are reassembled at the receiving end in correct order. In Datagram Packet Switching technique, the path is not fixed. Intermediate nodes take the routing decisions to forward the packets. Datagram Packet Switching is also known as connectionless switching.

23. Switching techniques in Computer Network 3) Packet Switching 2 ) Virtual Circuit Switching In the above diagram, A and B are the sender and receiver respectively. 1 and 2 are the nodes. Call request and call accept packets are used to establish a connection between the sender and receiver. When a route is established, data will be transferred. After transmission of data, an acknowledgment signal is sent by the receiver that the message has been received. If the user wants to terminate the connection, a clear signal is sent for the termination.

24. Switching techniques in Computer Network 3)Packet Switching Advantages Of Packet Switching Cost-effective: In packet switching technique, switching devices do not require massive secondary storage to store the packets, so cost is minimized to some extent. Therefore, we can say that the packet switching technique is a cost-effective technique. Reliable: If any node is busy, then the packets can be rerouted. This ensures that the Packet Switching technique provides reliable communication. Efficient: Packet Switching is an efficient technique. It does not require any established path prior to the transmission, and many users can use the same communication channel simultaneously, hence makes use of available bandwidth very efficiently .

25. Switching techniques in Computer Network 3)Packet Switching Disdvantages Of Packet Switching Packet Switching technique cannot be implemented in those applications that require low delay and high-quality services. The protocols used in a packet switching technique are very complex and requires high implementation cost. If the network is overloaded or corrupted, then it requires retransmission of lost packets. It can also lead to the loss of critical information if errors are nor recovered .

26. Switching techniques in Computer Network Multiplexing: The transmission medium is used to send the signal from sender to receiver. The medium can transmit only one signal at a time. If there are multiple signals to share one medium, then the medium must be divided in such a way that each signal is given some portion of the available bandwidth. For example: If there are 10 signals and bandwidth of medium is100 units, then the 10 unit is shared by each signal. When multiple signals share the common medium, there is a possibility of collision. Multiplexing concept is used to avoid such collision. Transmission services are very expensive.

27. Switching techniques in Computer Network Multiplexing: The 'n' input lines are transmitted through a multiplexer and multiplexer combines the signals to form a composite signal. The composite signal is passed through a Demultiplexer and demultiplexer separates a signal to component signals and transfers them to their respective destinations . Advantages of Multiplexing: More than one signal can be sent over a single medium. The bandwidth of a medium can be utilized effectively.

28. Switching techniques in Computer Network Multiplexing Techniques: Multiplexing techniques can be classified as :

29. Switching techniques in Computer Network Frequency-division Multiplexing (FDM): It is an analog technique. Frequency Division Multiplexing is a technique in which the available bandwidth of a single transmission medium is subdivided into several channels. In the above diagram, a single transmission medium is subdivided into several frequency channels, and each frequency channel is given to different devices. Device 1 has a frequency channel of range from 1 to 5 .

30. Switching techniques in Computer Network Frequency-division Multiplexing (FDM ): The input signals are translated into frequency bands by using modulation techniques, and they are combined by a multiplexer to form a composite signal. The main aim of the FDM is to subdivide the available bandwidth into different frequency channels and allocate them to different devices. Using the modulation technique, the input signals are transmitted into frequency bands and then combined to form a composite signal. The carriers which are used for modulating the signals are known as sub-carriers. They are represented as f1,f2..fn.

31. Switching techniques in Computer Network Frequency-division Multiplexing (FDM ): Network Transmitter Receiver

32. Switching techniques in Computer Network Frequency-division Multiplexing (FDM): Advantages Of FDM: FDM is used for analog signals. FDM process is very simple and easy modulation. A Large number of signals can be sent through an FDM simultaneously. It does not require any synchronization between sender and receiver. Disadvantages Of FDM: FDM technique is used only when low-speed channels are required. It suffers the problem of crosstalk. A Large number of modulators are required. It requires a high bandwidth channel. Applications Of FDM: FDM is commonly used in TV networks. It is used in FM and AM broadcasting. Each FM radio station has different frequencies, and they are multiplexed to form a composite signal. The multiplexed signal is transmitted in the air.

33. ▶ T he network l a y e r i s r e s ponsib l e f or th e d el i very of individual packets from the source host to the destination host Network Layer of OSI Model

34. The Net w ork Layer Introduction FUNCTIONS OF NETWORK LAYER Net w ork L a y er Design Issues Routing Algorithms Con g estion Control Algorithms References O UTLIN E I NTRODUCTION N ETWORK L AYER D ESIGN I SSUES R OUTING A LGORITHMS C ONGESTION C ONTROL A LGORITHMS FUNCTIONS OF NETWORK LAYER

35. The Net w ork Layer I NTRODUCTION I The network layer is concerned with getting packets from the source all the way to the destination. Getting to the destination may require making many hops at intermediate routers along the way. This function clearly contrasts with the function of the data link layer. The data link layer is concerned with only moving frames from one end of a wire to the other. Thus, the network layer is the lowest layer that deals with end-to-end transmission. To achieve its goals, the network layer must know about the topology of the network (i.e., the set of all routers and links). It should also choose appropriate paths through the network, even if it is large. Introduction FUNCTIONS OF NETWORK LAYER Net w ork L a y er Design Issues Routing Algorithms Con g estion Control Algorithms References

36. I NTRODUCTION II It must also take care when choosing routes to avoid overloading some of the communication lines and routes while leaving others idle. It must also handle problems when source and destination are in different networks. It is up to the network layer to deal with them.

37. I NTRODUCTION II I The network layer can also divide the huge packets into little chunks, if the packet is higher than the most extensive data link layer. The network reassembles the fragments into packets at the receiving end. Routers and Gateways act in the network layer. The communication of the network layer to the data link and transport layer is demonstrated in the figure given below −

38. Functions of Network Layer: Internetworking: An internetworking is the main responsibility of the network layer. It provides a logical connection between different devices .

39. Functions of Network Layer: Packetizing: A Network Layer receives the segment from the upper layer and converts them into packets. This process is known as Packetizing. It is achieved by internet protocol (IP ).

40. Functions of Network Layer: Addressing : A Network layer adds the source and destination address to the header of the frame. Addressing is used to identify the device on the internet .

41. Functions of Network Layer: Addressing : Network Addressing is one of the major responsibilities of the network layer. Network addresses are always logical, i.e., software-based addresses. A host is also known as end system that has one link to the network. The boundary between the host and link is known as an interface. Therefore, the host can have only one interface. A router is different from the host in that it has two or more links that connect to it. When a router forwards the datagram, then it forwards the packet to one of the links. The boundary between the router and link is known as an interface, and the router can have multiple interfaces, one for each of its links. Each interface is capable of sending and receiving the IP packets, so IP requires each interface to have an address. Each IP address is 32 bits long, and they are represented in the form of "dot-decimal notation" where each byte is written in the decimal form, and they are separated by the period. An IP address would look like 193.32.216.9 where 193 represents the decimal notation of first 8 bits of an address, 32 represents the decimal notation of second 8 bits of an address.

42. Functions of Network Layer : Addressing Type of IP Address: Classful IP Addressing Classless IP Addressing 1) Classful Addressing: An IP address is 32-bit long. An IP address is divided into Five sub-classes: Class A Class B Class C Class D Class E

43. Functions of Network Layer : Addressing 1) Classful Addressing: An IP address is divided into two parts: Network ID: It represents the number of networks . Host ID: It represents the number of hosts. In the diagram, we observe that each class have a specific range of IP addresses. The class of IP address is used to determine the number of bits used in a class and number of networks and hosts available in the class

44. Functions of Network Layer : Addressing 1) Class A: In Class A, an IP address is assigned to those networks that contain a large number of hosts . The network ID is 8 bits long. The host ID is 24 bits long. In Class A, the first bit in higher order bits of the first octet is always set to 0 and the remaining 7 bits determine the network ID. The 24 bits determine the host ID in any network . The total number of networks in Class A = 2 7 = 127 network address The total number of hosts in Class A = 2 24 - 2 = 16,777,214 host address IP addresses belonging to class A ranges from 1.x.x.x – 127.x.x.x

45. Functions of Network Layer : Addressing 2 ) Class B: In Class B, an IP address is assigned to those networks that range from small-sized to large-sized networks. The Network ID is 16 bits long. The Host ID is 16 bits long.. In Class B, the higher order bits of the first octet is always set to 10, and the remaining14 bits determine the network ID. The other 16 bits determine the Host ID. The total number of networks in Class B = 2 14 = 16383 network address The total number of hosts in Class B = 2 16 - 2 = 65534 host address IP addresses belonging to class B ranges from 128.0.x.x – 191.255.x.x.

46. Functions of Network Layer : Addressing 3 ) Class C: In Class C, an IP address is assigned to only small-sized networks. The Network ID is 24 bits long. The host ID is 8 bits long . In Class C, the higher order bits of the first octet is always set to 110, and the remaining 21 bits determine the network ID. The 8 bits of the host ID determine the host in a network. The total number of networks = 2 21 = 2097152 network address The total number of hosts = 2 8 - 2 = 254 host address IP addresses belonging to class C ranges from 192.0.0.x – 223.255.255.x

47. Functions of Network Layer : Addressing 4) Class D: In Class D, an IP address is reserved for multicast addresses . It does not possess subnetting . The higher order bits of the first octet is always set to 1110, and the remaining bits determines the host ID in any network. IP addresses belonging to class D ranges from 224.0.0.0 – 239.255.255.255.

48. Functions of Network Layer : Addressing 5) Class E : In Class E, an IP address is used for the future use or for the research and development purposes. It does not possess any subnetting . The higher order bits of the first octet is always set to 1111, and the remaining bits determines the host ID in any network . IP addresses of class E ranges from 240.0.0.0 – 255.255.255.254 .

49. Functions of Network Layer: Addressing Classful Network Architecture

50. Functions of Network Layer: Public and Private IP Addresses The are two types of Internet Protocol (IP) addresses: Public and Private. A router will typically have two types of network interfaces: An Internal Interface An external Interface Each of these interfaces will have an IP address .

51. Functions of Network Layer: Public and Private IP Addresses A Public IP address (External) is assigned to every device that connects to the Internet and each IP address is unique. Therefore, there cannot exist two device with the same public IP address. The public IP address is assigned to the device by the Internet Service Provider as soon as the device is connected to the Internet . A public IP address can be static, dynamic or shared.

52. Functions of Network Layer: Public IP as a Static IP address Public static - some times called Dedicated - means the IP address never changes and is tied to a single user, device, server or website .

53. Functions of Network Layer: Public IP as a Dynamic IP address Public dynamic - means the IP address can change from time-to-time (for example, when you lose connection and re-connect or the ISP might change the address periodically).

54. Functions of Network Layer: Public IP as a Shared IPs Public shared - in some cases, an ISP can assign a public IP address to a group of users, and then employ NAT to isolate their traffic.

55. Functions of Network Layer: Private IP address (Internal) is only used by devices communicating to each other on the same network. Devices with private IP addresses cannot connect to the Internet directly. Likewise , computers or other devices outside the local network cannot connect directly to a device with a private IP . An IP address is considered private if the IP number falls within one of the IP address ranges reserved for private networks such as a Local Area Network (LAN). The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private networks (local networks ): 10.0.0.0 - 10.255.255.255 (Total Addresses: 16,777,216) 172.16.0.0 - 172.31.255.255 (Total Addresses: 1,048,576) 192.168.0.0 - 192.168.255.255 (Total Addresses: 65,536)

56. Functions of Network Layer : Addressing What is Subnetting ? Subnetting is the practice of dividing a network into two or smaller networks. It increases routing efficiency, which helps to enhance the security of the network and reduces the size of the broadcast domain . This method divides a network into smaller subnets . It also helps you to reduce the size of the routing tables, which is stored in routers. Classless addressing / Subnetting

57. Functions of Network Layer : Addressing Classless addressing / Subnetting Why Use Subnetting ? Subnetting process helps to allocate IP addresses that prevent large numbers of IP network addresses from remaining unused. It helps you to maximize IP addressing efficiency. Extend the life of IPV4. Public IPV4 Addresses are rare. Dividing a single network into multiple networks. Converting Host bits into network bits. i.e. converting 0’s into 1’s. Sub netting can be done in three ways. Requirement of Network Requirement of Host / Notation

58. The key concept of sub netting is borrowing bits from the host portion of the network to create a sub network. Rules govern this borrowing, ensuring that some bits are left for a Host ID. The rules require that two bits remain available to use for the Host ID.

59. If 2 Bits available for Creating Subnets Address class Network bits Host bits Bits available for subnet Hosts CLASS A 8 24 24-2 = 22 CLASS B 16 16 16-2 = 14 CLASS C 24 8 8-2 = 6

60. 128 64 32 16 8 4 2 1 1 128 1 1 192 1 1 1 224 1 1 1 1 240 1 1 1 1 1 248 1 1 1 1 1 1 252 1 1 1 1 1 1 1 254 1 1 1 1 1 1 1 1 255 Binary place value B i n a r y Digit Decimal E q u i va lent Sub Net mask value

61. CIDR – Classless Inter-Domain Routing. CIDR addressing method allows the use of a prefix to designate the number of network bits in the mask For Example : 200.15.1.53/25 (CIDR Notation) In this example the CIDR value is /25 means the first 25 bits in the mask are network bits (1s)

62. Subnet mask : It is used to determine the network portion and Host portion of an IP address. Address Class Subnet mask Octet Format CLASS A 255.0.0.0 N.H.H.H CLASS B 255.255.0.0 N.N.H.H CLASS C 255.255.255.0 N.N.N.H N = Network H = Host

63. Network = 2 n [n = number of ON bits (1’s)] Host = 2 h [h = number of OFF bits (0’s)] Valid Host = Host – 2 * * First IP (Host) of Network is use for network address * Last IP (Host) of network is use for Broadcast address 192.168.1.0 255.255.255.0 11111111.11111111.11111111. 00000000 IP Address Subnet Mask Binary format Network Bits Host Bits

64. 192.168.1.0 divided into in 64 Hosts. Subnet mask Binary form CIDR Network Host Valid Host Block size New Binary form New Subnet mask New CIDR : 255.255.255.0 : 11111111.11111111.11111111.00000000 : /24 : 2 n => 2 2 = 4 : 2 h => 2 6 = 64 : Host – 2 => 64 – 2 = 62 : 256 – 192 = 64 : 11111111.11111111.11111111. 11 000000 : 255.255.255.192 : /26 n = no. of ON bits. h = no. of OFF bits

65. No . Network/Network ID Broadcast ID First Host Last Host 1 192.168.1.0 192.168.1.63 192.168.1.1 192.168.1.62 2 192.168.1.64 192.168.1.127 192.168.1.65 192.168.1.126 3 192.168.1.128 192.168.1.191 192.168.1.129 192.168.1.190 4. 192168.1.192 192.168.1.255 192.168.1.193 192.168.1.254 192.168.1.0 divided into in 64 Hosts.

66. 172.18.0.0 divided into in 8 Networks. Subnet mask Binary form CIDR Network Host V a l id H o s t Block Size : 255.255.0.0 : 11111111.11111111.00000000.00000000 : /16 : 2 n => 2 3 = 8 : 2 h => 2 13 = 8192 : Host – 2 => 8192 – 2 = 8190 : 256 – 224 = 32 New Binary form New Subnet mask New CIDR : 11111111.11111111. 111 00000.00000000 : 255.255.224.0 : /19 n = no. of ON bits. h = no. of OFF bits

67. S No Ne t w o rk / Ne t w o r k I D Broadcast ID First Host Last Host 1 172.18.0.0 172.18.31.255 172.18.0.1 172.18.31.254 2 172.18.32.0 172.18.63.255 172.18.32.1 172.18.63.254 3 172.18.64.0 172.18.91.255 172.18.64.1 172.18.91.254 4 172.18.92.0 172.18.127.255 172.18.92.1 172.18.127.254 5 172.18.128.0 172.18.159.255 172.18.128.1 172.18.159.254 6 172.18.160.0 172.18.191.255 172.18.160.1 172.18.191.254 7 172.18.192.0 172.18.223.255 172.18.192.1 172.18.223.254 8 172.18.224.0 172.18.255.255 172.18.224.1 172.18.255.254 172.18.0.0 divided into in 8 Networks.

68. Find the Broadcast ID of this network 110.60.21.15/11 Subnet mask Binary form CIDR Network Host Valid Host Block Size : 255.0.0.0 : 11111111.00000000.00000000.00000000 : /8 : 2 n => 2 3 = 8 : 2 h => 2 21 = 2097152 : Host – 2 => 2097152 – 2 = 2097150 : 256 – 224 = 32 New Binary form New Subnet mask New CIDR : 11111111. 111 00000.00000000.00000000 : 255.224.0.0 : /11 n = no. of ON bits. h = no. of OFF bits

69. 2 11 .32.0 . 11 .63.255.255 11 .32.0 . 1 11 .63.255.254 S No Ne t w o rk / Ne t w o r k I D Broadcast ID First Host Last Host 1 110.0.0.0 110.31.255.255 110.0.0.1 110.31.255.254 2 110.32.0.0 110.63.255.255 110.32.0.1 110.63.255.254 3 110.64.0.0 110.91.255.255 110.64.0.1 110.91.255.254 4 110.92.0.0 110.127.255.255 110.92.0.1 110.127.255.254 5 110.128.0.0 110.159.255.255 110.128.0.1 110.159.255.254 6 110.160.0.0 110.191.255.255 110.160.0.1 110.191.255.254 7 110.192.0.0 110.223.255.255 110.192.0.1 110.223.255.254 8 110.224.0.0 110.255.255.255 110.224.0.1 110.255.255.254 Find the Broadcast ID of this address 110.60.21.15/11

70. Routing The process of moving a packet of data from source to destination. Routing is usually performed by a dedicated device called a Router. It is the key feature of Internet because it enables messages to pass from one computer to another and eventually reach the target machine Functions of Network Layer:

71. Classification of Routing Algorithms Adaptive Algorithms These are the algorithms which change their routing decisions whenever network topology or traffic load changes. The changes in routing decisions are reflected in the topology as well as traffic of the network. Also known as Dynamic routing , these make use of dynamic information such as current topology, load, delay, etc. to select routes. Optimization parameters are distance, number of hops and estimated transit time.

72. Classification of Adaptive Algorithms (a) Isolated – In this method each, node makes its routing decisions using the information it has without seeking information from other nodes. The sending nodes doesn’t have information about status of particular link. Disadvantage is that packet may be sent through a congested network which may result in delay. Examples: Hot potato routing, backward learning. (b) Centralized – In this method, a centralized node has entire information about the network and makes all the routing decisions. Advantage of this is only one node is required to keep the information of entire network and disadvantage is that if central node goes down the entire network is done. (c) Distributed – In this method, the node receives information from its neighbors and then takes the decision about routing the packets. Disadvantage is that the packet may be delayed if there is change in between interval in which it receives information and sends packet.

73. Classification of Adaptive Algorithms (a) Isolated –

74. Non-Adaptive Algorithms These are the algorithms which do not change their routing decisions once they have been selected. This is also known as static routing as route to be taken is computed in advance and downloaded to routers when router is booted. (a) Flooding – This adapts the technique in which every incoming packet is sent on every outgoing line except from which it arrived. One problem with this is that packets may go in loop and as a result of which a node may receive duplicate packets. These problems can be overcome with the help of sequence numbers, hop count and spanning tree. (b) Random walk – In this method, packets are sent host by host or node by node to one of its neighbors randomly. This is highly robust method which is usually implemented by sending packets onto the link which is least queued.

75. Distance Vector Routing: https://www.youtube.com/watch?v=hkaYIg01dDk Link State Routing : https://www.youtube.com/watch?v=kW6zV-040SY Dijkastra’s Algorithm: https://www.youtube.com/watch?v=Lfb8qkXzHY0 Bellman Ford Algorithm: https://www.youtube.com/watch?v=SiI03wnREt4 Routing Algorithms Flooding and Flow control algorithm: https ://www.youtube.com/watch?v=hcXxnG1T3pE Non-Adaptive Algorithms Adaptive Algorithms

76. The Net w ork Layer Introduction Net w ork L a y er Design Issues Routing Algorithms Con g estion Control Algorithms References S TORE - AND -F ORWARD P ACKET S WITCHING I Components of a computer network: Hosts (computers, handheld deveices etc.) Switches. Routers. Wireless access points. D C B A E F Packet Process P1 Host H1 Router ISP’s equipment H2 LAN P2 F IGURE : The environment of the network layer protocols.

77. The transport layer is a 4th layer from the top. The main role of the transport layer is to provide the communication services directly to the application processes running on different hosts. The transport layer provides a logical communication between application processes running on different hosts. ▶ Process-to-process delivery

78. The transport layer provides a logical communication between application processes running on different hosts. Although the application processes on different hosts are not physically connected, application processes use the logical communication provided by the transport layer to send the messages to each other. The transport layer protocols are implemented in the end systems but not in the network routers .

79. A computer network provides more than one protocol to the network applications. For example, TCP and UDP are two transport layer protocols that provide a different set of services to the network layer . Each of the applications in the application layer has the ability to send a message by using TCP or UDP. The application communicates by using either of these two protocols. Both TCP and UDP will then communicate with the internet protocol in the internet layer. The applications can read and write to the transport layer. Therefore, we can say that communication is a two-way process.

80. The services provided by the transport layer are similar to those of the data link layer. The data link layer provides the services within a single network while the transport layer provides the services across an internetwork made up of many networks. The data link layer controls the physical layer while the transport layer controls all the lower layers. Services provided by the Transport Layer

81. The services provided by the transport layer protocols can be divided into five categories: End-to-end delivery Addressing Reliable delivery Flow control Multiplexing. Services provided by the Transport Layer

82. 1) End-to-end delivery: The transport layer transmits the entire message to the destination. Therefore, it ensures the end-to-end delivery of an entire message from a source to the destination. Services provided by the Transport Layer

83. 2 ) Reliable delivery : The transport layer provides reliability services by retransmitting the lost and damaged packets. Services provided by the Transport Layer The reliable delivery has four aspects: Error control Sequence control Loss control Duplication control

84. 2 ) Reliable delivery : i ) Error control Services provided by the Transport Layer The data link layer checks for the error between each network. If an error is introduced inside one of the routers, then this error will not be caught by the data link layer. It only detects those errors that have been introduced between the beginning and end of the link. Therefore , the transport layer performs the checking for the errors end-to-end to ensure that the packet has arrived correctly .

85. 2 ) Reliable delivery : ii) Sequence control Services provided by the Transport Layer On the sending end, the transport layer is responsible for ensuring that the packets received from the upper layers can be delivered to and used by the lower layers. On the receiving end, it ensures that the various segments of a transmission can be correctly reassembled.

86. 2) Reliable delivery: iii) Loss control Services provided by the Transport Layer Loss Control is a third aspect of reliability. The transport layer ensures that all the fragments of a transmission arrive at the destination, not some of them . On the sending end, all the fragments of transmission are given sequence numbers by a transport layer. These sequence numbers allow the receiver?s transport layer to identify the missing segment. 2 ) Reliable delivery : iv) Duplication Control Duplication Control is the fourth aspect of reliability. The transport layer guarantees that no duplicate data arrive at the destination . Sequence numbers are used to identify the lost packets; similarly, it allows the receiver to identify and discard duplicate segments.

87. 3 ) Flow Control Services provided by the Transport Layer Flow control is used to prevent the sender from overwhelming the receiver. If the receiver is overloaded with too much data, then the receiver discards the packets and asking for the retransmission of packets. This increases network congestion and thus, reducing the system performance. The transport layer is responsible for flow control. It uses the sliding window protocol that makes the data transmission more efficient as well as it controls the flow of data so that the receiver does not become overwhelmed. Sliding window protocol is byte oriented rather than frame oriented.

88. 4 ) Multiplexing: The transport layer uses the multiplexing to improve transmission efficiency. Services provided by the Transport Layer Upward multiplexing: Upward multiplexing means multiple transport layer connections use the same network connection. To make more cost-effective, the transport layer sends several transmissions bound for the same destination along the same path; this is achieved through upward multiplexing .

89. 4 ) Multiplexing: The transport layer uses the multiplexing to improve transmission efficiency. Services provided by the Transport Layer ii. Downward multiplexing: Downward multiplexing means one transport layer connection uses the multiple network connections . Downward multiplexing allows the transport layer to split a connection among several paths to improve the throughput. This type of multiplexing is used when networks have a low or slow capacity.

90. 5 ) Addressing : Services provided by the Transport Layer Data generated by an application on one machine must be transmitted to the correct application on another machine. In this case, addressing is provided by the transport layer. The transport layer provides the user address which is specified as a station or port. The port variable represents a particular TS user of a specified station known as a Transport Service access point (TSAP). Each station has only one transport entity. The transport layer protocols need to know which upper-layer protocols are communicating.

91. 5 ) Addressing : Services provided by the Transport Layer

92. ▶ T he sessio n la y e r i s respon s i ble f or d i a l og c ontrol and synchronization

93. Dialog control : The session layer allows two systems to enter into a dialog. ▶ It allows the communication between two processes to take place in either half duplex (one way at a time) or full-duplex (two ways at a time) mode. Synchronization : The session layer allows a process to add checkpoints, or synchronization points, to a stream of data. ▶ For example, if a system is sending a file of 2000 pages, it is advisable to insert checkpoints after every 100 pages to ensure that each 100-page unit is received and acknowledged independently. In this case, if a crash happens during the transmission of page 523, the only pages that need to be resent after system recovery are pages 501 to 523. Pages previous to 501 need not be resent.

94. ▶ T he present at i on l a y e r i s respon s i ble f or transl a t i on, compression, and encryption.

95. Translation : The processes (running programs) in two systems are usually exchanging information in the form of character strings, numbers, and so on. ▶ The information must be changed to bit streams before being transmitted. Because different computers use different encoding systems, the presentation layer is responsible for interoperability between these different encoding methods. ▶ The presentation layer at the sender changes the information from its sender- dependent format into a common format. ▶ The presentation layer at the receiving machine changes the common format into its receiver-dependent format.

96. Encryption : To carry sensitive information, a system must be able to ensure privacy. ▶ Encryption means that the sender transforms the original information to another form and sends the resulting message out over the network. ▶ Decryption reverses the original process to transform the message back to its original form. Compression : Data compression reduces the number of bits contained in the information. ▶ Data compression becomes particularly important in the transmission of multimedia such as text, audio, and video.

97. ▶ The application layer is responsible for providing services to the user

98. ▶ Network virtual terminal : A network virtual terminal is a software version of a physical terminal, and it allows a user to log on to a remote host. ▶ To do so, the application creates a software emulation of a terminal at the remote host. ▶ The user's computer talks to the software terminal which, in turn, talks to the host, and vice versa. ▶ The remote host believes it is communicating with one of its own terminals and allows the user to log on. ▶ File transfer, access, and management : This application allows a user to access files in a remote host (to make changes or read data), to retrieve files from a remote computer for use in the local computer, and to manage or control files in a remote computer locally.

99. ▶ Mail services : This application provides the basis for e- mail forwarding and storage. ▶ Directory services : This application provides distributed database sources and access for global information about various objects and services.

100. ▶ At each layer, additional information is added to the data packet ▶ An example would be information related to the IP protocol that is added at Layer 3

101. Data H ead er T r a iler A general concept of packets serves as a prerequisite to the understanding of the ISO-OSI model.

102. ▶ Packet arrival information ▶ Receiver’s address ▶ Sender’s address ▶ Synchronization character

103. ▶ Error correction code Character oriented VRC (Parity Checking) ▶ Packet oriented error correction codes LRC CRC