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Welcome to CS 334/534. Network of networks. BHM. CHL. NO. ATL. “Fig 1.5” – An internet. 4 Ethernet LANs linked by a WAN. Comer Figure 1.1 – Growth of the Internet. WORLD TOTALS. ► Population 2010: 6,845,609,960. ► Internet Users Dec 31 2000: 360,985,492.

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Welcome to CS 334/534

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Welcome to cs 334

Welcome

to

CS 334/534


Welcome to cs 334

Network of networks

BHM

CHL

NO

ATL

“Fig 1.5” – An internet

4 Ethernet LANs linked by a WAN


Welcome to cs 334

Comer Figure 1.1 – Growth of the Internet


Welcome to cs 334

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.”


Welcome to cs 334

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


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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 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


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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


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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 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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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


Welcome to cs 334

► 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


Welcome to cs 334

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


Welcome to cs 334

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


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Return to section 2.4.7 Wireless Networks and Ethernet

IEEE 802.11 standards for wireless LANs

We have 802.11g in the lab


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(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


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Figure 3 – Hidden Station Problem


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Figure 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

(b) Distribution

(c) Disassociation

(d) Reassociation


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Figure 5

AP acts like a bridge


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Figure 6


Welcome to cs 334

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


Welcome to cs 334

Wired Ethernet Frame Format

Wired: All frames are data frames

Wireless: Management, Control, and Data frames

Figure 6 - 802.11 frame format


Welcome to cs 334

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.


Welcome to cs 334

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)


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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)


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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


Welcome to cs 334

Net 2

Net 1

B?

C1

C2

Figure 3.1

Net 3

Net 1

Net 2

B1 ?

B2 ?

C2

C1

Figure 3.2


Welcome to cs 334

Comer figure 3.3 (a) user’s view

(b) structure of physical networks and routers


Welcome to cs 334

“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


Welcome to cs 334

0

31

| | |

0 | | |

A

10 | | |

B

110 | | |

C


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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


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Figure 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


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128.10.0.0

128.210.0.0

9.0.0.0

Figure 4.6 Example IP address assignment


Welcome to cs 334

BHM

CHL

NO

ATL

“Fig 1.5” – An internet

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


Welcome to cs 334

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.


Welcome to cs 334

Ch 5: Mapping Internet Addresses to Physical Addresses

Incoming IP Packet

router

destination


Welcome to cs 334

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.


Welcome to cs 334

5.11 ARP Encapsulation and Identification

0806

ARP MESSAGE

Figure 2.2 Ethernet Frame Format


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Figure 5.3 ARP Message Format


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5.12 ARP Protocol Format

ARP Message

0806


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