Transcript Chapter 5 : The Internet: Addressing & Services

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
http://www.isc.org/
Internet Domain Survey
147,344,723 / Jan 02
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 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
retrieving files
Connecting to the Internet
End users get connectivity from an ISP
(internet service provider)
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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
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11000000 11100100 00010001 00111001
(binary)
192.228.17.57 (decimal)
IP Address
長度：4 Bytes (32-Bit)
每一IP 位址包括兩個部份
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網路位址 (Network Address)
主機位址 (Host Address)
Host
Network
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。
Network
Subnet
Host
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
IP Address Formats
0 ~ 127
128 ~ 191
192 ~ 223
224 ~ 239
240 ~
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
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。
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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。
Routers and the IP Addressing
Principle
• Routers have two or more addresses. One for
each interface.
Routing Table
IF ((Mask[i] & Destination Addr) = = Destination[i])
Forward to NextHop[i]
IP Forwarding Process
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)
Domain Name System
32-bit IP addresses have two drawbacks
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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
TLD (Top-Level Domains)
Country Code Domains
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.uk, .de, .jp, .us, .tw., etc.)
Generic Domains
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.aero, .biz, .com, .coop, .edu, .gov, .info, .int, .mil, .mus
eum, .name, .net, and .org
IANA / ICANN
INTERNIC.NET
http://www.internic.net/
IRs (Internet Registry)
http://www.twnic.net/
DNS Database
Hierarchical database containing name,
IP address, and related information for
hosts
Provides name-to-address directory
services
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
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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.
DNS Operations
1. A user program requests for an IP address for a domain
2.
3.
4.
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.
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
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Can adjust to changes in delay and
throughput access
Examples: File transfer, e-mail, web access
Inelastic
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Does not adapt well, if at all, to changes
Examples: Real-time voice, audio and video
Requirements for Inelastic traffic
Throughput
Delay
Delay Variation
Packet Loss
IPv4 Type of Service Field
Allows user to provide guidance on individual
datagrams
3-bit precedence subfield
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Indicates degree of urgency or priority
Queue Service & Congestion Control
4-bit TOS subfield
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Provides guidance on selecting next hop
Route selection, Network Service, & Queuing
Discipline
RFC 1349
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
RFC 1633
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Integrated Services Architecture (ISA)
Resource ReSerVation Protocol (RSVP)
RFC 2205
Integrated Services Architecture
Enables provision of
QoS over IPnetworks
Features include
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Admission Control
Routing Algorithm
Queuing Discipline
Discard Policy
ISA Background
Functions
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Reservation Protocol
Admission Control
Management Agent
Routing Protocol
Forwarding Functions
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Packet Classifier and
Route Selection
Packet Scheduler
ISA Implemented in a Router
Resource Reservation Protocol - RSVP
A signaling protocol for applications to
reserve resources.
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
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Data flow identified by its destination
Flow Descriptor (reservation request)
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Flowspec
 Specify a desired QoS and is used to set
parameters of packet scheduler.
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Filter Spec
 Define the set of packets for which a
reservation is requested.
RSVP Message Types
Resv
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Originate at multicast group receivers
Create “soft states” within routers to
define resources
Propagate upstream
Path
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Provides upstream routing information
RSVP Operations
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 applicationbased assignment
RFC 2474
DSCP: DS CodePoint
CU: Currently Unused
DS Field
0
5
DSCP
X
X
X
X
X
X
6
7
CU
X
0
standards
000000 : Default (best-effort)
xxx000 : IPv4 Precedence
experimental
X
X
X
1
1
local use
X
X
X
0
1
experimental
local use
Future standards
DS Operation
Routers are either boundary nodes or interior
nodes
Interior nodes use per-hop behavior (PHB)
rules
Boundary nodes have PHB & traffic
conditioning
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Classifier
Meter
Marker
Shaper
Dropper
DS Domains
DS Traffic Conditioner
Traffic Conditioning Function
Classifier
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Separates submitted packets into classes
Meter
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Measures submitted traffic for conformance to a profile
Marker
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Re-mark packets with different codepoint as needed.
Shaper
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Delay packets as necessary to conform to traffic profile
Dropper
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Drop packets when the rates of packets exceeds that
specified in the traffic profile
Token Bucket Scheme