The Internet

Internet Structure

Administrative borders define:

• Autonomous Systems (AS)

  • Intra-domain routing;

  • Individual internal policies;

  • May use different metrics between domains;

  • Protocols: RIPv2, OSPFv2.

• AS interconnections

  • Inter-domain routing;

  • Connectivity information;

  • Protocols: BGP.

Internet: currently

Self-organized set of interconnected autonomous components.

• More than 60.000 autonomous domains (with more than 100K numbers allocated)

  • Single guarantee is running TCP-IP;

  • Works by packet switching;

  • More than 340 millions of registered domains (URL)!

Commercial traffic larger than non-commercial.

• Exponential growth in all numbers (number of users, traffic).

Different machines (networks) can offer different services.

• Each user can select what it uses.

Only bi-directional media that supports communications.

• One to one (unicast, e.g. email); one to many (multi-cast, e.g., electronic news).

NB: Internet networks are operated AUTONOMOUSLY

• After connecting to the Internet, the network becomes PART of the Internet.

Real structure

Apparently hierarchical.

• Backbone ISP provides service to increasingly smaller ISPs.

• Smaller ISPs eventually providing service end users.

But hierarchy is not respected.

• Private connection agreements;

• Mechanisms for improvement of the network;

• All companies provide service to (some) users;

• Service providers connect to multiple connection providers;

• Users connect to multiple ISPs.

“Data vs voice”: packet switching vs circuit switching

Great for burst information.

• Resource sharing;

• No call setup time.

When excessive congestion: delays and losses.

• Needs reliable data transfer protocols.

Providing circuit switching services ?

• For multimedia applications we need bandwidth and delay.

  • Problem not yet completely solved.

Transport service (operador/ISP) vs applications

Packet loss

Some apps (audio/video real time) handle losses.

Other applications (file transfer, telnet) require 100% of success in transmission.

Bandwidth

Some applications (multimedia) need a minimum bandwidth to be effective.

Other applications (“elastic applications”, ex. email, file transfer) use the bandwidth available.

Timing

Some applications (Internet voice, multiuser games) require low delays to be effective.

Other applications (without real time requirements) do not have strict delays end-to-end.

Elastic operations

Elastic applications

Interactive data transfer (e.g. HTTP, FTP).

• Sensitive to the medium delay, not to rare occurrences.

Bulk data transfer (e.g. mail, news).

• Not sensitive to delay;

• Best effort works.

Inelastic applications

Interactive applications

Sensistive to packet delay (telephony, gaming).

Maximum delay may be limited.

Non-interactive applications

Adapt to larger ranges of delays (streaming audio, video).

Application requirements

Applications	Losses	BW	Timing
File Transfer	lossless	elastic	no
E-mail	lossless	elastic	no
Web Documents	lossless	elastic	no
Real time audio/video	supports	audio: 5k-1Mbps video: 10k-5Mbps	yes, 100's ms
Streamed audio/video	supports	See above	yes, few secs
Interactive gaming	supports	Some Kpbs	yes, 100's ms
Finance applications	lossless	elastic	Yes and no