Our Last Class!!  summary  what does the future look like?

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

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

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 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

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

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 …

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)

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

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

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

 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

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!

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

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

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

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