Business data communications 4e chapter 5

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
 Packet Switching: Specialized message switching, with
very little delay


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


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


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 Discipline


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
 Marker
 Shaper
 Dropper


Token Bucket Scheme