1. InternetI M.Com

2. Network ... communication system for connectingend-systemsEnd-systems a.k.a. hostsPCs, workstationsdedicated computersnetwork components2 3. Multiaccess vs. Point-to-point Multiaccess means shared medium. many end-systems share the same physical communicationresources (wire, frequency, ...) There must be some arbitration mechanism. Point-to-point only 2 systems involved no doubt about where data came from !3 4. LAN - Local Area Network connects computers that are physicallyclose together ( < 1 mile). high speed multi-access Technologies: Ethernet 10 Mbps, 100Mbps Token Ring 16 Mbps FDDI 100 Mbps4 5. WAN - Wide Area Network connects computers that are physically farapart. long-haul network. typically slower than a LAN. typically less reliable than a LAN. point-to-point Technologies: telephone lines Satellite communications5 6. MAN - Metropolitan Area Network Larger than a LAN and smaller than a WAN- example: campus-wide network- multi-access network Technologies: coaxial cable microwave6 7. A Network of Networks roughly hierarchical Tier-1 ISPs provide national,international coverage Tier-2 ISPs provideregional coverage Tier-3 and lower levels providelocal coverage any tier may sell tobusiness and residentialcustomers any ISP may have alink to any other ISP(not strictly hierarchical)7 8. Internet Design Goals primary goal: interoperability among existing networks a network of networks obey administrative boundaries secondary goals fault tolerance multiple transport protocols support a variety of networks distributed management cost effective, low effort for host attachment,accountability first three were more important, so remaining fourdid not receive as much attention no mention of security8 9. Internet Design Principles minimal assumptions about services networkshould support ability to send packets no reliability or security end-to-end principle keep the core of the network as simple aspossible, put complex functionality at the edgesexception: significant performance improvement9 10. Network Models Using a formal model allows us to deal withvarious aspects of Networks abstractly.We will look at a popular model (OSIreference model). The OSI reference model is a layered model.10 11. Layering Divide a task into pieces and then solveeach piece independently (or nearly so). Establishing a well defined interfacebetween layers makes porting easier. Major Advantages: Code Reuse Extensibility11 12. The Internet Hourglass12 13. The Internet at each Hop13 14. Interface and Peer-to-peer Protocols Interface protocols describe communication betweenlayers on the same endpoint. Peer-to-peer protocols describe communicationbetween peers at the same layer.ProcessTransportNetworkData LinkProcessTransportNetworkData LinkInterface ProtocolsPeer-to-peer Protocols14 15. Whats a protocol?human protocols: whats the time? I have a question introductions specific msgs sent specific actions takenwhen msgs received,or other eventsnetwork protocols: machines rather thanhumans all communicationactivity in Internetgoverned by protocols15 16. Whats a protocol?a human protocol and acomputer networkprotocol:16HiHiGot thetime?2:00Q: Other human protocols?TCP connectionrequestTCP connectionresponseGet http://www.awl.com/kurose-rosstime 17. Protocol An agreed upon convention for communication. both endpoints need to understand the protocol. Protocols must be formally defined and unambiguous! Protocols define format, order of msgs sent and received among network entities, actions taken on msg transmission, receipt We will study lots of existing protocols and perhapsdevelop a few of our own.17 18. Client - Server A server is a process - not a machine ! A server waits for a request from a client. A client is a process that sends a requestto an existing server and (usually) waits fora reply.18