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TCP/IP Data Flow

TCP/IP Protocols

Internet Protocol Suite (TCP/IP)

Transmission Control Protocol /Internet Protocol is the set of communications protocols that used for the Internet. It was created by the Department of Defense of USA in order to preserve data integrity. This suite is a compact version of the OSI model and consists of four, instead of seven of OSI, layers:

  

The Process/Application layer defines protocols for node-to node application communication and also controls user-interface specifications.

The Host to Host layer defines protocols for setting up the level of transmission service for applications. It handles issues such as creating reliable end to end communication and ensuring the error free delivery of data.

The Internet layer designates the protocols relating the logical transmission of packets over the network. It gives IP addresses to the hosts and handles the routing of packets among the networks.

 The Link layer monitors the data exchange between the host and the network, overseeing hardware addressing and defining protocols for the physical transmission of data.

Ethernet Cabling

Ethernet cables connect network devices such as routers, switches and computers. They transmit data using the Ethernet protocol. The types of Ethernet cables are:

Straight-through cable

The straight-through cable is used to connect:

·        Computer to switch

·        Router to switch

Crossover cable

The crossover cable is used to connect:

·        Switch to Switch

·        Computer to Computer

·        Router to Computer

Data Encapsulation

Let’s start with a simple example.

Host A wants to transmit data through a network to the Host B.

Data from the Session Layer passes to the Transport Layer. There, a header will be put in front of the data that will provide reliable or unreliable delivery and perform error correction before retransmit. The data is now named Segment. Then the segment will go to the Network Layer where a new header will be added that contains information about the routing that will be needed in order the packet to reach the destination. The segment is now named Packet/Datagram. The next layer is the Data Link. The Data Link Layer encapsulates each packet in a Frame, and the frame’s header caries the hardware address of the source and the destination hosts. The finally step is to put the frame on the network. Before this it must first be put into a digital signal. Physical Layer is responsible for encoding these digits into a digital signal. The frame now is called bits.

All this process is named Data Encapsulation.

OSI Model

Open System Interconnection (OSI) was created by the International Organization for Standardization (ISO) in order to help vendors to create interoperable network devices and software. The OSI model is the primary architectural model for networks. It describes how data and network information are communicated from an application on one computer (i.e. mail, voip) through the network to an application on another computer. The OSI model approaches this communication though layers.

Application	Layer 7
Presentation	Layer 6
Session	Layer 5
Transport	Layer 4
Network	Layer 3
Data Link	Layer 2
Physical	Layer 1

Top-Down Approach of OSI Model

Application Layer

The application layer is the OSI layer closest to the end user. In other words, it provides a user interface and it comes into play when an application needs access to the network.

Presentation Layer

The Presentation Layer as its name states is responsible not only to present data to the Application layer but for data translation and code formatting.

Session Layer

The Session Layer controls the connections between computers. It is responsible for setting up, managing and then tearing down sessions between Presentation layer entities. It provides full-duplex, half-duplex or simplex operation.

Transport Layer

The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layer. In order to achieve this it segment and reassemble data from upper layer applications and unite it onto the same data stream. The Transport Layer can be connection-oriented or connectionless. The two famous protocol of this layer are TCP and UDP.

Network Layer

The Network Layer is responsible for packet forwarding including routing through routers. The connection model that used is connectionless. That means a packet can travel from a sender to a recipient without the recipient having to send an acknowledgement.

Router is a Layer 3 (Network Layer) device.

Data Link Layer

 The Data Link Layer provides the physical transmission of the data and handles error notification, network topology and flow control. In other words, Data Link Layer will ensure that messages are delivered to the proper device on a LAN using hardware addresses and translate messages from the Layer 3 into bits for the Physical Layer to transmit.

Switch is a Layer 2 device.

Physical Layer

The Physical Layer is the lowest layer in the OSI Model. It is a fundamental layer the logical data structures of the higher level functions in a network. Mainly, it defines the means of transmitting bits over a physical link connecting network devices.

Network Devices

Router

Routers are used to connect networks together, through routing packets from one network to another. A router is connected to two or more lines from different network. When a packet arrives, router examines the source and the destination of this and routes the packet accordingly. By default, routers break up a broadcast domain, which is the set of all devices on a network segment that hear all broadcast sent on that segment.  It is very important because when a host sends a broadcast, every device on the network must process that broadcast. When the router’s interface receive this broadcast it will discards it without forwarding it on to other networks.

Switch

Switch is a device that connects network segments. In contrast with routers, switch only “switches” frames from one port to another within the switched network. By default, switches break up collision domain. Collision occurs when more than one user attempts to send a packet on a network segment at the same time. Collisions decrease network efficiency on a collision domain because if a collision occurs the users have to retransmit at a later time.

A Brief Introduction

In order to start our journey to the world of Data Networks, it is mandatory to have some definitions.

A message is the information/data that a user wants to transmit to another user. It can contain any kind of data, including text, sound and images. Each message is cut up to packets in order to be transmitted over the media. 

A packet is the fundamental unit of information that is transmitted over packet-switched networks.

Packet switching is the process of the division of messages into packets before they are sent, transmitting each packet individually, and then reassembling them into the original message since all of them have arrived at the destination. Packet switching shares available network bandwidth between multiple communication sessions. The advantage of Packet switching is that network resources are managed by statistical multiplexing or dynamic bandwidth allocation in which a channel is effectively divided into an arbitrary number of logical variable bit rate channels or data streams. In other words, a channel is occupied only when a user transmits packets. Otherwise it is available to others users to transmit.

In a packet switching network, packets can follow different routes from the source to destination.

Contrary, Circuit switching is a process of implementing a communication network in which two nodes establish a dedicated channel (circuit) through the network before the nodes may communicate. The advantage of Circuit switching is that delay is constant during a connection but each channel cannot be used by other users until the circuit is released and a new connection is set up. Even if no actual communication is taking place, the channel remains unavailable to others users.

Channel is a physical transmission medium such as a Fiber Fiber or a logical connection over a multiplexed medium such as a radio channel. It is used to convey data from one or several sources (transmitters) to one or several destinations (receivers). A channel has a certain capacity for transmitting information that is measured by its bandwidth.

Bandwidth is the data transmission capacity of a channel. The greater a channel’s bandwidth, the more information it can carry per unit of time.

It is expressed in bits/second or multiplies of it (kilobits/sec, megabits/sec).