lec-39 - What's Next. Data Link Layer Introduction and...

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22 Nov 2008  BITS C481 (Computer Networks) 1 What’s Next… Data Link Layer Introduction and services Error detection and correction Multiple access protocols Link-layer Addressing Ethernet Link-layer switches (Hub, Bridge and Switch) PPP and HDLC Link virtualization: ATM, MPLS
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22 Nov 2008  BITS C481 (Computer Networks) 2 Point to Point Data Link Control One sender, one receiver, one link: easier than broadcast link: No Media Access Control No need for explicit MAC addressing e.g., dialup link, ISDN line Popular point-to-point DLC protocols: PPP (point-to-point protocol) HDLC: High level data link control (Data link used to be considered “high layer” in protocol stack!
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22 Nov 2008  BITS C481 (Computer Networks) 3 PPP Design Requirements [RFC 1557] Packet framing: Encapsulation of network-layer datagram in data link frame Carry network layer data of any network layer protocol (not just IP) at same time Ability to demultiplex upwards Bit transparency: must carry any bit pattern in the data field Error detection (no correction) Connection liveness: detect, signal link failure to network layer Network layer address negotiation: endpoint can learn/ configure each other’s network address
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22 Nov 2008  BITS C481 (Computer Networks) 4 PPP non-requirements No error correction/recovery No flow control Out of order delivery OK No need to support multipoint links (e.g., polling) Error recovery, flow control, data re-ordering  all relegated to higher layers!
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22 Nov 2008  BITS C481 (Computer Networks) 5 PPP Data Frame Flag: delimiter (framing) Address: does nothing (only one option) Control: does nothing; in the future possible multiple control fields Protocol: upper layer protocol to which frame delivered (eg, PPP- LCP, IP, IPCP, etc) info: upper layer data being carried check: cyclic redundancy check for error detection
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22 Nov 2008  BITS C481 (Computer Networks) 6 Byte Stuffing “Data transparency” requirement: data field must be allowed to include flag pattern <01111110> Q: is received <01111110> data or flag?
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This note was uploaded on 07/20/2009 for the course CONPUTER S BITS C481 taught by Professor Prof.virendersinghshekhawat during the Fall '08 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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lec-39 - What's Next. Data Link Layer Introduction and...

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