15 213 The course that gives CMU its Zip Internetworking April 17 2003 Topics Client server programming model Networks Internetworks Global IP Internet IP addresses Domain names Connections 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 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 S 03 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 3 graphics adapter disk controller network adapter disk network monitor 15 213 S 03 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 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 4 15 213 S 03 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 host 100 Mb s host hub host 100 Mb s ports 5 15 213 S 03 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 6 host 100 Mb s bridge Y 100 Mb s host host hub host host hub host host C 15 213 S 03 Conceptual View of LANs For simplicity hubs bridges and wires are often shown as a collection of hosts attached to a single wire host 7 host host 15 213 S 03 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 8 15 213 S 03 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 smoothes 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 9 TCP IP is the protocol for the global IP Internet 15 213 S 03 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 10 15 213 S 03 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 11 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 S 03 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 12 15 213 S 03 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 13 15 213 S 03 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 14 15 213 S 03 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 15 15 213 S 03 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 16 15 213 S 03 NSFNET Internet Backbone source www eef org 17 15 213 S 03 Current NAP Based Internet Architecture In the early 90 s commercial outfits were building their own high speed backbones connecting to NSFNET and selling access to their POPs to companies ISPs and individuals In 1995 NSF
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