Wireless Communication - TCP/IP

The original TCP/IP protocol was defined as four software layers built upon the hardware. Today, however, TCP/IP is thought of as a five-layer model with the layers named similar to the ones in the OSI model.

Comparison between OSI and TCP/IP Suite

When we compare the two models, we find that two layers, session and presentation, are missing from the TCP/IP protocol. The application layer in the suite is usually considered to be the combination of three layers in the OSI model.

The OSI model specifies which functions belong to each of its layers but the layers of the TCP/IP protocol suite contain relatively independent protocols that can be mixed and matched, depending on the needs of the system. The term hierarchical means that each upper level protocol is supported by one or more lower level protocols.

Layers in the TCP/IP Suite

The four layers of the TCP/IP model are the host-to-network layer, internet/network layer, transport layer and the application layer. The purpose of each layer in the TCP/IP protocol suite is detailed below.

 

The above image represents the layers of TCP/IP protocol suite.

Physical Layer

TCP/IP does not define any specific protocol for the physical layer. It supports all of the standard and proprietary protocols.

• At this level, the communication is between two hops or nodes, either a computer or router. The unit of communication is a single bit.

• When the connection is established between the two nodes, a stream of bits is flowing between them. The physical layer, however, treats each bit individually.

The responsibility of the physical layer, in addition to delivery of bits, matches with what mentioned for the physical layer of the OSI model, but it mostly depends on the underlying technologies that provide links.

Data Link Layer

TCP/IP does not define any specific protocol for the data link layer either. It supports all of the standard and proprietary protocols.

• At this level also, the communication is between two hops or nodes. The unit of communication however, is a packet called a frame.

• A frame is a packet that encapsulates the data received from the network layer with an added header and sometimes a trailer.

• The head, among other communication information, includes the source and destination of frame.

• The destination address is needed to define the right recipient of the frame because many nodes may have been connected to the link.

• The source address is needed for possible response or acknowledgment as may be required by some protocols.

LAN, Packet Radio and Point-to-Point protocols are supported in this layer

Network Layer

At the network layer, TCP/IP supports the Internet Protocol (IP). The Internet Protocol (IP) is the transmission mechanism used by the TCP/IP protocols.

• IP transports data in packets called datagrams, each of which is transported separately.
• Datagrams can travel along different routes and can arrive out of sequence or be duplicated.

IP does not keep track of the routes and has no facility for reordering datagrams once they arrive at their destination.

Transport Layer

There is a main difference between the transport layer and the network layer. Although all nodes in a network need to have the network layer, only the two end computers need to have the transport layer.

• The network layer is responsible for sending individual datagrams from computer A to computer B; the transport layer is responsible for delivering the whole message, which is called a segment, from A to B.

• A segment may consist of a few or tens of datagrams. The segments need to be broken into datagrams and each datagram has to be delivered to the network layer for transmission.

• Since the Internet defines a different route for each datagram, the datagrams may arrive out of order and may be lost.

• The transport layer at computer B needs to wait until all of these datagrams to arrive, assemble them and make a segment out of them.

Traditionally, the transport layer was represented in the TCP/IP suite by two protocols: User Datagram Protocol (UDP) and Transmission Control Protocol (TCP).

A new protocol called Stream Control Transmission Protocol (SCTP) has been introduced in the last few years.

Application Layer

The application layer in TCP/IP is equivalent to the combined session, presentation, and application layers in the OSI model.

• The application layer allows a user to access the services of our private internet or the global Internet.

• Many protocols are defined at this layer to provide services such as electronic mail file transfer, accessing the World Wide Web, and so on.

• The protocols supported in this layer are TELNET, FTP and HTTP.

 

FTP

FTP is a way to transfer files online. You might think of the sites you visit in your browser as “the internet,” but your browser only uses one protocol: HTTP. There are many other protocols that, collectively, make up the internet. IMAP and POP, for instance, are two protocols that email clients use to send and receive messages. XMPP is a protocol used to send and receive instant messages. FTP is another such protocol.

FTP stands for “File Transfer Protocol.” It’s also one of the oldest protocols in use today and is a convenient way to move files around. An FTP server offers access to a directory with sub-directories. Users connect to these servers with an FTP client, a piece of software that lets you download files from the server, as well as upload files to it.

Many internet users will never have any use for FTP, but it does have important uses, especially for those interested in studying internet data from the ground up. Here’s what you should know.

 

Teletype Network Protocol (Telnet)

Telnet, developed in 1969, is a protocol that provides a command line interface for communication with a remote device or server, sometimes employed for remote management but also for initial device setup like network hardware. Telnet stands for Teletype Network, but it can also be used as a verb; 'to telnet' is to establish a connection using the Telnet protocol.

Telnet is a protocol that allows you to connect to remote computers (called hosts) over a TCP/IP network (such as the internet). Using telnet client software on your computer, you can make a connection to a telnet server (that is, the remote host). Once your telnet client establishes a connection to the remote host, your client becomes a virtual terminal, allowing you to communicate with the remote host from your computer. In most cases, you'll need to log into the remote host, which requires that you have an account on that system. Occasionally, you can log in as guest or public without having an account.

Telnet clients are available for all major operating systems.

Command-line telnet clients are built into most versions of macOS, Windows, Unix, and Linux. To use these clients, go to their respective command lines (that is, the Terminal application in macOS, the shell in Unix or Linux, or the DOS prompt in Windows), and then enter:

  telnet host port

Replace host with the address of the service, and port with the port number on which the service runs (for example, 80 for http).