TCP/IP explained (little better than before)

TCP/IP Model – 5 Layers

TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet). When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP 

Application Layer (5)

The TCP/IP Application Layer protocols provide services to the application software running on a PC or Server such HTTP, FTP, SMTP, POP3, and much more. The application layer does not define the application itself, but it defines services that applications need. E.g. application HTTP defines how web browsers can pull the contents of a web page from a web server. Therefore, the application layer provides an interface between a browser running on a PC and a web services running on a web server.

Representation Overview as Part of App Layer: The TCP/IP Representation Layer part of the Operating System level where it converts incoming and outgoing data stream to represent it in a specific file format using a specific window such text, jpeg, and html window with the help of its appropriate program. In addition, data encryption happens at this layer as well since that’s where it can be represented.

Notice: that the Presentation Layer at TCP/IP Model is a feature included with Application Layer.

Session Overview as Part of App Layer: The TCP/IP Session Layer can be considered the manager of session between the PC and a remote PC or Server from setting up, coordinate, terminate, exchange, and manage the application sessions from starting point to the end point.

Notice: that the Session Layer at TCP/IP Model is a feature included with Application Layer.

Transport Layer (4)

Here where the Data get Segmented based on TCP or UDP Port numbers and IP Addresses, together “IP-Address:Port”  called ” TCP Socket or UDP Socket”. The Transport Layer uses the two most common protocols Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) for Segmenting. This article will mention little bit about TCP Error Recovery. Check Understanding TCP and UDP Protocols Article for More Information.

TCP Error Recovery Overview: uses the concept of Acknowledgments and to appreciate what the TCP does, you must think about the layers above the Transport Layer, starting from Application Layer. Technically, each layer in TCP/IP provides a service to the layer above it, like TCP Error-Recovery service provided especially for Application layer. TCP mechanism guarantee delivery of data across the Network. Therefore, many Application Layer protocols such HTTP requires guarantee data delivery across a network, hence, TCP port 80 is used to recover data segments due to corrupted frames on the way.

Network Layer (3)

Here where the segments get Packet. Network Layers includes major protocols. Most commonly used: Internet Protocol (IP). IP manage several services like IP Addressing, and IP Routing. This article compares IP Addressing and IP Routing logic concepts with another commonly known concept that uses Addressing and Routing: Postal Service.

Data-Link Layer (2)

Here where IP Packets get Framed, and here where the last piece of Software control protocol can be applied on the Data before it can be handled as frame to the Hardware Layer (Physical Layer) for bit transmission. Since Data Link Layer has to deal with different media technology, it includes more standards and protocols than Network Layer. For example, it includes all the variations of Ethernet protocols, along with several other LAN and Wan Technologies. Wide Area Network (WAN) protocol standards which differ significantly compared to Ethernet Standards because of the longer distance involved in transmitting the Data, hence, different type of cable technology used with WAN.

Such WAN Control Protocols are: Point-to-Point (PPP), High-Level Data-Link Control (HDLC), and WAN’s Frame Relay Control Protocols and standards, just to name a few. So in short, Data Link Layer defines the functions used in these Protocols such rules and controls to deliver the IP Packets that hold the data through different types of Physical media.

Physical Layer (1)

At this stage of the communication process and based on the figures above, the data has been segmented by the Transport Layer using destination and source TCP Port Numbers, placed into an IP packet by Network Layer using a destination and source IP addresses, encapsulated as Ethernet Header and Trailer forming a frame, with destination and source MAC addresses. Next: Physical Layer on the Downstream and based on the media used, creates an electrical, optical, or radiowave signals that represents the bits in each frame. These signals are then sent on the media one at a time. It is also the job of the Physical Layer to retrieve these individual signals from the media, restore them to their bit representations, and pass the bits up to the Data Link Layer as a complete frame.