Open Systems Interconnection (OSI) Model and TCP/IP Model

1. Overview

1.1 Open System Interconnection Model (OSI)

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard communication protocols. The model partitions a communication system into abstraction layers. The original version of the model had seven layers.

2. OSI Model

2.1 Application Layer (L7)

Application layer is used by network applications such as chrome, firefox, outlook, and skype using Protocols such as HTTP/s, SMTP, FTP, and so on. This layer provides services such as File Transfer, web surfing, emails, virtual terminals, and so on.

2.2 Presentation Layer(L6)

Presentation layer receives data from Application Layer. these data are characters and numbers. Presentation layer converts these data into binary format, compress data, and encrypt/decrypt data through SSL/TLS. 

• Translation
• Data Compression
• Encryption/Decryption

2.3 Session Layer (L5)

Session layer set up and manage connections that enables sending and receiving data.

• Session management
• Authentication
• Authorization

2.4 Transport Layer (L4)

2.4.1 Segmentation

Segmentation is a small data unit divided from data. Each segment contains the Destination port and sequence number. Port numbers help to direct each segmentation to approve an application. And sequences number help to assemble a segment in the correct order. 

2.4.2 Flow Control

Flow control manages to meet two different transrate devices. 

2.4.3 Error Control

Using Automatic repeat request scheme, re-request missing data. Using checksum, correct corrupted data.

2.4.4 Protocols on Transport Layer

• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)

2.4.5 Service types on Transport Layer

• Connection-oriented Transmission: Done by TCP
• Connectionless Transmission: Done by UDP

2.5 Network Layer (L3)

2.5.1 Logical Addressing: IPv4, IPv6, and Masking

2.5.2 Routing

Routing based on Logical addressing.

2.5.3 Path determination

A computer connects to the internet in a number of ways. Finding an optimal way from source to a destination called path determination.

• OSPF
• BGF
• IS-IS

2.6 Datalink Layer (L2)

Datalink layer receives data from Network layer.

2.6.1 Physical addressing

In other words, MAC addressing.

2.6.2 Access the media (Framing)

Controls how data is placed and received from the media which is Media Access Control and Error Detection.

2.6.3 Media Access Control

2.7 Physical Layer (L1)

Physical layer converts the digital bits into electrical, radio, or optical signals. Bit rate control is done at the physical layer and may define transmission mode as simplex, half-duplex, and full-duplex.

3. Summary

3.1 OSI 7 Layer Model

Layer		Protocol data unit(PDU)	Function	Examples
Host layers	Application	Data	High-level APIs including resource sharing, remote file access	HTTP, FTP, SSH, DNS, NFS, Telnet, IRC, SMTP, SNMP, etc.
	Presentation		Translation of data between a networking service and an application including character encoding, data compression, and encryption/decryption	SSL, SSH, IMAP, FTP, MPEG, JPEG
	Session		Managing communication sessions, i.e. continuous exchanges of information in the form of multiple back-and-forth transmissions between two nodes	API's, Sockets, WinSock, etc.
	Transport	Segment(TCP)/Datagram(UDP)	Reliable transmission of data segments between points on a network(End-to-end), including segmentation, acknowledgment, and multiplexing	TCP, UDP
Media layers	Network	Packet	Structuring and managing a multi-node network, including addressing, routing, and traffic control. Path determination and logical addressing.	IP, ICMP, IPSec, IGMP, etc.
	Datalink	Frame	Reliable transmission of data frame between two nodes connected by a physical layer.	Ethernet, PPP, Switch, Bridge, 802.11, MAC/LLC, HDP, Fibre channel, VALN, Q.921, Token Ring, etc..
	Physical	Bit	Transmission and reception of raw bitstreams over a physical medium. binary transmissions.	Fiber, Hubs, Wireless, Coax, Repeaters, RS-232, Rj45, V.34, 802.11.

3.2 TCP/IP Model

Layer	Functions	Examples
Application Layer	Represents data to the user, encoding, and dialog control	DNS, Telnet, SMTP, POP3, IMAP, DHCP, HTTP, FTP, SNMP, etc.
Transport Layer	Supports communication between diverse devices across diverse networks(End-to-end)	TCP, UDP
Internet Layer	Determine the best path through the network	IP, ARP, ICMP
Network Acces Layer	Controls the hardware devices and media that makeup the network	Ethernet, Frame Relay

 

3. Comparison

TCP/IP	OSI
TCP refers to Transmission Control Protocol IP refers to Internet Protocol	OSI refers to Open Systems Interconnection
TCP/IP has 4 layers	OSI has 7 layers
TCP/IP is more reliable	OSI is less reliable
TCP/IP does not have very strict boundaries	OSI has strict boundaries
TCP/IP follow a horizontal approach	OSI follows a vertical approach
TCP/IP uses both session and presentation layer in the application layer itself	OSI use different session and presentation layers
TCP/IP developed protocols then model	OSI developed model than protocol

4. References

https://www.youtube.com/watch?v=vv4y_uOneC0

https://chaeyoungdo.tistory.com/4?category=613557

https://en.wikipedia.org/wiki/OSI_model

https://en.wikipedia.org/wiki/Internet_protocol_suite

https://www.6connect.com/blog/moment-internet-history-osi-7-layer-burrito/

https://24itworld.wordpress.com/2016/08/04/iso-osi-model-layers-of-the-network/

https://community.fs.com/blog/tcpip-vs-osi-whats-the-difference-between-the-two-models.html

https://www.geeksforgeeks.org/tcp-ip-model/

http://ptgmedia.pearsoncmg.com/imprint_downloads/cisco/digitalstudyguide/9780134466194/ch31.html

https://www.journaldev.com/35984/osi-model?utm_source=browser&utm_medium=rss_notification&utm_id=91244.61653545123