Huber, M.N., Daigle, J N, Bannister, J, Gerla, M, Robrock Il, R.B. Networks The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Huber, M.N., Daigle, J.N., Bannister, J., Gerla, M., Robrock II, R.B. “Networks” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
72 Networks 72.1 B-ISDN Manfred N. Huber B-ISDN Services and applic Mode. Transmission of B-ISDN Signals.ATM Adaptation Layer.B-ISDN Signaling N. Daigle 72.2 Computer Communication General Networking Concepts Communication Network Architecture Local-Ar s and internets·Some Joseph Bannister Additional Recent Developments ty of Southern 2.3 Local-Area Networks California Information The LAn Service Model. Other Features. The Importance of Sciences Institute LAN Standards Mario gerla 72.4 The Intelligent Network University of california, Los A History of Intelligence in the Network. The Intelligent Network· ntelligent Network Systems· The CCS7 Network The Service Control point Data base 800 Richard B. robrock it Service. Alternate Billing Services. Other Services. The Bell Communications research Advanced Intelligent Network. Back to the Future 72.1 B-ISDN Manfred N. Huber Since the mid-1980s the idea of the integrated services digital network(ISDN)has become reality. In ISDN voice services with supplementary features and data services with a bit rate of up to 64 kbit/s are integrated in one network. For voice communication and many text and data applications the 64-kbit/s ISdn will be sufficient. Although it is minor as yet, there exists already a growing demand for broadband communication with bit rates from some megabits per second up to approximately 130 Mbit/s [Wiest, 1990](e.g, high-speed data communication, video communication, high-resolution graphics In order to provide the same advantages of isdn to broadband communication users, network operat and service providers, the development of an intelligent broadband-ISDN(B-ISDN)is necessary. The future B-iSDN will become the universal network integrating different kinds of services with their individual features and requirements. B-ISDN will support switched, semipermanent and permanent, point-to-point, and poin to-multipoint connections and provide on-demand, reserved, and permanent services. B-ISDN connection support packet mode and circuit mode services of mono-and/or multimedia type of a connection-oriented or connectionless nature in a unidirectional or bidirectional configuration [Handel and Huber, 1991b] B-ISDN Services and Applications As already mentioned, there exists some demand for broadband communication which originates from business customers as well as residential customers. In the residential area, on the one hand, people are interested in video distribution services for entertainment purposes, like television and high-definition TV; on the other c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 72 Networks 72.1 B-ISDN B-ISDN Services and Applications • Asynchronous Transfer Mode • Transmission of B-ISDN Signals • ATM Adaptation Layer • B-ISDN Signaling 72.2 Computer Communication Networks General Networking Concepts • Computer Communication Network Architecture • Local-Area Networks and Internets • Some Additional Recent Developments 72.3 Local-Area Networks The LAN Service Model • Other Features • The Importance of LAN Standards 72.4 The Intelligent Network A History of Intelligence in the Network • The Intelligent Network • Intelligent Network Systems • The CCS7 Network • The Service Control Point • Data Base 800 Service • Alternate Billing Services • Other Services • The Advanced Intelligent Network • Back to the Future 72.1 B-ISDN Manfred N. Huber Since the mid-1980s the idea of the integrated services digital network (ISDN) has become reality. In ISDN voice services with supplementary features and data services with a bit rate of up to 64 kbit/s are integrated in one network. For voice communication and many text and data applications the 64-kbit/s ISDN will be sufficient. Although it is minor as yet, there exists already a growing demand for broadband communication with bit rates from some megabits per second up to approximately 130 Mbit/s [Wiest, 1990] (e.g., high-speed data communication, video communication, high-resolution graphics). In order to provide the same advantages of ISDN to broadband communication users, network operators, and service providers, the development of an intelligent broadband-ISDN (B-ISDN) is necessary. The future B-ISDN will become the universal network integrating different kinds of services with their individual features and requirements. B-ISDN will support switched, semipermanent and permanent, point-to-point, and pointto-multipoint connections and provide on-demand, reserved, and permanent services. B-ISDN connections support packet mode and circuit mode services of mono- and/or multimedia type of a connection-oriented or connectionless nature in a unidirectional or bidirectional configuration [Händel and Huber, 1991b]. B-ISDN Services and Applications As already mentioned, there exists some demand for broadband communication which originates from business customers as well as residential customers. In the residential area, on the one hand, people are interested in video distribution services for entertainment purposes, like television and high-definition TV; on the other Manfred N. Huber Siemens J. N. Daigle University of Mississippi Joseph Bannister University of Southern California Information Sciences Institute Mario Gerla University of California, Los Angeles Richard B. Robrock II Bell Communications Research
cc1 vCc 2 GFC VPI I VCI PLT CLP HEC 口 rtual cha FIGURE 72.1 ATM principl hand, they will use video telephony with acceptable quality. Over the long term, video mail services and video retrieval services will become more important. ice and text are no longer sufficient for business customers. In the offices and factories of tomorrow, interactive broadband services will be required. Handling complex tasks in the future demands comprehensive ipport by services for voice, text, data, graphics, video, and documents. In addition to the individual services, the multimedia services and the simultaneous or alternating use of several services with multifunction work stations will gain importance [Armbruster, 1990] Interconnection of local-area networks(LANs)or large computers, computer-aided design, and computer aided manufacturing will become important data applications. The first video services will be video telephony and video conferencing(studio-to-studio and workstation video conferencing). Initially these services may have diminished quality, but for the long term Tv quality can be expected The bit rates of all services mentioned above are in the range of 2 to 130 Mbit/s( depending on the individual application). Taking into account that in the future more enhanced video coding mechanisms will be available, the required bit rates for video services will become lower without influencing quality significantly Asynchronous Transfer Mode In today's public switched networks the synchronous transfer mode(STM) predominates. Applying STM technology, for the duration of a connection a synchronous channel with constant bit rate is allocated to that onnection. StM does not fit very well for the integration of services with bit rates from some kilobits per second to 130 Mbit/s. Therefore, in B-Isdn a new transfer mode called asynchronous transfer mode(Atm) is used In ATM all kinds of information is transported in cells. A cell is a block of fixed length, which consists of a 5-octet cell header and a 48-octet cell payload(see Fig. 72.1 ). The cell header contains all necessary information for transferring the cell through the network and the cell payload includes the user information. The cell rate of a connection is proportional to the service bit rate. Only if information is available is a cell used by the connection. By having different routing labels, cells of different connections can be transported on the same transmission line (cell multiplexing). If no connection has information ready to transport, idle cells will be inserted Idle cells do not belong to any connection; they are identified by a standardized cell header ATM uses only cells; multiplexing and switching of cells is independent of the applications and of the bit rates of the individual connections. Applying ATM technology, the idea of one universal integrated network becomes a reality. However, the aTM technology also causes some problems. Because of the asynchronous ultiplexing buffers are necessary, which results in cell delay, cell delay variation, and cell loss. In order to compensate for these effects additional measures have to be provided e 2000 by CRC Press LLC
© 2000 by CRC Press LLC hand, they will use video telephony with acceptable quality. Over the long term, video mail services and video retrieval services will become more important. Voice and text are no longer sufficient for business customers. In the offices and factories of tomorrow, interactive broadband services will be required. Handling complex tasks in the future demands comprehensive support by services for voice, text, data, graphics, video, and documents. In addition to the individual services, the multimedia services and the simultaneous or alternating use of several services with multifunction workstations will gain importance [Armbrüster, 1990]. Interconnection of local-area networks (LANs) or large computers, computer-aided design, and computeraided manufacturing will become important data applications. The first video services will be video telephony and video conferencing (studio-to-studio and workstation video conferencing). Initially these services may have diminished quality, but for the long term TV quality can be expected. The bit rates of all services mentioned above are in the range of 2 to 130 Mbit/s (depending on the individual application). Taking into account that in the future more enhanced video coding mechanisms will be available, the required bit rates for video services will become lower without influencing quality significantly. Asynchronous Transfer Mode In today’s public switched networks the synchronous transfer mode (STM) predominates. Applying STM technology, for the duration of a connection a synchronous channel with constant bit rate is allocated to that connection. STM does not fit very well for the integration of services with bit rates from some kilobits per second to 130 Mbit/s. Therefore, in B-ISDN a new transfer mode called asynchronous transfer mode (ATM) is used. In ATM all kinds of information is transported in cells. A cell is a block of fixed length, which consists of a 5-octet cell header and a 48-octet cell payload (see Fig. 72.1). The cell header contains all necessary information for transferring the cell through the network and the cell payload includes the user information. The cell rate of a connection is proportional to the service bit rate. Only if information is available is a cell used by the connection. By having different routing labels, cells of different connections can be transported on the same transmission line (cell multiplexing). If no connection has information ready to transport, idle cells will be inserted. Idle cells do not belong to any connection; they are identified by a standardized cell header. ATM uses only cells; multiplexing and switching of cells is independent of the applications and of the bit rates of the individual connections. Applying ATM technology, the idea of one universal integrated network becomes a reality. However, the ATM technology also causes some problems. Because of the asynchronous multiplexing buffers are necessary, which results in cell delay, cell delay variation, and cell loss. In order to compensate for these effects additional measures have to be provided. FIGURE 72.1 ATM principle
Figure 72. 1 also shows the individual subfields of the cell header. The first field, called generic flow control (GFC), is only available at the user-network interface(UNI). Its main purpose is media access control in shared medium configurations(LAN-like configurations) within the customer premises [Goldner and Huber, 1991] The proposed GFC procedures are based either on the distributed queue algorithm or the reset timer control mechanism [Handel and Huber, 1991a]. At the network-node interface(NNI) these bits are part of the virtual The VPI together with the virtual channel identifier(vCI)form the routing label (identifier of the connec- on). The VPI itself marks only the virtual path(VP). The VP concept allows the flexible configuration of individual subnetworks(e.g, signaling network or virtual private network), which can be independent of the underlying transmission network. VP networks are under the control of network management. The bandwidth of a Vp will be allocated according to its requirements within the Vp network the individual connections are established and cleared down dynamically(by signaling The payload type field in the cell header differentiates the information in the cell payload of one connection (e.g, user information, operation and maintenance information for ATM). The value of the cell loss priority bit distinguishes cells that can be discarded under some exceptional network conditions without disturbing the quality significantly from those cells that may not be discarded. The last field of the cell header forms the header error control field. The cell header is protected against errors with a mechanism that allows the correction of a single bit error and the detection of multibit errors. The high transmission speeds for ATM cell transfer require very high-performance switching nodes. There fore, the switching networks(SNs) have to be implemented in fast hardware. Within the SN the self-routing principle will be applied [Schaffer, 1990]. At the inlet of the sn the cell is extended by an SN-internal header It is evident that the SN-internal operational speed has to be increased. When passing the individual switching elements, for the processing of the SN-internal header only simple hard-wired logic is necessary. This reduces the control complexity and provides a better failure behavior. When starting several years ago with the imple mentation of the ATM technology, only the emitter coupled logic(ECL) was available. Nowadays, the comple mentary metal-oxide semiconductor( CMOS) technology with its low power consumption is used [Fischer etal,1991] Transmission of b-isdn Signals Transmission systems at the UNI provide bit rates of around 150 and 622 Mbit/s. In addition to these rates, at the NNI around 2.5 Gbit/s and up to 10 Gbit/s will be used in the future [Baur, 1991]. In addition to the high capacity switching and multiplexing technology, high-speed transmission systems are required. Optical fibers are especially suitable for this purpose; however, for the lower bit rates coaxial cables can be used. Optical transmission uses optical fibers as the transmission medium in low-diameter and low-weight cables to provide large transmission capacities over long distances without the need for repeaters. Optical transmission equipment currently tends to mono-mode fiber and laser diodes with wavelengths of around 1310 nm. For both directions in a transmission system either two separate fibers or one common fiber with wavelength division multiplexing can be used. The second solution may be a good alternative for subscriber lines and short trunk lines[ Bauch, 1991] For ATm cell transmission, two possibilities exist, which are shown in Fig. 72. 2: synchronous pulse frame or continuous cell stream(cell-based). The basis for the pulse frame concept is the existing synchronous digital hierarchy(SDH). In SDH the cells are transported within the SDh payload; the frame overhead includes operation and maintenance(OAM)of the transmission system. In the cell-based system the oAm for the transmission system is transported within cells. The SDH solution is already defined, whereas for cell-based transmission some problems remain to be solved (e. g, OAM is not yet fully defined). ATM Adaptation Layer The ATM adaptation layer(AAL) is between the ATM layer and higher layers. Its basic function is the enhanced adaptation of the services provided by atM to the requirements of the layers above. In order to minimize the number of AaL protocols, the service classification shown in Fig. 72.3 was defined. This classification was made with respect to timing relation, bit rate, and connection mode. e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Figure 72.1 also shows the individual subfields of the cell header. The first field, called generic flow control (GFC), is only available at the user-network interface (UNI). Its main purpose is media access control in shared medium configurations (LAN-like configurations) within the customer premises [Göldner and Huber, 1991]. The proposed GFC procedures are based either on the distributed queue algorithm or the reset timer control mechanism [Händel and Huber, 1991a]. At the network-node interface (NNI) these bits are part of the virtual path identifier (VPI). The VPI together with the virtual channel identifier (VCI) form the routing label (identifier of the connection). The VPI itself marks only the virtual path (VP). The VP concept allows the flexible configuration of individual subnetworks (e.g., signaling network or virtual private network), which can be independent of the underlying transmission network. VP networks are under the control of network management. The bandwidth of a VP will be allocated according to its requirements. Within the VP network the individual connections are established and cleared down dynamically (by signaling). The payload type field in the cell header differentiates the information in the cell payload of one connection (e.g., user information, operation and maintenance information for ATM). The value of the cell loss priority bit distinguishes cells that can be discarded under some exceptional network conditions without disturbing the quality significantly from those cells that may not be discarded. The last field of the cell header forms the header error control field. The cell header is protected against errors with a mechanism that allows the correction of a single bit error and the detection of multibit errors. The high transmission speeds for ATM cell transfer require very high-performance switching nodes. Therefore, the switching networks (SNs) have to be implemented in fast hardware. Within the SN the self-routing principle will be applied [Schaffer, 1990]. At the inlet of the SN the cell is extended by an SN-internal header. It is evident that the SN-internal operational speed has to be increased. When passing the individual switching elements, for the processing of the SN-internal header only simple hard-wired logic is necessary. This reduces the control complexity and provides a better failure behavior. When starting several years ago with the implementation of the ATM technology, only the emitter coupled logic (ECL) was available. Nowadays, the complementary metal-oxide semiconductor (CMOS) technology with its low power consumption is used [Fischer et al., 1991]. Transmission of B-ISDN Signals Transmission systems at the UNI provide bit rates of around 150 and 622 Mbit/s. In addition to these rates, at the NNI around 2.5 Gbit/s and up to 10 Gbit/s will be used in the future [Baur, 1991]. In addition to the highcapacity switching and multiplexing technology, high-speed transmission systems are required. Optical fibers are especially suitable for this purpose; however, for the lower bit rates coaxial cables can be used. Optical transmission uses optical fibers as the transmission medium in low-diameter and low-weight cables to provide large transmission capacities over long distances without the need for repeaters. Optical transmission equipment currently tends to mono-mode fiber and laser diodes with wavelengths of around 1310 nm. For both directions in a transmission system either two separate fibers or one common fiber with wavelength division multiplexing can be used. The second solution may be a good alternative for subscriber lines and short trunk lines [Bauch, 1991]. For ATM cell transmission, two possibilities exist, which are shown in Fig. 72.2: synchronous pulse frame or continuous cell stream (cell-based). The basis for the pulse frame concept is the existing synchronous digital hierarchy (SDH). In SDH the cells are transported within the SDH payload; the frame overhead includes operation and maintenance (OAM) of the transmission system. In the cell-based system the OAM for the transmission system is transported within cells. The SDH solution is already defined, whereas for cell-based transmission some problems remain to be solved (e.g., OAM is not yet fully defined). ATM Adaptation Layer The ATM adaptation layer (AAL) is between the ATM layer and higher layers. Its basic function is the enhanced adaptation of the services provided by ATM to the requirements of the layers above. In order to minimize the number of AAL protocols, the service classification shown in Fig. 72.3 was defined. This classification was made with respect to timing relation, bit rate, and connection mode
SDH-based transmission Cell-based transmission Synchronous pulse frame( 125 us) Frame overhead Frame payload ATM onous digital hierarchy ATM FIGURE 72.2 Transmission principles for B-ISDN Class A Class B Class C Class D Timing relation between source and destination Not required Bitrate Constant variable Connection oriented Connection Connection mode FIGURE 72.3 AAL service classification The AAL protocols are subdivided into two parts. The lower part performs, at the sending side, the segmen- tation of long messages into the cell payload and, at the receiving side, reassembly into long messages. The upper part is service dependent and provides the AAL service to the higher layer B-ISDN Signaling For signaling in B-ISDN, existing protocols and infrastructure will be reused as much as possible. Figure 72.4 shows the protocol stacks for UNI and NNI. The upper part concerns signaling applications and the lower part signaling transfer. For the introduction of simple switched services in B-ISDN, at UNI and NNI, existing signaling application protocols will be reused. The 64-kbit/s ISDN-specific information elements will be removed and new B-ISDN specific information elements will be added. Right from the beginning these protocols will provide means that llow smooth migration toward future applications, which will include highly sophisticated features like mul timedia services [Huber et al., 1992]. This approach guarantees compatibility for future protocol versions. the NNi the existing signaling system no. 7( SS7)can be reused(see right part of the NNI protocol stack in Fig. 72.4). SS7 is a powerful and widespread network that will continue to be applied for rather a long period until ATM penetration has been reached. For the middle term, however, a fully ATM-based network will be available which also carries signaling messages(see left part of the NNI protocol stack in Fig. 72. 4). ATM-based signaling at the NNI needs a suitable AAL which provides the services of the existing message transfer part level 2 the UNI, right from the beginning, all kinds of traffic(including signaling) is carried within cells. An AAL for signaling at the UNI is also required. This aal has to provide the services of the existing layer 2 UNI e 2000 by CRC Press LLC
© 2000 by CRC Press LLC The AAL protocols are subdivided into two parts. The lower part performs, at the sending side, the segmentation of long messages into the cell payload and, at the receiving side, reassembly into long messages. The upper part is service dependent and provides the AAL service to the higher layer. B-ISDN Signaling For signaling in B-ISDN, existing protocols and infrastructure will be reused as much as possible. Figure 72.4 shows the protocol stacks for UNI and NNI. The upper part concerns signaling applications and the lower part signaling transfer. For the introduction of simple switched services in B-ISDN, at UNI and NNI, existing signaling application protocols will be reused. The 64-kbit/s ISDN-specific information elements will be removed and new B-ISDNspecific information elements will be added. Right from the beginning these protocols will provide means that allow smooth migration toward future applications, which will include highly sophisticated features like multimedia services [Huber et al., 1992]. This approach guarantees compatibility for future protocol versions. At the NNI the existing signaling system no. 7 (SS7) can be reused (see right part of the NNI protocol stack in Fig. 72.4). SS7 is a powerful and widespread network that will continue to be applied for rather a long period until ATM penetration has been reached. For the middle term, however, a fully ATM-based network will be available which also carries signaling messages (see left part of the NNI protocol stack in Fig. 72.4). ATM-based signaling at the NNI needs a suitable AAL which provides the services of the existing message transfer part level 2. At the UNI, right from the beginning, all kinds of traffic (including signaling) is carried within cells. An AAL for signaling at the UNI is also required. This AAL has to provide the services of the existing layer 2 UNI FIGURE 72.2 Transmission principles for B-ISDN. FIGURE 72.3 AAL service classification
B-ISDN UNI B-ISDN NNI B-ISUP B-ISUP B-DSS1 SCCP SCCP MTP level 3 MTP level 3 Signaling-AAL Signaling-AAL MTP level 2 Meta-signaling ATM layer ATM layer MTP level 1 Physical layer Physical layer B-DSS1 Broadband digital subscriber signaling system no. 1 B-IsUP Broadband-IsDN user part SCCP Signaling connection control part User-network interface FIGURE 72.4 Protocol stacks for B-ISDN signaling. protocol. The AAL for signaling at UNI and NNI will be common as much as possible. In contrast to the nNI, at the UNI meta-signaling is necessary. Meta-signaling establishes, checks, and removes the signaling channels between customer equipment and the central office in a dynamic way. The signaling channels at the NNI are semipermanent and, therefore, meta-signaling is not required Defining Terms Asynchronous transfer mode: A transfer mode in which the information is organized into cells; it is asyn- chronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic. TM adaptation layer: A layer which provides the adaptation of higher layers to ATM. Broadband: A service or system requiring transmission channels capable of supporting bit rates greater than 2 Mbit/s Cell: A block of fixed length which is subdivided into a cell header and an information field. The cell header contains a label which allows the clear allocation of a cell to a connection Integrated services digital network: A network which provides end-to-end digital connectivity to support a wide range of services, including voice and nonvoice services, to which users have access by a limited set of standard multipurpose user-network interfaces. Signaling: Procedures which are used to control (set up and clear down) calls and connections within a telecommunication network Synchronous digital hierarchy: A standard for optical transmission which provides transmission facilities with flexible add/drop capabilities to allow simple multiplexing and demultiplexing of signals Related Topic 72.2 Computer Communications Networ e 2000 by CRC Press LLC
© 2000 by CRC Press LLC protocol. The AAL for signaling at UNI and NNI will be common as much as possible. In contrast to the NNI, at the UNI meta-signaling is necessary. Meta-signaling establishes, checks, and removes the signaling channels between customer equipment and the central office in a dynamic way. The signaling channels at the NNI are semipermanent and, therefore, meta-signaling is not required. Defining Terms Asynchronous transfer mode: A transfer mode in which the information is organized into cells; it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic. ATM adaptation layer: A layer which provides the adaptation of higher layers to ATM. Broadband: A service or system requiring transmission channels capable of supporting bit rates greater than 2 Mbit/s. Cell: A block of fixed length which is subdivided into a cell header and an information field. The cell header contains a label which allows the clear allocation of a cell to a connection. Integrated services digital network: A network which provides end-to-end digital connectivity to support a wide range of services, including voice and nonvoice services, to which users have access by a limited set of standard multipurpose user-network interfaces. Signaling: Procedures which are used to control (set up and clear down) calls and connections within a telecommunication network. Synchronous digital hierarchy: A standard for optical transmission which provides transmission facilities with flexible add/drop capabilities to allow simple multiplexing and demultiplexing of signals. Related Topic 72.2 Computer Communications Networks FIGURE 72.4 Protocol stacks for B-ISDN signaling
References H Armbruster,"Blueprint for future telecommunications, Telcom Report International, vol. 13, no 1, Pp 5-8, 1990 H Bauch, Transmission systems for B-ISDN, IEEE LTS, Magazine of Lightwave Telecommunication, voL.2,no H. Baur,Technological perspective of telecommunications for the nineties, Integration, Interoperation and Interconnection: This Way to Global Services, Proceedings of the Technical Symposium, Geneva, part 2, vol. w. Fischer, O. Fundneider, E - H. Goeldner, and K.A. Lutz, A scalable ATM switching system architecture, IEEE Journal on Selected Areas in Communication, vol 9, no. 8, PP. 1299-1307, 1991 E. H. Goldner and M N. Huber, Multiple access for B-ISDN, " IEEE LTS, Magazine of Lightwave Telecommu nication, vol. 2, no 3, Pp. 37-43, 1991 R Handel and M.N. Huber, " Customer network configurations and generic flow control, International Journal of Digital and Analog Communication Systems, vol. 4, no 2, PP. 117-122, 1991a. R Handel and M.N. Huber, Integrated Broadband Networks--An Introduction to ATM-Based Networks, Reading, Mass.: Addison-Wesley, 1991b. M.N. Huber, V. Frantzen, and G. Maegerl,"Proposed evolutionary paths for B-ISDN signalling, Proceedings of the XIv International Switching Symposium, Yokohama, vol 1, Pp. 334-338, 1992. B Schaffer, ATM switching in the developing telecommunication network, Proceedings of the XIlI International Switching Symposium, vol. 1, Pp. 105-110, 1990 G Wiest, "More intelligence and flexibility for communication network--Challenges for tomorrow's switching ystems," Proceedings of the XIll International Switching Symposium, vol 5, PP. 201-204, 1990 Furthe oration CCITT Recommendations and CCITT Draft Recommendations concerning B-ISDN (parts of F, G, I and Q series), which are published by the International Telecommunication Union. Journals of the IEEE Communication Society(Communications Magazine, Journal on Selected Areas in Communications, LTS: Magazine of Lightwave Telecommunication, Networks, Transactions on Communications), which are published by the Institute of Electrical and Electronics Engineers, Inc International Journal of Digital and Analog Communication System, which is published by John Wiley Sons, Ltd. eedings of international conferences such as GLOBECOM, INFOCOM, International Conference Communications, International Conference on Computer Communication, International Switching Sympo- sium, International Symposium on Subscriber Loops and Services, and International Teletraffic Congres a detailed description of ISDN is given in ISDN--The Integrated Services Digital Network- Concepts, Methods, Systems, by P. Bocker, published by Springer-Verlag. 72.2 Computer Communication Networks . N. daigle A computer communication network is a collection of applications hosted on different machines and inter- connected by an infrastructure that provides communications among the communicating entities. while the s an application. In fact, one or all of the"applications"that are communicating may be human beings. 8 applications are generally understood to be computer programs, the generic model includes the human bei This section summarizes the major characteristics of computer communication networks. The objective is to provide a concise introduction that will allow the reader to gain an understanding of the key distinguishing characteristics of the major classes of networks that exist today and some of the issues involved in the intro- duction of emerging technologies There are a significant number of well-recognized books in this area. Among these are the excellent texts by Schwartz [ 1987], Tanenbaum [1988], and Spragins [1991], which have enjoyed wide acceptance by both students and practicing engineers and cover most of the general aspects of computer communication networks. Stallings e 2000 by CRC Press LLC
© 2000 by CRC Press LLC References H.Armbrüster, “Blueprint for future telecommunications,”Telcom Report International, vol. 13, no. 1, pp. 5–8, 1990. H. Bauch, “Transmission systems for B-ISDN,” IEEE LTS, Magazine of Lightwave Telecommunication, vol. 2, no. 3, pp. 31–36, 1991. H. Baur, “Technological perspective of telecommunications for the nineties,” Integration, Interoperation and Interconnection: This Way to Global Services, Proceedings of the Technical Symposium, Geneva, part 2, vol. 1 paper 1.1, 1991. W. Fischer, O. Fundneider, E.-H. Goeldner, and K.A. Lutz, “A scalable ATM switching system architecture,” IEEE Journal on Selected Areas in Communication, vol. 9, no. 8, pp. 1299–1307, 1991. E.-H. Göldner and M.N. Huber, “Multiple access for B-ISDN,” IEEE LTS, Magazine of Lightwave Telecommunication, vol. 2, no. 3, pp. 37–43, 1991. R. Händel and M.N. Huber, “Customer network configurations and generic flow control,” International Journal of Digital and Analog Communication Systems, vol. 4, no. 2, pp. 117–122, 1991a. R. Händel and M.N.Huber,Integrated Broadband Networks — An Introduction to ATM-Based Networks,Reading, Mass.: Addison-Wesley, 1991b. M.N. Huber, V. Frantzen, and G. Maegerl, “Proposed evolutionary paths for B-ISDN signalling,” Proceedings of the XIV International Switching Symposium, Yokohama, vol. 1, pp. 334–338, 1992. B. Schaffer, “ATM switching in the developing telecommunication network,”Proceedings of the XIII International Switching Symposium, vol. 1, pp. 105–110, 1990. G. Wiest, “More intelligence and flexibility for communication network—Challenges for tomorrow’s switching systems,” Proceedings of the XIII International Switching Symposium, vol. 5, pp. 201–204, 1990. Further Information CCITT Recommendations and CCITT Draft Recommendations concerning B-ISDN (parts of F, G, I and Q series), which are published by the International Telecommunication Union. Journals of the IEEE Communication Society (Communications Magazine, Journal on Selected Areas in Communications, LTS: Magazine of Lightwave Telecommunication, Networks, Transactions on Communications), which are published by the Institute of Electrical and Electronics Engineers, Inc. International Journal of Digital and Analog Communication System, which is published by John Wiley & Sons, Ltd. Proceedings of international conferences such as GLOBECOM, INFOCOM, International Conference on Communications, International Conference on Computer Communication, International Switching Symposium, International Symposium on Subscriber Loops and Services, and International Teletraffic Congress. A detailed description of ISDN is given in ISDN—The Integrated Services Digital Network— Concepts, Methods, Systems, by P. Bocker, published by Springer-Verlag. 72.2 Computer Communication Networks J. N. Daigle A computer communication network is a collection of applications hosted on different machines and interconnected by an infrastructure that provides communications among the communicating entities. While the applications are generally understood to be computer programs, the generic model includes the human being as an application. In fact, one or all of the “applications’’ that are communicating may be human beings. This section summarizes the major characteristics of computer communication networks. The objective is to provide a concise introduction that will allow the reader to gain an understanding of the key distinguishing characteristics of the major classes of networks that exist today and some of the issues involved in the introduction of emerging technologies. There are a significant number of well-recognized books in this area. Among these are the excellent texts by Schwartz [1987],Tanenbaum [1988], and Spragins [1991], which have enjoyed wide acceptance by both students and practicing engineers and cover most of the general aspects of computer communication networks. Stallings
[1990a, 1990b, 1990c] covers a broad array of standards in this area. Other books that have been found to be pecially useful by practitioners are those by rose [ 1990] and Black [1992] The latest developments are, of course, covered in the current literature, conference proceedings, and the notes of standards meetings. A pedagogically oriented magazine that specializes in computer communications networks is IEEE Network, but IEEE Communications and IEEE Computer often also contain interesting articles communications include the IEEE INFOCOM and ACM SIGCOMM series, which are heate or .often in this area. ACM Communications Review, in addition to presenting pedagogically oriented articles, often presents very useful summaries of the latest standards activities. Major conferences that specialize in computer We will begin our discussion with a brief statement of how computer networking came about and a capsule description of the networks that resulted from the early efforts. Networks of this generic class, called wide-area networks(WANs), are broadly deployed today, and there are still a large number of unanswered questions with respect to their design. The issues involved in the design of those networks are basic to the design of most networks, whether wide area or otherwise. In the process of introducing these early systems, we will describe and contrast three basic types of communication switching: circuit, message, and packet. We will next turn to a discussion of computer communication architecture, which describes the structure of communication-oriented processing software within a communication processing system. Our discussion is limited to the International Standards Organization/Open Systems Interconnection(ISO/OSI) reference model(ISORM) because it provides a framework for discussion of some of the modern developments in communications in general and communication networking in particular. This discussion is necessarily sim plified in the extreme, thorough coverage requiring on the order of several hundred pages, but we hope our brief description will enable the reader to appreciate some of the issues Having introduced the basic architectural structure of communication networks, we will next turn to a discussion of an important variation on this architectural scheme: the local-area network(LAN). Discussion ecause it helps to illustrate what the the architecture of LANs illustrates how the ISORM can be adapted for specialized purposes. Specifically, early network architectures anticipate networks in which individual node pairs are interconnected via a single link onnections through the network are formed by concatenating node-to-node connections LAN architectures, on the other hand, anticipate all nodes being interconnected in some fashion over the same communication link(or medium). This, then, introduces the concept of adaption layers in a natural way. It also illustrates that if the services provided by an architectural layer are carefully defined, then the can be used to implement virtually any service desired by the user, possibly at the price of some ine After discussing LANS, we will conclude our article with a discussion of two of the variants in packet transmission technology: frame relay and a recent development in basic transmission technology called the asyn chronous transfer mode, which is a part of the larger broadband integrated services digital network effort. These technologies are likely to be important building blocks for the computer co ication networks of the future General Networking Concepts Data communication networks have existed since about 1950. The early networks existed primarily for the purpose of connecting users of a large computer to the computer itself, with additional capability to provide communications between computers of the same variety and having the same operating software. The lessons learned during the first twenty or so years of operation of these types of networks have been valuable in preparing ne way for modern networks. For the purposes of our current discussion, however, we will think of commu- nication networks as being networks whose purpose is to interconnect a set of applications that are implemented on hosts manufactured by possibly different vendors and managed by a variety of operating systems Networking capability is provided by software systems that implement standardized interfaces specifically designed for the exchange of information among heterogeneous computers. buring the late 1960s, many forward-looking thinkers began to recognize that significant computing resources(that is, supercomputers)would be expensive and unlikely to be affordable by many of the researchers needing this kind of computer power. In addition, they realized that significant computing resources would number of research sites, then the cost of the resource could be shared by its uscm tce could be shared by a not be needed all of the time by those having local access. If the computing resor e 2000 by CRC Press LLC
© 2000 by CRC Press LLC [1990a, 1990b, 1990c] covers a broad array of standards in this area. Other books that have been found to be especially useful by practitioners are those by Rose [1990] and Black [1992]. The latest developments are, of course, covered in the current literature, conference proceedings, and the notes of standards meetings. A pedagogically oriented magazine that specializes in computer communications networks is IEEE Network, but IEEE Communications and IEEE Computer often also contain interesting articles in this area. ACM Communications Review, in addition to presenting pedagogically oriented articles, often presents very useful summaries of the latest standards activities. Major conferences that specialize in computer communications include the IEEE INFOCOM and ACM SIGCOMM series, which are held annually. We will begin our discussion with a brief statement of how computer networking came about and a capsule description of the networks that resulted from the early efforts. Networks of this generic class, called wide-area networks (WANs), are broadly deployed today, and there are still a large number of unanswered questions with respect to their design. The issues involved in the design of those networks are basic to the design of most networks, whether wide area or otherwise. In the process of introducing these early systems, we will describe and contrast three basic types of communication switching: circuit, message, and packet. We will next turn to a discussion of computer communication architecture, which describes the structure of communication-oriented processing software within a communication processing system. Our discussion is limited to the International Standards Organization/Open Systems Interconnection (ISO/OSI) reference model (ISORM) because it provides a framework for discussion of some of the modern developments in communications in general and communication networking in particular. This discussion is necessarily simplified in the extreme, thorough coverage requiring on the order of several hundred pages, but we hope our brief description will enable the reader to appreciate some of the issues. Having introduced the basic architectural structure of communication networks, we will next turn to a discussion of an important variation on this architectural scheme: the local-area network (LAN). Discussion of this topic is important because it helps to illustrate what the reference model is and what it is not. In particular, the architecture of LANs illustrates how the ISORM can be adapted for specialized purposes. Specifically, early network architectures anticipate networks in which individual node pairs are interconnected via a single link, and connections through the network are formed by concatenating node-to-node connections. LAN architectures, on the other hand, anticipate all nodes being interconnected in some fashion over the same communication link (or medium). This, then, introduces the concept of adaption layers in a natural way. It also illustrates that if the services provided by an architectural layer are carefully defined, then the services can be used to implement virtually any service desired by the user, possibly at the price of some inefficiency. After discussing LANs, we will conclude our article with a discussion of two of the variants in packet switching transmission technology: frame relay and a recent development in basic transmission technology called the asynchronous transfer mode, which is a part of the larger broadband integrated services digital network effort. These technologies are likely to be important building blocks for the computer communication networks of the future. General Networking Concepts Data communication networks have existed since about 1950. The early networks existed primarily for the purpose of connecting users of a large computer to the computer itself, with additional capability to provide communications between computers of the same variety and having the same operating software. The lessons learned during the first twenty or so years of operation of these types of networks have been valuable in preparing the way for modern networks. For the purposes of our current discussion, however, we will think of communication networks as being networks whose purpose is to interconnect a set of applications that are implemented on hosts manufactured by possibly different vendors and managed by a variety of operating systems. Networking capability is provided by software systems that implement standardized interfaces specifically designed for the exchange of information among heterogeneous computers. During the late 1960s, many forward-looking thinkers began to recognize that significant computing resources (that is, supercomputers) would be expensive and unlikely to be affordable by many of the researchers needing this kind of computer power. In addition, they realized that significant computing resources would not be needed all of the time by those having local access. If the computing resource could be shared by a number of research sites, then the cost of the resource could be shared by its users
Access Lines FIGURE 72.5 Generic computer communication network. Many researchers at this time had computing resources available under the scenario described in the first paragraph above. The idea of interconnecting the computers to extend the reach of these researchers to other computers developed. In addition, the interconnection of the computers would provide for comn among the researchers themselves. In order to investigate the feasibility of providing the interconnectivity Inticipated for the future using a new technology called packet switching, the Advanced Research Projects Agency(ARPA)of the Department of the Army sponsored a networking effort, which resulted in the computer communication network called the arpanet. The end results of the ARPA networking effort, its derivatives, and the early initiatives of many compar ch as at&T, DATAPOINT, DEC, IBM, and NCR have been far-reaching in the extreme. Any finitely delimited discussion of the accomplishments of those efforts would appear to underestimate their impact on our lives We will concentrate on the most visible product of these efforts, which is a collection of programs that allows applications running in different computers to intercommunicate. Before turning to our discussion of the software, however, we will provide a brief description of a generic computer communication network. Figure 72.5 shows a diagram of a generic computer communication network. The most visible components of the network are the terminals, the access lines, the trunks, and the switching nodes. Work is accomplished when the users of the network, the terminals, exchange messages over the network. The terminals represent the set of communication terminating equipment communicating over the network. quipment in this class includes, but is not limited to, user terminals, general-purpose computers, and database systems. This equipment, either through software or through human interaction, provides the functions equired for information exchange between pairs of application programs or between application programs and people. The functions include, but are not limited to, call set-up, session management, and message transmission control. Examples of applications include electronic mail transfer, terminal-to-computer connec tion for time sharing or other purposes, and terminal-to-database connections. Access lines provide for data transmission between the terminals and the network switching nodes. These connections may be set up on a permanent basis or they may be switched connections, and there are numerous transmission schemes and protocols available to manage these connections. The essence of these connections, however, from our point of view is a channel that provides data transmission at some number of bits per second ) called the channel capacity, C. The access line capacities may range from a few hundred bits per second to in excess of millions of bits per second, and they are usually not the same for all terminating equipments of a given network. The actual information-carrying capacity of the link depends upon the protocols employed to effect the transfer; the interested reader is referred to Bertsekas and Gallagher [1987], especially Chapter 2, for a general discussion of the issues involved in transmission of data over communication links Trunks, or internodal trunks, are the transmission facilities that provide for transmission of data between pairs of communication switches. These are analogous to access lines, and, from our point of view, they simply provide a communication path at some capacity, specified in bits per second. e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Many researchers at this time had computing resources available under the scenario described in the first paragraph above. The idea of interconnecting the computers to extend the reach of these researchers to other computers developed. In addition, the interconnection of the computers would provide for communication among the researchers themselves. In order to investigate the feasibility of providing the interconnectivity anticipated for the future using a new technology called packet switching, the Advanced Research Projects Agency (ARPA) of the Department of the Army sponsored a networking effort, which resulted in the computer communication network called the ARPANET. The end results of the ARPA networking effort, its derivatives, and the early initiatives of many companies such as AT&T, DATAPOINT, DEC, IBM, and NCR have been far-reaching in the extreme. Any finitely delimited discussion of the accomplishments of those efforts would appear to underestimate their impact on our lives. We will concentrate on the most visible product of these efforts, which is a collection of programs that allows applications running in different computers to intercommunicate. Before turning to our discussion of the software, however, we will provide a brief description of a generic computer communication network. Figure 72.5 shows a diagram of a generic computer communication network. The most visible components of the network are the terminals, the access lines, the trunks, and the switching nodes. Work is accomplished when the users of the network, the terminals, exchange messages over the network. The terminals represent the set of communication terminating equipment communicating over the network. Equipment in this class includes, but is not limited to, user terminals, general-purpose computers, and database systems. This equipment, either through software or through human interaction, provides the functions required for information exchange between pairs of application programs or between application programs and people. The functions include, but are not limited to, call set-up, session management, and message transmission control. Examples of applications include electronic mail transfer, terminal-to-computer connection for time sharing or other purposes, and terminal-to-database connections. Access lines provide for data transmission between the terminals and the network switching nodes. These connections may be set up on a permanent basis or they may be switched connections, and there are numerous transmission schemes and protocols available to manage these connections. The essence of these connections, however, from our point of view is a channel that provides data transmission at some number of bits per second (bps), called the channel capacity, C. The access line capacities may range from a few hundred bits per second to in excess of millions of bits per second, and they are usually not the same for all terminating equipments of a given network. The actual information-carrying capacity of the link depends upon the protocols employed to effect the transfer; the interested reader is referred to Bertsekas and Gallagher [1987], especially Chapter 2, for a general discussion of the issues involved in transmission of data over communication links. Trunks, or internodal trunks, are the transmission facilities that provide for transmission of data between pairs of communication switches. These are analogous to access lines, and, from our point of view, they simply provide a communication path at some capacity, specified in bits per second. FIGURE 72.5 Generic computer communication network
There are three basic switching paradigms: circuit, message, and packet switching. Circuit switching packet switching are transmission technologies while message switching is a service technology. In circuit switching, a call connection between two terminating equipments corresponds to the allocation of a prescribed set of physical facilities that provide a transmission path of a certain bandwidth or transmission capacity. These facilities are dedicated to the users for the duration of the call. The primary performance issues, other than ose related to quality of transmission, are related to whether or not a transmission path is available at call set-up time and how calls are handled if facilities are not available. Message switching is similar in concept to the postal system. When a user wants to send a message to one or more recipients, the user forms the message and addresses it. The message switching system reads the address and forwards the complete message to the next switch in the path. The message moves asynchronously through the network on a message switch-to-message switch basis until it reaches its destination. Message switching systems offer services such as mail boxes, multiple destination delivery, automatic verification of message delivery, and bulletin board. Communication links between the message switches may be established using circuit or packet switching networks as is the case with most other networking applications. Examples of message switching protocols that have been used to build message switching systems Mail Transfer Protocol (SMTP)and the International Telegraph and Telephone Consultative C (CCITT)X400 series. The former is much more widely deployed, while the latter has significantly capabilities, but its deployment is plagued by having two incompatible versions(1984 and 1988) problems. Many commercial vendors offer message switching services based on either one of the above protocols or a proprietary protocol In the circuit switching case, there is a one-to-one correspondence between the number of trunks between nodes and the number of simultaneous calls that can be carried. That is, a trunk is a facility between two switches that can service exactly one call, and it does not matter how this transmission facility is derived. Major design issues include the specification of the number of trunks between node pairs and the routing strategy used to determine the path through a network in order to achieve a given call blocking probability. When blocked calls are queued, the number of calls that may be queued is also a design question. a packet-switched communication system exchanges messages among users by transmitting sequences of packets which comprise the messages. That is, the sending terminal equipment partitions a message into a sequence of packets, the packets are transmitted across the network, and the receiving terminal equipment reassembles the packets into messages. The transmission facility interconnecting a given node pair is viewed a single trunk, and the transmission capacity of this trunk is shared among all users whose packets traverse both nodes. While the trunk capacity is specified in bits per second, the packet handling capacity of a node pair depends both upon the trunk capacity and the nodal processing power. In many packet-switched networks, the path traversed by a packet through the network is established during a call set-up procedure, and the network is referred to as a virtual circuit packet switching network. Other networks provide datagram service, a service that allows users to transmit individually addressed packets without the need for call set-up Datagram networks have the advantage of not having to establish connections before communication takes place, but they have the disadvantage that every packet must contain complete addressing information. Virtual circuit networks have the advantage that addressing information is not required in each packet, but have the disadvantage that a call set-up must take place before communication can occur. Datagram is an example of connectionless service while virtual circuit is an example of connection-oriented service. Prior to the late 1970s, signaling for circuit establishment was in-band. That is, in order to set up a call through the network, the call set-up information was sent sequentially from switch to switch using the actual circuit that would eventually become the circuit used to connect the end users. In an extreme case, this amounted to trying to find a path through a maze, sometimes having to retrace one's steps before finally emerging at the destination or just simply giving up when no path could be found. This had two negative characteristics: first, the rate of signaling information transfer was limited to the circuit speed, and second, the circuits that could have been used for accomplishing the end objective were being consumed simply to find a path between the end-points. This resulted in tremendous bottlenecks on major holidays, which were solved by virtually disal- lowing alternate routes through the toll switching network. An alternate out-of-band signaling system, usually called common-channel interoffice signaling(CCIS), was developed primarily to solve this problem. Signaling now takes place over a signaling network that is e 2000 by CRC Press LLC
© 2000 by CRC Press LLC There are three basic switching paradigms: circuit, message, and packet switching. Circuit switching and packet switching are transmission technologies while message switching is a service technology. In circuit switching, a call connection between two terminating equipments corresponds to the allocation of a prescribed set of physical facilities that provide a transmission path of a certain bandwidth or transmission capacity. These facilities are dedicated to the users for the duration of the call. The primary performance issues, other than those related to quality of transmission, are related to whether or not a transmission path is available at call set-up time and how calls are handled if facilities are not available. Message switching is similar in concept to the postal system. When a user wants to send a message to one or more recipients, the user forms the message and addresses it. The message switching system reads the address and forwards the complete message to the next switch in the path. The message moves asynchronously through the network on a message switch-to-message switch basis until it reaches its destination. Message switching systems offer services such as mail boxes, multiple destination delivery, automatic verification of message delivery, and bulletin board. Communication links between the message switches may be established using circuit or packet switching networks as is the case with most other networking applications. Examples of message switching protocols that have been used to build message switching systems are Simple Mail Transfer Protocol (SMTP) and the International Telegraph and Telephone Consultative Committee (CCITT) X.400 series. The former is much more widely deployed, while the latter has significantly broader capabilities, but its deployment is plagued by having two incompatible versions (1984 and 1988) and other problems. Many commercial vendors offer message switching services based on either one of the above protocols or a proprietary protocol. In the circuit switching case, there is a one-to-one correspondence between the number of trunks between nodes and the number of simultaneous calls that can be carried. That is, a trunk is a facility between two switches that can service exactly one call, and it does not matter how this transmission facility is derived. Major design issues include the specification of the number of trunks between node pairs and the routing strategy used to determine the path through a network in order to achieve a given call blocking probability. When blocked calls are queued, the number of calls that may be queued is also a design question. A packet-switched communication system exchanges messages among users by transmitting sequences of packets which comprise the messages. That is, the sending terminal equipment partitions a message into a sequence of packets, the packets are transmitted across the network, and the receiving terminal equipment reassembles the packets into messages. The transmission facility interconnecting a given node pair is viewed as a single trunk, and the transmission capacity of this trunk is shared among all users whose packets traverse both nodes. While the trunk capacity is specified in bits per second, the packet handling capacity of a node pair depends both upon the trunk capacity and the nodal processing power. In many packet-switched networks, the path traversed by a packet through the network is established during a call set-up procedure, and the network is referred to as a virtual circuit packet switching network. Other networks provide datagram service, a service that allows users to transmit individually addressed packets without the need for call set-up. Datagram networks have the advantage of not having to establish connections before communication takes place, but they have the disadvantage that every packet must contain complete addressing information. Virtual circuit networks have the advantage that addressing information is not required in each packet, but have the disadvantage that a call set-up must take place before communication can occur. Datagram is an example of connectionless service while virtual circuit is an example of connection-oriented service. Prior to the late 1970s, signaling for circuit establishment was in-band. That is, in order to set up a call through the network, the call set-up information was sent sequentially from switch to switch using the actual circuit that would eventually become the circuit used to connect the end users. In an extreme case, this amounted to trying to find a path through a maze, sometimes having to retrace one’s steps before finally emerging at the destination or just simply giving up when no path could be found. This had two negative characteristics: first, the rate of signaling information transfer was limited to the circuit speed, and second, the circuits that could have been used for accomplishing the end objective were being consumed simply to find a path between the end-points. This resulted in tremendous bottlenecks on major holidays, which were solved by virtually disallowing alternate routes through the toll switching network. An alternate out-of-band signaling system, usually called common-channel interoffice signaling (CCIS), was developed primarily to solve this problem. Signaling now takes place over a signaling network that is
