1. Application layer is responsible for identifying
and establishing the availability of desired
communication partner and verifying sufficient
resources exist for communication.
2. Some of the important application layer
protocols are: WWW, SMTP, FTP, etc.
1. This layer is responsible for presenting
the data in standard formats.
2. This layer is responsible for data compression,
decompression, encryption, and decryption.
3. Some Presentation Layer standards are:
JPEG, MPEG, MIDI, PICT, Quick Time, TIFF.
1. Session Layer is responsible for co-coordinating
communication between systems/nodes.
2. The Session Layer: The following are some
of the session layer protocols and interfaces:
a) Network File System (NFS), SQL, RPC (Remote
Procedure Call), X-Windows, ASP, DNA SCP.
1. The Transport Layer is responsible for
multiplexing upper-layer applications, session
establishment, and tearing-down of virtual circuits.
2. This layer is responsible for flow control,
to maintain data integrity.
1. There can be several paths to send a packet
from a given source to a destination. The primary
responsibility of Network layer is to send packets
from the source network to the destination network
using a per-determined routing methods.
2. Routers work at Network layer.
Data Link Layer
1. Data Link Layer is layer 2 of OSI reference
model. This layer is divided into two sub-layers
A. Logical Link Control (LLC) sub-layer:
It handles error control, flow control,
framing, and MAC sub-layer addressing.
B. Media Access Control (MAC) sub-layer:
It is the lower of the two sub-layers of
the Data Link layer. MAC sub-layer handles
access to shared media, such a Token passing
1. The actual flow of signals take place
through Physical layer. At Physical layer, the
interface between the DTE and DCE is determined.
The following are some of the standard interfaces
are defined at Physical layer: EIA/TIA-232,
EIA/TIA 449,V.24,V.35,X.21,G.703,HSSI (High
Speed Serial Interface).