1 Welcome to CS 334/534

2 “Fig 1.5” – An internet 4 Ethernet LANs linked by a WAN BHM NOATL CHL Network of networks

3 Comer Figure 1.1 – Growth of the Internet

4 WORLD TOTALS ► Population 2010: 6,845,609,960 ►Internet Users Dec : 360,985,492 ►Internet Users June : 1,966,514,816 ( %) ►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)

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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 - CSMA/CD - Like Post Office

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

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)

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

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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

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 ■ 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 Properties of a “switched” Ethernet Most new wired Ethernet installations are switched

20 IEEE standards for wireless LANs SpeedRangeRadio Frequency b11 Mbits/sec100 meters2.4 GHz a54 Mbits/sec 80 meters5 Ghz g54 Mbits/sec150 meters2.4 GHz n248 Mbits/sec 70 meters2.4 and 5 GHz We have g in the lab Return to section Wireless Networks and Ethernet

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

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 (c) Disassociation (b) Distribution (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 Figure frame format Wired Ethernet Frame Format Wired: All frames are data frames Wireless: Management, Control, and Data frames

29 Usage of Address Fields in 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 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) Another IBSS!

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

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

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

37 Net 1 Net 2 Figure 3.1 C1C2 B? B1 ?B2 ? C1 C2 Figure 3.2 Net 1 Net 2 Net 3

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 We regard each of the links in the WAN as a network Comer section 3.8: All Networks are Equal

40 | | | | | | 10 | | | 110 | | | A B C

41 Figure 4.1 The original classful IP addressing scheme IPv4 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

Dotted Decimal Notation

Internet Addressing Authority

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

46 Figure 4.6 Example IP address assignment

47 “Fig 1.5” – An internet BHM NOATL CHL Final router has to deliver packet to final destination over Ethernet network.

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

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

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.

51 Figure 2.2 Ethernet Frame Format ARP Encapsulation and Identification ARP MESSAGE

52 Figure 5.3 ARP Message Format

53 ARP Message ARP Protocol Format

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