MCSE : Security
18. The 7 layers of OSI model are:
1.
The Application Layer: Application layer is responsible for
identifying and establishing the availability of desired
communication partner and verifying sufficient resources exist for
communication. Some of the important application layer protocols
are: WWW, SMTP, FTP, etc.
2.
The Presentation Layer: This layer is responsible for presenting the
data in standard formats. This layer is responsible for data
compression, decompression, encryption, and decryption. Some
Presentation Layer standards are: JPEG, MPEG, MIDI, PICT, Quick
Time, TIFF.
3.
The Session Layer: Session Layer is responsible for co-ordinating
communication between systems/nodes. 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.
4.
The Transport Layer: The Transport Layer is responsible for
multiplexing upper-layer applications, session establishment, and
tearing-down of virtual circuits. This layer is responsible for flow
control, to maintain data integrity.
5.
The Network Layer: 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 pre-determined routing methods. Routers
work at Network layer.
6.
The Data Link Layer:
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.
B.
Media Access Control (MAC) sub-layer.
The LLC sub-layer handles error control, flow control, framing, and
MAC sub-layer addressing.
The MAC sub-layer 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 or Ethernet.
7.
Physical Layer: 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).
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