IPaddress, Internet Protocol address On a packet network like the Intemet, a number in each packet is used to identify individual senders and receivers.. Internet Protocol lP Classes Cla
Trang 1Fiber Optics Illustrated Dictionary
be conducting by electrochemical means, assuming
the solution is one that contains a compound that can
be made conducting
ionization current A current resulting when an
ap-plied electric field influences the movement of
elec-trical charges within an ionized medium
ionoscope A camera tube that incorporates an
elec-tron beam and a photoemitting screen where each cell
in the screen's mosaic produces a charge This charge,
or electric current, is proportional to the variations
of the light intensity in the image captured The
ionoscope produced the television image which was
then transmitted to the kinescope for viewing in the
days of live broadcasts Sometimes known by the
general use and older trademarked termiconoscope.
See kinescope
ionosphere 1 A series of layers of ionized gases
en-veloping the Earth, the most dense regions of which
extend from about 60 to 500km(this varies with
tem-perature and time ofday) 2 The portion ofthe Emth's
outer atmosphere which possesses sufficient ions and
electrons to affect the propagation ofradio waves In
this region, the sun's ultraviolet rays ionize gases to
produce free electrons; without these ionized
par-ticles, transmitted radio waves would continue out
into space without bouncing back The deflected path
of a radio transmission is effected by the direction of
the waves and the density of the ion layers it
encoun-ters See ionosphere sublayers, radio waves
ionosphere, celestial Aregion around a celestial body
comparable in ionic properties with the Earth's
iono-sphere
ionospheric sublayers/subregions The Earth's
iono-sphere has generally been classified into a number
of named regions, each of which has properties that
make it somewhat distinct from others These regions
are largely hypothetical models, as they may change
with the time of day or other factors and don't really
form distinct layers as might be implied by the
fol-lowing chart Nevertheless, the distinctions are
use-ful as a basis for study and for determining good times
for propagating radio frequencies through the iono-sphere, even though further refinement and changes are likely in understanding of the regions See Iono-spheric Subregions chart
ionospheric wave Sky wave A radio wave moving into earth's upper atmosphere When sky waves are reflected back, at about 2 to 30 MHz frequency ranges, they are known as short waves.See iono-sphere, ground wave, radio, short wave, skip distance
IPSee Intemet Protocol
IPaddress, Internet Protocol address On a packet network like the Intemet, a number in each packet is used to identify individual senders and receivers Under Intemet Protocol version 4 (IPv4), this is a 32-bit number, theoretically able to accommodate several billion possible addresses, although the ac-tual total is lower due to allocation ofsubtypes within the system
To be associated with the Intemet, a unique network address number must be assigned Once a network address has been assigned to a server, additional com-puters physically attached to that server (as a subnet) can be individually assigned numbers by the local system administrator (certain number pattems are suggested by convention for subnets)
The IPv4 address is a two-part address identifying the network and the individual devices on that network
Itis written as four decimal numbers separated by periods with each number representing a byte of the 4-byte Intemet Protocol (IP) address
The decimal numbers are in the range of 0 to 255 (all zeroes or all ones are reserved for administrative use) Periods are used to decimal references to different parts of the network as follows:
255.255.255.255 The left part of the address represents the network Depending upon the value in the first byte, the net-work address may beI,2, or 3 bytes long (see IP Class for further detail) A mask enables the rest of the ad-dress to be interpreted to remove a subnetwork num-ber, if applicable, to determine the host number
Ionospheric Subregions
Name Approx Location Notes
the same way as some of the regions which exist also at night Daytime ionospheric activity in this region can impair radio wave propagation
E region 100 to 120km The region which is most distinct in its characteristics
and most apt to be classified as a layer
FI and F2 regions 150 to 300 km F2 is always present and commonly used for radio
wave propagation, and has a higher electron density than FI,which is only active in the daytime The F2 region varies in height, and may sometimes go as high
as 400 km in the hottest part of the day
G region outer fringes of F Suggested as a distinct layer by some, but its existence
as a definable separate layer is debated
Trang 2less permanently assigned and those assigned on an
as-needed basis, respectively Many Internet Service
Providers assign temporary dynamic IP numbers to
their subscribers to extend limited IP resources to the
greatest number ofpeople As the Internet has grown,
it has become increasingly important to manage and
reuse IP number resources
The IP address is located through an email or domain
name lookup IF addresses can correspond to more
than one DNS, although a DNS does not have to have
an IP address The IF system is divided into classes,
assigned roughly according to the size ofthe network
See IF Class, Domain Name System, Internet
Proto-col, InterNIC
IP Broadcast over ATMAnIP multicast service in
development by the IP overATM Working Group for
supporting Internet Protocol (IF) broadcast
transmis-sions as a special case of multicast over
asynchro-nous transfer mode networks See RFC 2022,
RFC 2226 See the Appendix for details and diagrams
on ATM
IP Class Anetwork categorization system that
facili-tates the identification of networks connected to the
Internet as each network requires a unique address
illin order to be recognized on the Net by other
sys-tems
The system was originally organized into three
gen-eral classes, with some special cases Classes A, B,
and C were designated for unicast addresses; later,
Class D was designated for multiclass addresses, and
Class E was set aside for future use Certain bits and
to these classes and there were many discussions as
to how to assign and administer public and private network classes and addresses.AnIPv4 address is a 32-bit number within which the IP Class address is identified
The unprecedented demand for IP numbers for link-ing computers to the Internet resulted in the original scheme being quickly oversubscribed Thus, the original class scheme has been modified since its in-ception and IPv6 has been designed to accommodate many more Internet addresses The specific comments that follow pertain to IPv4, with additional newly de-veloped classes described in general terms In gen-eral, an IP Class address (IPv4) is organized as four 8-bit decimal numbers (octets) separated by periods: Class.Class Bit.Network ID.Host ID
e.g., 255.255.255.255 (general format) e.g., 192 168 O 42 (local networkill)
The amount of data designated for the Network ill and the Hostillvaries, depending upon the value in the leftmost byte and may be 1, 2, or 3 bytes Zeroes are used to designate unknown addresses with all zeroes (0.0.0.0) representing the default route Loopbacks are designated with 127 (e.g., 127.0.0.1) and broadcast packets are designated with 255 (in other words, each system on the local network will receive the message if255 is used)
Internet Protocol (lP) Classes
Class Range HIDBits Notes
Class A oto 127 0 A network service category similar to a private line for constant
bit-rate (CBR) services such as voice communications Class A networks have a I-byte network number and a 3-byte host number with 7 bits allocated to the networkIDand24bits reserved for the host ill Thus, Class A can support upto128 networks, each with
16 million hosts.
Class B 128 to 191 10 Class B networks have a 2-byte network number and a 2-byte host
number with 14 bits allocated to the network ill and 16 bits reserved for the host ill Thus, Class B can support up to 16,383 networks, each with 65,535 hosts.
Class C 192 to 233 110 A network service category for connection-oriented data (COD)
that is suitable for bursty applications but capable of functioning
at higher data rates than some other services Through multiplexing, Class C services can be used for administering shared services Class C networks have a I-byte network number and a 3-byte host number with 21 bits allocated to the network 10
and 8 bits for the hostID.Thus, Class C can support up to 2,097,151 networks, each with 256 hosts.
Class D 224 to 239 1110 A network service category for special and multicast networks.
Address assignments range from 224.0.0.0 to 255.255.255.0 Class E 240 to 255 1111 A network service category for experimental networks.
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The class definitions have been expanded and
ad-justed according to changing needs on the Internet,
although the first three classes retain the general
for-mat from larger to smaller networks See Internet
Pro-tocol Classes chart See address resolution, IP
ad-dress
IP echo host serviceAnetwork service protocol for
sending packet IP datagrams after exchanging IP
source and destination addresses See RFC 2075
IP forwardingThe process of receiving an Internet
Protocol (IP) data packet, determining how it will be
handled, and fOlWarding it internally or externally
For external fOlWarding, the interface for sending the
packet is also determined and, if necessary, the
me-dia layer encapsulation is modified or replaced for
compatibility
IP Multicast over ATM MLISInternet Protocol
multicasting over Multicast Logical IP Subnetwork
(MLIS) using ATM multicast routers A model
de-veloped to work over the Mbone, an emerging
multi-casting internetwork Designed for compatibility with
multicast routing protocols such as RFC 1112 and
RFC 1075 By the late 1990s, IP multicasting was
becoming an important mechanism for the delivery
ofbroadcast data over the Internet and thus multicast
technologies must be both flexible and robust to
handle the demand of thousands or millions ofusers
"tuning" in to the same Internet broadcast "station."
See enhancedTV
IP over AIMInternet Protocol over ATM
Imple-menting ATM involves the coordinated work ofmany
computer professionals and market suppliers of
net-working products and services As ATM is a broadly
defined fonnat intended to handle a variety ofmedia
over a variety of types of systems, there is no one
simple explanation for how IP over ATM is
accom-plished A number of subnet types need to be
sup-ported, including SVC and PVC-based LANs and
WANs There are also a number ofrelevant peer
mod-els, and end-to-end data transmission modmod-els,
includ-ing Classical IP, TUNIC and others
See asynchronous transfer mode for general
informa-tion See the appendix for diagrams and information
about layers See Internet Protocol, RFC 1577,
RFC 1755, RFC 1932
IP over ATM Working GroupMerged with the
ROLC Working Group to form Internetworking Over
NBMA (ION) See Internetworking Over NBMA
IP Payload Compression ProtocolIPComp A
loss-less Internet Protocol (IP) compression scheme for
reducing the size of IP datagrams, submitted as a
Standards Track RFC by Schacham et al in
Septem-ber 2001 The protocol increases overall performance
for hosts with sufficient computational power
com-municating over slow/congested links
Compression is applied before any fragmentation,
encryption, or authentication processes In addition,
in IPv6, outbound datagrams must be compressed
before the addition ofa Hop-by-Hop Options header
or a Routing Header, since this information must be
examined en route In IPComp, datagrams are
indi-vidually compressed/decompressed, since they may
arrive out oforder (or not at all) Inbound processing must support both compressed and noncompressed
IP datagrams and decompression is carried out only after security processing has been handled
In IPv4, compression is applied starting at the first octet following the IP header, continuing to thelast
datagram octet The IP header and options are not compressed In IPv6, IPComp is an end-to-end-type payload and must not be applied to routing and frag-mentation headers In IPv6, compression is applied starting at the fIrst IP Header Option field that does not carry information needed by nodes along the de-livery path The compressed payload size must be in whole octets
A number of applications of IPComp have been de-scribed, including IPComp using LZS (RFC 2395), IPComp using ITD-T V.44 packet method (RFC 3051) and IPComp using DEFLATE (RFC 2394) See RFC 3173 (obsoletes RFC 2393)
IP SecurityIPsec Asecurity architecture developed
in the mid-1990s to resolve some ofthe issues ofcon-ducting secure transactions on the Internet, particu-larly business-to-business and electronic commerce transactions The architecture encompasses protocols, associations, and algorithms for security, authentica-tion, and encryption
IPsec works at the IP network layer (contrast with Secure Sockets Layer) to provide packet encryption from a choice ofencryption algorithms ranging from public-key encryption to secure tunneling Originally, IPSec worked with an MD5 hashing algorithm, but this was found to be vulnerable to "collision" attacks, and reinforcement for MD5 and algorithm indepen-dence was added in later drafts
IPsec protocols are developed through an IETF work-ing group They may be optionally implemented into IPv4 but are mandatory for IPv6
IP switchingTechnology intended to improve trans-mission speeds and provide consistent bandwidth for Internet Protocol (IP) switching On a network, IP switching seeks to bring transmission speeds up to the capability of the underlying physical transport medium It does so by reducing delay in IP routing processing and by making the data transfer mecha-nism more circuit- than packet-switched
IP Telephony WGiptel group A working group of the IETF focused on research and development re-lated to the propagation and routing of information for Voice-over-IP (VoIP) protocols The iptel group defined the Telephony Routing over IP (TRIP) pro-tocol See Telephony Routing over IP
IPATMSee Internetworking over NBMA
IPCESee interprocess communication environment
IPCompSee IP Payload Compression Protocol
IPngIP Next Generation See IPv6
IPngWGIPng Working Group Achartered Internet Engineering Task Force (IETF) group developing the next generation Internet Protocol known as IPv6 Members of the Working Group come from various telecommunications industries, including suppliers of data network hardware, network software, and the telephone industry
Trang 4IPRASee Internet Policy Registration Authority.
IPSSee Internet Protocol Suite
IPSecSeeIPSecurity
IPSec Working GroupA division of the Internet
Engineering Task Force (IETF) working on standards
specifications for the IP Security protocol (IPSec)
Ipsilon Flow Management ProtocolIn ATM packet
networking, a protocol for instructing an adjacent
node to attach a layer label to a specified Internet
Pro-tocol (IP) packeiflow to route it through an IP switch
The label facilitates more efficient handling of the
flow by providing access to information about the
flow without consulting each individual IP datagram
This enables the flow to be switched rather than
routed
IFMP comprises the Adjacency Protocol and the
Re-direction Protocol IFMP messages are encapsulated
within an Internet Protocol version 4 (IPv4) packet
The IP header signals the IFMP message in its
proto-col field.Itis used in conjunction with the General
Switch Management Protocol See flow, General
Switch Management Protocol
IpsilonIPswitchAcommercial switch from Ipsilon,
which identifies a stream ofintemet Protocol (IP)
da-tagrams for the IP source and destination addresses,
and determines if they form part of a longer series
The Ipsilon Flow Management Protocol (IFMP) and
General Switch Management Protocol (GSMP) are
used in conjunction with specialized hardware to map
flow to an underlying network, switching direct IP
datagram flows across virtual circuits (VCs) This
scheme is most suitable for smaller networks See IP
switching
IPTel working groupThe IP Telephony working
group, within the IETF Transport Area, formed in the
late 1990s IPTel focuses on propagation of routing
information for Voice-over-IP (VoIP) protocols It is
responsible for a syntactic framework for call
pro-cessing and gateway attribute distribution protocols
The group has defined the Telephony Routing over
IP (TRIP) protocol to handle calls that need to be
routed between domains See iCalendar, Telephony
Routing over IP
IPv4Internet Protocol, Version 4 Developed in the
early 1980s, IPv4 was the Internet Protocol for the
1990s, expected to be superseded sometime in the
next decade by IPv6 IPv4 features 32-bit
address-ing, which is suitable for local area networks and
widely used there, but no longer sufficient to support
the exploding demands on the Internet See IPv6,
RFC 791
IPv6Internet Protocol, Version6.The Internet is a
large, complex cooperative network supporting
doz-ens ofoperating systems and types ofcomputer
plat-forms, tied together with many different circuits,
cables, switches, and routers As can be expected in
a system this diverse, a flexible, farsighted vision of
its future is needed to ensure not only that the
tech-nology does not become entrenched and obsolete
compared to new technologies that are released, but
also that it continues to retain the flexibility to
pro-for North American telephone systems As such, its evolution is of interest and concern to many, and de-signers and technical engineers have labored long hours to propose future deployments and to develop transition mechanisms to allow the Internet to remain
a living upgradable technology
IPv6 is a significant set ofnetwork specifications frrst recommended by the IPng Area Directors of the In-ternet Engineering Task Force (IETF) in 1994 and developed into a proposed standard later the same year The core protocols became an IETF Proposed Standard in 1995
IPv6 is sometimes called IP Next Generation (IPng) IPv6 was blended from a number of submitted pro-posals and designed as an evolutionary successor to IPv4, with expanded 128-bit addressing, autoconfigu-ration, and security features, greater support for ex-tensions and options, traffic flow labeling capability, and simplified header formats
See 6bone, CATNIP, ICMP, Internet Engineering Task Force, IPv4, X-Bone, TUBA, Simple Internet Transition, SIPP, RFC 1752, RFC 1883, RFC 1885
IPv6 addresses128-bit identifiers for interfaces, and sets of interfaces, with each interface belonging to a single node In most cases, a single interface may be assigned multiple IPv6 addresses from the following types: Anycast, Multicast, or Unicast
IPv6 extension headers Separate headers are pro-vided in IPv6 for encoding optional Internet-layer information This infonnation may be placed between the header and the upper-layer header in a packet These extension headers are identified by distinct
Next Header values In most cases (except for Hop-by-Hop headers), these extension headers are not ex-amined or processed along the delivery path until the packet reaches the node identified in the Destination Address (DA) field of the header Thus, extensions are processed in the order in which they appear in a packet
Extension headers are integer multiples of 8 octets, with multioctet fields aligned on natural boundaries Extension headers in original drafts of IPv6 include Hop-by-Hop, Type 0 Routing, Fragment, Destination, Authentication, and Encapsulating Security payload
If more than one is used in the same packet, a se-quence must be followed, both in listing and process-ing the extension headers Details can be seen in the extension headers chart See IPv6 Extension Head-ers chart See RFC 1826, RFC 1827
IPv6 flowA sequence ofpackets uniquely identified
by a source address combined with a nonzero flow label The packets are sent between a specified source and destination in which the source specifies special handling by the intervening routers This may be ac-complished by resource reservation protocol (RSVP)
or by information in the flow packets that may be
specified by extension headers There may be
mul-tiple flows at one time, in addition to traffic not as-sociated with a flow, and there is no requirement for packets to belong to flows
IPv6 flow labelA 20-bit field in the IPv6 header
Trang 5Fiber Optics Illustrated Dictionary
Packets not belonging to a flow have a label of zero,
otherwise the label is a combination of the source
address and a nonzero label, assigned by the flow's
source node Flow labels are chosen uniformly and
pseudo-randomly within the range of I to FFFFFF
hexadecimal, so routers can use them as hashkeys
IPv6 from IPv4 developments Some ofthe changes
proposed for improving and updating IPv4
incorpo-rated into the draft documents for IPv6 include:
increased address sizes (from 32 to 128 bits)
and addressable nodes
simplified autoconfiguration of addresses
increased scalability of multicast routing
new addressing provided through anycast
ad-dressing
simplification of header formats
improved support for extensions and relaxed
limits on length of options
flow labeling of packets to provide special
handling capabilities
removal of enforcement of packet lifetime
maximums
increased support for security, authentication,
data integrity, and confidentiality
IPv6 header format The header format of IPv6,
de-scribed in the draft RFC document, is shown in the
chart below
IPv6 over Ethernet networks IPv6 packets are
transmitted over Ethernet in the standard Ethernet
frames The IPv6 header is located in the data field,
followed immediately by the payload and any
pad-ding octets necessary to meet the minimum required
frame size The default MTU size for IPv6 packets
is 1500 octets, a size which may be reduced by a
Router Advertisement or by manual configuration of
nodes
IPv6 over Token-Ring networks Frame sizes of
IEEE 802.5 networks have variable maximums,
depending upon the data signaling rate and the number
of nodes on the network ring Consequently,
implementation over Token-Ring must incorporate
manual configuration or router advertisements to de-termine MTU sizes In a transparent bridging envi-ronment, a default MTU of 1500 octets is recom-mended in the absence of other information to pro-vide compatibility with common 802.5 defaults and Ethernet LANs In a source route bridging environ-ment, the MTU for the path to a neighbor can be found through a Media Access Control (MAC) level path discovery to access the largest frame (LF) sub-field in the routing information sub-field IPv6 packets are transmitted in LLC/SNAP frames in the data field, along with the payload
IPv6 security The IPv6 Draft specifies that certain security and authentication protocols and header for-mats be used in conjunction with IPv6 These are detailed separately as IP Authentication Header (RFC 1826), IP Encapsulating Security Payload (RFC 1827), and the Security Architecture for the In-ternet Protocol (RFC 1825)
IPv6 transition IPv6 is a very significant develop-ment effort intended to supplant IPv4, the circulatory system of the Internet Commercial implementation
of IPv6 began in the late 1990s Manufacturers and software developers are, in a sense, overhauling the Net in order to support the updated standard
As part of the transition process, the 6bone testbed project has been set up to provide testing ofIPv6 and various transition mechanisms This provides a vir-tual version of IPv6 that can run on existing IPv4 physical structures Various mechanisms for provid-ing IPv4/IPv6 interoperability are beprovid-ing developed, including the Simple Internet Transition (SIT) set of protocols SIT provides a mechanism for upgrade intended not to obsolete IPv4, but rather to gradually phase in IPv6, protecting the connectivity and finan-cial investment of the many IPv4 users
IPX See Internetwork Packet Exchange
IR See infrared
IRAC I infrared array camera 2 See Inter-department Radio Advisory Council 3 internal review and audit compliance
IRC I integrated receiver decoder A type of satellite
IPv6 Extension Headers
Extension Header Notes
Hop-by-Hop Option Unlike other headers, requires examination at each node
Jumbo Payload Option Used for packets with payloads longer than65,535octets
May not be used in conjunction with a fragment header
Routing Header (Type 0) Lists one or more intermediate nodes through which the transmission
must pass Similar to the IPv4 Loose Source and Record Route
Fragment Header Used by a source to send a packet larger than would fit on the path
MTU, as fragmentation in IPv6 is performed only by source nodes Destination Options A header used to carry optional information which is only examined at
the packet's destination node
No Next Header A value (59) in any IPv6 header or extension header which indicates
that nothing follows the header
Trang 6tiplexer This device is used in digital TV
broadcast-ing, especially with MPEG-2 encoded information
2 See International Record Carrier 3 See Internet
Relay Chat
IrDASee Infrared Data Association
IRE See Institute of Radio Engineers
IREQ interruptrequest.On interrupt-driven systems
such as widely distributed Intel-based desktop
micro-computers, the insertion and use of a PCMCIA card
causes an interrupt request signal to be generated to
notify the operating system to suspend the current
operation and temporarily process the request from
the hardware devices attached via the PCMCIA
in-terface See interrupt, IRQ
Iridium Aseries of low Earth orbit (LEO)
commu-nications satellites sponsored by Motorola Iridium
satellites began operations in the late 1990s They
in-truly global voice, data, facsimile,andGPS services The name is based upon the original estimate that 77 satellites would be needed to blanket the Earth, matching the element Iridium in the periodic table The number of satellites needed for global coverage has been reduced to 66 (which were operational by 2002), but the name has remained
IRIS AMacintosh-based videoconferencing system from SAT which provides video capabilities over ISDN lines with JPEG-encoded graphics See Cameo Personal Video System, Connect 918, CU-SeeMe, MacMICA
Irish Internet AssociationIIA A professional as-sociation supporting, educating, and representing those doing business via the Internet from Ireland, founded in 1997 http://www.iia.ie/
IrLAPSee InfraRed Link Access Protocol
Internet Protocol Version 6 (lPv6) Format
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
Traffic Class
Flow Label
Payload Length
Next Header
Hop Limit
Source Address
Destination Address
4-bit Internet Protocol (IP) version number=6 8-bit traffic class field
20-bit flow label 16-bit unsigned integer Length of the IPv6 payload, i.e., the rest of the packet following this IPv6 header, in octets Any extension headers present are considered part of the payload, i.e., included in the length count If this field
is zero, it indicates that the payload length is carried in a Jumbo Payload hop-by-hop option
8-bit selector Identifies the type of header immediately following the IPv6 header; uses the same values as the IPv4 Protocol field
8-bit unsigned integer Decremented by I by each node that forwards the packet The packet is discarded if Hop Limit is decremented to zero
128-bit address of the originator of the packet 128-bit address of the intended recipient of the packet (possibly not the end recipient, if a routing header is present)
Trang 7Fiber Optics Illustrated Dictionary
IRQinterrupt request.Asystem of implementing
computer processor interrupts that is not common to
all computer architectures, but which is
characteris-tic ofa large number ofIntel-based microcomputers
Many desktop computers can readily accommodate
several peripheral devices by just plugging them in
and installing a software device driver However,
since Intel interrupt-driven machines are prevalent
and some of the most frequent hardware
configura-tion problems encountered by users on these systems
are related to IRQ assignments, this section provides
extra detail to assist users in configuring their
sys-tems If a system locks up, freezes, or fails to
recog-nize a new device, or a device which was working
before a new device is installed, it may be due to an
IRQ conflict.
When using an application program and an interrupt
occurs, a signal is sent by the computer operating
system to the processor which tells it to pay
atten-tion to the signaling process and temporarily suspend
the current process The IRQ is a number assigned
to a specific hardware interrupt The types ofdevices
for which the system requires hardware interrupts
in-clude hard drives, CD-ROM drives, mice,joysticks,
keyboards, scanners, modems, floppy diskette
con-trollers, sound cards, and others IRQs are limited in
number and some are reserved for specific tasks
Aperipheral device often comes with a controller card
that fits into an expansion slot inside the computer
Sometimes there are small dip switches or jumpers
on the controller card or on the device itself(or both), which are set at the factory to a preferred, default, or mandatory IRQ number
On systems that use a manual IRQ system for hard-ware devices, it is necessary to assign the interrupts
to a corresponding device and a good idea to keep a list of the assignments On older ISA bus systems, almost the whole process had to be done by hand by the user With later EISA and Micro Channel buses, there is software assistance for detecting and man-aging IRQ assignments and sometimes it is possible
to set the IRQs through software, rather than chang-ing dip switches or jumpers
In earlier systems, interrupts could not be used by more than one device at a time, some were reserved, and only eight were available in total To complicate matters, some devices had to be associated with a specific interrupt, reducing the number of possible interrupt combinations on a system with several de-vices The IRQ may need to be changed in two places:
on the computer system and on the controller card or device To accommodate more devices, more recent machines added a second interrupt controller, increas-ing the total number ofinterrupts to 16 (though again, not all were available, as some were reserved or used for linking)
In general, lower IRQ numbers are higher priority than higher IRQ numbers when two are signaled at Interrupt Request (IRQ) Numbers and Functions
IRQ# INT Notes
0 08h Reserved for system timer
I 09h Reserved for keyboard
2 OAb Reserved for linking (chaining, cascading) upper eight interrupts through
interrupt #9
3 OBh Serial port COM2 and sometimes COM4
4 OCh Serial port COMI and sometimes COM3
5 ODh Originally assigned to a hard disk controller on 8-bit systems, later 16-bit
versions reserved this for a second parallel port (usually designated LPT2) May be available for use by a soundboard, parallel printer, or network interface card (NIC)
6 OEh Reserved for floppy diskette controller
7 OFh Reserved for first parallel printer, usually designated LPT I, by some software
applications programs (e.g., word processors), but not reserved by the operating system, and thus may be available
8 70h Reserved for realtime CMOS clock
9 71h Reserved Used for connection between lower eight and upper eight interrupts
Chained to interrupt #2 Insome systems, used for graphics controller
10 72h Available Often used for video display cards
II 73h Available May be used for a third IDE device
12 74h Available, although it may be used by a bus mouse (e.g., PS/2 mouse)
13 75h Reserved for math coprocessor-related functions
14 76h Reserved for non-SCSI controllers Typically used for IDE drives (typical-IDE
devices include CD-ROM drives, cartridge drives, and hard drives)
15 77h Available Sometimes used for SCSI controllers, or a second IDE controller
Trang 815 in priority.
Some peripheral controllers come factory set to a
spe-cific interrupt and cannot be changed Two such cards
with the same IRQ requirement cannot be used in the
computer at the same time There are situations where
users actually must physically swap out cards to
switch between devices It is wise to ask about IRQ
settings when considering the purchase of
"bargain-priced" peripherals
Since the interrupt system created administration and
configuration problems for users on machines with
several devices, some vendors developed the Plug and
Play system, which works in conjunction with
Win-dows 95 to ease the burden of setting and tracking
interrupts manually While this doesn't change the
ar-chitecture of the system and while not all vendors
have followed Plug and Play standards, it
neverthe-less assists users in managing their systems See
In-terrupt Request Numbers and Functions chart See
interrupt, Plug and Play
IRRSee Internet Routing Registry
IRSGSee Internet Research Steering Group
IRTFSee Internet Research Task Force
IS-54, IS-136See North American Digital Cellular
ISA1 See industry standard architecture 2 See
In-strumentation, Systems, and Automation Society
3 Instrumentation Society ofAmerica See
Interna-tional Society for Measurement&Control 4
Inte-grated Service Adapter 5 Interactive Services
Asso-ciation
ISC1 international switching center 2 See Internet
Software Consortium
ISC2International Information Systems Security
Cer-tification Consortium See International Information
System Security Association
ISCASee International Speech Communication
As-sociation
ISD1 See incremental service delivery 2 Internet
Standards document
ISDNIntegrated Services Digital Network ISDN
represents one of the important technologies
devel-oped in recent decades to further the transition of
communications networks from analog to digital
ISDN is a set of standards for digital data
transmis-sion designed to work over existing copper wires and
newer cabling media It began to spread in the late
1980s, and was becoming more prevalent in 2001,
in competition with combined telephone/cable
mo-dem services
ISDN is a telephone network system defined by the
lTU-T (formerly CCITT), which essentially uses the
wires and switches ofa traditional phone system, but
through which service has been upgraded so that it
can include end-to-end digital transmission to
sub-scribers Some systems include packets and frames,
as well (see packet switching and Frame Relay)
Nearly all voice switching offices in the u.S have
been converted to digital, but the link to subscribers
remains predominantly analog, so it has taken some
time to work out the logistics of supporting
compet-ing switchcompet-ing methods
channels(B channels) and signaling or X.25 packet
networking over delta channels (D channels)
Bchan-nels can also be aggregated (brought together) asH
channels.
ISDN provides an option for those who want faster data transfer than is offered on traditional analog phone lines, but can't afford the higher cost ofFrame Relay or T1 services ISDN transmission is many times faster (up to about 128 Kbps) than transmis-sion over standard phone services with a 28,800 bps modem Since the ISDN line doesn't have to modu-late the signal from digital to analog before transmis-sion and then demodulate it back to digital, but rather passes the digital signal through, it's faster It is also possible to use an ISDN line as though it were up to three lines, sending several different types of
nal standards such as RS-232 or V.35.A.terminal adaptor takes the place of a modem and is provided
in much the same way - as a separate component or
as an interface card that plugs into a slot
A network termination (NT 1) device is also com-monly used in ISDN installations, usually paid for
by subscribers and located at their premises
Not all cities or countries offer ISDN, but its avail-ability is increasing Many subscriber surcharge ser-vices, such as Caller ID, are available through an ISDN line
ISDN is available in most urban areas with a choice
of two levels of service as shown in the ISDN Basic Service Types chart
ISDN ANSI standardsThere are many important American National Standards (ANSI) ofCommittee
TI related to ISDN available from ANSI They are summarized by ANSI in the form of abstracts on the Web ANSI also distributes related ETSI standards documents Here is a sampling ofthose available for download for a fee See the ISDN ANSI Standards chart; it provides agood overview ofthe issues involved
in ISDN/B-ISDN implementation
ISDN associationsThere are a number of profes-sional trade associations associated with ISDN tech-nology Some of the more prominent national and international associations are listed in the ISDN As-sociations chart There are also many regional (e.g., state) ISDN groups See ISDN
ISDN bonding protocolAprotocol which facilitates the use of two ISDN bearer channels (B channels) to transmit a single data stream The bonding protocol provides dialing, synchronization, and aggregation services for setting up a second call Both synchro-nous and asynchrosynchro-nous bonding are supported by various standard and proprietary protocols
ISDN Caller Line IdentificationCLI A feature in which the call address of the caller is sent to the re-ceiving device through the delta channel(Dchannel)
This provides a means for the host router to authen-ticate the call and to apply any parameters which might be relevant to that particular call
Trang 9Fiber Optics Illustrated Dictionary
ISDN interfaces When ISDN services are
estab-lished, a number of links and connections are set up
to provide a path for digital transmissions between
the telephone switching office and the customer
equipment Each interface link in the path has been
designated and commonly used equipment given
names to aid in installation and clarity in
intercom-municating between the customer and the installer
The ISDN interfaces diagrams (following the ISDN
ANSI Standards chart) provide two common
sce-narios Note that these diagrams have been simplified
and that geographical and equipment variations
oc-cur There are some differences between ISDN
de-ployment in Europe and North America, and local
geographic differences are not indicated in the diagrams
ISDN Ordering Code IOC A system intended to
facilitate the installation ofISDN services by provid-ing the service provider with information about the customer's equipment needed for setup and configu-ration and smooth opeconfigu-ration through a standardized code associated with the model of the ISDN equip-ment This code is listed by a participating ISDN equipment vendor in the user manual that comes with the equipment Prior to the implementation ofthis
sys-tem,it could take hours to setupa new ISDN service IOC is a National ISDN initiative promoted by local exchange carriers (LECs), the National ISDN Coun-cil, the North American ISDN Users Forum, and Telcordia Telcordia administers the registry and assigns
an equipment supplier with an IOC upon registration See ISDN associations/National ISDN Registry of Customer Equipment and Ordering Codes
ISDN ANSI Standards No.Near Revised Title
T1.113-1995
Tl.236-2000
Tl.604-1990 (R2000)
T1.603-1990 (R2000)
TRNo.7
TRNo.15
TRNo.47
TRNo.62
T1.219-1991 (R1998)
T1.217-1991 (R1998)
Tl.239-1994
T1.218-1999
T1.216-1998
TI.602-1996 (R2000)
T1.241-1994
T1.625-I993 (R1999)
T1.620-1991 (R1997)
T1.6I9-I992 (RI999)
Tl.616-I992 (R1999)
T1.613-1991 (R1997)
T1.612-1992 (RI998)
T1.611-1991 (R1997)
T1.610-1998
T1.609-1999
T1.607-1998
T1.605-1991 (R1999)
Signaling System No.7, ISDN User Part Signaling System 7 (SS7) - ISDN User Part Compatibility Testing Minimal Set of Bearer Services for the ISDN Basic Rate Interface Minimal Set of Bearer Services for the ISDN Primary Rate Interface
3 DSO Transport of ISDN Basic Access on a DS 1 Facility Private ISDN Networking
Digital Subscriber Signaling System Number 1 (DSS I) - Codepoints for Integrated Services Digital Network (ISDN) Supplementary Services Digital Subscriber Signaling System Number 1 (DSS 1) Codepoints for Integrated Service Digital Network (ISDN) Supplementary Services (Supersedes TR No 47)
ISDN Management - Overview and Principles ISDN Management - Primary Rate Physical Layer ISDN Management - User-Network Interfaces Protocol Profile ISDN Management - Data Link and Network Layers
ISDN Management - Basic Rate Physical Layer ISDN Data-Link Layer Signaling Specification for Application at the User-Network Interface
ISDN Service-Profile Verification and Service-Profile Management ISDN Interface Management Services
ISDN Calling Line Identification Presentation and Restriction Supplementary Services
ISDN Circuit Mode Bearer Service Category Description MultiLevel Precedence and Pre-Emption MLPP Service, ISDN Supplementary Service Description
ISDN Call Hold Supplementary Services Digital Subscriber Signaling System No.1 DSS 1 ISDN Call Waiting ISDN Terminal Adaptation Using Statistical Multiplexing
Sigaling System Number 7 Supplementary Services for non-ISDN Subscribers
DSS 1 Generic Procedures for the Control of ISDN Supplementary Services Interworking between the ISDN UserNetwork Interface Protocol and the Signaling System No.7 ISDN User Part
ISDN Layer 3 Signaling Specifications for Circuit Switched Bearer Service for Digital Subscriber Signaling System No.1 DSSI
ISDN Basic Access Interface for Sand T Reference Points and Layer 1 Specification
Trang 10T 1.650-1995 (R2000)
T1.642-1995 (R2000)
Tl.250-1996
T1.632-1993 (RI999)
Tl.643-1998
T1.653-1996 (R2000)
T1.647-1995 (R2000)
ISDN Basic Access Interface for Use on Metallic Loops for Application at the Network Side of NT, Layer 1 Specification
ISDN Usage of the Cause Information Element in Digital Subscriber Signaling System Number I (DSS 1)
ISDN Supplementary Service Call DeflectionT1.403.01-1999 Network and Customer Installation Interfaces - (ISDN) Primary Rate Layer 1
Electrical Interfaces Specification (includes revision of Tl.408-1990 and partial revision ofT1.403-1995)
OAM&P - Extension to Generic Network Model for Interfaces between Operations Systems and Network Elements to Support Configuration Management - Analog and Narrowband ISDN Customer Service Provisioning ISDN Supplementary Service Normal Call Transfer
ISDN Explicit Call Transfer Supplementary Service ISDN Call Park Supplementary Service
ISDN Conference Calling Supplementary Service
B-ISDN (Broadband-ISDN)
T1.637-1999
Tl.629-1999
T1.640-1996
Tl.638-1999
Tl.645-1995
T 1.665-1997
T1.664-1997
T1.654-1996
Tl.646-1995
T1.657-1996 (R2000) ISDN Interworking between Signaling System No.7 ISDN User Part
B-ISUP and Digital Subscriber Signaling System No.2 (DSS2) T1.658-1996 (R2000) Extensions to the Signaling System No.7 - B-ISDN User Part, Additional
Traffic Parameters for Sustainable Cell Rate SCR and Quality of Service (QOS)
T1.663-1996 (R2000) B-ISDN Network Call Correlation Identifier
Tl.644-1995 (R2000) B-ISDN Meta-Signaling Protocol
T1.635-1999 B-ISDN ATM Adaptation Layer Type 5 Common Part - Functions and
Specification B-ISDN ATM Adaptation Layer 3/4 Common - Part Functions and Specification
Tl.662-1996 (R2000) B-ISDN ATM End System Address for Calling and Called Party
T1.656-1996 (R2000) ISDN Interworking between Signaling System No.7 ISDN User Part
B-ISUP and ISDN User Part (B-ISUP) B-ISDN Overview of B-ISDN NNI Signaling Capability Set 2, Step 1 B-ISDN Point-to-Multipoint Call/Connection Control
B-ISDN Operations and Maintenance Principles and Functions B-ISDN Physical Layer Specification for User-Network Interfaces Including DSI/ATM (Supersedes T1.624-1993)
B-ISDN Network Node Interfaces and Inter Network Interfaces Rates and Fonnats Specifications
Tl.652-1996(R2001) B-ISDN Signaling ATM Adaptation Layer - Layer Management for the
SAAL at the NNI B-ISDN Signaling ATM Adaptation Layer - Service-Specific Coordination Function for Support of Signaling at the Network Node Interface (SSCF at the NNI)
B-ISDN ATM Adaptation Layer - Service-Specific Coordination Function for Support of Signaling at the User-to-Network Interface (SSCF at the UNI) B-ISDN ATM Adaptation Layer - Service-Specific Connection Oriented Protocol (SSCOP)
B-ISDN Signaling ATM Adaptation Layer (SAAL) - Overview Description B-ISDN ATM Adaptation Layer for Constant Bit Rate Services Functionality and Specification
T1.627-1993 (RI999) B-ISDN ATM Layer Functionality and Specification
Tl.511-1997 B-ISDN ATM Layer Cell Transfer Performance
T1.624-1993 B-ISDN User-Network Interfaces Rates and Formats Specifications
(Superseded by T 1.646-1995) Tl.636-1999
T 1.630-1999