Carnegie Mellon Internetworking 15 213 Introduc0on to Computer Systems 19th Lecture Oct 28 2010 Instructors Randy Bryant and Dave O Hallaron 1 Carnegie Mellon A Client Server Transac8on 4 Client handles response Client process 1 Client sends request 3 Server sends response Server process Resource 2 Server handles request Note clients and servers are processes running on hosts can be the same or di erent hosts Most network applica8ons are based on the client server model A server process and one or more client processes Server manages some resource Server provides service by manipula0ng resource for clients Server ac0vated by request from client vending machine analogy 2 Carnegie Mellon Hardware Organiza8on of a Network Host CPU chip register le ALU system bus memory bus main memory I O bridge MI Expansion slots I O bus USB controller mouse keyboard graphics adapter disk controller network adapter disk network monitor 3 Carnegie Mellon Computer Networks A network is a hierarchical system of boxes and wires organized by geographical proximity SAN System Area Network spans cluster or machine room Switched Ethernet Quadrics QSW LAN Local Area Network spans a building or campus Ethernet is most prominent example WAN Wide Area Network spans country or world Typically high speed point to point phone lines An internetwork internet is an interconnected set of networks The Global IP Internet uppercase I is the most famous example of an internet lowercase i Let s see how an internet is built from the ground up 4 Carnegie Mellon Lowest Level Ethernet Segment host 100 Mb s host hub host 100 Mb s port Ethernet segment consists of a collec8on of hosts connected by wires twisted pairs to a hub Spans room or oor in a building Opera8on Each Ethernet adapter has a unique 48 bit address MAC address E g 00 16 ea e3 54 e6 Hosts send bits to any other host in chunks called frames Hub slavishly copies each bit from each port to every other port Every host sees every bit Note Hubs are on their way out Bridges switches routers became cheap enough to replace them means no more broadcas0ng 5 Carnegie Mellon Next Level Bridged Ethernet Segment A host host B host host X hub 100 Mb s bridge 100 Mb s hub 1 Gb s hub host host 100 Mb s host bridge 100 Mb s Y host host host hub host host C Spans building or campus Bridges cleverly learn which hosts are reachable from which ports and then selec8vely copy frames from port to port 6 Carnegie Mellon Conceptual View of LANs For simplicity hubs bridges and wires are oZen shown as a collec8on of hosts a ached to a single wire host host host 7 Carnegie Mellon Next Level internets Mul8ple incompa8ble LANs can be physically connected by specialized computers called routers The connected networks are called an internet host host host host host host LAN LAN router WAN router WAN router LAN 1 and LAN 2 might be completely di erent totally incompaHble e g Ethernet and Wi 802 11 T1 links DSL 8 Carnegie Mellon Logical Structure of an internet host router host router router router router router Ad hoc interconnec8on of networks No par0cular topology Vastly di erent router link capaci0es Send packets from source to des8na8on by hopping through networks Router forms bridge from one network to another Di erent packets may take di erent routes 9 Carnegie Mellon The No8on of an internet Protocol How is it possible to send bits across incompa8ble LANs and WANs Solu8on protocol socware running on each host and router smooths out the di erences between the di erent networks Implements an internet protocol i e set of rules governs how hosts and routers should cooperate when they transfer data from network to network TCP IP is the protocol for the global IP Internet 10 Carnegie Mellon What Does an internet Protocol Do Provides a naming scheme An internet protocol de nes a uniform format for host addresses Each host and router is assigned at least one of these internet addresses that uniquely iden0 es it Provides a delivery mechanism An internet protocol de nes a standard transfer unit packet Packet consists of header and payload Header contains info such as packet size source and des0na0on addresses Payload contains data bits sent from source host 11 Carnegie Mellon Transferring Data Over an internet LAN1 1 client server protocol soZware data data LAN1 adapter PH FH1 4 PH Internet packet header FH LAN frame header 8 data 7 data PH FH2 6 data PH FH2 LAN2 adapter Router LAN1 adapter data LAN2 protocol soZware PH FH1 LAN1 frame 3 Host B data internet packet 2 Host A LAN2 adapter PH FH1 LAN2 frame data PH FH2 5 protocol soZware 12 Carnegie Mellon Other Issues We are glossing over a number of important ques8ons What if di erent networks have di erent maximum frame sizes segmenta0on How do routers know where to forward frames How are routers informed when the network topology changes What if packets get lost These and other ques8ons are addressed by the area of systems known as computer networking 13 Carnegie Mellon Global IP Internet Most famous example of an internet Based on the TCP IP protocol family IP Internet protocol Provides basic naming scheme and unreliable delivery capability of packets datagrams from host to host UDP Unreliable Datagram Protocol Uses IP to provide unreliable datagram delivery from process to process TCP Transmission Control Protocol Uses IP to provide reliable byte streams from process to process over connec0ons Accessed via a mix of Unix le I O and func8ons from the sockets interface 14 Carnegie Mellon Hardware and SoZware Organiza8on of an Internet Applica8on Internet client host Internet server host Client User code Server TCP IP Kernel code TCP IP Sockets interface system calls Hardware interface interrupts Network adapter Hardware and rmware Network adapter Global IP Internet 15 Carnegie Mellon Basic Internet Components Internet backbone collec0on of routers na0onwide or worldwide connected by high speed point to point networks Network Access Point NAP router that connects mul0ple backbones ocen referred to as peers Regional networks smaller backbones that cover smaller geographical areas e g ci0es or states Point of presence POP machine that is connected to the Internet Internet Service Providers ISPs provide dial up or direct access to POPs 16 Carnegie Mellon NAP Based Internet Architecture NAPs link together commercial backbones provided by companies such as AT T and Worldcom Currently in the US there are about 50 commercial backbones connected by 12 NAPs
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