Session layer, Presentation Layer

1. Upper OSI Layers
DESEAR, HYACINTH
GALINO, JENNY

2. Session Layer

3. Responsibilities of the session layer
 Dialog control
 Synchronization
 Activity management
 Exception handling

4. Dialog Control
 COMMUNICATION
BETWEEN TWO
PROCESSES
 DECIDES WHOSE TURN IT
IS TO TALK
 IMPLEMENTED THROUGH
THE USE OF A DATA
TOKEN

5. Dialog Control

6. Synchronization
 ALLOWS A PROCESS TO
ADD CHECKPOINTS TO A
STREAM OF DATA
 ACHIEVED THROUGH THE
USE OF SEQUENCE
NUMBERS
 MAJOR AND MINOR
SYNCHRONIZATION
POINTS

7. Synchronization

8. Activity
Management
 IDENTIFIES WHERE DATA
STARTS AND ENDS
 DIVIDES DATA STREAM
INTO ACTIVITIES

9. Exception
Handling
 A GENERAL PURPOSE
MECHANISM FOR
REPORTING ERRORS

10. Session-layer protocols
 Point-to-Point Tunneling Protocol
(PPTP)
 Remote Procedure Call Protocol
(RPC)
 Real-time Transport Control
Protocol (RTCP)

11. Presentation Layer

12. Responsibilities of the presentation
layer
 Translation
 Encryption
 Compression

13. Translation
 INFORMATION IS
CHANGED TO BIT
STREAMS BEFORE IT IS
TRANSMITTED.
 RESPONSIBLE FOR
INTEROPERABILITY
BETWEEN DIFFERENT
ENCODING METHODS.
 MUST BE ABLE TO
TRANSLATE BETWEEN
MULTIPLE FORMATS BY
USING A COMMON
FORMAT

14. Common translation formats
 ASCII
 Binary
 EBCDIC
sample:
ASCII to binary

15. Encryption
 TO ENSURE PRIVACY OF
SENSITIVE INFORMATION
 TRANSFORMS ORIGINAL
INFORMATION TO OTHER
FORM BEFORE SENDING
IT OUT OVER THE
NETWORK. ACHIEVED BY
CRYPTOGRAPHY
 DECRYPTION IS THE
REVERSE OF
ENCRYPTION IT
TRANSFORMS THE
DECRYPTED
INFORMATION TO ITS
ORIGINAL READABLE
FORM

16. Sample forms of cryptography
 Microdots
 Merging words with images
 Ciphertext

17. Compression
 REPRESENT AN
INFORMATION SOURCE
AS ACCURATELY AS
POSSIBLE USING THE
FEWEST NUMBER OF
BITS
 COMPRESSING DATA
REDUCED STORAGE
AND/OR
COMMUNICATION COSTS
 IMPORTANT IN AREAS OF
DATA TRANSMISSION AND
DATA STORAGE SUCH AS
TEXT, AUDIO AND VIDEO

18. Why compression is important
 Reduced size of file to half is
equivalent to doubling the
capacity of the storage medium
 It becomes feasible to store data
at a higher, thus faster, level of
the storage hierarchy.

19. Why compression is important
 It reduce the load on the
input/output channels of the
computer system

20. Presentation Layer Protocols
 Apple Filing Protocol (AFP)
 External Data Representation
(XDR)
 X.25

21. That’s all folks!