The beginning


Experimental test from military

Connects computers in a network

Packets ~ Packages

Developed fast

Subnetworks emerged

Communication network that would be difficult to destroy

Centralized network was unmanageable


Everyone started to use it



0 or 1

0 - no 'current' (0V)

1- 'current' (0.5V)





Most various types


Local - Ethernet

Continental - Fiber Optics



Continental - Satellites

Everything comes down to bits



PAN | LAN | MAN | WAN | Internet

hosts - computers

Network connects hosts

Internetwork - network of networks

ISP controls a network that has a lot of hosts


Collection of interconnected networks

Uses ISP networks to connect Enterprise, Home networks

How it works?

Bit code travels to the router, it's transformed in bit code and goes to a physical layer (cables, satellites, ...)

A lot of different networks - agreement on both sides - Protocol


Internet Protocol - network layer

Unique address for each machine - mail and address

Eg: (8bits codify each part, so an IP has 32bits)


IPv4 format has limited address numbers (4billion)

Now changing for IPv6 (128bits)

Who cares about IP's?

We need names it's better for humans

DNS (Domain Name System)


Computer asks DNS server, do you know

No, but i'll ask around.

Found it, i'm gonna write it down

Here it is

 DNS servers are grouped and spread responsability (some keep .com, others .fr, .pt, .io, ....)

Now we need to deliver info effectively, how?

Not direct fashion, not specified route, not fixed path, it can change

Best path?

 depends on time, relations between companies, politics, not always the direct is the best way

Fault Tolerant

network keeps working when some routes are destroyed, needs to be Reliable

 Forwarding algorithms, in the link layer


Like packages in mail service

Can store information (bits, addresses)

Large things? 

break up into several packets that can travel in different routes at different times, or different order (forwarding algorithms)

The receptor waits and reassembles

Packets eg

1byte - 8bits

Image: 10Mbytes - 10 million bytes - billions of bits

Separete in packets

Don’t have drivers, they have destination IP and IP where they came from

Routers define the best route for each packet, the best one depends on time, relations between companies, politics, not always the direct is the best way


Transmission Control Protocol

Protocol from Transport Layer

It's a guaranteed mail service


Listenning a music in Spotify

Request on spotify

Song is split into many packets

 TCP sees each one and sends messages to confirm that everything was received

Sends it to you

With routers and this control system it’s easy to scale


Browser - App where you access web pages

URL (Uniform Resource Locator)

Ask for website

Browser talks with server, requests (GET, POST, PATCH, DELETE)

Server understands HTTP 

Hyper Text Transfer Protocol - Application Layer

Gives an HTML 

eg: Tumblr

GET /login - tumblr server will respond with HTML code from that specific page

HTML (Hyper Text Markup Language)

The browser can also request other types of files


HTTP Secure, HTTP over SSL

Secure communication over a network

HTTP in a secure connection (SSL connection)

Encrypted in the transport layer


There can be multiple hacking in all layers. As far as you go from App layer more difficult it is to hack.

90% of hacks are in App layer

HTTPS also allows you to have unique certificates which prove authenticity


Layers Flow

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by jbernardoviana


Public - 8/23/16, 9:16 AM