How the Internet Works Acknowledgment and Disclaimer: This presentation is supported in part by the National Science Foundation under Grant Any opinions, findings, and conclusions or recommendations expressed in these materials are those of the authors and do not necessarily reflect the views of the National Science Foundation.

How is the Internet connected together?

Basic Architecture ●The Internet is a network of networks R R R R

Basic Architecture ●The Internet is a network of networks in which host computers R R R R Hosts

Basic Architecture ●The Internet is a network of networks in which host computers are connected by routers. R R R R HostsRouters

Latency and Ping ● Latency is a measure of the time it takes a piece of data to reach its destination ● typically measured in milliseconds (ms) ● Wireless connections have higher latency than wired ● Ping is a networking utility to measure the latency on the Internet ● Ping takes a hostname or IP address as a parameter and sends a small test packet to the node that is echoed by it ● Once the echo is received time is measured ● Examples from linux ping ping ping

How does data travel through the Internet?

Packet Switching Messages are broken into fixed-sized packets -- e.g., P1, P2, P3. Message P1P2P3 Packets P1 P2 P3 1. Break the Message into Packets

Packet Switching Messages are broken into fixed-sized packets -- e.g., P1, P2, P3. Packets are routed independently ( →, →, →) Message P1P2P3 Packets P1 P2 P3 1. Break the Message into Packets 2. Send the packets to destination

Packet Switching Messages are broken into fixed-sized packets -- e.g., P1, P2, P3. Packets are routed independently ( →, →, →) The original message is re-assembled at the destination. Message P1P2P3 Packets P1 P2 P3 Message P1P2P3 Packets P1 P2 P3 1. Break the Message into Packets 2. Send the packets to destination 3. Reassemble the packets.

Packet Switching: Basic Ideas ●Motivated in the 1960s by the desire for a network that could withstand a nuclear attack: o A decentralized network with multiple paths between points A and B o Dividing the message into small packets that are routed independently o Each router along the path forwards packets to another router along the path

Decentralization and Redundancy ●Decentralized networks with redundant paths provide robustness in network design

Decentralization and Redundancy ●Decentralized networks with redundant paths provide robustness in network design Centralized Network A B

Decentralization and Redundancy ●Decentralized networks with redundant paths provide robustness in network design Centralized Network Vulnerability: Single route from A to B. The network is destroyed by knocking out the center. A B

Decentralization and Redundancy ●Decentralized networks with redundant paths provide robustness in network design Centralized Network Decentralized Network Vulnerability: Single route from A to B. The network is destroyed by knocking out the center. A B A B

Decentralization and Redundancy ●Decentralized networks with redundant paths provide robustness in network design Centralized Network Decentralized Network Vulnerability: Single route from A to B. The network is destroyed by knocking out the center. Robustness: Redundant routes from A to B. Network survives attacks to individual nodes. A B A B

Packet vs Circuit Switching ●In a circuit-switched network (telephones) there is a dedicated channel between A and B ●In a packet-switched network there is no sustained connection between A and B ●Browsing: Navigating from one page to another may seem like it’s a dedicated channel, but it’s not ●Packet switching increases redundancy and robustness

Traceroute ●Traceroute is a networking utility used to trace the route and measure delays of packets moving through the InternetTraceroute ●Traceroute repeatedly sends packets from the source to destination with increasing time to live (TTL or number of hops) starting at 1, 2, 3, … Source Destination ●It uses data received to build a list of hops 1 2 1

traceroute wikipedia.org Destination hostDie after this many hops Domain names and IP addresses of routers and hosts along the way Hop number Round trip times (RTT) or latency for 3 packets to the hop and back.

Internet Performance

Global Bandwidth ● Bandwidth speeds vary across the globe ● The current global average is 18.4 Mbps download ● Korea leads the world with 52.6 Mbps ● In the US the average is 24.4 Mbps

Broadband Access Broadband: high speed Internet service that is always on, typically through cable or DSL modems (Src: OECD)OECD 72.4% Penetration in OECD Countries 6 Countries have over 100% penetration 7 for 3 people in my house

Bandwidth ● Bandwidth or throughput is the rate at which data are downloaded or uploaded in a network. o Measured in Kilobits per second (Kbps) -- thousands, or o Megabits per second (Mbps) -- millions Click me