Typical computer system 15 213 The course that gives CMU its Zip Keyboard Internetworking Processor May 1 2001 Interrupt controller Mouse Keyboard controller Modem Serial port controller Printer Parallel port controller Local IO Bus Topics Protocol layering and encapsulation Internetworking with hubs bridges and routers The Internet Protocol IP The global Internet Memory IDE disk controller SCSI controller class30 ppt class30 ppt Display Network cdrom 2 CS 213 S 01 Protocols Generic network host A protocol defines the format of packets and the rules for communicating them across the network Different protocols provide different levels of service host OS code network adapter interface card Network adapter SCSI bus disk disk protocol stack Video adapter software software software hardware hardware hardware link link link simple error correction ethernet uniform name space unreliable best effort datagrams host host IP reliable byte streams TCP unreliable best effort datagrams process process UDP multimedia data retrieval HTTP Interconnect wires repeaters bridges and routers Crucial idea protocols leverage off of the capabilities of other protocols class30 ppt 3 class30 ppt CS 213 S 01 Page 1 4 CS 213 S 01 Protocol layering interface between user code and OS code Sockets interface Encapsulation Application program Protocols provide specialized services by relying on services provided by lowerlevel protocols i e they leverage lowerlevel services User code data User Interface API OS code User application program FTP Telnet WWW email Unreliable best effort datagram delivery processprocess User datagram protocol UDP Transmission control protocol TCP Internet Protocol IP Reliable byte stream delivery processprocess Network interface ethernet Unreliable best effort datagram delivery host host data IP datagram TCP segment header header data Ethernet frame IP datagram TCP segment header header header data IP Physical connection hardware OS adapter interface exception mechanism Adapter Adapter Network interface Network class30 ppt 5 class30 ppt CS 213 S 01 System area network SAN Metropolitan area network MAN same room meters 300 MB s Cray T3E Each network must stand on its own with no internal changes allowed to connect to the internet Communications should be on a best effort basis black boxes later called routers should be used to connect the networks No global control at the operations level Wide area network WAN same bldg or campus kilometers 10 Mb sEthernet 100 Mb s Fast Ethernet 100 Mb s FDDI 150 Mb s OC 3 ATM 622 Mb s OC 12 ATM nationwide or worldwide 1000 s of kilometers telephone system 1 544 Mb s T1 carrier 44 736 Mb s T3 carrier Global Internet 7 CS 213 S 01 Build a single network an interconnected set of networks or internetwork or internet out of a large collection of separate networks same city 10 s of kilometers 800 Mb s Gigabit Nectar Local area network LAN 6 The internetworking idea Kahn 1972 Basic network types class30 ppt TCP segment header TCP class30 ppt CS 213 S 01 Page 2 8 CS 213 S 01 Internetworking challenges Internetworking with repeaters Challenges heterogeneity lots of different kinds of networks Ethernet FDDI ATM wireless point to point how to unify this hodgepodge scale how to provide uniques names for potentially billions of nodes naming how to find all these nodes forwarding and routing r Repeaters also called hubs r in the figure directly transfer bits from their inputs to their outputs r Note internet refers to a general idea Internet refers to a particular implementation of that idea The global IP Internet r r class30 ppt 9 class30 ppt CS 213 S 01 10Base T application application transport transport network network data link data link physical physical Host on network A class30 ppt Repeater forwards bits 11 CS 213 S 01 Internetworking with repeaters Pros and cons Internetworking with repeaters Telnet FTP HTTP email 10 Pros Transparency LANS can be connected without any awareness from the hosts Useful for serving multiple machines in an office from one ethernet outlet Cons Not scalable ethernet standard allows only 4 repeaters more than 4 would introduce delays that would break contention detection No heterogeneity Networks connected with repeaters must have identical electrical properties Host on network B class30 ppt CS 213 S 01 Page 3 12 CS 213 S 01 Internetworking with bridges b Bridges b In the figure maintain a cache of hosts on their input segments b Selectively transfer ethernet frames from their inputs to their outputs Internetworking with bridges Telnet FTP HTTP email CSMA CD b 10Base T 13 transport transport network network data link data link physical class30 ppt CS 213 S 01 Internetworking with bridges Pros and cons Pros 14 Host on network B CS 213 S 01 Def An internetwork internet for short is an arbitrary collection of physical networks interconnected by routers to provide some sort of host to host packet delivery service Cons Transparency can be misleading looks like a single Ethernet segment but really isn t packets can be dropped latencies vary Homogeneity can only support networks with identical frame headers e g Ethernet FDDI however can connect different speed Ethernets Scalability tens of networks only bridges forward all broadcast frames increased latency 15 physical Bridge forwards ethernet frames Internetworking with routers Transparency LANS can be connected without any awareness from the hosts popular solution for campus size networks class30 ppt application Host on network A b class30 ppt application host host internet host host class30 ppt CS 213 S 01 Page 4 16 CS 213 S 01 Building an internet Building an internet cont We start with two separate unconnected computer networks subnets which are at different locations and possibly built by different vendors Next we physically connect one of the computers called a router in this case computer C to each of the networks A B C X Y Z A B adapter adapter adapter adapter adapter adapter adapter adapter Ethernet network 1 SCS ATM network 2 ECE C router adapter adapter network 1 SCS X Y Z adapter adapter adapter network 2 ECE Question How to present the illusion of one network class30 ppt 17 class30 ppt CS 213 S 01 Building an internet cont 128 2 250 1 128 2 250 2 A B adapter adapter 128 2 250 0 128 2 80 0 C router adapter network 1 SCS adapter 128 2 80 1 128 2 80 2 X Y At this point we have an internet consisting of 6 computers built from 2 original networks Each computer on our internet
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