Transcript OSI Model - Bryan Marshall

OSI Model
CBIS 3213 – Intro to IT
OSI Model
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Theoretical
Designed in 1983
Standardized
Reduced proprietary products
• Open Systems Interconnection (OSI) by International Organization for
Standardization (ISO)
• 7 Layers
• Breaks down communication process
Overview of the OSI Model
Functions
Protocols
Function
Data formatting, encryption, and data compression.
Protocols
Function
Protocols
Digital storage media command and control
(DSM-CC) is a toolkit for developing control
channels associated with MPEG-1 and MPEG-2
streams.
Function
Notes
1. Segmentation is the process of breaking down the larger PDU into smaller
units known as ‘segments’.
2. Reassembly is the process of reconstructing the data packets and moving
them back up the OSI model.
3. Sequencing is putting an ID on each segment to know where the data
begins and ends.
4. Connection (TCP) vs. Connectionless (UDP) in a connection oriented
protocol the Transport layer maintains a connection the entire time with
the other host.
5. Connection oriented protocols also do error checking. How would it be if
you emailed yourself a picture and only got half the picture?
Protocols
Function
Notes 1. Fragmentation, like segmentation, breaks down the TCP segments into the
size required by the network. Segmentation is the preferred method.
2. Hardware at this layer include: Routers and some Layer 3 switches.
3. Addressing scheme is the IP Address.
Protocols
Function
Notes
1. At this point the PDU is known as a “Frame”
2. Error checking on Frame Sequence (Frame Check Sequence)
3. Also uses Cyclic Redundancy Check (CRC) to verify if the frame was sent
undamaged.
4. Addressing type: MAC or Media Access Control Address (Hard coded into
NIC – HEX number (00:60:80:8C:00:54) 0-F = basically 1-16
a. The first six digits = Manufacture “Block ID”
b. The second six digits = “Device ID” unique to every device in the world.
Protocols
Function
Protocols
Encapsulation
• Like placing a smaller envelope into a larger envelope.
• As the packets are formed from Layer 7 down to Layer 1 they are
encapsulated.
• As the packets move from Layer 1 up to Layer 7 the are de-encapsulated,
each layer stripping off its necessary information.
WHAT AM I?
• Segments (L4) become packets (L3) which become frames (L2)
• Frames becomes signal (L1) (bits) 001101001100