Chapter 5 : The Internet: Addressing & Services

1. Chapter 5 : The Internet: Addressing & Services Business Data Communications, 4e

2. Internet History • Evolved from ARPANet (Defense Department’s Advanced Research Projects Agency Network) • ARPANet was developed in 1969, and was the first packet-switching network • Initially, included only four nodes: UCLA, UCSB, Utah, and SRI

18. http://www.isc.org/ Internet Domain Survey 147,344,723 / Jan 02

19. Switching Methods • Circuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays • MessageSwitching: Entire path is not dedicated, but long delays result from intermediate storage and repetition of message • Packet Switching: Specialized message switching, with very little delay

22. NSF and the Internet • In the 1980s, NSFNet extended packet-switched networking to non-ARPA organization; eventually replaced ARPANet • Instituted Acceptable Use Policies to control use • CIX (Commercial Internet eXchange) was developed to provide commercial internetworking

23. The World Wide Web • Concept proposed by Tim Berners-Lee in 1989, prototype WWW developed at CERN in 1991 • First graphical browser (Mosaic) developed by Mark Andreessen at NCSA • Client-server system with browsers as clients, and a variety of media types stored on servers • Uses HTTP (hyper text transfer protocol) for retrieving files

24. Connecting to the Internet • End users get connectivity from an ISP (internet service provider) • Home users use dial-up, ADSL, cable modems, satellite • Businesses use dedicated circuits connected to LANs • ISPs use “wholesalers” called network service providers and high speed (T-3 or higher) connections

25. Internet Addressing • 32-bit global internet address • Includes network and host identifiers • Dotted decimal notation • 11000000 11100100 00010001 00111001 (binary) • 192.228.17.57 (decimal)

26. Host Network IP Address • 長度：4 Bytes (32-Bit) • 每一IP 位址包括兩個部份 • 網路位址 (Network Address) • 主機位址 (Host Address) • 有時一網路會再分割為多個子網路，此時主機位址又再細分為子網路(Subnet)及主機(Host)兩個部份。 Subnet Host Network

27. Network Classes • Class A: Few networks, each with many hostsAll addresses begin with binary 0 • Class B: Medium networks, medium hostsAll addresses begin with binary 10 • Class C: Many networks, each with few hosts All addresses begin with binary 11

28. IP Address Formats 0 ~ 127 128 ~ 191 192 ~ 223 224 ~ 239 240 ~

32. Subnets & Subnet Masks • Allows for subdivision of internets within an organization • Each LAN can have a subnet number, allowing routing among networks • Host portion is partitioned into subnet and host numbers • See Table 5.2 for method of calculating subnet masks

33. 網路遮罩(Netmask) • 網路遮罩，將一IP位址中之代表網路及子網路位址之位元設為1，其餘設為0即為網路遮罩。 • Class A  255.0.0.0 • Class B  255.255.0.0 • Class C  255.255.255.0 • 網路遮罩與IP位址利用邏輯AND便可得到網路位址。

35. Routers and the IP Addressing Principle • Routers have two or more addresses. One for each interface.

36. Routing Table IF ((Mask[i] & Destination Addr) = = Destination[i]) Forward to NextHop[i]

37. IP Forwarding Process

38. Routing Protocols • Routing Each router must exchange information with its neighbors to construct the whole network topology. • Two types of routing scheme-distance-vector routing (e.g. RIP)-link-state routing (e.g. OSPF)

39. Domain Name System • 32-bit IP addresses have two drawbacks • Routers can’t keep track of every network path • Users can’t remember dotted decimals easily • Domain names address these problems by providing a name for each network domain (hosts under the control of a given entity) • See Figure 5.6 for example of a domain name tree

41. TLD (Top-Level Domains) • Country Code Domains • .uk, .de, .jp, .us, .tw., etc.) • Generic Domains • .aero, .biz, .com, .coop, .edu, .gov, .info, .int, .mil, .museum, .name, .net, and .org IANA / ICANN IRs (Internet Registry) INTERNIC.NET http://www.internic.net/ http://www.twnic.net/

42. DNS Database • Hierarchical database containing name, IP address, and related information for hosts • Provides name-to-address directory services

43. Key Features of DNS Database • Variable-depth hierarchy • Allow unlimited levels. Use “.” as level delimiter. • Distributed Database • The database resides in DNS servers scattered throughout the Internet. • Distribution controlled by the database • The DNS database is divided into separately managed zones, which are managed by separate administrators. • Distribution and update of records is controlled by the database software.

44. DNS Operations • A user program requests for an IP address for a domain name. • A resolver module in the local host or local ISP formulates a query for the local name server. • A local name server checks to see if the name is in its local database or cache, and if so, returns the IP address to the requester. Otherwise, the name server queries other available name servers, staring down from the root or as high up the tree as possible. • The user program is given the IP address or an error message.

46. Quality of Service (QoS) • Real-time voice and video don’t work well under the Internet’s “best effort” delivery service • QoS provides for varying application needs in Internet transmission

47. Categories of Traffic • Elastic • Can adjust to changes in delay and throughput access • Examples: File transfer, e-mail, web access • Inelastic • Does not adapt well, if at all, to changes • Examples: Real-time voice, audio and video

48. Requirements for Inelastic traffic • Throughput • Delay • Delay Variation • Packet Loss

50. IPv4 Type of Service Field • Allows user to provide guidance on individual datagrams • 3-bit precedence subfield • Indicates degree of urgency or priority • Queue Service & Congestion Control • 4-bit TOS subfield • Provides guidance on selecting next hop • Route selection, Network Service, & Queuing Discipline