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 networkInitially, included only four nodes: UCLA, UCSB, Utah, and SRI

Internet Domain Survey147,344,723 / Jan 02

http://www.isc.org/

Switching Methods

Circuit SwitchingCircuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delaysMessageMessage SwitchingSwitching: Entire path is not dedicated, but long delays result from intermediate storage and repetition of messagePacket SwitchingPacket 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 ARPANetInstituted Acceptable Use Policies to control useCIX (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 1991First graphical browser (Mosaic) developed by Mark Andreessen at NCSAClient-server system with browsers as clients, and a variety of media types stored on serversUses 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 addressIncludes network and host identifiersDotted decimal notation 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 網路位址 (Network Address) 主機位址 (Host Address)

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 Host

Network HostSubnet

Network Classes

Class A: Few networks, each with many hostsAll addresses begin with binary 0Class B: Medium networks, medium hostsAll addresses begin with binary 10Class 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 organizationEach LAN can have a subnet number, allowing routing among networksHost portion is partitioned into subnet and host numbersSee 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。 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 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 .uk, .de, .jp, .us, .tw., etc.)

Generic Domains .aero, .biz, .com, .coop, .edu, .gov, .info, .int, .mil

, .museum, .name, .net, and .org

http://www.internic.net/

IANA / ICANN

IRs (Internet Registry)INTERNIC.NET

http://www.twnic.net/

DNS Database

Hierarchical database containing name, IP address, and related information for hostsProvides 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 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 Operations1. A user program requests for an IP address for a

domain name.2. A resolver module in the local host or local ISP

formulates a query for the local name server.3. 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.

4. 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 serviceQoS 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

Requirements for Inelastic traffic

Throughput Delay Delay Variation Packet Loss

IPv4 Type of Service Field

Allows user to provide guidance on individual datagrams3-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

RFC 1349RFC 1349

Integrated Services

Routers require additional functionality to handle QoS-based serviceIETF is developing suite of standards to support thisTwo standards have received widespread support Integrated Services Architecture (ISA) Resource ReSerVation Protocol (RSVP)

RFC 1633

RFC 2205

Integrated Services Architecture

Enables provision of QoS over IP-networksFeatures include Admission Control Routing Algorithm Queuing Discipline Discard Policy

ISA Background Functions

Reservation ProtocolReservation Protocol Admission ControlAdmission Control Management Agent Routing Protocol

Forwarding Functions Packet ClassifierPacket Classifier and

Route Selection Packet SchedulerPacket 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 resourcesCan be used in unicast or multicast transmissionsReceivers (not senders) initiate resource reservations

RSVP Data Flows

Session Data flow identified by its destination

Flow Descriptor (reservation request) Flowspec

Specify a desired QoS and is used to set parameters of packet scheduler.

Filter Spec Define the set of packets for which a

reservation is requested.

RSVP Message Types

Resv Originate at multicast group receivers Create “soft states” within routers to

define resources Propagate upstream

Path Provides upstream routing

information

RSVP Operations

Differentiated Services (DS)

Provides QoS based on user group needs rather than traffic flowsCan use current IPv4 octetsService-Level Agreements (SLA) govern DS, eliminating need for application-based assignment

RFC 2474RFC 2474

DS Field

DSCP CU

0 5 6 7

DSCP: DS CodePointCU: Currently Unused

X X X X X 0

X X X X 1 1

X X X X 0 1

standards

experimentallocal use

experimentallocal useFuture standards

000000 : Default (best-effort)xxx000 : IPv4 Precedence

DS Operation

Routers are either boundary nodes or interior nodesInterior nodes use per-hop behavior (PHB) rulesBoundary nodes have PHB & traffic conditioning Classifier Meter Marker Shaper Dropper

DS Domains

DS Traffic Conditioner

Traffic Conditioning Function Classifier Separates submitted packets into classes

Meter Measures submitted traffic for conformance to a profile

Marker Re-mark packets with different codepoint as needed.

Shaper Delay packets as necessary to conform to traffic profile

Dropper Drop packets when the rates of packets exceeds that

specified in the traffic profile

Token Bucket Scheme