Network Architecture Models: Layered CommunicationsLearning objectiveHybrid TCP/IP-OSI ModelLayered CommunicationsLayer Cooperation on the User PCSlide 6EncapsulationSlide 8Slide 9Slide 10Slide 11Slide 12Slide 13TCP segmentTCP SegmentUDP SegmentIP PacketLayer Cooperation on the WebserverSlide 19Slide 20Hybrid TCP/IP and Windows LayeringWindows Architecture implementationSummary QuestionsSummary Questions (cont.)Additional slidesThe First RouterLayer Cooperation on the First RouterSlide 28Slide 29Slide 30Slide 31Network Architecture Models: Layered CommunicationsSchool of BusinessEastern Illinois University © Abdou Illia, Fall 2014(September 10, 2014 )Encapsulation and De-encapsulation2Learning objectiveUnderstand the principles of layered communications3Hybrid TCP/IP-OSI ModelLayers Sample protocols for Web accessApplication HTTPTransport TCPInternet IPData Link Ethernet, PPPPhysical Ethernet, Modem standards, Telephone standards4Layered CommunicationsApplication programs on different computers cannot communicate directly–There is no direct connection between them!–They need to use an indirect communication systemBrowserBrowserTransTransIntIntDLDLPhyPhyUser PCWeb AppWeb AppTransTransIntIntDLDLPhyPhyWebserverHTTP RequestHTTP Request5Layer Cooperation on the User PCApplication layer passes HTTP-request to Transport layer ApplicationApplicationTransportTransportInternetInternetData LinkData LinkHTTP RequestHTTP RequestPhysicalUser PC6Layer Cooperation on the User PCTransport layer creates a TCP segment–HTTP request is put in the data field–A TCP header is addedSo, Transport layer “encapsulates” HTTP request within a TCP segmentHTTP RequestHTTP RequestTCP-HTCP-HTCP SegmentDataFieldTCPHeader7EncapsulationEncapsulation is:–Embedding a received message in the data field of a new messageExample: TCP encapsulates HTTP request in the data field of a new massage called TCP SegmentHTTP RequestHTTP RequestTCP-HTCP-HTCP SegmentDataFieldTCPHeader8Layer Cooperation on the User PCTransport layer passes the TCP segment down to the Internet layerApplicationApplicationTransportTransportInternetInternetData LinkData LinkTCP segmentTCP segmentPhysicalUser PC9Layer Cooperation on the User PCInternet Layer encapsulates TCP Segment within an IP packet–An IP packet to deliver a TCP segment has a TCP segment in its data fieldTCP segmentTCP segmentIP-HIP-HIP PacketDataFieldIPHeader10Layer Cooperation on the User PCThe Internet layer passes the IP packet to the Data Link layer–Internet layer messages are called packetsApplicationApplicationTransportTransportInternetInternetData LinkData LinkIP packetIP packetPhysicalUser PC11Layer Cooperation on the User PCData Link Layer encapsulates IP Packet within a PPP Frame–Data Link layer messages are called frames–PPP frame has IP packet in data field–PPP frame has a PPP Trailer and a PPP HeaderPPP Frame Encapsulating an IP PacketPPP-TPPP-TIP packetIP packetPPP-HPPP-H12Layer Cooperation on the User PCThe Data Link layer passes the PPP frame to the Physical layer, which delivers it to the Physical layer on the first router, one bit at a time (no message at the Physical layer)ApplicationApplicationTransportTransportInternetInternetData LinkData LinkPhysical (10110 …)User PCPPP framePPP frameTo firstrouter13PPP-TPPP-TLayer Cooperation on the User PCRecap: Adding Headers and Trailers:ApplicationApplicationTransportTransportInternetInternetData LinkData LinkHTTP req.HTTP req.PhysicalUser PCHTTP req.HTTP req.TCP-HTCP-HHTTP req.HTTP req.TCP-HTCP-HIP-HIP-HHTTP req.HTTP req.TCP-HTCP-HIP-HIP-HPPP-HPPP-H14TCP segmentSource Port # and Destination Port #:–Contain reference # of application programs at both ends–Used (together with IP address) to identify the application programSequence Number:–Indicates position of this segment within sequence of segments–Used to perform error recovery (e.g. loss of continuity)TCP message has a Flags Field (three of which widely used)–SYN bit set to 1 to request a connection–ACK bit set to 1 to acknowledge a received TCP segment–FIN bit set to 1 to inform of a connection closureSource Port # (16) Destination Port # (16)Sequence Number (32 bits)Acknowledgement Number (32 bits)Hdr Len(4)Flags (6) Window Size (16)Options (if any) PADBit 0 Bit 31Reserved (6)TCP Checksum (16) Urgent Pointer (16)Data FieldTCP Header15TCP SegmentTransmission Control Protocol. Src Port http (80). Dst Port 1958). Seq: 3043958669. Ack: 937013559. Len:0Source port: http (80)Destination port: 1958 (1958)Sequence number: 3043958669Acknowledgment number: 937013559header length: 24 bytes Flags_0xx0012 (SYN, ACK)Ө0………. = Congestion window reduced (CWR): not set..0…….. = ECN-Echo: not set…0……..= Urgent: Not set….1…….= Acknowledgment: Set……0…..= Push: Not set…….0….= Reset: Not set……..1…= Syn: Set………0..= Fin: Not setWindow size: 5840Checksum: 0x206a (correct) Options: (4 bytesӨMaximum segment size: 1460 byte16UDP SegmentSource Port Destination PortDataDean (2004:161)Length ChecksumData0 16 3117IP PacketVersionDifferentiatedservicesIdentificationTime to liveHeaderlengthReservedRSTACKPSHURGSYNFINSliding-window sizeOptions PaddingDataIHL Total lengthFlags Fragment offsetProtocol Header checksumSource IP addressDestination IP addressContains:–IP version used–Source IP address –Destination IP address, etc.18Layer Cooperation on the WebserverSituation reverse to Situation on User PC (De-encapsulation)ApplicationApplicationTransportTransportInternetInternetData LinkData LinkPhysicalUser PC Webserver19Layer Cooperation on the WebserverData Link layer processes the DL-Frame’s header and trailer to deencapsulate the IP packetData Link layer passes the IP packet to the Internet layerApplicationApplicationTransportTransportInternetInternetData LinkData LinkIP-PacketIP-PacketDL-Frame containing IP packet in data fieldDL-Frame containing IP packet in data fieldPhysicalFinal Router Webserver20Layer Cooperation on the WebserverSuccessively pass up layer messages–Other layers pass successive data fields (containing next-lower layer messages) up to the next-higher layerApplicationApplicationTransportTransportInternetInternetData LinkData LinkPhysicalFinal Router WebserverPPP-TPPP-THTTP req.HTTP req.HTTP req.HTTP req.TCP-HTCP-HHTTP req.HTTP req.TCP-HTCP-HIP-HIP-HHTTP req.HTTP req.TCP-HTCP-HIP-HIP-HPPP-HPPP-HIP PacketTCPsegmentHTTP