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Our Last Class!!

Our Last Class!!. summary what does the future look like?. Summary: let's follow a packet. Summary: let's follow a packet. Application user enters URL into WWW browser URL may be text, audio, video with different requirements

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Our Last Class!!

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  1. Our Last Class!! • summary • what does the future look like?

  2. Summary: let's follow a packet

  3. Summary: let's follow a packet Application • user enters URL into WWW browser • URL may be text, audio, video with different requirements • browser determines host names, uses DNS to get server's IP address API • browser (client) creates stream socket, socket() • client calls connect(), server port 80 • upon return from connect(), will call rcvfrom() to read returned data

  4. Summary (cont.) Transport Layer • connect() call causes TCP connection to be established. • choose initial sequence number • generate SYN packet, server IP address, port 80 • TCP forms packet, computes checksum • TCP calls IP (no congestion control on SYN), passing SYN packet and IP address info

  5. Summary (cont.) Network Layer • adds IP source, destination address in IP packet • IP forwarding consults routing table • routing table computed by RIP, or OSPF intradomain protocol • routing table gives IP address of, and local interface to get to, next router (i.e., on its LAN), R, on route to destination • runs ARP to get 802.3 physical address corresponding to R1's IP address • ARP will generate Ethernet broadcast packet on LAN, requesting R1 to reply with its phys address • R1 replies with physical address

  6. Summary (cont.) Data Link Layer • TCP SYN packet (inside IP packet), as payload in Ethernet packet sent onto LAN using Ethernet protocol • transparent bridge may be involved (not shown) Physical Layer • Ethernet packet transmitted at 10, or 100 Mbps

  7. Summary (cont.) At router R1 • physical layer receives Ethernet packet, passes it up • data link layer computes OK checksum, removes IP packet, passes up • network layer consults routing table • routing table was computed using BGP interdomain routing • passes IP packet down to data link layer …

  8. Summary (cont.) At Router R2 • DLC packet arrives from "net", passed up to network layer • network layer determines outgoing interface to get to host B • RIP or OSPF intradomain routing protocol computed tables • DLC Ethernet packet sent (R2 knew/learned B's physical layer address)

  9. Summary (cont.) At Host B • Ethernet packet arrives, checksum OK, pass up to IP • IP layer extracts TCP packet, demultiplexes up to TCP (note: not UDP packet) • TCP sees SYN packet • server must have previously opened socket and made accept(), else SYN dropped • TCP determines flow control window, chooses initial sequence # • sends SYNACK back

  10. Summary (cont). At Host A • SYNACK eventually received • send transport-level ACK to B • move to established state • return from connect() system call Epilogue • host A can now perform sendto() • host B (after receiving ACK) will perform rcvfrom() and will eventually receive http command and send response • will use TCP • congestion and flow control • R1, R2 and A, B (network layer and below) act exactly same with data as with SYN packet

  11. Gazing into the Crystal Ball General trends • ubiquity of communications • network-capable appliances (e.g., IP thermostat) • issues of scale important: billions of network-connected devices • mobility important : people move and need to communicate • multimedia important: it is how people communicate • increasing link rates, but bandwidth not free in near future • increased # "users" • increased access bandwidths • increased bandwidth requirements of enabled applications

  12. security critical concern • ubiquitous high bandwidth to home (ADSL, cable modems) a major driver for future • games, VR, education, information, entertainment • merger of networking and telephony • broadcast entertainment (TV), WWW, and ?? • agents, other technologies for dealing with large amounts of distributed, changing data

  13. The Very Last Note Page! • networking: will play a central role in all future computing systems • this course: • specific architectures, protocols, API's • fundamental issues: reliable data transfer, flow/congestion control, routing, multiple access, security • remember: you learned it HERE!

  14. Final Exam • similar to midterm • 5 problems • potpourri (all of course) • FSM for protocol • network layer • data link layer • security

  15. Network Layer • virtual circuit vs. datagram • two approaches to calculating routes • link state (OSPF) • distance vector (RIP, BGP) • intradomain, interdomain, hierarchical routing • broadcast/multicast routing • reverse path forwarding • core based trees • salient features of IP (v4, v6), ATM

  16. Data Link • functionality (framing, reliable communications, multiple access) • multiple access algorithms (Ethernet, ALOHA, slotted ALOHA, reservation, TDMA, token ring/bus,…) • advantages/disadvantages (low loads, high loads) • ARP • interconnected LANS, bridges

  17. security: • private/public key systems (DES, RSA) • authentication • digital signatures • key distribution • network management • functionality • SNMP, MIBs, … • QoS • issues • components

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