A Client Server Transaction 15 213 Most network applications are based on the clientclient server model The course that gives CMU its Zip Internetworking November 10 2006 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 Topics 1 Client sends request Client server programming model Networks Internetworks Global IP Internet Client process 4 Client handles response z IP addresses z Domain names z Connections 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 15 213 F 06 2 class21 ppt Hardware Org of a Network Host CPU chip register file Computer Networks A network is a hierarchical system of boxes and wires organized by geographical proximity ALU system bus memory bus SAN System Area Network spans cluster or machine room LAN local area network spans a building or campus Switched Ethernet Quadrics QSW main memory I O bridge MI Ethernet is most prominent example An internetwork internet internet is an interconnected set of networks I O bus USB controller mouse keyboard graphics adapter WAN wide area network spans country or world Typically high speed point to point phone lines Expansion slots 3 Server process disk controller network adapter disk network monitor 15 213 F 06 The Gobal IP Internet uppercase I is the most famous example of an internet lowercase i Let Let s see how we would build an internet from the ground up 4 15 213 F 06 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 host host 100 Mb s Next Level Bridged Ethernet Segment Spans building or campus Bridges cleverly learn which hosts are reachable from which ports ports and then selectively copy frames from port to port host A 100 Mb s B host hub host host hub 100 Mb s ports Operation host X bridge hub 100 Mb s 1 Gb s 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 hub 100 Mb s Every host sees every bit host Note Hubs are on their way out Bridges switches routers became cheap enough to replace them means no more broadcasting 15 213 F 06 5 host bridge Y host host 100 Mb s host hub host host host C 15 213 F 06 6 Conceptual View of LANs Next Level internets For simplicity hubs bridges and wires are often shown as a collection of hosts attached to a single wire Multiple incompatible LANs can be physically connected by specialized computers called routers routers The connected networks are called an internet internet host host host 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 7 15 213 F 06 8 15 213 F 06 Logical Structure of Internet host router router host The Notion of an internet Protocol router How is it possible to send bits across incompatible LANs and WANs router router Solution protocol software running on each host and router smooths out the differences between the different networks router Ad hoc interconnection of networks z No particular topology z Vastly different router link capacities Send packets from source to destination by hopping through 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 z Router forms bridge from one network to another TCP IP is the protocol for the global IP Internet z Different packets may take different routes 15 213 F 06 9 What Does an internet Protocol Do 15 213 F 06 10 Transferring Data Over an internet 1 Provides a naming scheme An internet protocol defines a uniform format for host addresses 1 Each host and router is assigned at least one of these internet addresses that uniquely identifies it An internet protocol defines a standard transfer unit packet Packet consists of header and payload z Header contains info such as packet size source and client server protocol software internet packet data 3 data LAN1 adapter PH FH1 12 data 7 data PH FH2 6 data PH FH2 LAN2 adapter LAN2 adapter LAN2 frame 4 15 213 F 06 Router LAN1 adapter LAN1 8 protocol software PH FH1 LAN1 frame destination addresses z Payload contains data bits sent from source host 11 Host B data 2 2 Provides a delivery mechanism Host A data PH FH1 data protocol software LAN2 PH FH2 5 15 213 F 06 Other Issues Global IP Internet We are glossing over a number of important questions Most famous example of an internet 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 Based on the TCP IP protocol family z Provides basic naming scheme and unreliable delivery capability of packets datagrams from host to host UDP Unreliable Datagram Protocol z Uses IP to provide unreliable datagram delivery from process What if packets get lost to process These and other questions are addressed by the area of systems known as computer networking 15 213 F 06 13 Hardware and Software Org of an Internet Application Internet client host Internet server host TCP Transmission Control Protocol z 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 interface 14 An Internet backbone is a collection of routers nationwide or worldwide connected by highhigh speed pointpoint toto point networks User code Server A Network Access Point NAP is a router that connects multiple backbones sometimes referred to as peers peers TCP IP Kernel code TCP IP Regional networks are smaller backbones that cover smaller geographical areas e g cities or states Hardware interface interrupts Network adapter Hardware and firmware Network adapter Global IP Internet 15 213 F 06 Basic Internet Components Client Sockets interface system calls 15 IP Internet protocol A point of presence POP is a machine that is connected to the Internet Internet Service Providers ISPs provide dialdial up or direct access to POPs POPs 15 213 F 06 16 15 213 F 06 NAP Based Internet Architecture NAPs link together commercial backbones provided by
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