InternetworkingA Client-Server TransactionComputer NetworksLowest Level: Ethernet SegmentNext Level: Bridged Ethernet SegConceptual View of LANsNext Level: internetsNotion of an internet ProtocolWhat Does an internet Protocol Do?Transferring Data via an internetOther IssuesGlobal IP InternetHardware and Software Org of an Internet ApplicationBasic Internet ComponentsThe Internet Circa 1993NSFNET Internet BackboneEnter Al GoreCurrent NAP-Based Internet ArchitectureAbstracted Internet HiearchyNetwork Access Points (NAPs)Programmer’s View of Internet1. IP (v4) AddressesDotted-Decimal Notation2. Internet Domain NamesDomain Naming System (DNS)Properties of DNS Host EntriesA Program That Queries DNSQuerying DNS from the Command Line3. Internet ConnectionsPutting it all Together: Anatomy of an Internet ConnectionNext TimeInternetworkingInternetworkingTopicsTopicsClient-server programming modelNetworksInternetworksGlobal IP InternetIP addressesDomain namesConnectionsCS 105“Tour of the Black Holes of Computing”– 2 –CS 105A Client-Server TransactionA Client-Server TransactionClientprocessServerprocess1. Client sends request2. Server handlesrequest3. Server sends response4. Client handlesresponseResource(Almost) every network application is based on client-(Almost) every network application is based on client-server model:server model:A server process and one or more client processesServer manages some resourceServer provides service by manipulating resource for clientsNote: clients and servers are processes running on hosts (can be same or different hosts)– 3 –CS 105Computer NetworksComputer NetworksA network is a hierarchical system of boxes and wires A network is a hierarchical system of boxes and wires organized by geographical proximityorganized by geographical proximityLAN (local area network) spans building or campusEthernet is most prominent example802.11 (wireless) becoming more importantWAN (wide-area network) spans country or worldTypically high-speed point-to-point copper or fiber linesAlso microwave and satellite links in some situationsAn An internetworkinternetwork ( (internetinternet) ) is an interconnected set of is an interconnected set of networksnetworksGlobal IP Internet (uppercase “I”) is most famous example of an internet (lowercase “i”)Let’s look at how to build an internet from ground upLet’s look at how to build an internet from ground up– 4 –CS 105Lowest Level: Ethernet SegmentLowest Level: Ethernet SegmentEthernet segment consists of collection of Ethernet segment consists of collection of hostshosts connected by wires (twisted pairs) to a connected by wires (twisted pairs) to a hubhub - replaces common ‘wire’, ‘bus’ - replaces common ‘wire’, ‘bus’ Spans room or floor in a buildingSpans room or floor in a buildingOperationOperationEach Ethernet adapter has unique 48-bit addressHosts send bits to any other host in chunks called framesHub slavishly copies each bit from each port to every other portEvery adapter sees every bit; choose s which frames to hand to systemAlternative: switch copies bits only to proper destination porthosthost hosthub100 Mb/s100 Mb/sports– 5 –CS 105Next Level: Bridged Ethernet SegNext Level: Bridged Ethernet SegSpans building or campusSpans building or campusBridges cleverly learn which hosts are reachable from which ports and then selectively Bridges cleverly learn which hosts are reachable from which ports and then selectively copy frames from port to port. How? Frames have source and destination addresses….copy frames from port to port. How? Frames have source and destination addresses….hosthost host host hosthub hubbridge100 Mb/s100 Mb/shosthosthub100 Mb/s 100 Mb/s1 Gb/shosthost hostbridgehosthosthubA BCXY– 6 –CS 105Conceptual View of LANsConceptual View of LANsFor simplicity, hubs, bridges, and wires are often shown as collection of hosts attached to a single wire:For simplicity, hubs, bridges, and wires are often shown as collection of hosts attached to a single wire:hosthost host...– 7 –CS 105Next Level: internetsNext Level: internetsMultiple incompatible LANs can be physically connected by specialized Multiple incompatible LANs can be physically connected by specialized computers called computers called routersroutersThe connected networks are called an The connected networks are called an internetinternethosthost hostLAN 1...hosthost hostLAN 2...router router routerWAN WANLAN 1 and LAN 2 might be completely different, totally incompatible LANs (e.g., Ethernet and ATM)– 8 –CS 105 Notion of an internet Protocol Notion of an internet ProtocolHow is it possible to send bits across incompatible How is it possible to send bits across incompatible LANs and WANs?LANs and WANs?Solution: Solution: protocol softwareprotocol software running on each host and running on each host and router smooths out differences between different router smooths out differences between different networksnetworksImplements an Implements an internet protocolinternet protocol (i.e., set of rules) that (i.e., set of rules) that governs how hosts and routers should cooperate governs how hosts and routers should cooperate when they transfer data from network to networkwhen they transfer data from network to network•TCP/IP is protocol (family) for global IP Internet– 9 –CS 105What Does an internet Protocol Do?What Does an internet Protocol Do?1. Provides naming scheme1. Provides naming schemeDefines uniform format for host addressesEach host (and router) is assigned at least one internet address that uniquely identifies it2. Provides delivery mechanism2. Provides delivery mechanismAn internet protocol defines a standard transfer unit (packet)Packet consists of header and payloadHeader: contains info such as packet size, source and destination addressesPayload: contains data bits sent from source hostEncapsulation - key to network messages– 10 –CS 105Transferring Data via an internetTransferring Data via an internetprotocolsoftwareclientLAN1adapterHost Adatadata PH FH1data PHdata PH FH2LAN1LAN2datadata PH data PH FH2(1)(2)(3)(4)(5)(6)(7)(8)internet packetLAN2 frameprotocolsoftwareLAN1adapterLAN2adapterRouterFH1data PHprotocolsoftwareserverLAN2adapterHost BFrame– 11 –CS 105Other IssuesOther IssuesWe are glossing over several important questions:We are glossing over several important
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