Data Link Layer Flashcards Preview

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Flashcards in Data Link Layer Deck (22):
0

Main idea

Provides means for exchanging data frames over a common media

Detect and possibly correct errors that may occur in physical layer (crc?)

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Main function 2

Controls how data is placed into medium via Mac and error detection techniques

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Network

Two or more devices connected by a common medium

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Sublayers

Upper sublayer = LLC (frames network layer packet, identifies network layer protocol)
Lower sublayer = MAC (addresses, marks beginning and end of frame)

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MAC depends on

Media sharing, topology

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MAC methods for share media

Controlled (deterministic; ex: token ring, fddi)
Contention (CSMA; transmit at any time)

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Full duplex

Receive, transmit simultaneously

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Half duplex

Receive, transmit one at a time

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Ethernet

CSMA/CD

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Wireless

CSMA/CA

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Physical topology

Actual arrangement of nodes an physical connections between them

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Logical topology

The way a network transfers frames from one nose to the next

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P2P

Two nodes directly connected; MAC method used by DLL determined by logical point to point; use of intermediate devices don't affect local topology

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Characteristics of multi access topology

Data from a node can be placed at any one time
Only node for which it is for process contents of frame
Typically uses CSMA/CD OR CSMA/CA

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Token passing (ring topology)

Each node receives a frame until it reaches its destination
Usually only one frame at a time is usually carried by the media

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Fragile environment

More controls, larger header and trailer

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Protected

Less controls; smaller header and trailer

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Physical addressing

Aka MAC address

Used to transport frame across shared local media from DLL

ONLY USED FOR LOCAL DELIVERY

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Error detection techniques

Cyclic redundancy check matches initial and received

Frame check sequence: DLL because this is where data is transferred across the media

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Encapsulation

Encapsulates packet by a header and trailer

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Header includes...

Start frame 8 bytes
Addressing DLL source dest address 12 bytes
Type of pdu in frame (what kind of data is being sent or length of frame) 2 bytes
Control
Priority/Qos

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Preamble

Used for synchronization; contains delimiter to mark end of the timing information