Computer Networks Sándor Laki ELTE-Ericsson Communication Networks Laboratory ELTE FI – Department Of Information Systems
[email protected] http://lakis.web.elte.hu Based on the slides of Laurent Vanbever. Further inspiration: Scott Shenker & Jennifer Rexford & Phillipa Gill Last week on Computer Networks Overview What is a network made of? Three main components End-points Switches Links Overview How to share network resources? Resource handling Two different approaches for sharing Reservation On-demand Reserve the needed Send data when needed bandwidth in advance Packet-level multiplexing Flow-level multiplexing Pros & Cons Pros Cons Predictable performance Low efficiency Bursty traffic Short flows Simple and fast switching Complexity of circuit establ./teard. once circuit established Increased delay New circuit is needed in case of failures Implementation Reservation On-demand Circuit-switching Packet-switching e.g. landline phone networks e.g. Internet Packets Overview How to organize the network? Tier-1 ISP Tier-1 ISP IXP Tier-2 ISP Tier-2 ISP Access ISP Access ISP This week How does communication happen? How do we characterize it? Briefly… The Internet should allow processes on different hosts to exchange data everything else is just commentary… Ok, but how to do that in a complex system like the Internet? University net Phone company CabelTV company Enterprise net To exchange data, Alice and Bob use a set of network protocols Alice Bob A protocol is like a conversational convention The protocol defines the order and rules the parties