News and Notes 4/20 Thursday’s class will be a course review –will make comments about relative importance of topics for final Thursday’s class will also have formal course evaluation –very important! Several people have requested more time for HW4 Our final deal: –all present in Thursday’s class have until Tue 4/27 to submit HW4 –will pass around attendance sheet –those not at Thursday’s class must meet original HW4 deadline which, of course, is Thursday

Game Theory and the Internet Networked Life CSE 112 Spring 2004 Prof. Michael Kearns

The Internet: What is It? The Internet is a massive network of connected but decentralized computers Began as an experimental research NW of the DoD (ARPAnet) in the 1970s All aspects (protocols, services, hardware, software) evolved over many years Many individuals and organizations contributed Designed to be open, flexible, and general from the start Completely unlike prior centralized, managed NWs –e.g. the AT&T telephone switching network

Internet Basics Can divide all computers on the Internet into two types: –computers and devices at the “edge” your desktop and laptop machines big compute servers like Eniac your web-browsing cell phone, your Internet-enabled toaster, etc. –computers in the “core” these are called routers they are very fast and highly specialized; basically are big switches Every machine has a unique Internet (IP) address –IP = Internet Protocol –like phone numbers and physical addresses, IP addresses of “nearby” computers are often very similar IP addresses are how everything finds everything else! Note: the Internet and the Web are not the same! –the Web is one of many services that run on the Internet

Internet Packet Routing At the lowest level, all data is transmitted as packets –small units of data with addressing and other important info –if you have large amounts of data to send (e.g. a web page with lots of graphics), it must be broken into many small packets –somebody will have to reassemble them at the other end All routers do is receive and forward packets –forward packet to the “next” router on path to destination –they only forward to routers they are physically connected to –how do they know which neighboring router is “next”? Routing tables: –giant look-up tables –for each possible IP address, indicates which router is “next” e.g. route addresses of form *.* to neighbor router A route * to neighbor router B, etc. –need to make use of subnet addressing (similar to zip codes) –distributed maintenance of table consistency is complex must avoid (e.g.) cycles in routing requires distributed communication/coordination among routers Two handy programs: traceroute and nslookup

The IP (Internet Protocol) There are many possible conventions or protocols routers could use to address issues such as: –what to do if a router is down? –who worries about lost packets? –what if someone wants their packets to move faster? However, they all use a single, simple protocol: IP IP offers only one service: packet delivery –with no guarantee of delivery –with no levels of service –with no notification of lost or delayed packets –knows nothing about the applications generating/receiving packets –this simplicity is its great strength: provides robustness and speed Higher-level protocols are layered on top of IP: –TCP: for building connections, resending lost packets, etc. –http: for the sending and receiving of web pages –ssh: for remote access to edge computers –etc. etc. etc.

Competition in the Internet You and I both want to download the Starr report –I’d like to get the material as quickly as possible; so would you –connectivity to the hosting server is a finite resource –we’re in competition I want to watch “The Matrix” in streaming high-res video –you just want to read your –real-time arrival of packets is important to me; not to you –I might be willing to pay more for “priority service” packet delivery Many of us want to watch “The Matrix” (multicast) –those of “near” each other (e.g. Penn) might share costs share common route from source until final hop –some parties might be more isolated e.g. lone Wyoming Tech grad student his route has little overlap with anyone else –how should we pay?

Case Study: Selfish Routing Standard Internet routing: –route your traffic follows entirely determined by routing tables –out of your control –generally based on shortest paths, not current congestion! Source routing: –you specify in the packet header the exact sequence of routers –better be a legitimate path! –in principle, can choose path to avoid congested routers Source routing as a game: –traffic desiring to go from A to B (a flow) viewed as a player number of players = number of flows (huge) –actions available to a flow: all the possible routes through the NW number of actions = number of routes (huge) –penalty to a flow following a particular route: latency in delivery –rationality: if flow can get lower latency on a different route, it will! Let’s look at T. Roughgarden’s excellent slides on the topicT. Roughgarden’s excellent slides –we will examine the material in pages 1-23

Case Study: QoS QoS = Quality of Service –many varying services and demands on the Internet real-time delivery not critical chat: near real-time delivery critical; low-bandwidth voice over IP: real-time delivery critical; low-bandwidth teleconferencing/streaming video: real-time critical; high-bandwidth –varying QoS guarantees required not much more than IP required; must retransmit lost packets chat/VoIP: two-way connection required telecon/streaming: high-bandwidth two-way connections Must somehow be built on top of IP Whose going to pay for all of this? How much? –presumably companies offering the services –costs passed on to their customers What should the protocols/mechanism look like? There are many elaborate answers to these questions…

Brief Aside: Differential Pricing Suppose party P produces a research report at cost $1000 Only two possible customers, A and B –A values the report at $400, B at $900 –If P charges $400: both A and B buy, P makes $800 < $1000 –If P charges $900, only B buys, P makes $900 < $1000 Solution: charge each their valuation, P makes $1300 Fairness questions Differential pricing? –first class vs. coach airfaire and other “premium” services

QoS and the Paris Metro Paris Metro (until recently) –two classes of service: first (expensive) and coach (cheaper) –exact same cars, speed, destinations, etc. –people pay for first class: because it is less crowded because the type of person willing/able to pay first class is there etc. –self-regulating: if too many people are in first class, it will be come less attractive Andrew Odlyzko’s PMP protocol for QoS: –divide the Internet into a small number of identical virtual NWs –simply charge different prices for each –an entirely economic solution –California toll roads