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| TCP/IP vs OSI and the corresponding protocols |
Physical
The
physical layer represents the physical elements used to transport the data on
the network. This layer implements different technologies and some protocols like DSL and ISDN. RJ45, Ethernet, Circuit switching and
multiplexing are things that can be placed on the physical layer. A hub or repeater
is an example of devices that runs at the layer 1.
Data-Link
The
data-link layer is the only layer of the osi model that is devised in two more
sub-layer called the Logical Link Layer (LLC) and the Media access control
layer (MAC). The data-link layers deal with protocols that works mainly with
the mac address, like ARP (Address resolution protocol) and PPP (Point-to-point
protocol). Specified by the iso, this is
the layer that should also manage flow control via CSMA (Carrier sense multiple
access), where in reality most of this process happens on a higher level of the
OSI. A switch is an example of a device that runs at the layer 2.
Network
This is the
layer that will take care of routing and forwarding of the packet. This is also
the layer that implements TCP and UDP protocols. A router is an example of a device which
operates at the layer 3.
Transport
On the
transport layer 4 is where the flow control and reliability of the transmission
happens. As packets can be lost in the transport due to collisions and network
congestion, the reliability is accomplished either by ACKs or checksums and requests
a packet to be resent.
The
congestion control is accomplished by CSMA which stands for Carrier sense
multiple access. There is two principal way for CSMA to operates which are CA
(Collision Avoidance) used mainly for wireless network. The other one being CD
(Collision Detection) used for wired networks.
Session
This layer
establishes, manages and closes sessions for the process and applications. This layer has some common tunneling protocols
like L2TP (Layer 2 tunneling protocol) and L2F (Layer 2 forwarding protocol).
Some authentication protocols like PAP (Password authentication protocol) are
present at the session layer 5.
Presentation
The
presentation layer is where information is formatted following different
standards. This is a translation layer that is responsible for delivery and formatting
the information from the application layer. Common file formats like JPEG and
PNG are part of this layer. Note that TLS, which supersedes the SSL protocol,
is implemented at the presentation layer while SSL operates at the session
layer.
Application
This layer
is used for all communication protocols. This is where the most common
protocols reside, FTP, HTTP, SMTP and POP3 operates at this layer to name a
few.
