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internet services

  1. 1. 15-213 “ The course that gives CMU its Zip!” Internetworkin g May 1, 2001 Topics • Protocol layering and encapsulation • Internetworking with hubs, bridges, and routers • The Internet Protocol (IP) • The global Internetclass30.ppt
  2. 2. Typical computer system Keyboard Mouse Modem Printer Interrupt Keyboard Serial port Parallel portProcessor controller controller controller controller Local/IO Bus IDE disk SCSI Video Network Memory adapter controller controller adapter SCSI bus disk Display Network disk cdrom class30.ppt –2– CS 213 S’01
  3. 3. Generic network host host OS code protocol software software software stack hardware hardware hardwarenetwork adapter/ link link linkinterface card Interconnect (wires, repeaters, bridges, and routers) class30.ppt –3– CS 213 S’01
  4. 4. ProtocolsA protocol defines the format of packets and the rules for communicating them across the network.Different protocols provide different levels of service: • 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)Crucial idea: protocols leverage off of the capabilities of other protocols. class30.ppt –4– CS 213 S’01
  5. 5. Protocol layeringinterface betweenuser code and OS Protocols provide specializedcode services by relying on services(Sockets interface) provided by lower-level protocols (i.e., they leverage lower-level services). User application program (FTP, Telnet, WWW, email) ReliableUnreliable User datagram protocol Transmission control byte streambest effort (UDP) protocol (TCP) deliverydatagram (process-delivery Internet Protocol (IP) process)(process-process) Network interface (ethernet) Unreliable best effort hardware Physical datagram connectio delivery n (host- host) class30.ppt –5– CS 213 S’01
  6. 6. Encapsulation Application programUser code data User Interface (API)OS code TCP segment TCP header data IP datagramTCP segment IP header header data OS/adapter interface (exception mechanism)Ethernet frame IP datagramTCP segment header header header data Adapter Adapter/Network interface Network class30.ppt –6– CS 213 S’01
  7. 7. Basic network typesSystem area network Metropolitan area (SAN) network (MAN) • same room (meters) • same city (10’s of • 300 MB/s Cray T3E kilometers) • 800 Mb/s Gigabit NectarLocal area network (LAN) Wide area network • same bldg or campus (WAN) (kilometers) • nationwide or worldwide • 10 Mb/sEthernet (1000’s of kilometers) • 100 Mb/s Fast Ethernet • telephone system • 100 Mb/s FDDI • 1.544 Mb/s T1 carrier • 150 Mb/s OC-3 ATM • 44.736 Mb/s T3 carrier • 622 Mb/s OC-12 ATM • Global Internet class30.ppt –7– CS 213 S’01
  8. 8. The internetworking idea (Kahn, 1972)Build a single network (an interconnected set of networks, or internetwork, or internet) out of a large collection of separate networks. • 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. class30.ppt –8– CS 213 S’01
  9. 9. InternetworkingChallenges: 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)Note: internet refers to a general idea, Internet refers to a particular implementation of that idea (The global IP Internet). class30.ppt –9– CS 213 S’01
  10. 10. Internetworking with repeaters r Repeaters (also called hubs) (r in the figure) directly transfer bits from their r inputs to their outputs r rclass30.ppt – 10 – CS 213 S’01
  11. 11. Internetworking with repeatersTelnet,FTP, application applicationHTTP,email transport transport network network data link data link 10Base-T physical physical Host on Repeater Host on network A (forwards bits) network B class30.ppt – 11 – CS 213 S’01
  12. 12. Internetworking with repeaters: Pros and consPros • 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. class30.ppt – 12 – CS 213 S’01
  13. 13. 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. b bclass30.ppt – 13 – CS 213 S’01
  14. 14. Internetworking with bridgesTelnet,FTP, application applicationHTTP,email transport transport network network CSMA/CD data link data link 10Base-T physical physical Host on Bridge Host on network A (forwards ethernet network B frames) class30.ppt – 14 – CS 213 S’01
  15. 15. Internetworking with bridges:Pros Pros and cons • Transparency – LANS can be connected without any awareness from the hosts – popular solution for campus-size networksCons • 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 class30.ppt » increased latency – 15 – CS 213 S’01
  16. 16. Internetworking with routersfor short) is anDef: An internetwork (internet arbitrary collection of physical networks interconnected by routers to provide some sort of host-to-host packet delivery service. host host internet host host class30.ppt – 16 – CS 213 S’01
  17. 17. Building an internetWe start with two separate, unconnected computer networks (subnets),which are at different locations, and possibly built by different vendors. A B C X Y Z adapter adapter adapter adapter adapter adapter Ethernet ATM network 1 (SCS) network 2 (ECE) Question: How to present the illusion of one network? class30.ppt – 17 – CS 213 S’01
  18. 18. Building an internet (cont)Next we physically connect one of the computers, called a router (in this case computer C), to each of the networks. A B C (router) X Y Z adapter adapter adapter adapter adapter adapter adapter network 1 (SCS) network 2 (ECE) class30.ppt – 18 – CS 213 S’01
  19. 19. Building an internet (cont) Finally, we run a software implementation of the Internet Protocol (IP) on each host and router. IP provides a global name space for the hosts, routing messages between network1 and network 2 if necessary. 128.2.250.0IP addresses: 128.2.250.1 128.2.250.2 128.2.80.0 128.2.80.1 128.2.80.2 128.2.80.3 A B C (router) X Y Z adapter adapter adapter adapter adapter adapter adapter network 1 (SCS) network 2 (ECE) class30.ppt – 19 – CS 213 S’01
  20. 20. Building an internet (cont)At this point we have an internet consisting of 6 computers built from2 original networks. Each computer on our internet can communicatewith any other computer. IP provides the illusion that there is justone network. 128.2.250.1 128.2.80.1 internet 128.2.250.2 128.2.80.2 128.2.80.3 128.2.250.0 128.2.80.3 class30.ppt – 20 – CS 213 S’01
  21. 21. Internetworking with routersTelnet,FTP, application applicationHTTP,email transport transport IP network network CSMA/CD data link data link 10Base-T physical physical Host on Router Host on network A (forwards IP packets) network B class30.ppt – 21 – CS 213 S’01
  22. 22. IP: Internetworking with routers IP is the most successful Many different kinds protocol ever developed of applications and Keys to success: higher-level • simple enough to implement on top protocols of any physical network – e.g., two tin cans and a string. IP • rich enough to serve as the base for implementations of more complicated protocols and applications. Many different – The IP designers never dreamed kinds of something like the Web. of networks • “rough consensus and working code” The “Hourglass Model”, – resulted in solid implementable Dave Clark, MIT specs.class30.ppt – 22 – CS 213 S’01
  23. 23. Internet protocol stack Berkeley sockets interface User application program (FTP, Telnet, WWW, email) ReliableUnreliable User datagram protocol Transmission control byte streambest effort (UDP) protocol (TCP) deliverydatagram (process-delivery Internet Protocol (IP) process)(process-process) Network interface (ethernet) Unreliable best effort hardware Physical datagram connectio delivery n (host- host) class30.ppt – 23 – CS 213 S’01
  24. 24. IP service modelIP service model: • Delivery model: IP provides best-effort delivery of datagram (connectionless) packets between two hosts. – IP tries but doesn’t guarantee that packets will arrive (best effort) – packets can be lost or duplicated (unreliable) – ordering of datagrams not guaranteed (connectionless) • Naming scheme: IP provides a unique address (name) for each host in the Internet.Why would such a limited delivery model be useful? • simple, so it runs on any kind of network • provides a basis for building more sophisticated and user- friendly protocols like TCP and UDPclass30.ppt – 24 – CS 213 S’01
  25. 25. IP datagram delivery: Example internet Network 1 (Ethernet) H1 H2 H3 H7 R3 H8 Network 2 (Ethernet) R1 Network 4 R2 (Point-to-point) Network 3 (FDDI) H4 H5 H6class30.ppt – 25 – CS 213 S’01
  26. 26. IP layeringProtocol layers used to connect host H1 to host H8 in exampleinternet. H1 R1 R2 R3 H8 TCP TCP IP IP IP IP IP ETH ETH FDDI FDDI P2P P2P ETH ETH class30.ppt – 26 – CS 213 S’01
  27. 27. Basic Internet components An Internet backbone is a collection of routers (nationwide or worldwide) connected by high-speed 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.class30.ppt – 27 – CS 213 S’01
  28. 28. The Internet circa 1993In 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.class30.ppt – 28 – CS 213 S’01
  29. 29. The Internet backbone (circa 1993)class30.ppt – 29 – CS 213 S’01
  30. 30. Current NAP-based Internet architectureIn 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 decommissioned NSFNET, and fostered creation of a collection of NAPs to connect the commercial backbones.Currently in the US there are about 50 commercial backbones connected by ~12 NAPs (peering points).Similar architecture worldwide connects national networks to the Internet. class30.ppt – 30 – CS 213 S’01
  31. 31. Internet connection hierarchy NAP NAP NAP colocation sites Backbone Backbone Backbone Backbone POP POP POP POP POP POP POP T3 Regional net ISP Big Business POP POP POP POP POP POP POP dialup dialup T1 T1ISP (for individuals) Small Business Pgh employee DC employee class30.ppt – 31 – CS 213 S’01
  32. 32. Network access points (NAPs) Note: Peers in this context are commercial backbones..droh Source: Boardwatch.comclass30.ppt – 32 – CS 213 S’01
  33. 33. MCI/WorldCom/UUNET Global Backbone Source: Boardwatch.comclass30.ppt – 33 – CS 213 S’01

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