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Welcome

to

CS 334/534

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“Fig 1.5” – An internet

4 Ethernet LANs linked by a WAN

BHM

NO ATL

CHL

Network of networks

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Comer Figure 1.1 – Growth of the Internet

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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.”

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2.2 Two Approaches to Network Communication

* circuit-switched networks (telephone)

3 phases:establish connection between end pointsuse 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

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2.4 Ethernet Technology

Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)

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2.4.5 Properties of an EthernetEthernet 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

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2.4.8 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 bymanufacturer

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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 modeInterface processes only packets with destination * its own unicast address * the network broadcast address

■ promiscuous modeInterface process all received packets (including those addressed to other stations)

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Figure 2.1 (with hub)

Figure 2.2 Format of an Ethernet frame (packet)

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► 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”

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►” 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”

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switch

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► 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

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2.4.5 Properties of an EthernetEthernet 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

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■ 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

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IEEE 802.11 standards for wireless LANs

Speed Range Radio Frequency

802.11b 11 Mbits/sec 100 meters 2.4 GHz

802.11a 54 Mbits/sec 80 meters 5 Ghz

802.11g 54 Mbits/sec 150 meters 2.4 GHz

802.11n 248Mbits/sec

70 meters 2.4 and 5 GHz

We have 802.11g in the lab

Return to section 2.4.7 Wireless Networks and Ethernet

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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

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Figure 3 – Hidden Station Problem

23Figure 4 – CSMA/Collision Avoidance

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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

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Figure 5

AP acts like a bridge

26Figure 6

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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

28Figure 6 - 802.11 frame format

Wired Ethernet Frame Format

Wired: All frames are data frames

Wireless: Management, Control, and Data frames

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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.

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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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Client request

Addr 1 - immediate destination - AP

Addr 2 – client address

Addr 3 – ultimate destination (DA)

Example 2 – ESS with 802.3 (wired) DS, client-server transaction

Server reply

Addr 1 – client

Addr2 – immediate source (AP)

Addr3 – original source (server)

On 802.11 segment

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Example 3 – ESS with 802.11 (wireless) DS

AP1 AP2

Addr 1 – AP2

Addr 2 – AP1

Addr 3 – ultimate dest

Addr 4 – original source

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“Fig 1.5” – An internet

4 Ethernet LANs linked by a WAN

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Net 1 Net 2

Figure 3.1

C1 C2B?

B1 ? B2 ?C1 C2

Figure 3.2

Net 1 Net 2Net 3

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

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“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

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| | |

0 31

0 | | |

10 | | |

110 | | |

A

B

C

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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

42Figure 4.4 Special forms of IP addresses

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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

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4.14 Internet Addressing Authority

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Figure 4.5 Logical connection of

Two networks to the Internet backbone

46Figure 4.6 Example IP address assignment

128.10.0.0

128.210.0.09.0.0.0

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“Fig 1.5” – An internet

BHM

NO ATL

CHL

Final router has to deliver packet to final destination over Ethernet network.

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Figure 2.2 Format of an Ethernet Frame

Destination Ethernet Address

Final Router has to deliver packet over Ethernet network.

IP Packet0800

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.

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router

destination

Ch 5: Mapping Internet Addresses to Physical Addresses

Incoming IP Packet

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Comer Section 5.10 ARP Implementation

■ action when sending an ARP requestdetain 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 timerif no, make new entry and start timer

further action depends on two sub-cases:

* incoming ARP message was a requestlook 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.

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Figure 2.2 Ethernet Frame Format

0806

5.11 ARP Encapsulation and Identification

ARP MESSAGE

52Figure 5.3 ARP Message Format

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ARP Message

0806

5.12 ARP Protocol Format

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