Layer # Name Mnemonic Encapsulation Units Devices or Components Keywords/Description
7 Application All data PC Network services for application processes, such as file, print, messaging, database services
6 Presentation People data Standard interface to data for the application layer. MIME encoding, data encryption, conversion, formatting, compression
5 Session Seem data Inter-host communication. Establishes, manages and terminates connection between applications
4 Transport To segments End-to-end connections and reliability. Segmentation/de-segmentation of data in proper sequence. Flow control
3 Network Need packets router Logical addressing and path determination. Routing. Reporting delivery errors
2 Data Link Data frames bridge, switch, NIC Physical addressing and access to media. Two sub-layers: Logical Link Control (LLC) and Media Access Control (MAC)
1 Physical Processing bits repeater, hub, tranciever Binary transmission signals and encoding. Layout of pins, voltages, cable specifications, modulation
The TCP/IP Network Model
The TCP/IP protocol suite forms the basis of the Internet. It is the most widely used form of networking between computers. TCP/IP is a combination of protocols at different layers that is designed around simple 4-layer scheme. It combines/splits some adjacent OSI layers, and omits some features. The 4-layer TCP/IP model is also known as the DARPA model, named after the U.S. government agency that initially developed TCP/IP. The 4 layers are as follows:
Layer 1 – Link – The Link layer defines the device driver and network hardware (network interface card).
Layer 2 - Network – The Network layer handles basic communication, addressing and routing. IP, ICMP, ARP and IGMP protocols are at the network layer.
Layer 3 - Transport – The Transport layer handles flow of data among applications. It segments data into packets for transport over the network. TCP and UDP operate at the transport layer.
Layer 4 - Application – The Application layer handles details of the particular end-user applications. Commonly used TCP/IP applications include Telnet, FTP, SMTP, SNMP, DNS, RIP, NFS, NTP, Trace-route.
TCP/IP Protocol Stack
TCP/IP Layer TCP/IP Protocols
4 Application data FTP, HTTP, POP3, IMAP, telnet, SMTP, DNS, TFTP
3 Transport segments TCP, UDP, IGMP, ICMP
2 Internet packets IP – IPSEC
1 Network Access/ Interface frames Ethernet – Token Ring – Frame Relay – ATM
bits (Hardware)
SIMILARITIES
The main similarities between the two models are:
Both of the models share a similar architecture. This can be illustrated by the fact that both of them are constructed with layers.
Both of the models share a common “application layer”. However in practice this layer includes different services depending upon each model.
Both models have comparable transport and network layers.- This can be illustrated by the fact that whatever functions are performed between the presentation and network layer of the OSI model similar functions are performed at the Transport layer of the TCP/IP model.
Knowledge of both models is required by networking professionals.
Both models assume that packets are switched.- Basically this means that individual packets may take differing paths in order to reach the same destination.
DIFFERENCES
The main differences between the two models are:
TCP/IP Protocols are considered to be standards around which the internet has developed. The OSI model however is a ”generic, protocol – independent standard.”
TCP/IP combines the presentation and session layer issues into its application layer.
TCP/IP combines the OSI data link and physical layers into the network access layer.
TCP/IP appears to be a more simpler model and this is mainly due to the fact that it has fewer layers.
TCP/IP is considered to be a more credible model- This is mainly due to the fact because TCP/IP protocols are the standards around which the internet was developed therefore it mainly gains creditability due to this reason. Where as in contrast networks are not usually built around the OSI model as it is merely used as a guidance tool.
The OSI model consists of 7 architectural layers whereas the TCP/IP only has 4 layers.
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