describe the structure of a packet and what are they
- Packet header:
- destination IP address
- packet number
- sender’s address
- payload - actual data being transmitted
- trailer - marks end of packet
Describe the process of packet switching
- Data broken down into packets
- Each path given a sequence number and sent on its way
- Each packet takes a different route depending on quickest + cheapest route at the time
- Routers control packet’s route
- Packets may arrive out of order –> Once last packet arrives : sequence number used to put in correct order –> data reconstructed correctly
what is packet switching
controls the sending and receiving of packets across a network or the Internet
what is simplex transmission
- Data bits sent one at a time down one cable
what is parallel transmission
several bits sent simultaneously in both directions
what is the disadvantage with serial transmission
lower transmission speed
what is the advantage with serial transmission
- lower interference
- more reliable over longer distances
- smaller, simpler, cheaper connections to produce
what is the disadvantage with parallel transmission
- interference issues between wires
- data corruption can occur over long distances
- data bits travelling parallel to each other can move at different speeds causing then to arrive out of sync = skewing
what is the advantage with parallel transmission
- very fast data transfer
- can send data in both directions at the same time
what is serial transmission used with
USB (Universal Serial Bus) interface
give the advantages of using an USB
- Do not suffer from skew and crosstalk - unlike parallel
- is compatible to lots of difference devices - universal industrial standard
- Easy to set up - cant be inserted the wrong way round - convenient, robust
- Devices are automatically detected and drivers are automatically loaded for communication
- supports several transmission rates
what type of transmission in used in a USB
serial
name 3 drawbacks of the USB
- Can be no longer than 5 m
- Small + Easy to loose
- Cannot be used in motherboard can only use parallels because not fast enough
what is a USB and how is it used to transmit data
USB stands for Universal Serial Bus and this is a predominately a serial wire which transmits data on bit at a time from one device to another.
- It is easy, fast and compatible to mostly all devices as it is the universal standard.
- It does not suffer from crosstalk or skew so it is relatively fast to transmit data.
what is skew
- Each wire in a parallel cable has slightly different properties
- Signals arrive a slightly different times
- The receiver must wait until all lines are received until the next set of bits may be sent
when does crosstalk occur
- Crosstalk may occur when a signal on one line creates a disturbance in another line
- This may cause a bit to be reversed in a parallel line
- The longer a cable is the more chance of interference
- Bits in adjacent + neighbouring wire in parallel transmission flips from 0 to 1 or 1 to 0 due a disturbance
how to reduce skew
Transmission needs to be over very short distances
simplex transmission =
data travels in one direction only down a single cable
Half - duplex transmission
data can travel in both directions along a single cable, but not simultaneously
Full -duplex transmission =
data can travel in both directions simultaneously using 2 communication channels
where is simplex transmission used
sending data from a computer to a monitor
where is half-duplex transmission used
a printer cable which waits for the data to be received before sending back a ‘low ink’ message
where is full-duplex transmission used
- Networking for Internet cables can send and receive data at the same time
what are the advantages of simplex transmission
- Cheap as only one wire is used
- It has no traffic issues.
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PAPER 2 - Algorithms, Programming, Logic46
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Data Packaging9
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Data transmission17
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Error Detection15
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Data representation - Number systems (paper 1)35
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MIN and MAX programs5
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Data representation - Text, sound, images and compression (paper 1)32
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Data Transmission32
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Data Transmission - Error Detection, Check Digits, Encryption27
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Hardware - Computer Architecture30
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Hardware - CPU Performance22
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Hardware - Input + Output devices43
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Data Storage37
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Network Hardware7
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Programming language, translators, IDEs11
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The Internet and the World Wide Web12
