ICC Module 3 Lesson 4 – Networking 1 / 16 © 2015 Ph. Janson Information, Computing & Communication Networking – Clip 3 – Protocol encapsulation School.

PowerPoint Presentation

Networking Clip 3 Protocol encapsulationSchool of Computer Science & CommunicationsPh. Janson, W. Zwaenepoel

Information, Computing & CommunicationICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThis video clip is part of the E.P.F.L. introductory course on Information, Computing, and Communication.It is the third in a set of video clips on computer communication & networking.

1OutlineComputer communication basicsClip 1 Protocols & messagesClip 2 Protocol layersClip 3 Protocol encapsulationClip 4 Switching

Internet basicsClip 5 Internet topology & interfacesClip 6 Internet addressing & routingClip 7 Internet route calculationClip 8 Internet protocols

Computer network paradigmsClip 9 Network paradigmsIntro clipPrevious clipNext clip

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonIt discusses the fundamental notion of protocol encapsulation

2Encapsulation = embedding / nesting of protocolsEach protocol in its own layerEach protocol with its own header

Upon sending: protocol encapsulation

Protocol layer N:Takes messages coming from layer N+1 (incl. headers of layers N+1, N+2, )Tacks its own layer N protocol header in front of themAnd Passes the resulting messages to layer N-1 if N>1Or transmits them to the network if N=1

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonIn the first video clip of this series we saw that a protocol involves a number of functions that require that each protocol message carry corresponding protocol bits in a header.In the second video clip just preceding this one we saw that, while communication happened logically / conceptually between peer protocol layer implementations on communicating computers, practically / physically such communication is actually relayed through lower protocol layers and across the (only) real physical-layer connectionsbetween pairs of adjacent computers and routers through the entire network.

The legitimate question to then ask is how does this relaying through lower layers happen?The answer differs on the sending and receiving sides.-On the sending side, protocol layer NTakes any message coming from protocol layer N+1, incl. its layer N+1 headerTacks in front of it its own layer N headerAnd passes the resulting message down to layer N-1 or across the physical-layer connection if N=13Encapsulation on the sending sideProgram ApplicationTransportNetworkLinkPhysicaldata

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThus when a program wants to send data to a peer program on another computer on the other side of a network,4Encapsulation on the sending sidedatadatah5Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonIt passes that data to the proper application protocol layer, which prefixes the data with the corresponding application protocol header (h5 in this example)5Encapsulation on the sending sidedatadatadatah5h5h4Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe application protocol layer in turn passes the resulting message to the transport protocol, which prefixes it with its own transport protocol header (h4 in this example)

6Encapsulation on the sending sidedatadatadatadatah5h5h5h4h4h3Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe transport protocol layer in turn passes the resulting message to the network protocol, which prefixes it with its own network protocol header (h3 in this example)

7Encapsulation on the sending sidedatadatadatadatadatah5h5h5h5h4h4h4h3h3h2Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe network protocol layer in turn passes the resulting message to the link protocol, which prefixes it with its own link protocol header (h2 in this example)8Encapsulation on the sending sidedatadatadatadatadatadatah5h5h5h5h5h4h4h4h4h3h3h3h2h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe link protocol layer in turn passes the resulting message to the physical-layer protocol, which prefixes it with its own physical protocol header (h1 in this example)and the physical protocol layer finally sends the resulting message across the actual physical wire or wireless medium onto the adjacent device (router or receiving computer) on the network, on its way to the designated receiving computer.

9Encapsulation = embedding / nesting of protocolsEach protocol in its own layerEach protocol with its own header

Upon receiving: protocol decapsulation

Protocol layer N:Receives messages From the network if N=1From layer N-1 if N>1Interprets and removes its own layer N protocol headerAnd passes the resulting messages to layer N+1 (incl. headers for layers N+1, N+2, )

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonOn the receiving side, the process is simply reversed.Protocol layer NReceives a message from layer N-1 or over the physical-layer connection if N=1Processes the incoming layer N protocol header and removes it from the messageAnd pushes it up to protocol layer N+1 together with the still-attached layer N+1 header

10Decapsulation on the receiving sidedatah5h4h3h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThus when a message arrives through a physical wire or medium with its five attached headers

11Decapsulation on the receiving sidedatadatah5h5h4h4h3h3h2h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe physical protocol layer on the receiving side processes and removes its own physical layer header (h1) and passes the remainder of the message to the link layer.12Decapsulation on the receiving sidedatadatadatah5h5h5h4h4h4h3h3h3h2h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe link layer processes and removes its own link layer header (h2) and passes the remainder of the message to the network layer.

13Decapsulation on the receiving sidedatadatadatadatah5h5h5h5h4h4h4h4h3h3h3h2h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe network layer processes and removes its own network layer header (h3) and passes the remainder of the message to the transport layer.

14Decapsulation on the receiving sidedatadatadatadatadatah5h5h5h5h5h4h4h4h4h3h3h3h2h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonThe transport layer processes and removes its own transport layer header (h4) and passes the remainder of the message to the application layer.

15Decapsulation on the receiving sidedatadatadatadatadatadatah5h5h5h5h5h4h4h4h4h3h3h3h2h2h1Program ApplicationTransportNetworkLinkPhysical

ICC Module 3 Lesson 4 Networking# / 16 2015 Ph. JansonAnd the application layer processes and removes its own application header (h5) and delivers the actual data to the destination program on the receiving computer.

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