Business data communications 4e chapter 5

Switching Methods Circuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays  Message Switching: Entire path is not

Chapter 5 : The Internet:

Addressing & Services

Business Data Communications, 4e

 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

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

 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

 Two standards have received widespread support

 Integrated Services Architecture (ISA)

 Resource ReSerVation Protocol (RSVP)

Integrated Services Architecture

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

Token Bucket Scheme