Voice Over IPv6. Architectures for Next Generation Vol: P Networks

364 Pages·2006·10.326 MB·English

by  Daniel Minoli (Auth.)

Preface
Voice over IP (VoIP) in particular and Voice over Packet (VoP) in general have been advocated and studied
since the mid 1970s. It was the advent of DSP technology for voice compression in the late 1980s and early
1990s that gave these services the impetus they needed to enter the mainstream. Commercial-grade tech-
nologies and services started to appear in the 1996-7 timeframe and books on the topic started to appear in
1998, with Mr. Minoli's co-authored Delivering Voice over IP book (Wiley, April ,1 1998) being the first
text on the market on this topic. A lot has transpired since then. Now, enterprise networks, cellular carriers,
voice-over-cable carriers, "triple-play" carriers, "pure-play VoIP carriers," and even traditional voice carriers
are all moving rather aggressively to a VoIP paradigm.
A fair degree of commercial success can be acknowledged as of 2006. Small-to-medium size enterprises are
using the technology to save money on trunking costs. Large-size enterprises are using the technology for
mobility support and related functional enhancements, including "presence-related functions" and unified
messaging. Large-size companies are also using this technology for Contact Center support, particularly for
hosted ACD-capabilities and for virtual Contact Centers (where agents are distributed throughout al large
geographic area.) Carriers are deploying these services to generate new revenues, stem the movement away
from traditional TDM services, and enter new markets (e.g., "triple-play" applications.)
However, there are two fundamental problems that currently pose a significant risk to the scalability of VoIP
to a large-population base along with guaranteed "industrial-grade" service levels. The first problem is lack
of de-facto intrinsic QoS in many of the IP networks deployed around the globe (both at the carrier level and
at the enterprise level.) The second problem relates to end-to-end integrity of the signaling and bearer path
for VoIE specifically the fact that VoIP packets have a "difficult" time being carrier across firewalls, not only
because of protocol considerations, but, at the practical level, because of the Network Address Translation
(NAT) issues. Additionally, one can also cite overall security concerns as another potentially problematic
issue.
What were the "bragging rights" of the large national voice carriers across the world (particularly under the
auspices of the ITU-T) were the assertions that, in true fact, "...(with TDM) any one in the world could call
anyone else in the world, any time, any where, and be able to support a good-quality telephonic conversa-
tion..." That is an elusive, currently-unachievable goal for the VoIP industry...
This book is a vade mecum on IPv6 opportunities for carrier-class VoIE Specifically, it looks at the use of
IPv6 to support a next-generation, carrier-class VoIP environments, which we call VoIPv6. IPv6 offers the
potential of achieving the scalability, reacheability, end-to-end interworking, QoS, and commercial-grade
robustness for VoIP that are mandatory mileposts of the technology if indeed it is to replace the TDM infra-
structure around the world, in the true sense of the word sens the marketing hype... Specifically, IPv6 can be
employed to addresses the QoS and NAT issues. While some technologists may argue that "there is nothing
one can do about QoS with IPv6 that one cannot do with IPv4," or "NATs will not disappear just because
xi
Preface
IPv6 has a larger native address space because there are a number of reasons for isolating a private address
domain behind a firewall that are unrelated with the scarcity of IPv4 addresses," such arguments exhibit
some naivet6: one can cite literally dozens of examples where ostensibly the claim that "there is nothing that
technology n + 1 can do that technology n can't do" has been made in the past 40 years, yet, the technology
marches on inexorably to new approaches and new modalities. Specifically, in this context, the question we
believe is operative is not if "IPv4 will be replaced," but simply "when it will be replaced". The position
of this textbook is not that there are certain things that cannot be done one way or another with IPv4, just
that, in our opinion, the most optimal way to build next-generation VoIP systems that have the scope, reach,
ubiquity, reliability, and robustness of the current commercial PSTN is with IPv6 - other approaches may be
possible, but may not be as optimal.
This book is the first book of its kind to address this issue as a macro-level scalability requirement. The book
basically is comprised of two sections: an opening section (Chapters 1-5) that looks at VoIP applications and
motivations, and the second part (Chapters 6-8) focuses on the IPv6 itself.
After an introduction in Chapter ,1 we provide a quick tutorial in Chapter 2 on VoIP and in Chapter 3 on
SIP and signaling. Chapter 4 continues that basic discussion by examining the area of "presence" which rep-
resents a value-added set of VoIP-based capabilities. Chapter 5 discusses the issues associated with current
VoIP implementations, as highlighted above.
Chapter 6 provides a basic introduction to IPv6. Chapter 7 discusses the delivery of voice-over-packet in an
IPv6 environment. Chapter 8 provides some basic discussion of the transition issues including interworking
between IPv6 and IPv4. Europe and Asia are currently leading in the planning of IPv6 networks.
In general, telecom areas of (industry) growth in the short-to-medium term (say four-to-seven years) include
VoIE wireless, security, IPv6, Grid Computing, Ubiquitous Computing, and nanotechnology (nanoelectron-
ics, nanophotonics, and quantum computing). This book covers several of these themes.
This book should prove useful to VoIP equipment vendors, VoIP service providers (e.g., cellular carri-
ers, voice-over-cable carriers, "triple-play" carriers, "pure-play VoIP carriers," and even traditional voice
carriers), enterprise customers, researchers, planners, and educators. Portions of this book are based on
particularly-selected RFC material: given the emerging nature of the topic and the status of the 3G service
proposals, this contextual assembly of the information should be useful and should read as logically well
organized. We explicitly credit the developers of these RFCs as the "intellectual" trust behind the mate-
rial. This derivative assembly of material comments on or otherwise explains selected RFC material, and
intend to assist in their implementation/understanding/dissemination. The synthesis provided in this text is
much more than an anthology of relevant specs or documents - but recognizing that the IETF has created
an extremely valuable and very lucid exposition on these exact issues, we find that said materials provide
an excellent foundation for a study of VoIPv6; hence, their synthesis herewith. The book in not principally
designed to be a pure pedagogical introduction to VoIP itself, however, a fair amount of basic material
in included to make the book relatively self-contained; for basic introductions to VoIP there are several
textbooks, including, but not limited to, this author's market-first books listed in the Reference section; the
principal focus here is on the IPv6 perspective.
There is an extensive body of research literature on the topic of SIP, IPv6, NAT, and related issues (as noted
in the appendix of Chapter .)1 This text is intended only as a first-read on the topic. The bibliography in
Chapter 1 is an excellent source of useful additional information.
xii
stnemgdelwonkcA
The following researchers are amply acknowledged for the contributions made to the topics discussed in this
book, which were sources for the present treatment, analysis, and discussion:
.S Deering, R. Hinden; R. Gilligan, E. Nordmark, M. Day, J. Rosenberg, H. Sugano; J. Weinberger,
C. Huitema, R. Mahy; H. Schulzrinne, G. Camarillo, A. Peterson, R. Sparks, M. Handley, E. Schooler;
E Srisuresh, J. Kuthan, A. Molitor, and A. Rayhan.
xiii
1
CHAPTER
Introduction
1.1 Overview
Voice over Internet Protocol (VolP), in particular, and Voice over Packet (VoP), in general, have been
advocated and studied since the late-1970s. The reality is, however, that until the late 1990s, voice- and
video-over-packet networks have been mostly used for pre-stored kinds of media solutions, namely, for one-
way download of sound files or video files that were played in nonreal time at the user's personal computer,
or at most, for a simplex transmission path with a relatively large intrinsic delay, such as Internet radio. At
this juncture, however, there is a discernible movement afoot in the industry to affect the transition to a con-
verged, fully multimedia-enabled, real-time packet-based communication infrastructure for both enterprise
networks and for carriers' network environments in support of commercial-grade real-time voice, commer-
cial-grade video, and commercial-grade Video-On-Demand (VOD) services. These converged networks will
allow voice, video, data, and images to be delivered anywhere in the world, at any time, and with any kind of
user's communication device and network access service ,]~o899INIM[ ,]20899INIM[ ,]102002NIM[ .]202002NIM[
It was the advent of Digital Signal Processing (DSP) technology for voice and video compression in the
late 1980s and early 1990s that gave multimedia-over-packet services the impetus they needed to enter
the mainstream. Commercial-grade VolP technologies and services started to appear in the early 2000s in
First-Generation 1( G) networks. A lot has transpired since then; enterprise networks, cellular carriers, Voice-
over-Cable (VoCable) carriers, "triple-play" carriers, "pure-play VolP carriers," and even traditional voice
carriers are all moving rather aggressively to a VolP paradigm. This is a Second-Generation (2G) technol-
ogy. Next generation third-wave (3G) technology is just 2-3 years away.
A fair degree of commercial success can be acknowledged with regard to 2G VolP networks as of press time.
Small-to-medium sized enterprises are using the technology to save money on trunking costs. Large-size
enterprises are using the technology for mobility support and related functional enhancements, includ-
ing "presence-related functions" and unified messaging. Roaming from Ethernet-based phones to cellular
service is beginning to be supported. Large-sized companies are also using this technology for contact center
support, particularly for hosted Automatic Call Distribution (ACD)-capabilities and for virtual contact cen-
ters (where agents are distributed throughout a large geographic area). Carriers are deploying these services
to generate new revenues, replace (substitute) the revenue movement away from traditional Time Division
Multiplexing (TDM) services and, enter new markets (for example, "triple-play" applications.)
Despite recent successes, there are two fundamental problems that currently pose a significant risk to the
unconstrained scalability of VolP to a large-population base along with guaranteed "industrial-grade" service
levels. The first problem is lack of de facto intrinsic Quality of Service (QoS) in many of the IP networks
deployed around the globe (both at the carrier level and at the enterprise level). The second problem relates
to end-to-end integrity of the signaling and bearer path for VolP, specifically the fact that VolP packets have
a "difficult" time being carried across firewalls, not only because of protocol considerations, but, at the
Chapter I
practical level, because of Network Address Translation (NAT) issues. Additionally, one can also cite overall
security concerns, such as eavesdropping and hacking as another potentially problematic issue. Next-genera-
tion 3G VoIP networks are now on the drawing board to address these issues, specifically, scalability and
commercial-grade reliability; these networks are based on IPv6.
The "bragging fights" of the large international voice carriers across the world (particularly under the aus-
pices of the International Telecommunication Union [ITU]) were the assertions that, in true fact, "...(with
TDM) anyone in the world could call anyone else in the world, any time, any where, and be able to support
a good-quality telephonic conversation ..." Frankly, this is an elusive, currently-unachievable goal for the
VoIP industry. IPv6 offers the potential of achieving the scalability, reachability, end-to-end interworking,
QoS, and commercial-grade robustness levels for VoIP that are mandatory mileposts of the technology if it is
indeed to eventually replace the TDM infrastructure around the world, in the true sense of the word sans the
marketing hype. Specifically, IPv6 deals with the QoS and NAT issues.
This is the first book of its kind to address the issue of macro-level scalability requirements and IPv6's op-
portunity in this context.
IPv6 is considered to be the next-generation Internet protocol [HUI199701], [HAG200201], [MUR200501],
], [SOL200401 ], [ITO200401 [MIL 107991 ], [MIL200001 ], ], [GRA200001 102002VAD[ ], [LOS200301], ], [LEE200501
[GON199801], [DEM200301], [GOS200301], and [WEG199901]. The current version of IPv4 has been in use for
almost thirty years and exhibits (some) challenges in supporting emerging demands for address space
cardinality, high-density mobility, and strong security--this is particularly true in developing domestic
and defense department applications utilizing peer-to-peer networking. IPv6 is an improved version of the
Internet protocol that is designed to coexist with IPv4 and eventually provide better overall internetworking
capabilities than IPv4 .]104002VPI[ Proponents see applications in a whole gamut of environments, including
VoIE third-generation Wi-Fi, and security .]105002LSI[
IPv6 was initially developed in the early 1990s because of the anticipated need for more addresses based on
forecasted Internet growth; that is, cell phone deployment, PDA introduction, smart appliances, and billions
of new users in developing countries (e.g., in China, India, and so on.). New technologies such as VoIE
always-on Internet access (for example, DSL and cable), Ethernet to the home, and evolving ubiquitous
computing applications are driving and/or will be driving this need even more in the next few years.
NAT-based accommodation is but a short-term solution against this anticipated growth phenomenon and a
better solution is needed. Basic Network Address Translation (Basic NAT) is a method in which IP ad-
dresses are mapped from one group to another, transparent to end users. Specifically, private "nonregistered"
addresses are mapped to a small set (as small as )1 of legal addresses. This, however, impacts the general
addressability, accessibility, even "individuality" of the device. Network Address Port Translation (NAPT)
is a method by which many network addresses and their Transmission Control Protocol/User Datagram Pro-
tocol (TCP/UDP) ports are translated into a single network address and its TCP/UDP ports. Together, these
two operations, referred to as traditional NAT, provide a mechanism utilized in IPv4 to connect a realm with
private addresses to an external realm with globally-unique registered addresses .]101002IRS[
There is a recognition that NAT techniques makes the Internet, the applications, and even the devices more
complex, which in turn implies a cost overhead 105002VPI[ .] The expectation is that IPv6 can make every IP
device less expensive, more powerful, and even consume less power; the power issue is not only important
for environmental reasons, but also improves operability (e.g., longer battery in portable devices, such as cell
phones) .]105002VPI[ The market has associated IPv6 with "lots of addressing," but planners do not yet real-
ize that it does a lot of other things too [MAL200501 .] IPv6 can improve the Internet or a firm's intranet, with
benefits such as:
Introduction
• expanded addressing capabilities;
• serverless autoconfiguration (plug-and-play) and reconfiguration;
• more efficient and robust mobility mechanisms;
• end-to-end security, with built-in, strong IP-layer encryption and authentication;
• streamlined header format and flow identification;
• enhanced support for multicast and QoS and,
• extensibility: improved support for options/extensions.
Corporations and government agencies will be able to achieve a number of improvements with IPv6. While
the basic functions of Internet protocols are to move information across networks, IPv6 has more capabili-
ties built into its foundation than IPv4. A key capabilitymand the reason research began to replace IPv4--is
the significant increase in address space. Consumers look for "plug-and-play" simplicity, collaboration (e.g.,
distributed games), and mobility. IPv6 is a natural convergence protocol for tomorrow's IP-centric world, as
depicted in Figure 1.1 .]105002LS[[
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Figure 1.1:IPv6 applicability, including VolP and personal telephony.
For example, in an IPv6 environment, all equipment can have a "legal"/globally-unique IP address, so that equip-
ment can be uniquely tracked; while today, all Ethernet devices have a unique Media Access Control (MAC)
address. Not all devices are Ethernet, hence, the challenge in this respect. Today's inventory management cannot
be achieved with IP; it follows that someone has to manually walk around at various times during the inventory
cycle to ensure each desktop computer is where it is supposed to be. With IPv6, one can use the network to verify
that such equipment is there. Even non-IT equipment in the field can also be tracked, by having an IP address
permanently assigned to it.
Chapter I
More network security is embedded in IPv6 than in IPv4. Also, it has extensive automatic configuration
(autoconfiguration) mechanisms; with IPv4 one needs to add mechanisms such as Dynamic Host Configura-
tion Protocol (DHCP) and others to make it happen, while IPv6 reduces the IT burden making configuration
essentially plug-and-play.
In general, telecom areas of (industry) growth in the short-to-medium term (say four to seven years) include
VolP, wireless, security, IPv6, grid computing, ubiquitous computing, and nanotechnology (nanoelectronics,
nanophotonics, and quantum computing). This book covers several of these themes.
IPv6 is now gaining momentum globally, with a lot of interest and activiitny Europe and Asia. There is also
incipient traction in the U.S., and it's only a matter of time before a transition will need to occur worldwide. For
example, the U.S. Dept. of Defense (DoD) announced in 2003 that from October ,1 2003, all new developments
and procurements had to be lPv6-capable. The DoD's goal is to complete the transition to IPv6 for all intra- and
internetworking across the agency by 2008 .]10500ev~[ In 2005, the U.S. Government Accountability Office
(GAO) recommended that all agencies become proactive in planning a coherent transitiont o I~6 .]105002LAM[
VoIP systems, and even more so mobile devices, require end-to-end interworking between entities such as
VoIP network elements/gatekeepers/gateways, Session Initiation Protocol (SIP) servers/proxies/registrars,
IEEE 802.11 wired and wireless LANs, protocol firewalls, stateful firewalls, application gateways/session
border controllers, (IP security protocol ) IPSec appliances, Virtual Private Network (VPN) nodes, DHCP
servers, DNS servers/proxies, desktop systems and desktop (as well as back-end) applications. Some of
these elements do not work as well as one would like in an IPv4 environment. Naturally, these observa-
tions apply to pure IP VoIP networks, with end-to-end IP delivery across the enterprise network or across
a carrier's (or carriers') network(s). A number of institutions are currently deploying a hybrid approach
(particularly where the Private Branch Exchanges (PBX) has been fully depreciated but is still working),
which consists of an IP upgrade to serve the "station side," but a traditional TDM switching fabric and TDM
trunking on the "network side." Only a fully IP-based system can deliver all of the mobility, productivity,
and enhancements that are promised by VoIP. Hence, a transition to the pure IP environment is only a matter
of time; in turn, this will raise the NAT, firewall, and scalability issues we are describing.
Some proponents see aggressive inroads for VoIP (while others see a more modest path to penetration.) For
example, U.K. market research firm Analysys claimed in 2005 that traditional residential telephone service
"will whither away in Western Europe in the next four years"; specifically, mobile service and VoIP will ac-
count for 60% of all residential voice service expenditures by 2010 according to the firm .]105002BOM[ "The
mass market for voice services in Western Europe is being transformed by the substitution of mobile and
new VoIP services for traditional fixed-voice services, and we expect that in five years 45% of voice minutes
will be made from a mobile or VoIP connection, compared to 28% in 2004." According to Analysys, overall,
a quarter of households in Western Europe will switch away from so-called Plain Old Telephony Services
(POTS) by 2010 to a combination of mobile and VoIP service, the report concluded. About 45% of all voice
minutes by residential customers will be made from one of those two newer types of connections, according
to the research firm. By 2010, VolP over broadband connections could account for 9.6% of all voice minutes.
Other observers are more conservative in their estimates. Because VoIP over broadband is inexpensive, the
percentage of users' incomes spent on voice service will decrease in coming years. All of this points to the
need for VoIP scalability and IPv6 as a subtending technology to support such scalability.
1.2 Introductory Overview of IPv6
IP was designed in the 1970s with the purpose of connecting computers that were in separate geographic
locations. Computers in a campus were connected to each other by means of local networks, but these local
networks were separated into stand-alone islands. Internet, as a name to designate the protocol, and later the
Introduction
name of the worldwide information network, simply means "intemetwork"--that is, a connection between
networks. In the beginning, the protocol had an only military use, but computers from universities, users,
and enterprises were soon added. Internet as a worldwide information network is the result of the practical
application of the IP protocol, that is, the result of the interconnection of a large set of information networks
existing in the world .]105002vpI[ The current generation of IP protocol is IPv4. Starting in the early 1990s,
developers realized that the communication needs of the twenty-first century needed a protocol with some
new features and capabilities, while at the same time retaining the useful features of the existing protocol.
While link-level communication does not generally require a node identifier (address) because the remote
device is intrinsically identified with the link's remote sink, communication over a group of links (a net-
work) does require unique node identifiers (addresses). The IP address is an identifier that is assigned to each
device connected to an IP network. In this setup, different elements taking part in the network (servers, rout-
ers, user computers, gateways, etc.) communicate among them using their IP address as the identifier. The
issue relates to the question if a device can have its own dedicated, permanent, globally-unique, "registered"
IP address, or if it needs to operate only via the use of a temporary nonglobally-unique IP address. Version
4 of the IP protocol addresses consist of four octets. For ease of human conversation, IP protocol addresses
are represented as numbers separated by periods, for example: 166.74.110.83, where the decimal number is
a shorthand (and corresponds to) the binary code described by the byte in question (an 8-bit number takes a
value from 0-255 range). Since the IPv4 address has 32 bits there are nominally 2 23 different IP addresses
(approximately 4 billions nodes, if all combinations are used).
IPv6 is the Intemet's next-generation protocol, which was at first called IPng, Internet Next Generation. IPv6
is the upgrade of the data networking protocol in which the Internet at large, and nearly all enterprise networks
are based on. The Internet Engineering Task Force (IETF) developed the basic specifications during the 1990s
to eventually support a migration to a new environment. IPv6 is defined in RFC 2460, "Internet Protocol, Ver-
sion 6 (IPv6) Specification" S. Deering, R. Hinden (December 1998), which obsoletes RFC 1883 (the "version
5" reference was employed for another use: an experimental real-time streaming protocol. To avoid any confu-
sion, it was decided not to make use of this nomenclature). The IPv6 protocol apparatus is described by the
100+ IETF RFCs identified in Appendix B (some have been obsoleted and/or replaced.)
1.2.1 IPv6 Benefits
IPv4 has demonstrated, by means of its long life, to be a flexible and powerful mechanism. However, IPv4
is starting to exhibit limitations, not only with reference to the need for raw increase of the IP address space,
driven, for example, by new populations of users in large countries like China and India, along with new
technologies with "always connected devices" (xDSL, cable, PDAs, UMTS mobile telephones, etc), but also
in reference of VoIP both in terms of the NAT issue as well as the QoS issue.
IPv6 tackles these problems by creating a new IP address format, so that the number of IP addresses will not
exhaust for several decades or longer, even though an entire new crop of devices are expected to connect to
the Internet, under the thrust of the coming wave of Ubiquitous Computing (also known as Pervasive Com-
puting). IPv6 also adds improvements in areas such as routing and network autoconfiguration. New devices
that connect to the Internet will be "plug-and-play" devices. With IPv6, one is not required to configure
dynamic nonpublished local IP addresses, the gateway, the subnetwork mask, or any other parameters. The
equipment is plugged into the network and it obtains all requisite configuration data .]105002VPI[
The advantages of IPv6 can be summarized as follows:
Scalability: IPv6 has 128-bit addresses versus 32-bit IPv4 addresses. With IPv4, the theoretical num-
ber of available IP addresses is 232-101°. IPv6 offers a 8212 space. Hence, the number of available
unique node addressees are 8212 10
,~, 40.
Chapter I
Security: IPv6 includes security in its specifications such as information encryption and authentication
of the source of the communication.
Real-time applications: To provide better support for real-time traffic (e.g., VolP, IPTV), IPv6 includes
in its specifications "labeled flows." By means of this mechanism, routers can recognize the
end-to-end flow to which transmitted packets belong to. This is similar to the service offered by
Multiprotocol Label Switching (MPLS), but it is intrinsic with the IP mechanism rather than an
add-on. Also, it preceded this MPLS feature by a number of yeas.
Plug-and-play: IPv6 includes in its standard a "plug-and-play" mechanism that facilitates the connec-
tion of equipment to the network. The requisite configuration is automatically made (as is the case
today with Ethernet).
Mobility: IPv6 includes more efficient and enhanced mobility mechanisms.
Optimized protocol: IPv6 embodies IPv4 best practices, but removes unused or obsolete IPv4 character-
istics; this results in a better-optimized Internet protocol.
Addressing and routing: IPv6 improves the addressing and routing hierarchy.
Extensibility: IPv6 has been designed to be extensible and offers optimized support for new options and
extensions.
1.2.2 Network Address Translation Issues in IPv4
As noted, IPv4 theoretically allows up to 2 23 addresses, based on a four-octet address space. Legal, glob-
ally-unique addresses are assigned by the Internet Assigned Numbers Authority (IANA). IP addresses are
addresses of computer nodes at layer 3. Each device on a network (whether the Internet or an intranet) must
have a unique address; in IPv4 the layer 3 address is a 32-bit (4-byte) binary address used to identify a host's
network ID as well as the host's own ID. As noted, it is represented by the nomenclature a.b.c.d (each of
these being from 1 to 255-0 has a special meaning); for example, 167.168.169.170, or 232.233.229.209, or
200.100.200.100, etc. The network portion can contain either a network ID or a network ID and a subnet ID.
The IP address can be from an officially-assigned range, or from an internal (but not globally-unique) block.
Internal intranet addresses may be in other ranges, for example, in the 10.0.0.0 or 192.0.0.0 range. In the
latter case, a NAT function is employed to map the internal addresses to an external legally-assigned number
when the private-to-public network boundary is crossed by a packet. This, however, imposes a number of
limitations, particularly since the number of registered external addresses available to a company is almost
invariably much smaller (as small as )1 than the number of internal devices requiting an address.
The 32-bit address can be represented as AdrTypelnetIDIhosted. Every network and every host or device
has a unique network address, by definition, although such address may not be globally-unique. Figure 1.2
depicts the traditional address classes.
Address Class A. Class A uses the first bit of the 32-bit space (bit 0) to identify it as a Class A address;
this bit is set to 0. Bits 1 to 7 represent the network ID, and bits 8 through 31 identify the PC, ter-
minal device, VoIP handset, or host/server on the network. This address space supports 2 7- 2 = 126
networks and approximately 16 million devices (2 )42 on each network. By convention, the use of
an "all ls" or "all 0s" address for both the Network ID and the Host ID is prohibited (which is the
reason for subtracting the 2 above.)
Address Class B. Class B uses the first two bits (bit 0 and bit )1 of the 32-bit space to identify it as a
Class B address; these bits are set to 10. Bits 2 to 51 represent the network ID, and bits 16 through
31 identify the PC, terminal device, VoIP handset, or host/server on the network. This address space
supports 214- 2 = 16,382 networks and 212- 2 = 65,134 devices on each network.
Introduction
817161514131211 11817161514131211 81716151413121118171615141312
Address Class Network DI Host DI
Class A
81716151413121 118171615141312111817161514131211
12131415161718
Iol
Network DI Host DI
Class B
211 817161514131211181716151413 8171615141312111817161514131211
1 0 Network lD Host DI
Class C
817161 5211411312111817161514131211181716151413 817161514131211
1101 Host DI
Class D
8171615141312111817161514131211181716151413121118171615141312111
I11111 !ol sserddA
Multicast
Figure 1.2: Traditional address sessalc for PI .sserdda
Address Class C. Class C uses the first 3 bits (bit 0, bit ,1 and bit 2) of the 32-bit space to identify it
as a Class C address; these bits are set to 110. Bits 3 to 23 represent the network ID, and bits 24
through 31 identify the PC, terminal device, VolP handset, or host/server on the network. This ad-
dress space supports about 2 million networks 122( - 2) and 82 - 2 = 254 devices on each network.
Address Class D. This class is used for broadcasting: multiple devices (all devices on the network)
receive the same packet. Class D uses the first 4 bits (bit 0, bit ,1 bit 2, and bit 3) of the 32-bit space
to identify it as a Class D address; these bits are set to 1110.
Classless Interdomain Routing (CIDR) is yet another mechanism that was developed to help alleviate the
problem of exhaustion of IP addresses and growth of routing tables. CIDR is described in RFC 1518, RFC
1519, and RFC 2050. The concept behind CIDR is that blocks of multiple addresses (for example, blocks
of Class C addresses) can be combined, or aggregated, to create a larger classless set of IP addresses, with
more hosts allowed. Blocks of Class C network numbers are allocated to each network service provider;
organizations using the network service provider for Internet connectivity are allocated subsets of the service
provider's address space as required. These multiple Class C addresses can then be summarized in routing
tables, resulting in fewer route advertisements. CIDR mechanism can be applied to blocks of Class A, B, and
C addresses .]104002AET[ All of this assumes, however, that the institution in question already has an assigned
set of "legal" IP addresses; it does not address the issue of how to get additional "legal" (registered) glob-
ally-unique IP addresses.
During the 1980s, a great quantity of "legal" addresses were allocated to firms and organizations without
stringent control; as a result, many organizations have more addresses that they actually need, giving rise
to the present dearth of available "registerable" Layer 3 addresses. Furthermore, not all IP addresses can be
used due to the fragmentation described above. One approach to the issue would be a renumbering and a
reallocation of the IPv4 addressing space. However, this is not as simple as it seems since it requires world-
wide coordination efforts. Moreover, it would still be limited for the human population and the quantity of
devices that will be connected to Internet in the medium-term future 105002VPI[ .]