Link Layer (R3)

Link Layer (R3) - CSCI 232 - Computer Networking Link Layer...

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CSCI 232 - Computer Networking Link Layer George Blankenship 1 Link Layer George Blankenship 1 CSCI 232 Computer Networking: Link Layer George Blankenship Link Layer George Blankenship 2 Lesson Outline • Concepts – Protocol properties –F l ow c o n t r o l – Error control • Non-shared media – General principles – HDLC • Shared Media – General principles –W i r e d LAN • 802.3 and 802.5 – Wireless LAN • 802.11 and 802.15 – Wide area access • Frame relay Link Layer George Blankenship 3 Protocol perspective • Virtual connection is from link layer to link layer – link layer hides physical layer from service requestors (network layer) – encodes messages for peer link layer • Actual connection is from physical layer to physical layer – service request to physical layer sends message •Concepts –Protocol –Flow –Error –Control •Non-shared •Shared
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CSCI 232 - Computer Networking Link Layer George Blankenship 2 Link Layer George Blankenship 4 Message Movement System 1 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Service Interface Real Interface System 2 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Service Interface Real Interface Real Interface Virtual Interface •Concepts –Protocol –Flow –Error –Control •Non-shared •Shared Link Layer George Blankenship 5 Basic Properties • Flow Control – Pace the flow to the speed of the receiver – Maximize the media utilization • Error Detection – Recognize traffic with errors • Error Control – Recover from traffic with errors •Concepts –Protocol –Flow –Error –Control •Non-shared •Shared Link Layer George Blankenship 6 Flow Control • Message can only be sent with permission – receiver issues permission when able to receive – sender must hold message until permitted • Unbuffered flow control – send, then wait for permission • Buffered flow control – receiver issues permission for n messages – sender may send n, then waits •Concepts –Protocol –Flow –Error –Control •Non-shared •Shared
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CSCI 232 - Computer Networking Link Layer George Blankenship 3 Link Layer George Blankenship 7 Probability of Error •P b (BER): probability that a bit will be received inverted 1 : Probability that a PDU of size F will not be received in error P 1 = (1-P b ) F (BER=10 -6 , P 1 =.999) 2 : Probability that a PDU will be received with undetected error P 2 = 1-P 1 (P 2 =10 -3 , 1 of 1000) •Concepts –Protocol –Flow –Error –Control •Non-shared •Shared Link Layer George Blankenship 8 Types of Error • An error occurs when a bit is altered between transmission and reception • Single bit errors – One bit altered – Adjacent bits not affected – White noise • Burst errors –L e n g t h B – Contiguous sequence of B bits in which first last and any number of intermediate bits in error – Impulse noise – Fading in wireless – Effect greater at higher data rates •Concepts –Protocol –Flow –Error –Control •Non-shared •Shared Link Layer
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This note was uploaded on 09/03/2010 for the course CS 232 taught by Professor Susan during the Summer '09 term at GWU.

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Link Layer (R3) - CSCI 232 - Computer Networking Link Layer...

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