54 lines
2.0 KiB
Markdown
54 lines
2.0 KiB
Markdown
# 2. Data link Layer
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The Data Link Layer is responsible for handling the data transfer between two devices on the **same** network. (so a bit like the Network Layer)
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The Data Link Layer also splits up packets into smaller chunks called a frame. The reverse happens on the receiving device (reassembling frames into packets).
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Like the Network Layer the Data Link Layer is also responsible for flow control and error checking.
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## Error Detection
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Transmissions are not always error free. In case of an error, it should be detected and the message should be re transmitted (whenever possible)
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Detecting errors are handled by different algorithms:
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- Parity bits
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- CRC
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## Data Framing
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Data is split up in smaller chunks called frames. For each frame we add some extra data:
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- Who is sender?
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- Who is receiver?
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- Length of chunk
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- Type of chunk (normal message, error message, control message)
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- Error checking values (ex. CRC code)
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- Data and metadata are put in single message called frame
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## Ethernet Protocol
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Ethernet is a protocol used at the data link layer of wired networks.
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Ethernet uses specific hardware addresses to identify hosts on a network.
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These 6-byte-integer addresses are names Medium Access Control (MAC Address)
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Ethernet frame has the following format:
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![[ethernet-frame.png]]
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## Wireless networks
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Wireless networks do not use a physical medium for data transmission. The data is send through radio waves.
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- Each member of a wireless network is called a station.
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Networks are implemented in different sizes:
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- Wireless local area networks (WLAN)
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- Wireless Metropolitan Area Networks (WMAN)
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- Wireless Wide Area Networks (WWAN)
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### BSS Network
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A BSS is a network with a specific station called Access Point.
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All transmissions from a station to another are trough the Access Point.
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Access Points also connect the network (BSS) other networks, hence the name internet.
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### AD-HOC Networks
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AD-HOC networks do not have a central node (access point).
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Every station can send data directly to a other station. |