15 213 The course that gives CMU its Zip Internetworking Nov 20 2001 Topics internets The Global IP Internet Programmer s view of the Internet class25 ppt A client server transaction Every network application is 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 1 client sends request client process 4 client handles response server process 3 server sends response resource 2 server handles request Note clients and servers are processes running on hosts can be the same or different hosts class25 ppt 2 CS 213 F 01 Hardware organization 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 mousekeyboard class25 ppt graphics adapter disk controller network adapter disk network monitor 3 CS 213 F 01 Computer networks A network is a hierarchical system of boxes and wires organized by geographical proximity 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 IP Internet is the most famous example of an internetwork Let s see how we would build an internetwork from the ground up class25 ppt 4 CS 213 F 01 Lowest level Ethernet segment Ethernet segment consists of a collection of hosts connected by wires twisted pairs to a hub Spans room or floor in a building host host 100 Mb s host 100 Mb s hub ports 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 class25 ppt 5 CS 213 F 01 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 host host X bridge hub 100 Mb s hub 100 Mb s 1 Gb s hub host 100 Mb s host bridge Y host 100 Mb s host host host hub host host C class25 ppt 6 CS 213 F 01 Conceptual view of LANs For simplicity hubs bridges and wires are often shown as a collection of hosts attached to a single wire host class25 ppt host 7 host CS 213 F 01 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 ATM class25 ppt 8 CS 213 F 01 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 TCP IP is the protocol for the global IP Internet class25 ppt 9 CS 213 F 01 What does an internet protocol do Naming scheme The 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 Delivery mechanism The 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 class25 ppt 10 CS 213 F 01 Transferring data over an internet 1 client server protocol software data data LAN1 adapter PH FH1 Router LAN1 adapter LAN1 8 data 7 data PH FH2 6 data PH FH2 protocol software PH FH1 LAN1 frame 3 Host B data internet packet 2 Host A LAN2 adapter LAN2 adapter LAN2 frame 4 data PH FH1 data PH FH2 5 protocol software class25 ppt 11 CS 213 F 01 LAN2 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 questions form the heart of the area of computer systems known as networking class25 ppt 12 CS 213 F 01 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 processto process TCP Transmission Control Protocol uses IP to provide reliable byte streams like files from process to process Accessed via a mix of Unix file I O and functions from the Berkeley sockets interface class25 ppt 13 CS 213 F 01 Hardware and software organization of an Internet application Internet client host Internet server host client user code server TCP IP kernel code TCP IP network adapter hardware network adapter sockets interface system calls hardware interface interrupts Global IP Internet class25 ppt 14 CS 213 F 01 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 dialup or direct access to POPs class25 ppt 15 CS 213 F 01 The Internet circa 1993 In 1993 the Internet consisted of one backbone NSFNET that connected 13 sites via 45 Mbs T3 links Merit Univ of Mich NCSA Illinois Cornell Theory Center Pittsburgh Supercomputing Center San Diego Supercomputing Center John von Neumann Center Princeton BARRNet Palo Alto MidNet Lincoln NE WestNet Salt Lake City NorthwestNet Seattle SESQUINET Rice SURANET Georgia Tech Connecting to the Internet involved connecting one of your routers to a router at a backbone site or to a regional network that was already connected to the backbone class25 ppt 16 CS 213 F 01 The Internet backbone circa 1993 class25 ppt 17 CS 213 F 01 Current NAP based Internet architecture In the early 90 s commercial outfits were building their own high speed backbones
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