Welcome to CS 334/534

1. Welcome to CS 334/534

2. Network of networks BHM CHL NO ATL “Fig 1.5” – An internet 4 Ethernet LANs linked by a WAN

3. Comer Figure 1.1 – Growth of the Internet

4. WORLD TOTALS ► Population 2010: 6,845,609,960 ►Internet Users Dec 31 2000: 360,985,492 ►Internet Users June 30 2010: 1,966,514,816 (+444.8 %) ►Penetration of population: 28.7 % August 2010: “ Sometime this month, the 5 billionth device will plug into the Internet” “Today, there are over 1 billion computers that regularly connect to the Internet.” “But cellular devices, such as Internet-connected smartphones, have outstripped that total and are growing at a much faster rate.”

5. 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 disadvantage: traffic spike may overload

6. 2.4 Ethernet Technology Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)

8. 2.4.5 Properties of an Ethernet Ethernet was “designed to be” i.e. “classical” or “original” Ethernet ■ shared bus ■ broadcast technology ■ best-effort delivery ■ distributed access control - shared bandwidth - only one station transmitting at a time - “half duplex” (station transmits XOR receives) - all stations receive all messages - Like Post Office - CSMA/CD

9. 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

10. 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)

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

14. ► Bridge is “store and Forward” device, operating at frame level ►2 interfaces operting in promiscous mode, frame buffer for each interface ►receives frame, checks for validity before forwarding – no “runts”

15. ►” An (almost) arbitrary number of Ethernets can be connected together with bridges” ►”A set of bridged segments acts like a single Ethernet” (“transparent”) ► “Most bridges . . . Make intelligent decisions about which frames to forward” -- No “runts” ► Special case when bridge first powered up -- “flooding”

16. switch

17. ► No waiting to transmit ► not CSMA/CD ► If we upgrade switch with fast backplane, we can have multiple transmissions at same time ► Special case – station can be transmitting and receiving at same time - Full Duplex

18. 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

19. Properties of a “switched” Ethernet ■ not shared bus - point-to-point connections - not shared bandwidth - “full duplex” (station can be 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 Most new wired Ethernet installations are switched

20. Return to section 2.4.7 Wireless Networks and Ethernet IEEE 802.11 standards for wireless LANs We have 802.11g in the lab

21. (Independent) Basic Service Set (ad-hoc network) Figure 1 Extended Service Set (infrastructure network) New components: Distribution System each BSS has an Access Point Figure 2

22. Figure 3 – Hidden Station Problem

23. Figure 4 – CSMA/Collision Avoidance

24. Independent Basic Service Set (IBSS) Station Service (SS) must be provided by all stations: (a) Authentication (b) Deauthentication (c) Privacy (d) Data Unit Delivery Extended Service Set (ESS) Additional services that must be provided by the access point/distribution system: (a) Association (b) Distribution (c) Disassociation (d) Reassociation

25. Figure 5 AP acts like a bridge

26. Figure 6

27. Network, BSS, and Station Identification In the Network Lab: BSSID is 00:06:25:49:B3:B2 (MAC address of Access Point) Each station identification is its MAC address ESSID is netlab_w

28. Wired Ethernet Frame Format Wired: All frames are data frames Wireless: Management, Control, and Data frames Figure 6 - 802.11 frame format

29. Usage of Address Fields in 802.11 Address 1 identifies the immediate receiver (the unit that will process the frame) Address 2 identifies the transmitter (the unit that transmits the frame and will receive the acknowledgment) Usage of other addresses is situation-dependent.

30. Another IBSS! Example 1 – IBSS For frames traveling within an IBSS: Address 1 is the destination address Address 2 is the source address Address 3 is the BSSID (used as a filter, since IBSSs may overlap)

32. Example 2 – ESS with 802.3 (wired) DS, client-server transaction On 802.11 segment Client request Addr 1 - immediate destination - AP Addr 2 – client address Addr 3 – ultimate destination (DA) Server reply Addr 1 – client Addr2 – immediate source (AP) Addr3 – original source (server)

34. Example 3 – ESS with 802.11 (wireless) DS AP1 AP2 Addr 1 – AP2 Addr 2 – AP1 Addr 3 – ultimate dest Addr 4 – original source

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

37. Net 2 Net 1 B? C1 C2 Figure 3.1 Net 3 Net 1 Net 2 B1 ? B2 ? C2 C1 Figure 3.2

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

39. “Fig 1.5” – An internet 4 Ethernet LANs linked by a WAN Comer section 3.8: All Networks are Equal We regard each of the links in the WAN as a network

40. 0 31 | | | 0 | | | A 10 | | | B 110 | | | C

41. IPv4 Figure 4.1 The original classful IP addressing scheme IP addresses specify network connections A router must have at least two IP addresses, with different network parts

42. Figure 4.4 Special forms of IP addresses

43. 4.11 Dotted Decimal Notation 1 0 0 0 1 0 1 0 0 0 0 1 1 0 1 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 1 0 138 . 26 . 66 . 6

44. 4.14 Internet Addressing Authority

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

46. 128.10.0.0 128.210.0.0 9.0.0.0 Figure 4.6 Example IP address assignment

47. BHM CHL NO ATL “Fig 1.5” – An internet Final router has to deliver packet to final destination over Ethernet network.

48. Final Router has to deliver packet over Ethernet network. The ONLY way data can move over an Ethernet is in the payload of an Ethernet frame. 0800 IP Packet Destination Ethernet Address Figure 2.2 Format of an Ethernet Frame From the incoming packet final router knows the destination IP address. We have to find the Ethernet address corresponding to the destination IP address.

49. Ch 5: Mapping Internet Addresses to Physical Addresses Incoming IP Packet router destination

50. 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) in either case 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 since reply is unicast,this machine earlier sent an ARP request for the IP address in the reply so release outgoing data message from queue, incorporate packet into outgoing frame and transmit.