CO526 Distributed Systems and Networks
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State the name of each layer in the ISO seven-layer model
- Layer 7 - Application
- Layer 6 - Presentation
- Layer 5 - Session
- Layer 4 - Transport
- Layer 3 - Network
- Layer 2 - Data Link
- Layer 1 - Physical
Give some disadvantages of standardizing
- Standardizing when research is incomplete, thus leading to poor standards.
- Standards can be overly complex and thus restrictive on new people entering the market.
- Standards may be incomplete.
- Standards may become irrelevant as technology advances.
State the purpose of the Physical layer in ISO seven-layer network model.
Bit transmission across some sort of transmission meidum
State the purpose of the Data Link layer in ISO seven-layer network model.
Blocking bits together to control flow and checking that they arrived correctly
State the purpose of the Network layer in ISO seven-layer network model.
Routing blocks of bits through a network
State the purpose of the Transport layer in ISO seven-layer network model.
Receives the blocks at the destination (and passes them to the right application)
State the purpose of the Session layer in ISO seven-layer network model.
Synchronization and Dialogue control. Managing sessions between applications.
State the purpose of the Presentation layer in ISO seven-layer network model.
Syntax and semantics of the information. (Encrypting / Decrypting, Data representation)
State the purpose of the Application layer in ISO seven-layer network model.
Name the internet layers
- Application Layer
- Transport Layer
- Internet Protocol Layer
- Network Interface Layer
- Physical Net Layer
Which layers of the Intenet model correspond with that of the OSI seven-layer model.
- Internet Application - OSI Application
- Internet Application - OSI Presentation
- Internet Application - OSI Session
- Internet Transport - OSI Transport
- Internet Internet Protocol - OSI Network
- Internet Network Interface - OSI Data Link
- Internet Physical - OSI Physical
Why is layering (abstraction) a good idea?
- Focus on the individual processes
- Debugging and maintenance is easier
What is a protocol?
"A set of rules and regulations agreed by two parties in order to govern communication."
What is framing and why is it used?
It is where a raw bit stream is broken up into groups of bits (called frames). This is to enable error and flow control.
Data Link Protocol: What would be an unrestricted protocol?
A protocol whereby the sender could send frames as fast as it wanted. (Unrestricted send speed)
Data Link Protocol: What would be a restricted protocol?
- (Stop-and-wait protocol)
- Sender sends a frame and then waits for an acknowledgement (ACK)
- Receiver waits for a frame and then sends an acknowledgement (ACK) when it has received one.
Data Link Protocol: What is put in place to help tackle a noisy channel?
- Sender times out if it doesn't receive an acknowledgement (ACK). It will then re-send the same frame.
- We use sequence numbers so that the receiver can check that the expected frame has been received. The receiver then sends an acknowledgement (ACK) back to the sender.
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