Welcome to CS 334/534

1. Welcome to CS 334/534

2. “Fig 1.5” – An internet 4 LANs linked by a WAN

3. Comer Figure 1.1 – Growth of the Internet

4. 2.2 Two Approaches to Network Communication * circuit-switched networks(telephone) 3 phases: establish connection between end points use connection relinquish connection disadvantage: cost independent of use * packet-switched networks(post office) at source, data divided into packets packets individually sent from source to destination data reassembled at destination advantage: can share transport facilities \My Doc\cs\cs434\s04\circuit packet.doc

5. 2.4 Ethernet Technology Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)

7. 2.4.5 Properties of an Ethernet Ethernet was “designed to be” i.e. “classical” or “original” Ethernet ■ shared bus - shared bandwidth - only one station transmitting at a time - “half duplex” (station transmits XOR receives) ■ broadcast technology - all stations receive all messages ■ best-effort delivery ■ distributed access control - CSMA/CD

8. 2.4.8 Ethernet Hardware Addresses 6 bytes total - globally unique High-Order 3 bytes:assigned to manufacturer by IEEE Low-Order 3 bytes:serial number assigned by manufacturer Destination address as filter An Ethernet station receiving packet checks destination address ignores packet if not intended for this station

9. Ethernet Addresses – continued Types of Destination address An address can be used to specify ■ a single, specific station on this network (“unicast address”) ■ all stations on this network (“broadcast address”) ■ a subset of stations on this network (“multicast address”) Interface Modes of Operation ■ normal mode Interface processes only packets with destination * its own unicast address * the network broadcast address ■ promiscuous mode Interface process all received packets (including those addressed to other stations)

10. Figure 2.1 (with hub) Figure 2.2 Format of an Ethernet frame (packet)

14. 2.4.5 Properties of an Ethernet Ethernet was “designed to be” i.e. “classical” or “original” Ethernet ■ shared bus - shared bandwidth - only one station transmitting at a time - “half duplex” (station transmits XOR receives) ■ broadcast technology - all stations receive all messages ■ best-effort delivery ■ distributed access control - CSMA/CD

15. Properties of a “switched” Ethernet ■ not shared bus - point-to-point connections - not shared bandwidth - “full duplex” (station transmitting and receiving) ■ not broadcast technology - stations receive only their own messages ■ best-effort delivery ■ no access control needed - private frame buffer - no entrance collisions - not CSMA/CD - exit port collision

16. Comer Figure 3.1 Two physical networks connected by a router Comer Figure 3.2 Three networks connected by two routers

17. Comer figure 3.3 (a) user’s view (b) structure of physical networks and routers

18. “Fig 1.5” – An internet 4 LANs linked by a WAN

19. Figure 4.1 The original classful IP addressing scheme

20. Figure 4.4 Special forms of IP addresses

22. Figure 4.5 Logical connection of Two networks to the Internet backbone

23. Figure 4.6 Example IP address assignment

24. Figure 2.2 Format of an Ethernet Frame

26. 0806 Figure 2.2 Ethernet Frame Format

27. Comer Section 5.10 ARP Implementation ■ action when sending an ARP request detain outgoing data message in queue until ARP reply received ■ action when receiving an ARP message either request or reply contain mapping(s), so look in ARP cache to see if receiver already has an entry for the sender. if yes, overwrite physical address (quickest way) and reset timer if no, make new entry and start timer further action depends on two sub-cases: * incoming ARP message was a request look at target IP address; if it’s for this machine, generate ARP reply * incoming ARP message was a reply did this machine earlier send an ARP request for the IP address in the reply? if yes, release outgoing data message from queue, incorporate packet into outgoing frame. if no, no further action

28. Figure 5.3 ARP Message Format

29. ARP Message 0806

30. Chapter 6 – Internet Protocol: Connectionless Datagram Delivery Chapter 6 is about this level

31. Figure 6.3 Format of an IP Datagram

32. Figure 6.3 Format of an IP Datagram

34. 0800 Figure 2.2 Ethernet Frame Format

35. Figure 6.7 Where Fragmentation Occurs

36. Figure 6.8 (a) Original Datagram carrying 1400 octets of data (b) Three fragments for a network MTU of 620; each fragment is a complete datagram, with header!