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Transcript
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