12_MPLS_spring10

12_MPLS_spring10 - Multi-Protocol Label Switching (MPLS)...

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TCP/IP Essentials EL5373 Supplement Topic EL5373 Supplement Topic Multi Multi - - Protocol Label Protocol Label Switching (MPLS) Switching (MPLS) Spring 2010
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Polytechnic Institute of NYU Slide 2 zjzhao Multi-Protocol Label Switching (MPLS) •MPLS is a virtual-circuit packet switching technology overlaid on the datagram packet-switched Internet. •Attach short labels (20 bits) to network packets which describe how to forward them through the network. –Located after the layer two header and before the IP header. –Used to make forwarding decisions –Independent of any routing protocol. •Provides a mechanism for engineering network traffic patterns.
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Polytechnic Institute of NYU Slide 3 zjzhao Packet Switching vs. Circuit Switching Packet switching • Data traffic divided into packets – Each packet contains its own header (with address) – Packets sent separately through the network • Destination reconstructs the message Analogy example: sending a letter through postal system Circuit switching • Source first establishes a connection to the destination – Each switch on the path may reserve bandwidth • Source ends data over the connection – No destination address, since switches know the path • Source tears down the connection when done Analogy example: voice conversation on telephone network
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Polytechnic Institute of NYU Slide 4 zjzhao Virtual Circuits Hybrid of packet and circuit switching • Logical circuit between a source and destination • Packets from different VCs multiplex on a link Virtual Circuit Identifier (VC ID) • Source set-up: establish path for the VC • Switch: mapping VC ID to an outgoing link • Packet: fixed length label in the header 1 2 Link 7 Link 14 Link 8 1 Æ 14 2 Æ 8 1 Æ 7 2 Æ 7
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Polytechnic Institute of NYU Slide 5 zjzhao Virtual Circuits Similar to IP Datagrams Data divided in to packets • Sender divides the data into packets • Packet has an address (e.g., IP address or VC ID) Store-and-forward transmission • Multiple packets may arrive at once • Need buffer space for temporary storage Multiplexing on a link • No reservations: statistical multiplexing – Packets are interleaved without a fixed pattern • Reservations: resources for group of packets – Guarantees to get a certain number of “slots”
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Slide 6 zjzhao Virtual Circuits Differ from IP Datagrams Forwarding look-up • Virtual circuits: fixed-length connection id • IP datagrams: destination IP address Initiating data transmission • Virtual circuits: must signal along the path • IP datagrams: just start sending packets Router state • Virtual circuits: routers know about connections • IP datagrams: no state, easier failure recovery Quality of service
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This note was uploaded on 11/02/2010 for the course EL 537 taught by Professor Zhaozhengxue during the Spring '10 term at NYU Poly.

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12_MPLS_spring10 - Multi-Protocol Label Switching (MPLS)...

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