1Midterm ReviewEECS 122: Lecture 1Department of Electrical Engineering and Computer SciencesUniversity of CaliforniaBerkeleyMarch 9, 2006EECS122 Lecture Midterm Review2Review: Check List Big Picture Layers Where protocols are implemented Switching Techniques Applications DNS HTTP SMTP Transport Network Layer: Routing Protocols Class-Based; Classless Addressing Dijkstra; Bellman-Ford BGP Network Layer Forwarding Architecture: Input, Output Fabric Architectures: Shared Bus, Shared Mem, Switched Basic Performance Metrics (Packet Delay, Little’s Law) QoS Max Min Fairness Mechanisms for QoS Scheduling: Fairness, GPS, WFQ Intserv, Diffserv Internet Multimedia Streaming and VOIPMarch 9, 2006EECS122 Lecture Midterm Review3The internet consists of many networksTier 1 ISPTier 1 ISPTier 1 ISPNAPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPlocalISPlocalISPlocalISPlocalISPlocalISPTier 3ISPlocalISPlocalISPlocalISPMany InternetService Providersat each level of theHierarchyMarch 9, 2006EECS122 Lecture Midterm Review4Two fundamentally different ways to forward information Circuit Switched Information is exchanged in units of “calls” Network resources are reserved for the duration of the call Example: The Phone Network Once a call goes through, subsequent calls cannot degrade call quality Packet Switched Information is exchanged in units of “packets” Typically, no resources are reserved Datagram: Each packet is forward independently Example: The Internet Virtual Circuit: All the packets from a given stream take the same path through the network Example: ATM, ISDN, IntservMarch 9, 2006EECS122 Lecture Midterm Review5Backbone Network March 9, 2006EECS122 Lecture Midterm Review6Metropolitan Area Network2March 9, 2006EECS122 Lecture Midterm Review7Campus NetworkMarch 9, 2006EECS122 Lecture Midterm Review8Local Area NetworkMarch 9, 2006EECS122 Lecture Midterm Review9The network edge: end systems (hosts): run application programs e.g. Web, email at “edge of network” client/server model client host requests, receives service from always-on server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Gnutella, KaZaA, SkypeMarch 9, 2006EECS122 Lecture Midterm Review10The Network Core Many interconnected “sub-networks” Many different architectures Advertises a “service” to the end devices E.g. Phone network v/s the InternetMarch 9, 2006EECS122 Lecture Midterm Review11Internet protocol stack application: supporting network applications FTP, SMTP, HTTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire”applicationtransportnetworklinkphysicalMarch 9, 2006EECS122 Lecture Midterm Review12ticket (purchase)baggage (check)gates (load)runway (takeoff)airplane routingdepartureairportarrivalairportintermediate air-trafficcontrol centersairplane routing airplane routingticket (complain)baggage (claimgates (unload)runway (land)airplane routingticketbaggagegatetakeoff/landingairplane routingLayering of airline functionalityLayers: each layer implements a service via its own internal-layer actions relying on services provided by layer below3March 9, 2006EECS122 Lecture Midterm Review13An Advanced View of Internet Layering Almost Any kind of application can write directly on IP Including new transport protocols IP cannot be avoided As long as the routers speak IP, any application that can make do with datagram service can be written and implemented on the end devices. No co-ordination, standards activity etc. is required!!NetworkIPTCP UDPApplicationBGP HTTP RTP TFTPTCP UDPIPEthernet FDDI Token Etc.March 9, 2006EECS122 Lecture Midterm Review14messagesegmentdatagramframesourceapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMdestinationapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMnetworklinkphysicallinkphysicalHtHnHlMHtHnMHtHnHlMHtHnMHtHnHlMHtHnHlMrouterswitchEncapsulationMarch 9, 2006EECS122 Lecture Midterm Review15Application Protocols Host-Host: HTTP, SMTP Host-Network: DNS Network-Network: Routing Protocols (e.g. OSPF)The Core providesa network service to the hostsHostHostMarch 9, 2006EECS122 Lecture Midterm Review16DNS Features Hierarchical Namespace Distributed architecture for storing names Nameservers assigned zones of the hierarchical namespace Backup servers available for redundancy Administration divided along the same hierarchy DNS client is simple: Resolver Client server interaction on UDP Port 53 (but can use TCP if desired)rooteducomgov milorgnet uk frberkeleymiteecssimsargusMarch 9, 2006EECS122 Lecture Midterm Review17Three kinds of DNS servers Top-level domain (TLD) servers: responsible for com, org, net, edu, etc, and all top-level country domains uk, fr, ca, jp. Network solutions maintains servers for com TLD Educause for edu TLD Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail). Can be maintained by organization or service provider Local DNS Server: When a host makes a DNS query, query is sent to its local DNS server Acts as a proxy, forwards query into hierarchy The Local server is not a part of the DNS hierarchyMarch 9, 2006EECS122 Lecture Midterm Review18How does a name get resolved Query “walks” its way up and down the hierarchy Iterated query I don’t know, but here’s who to ask next Recursive query I don’t know right now, but I’ll get back to you…4March 9, 2006EECS122 Lecture Midterm Review19HTTPHTTP: hypertext transfer protocol Web’s application layer protocol client/server model client: browser that requests, receives, “displays” Web objects server: Web server sends objects in response to requests Stateless ProtocolPC runningExplorerServer runningApache WebserverMac runningNavigatorHTTP requestHTTP requestHTTP responseHTTP responseMarch 9, 2006EECS122 Lecture Midterm Review20HTTP Uses TCP: client initiates TCP connection (creates socket) to server, port 80 server accepts TCP connection from client HTTP
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