graphic with four colored squares

Introduction to the Architecture of the Internet

Ross Shaull, Brandeis University

Who is Ross?

What is Systems Research?

The Internet as Fancy Picture

The following image was generated by Matt Britt for the Wikipedia article on the Internet. It depicts a partial map of the hosts reachable on the Internet, using data found at

Partial map of the Internet, generated by Matt Britt

Partial map of the Internet. Source: Wikipedia.

The Internet as Cartoon

A better way for us to start visualizing the Internet is as an opaque cloud to which hosts connect.

Internet as a cloud

The Internet and two hosts, a client and a server.

Growth of the Internet

In the following table, the number of computers estimates the number of hosts on the Internet. The number of managers refers to the number of managers in charge of critical, central Internet architecture.

  Number of Computers Number of Managers
1980 10^2 1
1990 10^5 10^1
2000 10^7 10^2
2005 10^8 10^3

Source: Comer, Douglas E. Internetworking with TCP/IP. 5th ed. p9.

A (Very) Short History of the Internet: 1960s

A (Very) Short History of the Internet: 1970s

A (Very) Short History of the Internet: 1980s

A (Very) Short History of the Internet: 1990s

Basic Ideas

Switching: Connecting One Host to Another

Old-style telephone switchboard

Telephone Switchboard

Source: Posted to Wikipedia courtesy of Joseph A. Carr

Circuit Switching: Multiplexing

Time-division multiplexing

Time-Division Multiplexing


Packet Switching


Cables Over the Years

What is the Internet made of? Cables? What about wireless?

10 base 2 Coaxial Ethernet Cable

(1980s) 10base2 Coaxial Ethernet Cable (aka thinnet) — 10 MBit/s

Source: Wikipedia Article on 10base2

Category 5 Twisted Pair Ethernet Cable

(1990s) Category 5 Twisted Pair — Up to 1Gbit/s

Source: Wikipedia Article on Category 5 cable

Addressing for Ethernet: IP

IP Address Exhaustion

Classful addressing wastes addresses. Class C restricts an organization to 254 hosts, yet the next class, Class B, allocates over 65,000 host addresses! How to cope with this problem?

Internet Address Book: DNS

DNS stands for Domain Name Service.

Domains and Names


The US has a country code (.us) too, but it's not typically used (some government sites use it).

Sometimes countries sell their domains to companies, like Tuvalu (who knows what their TLD is?).

Some DNS Details

DNS hierarchy


Routing: Hosts and Hops

Routing: Survivability


TCP and Encapsulation

OSI Model

7-Layer OSI Model

For example, HTTP, the protocol of the Web, is encapsulated in TCP to establish a reliable stream between a client and a web server.

Another Tool Break

Routing to the Backbone

Border Gateway Protocol

BGP between Providers

Source: cisco

Backbone Agreements

Again, What is the Internet?

Net Neutrality

Where to next?