The Internet

1. The Internet • Global scale, general purpose, heterogeneous-technologies, public, computer network • Internet Protocol • Open standard: Internet Engineering Task Force (IETF) as standard body ( http://www.ietf.org ) • Technical basis for other types of networks • Intranet: enterprise IP network • Developed by the research community Internet Design

2. Services Provided by the Internet • Shared access to computing resources • Telnet (1970’s) • Shared access to data/files • FTP, NFS, AFS (1980’s) • Communication medium over which people interact • Email (1980’s), on-line chat rooms (1990’s) • Instant messaging, IP Telephony (2000’s) • A medium for information dissemination • USENET (1980’s) • WWW (1990’s) • Replacing newspaper, magazine • Audio, video (2000’s): peer-to-peer systems • Replacing radio, telephony, TV, … Internet Design

3. Origin of Internet? Started by U.S. research/military organizations: • Three Major Actors: • DARPA: Defense Advanced Research Projects Agency • funds technology with military goals • DoD: U.S. Department of Defense • early adaptor of Internet technology for production use • NSF: National Science Foundation • funds university Internet Design

4. Growth of the Internet • Number of Hosts on the Internet: Aug. 1981 213 Oct. 1984 1,024 Dec. 1987 28,174 Oct. 1990 313,000 Oct. 1993 2,056,000 Apr. 1995 5,706,000 Jan. 1997 16,146,000 Jan. 1999 56,218,000 Jan. 2001 109,374,000 Jan. 2003 171,638,297 Jul 2004 285,139,107 Jul 2005 353,284,187 Internet Design

5. Today’s Internet Internet: “networks of networks” at global scale! International lines NAP Internic 3G cellular networks regional network national network on-line services ISP ISP company university access via modem company LANs WiFi Internet Design

6. roughly hierarchical at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage treat each other as equals NAP Tier-1 providers also interconnect at (public/private) Internet exchange points, or private peering links Tier-1 providers interconnect (peer) privately Internet Structure: Network of Networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Internet Design

7. “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs IXP Tier-2 ISPs also peer privately with each other, interconnect at IXPs • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet • tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet Structure: Network of Networks Internet Design

8. “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier-2 ISP Tier 1 ISP NAP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet Structure: Network of Networks Internet Design

9. a packet passes through many networks! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Tier-2 ISP Tier-2 ISP Tier 1 ISP Try a traceroute! Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet Structure: Network of Networks host/network edge: IP addresses, port no’s network core: intra-domain vs. inter-domain routing Internet Design

10. Who Runs the Internet “nobody” really! • standards: Internet Engineering Task Force (IETF) • names/numbers: The Internet Corporation for Assigned Names and Numbers (ICANN) • operational coordination: IEPG(Internet Engineering Planning Group) • networks: ISPs (Internet Service Providers), NAPs (Network Access Points), …… • fibers: telephone companies (mostly) • content: companies, universities, governments, individuals, …; Internet Design

11. Internet “Governing” Bodies • Internet Society (ISOC): membership organization • raise funds for IAB, IETF& IESG, elect IAB • Internet Engineering Task Force (IETF): • a body of several thousands or more volunteers • organized in working groups (WGs) • meet three times a year + email • Internet Architecture Board • architectural oversight, elected by ISOC • Steering Group (IESG): approves standards, • Internet standards, subset of RFC • RFC: “Request For Comments”, since 1969 • most are not standards, also • experimental, informational and historic(al) Internet Design

12. Internet Names and Addresses • Internet Assigned Number Authority (IANA): • keep track of numbers, delegates Internet address assignment • designates authority for each top-level domain • InterNIC, gTLD-MOU, CORE: • hand out names • provide “root DNS service” • RIPE, ARIN, APNIC: • hand out blocks of addresses Many responsibilities (e.g., those of IANA) are now taken over by the Internet Corporation for Assigned Names and Numbers (ICANN) Internet Design

13. Internet Hourglass Architecture Internet Design

14. Implications of Hourglass A single Internet layer module: • Allows all networks to interoperate • all networks technologies that support IP can exchange packets • Allows all applications to function on all networks • all applications that can run on IP can use any network • Simultaneous developments above and below IP Internet Design

15. Internet Names and Addresses • host and domain names • other “names”: email addresses, URLs, … • IP addresses: logical, with global reachability • IPv4: 32 bits, IPv6: 128 bits, “global” • two-level hierarchy: network part and host part • CIDR: network prefixes, e.g., 128.101.0.0/24 • Network Address Translation (NAT) complicates global reachability • MAC (and other physical-layer) addresses • used and understood by “native” physical technologies! According to Shoch (IEEE COMPCON’78) • name: identifies what you want • address: identifies where it is • route: identifies how to get there Internet Design

16. Internet Standardization Process • All standards of the Internet are published as RFC • But not all RFCs are Internet Standards • A typical (but not only) way of standardization is: • Internet Drafts • RFC • Proposed Standard • Draft Standard (requires 2 working implementation) • Internet Standard (declared by IAB) • David Clark, MIT 1992: “We reject: kings, presidents, and voting. We believe in: rough consensus and running code.” Internet Design

17. Architectural Principles (not unique to networks!) Zhi-Li’s version (synthesized from various sources) • End-to-end argument • functionality placement • Modularity • Increase inter-operability and manage complexity • vertical partition -> layered architecture • horizontal partition? • Keep it simple, stupid (KISS principle) • Occam’s Razor: choose simplest among many solutions! • complicated design increases system coupling (inter-dependence), amplifies errors, .. • don’t over-optimize! • Separating policies from mechanisms • decouple control from data • “semantics-free” • Design for scale • hierarchy, aggregation, … Internet Design

18. Network Architecture What is (Network) Architecture? • not the implementation itself • “design blueprint” on how to “organize” implementations • what interfaces are supported • where functionality is implemented • Two Basic Architectural Principles • Modularity (e.g., layering) • how to break network functionality into modules • End-to-End Argument • where to implement functionality Internet Design

19. Some Design/Implementation Principles • virtualization • indirection • soft state vs. hard state • fate sharing • randomization • expose faults, don’t suppress/ignore • caching • …… Internet Design

20. Original Internet Design Goals[Clark’88] In order of importance: • Connect existing networks • initially ARPANET and ARPA packet radio network • Survivability • ensure communication service even with network and router failures • Support multiple types of services • Must accommodate a variety of networks • Allow distributed management • Allow host attachment with a low level of effort • Be cost effective • Allow resource accountability Internet Design

21. Priorities • The effects of the order of items in that list are still felt today • E.g., resource accounting is a hard, current research topic • Different ordering of priorities would make a different architecture! • How well has today’s Internet satisfied these goals? • Let’s look at them in detail Internet Design

22. 0. Connecting Existing Networks 1974: multiple unconnected networks • ARPAnet • data-over-cable networks • packet satellite network (Aloha) • packet radio network .. differing in: • addressing conventions (i.e., address formats) • packet formats and packet sizes • Performance: bandwidth, latency, loss rate, … • error recovery mechanisms • routing • How to inter-network various (heterogeneous) network technologies? Internet Design

23. Cerf & Kahn: Interconnecting Two Networks • “…interconnection must preserve intact the internal operation of each network.” • “ ..the interface between networks must play a central role in the development of any network interconnection strategy. We give a special name to this interface that performs these functions and call it a GATEWAY.” • “.. prefer that the interface be as simple and reliable as possible, and deal primarily with passing data between networks that use different packet-switching strategies • “…address formats is a problem between networks because the local network addresses of TCP's may vary substantially in format and size. A uniform internetwork TCP address space, understood by each GATEWAY and TCP, is essential to routing and delivery of internetwork packets.” satellite net ARPAnet Internet Design

24. Design Alternatives • Through translation/mapping: • Map one address format to another: nxn mappings • Difficulty in dealing with different features supported by networks • Scales poorly with # of network types, addition of new types • Virtualization: • Provide one common format overlaid on top of “lower-level” addresses • Map lower level addresses to common format: nx1 and 1xn mappings • role of ARP, encapsulation/decapsulation • Layering necessary • but what info from “lower layer” (underlying “physical” networks) to hide, and what to expose! Internet Design

25. Gateway Alternative • Translation • Difficulty in dealing with different features supported by networks • Scales poorly with number of network types (N^2 conversions) • Standardization/Virtualization • “IP over everything” • Minimal assumptions about network • Hourglass design Internet Design

26. Internetwork layer: • addressing: internetwork appears as a single, uniform entity, despite underlying local network heterogeneity • network of networks Design of Original Internet via Gateways(cf. Cerf and Kahn) Gateway: • “embed internetwork packets in local packet format or extract them” • route (at internetwork level) to next gateway gateway satellite net ARPAnet Internet Design

27. source address local header dest. address flag field byte count text checksum seq. # TCP identifier network 8 16 Historical Aside: Proposed Internetwork packet in 1974: Internet Design

28. Cerf & Kahn’s Internetwork Architecture What is virtualized? • two layers of addressing: internetwork and local network • new layer makes everything homogeneous at internetwork layer • underlying local network technology (cable, satellite, 56K modem) is “invisible” at internetwork layer Internet Design

29. 1. Survivability • As long as the network is not partitioned, two endpoints should be able to communicate • Failures (excepting network partition) should not interfere with endpoint semantics (why?) • Maintain state only at end-points • Fate-sharing, eliminates network state restoration • stateless network architecture (no per-flow state) • Routing state is held by network (why?) • No failure information is given to ends (why?) Internet Design

30. Survivability (cont’d) • If network disrupted and reconfigured: • Communicating entities (“end systems”) should not care! • No higher-level state reconfiguration • How to achieve such reliability? • Where can communication state be stored? Internet Design

31. Fate Sharing Connection State State No State • Lose state information for an entity if (and only if?) the entity itself is lost. • Examples: • OK to lose TCP state if one endpoint crashes • NOT okay to lose if an intermediate router reboots • Is this still true in today’s network? • NATs and firewalls Internet Design

32. Soft-State • Basic behavior • Announce state • Refresh state • Timeout state • Penalty for timeout – poor performance • Robust way to identify communication flows • Possible mechanism to provide non-best effort service • Helps survivability Internet Design

33. End-to-End Argument • Deals with where to place functionality • Insidethe network (in switching elements) • At the edges • Argument: • There are functions that can only be correctly implemented by the endpoints – do not try to completely implement these elsewhere Internet Design

34. Discussion • Is there any need to implement reliability at lower layers? • Yes, but only to improve performance • If network is highly unreliable • Adding some level of reliability helps performance, not correctness • Don’t try to achieve perfect reliability! • Implementing a functionality at a lower level should have minimum performance impact on the applications that do not use the functionality Internet Design

35. Design Challenges and Trade-offs • Install functions in network that aid application performance…. • …without limiting the application flexibility of the network • Trade-offs: • application has more information about the data and semantics of required service (e.g., can check only at the end of each data unit) • lower layer has more information about constraints in data transmission (e.g., packet size, error rate) • Note: these trade-offs are a direct result of layering! Internet Design

36. Do These Belong in the Network? • Multicast? • Routing? • Quality of Service (QoS)? • Name resolution? (is DNS “in the network”?) • Web caches? Internet Design

37. 2. Types of Service • Best effort delivery • All packets are treated the same • Relatively simple core network elements • Building block from which other services (such as reliable data stream) can be built • Contributes to scalability of network • No QoS support assumed from below • Accommodates more networks • Hard to implement without network support • QoS is an ongoing debate… Internet Design

38. Types of Service (cont’d) • TCP vs. UDP • Elastic apps that need reliability: remote login or email • Inelastic, loss-tolerant apps: real-time voice or video • Others in between, or with stronger requirements • Biggest cause of delay variation: reliable delivery • Today’s net: ~100ms RTT • Reliable delivery can add seconds. • Original Internet model: “TCP/IP” one layer • First app was remote login… • But then came debugging, voice, etc. • These differences caused the layer split, added UDP Internet Design

39. 3. Varieties of Networks • Minimum set of assumptions for underlying net • Minimum packet size • Reasonable delivery odds, but not 100% • Some form of addressing unless point to point • Important non-assumptions: • Perfect reliability • Broadcast, multicast • Priority handling of traffic • Internal knowledge of delays, speeds, failures, etc. • Much engineering then only has to be done once Internet Design

40. The “Other” goals • 4. Management • Each network owned and managed separately • Will see this in BGP routing especially • 5. Attaching a host • Not awful; DHCP and related autoconfiguration technologies helping. • 6. Cost effectiveness • Economies of scale won out • Internet cheaper than most dedicated networks • Packet overhead less important by the year • But… Internet Design

41. 7. Accountability • Huge problem. • Accounting • Billing? (mostly flat-rate. But phones are moving that way too - people like it!) • Inter-provider payments • Hornet’s nest. Complicated. Political. Hard. • Accountability and security • Huge problem. • Worms, viruses, etc. • Partly a host problem. But hosts very trusted. • Authentication • Purely optional. Many philosophical issues of privacy vs. security. • Greedy sources aren’t handled well Internet Design

42. Other IP Design Weaknesses • Weak administration and management tools • Incremental deployment difficult at times • Result of no centralized control • No more “flag” days • Are active networks the solution? Internet Design

43. Internet Motto We reject kings , presidents, and voting. We believe in rough consensus and running code.” David Clark Internet Design

44. Real Goals • Something that works….. • Connect existing networks • Survivability (not nuclear war…) • Support multiple types of services • Accommodate a variety of networks • Allow distributed management • Easy host attachment • Cost effective • Allow resource accountability Internet Design

45. Summary: Internet Architecture • Packet-switched datagram network • IP is the “compatibility layer” • Hourglass architecture • All hosts and routers run IP • Stateless architecture • No per flow state inside network TCP UDP IP Satellite Ethernet ATM Internet Design

46. Summary: Minimalist Approach • Dumb network • IP provide minimal functionalities to support connectivity • Addressing, forwarding, routing • Smart end system • Transport layer or application performs more sophisticated functionalities • Flow control, error control, congestion control • Advantages • Accommodate heterogeneous technologies (Ethernet, modem, satellite, wireless) • Support diverse applications (telnet, ftp, Web, X windows) • Decentralized network administration • Beginning to show age • Unclear what the solution will be  probably IPv6 Internet Design

47. Questions • What priority order would a commercial design have? • What would a commercially invented Internet look like? • What goals are missing from this list? • Which goals led to the success of the Internet? Internet Design

48. Requirements for Today’s Internet Some key requirements (“-ities”) • Availability and reliability • “Always on”, fault-tolerant, fast recovery from failures, … • Quality-of-service (QoS) for applications • fast response time, adequate quality for VoIP, IPTV, etc. • Scalability • millions or more of users, devices, … • Mobility • untethered access, mobile users, devices, … • Security (and Privacy?) • protect against malicious attacks, accountability of user actions? • Manageability • configure, operate and manage networks • trouble-shooting network problems • Flexibility, Extensibility, Evolvability, ……? • ease of new service creation and deployment? • evolvable to meet future needs? Internet Design