Internetworking Technologies
An Engineering Perspective
Rahul Banerjee
Computer Science & Information Systems Group
Birla Institute of Technology & Science
Pilani, India
Prentice-Hall of India
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Internetworking Technologies
An Engineering Perspective
Rahul Banerjee
Computer Science & Information Systems Group
Birla Institute of Technology & Science
Pilani, India
Prentice-Hall of India
This small initiative is dedicated to my loving parents
Mrs. Purnima Banerjee
Mr. Ramanand Banerjee
Who have been the guiding lights of my life and to whom I owe whatever
little I have been able to achieve.
-Rahul Banerjee
and related important concepts. The second part of the book takes up the system-level
architectures. Third part of the book primarily comprises of application-level architectures
and a small Internet programming primer. Finally the Appendices present a set of
research / development draft papers that have emanated from the projects discussed in
the Part-three. Appendices also include a literature guide and a bibliography to help
readers in quickly identifying the initial foundation documents and related status reports
wherever applicable.
Like any work of this nature, this work may have a few errors that may have
escaped unnoticed. Students and peers are the best judges of any such endeavour and
their constructive criticisms as well as suggestions are most welcome.
I would fail in his duty if I do not gratefully acknowledge the support,
encouragement and inspiration that I received from my friends and colleagues. I am
thankful to Dr. S. Venkateswaran (Director: BITS), Dr. B. R. Natarajan (Dean of DLP at
BITS), Dr. K. R. V. Subramanian, CEO: Answerpal.com Bangalore, Dr. Rajeev Kumar of
IIT Kharagpur, Dr. Sathya Rao of Telscom SA (Switzerland), Dr. Pascal Lorenz of UoHA
(France), Dr. Bernardo Martinez of Versaware Inc. (Spain), Dr. Torsten Braun of UoB
(Switzerland), Dr. Robert Fink of UCB (USA), Mr. Ishwar Bhat (Librarian: BITS) and Dr.
Latif Ladid of Ericsson (Luxembourg) for their support and encouragement in many
forms. In particular, I wish to express my gratitude towards my parents: Mr. Ramanand
Banerjee and Mrs. Purnima Banerjee; my life-companion: Reena and little Ananya for all
their love and support. Prof. Mahesh M. Bundle, Ms. Krishnapriya D. Bhardwaj, Mr.
Ashaf Badar and Mr. Anand Gangele deserve special thanks for being there all the time
whenever I needed them. Mr. Narendra Saini and Mr. Ashok Jitawat took expert care of
typesetting in the camera-ready form and my heartfelt thanks go to them. The Prentice-
Hall team of Mr. Ashok Ghosh, Mr. Vasudevan, Mr. Malay Ranjan Parida and Mohd.
Shamim were instrumental in timely execution of the project.
Finally, I am also thankful to all my students – present and past –- for providing
me the reasons to take up this project.
BITS, Pilani Rahul Banerjee
November 21, 2002
Contents
Preface
Part-I Internetworking, Multimedia, Compression and Intelligent
Agent Technology Basics
2.11 Estimating Bandwidth Requirements for Multimedia Internetworks: Factors and Issues
4.12 The JAFMAS Technology Architecture 41 4.13 Summary 41 4.14 Recommended Readings 42 4.15 Exercises 43
Part-II Internetworking System Architectures
5. The TCP/IPv6 Internetworking Architecture
5.1 Introduction 44 5.2 The TCP/IPv6 Architecture: An Introduction 45 5.2.1 The Application Layer 45 5.2.2 The TCP/UDP Layer 45 5.2.3 Internet Layer 47 5.2.4 Host to Network Interface 48 5.3 The Internet Protocol 48 5.3.1 IPv4 Options 50 5.3.2 IPv4 and the World of Classes 50 5.3.3 Concept of Subnetting and Supernetting 51 5.3.4 On the Internet Control Message Protocol (ICMP) 53 5.3.5 On the Internet Group Management Protocol (IGMP) 53 5.3.6 The Address Resolution Protocol (ARP) 54 5.3.7 The Reverse Address Resolution Protocol (RARP) 54 5.3.8 Mobile IP 55 5.3.9 The Internet Protocol Version 6 (IPv6) 56 5.3.9.1 Major Goals of IPv6 Design 56 5.3.9.2 On the EUI-64 Addresses and the Link Local Addresses 57 5.3.9.3 How to convert a 48-bit Ethernet Address into the IEEE EUI- Address?
5.3.9.4 What about the networks for which no IEEE 802 address is available?
5.3.9.5 The IPv6 Base Header Design 58 5.3.9.6 The IPv6 Extension Header Structure 59 5.3.10 IPv6 Versus IPv4: A Brief Comparison 62 5.3.11 The IPv6 Address Notations 63 5.3.12 Address Issues in IPv6 63 5.3.12.1 Valid Address-Lifetime 64 5.3.12.2 Preferred Address-Lifetime 64 5.3.13 Address Autoconfiguration / Plug-and-Play Support in IPv6 64 5.3.13.1 Associated Factors of Autoconfiguration 64 5.3.13.2 Stateless Autoconfiguration 65 5.3.13.3 The Stateful Autoconfiguration 65 5.3.14 Time-sensitive IPv6 MM Traffic Over the Ethernet 67 5.3.15 A Quick Note on Mobile IPv6 69 5.3.16 On the Current State of IPv6 Research, Development and Deployment Around the World
5.4 On the Congestion Control in Interneworks 71 5.4.1 Congestion Control Strategies 71 5.4.1.1 The Anticipatory Buffer Allocation Scheme 71 5.4.1.2 ‘Arbitrary Packet Rejection-based’ / ‘Reject-on-Getting-Full’ Congestion Control Scheme
5.4.1.3 Selective Packet Rejection based Congestion Control Scheme 72 5.4.1.4 Permit-based / Token-based / Isarithmic Congestion Control Scheme
Scheme
5.5.5 The Transport Service Access Point (TSAP) and the Network Service Access Point (NSAP)
5.5.6 QoS Considerations in the TL As Used During the Option Negotiation Process
5.5.7.3 Of the Crashes and Crash Recovery Mechanisms and Strategies applicable to the TCP/IP Architecture
11. Internet Commerce Architectures
- 1.1 Introduction 1. Introductory Concepts in Internetworking
- 1.2 Constituents of an Internetwork
- 1.3 Hierarchy in Internetworks
- 1.4 Classification of Internetworks
- 1.5 Local Area / Campus Internetwork Design: Practice and Trends
- 1.6 Competing LAN Technologies
- 1.7 Wide Area Internetwork Design: Practice and Trends
- 1.8 Competing WAN Technologies
- 1.8.1 Wide Area Technology: Other Classification Schemes
- 1.9 Steps Involved in Internetwork Design
- 1.10 Primary Design Goals of Internetwork Design
- 1.11 The Hierarchical Internetworking Design Models
- 1.11.1 The Hierarchical Internetworking Design Models: The Architectural View
- 1.12 Summary
- 1.13 Recommended Readings
- 1.14 Exercises
- 2.1 Introduction 2. The Multimedia Internetworking Technology Basics
- 2.2 Elements of Multimedia Communication
- 2.3 Defining Multimedia Internetwork
- 2.3.1 Examples of the Multimedia Internetwork in Action
- 2.4 Multimedia Internetworks: When to go for them?
- 2.5 Principles of Redesign and Upgrading of Data-Intranets to Multimedia Intranets
- 2.6 Multimedia Internetwork Requirements
- 2.7 Multimedia Internetwork Integration
- 2.8 A Generic Classification of Multimedia Internetworks
- 2.9 Link based Classification of Multimedia Internetworks
- 2.9.1 Point-to-Point Unidirectional Multimedia Internetwork applications
- 2.9.2 Point-to-Point Bi-directional Multimedia Internetwork applications
- 2.9.3 Point-to-Multi-point Unidirectional Multimedia Internetwork applications
- 2.9.4 Point-to-Multi-point Bi-directional Multimedia Internetwork applications
- 2.10 Interactive Multimedia Internetworks: Major Design Factors
- 2.12 The Bandwidth Factor
- 2.13 Networked Interactive Multimedia Video
- 2.14 Videoservers
- 2.15 Multimedia Broadcast Standards
- 2.16 Summary
- 2.17 Recommended Readings
- 2.18 Exercises
- 3.1 Introduction 3. The Data Compression Technology Basics
- 3.2 Space / Storage Compression
- 3.3 Lossy versus Lossless Data Compression - 3.3.1 Lossless Compression - 3.3.2 Lossy Compression
- 3.4 Graphics Metafiles
- 3.5 Language-based Redundancy Probabilities
- 3.6 Primary Classes of Data Encoding Techniques - 3.6.1 Entropy Encoding - 3.6.2 Source Encoding - 3.6.3 Statistical Encoding / Arithmetic Compression Technique - 3.6.4 Repetitive Sequence Suppression based Encoding Technique - 3.6.5 Differential Source Encoding Techniques - 3.6.6 The Transform based Source Encoding Techniques - 3.6.7 Huffman Encoding Techniques - 3.6.8 Adaptive Huffman Encoding - 3.6.9 The Lampel-Ziv Encoding Techniques - 3.6.10 The Lampel-Ziv Welsh (LZW -78) Encoding Technique - 3.6.11 The V.42 bis / British Telecom Lampel-Ziv (BTLZ) Compression - 3.6.11.1 Dictionary Pruning - 3.6.12 Discrete Cosine Transform based Compression Scheme - 3.6.13 Wavelets based Compression Scheme - 3.6.14 Fractal Compression Scheme - 3.6.15 Digital Video Interactive (DVI) Compression Scheme - 3.6.16 Other Compression Tools
- 3.7 The GIF Compression
- 3.8 The PNG Compression
- 3.9 The JPEG Compression
- 3.10 The MPEG Compression
- 3.11 Summary
- 3.12 Recommended Readings
- 3.13 Exercises
- 4.1 Introduction 4. The Intelligent Agent Technology in Internetworking
- 4.2 Intelligent Software Systems
- 4.3 Intelligent Agents
- 4.4 Attributes of Intelligent Agents
- 4.5 Intelligent Architectures
- 4.6 Internetworking Applications of Intelligent Agents
- 4.7 Role of Agents
- 4.8 Components of IA based Distributed Systems
- 4.9 Other Aspects of Intelligent Agents
- 4.10 IBM Aglet Technology Architecture
- 4.11 The Stanford’s JAT Technology Architecture
- 5.4.1.5 The Choke Packet Scheme of Congestion Control
- 5.4.2 Deadlock due to congestion
- 5.5 More on the Generic Transport Layer Concepts
- 5.5.1 Transport Layer Responsibilities
- 5.5.2 Generic Transport Service Primitives
- 5.5.3 Generic Transport Service Primitives
- 5.5.4 Transport Service Primitives: The Berkeley Sockets Set for the TCP
- 5.5.7 Inside the TCP - 5.5.7.1 About the TCP Ports - 5.5.7.2 The 3-Way Handshake in TCP - 5.5.7.4 Client Crash Recovery Strategies - 5.5.7.5 Server Crash Recovery Strategies
- 5.6 About Application Client and Application Server Processes
- 5.7 Summary
- 5.8 Recommended Readings
- 5.9 Exercises
- 6.1 Introduction 6. The Internetwork Routing Architectures
- 6.2 About Routing Terminology
- 6.3 Classification of Routing Architectures
- 6.4 Shortest Path Routing - 6.4.1 Dijkstra’s Algorithm
- 6.5 Flooding Based Routing - 6.5.1 Pure Flooding Algorithm - 6.5.2 Hop Count based Flooding Algorithm - 6.5.3 Selective / Direction-Constrained Flooding Algorithm
- 6.6 Flow-based Routing Algorithm
- 6.7 Distance Vector Routing Algorithm
- 6.8 Link-State Routing Algorithm
- 6.9 Hierarchical Routing Architectures - 6.9.1 The Interior Gateway Protocol (IGP) - 6.9.2 The Interior Gateway Routing Protocol (IGRP) - 6.9.3 The Exterior Gateway Protocol (EGP) - 6.9.4 The Border Gateway Protocol (BGP)
- 6.10 Issues in Hierarchical Routing Architectures
- 6.11 Summary
- 6.12 Recommended Readings
- 6.13 Exercises
- 10.8 Case Study of the CMU Digital Library Architecture
- 10.9 Case Study of the JournalServerSM Virtual Digital Library Architecture
- 10.10 Summary
- 10.11 Recommended Readings
- 10.12 Exercises
- 11.1 Introduction
- 11.2 Principal Objectives of Internet Commerce
- 11.3 Fundamental Components of Internet Commerce Frameworks
- 11.4 Electronic Data Interchange (EDI)
- 11.5 The EDI Architecture
- 11.6 Electronic Funds Transfer (EFT)
- 11.7 Secure Electronic Transactions (SET)
- 11.8 The SET Architecture
- 11.9 The X.400 Standard-based Solution
- 11.10 The MIME-based Solution
- 11.11 Smart Cards and other Solutions
- 11.12 On the Digital Signature and Digital Certificates
- 11.13 The I-Commerce Gateways
- 11.14 Summary
- 11.15 Recommended Readings
- 11.16 Exercises
- 12.1 Introduction 12. Internet Programming
- 12.1.1 Linux Network Programming Basics Revisited
- 12.1.2 A Subset of Address Families Used in Linux Environment
- 12.1.3 A Subset of Protocol Families Used in Linux Environment
- 12.1.4 Socket Errors (ERRNO VALUES)
- 12.2 The World Wide Web and the Hypertext Transfer Protocol
- 12.3 The World Wide Web and Uniform Resource Locators (WWW & URLs)
- 12.4 The World Wide Web and File Transfer Protocol (WWW & FTP)
- 12.5 The Common Gateway Interface (CGI)
- 12.5.1 The Common Gateway Interface (CGI) and PERL
- 12.5.2 Invoking the PERL
- 12.5.3 Select command-line switches and options
- 12.5.4 Data Types in PERL
- 12.5.5 File Handles in PERL
- 12.5.6 File Access Symbols
- 12.5.7 Relational Operators
- 12.5.8 Logical Operators
- 12.5.9 Conditional Operators
- 12.6 The Server Side Includes: An Example
- 12.7 Java Technologies
- 12.7.1 The Concept of the Java Threads
- 12.7.1.1 Creating threads
- 12.7.2 The Java Script: A Scripting Language
- 12.7.2.1 Java Script, HTML and Frames
- 12.7.2.2 Java Script: A Partial Event List
- 12.7.2.3 The Visual Basic Script and its Position vis-à-vis Java Script
- 12.7.1 The Concept of the Java Threads
12.8 The ActiveX Scripting Services 162 12.8.1 Classes of ActiveX Scripting Components 162 12.8.2 The VB Script and the Visual Basic 162 12.9 XML: A Quick Look 162 12.9.1 XML and Java: A Quick Look 163 12.10 Summary 163 12.11 Recommended Readings 164 12.12 Exercises 165
Appendices
A-1 A Revised Version of the IETF Internet Draft on the IPv6 Quality-of-Service through the Modified Flow-label Specification A-2 A Revised Version of the IETF Internet Draft on the IPv6 Quality-of-Service through the Modified Hop-by-Hop Extension Header Specification A-3 A Quick-view Chart of Major Internetworking Research and Development Initiatives Around the World A-4 Bibliography
Index
Chapter –
Introductory Concepts in Internetworking
1.1 Introduction
With each passing day, the people living in all parts of the world are getting closer to
one-another, thanks to the years of human quest for making this world a better place to
live! Several thousands of man-hours have made this journey towards this level of
technological advancements possible. One of the basic tools that made us witness this
global shrinking possible is the computer communication (‘ compunication ’ to the gifted
coiners of the words!). An outstanding contribution that has accelerated this growth of
information technology and thereby helped people to come closer than ever, in terms of
collaborative activities at the least, is the Internet.
As the computers got smaller, cheaper and yet more powerful, more and more
organizations, companies and people began having their own private networks --- even
internetworks , in case of large organizations. Most of them wanted to join the rest of the
information world by further connecting to the Internet. In fact, some of the organizations
went a little ahead! They used the Internet as a vehicle of communication between their
remotely located private networks / internetworks. Clearly, all of these developments
saw the internetworking technology to evolve as an important technology in its own right!
Times changed. And, as usual, this technology saw itself growing into several divergent
but interrelated segments -- from Telerepair to Telemedicine to Interactive Video-on-
Demand -- not to mention the Internet Commerce that glued it all. This work attempts to
introduce you to this wonder world of technology in a step-wise and guided manner!
Interaction Goals
Objectives of this chapter are to define internetworks, discuss their basic
constituents, learn about the advantages they offer, realize the design problems
they pose, learn various design-specific concepts and appreciate the wide spectrum
of applications they may be closely associated with. Additionally, the chapter also
attempts to motivate further exploration by providing certain useful pointers, Self
Assessment Questions and Exercises -- together; these aids aim to extend the
coverage of the topic beyond the classroom interaction.
At the end of this chapter, you should be able to:
- Identify an internetwork as the Internet, Intranet or Extranet;
- Identify the design issues in each of these cases,
- Identify the right way to hook-up two internetworks,
- Analyze the correctness of the internetwork design approach,
- Tell about how to extend an existing design without throwing away existing
setup.
The treatment presupposes the working knowledge of Computer Networks and
some exposure to Operating Systems and Data Communication areas
1.2 Constituents of an Internetwork
An Internetwork may be defined as a network of computer communication networks
every authorized member of which could communicate with every other authorized
member (node) directly or indirectly.
It may consist of several Local, Metropolitan or Wide Area Networks interconnected via a
LAN, MAN or a WAN oriented communication technology, depending upon the specific
context of use.
1.3 Hierarchy in Internetworks
Theoretically speaking, a single level hierarchy , i.e. a flat hierarchy is possible to attain in
case of any network. Similarly, a flat internetwork is possible. Unlike the local area
networks , where hierarchical architecture is seldom used, it is common to find both local
as well as wide area internetworks having a two or greater levels of hierarchy. Reason
can be many -- the greater degree of administrative control, the reduced routing table
space requirements, drastically lesser search time or support for incremental growth. An
internetwork may have a flat or multilevel (Tree-like) hierarchy. The number of levels
depends upon several factors:
- Costs, Capacity and Number of Routers in the Internetwork
- Total Number of Networks in an Internetwork
- Degree of Administrative and Security Control Desired
F. Kamoun & L. Kleinrock suggested a simple rule of thumb for determining an
acceptable number of levels of hierarchy :
If number of routers is ‘N’ , then
Number of levels of hierarchy = ln (N)
1.4 Classification of Internetworks
There exist three classes of Internetworks for most of the practical and analytical
purposes:
- The Global Public Internetwork: The Internet
- The Wholly Owned / Private Internetworks: Intranets
- The Hybrid Internetwork-- private networks / internetworks
connected through the Internet: Extranets
1.5 Local Area / Campus Internetwork Design: Practice and Trends
Traditionally, a Campus Internetwork is a campus-wide internetwork of individual LANs,
which may be geographically spread over the part or whole of a single campus. In
common practice, a single organization or institution wholly owns the entire campus
internetwork including its communication subnet.
Usually, the campus internetworks use LAN technology; however, it is possible to use
WAN technology, when so desirable. The latter may be desirable in some cases when
Major Features of Layer-3 Switches include:
- Layer-3 LAN Switches (often a functional element of a
multi-layer LAN switch) operate at the Network Layer.
- They provide switched routing functions with great degree
of configurability in terms of QoS, Traffic Control, Subnet
Security etc. apart from Scalability and Stability.
- They are, however, relatively poorly suited to real-time
traffic.
- Choice of a conventional router or a Layer-3 Switch
depends on several factors including connection issues ,
cost constraints and level of required security etc.
Major Features of ATM LAN Switches are as follows:
- ATM LAN Switches offer high-speed LAN switching and allow
a high bandwidth.
- They provide switched routing functions in a way somewhat
similar to the non-ATM LAN switches.
- They also offer a guaranteed QoS, guaranteed orderly arrival
of data units, easy Traffic Control, Subnet Security etc.
- They inherently suit real-time traffic requirements. The ATM
LANE technology allows MAC-sub layer compatibility with
other common LAN protocols and therefore existing LAN
applications may continue to run atop an ATM LAN as if they
are running in their native LAN environments.
- Additionally, this permits the VLAN (Virtual LAN) technology to
be employed, when so desired.
1.7 Wide Area Internetwork Design: Practice and Trends
The term ‘wide area’ in the world of networking refers to geographically separate
areas and is different from the term ‘metropolitan area’. Basically, what is a LAN or a
LAI to a ‘local area’ the same is WAN or a WAI to a ‘wide area’.
Design considerations for a WAN / WAI are, however, radically different than those
of the LAN / LAI. Technology classes for local and wide area networks and
internetworks overlap each other.
1.8 Competing WAN Technologies
Circuit Switching Technologies :
- Users can use the whole channel bandwidth assigned to them without any
fear of blockade, infringement or delay.
- Well suited to real-time applications and the applications where delays can
create serious problems.
- Once allotted, the channel and its entire bandwidth is reserved for the user
until the circuit is explicitly released / terminated even when the channel is
idle or only a fraction of the bandwidth is in use. This leads to inefficiency,
poor channel utilization and longer waiting periods for others willing to use the
channel.
Packet Switching Technologies :
- Users can share the available channel bandwidth amongst them without
being aware of this fact.
- As the channel and its entire bandwidth is not reserved / monopolized,
whenever the channel is idle or in partial use, anyone else is allowed to make
use of it; and hence it offers greater average efficiency, better channel
utilization and smaller mean waiting period for others willing to use the
channel.
Virtual Circuit Switching Technologies :
- These technologies attempt to provide the best of packet switching as
well as circuit switching worlds and display some of the features of
each of these.
- These technologies offer low latency period and promise high
throughput.
- As the bandwidth requirement soars, in many situations, these
technologies actually offer cheaper routing elements compared to
those of the packet switching schemes.
- Generally, these technologies demonstrate greater suitability to real-
time traffic than their packet switching counterparts.
1.8.1 Wide Area Technology: Other Classification Schemes
In yet another classification, we may further regroup these technologies into classes
like ATM (WAN / WAI) / Frame Relay / X.25 / ISDN / Leased Line / VSAT / Cellular
Radio / Terrestrial Microwave / Switched Multimegabit Data Service.
In a nutshell, it may be said that there may be several overlapping classification
schemes that may be applied to any set of such technologies. Some of the schemes
may consider the PL features as the basis whereas some other schemes may
consider DLL (MAC sub layer in particular) or NL features as their basis of
classification.
What is common to all of the WAN classification schemes is the fact that none of
them is usually classified with respect to any layer higher than the Layer-3 (i.e. the
Network Layer in the OSI model ).
1.9 Steps Involved in Internetwork Design
Requirement analysis : Statistical analysis of the specific and general requirements
of an internetwork and its various segments in terms of hourly, six-hourly, twelve-
1.11 The Hierarchical Internetworking Design Models
Hierarchical Internetworking design models permit layered modular design of
internetworks. They make it easy to accommodate design changes. Moreover, their
modular design permits easy expandability of an internetwork as per the growing needs
of the environment of operation.
Hierarchical Internetworking models compared to the huge monolithic network design
models / architectures , obviate the need to make large-scale, and often expensive,
changes influencing several component sub-systems. Another plus offered by these
models is the ease and effectiveness of the fault isolation.
1.11.1 The Hierarchical Internetworking Design Models: The Architectural View
Hierarchical Internetworking models are basically three-layer models:
Layer-1 comprises of the functional building blocks, which ensure optimal Transport
operations between the involved network locations. This layer handles high-speed
switching and related issues and is often called the Core or Backbone Layer.
Layer-2 often called as the Distribution Layer is primarily responsible for providing
connections between the requested sites as per a structured / default policy.
Layer-3 is the layer that is primarily responsible for controlling (and optionally
monitoring) the user access to one or more segments of a designated internetwork /
network. This layer is often called as the Local Access Layer for this reason.
1.12 Summary
Internetworks have come of age. Unlike the early days of internetworking, when only the
computer science departments of a few privileged universities and select defense and
telecom organizations were the major users as well as developers of this technology,
now even laymen, housewives and children not only use these internetworks but many a
times, actually contribute themselves to this core area. The best-known internetwork is
the public Internet -- which saw unparalleled growth (or was that an explosion?) soon
after emergence of the World Wide Web technology.
Although, it is the best-known type, the Internet is not the only known type of
internetwork. Due to the reasons of varied degrees of privacy, security, administrative
policy, distances, data transmission needs and associated economics of scale, a few
other derivative technologies have begun evolving into their own -- most promising of
these categories are the Intranet Technologies and the Extranet Technologies. Though
they have a lot in common, because of the situations / circumstances of their use, they
can be easily identified as different, though related, entities.
There exist several areas of overlap -- right from the switching technologies to the
routing protocols and congestion control strategies! Each type of internetwork needs to
address issues like stability, worst-case response time, availability, synchronization,
concurrency control and resource sharing without policy violation as well.
Hierarchical or tree-structured internetworks are commonly used for the reasons of
saving in terms routing table space and search time amongst several reasons like
greater degree of administrative control such arrangements offer. However, not every
such arrangement is always by choice -- at times, it just happens (for instance, as a
result of incremental unplanned growth of networks within an environment).
Although, there do exist monolithic internetwork designs, mostly, these designs create
serious problems in terms of technology upgrade and maintenance. The only advantage
some of these designs do offer is their relatively low development time. Naturally,
functionally layered architectural designs are becoming increasingly popular for medium
to large internetworks. Often, these hierarchical design models are three layer
architectures, comprising of the Core Layer / Backbone Layer, Distribution Layer and
Local Access Layer. It is possible to have a design that may not really conform to this
layering pattern necessarily. What cannot be ignored is the functionality that a layer is
supposed to offer! Whatever be your design choice and strategy, you have to provide
the minimal set of functionalities these layers put together provide.
1.13 Recommended Readings