Chapter 5 : The Internet: Addressing & Services Business Data Communications, 4e 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 Switching Methods Circuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays Message Switching: Entire path is not dedicated, but long delays result from intermediate storage and repetition of message NSF and the Internet In the 1980s, NSFNet extended packetswitched 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 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 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 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) Network Classes Class A: Few networks, each with many hosts All addresses begin with binary 0 Class B: Medium networks, medium hosts All addresses begin with binary 10 Class C: Many networks, each with few hosts All addresses begin with binary 11 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 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 DNS Database Hierarchical database containing name, IP address, and related information for hosts Provides name-to-address directory services 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 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 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 Integrated Services Routers require additional functionality to handle QoS-based service IETF is developing suite of standards to support this Two standards have received widespread support Integrated Services Architecture (ISA) Resource ReSerVation Protocol (RSVP) Integrated Services Architecture Enables provision of QoS over IP-networks Features include Admission Control Routing Algorithm Queuing Discipline Discard Policy ISA Background Functions Reservation Protocol Admission Control Management Agent Routing Protocol Forwarding Functions Classifier and Route Selection Packet Scheduler Resource Reservation Protocol A tool for prevention of congestion through reservation of network resources Can be used in unicast or multicast transmissions Receivers (not senders) initiate resource reservations RSVP Data Flows Session Data flow identified by its destination Flow Descriptor (reservation request) Flowspec Filter Spec RSVP Message Types Resv Originate at multicast group receivers Create “soft states” within routers to define resources Propagate upstream Path Provides upstream routing information Differentiated Services (DS) Provides QoS based on user group needs rather than traffic flows Can use current IPv4 octets Service-Level Agreements (SLA) govern DS, eliminating need for application-based assignment DS Operation Routers are either boundary nodes or interior nodes Interior nodes use per-hop behavior (PHB) rules Boundary nodes have PHB & traffic conditioning Classifier Meter Token Bucket Scheme