Fiber Optics Illustrated Dictionary - Part 53 pptx

Fiber Optics Illustrated Dictionary be conducting by electrochemical means, assuming the solution is one that contains acompound that can be made conducting. ionization current A current resulting when an applied electric field influences the movement ofelec- trical charges within an ionized medium. ionoscope Acamera tube that incorporates an electron beam and aphotoemitting 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 term iconoscope. See kinescope. ionosphere 1. Aseries oflayers ofionized gases en- veloping the Earth, the most dense regions of which extend from about 60 to 500 km (this varies with tem- perature and time of day). 2. The portion of the Emth's outer atmosphere which possesses sufficient ions and electrons to affect the propagation of radio 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, celestialAregion around acelestial body comparable in ionic properties with the Earth's ionosphere. ionospheric sublayers/subregions The Earth's ionosphere has generally been classified into a number of named regions, each ofwhich 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 following chart. Nevertheless, the distinctions are use- ful as a basis for study and for determining good times for propagating radio frequencies through the ionosphere, 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 ionosphere, ground wave, radio, short wave, skip distance. IP See Intemet Protocol. IP address, 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 of subtypes 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 computers 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. It is 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 of0 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 network address may be I, 2, or 3 bytes long (see IP Class for further detail). Amask enables the rest ofthe address to be interpreted to remove a subnetwork number, ifapplicable, to determine the host number. Ionospheric Subregions Name Approx. Location Notes D region A daytime phenomenon and hence not characterized in 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 120 km 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 ofF Suggested as a distinct layer by some, but its existence as a definable separate layer is debated. 512 © 2003 by CRC Press LLC There are static IPs and dynamic IPs: those more or less 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 of people. 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 of the network. See IF Class, Domain Name System, Internet Proto- col, InterNIC. IP Broadcast over ATM An IP multicast service in development by the IP over ATM Working Group for supporting Internet Protocol (IF) broadcast transmissions as a special case of multicast over asynchronous transfer mode networks. See RFC 2022, RFC 2226. See the Appendix for details and diagrams on ATM. IP ClassA network categorization system that facilitates the identification of networks connected to the Internet as each network requires a unique address ill in order to be recognized on the Net by other systems. The system was originally organized into three general 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 Internet Protocol (IP) address ranges were assigned to these classes and there were many discussions as to how to assign and administer public and private network classes and addresses. An IPv4 address is a 32-bit number within which the IP Class address is identified. The unprecedented demand for IP numbers for linking 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 developed classes described in general terms. In general, an IP Class address (IPv4) is organized as four 8-bit decimal numbers (octets) separated by periods: Class. Class Bit.Network ID.Host ID "'''' 1/ e.g., 255.255.255.255 (general format) e.g., 192. 168. O. 42 (local network ill) The amount ofdata designated for the Network ill and the Host ill varies, 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 HID Bits 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 network ID and 24 bits reserved for the host ill. Thus, Class A can support up to 128 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 host ID. 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. 513 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary The class definitions have been expanded and ad- justed according to changing needs on the Internet, although the first three classes retain the general format from larger to smaller networks. See Internet Pro- tocol Classes chart. See address resolution, IP address. IP echo host service A network service protocol for sending packet IP datagrams after exchanging IP source and destination addresses. See RFC 2075. IP forwarding The process of recei ving an Internet Protocol (IP) data packet, determining how it will be handled, and fOlWarding it internally or externally. F or external fOlWarding, the interface for sending the packet is also determined and, if necessary, the media layer encapsulation is modified or replaced for compatibility. IP Multicast over ATM MLIS Internet Protocol multicasting over Multicast Logical IP Subnetwork (MLIS) using ATM multicast routers. A model developed to work over the Mbone, an emerging multicasting 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 of broadcast data over the Internet and thus multicast technologies must be both flexible and robust to handle the demand of thousands or millions of users "tuning" in to the same Internet broadcast "station." See enhanced TV. IP over AIM Internet Protocol over ATM. Imple- menting ATM involves the coordinated work of many computer professionals and market suppliers of networking products and services. As ATM is a broadly defined fonnat intended to handle a variety of media 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 supported, including SVC and PVC-based LANs and WAN s. There are also a number of relevant peer models, and end-to-end data transmission models, including Classical IP, TUNIC and others. See asynchronous transfer mode for general information. See the appendix for diagrams and information about layers. See Internet Protocol, RFC 1577, RFC 1755, RFC 1932. IP over ATM Working Group Merged with the ROLC Working Group to form Internetworking Over NBMA (ION). See Internetworking Over NBMA. IP Payload Compression Protocol IPComp. 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 individually compressed/decompressed, since they may 514 arrive out of order (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 the last 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 fragmentation headers. In IPv6, compression is applied starting at the fIrst IP Header Option field that does not carry information needed by nodes along the delivery path. The compressed payload size must be in whole octets. A number of applications of IPComp have been described, 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 Security IPsec. A security architecture developed in the mid-1990s to resolve some of the issues of conducting secure transactions on the Internet, particu- larly business-to-business and electronic commerce transactions. The architecture encompasses protocols, associations, and algorithms for security, authentication, and encryption. IPsec works at the IP network layer (contrast with Secure Sockets Layer) to provide packet encryption from a choice of encryption 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 working group. They may be optionally implemented into IPv4 but are mandatory for IPv6. IPswitching Technology intended to improve transmission 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 mechanism more circuit- than packet-switched. IP Telephony WG iptel group. A working group of the IETF focused on research and development related to the propagation and routing of information for Voice-over-IP (VoIP) protocols. The iptel group defined the Telephony Routing over IP (TRIP) protocol. See Telephony Routing over IP. IPATM See Internetworking over NBMA. IPCE See interprocess communication environment. IPComp See IP Payload Compression Protocol. IPng IP Next Generation. See IPv6. IPngWG IPng Working Group. A chartered 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. © 2003 by CRC Press LLC IPQ See Initial Public Offering. IPRA See Internet Policy Registration Authority. IPS See Internet Protocol Suite. IPSec See IP Security. IPSec Working Group A division of the Internet Engineering Task Force (IETF) working on standards specifications for the IP Security protocol (IPSec). Ipsilon Flow ManagementProtocol In 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 protocol field. It is used in conjunction with the General Switch Management Protocol. See flow, General Switch Management Protocol. Ipsilon IP switchA commercial switch from Ipsilon, which identifies a stream ofintemet Protocol (IP) datagrams for the IP source and destination addresses, and determines if they form part ofa 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 group The 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 processing 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. IPv4 Internet 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 addressing, 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. IPv6 Internet Protocol, Version 6. The Internet is a large, complex cooperative network supporting doz- ens of operating 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 technology does not become entrenched and obsolete compared to new technologies that are released, but also that it continues to retain the flexibility to provide universal access, much as is guaranteed by law for North American telephone systems. As such, its evolution is ofinterest 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 of network 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, autoconfiguration, and security features, greater support for extensions 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 addresses 128-bit identifiers for interfaces, and sets ofinterfaces, 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 provided 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 N ext Header values. In most cases (except for Hop- by-Hop headers), these extension headers are not examined 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 of8 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 sequence must be followed, both in listing and processing the extension headers. Details can be seen in the extension headers chart. See IPv6 Extension Head- ers chart. See RFC 1826, RFC 1827. IPv6 flow A sequence of packets 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 multiple flows at one time, in addition to traffic not associated with a flow, and there is no requirement for packets to belong to flows. IPv6 flow label A 20-bit field in the IPv6 header. 515 © 2003 by CRC Press LLC Fiber 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 of the 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 addressing simplification ofheader formats improved support for extensions and relaxed limits on length ofoptions 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, described 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 RouterAdvertisement 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 determine MTU sizes. In a transparent bridging environment, a default MTU of 1500 octets is recommended in the absence ofother information to provide compatibility with common 802.5 defaults and Ethernet LANs. In a source route bridging environment, 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 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 formats 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 development 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 virtual version of IPv6 that can run on existing IPv4 physical structures. Various mechanisms for providing IPv4/IPv6 interoperability are being 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 ofsatellite 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 than 65,535 octets. 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. 516 © 2003 by CRC Press LLC receiving device which can be integrated with a mul- tiplexer. 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. IrDA See Infrared Data Association. IRE See Institute of Radio Engineers. IREQ interrupt request. On interrupt-driven systems such as widely distributed Intel-based desktop microcomputers, the insertion and use ofa 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 interface. See interrupt, IRQ. Iridium A series of low Earth orbit (LEO) communications satellites sponsored by Motorola. Iridium satellites began operations in the late 1990s. They incorporate FDMA/TDMA techniques and provide truly global voice, data, facsimile, and GPS 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 Association IIA. A professional association supporting, educating, and representing those doing business via the Internet from Ireland, founded in 1997. http://www.iia.ie/ IrLAP See InfraRed Link Access Protocol. Internet Protocol Version 6 (lPv6) Format o 1 2 3 01234 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 345 6 7 8 901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Iversionl Traffic Class I Flow Label I +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I Payload Length I Next Header I Hop Limi t I +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I I + + I I + Source Address + I I + + I I +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I I + + I I + Destination Address + I I + + I I +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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, ifa routing header is present) 517 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary IRQ interrupt request. A system 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 configuration problems encountered by users on these systems are related to IRQ assignments, this section provides extra detail to assist users in configuring their systems. 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 of devices for which the system requires hardware interrupts include hard drives, CD-ROM drives, mice,joysticks, keyboards, scanners, modems, floppy diskette controllers, sound cards, and others. IRQs are limited in number and some are reserved for specific tasks. A peripheral 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 apreferred, default, or mandatory IRQ number. On systems that use a manual IRQ system for hardware 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 managing IRQ assignments and sometimes it is possible to set the IRQs through software, rather than changing 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 devices. 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, increasing the total number of interrupts 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. In some 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. 518 © 2003 by CRC Press LLC the same time, except that IRQs 3 to 8 come after IRQ 15 in priority. Some peripheral controllers come factory set to a specific 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 architecture of the system and while not all vendors have followed Plug and Play standards, it nevertheless assists users in managing their systems. See In- terrupt Request Numbers and Functions chart. See interrupt, Plug and Play. IRR See Internet Routing Registry. IRSG See Internet Research Steering Group. IRTF See Internet Research Task Force. IS-54, IS-136 See North American Digital Cellular. ISA 1. See industry standard architecture. 2. See In- strumentation, Systems, and Automation Society. 3. Instrumentation Society of America. See Interna- tional Society for Measurement & Control. 4. Inte- grated Service Adapter. 5. Interactive Services Asso- ciation. ISC 1. international switching center. 2. See Internet Software Consortium. ISC2 International Information Systems Security Cer- tification Consortium. See International Information System Security Association. ISCA See International Speech Communication As- sociation. ISD 1. See incremental service delivery. 2. Internet Standards document. ISDN Integrated Services Digital Network. ISDN represents one of the important technologies developed in recent decades to further the transition of communications networks from analog to digital. ISDN is a set of standards for digital data transmission 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 modem 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 subscribers. 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 switching methods. ISDN provides voice and data services over bearer channels (B channels) and signaling or X.25 packet networking over delta channels (D channels). B channels can also be aggregated (brought together) as H 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 of Frame Relay or T1 services. ISDN transmission is many times faster (up to about 128 Kbps) than transmission 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 transmission 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 trans- ~~:l~;r~~~~~1~1~:r!~~ ~=~~=~ JfB nal standards such as RS-232 or V.35. A. terminal adaptor takes the place ofa 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 commonly 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 services, 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 standards There are many important American National Standards (ANSI) of Committee 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 of those available for download for a fee. See the ISDN ANSI Standards chart; it provides a good overview of the issues involved in ISDN/B-ISDN implementation. ISDN associations There are a number of professional trade associations associated with ISDN technology. 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 protocolA protocol 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 asynchronous bonding are supported by various standard and proprietary protocols. ISDN Caller Line Identification CLI. A feature in which the call address of the caller is sent to the receiving device through the delta channel (D channel). 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. 519 © 2003 by CRC Press LLC Fiber 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 of ISDN services by providing the service provider with information about the customer's equipment needed for setup and configuration and smooth operation through a standardized code associated with the model of the ISDN equipment. This code is listed by a participating ISDN equipment vendor in the user manual that comes with the equipment. Prior to the implementation of this system, it could take hours to set up a new ISDN service. IOC is aNational 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 supplierwith an IOC upon registration. See ISDN associations/National ISDN Registry of Customer Equipment and Ordering Codes. ISDNANSI Standards No.Near Revised Title 520 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 T 1.609-1999 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 ofBearer Services for the ISDN Basic Rate Interface Minimal Set ofBearer Services for the ISDN Primary Rate Interface 3 DSO Transport of ISDN Basic Access on a DS 1Facility 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 1Generic Procedures for the Control of ISDN Supplementary Services Interworking between the ISDN U serN etwork 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 © 2003 by CRC Press LLC No.Near Revised Title T1.601-1999 T1.650-1995 (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 T1.665-1997 T 1. 664-1997 T1.654-1996 Tl.646-1995 T1.657-1996 (R2000) B-ISDN Interworking between Signaling System No.7 B-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) B-ISDN Interworking between Signaling System No.7 B-ISDN User Part B- ISUP and ISDN User Part (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 T1.646-1995) Tl.636-1999 T1.630-1999 521 © 2003 by CRC Press LLC . 2 345 6 7 8 901 +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ -+ Iversionl Traffic Class I Flow Label I +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ -+ I Payload Length I Next Header I Hop Limi t. Flow Label I +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ -+ I Payload Length I Next Header I Hop Limi t I +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ -+ I I + + I I + Source Address + I I + + I I +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ -+ I I + + I. I + + I I +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ - +-+ -+ Version Traffic Class Flow Label Payload Length Next Header Hop Limit Source Address Destination Address 4-bit Internet Protocol (IP) version number =

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