Challenges for the Future of Networking

1. Challenges for the Future of Networking Presentation given at the e-Science Institute, Edinburgh September 14, 2006 Gregor v. Bochmann School of Information Technology and Engineering (SITE) University of Ottawa Canada http://www.site.uottawa.ca/~bochmann/talks/FutureNetworking Gregor v. Bochmann, University of Ottawa

2. Abstract The technical foundations for the Internet were developed more than 30 years ago. Since over 10 years, it has developed into a general communication infrastructure used by people and industry for a variety of applications. While e-mail and the Web were first the most important applications, newer developments have introduced wireless communication and new applications, including multimedia, e-commerce, etc. Certain applications, e.g. in the area of e-science, have extreme requirements in terms of bandwidth or delay that cannot be provided by the current Internet. - This talk will give a personal view of the challenges that must be faced for the future of the Internet and the distributed applications using it, including managerial and technical aspects. Some of these issues are (1) the integration of wireless LANs and ad-hoc networks with the wired network, (2) fast optical switching, (3) user-empowered network management, (4) security and trust management, (5) standards for distributed applications (e.g. Service Oriented Architecture) and (6) ubiquitous computing. The talk will provide a general discussion of these issues and present certain examples of innovative applications. Gregor v. Bochmann, University of Ottawa

3. Overview • The current Internet and applications • Research management - Grand Challenges • Research issues in networking • Optical networks (the physical level) • Issues for distributed applications • Conclusions Gregor v. Bochmann, University of Ottawa

4. Internet: Some Characteristics • Packet switching • Buffered in each router or switch (delay) • IP : connection-less • Logically simple, but requiring address look-up for each packet • Connection-oriented service allows for more efficient switching, e.g. new MPLS technology • There are not enough addresses. Solutions: • use of internal addresses and address translation (NAT); however, internal addresses are not reachable • or better: use IPv6 • TCP : controls flow between end-systems • Provides reliable information flow • Many applications need a logical connection between processes running in different hosts • Not suitable for interactive voice or video traffic (retransmission introduces delays) • Not suitable for very large bandwidths (order of Gbps) • UDP : non-reliable alternative to TCP Gregor v. Bochmann, University of Ottawa

5. Some extreme applications • Large bandwidth and low delay : Video teleconference (e.g. round-trip delay of 0.1 sec at 10 000 km) • Need for multicasting: video broadcasting (e.g. 10 Mbps to 10 000 users : 100 Gbps) • Extreme large bandwidth: e.g. 10 Gbps for e-science applications • Extremely low delays: tele-manipulation (e.g. eye surgery training); distributed music ensemble • Ad hoc networking (without fixed infrastructure) • people in local meeting • Sensor networks (large number of sensors, low battery life, may fail) Gregor v. Bochmann, University of Ottawa

6. Existing communications infrastructures • Terrestrial transmission infrastructures • Optical fibres • Wavelength division multiplexing (each wavelength : typically 10 Gbps) • For transmission, data is converted (from the electrical domain) into the optical domain (and back, by the receiver) • 10 Gbps is too much for most applications, it must be shared • Bandwidth sharing for telephony (end-to-end flows of fixed bandwidth, not packet switching) • Sonet or SDH (time division multiplexing) • ATM (cell switching) • Packet switching may be used for this purpose (switching in the electrical domain) • Packet switch could use 10 Gbps wavelength, or a fraction provided by SDH • Time sharing through photonic switching, e.g. burst switching • Cellular networks (designed for telephony) • Fixed wireless networks (WIFI) Gregor v. Bochmann, University of Ottawa

7. Network management and scalability • Need for interworking between different domains (subnetworks belonging to different organizations) • Limited visibility • Service level agreements (static – dynamic) • Large number of … (scalability) • Domains • Routers / switches • Host computers • Communicating devices (terminals, phones, TVs, kitchen stoves, etc.) • Security and reliability • A faulty behavior of a single router should only have local impact; idem for failures Gregor v. Bochmann, University of Ottawa

8. R&D - a long path: From new idea to market place • Typical time : 20 years • Example: Modeling distributed systems by state transition diagrams • 1969: Bartlett describes a communication protocol with finite state machines (FSM) • 1976: First version of SDL includes FSM notation • 1977: Bochmann and Gecsei propose Extended FSMs for modeling communication protocols • 1980ies: Standardization of formal description techniques (FDTs) by ISO and ITU, including SDL; university-based tool development • 1987: Harel proposes State Charts (including certain extensions of above notations) • 1990ies: Commercial development of software tools supporting these notations • 1995 ?: Unified Modeling Language (UML) defined by OMG • Around 2005: Integration between SDL and UML Version 2 Gregor v. Bochmann, University of Ottawa

9. The research planning process (A) • Funding of research and development • By industry (internal or external research) • Objective: improve competitiveness • Better products • Better development and production methods • Only larger companies perform longer term research and planning • By government organizations (industrial and university research) • Improve competitiveness of country • Competent people • Improve global competitiveness of local industry • Development of Intellectual Property (IP) to be used by local industry • Difficulty of prioritizing the different fields of science and technology • Give equal chances to all disciplines ? • Declare certain fields as « national priority » ? • Let industry buy-in for joint government-industry funding programs Gregor v. Bochmann, University of Ottawa

10. The research planning process (B) • Community-based research planning • Consensus building: through mailing lists, discussions at workshops / conferences, research collaborations • Examples: • The UK Grand Challenges: a perspective on long-term basic and applied research • NSF (USA) Workshop on Overcoming Barriers to Disruptive Innovation in Networks • Research program of E-NEXT (a EU - FP6 Network of Excellence) • “CoNEXT” conference in Toulouse, Oct. 2005 http://dmi.ensica.fr/conext/ • Canadian research network on Agile All-Photonic Networks (AAPN, funded by NSERC and 6 industrial partners) Gregor v. Bochmann, University of Ottawa

11. Grand Challenges(defined in the UK) • See http://www.ukcrc.org.uk/grand_challenges/index.cfm • “Definition of a Grand Challenge • A grand challenge should be defined as to have international scope, so that contributions by a single nation to its achievement will raise our international profile. • The ambition of a grand challenge can be far greater than what can be achieved by a single research team in the span of a single research grant. • The grand challenge should be directed towards a revolutionary advance, rather than the evolutionary improvement of legacy products that is appropriate for industrial funding and support. • The topic for a grand challenge should emerge from a consensus of the general scientific community, to serve as a focus for curiosity-driven research or engineering ambition, and to support activities in which they personally wish to engage, independent of funding policy or political considerations. “ (Note: the quotes, here and in subsequent slides, indicate that the text is copied from the source documentation) • The following two slides are from Robin Milners talk “A scientific horizon for computing” at the World Congres 2004 of the International Federation for Information Processing (IFIP), held in Toulouse. Gregor v. Bochmann, University of Ottawa

12. Grand Challenge Exercise Gregor v. Bochmann, University of Ottawa

13. Note: No GC is dedicated to networking issues UK Grand Challenge Proposals Gregor v. Bochmann, University of Ottawa

14. Ubiquitous Computing Grand Challenge • Combination of GC 2 and GC 4 • See http://www-dse.doc.ic.ac.uk/Projects/UbiNet/GC/index.html • Objective: “We propose to develop scientific theory and the design principles of Global Ubiquitous Computing together, in a tight experimental loop.” • “Engineering challenges: • design devices to work from solar power, are aware of their location and what other devices are nearby, and form cheap, efficient, secure, complex, changing groupings and interconnections with other devices; • engineer systems that are self-configuring and manage their own exceptions; • devise methods to filter and aggregate information so as to cope with large volumes of data, and to certify its provenience. • business model for ubiquitous computing, and other human-level interactions. “ Gregor v. Bochmann, University of Ottawa

15. Ubiquitous Computing Grand Challenge (ii) • “Scientific challenges: • discover mathematical models for space and mobility, and develop their theories; devise mathematical tools for the analysis of dynamic networks; • develop model checking, as well as techniques to analyse stochastic aspects of systems, as these are pervasive in ubiquitous computing; • devise models of trust and its dynamics; • design programming languages for ubiquitous computing. “ • A comment: It is not clear where – in the context of ubiquitous computing – Networking stops and Computing starts. In fact, networking involves much distributed systems management (including databases); and for the Internet applications, the application layer protocols are just as important as (if not more than) the underlying networking protocols. • Note: Milner has developed a new description formalism “Bigraphs for Mobile Processes “ ( see http://www.cl.cam.ac.uk/users/rm135/ ) Gregor v. Bochmann, University of Ottawa

16. Research topics in “Networking” Architectural levels of Networking Technology a narrow-waisted hourglass model: Issues • Network layer: • new wireless technologies: cellular, LAN, PAN, ad-hoc, sensor, etc. • Integration with wire-line Internet • Higher bandwidth • Inter-layer control and management according to application needs • Physical layer: technology push • Faster electronic components, e.g. 10 Gbps Ethernet • Fast optical switching • Trend: IP over Dense Wavelength Division Multiplexing (DWDM); elimination of intermediate layers of ATM, SONET; however, it may be IP over MPLS over DWDM. • Application layer • many new applications: importance of multimedia application will increase • New protocols for organizing applications: Web Services, Grid, peer-to-peer • New ways for identifying and searching services, including concern for security and trust Network service Gregor v. Bochmann, University of Ottawa

17. Overcoming Barriers to Disruptive Innovation in Networks Workshop organized by NSF (USA) • “Overcoming Barriers to Disruptive Innovation in Networking” (Jan. 2005) • see http://www.arl.wustl.edu/netv/noBarriers_final_report.pdf Starting point: “ The Internet is ossified: … Adopting a new architecture not only requires modifications to routers and host software, but given the multi-provider nature of the Internet, also requires that ISPs jointly agree on that architecture. The need for consensus is doubly damning; not only is agreement among the many providers hard to reach, it also removes any competitive advantage from architectural innovation. This discouraging combination of difficulty reaching consensus, lack of incentives for deployment, and substantial costs of upgrading the infrastructure leaves little hope for fundamental architectural change. “ Gregor v. Bochmann, University of Ottawa

18. NSF workshop (ii) • Requirements for the new Internet: • “ Minimize trust assumptions: the Internet originally viewed network traffic as fundamentally friendly, but should view it as adversarial; • Enable user choice: the Internet was originally developed independent of any commercial considerations, but today the network architecture must take competition and economic incentives into account; • Allow for edge diversity: the Internet originally assumed host computers were connected to the edges of the network, but host-centric assumptions are not appropriate in a world with an increasing number of sensors and mobile devices; • Design for network transparency: the Internet originally did not expose information about its internal configuration, but there is value to both users and network administrators in making the network more transparent; and • Meet application requirements: the Internet originally provided only a best-effort packet delivery service, but there is value in enhancing (adding functionality to) the network to meet application requirements. “ • Identified 7 areas of research (see next slides) Gregor v. Bochmann, University of Ottawa

19. 7 research areas: • Security • Economic incentives • Address binding • End-host assumptions • User-level route choice • Control and management • Meeting application requirements (see next slides) Gregor v. Bochmann, University of Ottawa

20. Security • Problem indications • “traffic must be viewed as adversarial rather than cooperative” • “To take one example, a single mistyped command at a router at one ISP recently caused widespread, cascading disruption of Internet connectivity across many of its neighbors.” • Benefits of better security • “ improve network robustness through protocols that work despite misbehaving participants, • enable security problems to be addressed quickly once identified, • isolate ISPs, organizations, and users from inadvertent errors or attacks; • prevent epidemic-style attacks such as worms, viruses, and distributed denial of service; • enable or simplify deployment of new high-value applications and critical services that rely on Internet communication such as power grid control, on-line trading networks, or an Internet emergency communication channel; and • reduce lost productivity currently aimed at coping with security problems via patching holes, recovering from attacks, or identifying attackers. “ Gregor v. Bochmann, University of Ottawa

21. Security (ii) • Interesting architectural approaches: • “prevent denial of service by allowing a receiver to control who can send packets to it “ • “making firewalls a fully recognized component of the architecture instead of an add-on that is either turned off or gets in the way of deploying new applications. A clean specification for security that makes clear the balance of responsibility for routers, for operating systems and for applications can move us from the hodge-podge of security building blocks we have today to a real security architecture “ • “A careful design of mechanisms for identity can balance, in an intentional way rather than by accident, the goals of privacy and accountability. Ideally, the design will permit us to apply real world consequences (e.g. legal or financial) for misbehavior. “ Gregor v. Bochmann, University of Ottawa

22. Economic incentives • Proposition: “A future design for an Internet should take into account that a network architecture induces an industry structure, and the economic structure of that industry. The architecture can use user choice (to impose the discipline of competition on the players), indications of value flow (to make explicit the right direction of payment flow), and careful attention to what information is revealed and what is kept hidden (to shape the nature of transactions across a competitive boundary). “ Gregor v. Bochmann, University of Ottawa

23. Address binding • Problem with IP addresses • There are not enough – solution: IPv6 • They serve as machine identity (instead of only identifying the network attachment point, the location) • this leads to difficulties for mobile devices (e.g. Mobile IP routing is not straightforward – IP address changing dynamically) • IP address (as machine identifier) also used for security • Proposed solution approaches • Host Identity Protocol • It provides secure host identification • Routing is based on IP addresses that are treated only as ephemeral locators • “… end-points (as equated with physical machines or operating systems) need not have any globally known identity at all. Instead, application level entities have shared identities … , and higher level name spaces such as a redesigned DNS are used to give global names to services, so that they can be found. “ Gregor v. Bochmann, University of Ottawa

24. End host assumptions • Issues with sensor networks • sensors may be intermittently connected • routing may be based on data values • Solution approaches: Overlay networks • Overlay for realizing special routing functions, e.g. diffusion routing • Overlay for delay-tolerant routing (e.g. for e-mail; also allowing “access in a variety of impoverished and poorly connected regions “) Gregor v. Bochmann, University of Ottawa

25. User-level route choice • Objectives: increase the user’s choice and introduce more competition • “ Instead of applying a "one-size-fits-all" policy to their traffic, ISPs could perform routing and traffic engineering based upon the user traffic preferences … offer unique policies such as keeping all traffic within the continental United States for security reasons. “ • “ This selection creates a more complex economic environment; it offers potential rewards in user choice and competition, but requires solutions to issues of accounting, pricing, billing, and inter-ISP contracts. “ Gregor v. Bochmann, University of Ottawa

26. Control and management • Statement: Management of the Internet is very complex (for all parties involved) • Solutions: not clear (there are references to ongoing work) • One problem: limited visibility of internal parameters from outside the network (opaqueness) • A network should “support communication of operationally relevant information to each other. Such information could be aggregated and analyzed, thereby facilitating load balancing, fault diagnosis, anomaly detection, application optimization, and other traffic engineering and network management functions.” • One needs a compromise between information hiding and visibility for management. Gregor v. Bochmann, University of Ottawa

27. IP Network service Meeting application requirements • Protocol layer architecture is a narrow-waisted hourglass model • Additional requirements: • “QoS control, multicast, anycast, policy-based routing, data caching …” • Possible solutions: • Add more functions to IP layer • Use overlay networks to provide additional functions Gregor v. Bochmann, University of Ottawa

28. Some personal comments Overlay networks • Principle: A certain number of servers connected to the Internet play the role of « virtual routers » in the overlay network. Note: This is the way MBone implements multicasting over the current IP Internet service. • The NSF workshop stresses the use of overlay networks for experimentation with new approaches • Could such architectures present the final solution ? • NO, overlay technology, such as peer-to-peer computing, may be useful for certain applications, but cannot be a solution for building a network • Existing well-known applications • Napster and BitTorrent media distribution, and other peer-to-peer applications • Multicasting of multimedia presentations, possibly including different quality variants • A Testbed:US-based Planetlab http://planet-lab.org/; see also http://www.arl.wustl.edu/netv/main.html Gregor v. Bochmann, University of Ottawa

29. Some personal comments (2) • Lightpaths - “Underlay Networks“ ? • Experimental research networks provide high-bandwidth “lightpaths“ between different sites for e-science and other applications that require guaranteed high-bandwidth connections. • For an overview of current applications, see http://www.internet2.edu/presentations/fall05/20050920-lambdas-sauver.htm • User-Controlled Lightpath Provisioning (UCLP) allows the e-science users to establish lightpaths dynamically through a graphic user interface. • Note: UCLP has been initiated in Canada with partial funding from Canarie (the Canadian research network), see for instance http://www.uclp.ca • These networks make use of user-owned fibers and condominium facilities for long-haul transmission and switching • This is not an overlay, but also provides a new networking service, independently from the existing Internet. The Internet can be built on top of it. Gregor v. Bochmann, University of Ottawa

30. Some personal comments (3) • Packets vs. (virtual) connections • The old debate between packet switching and circuit switching (from the 1970ies) is not dead !! • Distinction: In packet switching, the header of the packet/frame/cell/burst contains the destination address; in circuit switching, it contains a number (label) identifying the circuit (in TDM, this number is the timing position). • MPLS (label switching) provides packet switching over dynamically established paths (virtual connections) • Optical lightpaths are connection-oriented. It is expected that existing ROADM (Reconfigurable optical add/drop multiplexers) technology will be widely deployed within a few years; see for instancehttp://lw.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=203231&VERSION_NUM=1 • An optical lightpath at a given wavelength is very large, typically 10 Gbps. Sub-multiplexing of a lightpath in the time domain is proposed by many research projects; • Sharing between packets or virtual connections ?? Gregor v. Bochmann, University of Ottawa

31. Some personal comments (4) • Appearently contradictory approaches • IP : packet-oriented switching • The concept of virtual connections are natural for providing QoS guarantees. • The lower layers of broadband wireline networks appear to use connection-oriented technologies. • The overlay networks would like to obtain more visibility about the performance aspects of the underlying IP service. • Suggestion: Maybe there should be more visibility at the IP service level about the underlying virtual and physical circuits that exist within the network and their performance parameters; and the application should have some choice about the routing of its data. Gregor v. Bochmann, University of Ottawa

32. Optical networks • Currently deployed: • optical transmission with DWDM • Some optical switching • Note: most “optical switches“ convert the optical signal into the electrical domain and perform the switching in the electrical domain. • Expected to be deployed: • ROADM used for transparent optical switching in the millisecond speed range; good for protection switching and bandwidth on demand. Gregor v. Bochmann, University of Ottawa

33. Burst switching • Question:Can one do packet switching in the optical domain (without oeo conversion)? • At a switching speed of 1 μs, one could switch bursts of 10 μs length (typically containing many packets) • Traditional packet switching involves packet buffering in the switching nodes. Should one introduce optical buffers in the form of delay lines? • The term “burst switching“ originally meant “no buffering”: in case of conflict for an output port, one of the incoming bursts would be dropped. • Note:Burst switching allows to share the large optical bandwidth among several virtual connections. Gregor v. Bochmann, University of Ottawa

34. AAPNAn NSERC Research NetworkThe Agile All-Photonic Network Project leader: David Plant, McGill UniversityTheme 1: Network architecturesGregor v. Bochmann, University of OttawaTheme 2: Device technologies for transmission and switching Gregor v. Bochmann, University of Ottawa

35. AAPN Professors (Theme 1 in red) • McGill: Lawrence Chen, Mark Coats, Andrew Kirk, Lorne Mason, David Plant (Theme #2 Lead), and Richard Vickers • U. of Ottawa: Xiaoyi Bao, Gregor Bochmann (Theme #1 Lead), Trevor Hall, and Oliver Yang • U. of Toronto: Stewart AitchisonandTed Sargent • McMaster: Wei-Ping Huang • Queens: John Cartledge (Theme #3 Lead) • Note: Theme 2 deals with device technologies for transmission and switching For further information see: http://www.aapn.mcgill.ca/ Gregor v. Bochmann, University of Ottawa

36. The AAPN research network • Our vision: Connectivity “at the end of the street” to a dynamically reconfigurable photonic network that supports high bandwidth telecommunication services. • Technical approach: • Simplified network architecture (overlaid stars) • Specific version of burst switching • Fixed burst size, coordinated switching at core node for all input ports (this requires precise synchronization between edge nodes and the core) • See for instance http://beethoven.site.uottawa.ca/dsrg/PublicDocuments/Publications/Hall05a.pdf • Burst switching with reservation per flow (virtual connection), either fixed or dynamically varying • See for instance http://beethoven.site.uottawa.ca/dsrg/PublicDocuments/Publications/Agus05a.pdf Gregor v. Bochmann, University of Ottawa

37. Agile All-Photonic Network • Provisions sub-multiples of a wavelength • Large number of edge nodes Edge node with slotted transmission (e.g. 10 Gb/s capacity per wavelength) Fast photonic core switch (one space switch per wavelength) AAPN Opto-electronic interface AAPN AAPN Overlaid stars architecture

38. Starting Assumptions • Avoid difficult technologies such as • Wavelength conversion • Optical memory • Optical packet header recognition and replacement • Current state of the art for data rates, channel spacing, and optical bandwidth • Simplified topology based on overlaid stars • Edge based control in small/medium size edge nodes Gregor v. Bochmann, University of Ottawa

39. Starting Assumptions (ii) • No distinction between long-haul and metro networks • Fast optical space switching (<1 msec) • Slotted Time Division Multiplexing (TDM) or slotted burst switching • Need for fast compensation of transmission impairments (<1 msec) Gregor v. Bochmann, University of Ottawa

40. Bandwidth allocation schemes For flows between edge nodes • Optical wavelength: Whole wavelength (for large bandwidth flows) – like the PetaWeb explored by Nortel Networks • Optical circuit: One or several time slots within each TDM frame • Burst switching: individual bursts (with or without reservation) • Coordination by controller at core node • Signaling protocol between edge and core node (suitable for metro and long-haul networks) Gregor v. Bochmann, University of Ottawa

41. Integration higher layer (MPLS and IP) • MPLS flows passing through the AAPN • With N edge nodes, there are N x N links in the AAPN (scalability problem for IP routing protocol) • “Virtual router” star architecture • OSPF sub-areas • How to find optimal inter-area route (work sponsored by Telus) Gregor v. Bochmann, University of Ottawa

42. Deployment aspects - Questions • Long-haul or Metro ? • connectivity “at the end of the street”; to a server farm • AANP as a backbone network ? • High capacity (many wavelengths) or low capacity (single or few wavelengths) ? • Multiple core nodes ? • For reliability • For load sharing • Transmission infrastructure ? • Using dedicated fibers • Using wavelength channels provided by ROADM network Gregor v. Bochmann, University of Ottawa

43. Issues forDistributed applications • Multimedia • Ubiquitous computing and location-awareness • Service-oriented architecture and Grid computing • Making it easy for the end-user • Scalability – peer-to-peer computing • Related technologies • Security • Trust management • Software development technology Gregor v. Bochmann, University of Ottawa

44. Distributed multimedia applications • The basics are relatively well understood • Video requires high bandwidth • Conversational applications require short transmission delays • In many cases, multicasting is required (possibly provided through the overlay approach) • Aspects to be further explored • Shared virtual environments, e.g. for collaborative work or games • Tactile applications; tele-haptics require very short delays • Quality of service management for multiple receivers; media transcoding Gregor v. Bochmann, University of Ottawa

45. Example: Locating suitable transcoding servers (El-Khatib) See http://beethoven.site.uottawa.ca/dsrg/PublicDocuments/Publications/ElKh04c.pdf Gregor v. Bochmann, University of Ottawa

46. Ubiquitous computing and location-awareness • See Grand Challenge • Example: Some issues encountered in our project on teleconferencing for mobile users • Problem: In ad-hoc environment (e.g. on a trip) find out what devices may be useful to the user to establish a video-conference with a friend in another country. • Consider quality of service (QoS) negotiation to find most suitable devices according to the user’s preferences and the remote site. • Assumption: User has a PDA that can detect through short-range wireless communication (e.g. Bluetooth) which devices are available in the environment. • Approach: We use a Home Directory to store the preferences of the user; it must be down-loaded into the PDA for processing (it may be a rented PDA). See http://beethoven.site.uottawa.ca/dsrg/PublicDocuments/Publications/ElKh04a.pdf Gregor v. Bochmann, University of Ottawa

47. Alice Bob’s HDA 2 3 1 7 Internet 5 6 4 4 PA (PDA) 5 Alice’s HDA 4 7 5 5 5 4 4 5 4 Example: Device selection in an ad-hoc environment Gregor v. Bochmann, University of Ottawa

48. Example: Session mobility and QoS adaptation Gregor v. Bochmann, University of Ottawa

49. Service-oriented architecture and Grid applications • Concepts • RPC for accessing services • Directory service • Realizations: CORBA, Jini (Java environment) • WS and SOA:use similar concepts • Use HTTP and SOAP (based on XML) • Workflow specifications (BPEL, etc.) • Advantages: • use of HTTP (firewalls) • programming language independent (like CORBA) Gregor v. Bochmann, University of Ottawa

50. Notes on XML • text-oriented encoding of data structures (based on SGML, like HTML) • used for storage and/or transmission • Data structure (type) definition in the form of DTD or XML Schema • Developed by WWW Consortium http://www.w3.org/ • Used for a multitude of applications, see for instance list of resources at http://www.extensinet.com/ Gregor v. Bochmann, University of Ottawa