Unit 3 - Network Protocols (TCP/IP, SMTP) PDF

UNIT-3  Network protocol: tcp/ip, smtp TCP/IP stands for Transmission Control Protocol/Internet Protocol and is a suite of communication protocols used to interconnect network devices on the internet. TCP/IP is also used as a communications protocol in a private...

UNIT-3  Network protocol: tcp/ip, smtp TCP/IP stands for Transmission Control Protocol/Internet Protocol and is a suite of communication protocols used to interconnect network devices on the internet. TCP/IP is also used as a communications protocol in a private computer network -- an intranet or extranet. TCP  It ensures a reliable and orderly delivery of packets across networks.  TCP is a higher-level smart communications protocol that still uses IP as a way to transport data packets, but it also connects computers, applications, web pages and web servers.  TCP defines how applications can create channels of communication across a network.  It manages how a message is assembled into smaller packets before they're transmitted over the internet and reassembled in the right order at the destination address.  TCP operates at Layer 4, or the transport layer, of the Open Systems Interconnection (OSI model).  TCP is a connection-oriented protocol, which means it establishes a connection between the sender and the receiver before delivering data to ensure reliable delivery. IP  IP is a low-level internet protocol that facilitates data communications over the internet.  IP delivers packets of data that consist of a header, which contains routing information, such as the source and destination of the data and the data payload itself.  It defines how to address and route each packet to ensure it reaches the right destination. Each gateway computer on the network checks this IP address to determine where to forward the message.  IP operates at Layer 3, or the network access layer, of the OSI model.  IP is a connection-less protocol, which means it doesn't guarantee delivery nor does it provide error checking and correction. SMTP Simple Mail Transfer mechanism (SMTP) is a mechanism for exchanging email messages between servers. It is an essential component of the email communication process and operates at the application layer of the TCP/IP protocol stack. SMTP is a protocol for transmitting and receiving email messages. SMTP is an application layer protocol. The client who wants to send the mail opens a TCP connection to the SMTP server and then sends the mail across the connection. The SMTP server is an always-on listening mode. As soon as it listens for a TCP connection from any client, the SMTP process initiates a connection through port 25. After successfully establishing a TCP connection the client process sends the mail instantly. Components of SMTP  Mail User Agent (MUA): It is a computer application that helps you in sending and retrieving mail. It is responsible for creating email messages for transfer to the mail transfer agent(MTA).  Mail Submission Agent (MSA): It is a computer program that receives mail from a Mail User Agent(MUA) and interacts with the Mail Transfer Agent(MTA) for the transfer of the mail.  Mail Transfer Agent (MTA): It is software that has the work to transfer mail from one system to another with the help of SMTP.  Mail Delivery Agent (MDA): A mail Delivery agent or Local Delivery Agent  Dhcp and dns Dynamic Host Configuration Protocol is a network protocol used to automate the process of assigning IP addresses and other network configuration parameters to devices (such as computers, smartphones, and printers) on a network. Instead of manually configuring each device  with an IP address, DHCP allows devices to connect to a network and receive all necessary network information, like IP address, subnet mask, default gateway, and DNS server addresses, automatically from a DHCP server. This makes it easier to manage and maintain large networks, ensuring devices can communicate effectively without conflicts in their network settings. DHCP plays a crucial role in modern networks by simplifying the process of connecting devices and managing network resources efficiently. DHCP works on the Application layer of the UDP Protocol. The main task of DHCP is to dynamically assigns IP Addresses to the Clients and allocate information on TCP/IP configuration to Clients. For more, you can refer to the Article Working of DHCP. The DHCP port number for the server is 67 and for the client is 68. It is a client- server protocol that uses UDP services. An IP address is assigned from a pool of addresses. In DHCP, the client and the server exchange mainly 4 DHCP messages in order to make a connection, also called the DORA process, but there are 8 DHCP messages in the process. DNS The Domain Name System (DNS) is the phonebook of the Internet. Humans access information online through domain names, like nytimes.com or espn.com. Web browsers interact through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resource. DNS server types There are several server types involved in completing a DNS resolution. The following list describes the four name servers in the order a query passes through them. They provide the domain name being sought or referrals to other name servers. Recursive server. The recursive server takes DNS queries from an application, such as a web browser. It’s the first resource the user accesses and either provides the answer to the query if it has it cached or accesses the next-level server if it doesn’t. This server may go through several iterations of querying before returning an answer to the client. Root name server. This server is the first place the recursive server sends a query if it doesn’t have the answer cached. The root name server is an index of all the servers that will have the information being queried. These servers are overseen by the Internet Corporation for Assigned Names and Numbers, specifically a branch of ICANN called the Internet Assigned Numbers Authority. TLD server. The root server directs the query based on the top-level domain – the.com,.edu or.org in the URL. This is a more specific part of the lookup. Authoritative name server. The authoritative name server is the final checkpoint for the DNS query. These servers know everything about a given domain and deal with the subdomain part of the domain name. These servers contain DNS resource records with specific information about a domain, such as the A record. They return the necessary record to the recursive server to send back to the client and cache it closer to the client for future lookups.  OSI model OSI stands for open system interconnection. It has been developed by ISO(international organization for standardization )in the year 1984. It is a 7 layer architecture it each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe. 1. Physical layer  The lowest layer of the OSI reference model. It is a responsible for actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for transmitting individual bits from one node to the next. When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the data link layer, which will put the frame back together. 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 s error-free from one node to another, over the physical layer. When a packet arrive in a network, it is responsibility of data link layer to transmit it to the host using its MAC address. 3. Network layer The network layer works for the transmission of data from one host to the other located in different networks. It also take care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available. The sender and receivers IP addresses are placed in the header by the network layer. 4. Transport layer The transport layer provides services to the application layer and takes services from network layer. The data in the transport layer is referred to as segments. It is responsible for the end to end delivery of the complete message. The transport layer also provides the acknowledgement of the successful data transmission and re-transmits the data if the error is found. 5. Session layer This layer is responsible for the establishment of connection, maintenance of the sessions, authentication, and also ensure security. The layer allows the two processes to establish, use and terminate a connection. The session layer Allows two system to start communication with each other in half-duplex or full-duplex.  5. Presentation layer 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.  Conversion: for example, ASCII to EBCDIC.  Encryption: data encryption translates the data into another from or code. The encrypted data is known as the cipher text and the decryption 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 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 provides procedure 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.  Tcp/ip reference model The OSI model it was designed to describe the functions of the communication system by dividing the communication produce into smaller and similar components. But when we talk about the tcp/ip model, it was designed and developed by department of defence in 1960s and is based on standard protocols. The TCP/IP model is a concise version of the osi model. It contains four layers.  1. Network access layer: This layer corresponds to the combination of data link layer and physical layer of the osi model. It looks out for hardware addressing and the protocols present in this layer allows for the physical transmission of data. It is described as residing in layer 3, being encapsulated by layer 2 protocols. 2. Internet layer This layer parallels the functions of osi network layer. It defines the protocols which are responsible for logical transmission of data over the entire network. The main protocols residing at this layer are: 1. Ip Stands for internet protocol and it is responsible for delivering packets from the source host to the destination by looking at the ip addresses in the packet header. ip has 2 versions: ipv4 and ipv6. 2. ICMP Stands for internet control message protols.it is encapsulated within ip datagrams and is responsible for providing hosts with information about network problems. 3. ARP Stands for address resolution protocol. Its job to find the hardware address of a host from a known ip address. 3. Transport 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:  1. Trasmission 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 increase cost. 2. User datagram protocol (UDP) - on the other hand does not provide any such features. It is the go-to protocol 4. Application layer This layer perform the functions of top three layers of 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, SSH, SMTP.  Switching 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.in computer networking, Switching is the process of transferring data packets from one device to another in a network, or from one network to another, using specific devices called switches Switching takes place at the Data Link layer of the OSI Model. This means that after the generation of data packets in the Physical Layer, switching is the immediate next process in data communication. What is a Switch? A switch is a hardware device in a network that connects other devices, like computers and servers. It helps multiple devices share a network without their data interfering with each other. A switch works like a traffic cop at a busy intersection. When a data packet arrives, the switch decides where it needs to go and sends it through the right port. A switch is a dedicated piece of computer hardware that facilitates the process of switching i.e., incoming data packets and transferring them to their destination. A switch works at the Data Link layer of the OSI Model. A switch primarily handles the incoming data packets from a source computer or network and decides the appropriate port through which the data packets will reach their target computer or network. Types of Switching There are three types of switching methods:  Message Switching  Circuit Switching  Packet Switching Circuit Switching o Circuit switching is a switching technique that establishes a dedicated path between sender and receiver. o In the Circuit Switching Technique, once the connection is established then the dedicated path will remain to exist until the connection is terminated.  o Circuit switching in a network operates in a similar way as the telephone works. o A complete end-to-end path must exist before the communication takes place. o 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. o Circuit switching is used in public telephone network. It is used for voice transmission. o Fixed data can be transferred at a time in circuit switching technology. Communication through circuit switching has 3 phases: o Circuit establishment o Data transfer o Circuit Disconnect Advantages Of Circuit Switching: o In the case of Circuit Switching technique, the communication channel is dedicated. o It has fixed bandwidth. Disadvantages Of Circuit Switching: o Once the dedicated path is established, the only delay occurs in the speed of data transmission. o It takes a long time to establish a connection approx. 10 seconds during which no data can be transmitted. o It is more expensive than other switching techniques as a dedicated path is required for each connection. o It is inefficient to use because once the path is established and no data is transferred, then the capacity of the path is wasted. o In this case, the connection is dedicated therefore no other data can be transferred even if the channel is free. Message Switching o 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. o In Message Switching technique, there is no establishment of a dedicated path between the sender and receiver. o 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. o Message switches are programmed in such a way so that they can provide the most efficient routes. o 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.  o Message switching treats each message as an independent entity. o o Advantages Of Message Switching o Data channels are shared among the communicating devices that improve the efficiency of using available bandwidth. o Traffic congestion can be reduced because the message is temporarily stored in the nodes. o Message priority can be used to manage the network. o The size of the message which is sent over the network can be varied. Therefore, it supports the data of unlimited size. o Disadvantages Of Message Switching o The message switches must be equipped with sufficient storage to enable them to store the messages until the message is forwarded. o The Long delay can occur due to the storing and forwarding facility provided by the message switching technique. o Packet Switching o 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.  o The message splits into smaller pieces known as packets and packets are given a unique number to identify their order at the receiving end. o Every packet contains some information in its headers such as source address, destination address and sequence number. o Packets will travel across the network, taking the shortest path as possible. o All the packets are reassembled at the receiving end in correct order. o If any packet is missing or corrupted, then the message will be sent to resend the message. o If the correct order of the packets is reached, then the acknowledgment message will be sent. Disadvantages Of Packet Switching: o Packet Switching technique cannot be implemented in those applications that require low delay and high-quality services. o The protocols used in a packet switching technique are very complex and requires high implementation cost. o 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.