Carnegie Mellon Introduction to Computer Systems 15 213 fall 2009 20th Lecture Nov 4th Instructors Majd Sakr and Khaled Harras Carnegie Mellon Today Internetworking Networks Global IP Internet Carnegie Mellon A Client Server Transaction 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 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 Carnegie Mellon 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 mouse keyboard graphics adapter disk controller network adapter disk network monitor Carnegie Mellon 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 Global IP Internet uppercase I is the most famous example of an internet lowercase i Let s see how an internet is built from the ground up Carnegie Mellon Lowest Level Ethernet Segment host 100 Mb s host hub host 100 Mb s port Ethernet segment consists of a collection of hosts connected by wires twisted pairs to a hub Spans room or floor in a building Operation Each Ethernet adapter has a unique 48 bit address MAC 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 Carnegie Mellon Next Level Bridged Ethernet Segment A host host hub B host host X 100 Mb s bridge 100 Mb s hub 1 Gb s hub 100 Mb s bridge host 100 Mb s host host hub Y host host host host host C Spans building or campus Bridges cleverly learn which hosts are reachable from which ports and then selectively copy frames from port to port Carnegie Mellon Conceptual View of LANs For simplicity hubs bridges and wires are often shown as a collection of hosts attached to a single wire host host host Carnegie Mellon 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 host LAN router WAN router WAN router LAN 1 and LAN 2 might be completely different totally incompatible e g Ethernet and Wifi 802 11 T1 links DSL Carnegie Mellon Logical Structure of an internet host router host router 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 Carnegie Mellon 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 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 Carnegie Mellon What Does an internet Protocol Do 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 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 Carnegie Mellon Transferring Data Over an internet LAN1 1 client server protocol software data PH data PH LAN2 8 data 7 data PH FH2 6 data PH FH2 protocol software FH1 LAN1 frame 3 Host B data internet packet 2 Host A LAN1 adapter LAN2 adapter Router FH1 LAN1 adapter LAN2 adapter LAN2 frame 4 PH Internet packet header FH LAN frame header data PH FH1 data protocol software PH FH2 5 Carnegie Mellon 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 Carnegie Mellon Today Internetworking Networks Global IP Internet Carnegie Mellon 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 Carnegie Mellon Hardware and Software Organization 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 Global IP Internet Network adapter Carnegie Mellon Basic Internet Components Internet backbone collection of routers nationwide or worldwide connected by high speed point to point networks Network Access Point NAP router that connects multiple backbones often referred to as peers Regional networks smaller backbones that cover smaller geographical areas e g cities or states Point of presence POP machine that is connected to the Internet Internet Service Providers ISPs provide dial up or direct access to POPs Carnegie Mellon NAP Based Internet Architecture NAPs link together commercial backbones provided
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