Computer Networks with Internet Technology

1. Computer Networks with Internet Technology Chapter 01 Data Networks and The Internet

2. Data Networks • Communication by transmitting data intermediate switching nodes • Switching nodes not concerned with content • End devices referred to as stations • Computers, terminals, telephones, etc. • Nodes connected in some topology by transmission links • Station attaches to node • Collection of nodes is a communications network

3. Figure 1.1Simple Switching Network

4. Circuit Switching • Dedicated path between two stations • Connected sequence of links between nodes • E.g telephone network • Communication involves three phases • Circuit establishment • Data transfer • Circuit disconnect

5. Circuit Establishment • Station A to node 4 requesting connection to station E • Circuit from A to 4 usually dedicated line • Node 4 finds next leg to node 6 • Based on routing information, availability, cost, node 4 selects circuit to node 5 • Allocates a free channel • TDM [time-division multiplexing] • FDM [frequency-division multiplexing] • Node 4 requests connection to E • And so on

6. Data Transfer • Data may be digital (e.g., terminal to host) or analog (e.g., voice) • Signaling and transmission may each be digital or analog • Path is A-4 circuit, internal switching through 4, 4-5 channel, internal switching through 5, 5-6 channel, internal switching through 6, 6-E circuit • Generally, full duplex (data in both directions)

7. Circuit Disconnect • Connection terminated • Usually by one of the stations • Signals to 4, 5, and 6 to de-allocate resources

8. Circuit Switching - Notes • Connection established before data transmission begins • Channel capacity must be available and reserved. • Nodes must have capacity to handle connection • Switches must have intelligence to make allocations and devise route • Can be inefficient • Capacity dedicated for duration of connection • Even if no data are being transferred • For voice, utilization high, but still doesn’t approach 100% • For terminal connection, may be idle most of the time • Delay prior to data transfer for call establishment • Once circuit established, network transparent to users • Data transmitted at fixed rate • No delay other than propagation • Delay at node negligible

9. Packet Switching • 1970 • Evolved substantially since • Basic technology fundamentally the same today • One of few effective technologies for long-distance data communications • Frame relay and ATM (see later) variations • Carries directly to Internet • Advantages: flexibility, resource sharing, robustness, responsiveness • Cost: elaborate algorithms to cope with time delay and overhead penalties of network operation

10. Packet Switching – Circuit Switching Issues • Designed for voice • Resources dedicated to particular call • For voice, high utilization • Most of the time, someone is talking • For data  • Line idle much of the time • Constant data rate • Limits interconnection of variety of host computers and terminals

11. Packet Switching – Basic Operation • Data are transmitted in short blocks, called packets • Typical upper bound 1000 octets (bytes) • Longer messages broken up into series of packets • Each packet contains part (or all for short message) of user's data plus some control information • Control information includes network routing • At each node, packet is received, stored briefly, and passed on to the next node • Transmitting computer sends message as sequence of packets • Packet includes control information including destination station • Packets sent to node to which sending station attaches • Node stores packet briefly, determines next leg of route, and queues packet to go out on that link • When link is available, packet is transmitted to next node • All packets eventually work their way through network

12. Figure 1.2 The Use of Packets

13. Packet Switching – Advantages • Line efficiency greater • Node-to-node link dynamically shared by many packets • Data-rate conversion • Each station connects to its node at its proper data rate • Nodes act as buffers • Packets accepted, even under heavy traffic, but delivery delay increases • Circuit switching networks would block new connections • Priorities can be used

14. Packet Switching – Disadvantages • Delay • Transmission delay equal to length of packet divided by incoming channel rate • Variable delay due to processing and queuing • Packets may vary in length • May take different routes • May be subject to varying delays • Overall packet delay can vary substantially (jitter) • Not good for real-time applications like voice and real-time video • Overheads including address of destination, sequencing information added to packet • Reduces capacity available for user data • More processing required at node

15. Switching Technique –Datagram • Datagram: each packet treated independently • No reference to packets that have gone before • Each node chooses next node on path • Packets with same destination address do not follow same route • May arrive out of sequence • Exit node or destination restores packets to original order • Packet may be destroyed in transit • Either exit node or destination detects loss and recovers • Call setup avoided • For an exchange of a few packets, datagram quicker • More flexible. • E.g. Routing away from the congestion • Delivery is inherently more reliable • If a node fails, subsequent packets may be re-routed

16. Figure 1.3Packet Switching:Datagram Approach

17. Switching Technique –Virtual Circuit • Preplanned route established before packets sent • All packets follow same route • Similar to circuit in circuit-switching network • Hence virtual circuit • Each packet has virtual circuit identifier • Nodes on route know where to direct packets • No routing decisions • Not dedicated path, as in circuit switching • Packet still buffered at node and queued for output • Routing decision made oncefor that virtual circuit • Network may provide services related to virtual circuit • Sequencing and error control • Packets should transit more rapidly • If node fails, all virtual circuits through node lost

18. Figure 1.4PacketSwitching:Virtual-CircuitApproach

19. Figure 1.5Effect of Packet SizeonTransmissionTime

20. Routing • Adaptive routing • Routing decisions change as conditions on network change • Failure of node or trunk • Congestion • Route around congestion • Requires exchange of network state information • Tradeoff between quality of information and overhead

21. Frame Relay • Considerable overhead in packet-switching schemes to compensate for errors • Additional bits added to packet for redundancy • Additional processing at stations and nodes to detect and recover from errors • Modern systems more reliable • Any remaining errors caught in systems above packet-switching logic • Original packet-switching networks data rate 64 kbps • Frame relay networks up to 2 Mbps • Strip out most error control overhead • Uses variable-length packets (frames)

22. Asynchronous Transfer ModeATM or Cell Relay • Little overhead for error control • Fixed-length packets (cells) • Processing overhead reduced • Designed to work at 10s, 100s of Mbps, and Gbps • Small, fixed-size cells are efficient • Can offer constant-data-rate channel using packet-switching • Also evolution from circuit switching • Allows definition of multiple virtual channels • Data rates dynamically defined at virtual channel setup • Extends circuit switching to allow multiple channels with data rates set on demand

23. Local Area NetworksLAN • Small scope • Typically single building or a cluster of buildings • Leads to different technical solutions • Usually LAN owned by same organization that owns attached devices • For WANs, a significant fraction of the network assets are not owned. • May be a substantial capital investment for both purchase and maintenance. • Network management responsibility falls on owner • Data rates of LANs typically much greater than WANs • Most common are switched LANs and wireless LANs • E.g. Ethernet, ATM, Fibre Channel, WiFi (802.11) • More later

24. Metropolitan Area NetworksMAN • Between LANs and WANs • Traditional point-to-point and switched networks in WANs inadequate for growing needs of organizations • Requirement for high capacity private and public networks at low costs over a large area • E.g. Wireless networks, metropolitan extensions to Ethernet

25. The Internet History (1) - Background • Evolved from ARPANET, 1969 Advanced Research Projects Agency (ARPA),U.S. Department of Defense • First operational packet-switching network • Began in four locations: UCLA, University of Santa Barbara, the University of Utah, and SRI (Stanford Research Institute) • Today tens of millions of hosts • Hundreds of millions of users • Nearly 200 countries • Number of connections growing exponentially • Allowed devices from different manufacturers and with different data rates to communicate • Used adaptive routing

26. Figure 1.6Number ofInternet Hosts

27. The Internet History (2) - Applications • Telnet provided common denominator terminal • Software written support “Telnet terminal,” • Any terminal could interact with any computer • File Transport Protocol (FTP) offered similar open functionality • Transparent transfer of files from one computer to another • Overcomes different word sizes, different bit orders and different word formats • First “killer app” was electronic mail • Previously all single computer systems • 1972, Ray Tomlinson of Bolt Beranek and Newman (BBN) • Distributed mail service across network using multiple computers • 1973 three quarters of all ARPANET traffic was e-mail

28. The Internet History (3) – TCP/IP • Packet-switching applied to tactical radio communication (packet radio) and satellite communication (SATNET) • Different communication environments • Certain parameters, e.g. maximum packet size, different • Vint Cerf and Bob Kahn of ARPA developed protocols for communicating across arbitrary, multiple, packet-switched networks (internetting) • May 1974 Transmission Control Protocol • Refined by ARPANET community • Major contributions from participants from European Networks, such as Cyclades (France), and EIN • Leading to TCP and IP • Basis for TCP/IP protocol suite • 1982-1983, ARPANET switched from NCP to TCP/IP • Many networks connected using TCP/IP • Use of ARPANET restricted to ARPA contractors

29. The Internet History (4) – National Science Foundation • Extended support to other computer research groups • CSNET in 1980-1981 • 1986, extended Internet support to general research community • NSFNET backbone • Originally designed to interconnect six NSF funded supercomputer centers across USA and to supercomputer users • Eventually, interconnection through NSF backbone to regional packet switched networks across USA • In 1990 ARPANET was shut down

30. The Internet History (5) – Acceptable Use Policies • In many countries (including United States until 1995) national governments subsidized the Internet backbone • Acceptable use policies limited commercial activities • Research and educational (and of course government) use only • The “culture” of the Internet imposed additional informal limitations on commercial uses

31. The Internet History (6) – Internet Interconnection Points • 1991 almost all commercial TCP/IP service in USA provided by: • General Atomics • Operated CERFnet (a California regional network) • Performance Systems International • PSINet (commercial spin-off from New York’s NYSERnet) • UUNET Technologies • Commercial Internet service provider that owned Alternet • Did not use NSF backbone on own networks • Not subject to Acceptable Use Policy • Communication between their networks did use NSF backbone • Under the policy

32. The Internet History (7) –CIX • Commercial Information Interchange • Originally mechanism to interchange traffic at a West Coast router • Each network’s customers access customers on others’ networks at no extra charge • 1996, CIX had 147 member networks • No settlements • No traffic based fees for use • Similar interconnection point (1994) in England • London Internet Exchange (LINX) • 1996, it had 24 member networks • 1991, U.S. government said it would no longer subsidize Internet after 1995 • Mandated network access points • Now three, New York, Chicago, and San Francisco • Metropolitan area exchanges, MAE East and MAE West • U.S. part of Internet opened to commercial activity

33. Figure 1.7U.S. Internet Access Points

34. The Internet History (8) –The World Wide Web • Spring 1989, at CERN (the European Laboratory for Particle Physics) • Englishman Tim Berners‑Lee proposed a distributed hypermedia technology to exchange research findings over Internet • 1991 prototype World Wide Web (WWW or the Web) developed at CERN using NeXT computer as a platform • End of 1991, limited release of line-oriented browser or reader • Explosive growth came with first graphically oriented browser, Mosaic, 1993 • NCSA Center, University of Illinois • Mark Andreasson and others • Two million copies delivered over Internet • Now ubiquitous

35. The Internet History (9) –What is the Web • Internationally distributed collection of multimedia files supported by clients (users) and servers (information providers) • Each file addressed in consistent manner using its Uniform Resource Locator (URL) • Viewed by clients using browsers • E.g. Netscape Navigator, Microsoft’s Internet Explorer • There are others! • Usually graphical display and support for multimedia • Move from file to file by clicking with mouse highlighted text or image (link) • Layout of display controlled by Hypertext Markup Language (HTML) • Embedded commands in text files • Specify fonts, colors, images and their placement and links • Hypertext Transfer Protocol (HTTP) • Protocol used in TCP/IP networks for fetching WWW files • More later

36. The Internet History (10) –The Internet Today • Users connect through an Internet service provider (ISP) • Home users • Major online services such as America Online and Compuserve • Connect to ISPs over phone lines using modems at 56.6 kbps • OK for e-mail but marginal for graphics-intensive Web surfing • New alternatives include ISDN, ADSL, and cable modem • Work users • Workstations or PCs connected to LANs • LAN connects through trunks to ISP • T-1 or T-3 connection for large organizations • Smaller organizations may use 56 kbps or ISDN connections • ISPs connected by "wholesalers,“ • Network service providers • They interconnect using Internet connection points • T-3 rates or ATM connections

37. The Internet History (11) –Commercial Use • Acceptable Use Policy limited early commercial use to research and educational • Some informational activities that could be considered marketing went on • First commercial applications were mainly informational • Sales, marketing, public relations • Electronic data interchange (EDI) • Intercompany invoices, billing, etc. • Designed for dedicated WAN • America Online, bulletin board type services dealing with technical and usage problems

38. The Internet History (12) –Direct Sales • Initially Internet did not support online transactions well • No easy to use graphical user interface • World Wide Web not commonly available until 1993 • Initially little support for submitting information (forms) to server • No security • No effective payment systems • Credit card? • People uncomfortable sending credit card numbers over Internet • If information not encrypted it is easy to “listen in” • Several files of customer's credit card numbers on merchant’s computers have been compromised • Privacy concerns • “data mining,” • Collecting customer transaction information to improve targeting of marketing

39. Figure 1.8A NetworkConfiguration

40. Intranets • Implementation of Internet technologies within a corporate organization, rather than for external connection to the global Internet • Rapid prototyping and deployment of new services • Scales effectively • Virtually no user or developer training required • Services and user interfaces familiar from Internet • All platforms with complete interoperability • Open architecture • Lots of add-on applications available • Range of distributed computing architectures • Few central servers or many distributed servers • Support of "legacy" information sources • databases, word processing documents, groupware • Range of media types (audio, video, interactive applications) • Inexpensive to start 

41. Intranets and the Web • Web has become universal information interface • Management-employee communication • Job-related information • Departmental- and project-level information and services. • Set up Web pages to disseminate information and maintain project data • Easy to develop Web pages for specific needs • Connect Web service to database • Ease of administration • Deployment • Development speed • Flexible information presentation  • Limited functionality • Stateless operation

42. Figure 1.9Web/Database Connectivity

43. Other Intranet TechnologiesElectronic Mail • Electronic Mail • Most heavily used network application in corporate world • Attach documents multimedia to mail messages • Electronic mailing list • Alias with multiple destinations

44. Other Intranet TechnologiesNetwork News or USENET • Collection of electronic bulletin boards • Work in similar way to Internet mailing lists • Subscribe to news group to you receive all messages posted to that group • May post message that available to all subscribers • Mechanics different from e-mail lists • Distributed network of sites that collect and broadcast news group entries • Need access to USENET node • Messages are archived at news sites • Organized by subject matter (thread) • Readily adapted to form an intranet news service

45. Extranets • Makes use of TCP/IP protocols and applications • Especially the Web • Provides outside clients access to corporate resources • Suppliers and customers • Through the Internet or other networks • Security • Resources available to outside parties • Privacy and authentication concerns must be addressed • Access • Long-distance dial-up access • Internet access to intranet with security • Authentication of users and encryption of communications • Internet access to an external server • Duplicates some intranet data • Internet access to external server that originates database queries to internal servers • Virtual private network (VPN)

46. Required Reading • Stallings, W. [2003], Computer Networks with Internet Technology, Prentice Hall, Upper Saddle River NJ. Chapter 1 • Web site for book: http://WilliamStallings.com/ • Any and all links from this site