Computer Networks and Distributed Systems

Thebestindonesia.com – Like the OSI model, the TCP/IP architecture is divided into several layers. There are four known layers in this architecture, namely: network access, internet, transport, and application. Comparison between the layers in the OSI architecture and the TCP/IP architecture can be seen in the following figure:

Comparison of layers on OSI and TCP/IP

The Network Access Layer provides the protocols needed to serve access to communication networks, such as Local Area Network Protocols in this layer connecting a communication point with one of the hosts associated with it. Some examples of commonly used protocol standards include Ethernet, IEEE 802, and X.25.

The Internet Layer stores the procedures to transfer data between hosts on different networks. Inside there is a routing function. This protocol works between hosts and routers. The router is a processor that connects two computer networks. Its primary function is to relay data between networks using inter-network protocols (internetwork protocol). The protocol used at this layer is the Internet protocol (IP).

The Transport Layer provides the logic to ensure that data exchanged between hosts is guaranteed reliability. Besides that, this layer also delivers data to the intended application. The protocol at this layer is known as the Transmission Control Protocol (TCP).

The Application Layer contains the protocols required by certain applications. Each application has a specific protocol, for example, Simple Mail Transfer Protocol (SMTP), File Transfer Protocol (FTP), and TELNET.

TCP/IP operations

The following figure shows how the protocol is configured for communication needs. Look at figure 7.3. below so that we can understand the technical operation of the TCP / IP:

A communication system may consist of several smaller network parts called subnetworks. A network access protocol is required to connect a computer to the subnetwork, for example, Ethernet. This protocol allows sending data from one host to another through several subnetworks.

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Internet protocol (IP) is implemented at each end of a subnetwork that connects it to other subnetworks. This IP works as a relay that moves data blocks from one host to another through some routers. This IP keeps track of the tracks of these data blocks to ensure they are delivered to the intended application.

To establish successful communication, each entity in the system must have a unique address. In this case, two observation systems are needed. Each host in a subnetwork must have an outstanding global internet address, and each process in a host must also have a unique address, the last of which is commonly referred to as a port.

A simple TCP/IP operation can be described as follows. A process is running on port I of host A sends a message to another process on port 2 of host B. The process on A will submit a letter to TCP, including the destination address (host B, port 2). TCP hands over the letter to IP to send a message to host B. IP then hands over the letter to the network access layer with instructions to send it to router X. To perform this operation, the message from the process to TCP is divided into smaller data blocks to facilitate management data. TCP gives each of these data blocks control information (information control), which is called the TCP header. The combination of control information and data blocks forms a TCP segment. The information contained in this TCP header includes:

• The destination port, when the TCP entity on host B receives a segment, must know to whom the data should be sent.
• Sequence numbers. TCP memory segments are sequential, so if the data sent arrives at host B in an unordered condition, then TCP on host B will re-order it.
• Checksum: In sending TCP data, it includes a code that functions to check the data sent. If there is a difference in coding between the data transmitted and the data received, this indicates an error in the transmission, then the data transmission process will be repeated.

Then TCP hands over each data segment sent to IP, with instructions to send it to host B. This data segment must be sent through one or many subnetworks relayed through one or several intermediate routers. This process also requires control information. For that, IP adds a header for each data segment and then forms data units called IP datagrams.

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Each IP datagram is presented to the network access layer for transmission through subnetwork 1. Next, the network access layer adds the necessary headers to form a packet or frame. This packet is sent through the subnetwork to router X. The information contained in each packet header is:

• Subnetwork addresses. The goal, in this case, is that the subnetwork must know which device each packet is addressing.
• Request for facilities (facilities request) Is a network access protocol that may require a certain number of subnetwork facilities, such as priority.

On router X, the header is parsed, and the IP header is checked. Based on the destination address in the IP header, the IP module on the router, X, will direct the datagram to subnetwork two and host B. When the data packet arrives at the destination host (host B), the reverse process occurs, namely the decomposition of data units to the destination process.

TCP/IP applications

Some of the applications of TCP / IP, which will be discussed in the following sub-chapters, include:

Simple Mail Transfer Protocol (SMTP). The SMTP protocol provides the most spartan electronic mail facility. SMTP provides a mechanism for sending messages across several different hosts. The facilities offered by SMTP include mailing lists, return receipts, and forwarding.

File Transfer Protocol (FTP). This protocol sends files from one system to another under user control. The file sent can be a text file or a binary file.

TELNET. Through this facility, a user on a terminal or PC can log on remotely from another computer. This log-on process is done as if it were directly with the intended computer.