Introduction to Computer Networks Network devices and ...jamhour/Download/pub... · Introduction to Computer Networks Network devices and protocols Edgard Jamhour . Edgard Jamhour

Edgard Jamhour

Introduction to Computer Networks

Network devices and protocols

Edgard Jamhour

Edgard Jamhour

A B C

B A DATA

frame

CRC .

Shared medium – bus topology

Ethernet is a technology for implementing local area networks

(LANs), and it is based on the principle of physical broadcast.

Edgard Jamhour

A frame is the smallest structure of information transmitted over a

local network.

B A DADOS CRC

Tail Header

Destination Physical Address

Source Physical Address

Type

Quadro Ethernet II

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A B C

Listening Listening

Frames in a waiting queue

In non-switched Ethernet, only one computer can transmit at a

time.

Edgard Jamhour

The propagation time between hosts affects the maximum

performance of the network.

A

B

A Transmits

B Transmits B Receives

Propagation time from A to B

A Receives

t T

L = distância

to to+ t to+ T+ t

Edgard Jamhour

The maximum occupancy of the medium decreases with both: the

distance between computers and the transmission rate.

• Minimum Ethernet frame size defined by the standard

– 64 bytes

• Propagation speed of the electrical signal in a copper wire:

– 200 000 Km / s

efficiency = T/(T+t)

efficiency : 10Mbps X 200m = 98%

efficiency : 100Mbps X 200m = 83,6%

efficiency : 100Mbits X 800 m = 56,1%

…


distance

efficiency

1

0

Edgard Jamhour

Even with computers listening before transmitting medium, there is a

possibility of collision.

A

B

A Transmits

B Transmits

B Receives t

A Receives

Collision detected by A

Collision detected by B

t= to t= t1 t= to+t

t

t= t1+t

Edgard Jamhour

The distance between computers increases the collision probability

• Minimum Ethernet frame size defined by the standard

– 64 bytes

• Propagation speed of the electrical signal in a copper wire:

– 200 000 Km / s

efficiency = 1/(1 + 6,44 t/T)




distance

efficiency

1

0

Edgard Jamhour

Hubs or concentrators are devices which internally simulate the

construction of a physical bus.

C A C A

A

1 2 3

hub

B C

C A

A

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The introduction of swiches changes the operation of the Ethernet to

the “swiched” mode.

PORT

1

ADDRESSES

A

A

1 2 3

C A ... (1)

C A ... C A ... (2) (2)

switch

B C

Initial State

PORT

ADDRESSES

After A transmission

PORT

1

3

ADDRESSES

A

C

After C transmission

A

1 2 3

A C ... (3) A C ... (4)

switch

B C

Edgard Jamhour

Each switch port defines a collision domain. This is only possible

collision between computers connected to the same port.

A

1 2 3

switch

hub

B C D

hub

E F G

Forwarding Table

PORT

1

2

3

COMPUTER

A,B,C

D,E,F

G

Edgard Jamhour

Although significantly improve network performance, Switches still have

limited scalability.

Switch 1

PORT

1

2

3

4

ADDRESS

D,E,F,G,H,I

A

B

C

A B C

switch 1

2 4 3

D E F

G H I

5

switch 1

2 4 3 5

switch 1

2 4 3 5

Switch 2

PORT

1

2

3

4

5

ADDRESS

A,B,C

D

E

F

G,H,I

Switch 3

PORT

2

3

4

5

ADDRESS

G

H

I

A,B,C,D,E,F

Edgard Jamhour

The WAN (Wide Area Networks) uses a different address scheme that

allows you to connect an unlimited number of switches in arbitrarily

large distances.

Router

1

Router

3

LAN

LAN

switch switch

switch

WAN

Router

2

LAN

LAN

Net 1 Net 2

Net 3

1 2

3

1 2

3

1

3 2

Tabela de Roteamento

Port

1

2

3

Network

Net 3

Net 1

Net 2

Other

Info.

.....

Edgard Jamhour

IP addresses have 32 bits, i.e. 4 bytes, represented in dotted decimal

notation.

10000000 00001010 00000010 00011110

2726252423222120 2726252423222120 2726252423222120 2726252423222120

27=128 23+21=10 21=2 24+23+22+21=30

128.10.2.30

Dot-decimal

notation

Binary

notation

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Packets are transported in the payload of frames

CRC Data Destination Source Destination Soruce

Packet

Frame

Physical Addresses: defined by Ethernet

Network Adresses: defined by IP

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Grouping computers into networks allows to reduce the amount of

information in the router's table.

SWITCH

SWITCH

A c

NET 200.0.0.0/8

NET 210.0.0.0/8

X

Y

200.0.0.1 200.0.0.2 200.0.0.3 Z M

210.0.0.1

Z

If 200... Send to x

If 210 ... Send to y

M 66.1.2.3 210.0.0.2

E Y 66.1.2.3 210.0.0.2

B

D

210.0.0.3

E

210.0.0.4

F

Edgard Jamhour

Packets are independent of the physical medium. Frames, however,

must change to adapt to the data-link technology.

1 2

200.17.176.x

Ethernet

Technology

PPP over

phone line

Token-Ring

Technology

Packet is always the same

Frame is dependent on the data link technology

LAN 1

200.0.0.0/8

LAN 2

210.0.0.0/8

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Transport protocols, such as TCP and UDP, are responsible to deliver

the payload of packets to the process.

Computador 2

Computador 1

TCP

IP

Ethernet

Physical Address

IP Address

Port

1024

Process

A

Process

bus

UDP

Port Port

Process

TCP

IP

Ethernet

Physical Address

IP Address

Port

Process Process

B

UDP

Port

80 Port

Process

1024 80 Payload

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Port numbers are addresses used by TCP and UDP. Well-known ports

are mapped to the standard applications defined by IANA (Internet

Assigned Number Authority)

0

1023

1024

49151

Well-known port (requires root privileges)

Registered ports

49152

65535

Dynamic or private ports

Edgard Jamhour

Protocol Data Unit (PDU): Frame, Packet, Segment

(TCP)/Datagram(UDP)

crc src dst src dst src

Packet

Frame

Physical

Addresses

IP Addresses

dst payload

Port Numbers

Segment or Datagram

protocol

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Application protocols define a set of standard messages that permit

clients and servers from different vendors to communicate.

crc src dst src dst src dst Application Protocol protocol

mail from: <...>

rcpt to: <...>

data

250 ok

250 ok

354 End data with <CR><LF>.<CR><LF>

dados <CR><LF>.<CR><LF>

SMTP

Client

SMTP

Server

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Ethernet is not considered part of the TCP/IP protocol stack

Packing

sequence

Data

application

segment/

datagram

packet

frame

Application Application

Layer

HTTP, FTP,

SMTP, etc

Operating

System

Transport

Layer

TCP, UDP

Network Layer

IP

N.I.C.

Ethernet

Edgard Jamhour

Open Systems Interconnection Model (OSI) is a conceptual model that

permits to classify network equipments and protocols.

Layer

7

Application Application dependent protocols Proxy, Layer 7 Firewall,

Hosts

Layer

6

Presentation Data transformation, compression and

encryption

Hosts

Layer

5

Session Session establishment, maintenance and

termination

Hosts

Layer

4

Transport Inter-process communication Layer 4 Firewalls, Proxy

Socks

Layer

3

Network Inter-LAN communication (routing) Router

Layer

2

Data Link Intra-LAN communication (forwarding) Switches, Bridges

Layer

1

Physical Physical representation of bits (electrical,

wireless or optical) and medium transportation

(cable, modulation, etc.)

Hubs, Repeaters

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2

11

3

4

5

6

7

Send process

7

payload

7 6

payload

7 6 5

payload

7 6 5 4

payload

7 6 5 3

payload

7 6 5 4

4

3 2

payload

7 6 5 4 3 2 1

2

E 1

2

11

3

4

5

6

7

Receive Process

payload

7

payload

7 6

payload

7 6 5

payload

7 6 5 4

payload

7 6 5 3

payload

7 6 5 4

4

3 2

payload

7 6 5 4 3 2 1

2

E 1

data data

PPDU

SPDU

TPDU

NPDU

DL-PDU

APDU payload

0 1 0 0 1 0 0 ...

packet

frame

segment/data

gram

Each protocol transports the PDU of the protocol of the above layer.

Headers are added during transmission and removed during reception.

Edgard Jamhour

Protocols can be classified according to the OSI model. Only one

protocol of each layer can be used at a time.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Ethernet, WiFi, PPP, HDLC, Token-

Ring, Frame-Relay, etc.

IP, IPX, ARP

TCP, UDP, SPX, NetBEUI

HTTP, FTP, SMB, SMTP, POP3,

IMAP4, DNS,

DHCP, EDI, BitTorrent, etc

ATM, MPLS

1

6

5

4

3

2

7

2.5

USB, RS-232, BlueTooth, Modem, etc.

NetBIOS, Sockets, RPC

SSL, MIME

Edgard Jamhour

Conclusion

• Protocols and Network Equipments

• Differences between LAN and WAN

• TCP/IP Protocol Stack

• Network Layer Model

Documents

Introduction to Computer Networks Network devices and ...jamhour/Download/pub... · Introduction to Computer Networks Network devices and protocols Edgard Jamhour . Edgard Jamhour