1. Lesson Objectives Aims You should know about: 1.3.3:
Characteristics of networks and the importance of protocols and standards
The internet structure:
TCP/IP stack
DNS
Protocol Layering

2. Bit Rate
Bandwidth may also be expressed as a “bit rate”
This is usually a description of an applications requirements
Video streaming – high bit rate
Sending – low bit rate

3. Errors will occur in data transmission
Error Checking
Errors will occur in data transmission
There are three steps used to handle these errors:
Error detection/checking
Error correction (parity)
Re-sending of packets if necessary

4. A terrible way of detecting errors:
Echo Error detection
A terrible way of detecting errors:
Computer A sends a packet
Computer B receives it and sends a copy straight back
Computer A compares it to see if any errors have occurred
Problems:
Doubles traffic
Errors could be introduced on the way back!
Very inefficient

5. A calculation performed on a packet of data then added to the header
Checksum
A calculation performed on a packet of data then added to the header
Only a few bits long
Re-calculated on receipt
If the checksums don’t match – error
CRC – used in TCP/IP

6. Parity
Odd or even parity
Simply adding a single bit to the end of a byte of data
If a bit changes, it will no longer have parity
If two bits are changed, problem!
When used in blocks, can be used for error correction – see fantastic demo on the board now…

7. A set of rules stating exactly how a network should operate:
Protocols
A standard
A set of rules stating exactly how a network should operate:
Initiating communication
Sending data
Receiving data
Error detection method
Error correction method
All devices on a network must operate using the same standard

8. Selecting a protocol
The choice of protocol may be based on a number of aspects:
Physical aspects:
wired or wireless
serial or parallel data transmission
synchronous/asynchronous
copper or fibre optic
duplex mode
Logical aspects:
bit rate
error detection
packet size
ordering of packets
routing
compression and encryption
digital signatures

9. Things you need to know
What is a protocol?
What are some examples
How do they work?
Why are they in stacks?
What happens at each layer?

10. You know it’s bad when clip art happens…
The OSI model is NOT THE SAME as the TCP/IP stack and you must NOT confuse the two!!!

11. Task Starting at P209: Make notes on protocols Include diagrams
Make sure you know why they are stacks
Include information about what happens at each layer

12. Review/Success Criteria