OSI and TCP/IP Models
The OSI Reference Model
- Planned to be a protocol stack for use
- Reference & communication model
- Used for troubleshooting
- It divides a complex process into small and
realizable units
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| The OSI Reference Model |
Data Encapsulation:
The basic action of OSI
– Each layer responds services from superior layer
and issue services to the subordinate
– data moves into this seven layers to get the control
information
- Control informations are added in header & footer
- Headers and footer are fields that contain control
information
- Like post message
Each layer has its own PDU (Protocol Data Unit) which
contains different information
The PDU contains of a header and data field
Horizontal Connection
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| Horizontal Connection |
Encapsulation Words
Packet
– Naming data unit in each step
- The data traveling through the media
Frame
- In data link layer
Datagram
– In network layer
Segment
– In transport layer
– Sequence
- Collection of segments
Message
– In Application layer
Encapsulation
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| Encapsulation |
The difference between OSI and TCP/IP Models
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| OSI and TCP/IP Models |
TCP Packet Structure
TCP Source Port - Port of sending host
Destination Port – Port of End Point Destination
Sequence # – Sequence of Bytes transmitted
in a segment, required to verify that all bytes are
received
Acknowledgment Number – The sequence number
of the byte the local host expects to receive next
Data Length – Length of the TCP Segment
Flags – Specified what content is in the segment
Window – How much space is currently available in
the TCP window
Checksum – Verify that the Header is not corrupted
TCP Port
A TCP port provides a specific location for delivery of
TCP Segments. Port Numbers below 1024 are well-
known, and are assigned by:
Internet Assigned Numbers Authority (IANA)
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| TCP Port |
Well-Known ports
– For network applications
– Range
1-1023
Registered ports
– Range
1024 – 49151
– Can be either source or destination
– Used by organizations to register specific applications
such as IM application
Private ports
– Range
49152 through 65535
– Used as source ports, these ports can be used by any applications
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