how data travels through the internet

Overview

  • Internet as a worldwide collection of computers that are linked together. These global connections form a common wide area network, also known as the world wide web.

  • This global connection allows information exchange at any time of day, 365 days a year: every day, around the clock. In the transcript: you can exchange information with someone down the street or halfway around the world at any time of day, three hundred and sixty five days a year. 365 days365\text{ days}

  • When you press the enter key to send information, the data is broken into smaller pieces called data packets to enable shared use of the network.

  • Packets are reassembled at the receiver’s computer.

Data Packets and Key Contents

  • Each data packet contains:

    • A piece of your original information.

    • The IP address of the origin (sender) and the destination computer.

  • Some packets may also contain:

    • A sequence number, if the sending application guarantees delivery.

    • Other bits of information needed for controlling and checking content (e.g., checksums, headers).

  • Data packets may use different routes through the Internet network to reach the same destination.

  • Example/metaphor: all red cars have the same IP address (same origin and destination) but travel on different routes to reach the destination.

Transmission Path and Speed Factors

  • After leaving your device, data packets go to your Internet Service Provider (ISP) which then forwards them to the Internet.

  • Speed of data packets depends on two main factors:

    • The type of Internet connection (e.g., DSL, wireless, mobile broadband are faster than dial-up and older broadband).

    • The size of the data packets: larger packets can travel slower because they take longer to push through the network.

  • Analogy: larger packets are like large trucks that take longer to accelerate and may travel at slower effective speeds.

  • The speed of packets can be summarized as a function of connection type and packet size: the faster the connection and the smaller the packet on average, the quicker the data reaches its destination.

The Internet as a Network of Interconnecting Routers

  • The Internet is a series of many interconnecting networks.

  • Routers act as traffic cops, directing data packets along the best current paths.

  • A router determines the best path for packets based on:

    • Speed and current traffic loads.

    • Number and size of other traveling data packets.

  • Routers regularly communicate with each other to share route information so they know which routes provide the fastest delivery.

  • These known routes are stored in the router’s memory as routing tables.

  • Route choice can vary over time due to:

    • Traffic amount

    • Packet size

    • Type of data

  • As a result: data packets may arrive at different times or may not arrive at all, even for the same destination.

On-Ramps, Off-Ramps, and Destination Access

  • The data packets eventually reach the destination computer’s local ISP, which serves as the destination’s off ramp for the data.

  • Each ISP maintains its own router that knows the final path to the destination computer.

  • The purpose of ISP routers is to:

    • Determine the fastest routes to customer computers.

    • Provide an on-ramp to the Internet and an off-ramp to the customer’s network.

  • Although ISPs interact with the broader Internet, their local function is to efficiently deliver packets to the end user.

Reassembly, Ordering, and Reliability

  • When packets arrive at the destination computer, the system begins reassembling them in the correct order.

  • If the packets include sequence numbers, the computer uses them to:

    • Assemble data in the proper sequence.

    • Detect missing packets and request retransmission for any that were lost during transit.

Key Takeaways about Data Flow on the Internet

  • All data is broken into smaller parts for transmission over the Internet.

  • Not all data packets take the same route between sending and receiving computers.

  • The application used to send data determines whether delivery is guaranteed (reliability guarantees).

  • The speed at which data packets travel is affected by Internet traffic (congestion).

  • High data traffic can lead to buffering or poor streaming quality (e.g., music or video cutting out or becoming pixelated).

  • The Internet’s architecture relies on packet switching, routing, and end-to-end principles to deliver data efficiently.