1 A Taxonomy of Communication Networks Y. Richard Yang 1/12/20122 Outline Ø Recap q A taxonomy of communication networks q Summary3 Recap ❒ A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission or receipt of a message or other events. ❒ Some implications of the past: ❍ ARPANET is sponsored by ARPA → ❍ The initial IMPs (routers) were made by a small company → ❍ Many networks → ❍ Commercialization → design should survive failures internetworking: need a network to connect networks keep the network simple architecture supporting decentralized, autonomous systems4 Backbone ISP ISP ISP Recap: Internet Physical Infrastructure Residential access ❍ Cable ❍ Fiber ❍ DSL ❍ Wireless Campus access, e.g., ❍ Ethernet ❍ Wireless ❒ The Internet is a network of networks ❒ Each individually administrated network is called an Autonomous System (AS)5 Source: http://www.internet2.edu/info/6 Source: http://www.internet2.edu/info/7 Recap: Internet ISP Connectivity ❒ Roughly hierarchical ❍ Divided into tiers ❍ Tier-1 ISPs are also called backbone providers, e.g., AT&T, Verizon, Sprint, Level 3, Qwest ❒ An ISP runs (private) Points of Presence (PoP) where its customers and other ISPs connect to it ❒ ISPs also connect at (public) Internet Exchange Point (IXP) ❍ public peering http://en.wikipedia.org/wiki/List_of_Internet_exchange_points_by_size8 Northern CrossRoads (NoX) Aggregation Point (AP) http://www.uis.harvard.edu/emerging_technologies/Northern_Crossroads_Map.gif9 http://www.oregon-gigapop.net/images/OregonGigapop2.gif10Summary: Internet State ❒ Global Internet ❍ 39,908 ASs (and growing) ❒ Routing overhead/convergence ❍ AS updates • 2 per second on average • 7000 per second peak rate ❍ Convergence after a single event can take up to tens of minutes 11 http://bgp.potaroo.net/as2.0/bgp-active.html12 Observing the Internet ❒ Read the manual traceroute, and try it on a zoo machine % /usr/sbin/traceroute <machine_name> q Look at the web sites of the routers you see through traceroute q Try fixedorbit look for info about a network: http://www.fixedorbit.com/search.htm13 Roadmap ❒ So far we have looked at only the topology and physical connectivity of the Internet: a mesh of computers interconnected via various physical media ❒ A fundamental question: how are data (the bits) transferred through communication networks?14 Outline q Admin. and recap Ø A taxonomy of communication networks q Summary15 Broadcast vs. Switched Communication Networks ❒ Broadcast networks ❍ nodes share a common channel; information transmitted by a node is received by all other nodes in the network ❍ examples: TV, radio ❒ Switched networks ❍ information is transmitted to a small sub-set (usually only one) of the nodes communication networks broadcast networks switched networks16 ❒ Circuit switching: dedicated circuit per call/session: ❍ e.g., telephone, GSM High-Speed Circuit-Switched Data (HSCSD) ❒ Packet switching: data sent thru network in discrete “chunks” ❍ e.g., Internet, 3G data A Taxonomy of Switched Networks communication networks switched networks broadcast networks circuit-switched networks (e.g. telephone) packet-switched networks (e.g. Internet)17 Outline q Admin. and review Ø A taxonomy of communication networks Ø circuit switched networks ¦ packet switched networks ¦ circuit switching vs. packet switching18 Circuit Switching ❒ Each link has a number of “circuits” ❍ sometime we refer to a “circuit” as a channel or a line ❒ An end-to-end connection reserves one “circuit” at each link First commercial telephone switchboard was opened in 1878 to serve the 21 telephone customers in New Haven, Connecticut19 Circuit Switching: Resources/Circuits (Frequency, Time and others) ❒ Divide link resource into “circuits” ❍ frequency division multiplexing (FDM) ❍ time division multiplexing (TDM) ❍ others such as code division multiplexing (CDM), color/lambda division20 Circuit Switching: The Process ❒ Three phases 1. circuit establishment 2. data transfer 3. circuit termination21 circuit establishment DATA data transmission circuit termination Host A Host B Node 1 Node 2 propagation delay from A to Node 1 propagation delay from B To A processing delay at Node 1 Timing Diagram of Circuit Switching22 Delay Calculation in Circuit Switched Networks Transmission delay: ❒ R = reserved bandwidth (bps) ❒ L = message length (bits) ❒ time to send a packet into link = L/R Propagation delay: ❒ d = length of physical link ❒ s = propagation speed in medium (~2x105 km/sec) ❒ propagation delay = d/s ❒ Propagation delay: delay for the first bit to go from a source to a destination ❒ Transmission delay: time to pump data onto link at line rate DATA d/s L/R23 An Example ❒ Propagation delay ❍ suppose the distance between A and B is 4000 km, then one-way propagation delay is: ❒ Transmission delay ❍ suppose we reserve a one-slot HSCSD channel • each HSCSD frame can transmit about 115 kbps • a frame is divided into 8 slots ❍ then the transmission delay of using one reserved slot for a message of 1 Kbits: msskmkm20/000,2004000=mskbpskbit s70141≈24 An Example (cont.) ❒ Suppose the setup message is very small, and the total setup processing delay is 200 ms ❒ Then the delay to transfer a message of 1 Kbits from A to B (from the beginning until host receives last bit) is: ms33070202020020 =++++DATA 20 + 200 20 20 7025 Outline q Admin. and review Ø A taxonomy of communication networks ¦ circuit switched networks Ø packet switched networks26 Packet Switching Each end-to-end data flow (i.e., a sender-receiver pair) divided into packets ❒ Packets have the following structure: • header and trailer carry control information (e.g., destination address, check sum) • where is the control information for circuit switching? ❒ At each node the entire packet is received, processed (e.g., routing), stored briefly,