15 213 The course that gives CMU its Zip Internetworking Nov 4 2008 Topics class19 ppt Client server programming model Networks Internetworks Global IP Internet IP addresses Domain names Connections A Client Server Transaction Most network applications are based on the client server model A server process and one or more client processes Server manages some resource Server provides service by manipulating resource for clients Server activated by request from client vending machine analogy 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 different hosts 2 15 213 F 08 Internet Traffic Mostly Client Server Web Internet Video 2007 Youtube is 10 of Internet traffic Exception Peer to peer 3 Each host acts as client server 15 213 F 08 Hardware Org of a Network Host CPU chip register file ALU system bus memory bus main memory I O bridge MI Expansion slots I O bus USB controller mouse keyboard 4 graphics adapter disk controller network adapter disk network monitor 15 213 F 08 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 Gobal IP Internet uppercase I is the most famous example of an internet lowercase i Let s see how we would build an internet from the ground up 5 15 213 F 08 Lowest Level Ethernet Segment Ethernet segment consists of a collection of hosts connected by wires twisted pairs to a hub hub Spans room or floor in a building Operation Each Ethernet adapter has a unique 48 bit address 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 broadcasting host 100 Mb s host hub host 100 Mb s ports 6 15 213 F 08 Next Level Bridged Ethernet Segment Spans building or campus Bridges cleverly learn which hosts are reachable from which ports and then selectively copy frames from port to port A host B host hub host 100 Mb s host X bridge 100 Mb s 1 Gb s hub host 7 host 100 Mb s bridge Y 100 Mb s host host hub host host hub host host C 15 213 F 08 Conceptual View of LANs For simplicity hubs bridges and wires are often shown as a collection of hosts attached to a single wire host 8 host host 15 213 F 08 Next Level internets Multiple incompatible LANs can be physically connected by specialized computers called routers The connected networks are called an internet host host host host host LAN 1 host LAN 2 router WAN router WAN router LAN 1 and LAN 2 might be completely different totally incompatible LANs e g Ethernet and Wifi 802 11 T1 links DSL 9 15 213 F 08 Logical Structure of Internet router host router host router router router router Ad hoc interconnection of networks No particular topology Vastly different router link capacities Send packets from source to destination by hopping through networks Router forms bridge from one network to another Different packets may take different routes 10 15 213 F 08 The Notion of an internet Protocol How is it possible to send bits across incompatible LANs and WANs Solution protocol software running on each host and router smooths out the differences between the different networks Implements an internet protocol i e set of rules that governs how hosts and routers should cooperate when they transfer data from network to network 11 TCP IP is the protocol for the global IP Internet 15 213 F 08 What Does an internet Protocol Do 1 Provides a naming scheme An internet protocol defines a uniform format for host addresses Each host and router is assigned at least one of these internet addresses that uniquely identifies it 2 Provides a delivery mechanism An internet protocol defines a standard transfer unit packet Packet consists of header and payload Header contains info such as packet size source and destination addresses Payload contains data bits sent from source host 12 15 213 F 08 Transferring Data Over an internet 1 Host A Host B client server data protocol software internet packet 2 data 3 data LAN1 adapter PH FH1 4 13 Router LAN1 adapter LAN1 data data 7 data PH FH2 6 data PH FH2 protocol software PH FH1 LAN1 frame 8 LAN2 adapter PH FH1 LAN2 adapter LAN2 frame data protocol software LAN2 PH FH2 5 15 213 F 08 Other Issues We are glossing over a number of important questions What if different networks have different maximum frame sizes segmentation 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 questions are addressed by the area of systems known as computer networking 14 15 213 F 08 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 connections Accessed via a mix of Unix file I O and functions from the sockets interface 15 15 213 F 08 Hardware and Software Org of an Internet Application 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 firmware Network adapter Global IP Internet 16 15 213 F 08 Basic Internet Components An Internet backbone is a collection of routers nationwide or worldwide connected by highspeed point to point networks A Network Access Point NAP is a router that connects multiple backbones sometimes referred to as peers Regional networks are smaller backbones that cover smaller geographical areas e g cities or states A point of presence POP is a machine that is connected to the Internet Internet Service Providers ISPs provide dial up or direct access to POPs 17 15 213 F 08 NAP Based Internet Architecture
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