EE450-U7-DataLinkLayer-Nazarian-Summer11

EE450-U7-DataLinkLayer-Nazarian-Summer11 - University of...

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Unformatted text preview: University of Southern California University of Southern California Viterbi School of Engineering Viterbi School of Engineering EE450 omputer Networks Computer Networks ata Link Layer Data Link Layer Shahin Nazarian Summer 2011 Data Link Layer (DLL) – a Link to Link Protocol • Every layer provides a set of services and provides it to the layer it _____ it • DLL (Layer 2) is a link-to-link basis (not end-to-end basis) protocol • Receiver side needs to synch frame (to know where it starts where it nds ) ceiver the other side of ends.) Receiver is the other side of the link • Physical layer transmits the bit and makes sure no duplicate or missing bit exists, but DLL handles the errors (caused by noise or signal Shahin Nazarian/EE450/Summer 2011 attenuation) 2 Where Is The Link Layer (LL) Implemented? • LL is implemented in each and every node • uch of LL controller’s functionality Example: host link layer Much of LL controller s functionality is implemented in hardware • LL is implemented in “adaptor” (aka r host schematic application transport Network Interface Card or ____ card) • E.g., Ethernet card (Intel’s 254x controller) PCM IA cpu memory host us network link 8254x controller), PCM-CIA card (plug-in to PC’s PCI card slot), 802.11 card (Atheros R5006) controller physical transmission bus (e.g., PCI) link physical AR5006) • Implements ___, Physical layer • Attaches into node’s system buses network adapter card (aka network Interface card) Shahin Nazarian/EE450/Summer 2011 • LL is a combination of hardware, software, and firmware 3 Some DLL Services 1. 1. Framing Framing • Frame _____________ , adding header and trailer and ncapsulating acket into frame encapsulating packet into frame 2. 2. Error Error detection detection, done by the receiver node, using parity checks, FCS FCS ( Frame ______ _______ Frame ______ _______ ,) etc. rr r c ntr l rr r c ntr l ne by receiver n de usin ne f the f ll win 3. 3. Error control, Error control, done by receiver node, using one of the following (note that the transport layer _____________ error correction) • Drop the Frame – Receiver simply drops the frame • _____ _____ ( Automatic Repeat Automatic Repeat reQuest reQuest ) protocols • rror correction Error correction 4. 4. Flow Flow control control (to prevent buffer overflow at the receiver, i.e., to ensure the receiver is not ___________ by the sender) Shahin Nazarian/EE450/Summer 2011 • Stop & Wait • Sliding Sliding _______ Protocol _______ Protocol 4 Error Control, Flow Control Error Control Error Control • 1 st technique [simplest approach]: In case error is etected receiver will drop the frame so automatically detected, receiver will drop the frame. so automatically packet is dropped as well • 2 nd technique: Receiver will request from the sender (Note: not the end node, but the node on the other side of the link) to retransmit using ARQ • rd chnique Receiver is not only able to detect the 3 technique: Receiver is not only able to detect the...
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This note was uploaded on 08/27/2011 for the course EE 450 taught by Professor Zahid during the Summer '06 term at USC.

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EE450-U7-DataLinkLayer-Nazarian-Summer11 - University of...

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