CS 105 Tour of the Black Holes of Computing Internetworking Topics Client server programming model Networks Internetworks Global IP Internet IP addresses Domain names Connections A Client Server Transaction Almost every network application is based on clientserver 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 same or different hosts 2 CS 105 Computer Networks A network is a hierarchical system of boxes and wires organized by geographical proximity LAN local area network spans building or campus Ethernet is most prominent example 802 11 wireless becoming more important WAN wide area network spans country or world Typically high speed point to point copper or fiber lines Also microwave and satellite links in some situations An internetwork internet is an interconnected set of networks Global IP Internet uppercase I is most famous example of an internet lowercase i Let s look at how to build an internet from ground up 3 CS 105 Lowest Level Ethernet Segment Ethernet segment consists of collection of hosts connected by wires twisted pairs to a hub replaces common wire bus Spans room or floor in a building Operation Each Ethernet adapter has 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 Alternative switch copies bits only to proper destination port Every adapter sees every bit chooses which frames to hand to system host 100 Mb s host hub host 100 Mb s ports 4 CS 105 Next Level Bridged Ethernet Seg Spans building or campus Bridges cleverly learn which hosts are reachable from which ports and then selectively copy frames from port to port How Frames have source and destination addresses A host B host hub host 100 Mb s host X bridge 100 Mb s 1 Gb s hub host 5 host 100 Mb s bridge Y 100 Mb s host host hub host host hub host host C CS 105 Conceptual View of LANs For simplicity hubs bridges and wires are often shown as collection of hosts attached to a single wire host 6 host host CS 105 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 7 CS 105 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 differences between 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 8 TCP IP is protocol family for global IP Internet CS 105 What Does an internet Protocol Do 1 Provides naming scheme Defines uniform format for host addresses Each host and router is assigned at least one internet address that uniquely identifies it 2 Provides 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 9 Encapsulation key to network messages CS 105 Transferring Data via an internet 1 Host A Host B client server data protocol software internet packet 2 data 3 data LAN1 adapter PH FH1 4 10 Router LAN1 adapter LAN1 data data 7 data PH 6 data PH FH2 protocol software PH Frame 8 LAN2 adapter PH FH1 LAN2 adapter LAN2 frame data LAN2 PH FH2 5 protocol software CS 105 Other Issues We are glossing over several important questions What if different networks have different maximum frame sizes segmentation How do routers know where to forward frames How do routers learn 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 CS 125 11 CS 105 Global IP Internet Most famous example of an internet Based on 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 mix of Unix file I O and functions from the sockets interface 12 CS 105 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 13 CS 105 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 14 CS 105 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 15 CS 105 NSFNET Internet Backbone source www eef org 16 CS 105 Enter Al Gore Myth Al Gore claimed to have invented the Internet Fact In a 1999 interview Al Gore said During my service in the United States Congress I took the initiative in creating the Internet Fact Dave Farber Vint Cerf and Bob Metcalfe have all supported the statement Fact Al Gore introduced and supported many bills funding the
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