Tài liệu MIDDLEWARE NETWORKS- P2 doc

This page intentionally left blank. TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. C HAPTER 2 Technology Overview This chapter lays out the background needed to understand IP service platforms, and in particular the synergistic technological developments that are transforming the communications industries. The spectrum of the interrelated topics is very broad. We view them from the unifying perspective of network middleware that spans the gamut from the physical network fabric to the applications themselves. In this chapter we focus on the key technologies needed by the IP service platform, and how these tech - nologies are directly impacted by such a platform. We also identify their significance and relationships to other technologies. Beginning with developments in the circuit - switched networks that make up our telephone systems, we then explore their relation - ship to packet networks – such as the Internet – that carry our data in a multitude of forms, and the services these networks offer. Coincident innovations in the software industries extend the client and server technologies and thus imbue the Internet with a dynamic and interactive presence. From this technological mosaic emerges the sub - strate for reliable systems enabling businesses and consumers through the 21 St Cen - tury. 2.1 Public Switched Telephone Network (PSTN) To most of us, the oldest and most pervasive communication network in the world is the Public Switched Telephone Network (PSTN). This is the familiar global voice tele - phone network that provides telephone to anyone with a telephone and access rights. Today, PSTN spans every country and territory in the world. Since the invention of the telephone in the late 1800’s, PSTN has steadily grown out of the original Bell System network developed by AT&T. In the U.S., it is made up of 196 geographical local access and transport areas (LATAs) that are serviced by one or more Local Exchange Carriers (LECs). Some of the well known LECs are GTE, Ameritech, NYNEX, Bell Atlantic, Bell TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 28 M IDDLEWARE N ETWORKS: C ONCEPT, D ESIGN AND D EPLOYMENT South, and Southwestern Bell. Inter - LATA traffic is provided by the Interexchange Car - riers (IXCs). Examples of IXCs are AT&T, MCI WorldCom, Sprint, and Interliant. The three - digit area codes are assigned to LECs within a given LATA. This relationship between LATAs, LECs and IXCs is shown in Figure 2 - 1. Typical cus - tomers connect their premises equipment over a local loop to the LEC’s closest central office (CO). The LEC connects its COs through a number of lines to its switching cen - ters, called tandem offices (TA). The inter - LATA calls are switched to an IXC’s point of presence (POP) based on the customer’s choice of long distance providers. Once the call leaves the LATA and enters the IXC network, it may get switched through multiple provider’s networks based on their peering arrangements. Figure 2 - 1: The LATA view of PSTN As part of “our” telephone network we may also think of wireless cell phones (see Figure 2 - 2). This service is supported by a separate network using different technolo - gies from the wireline PSTN however, the two are closely peered and offer seamless exchange of voice services. Unfortunately, there are several competing service stan - dards including different ones for analog and digital; these include the advanced mobile phone service (AMPS) for analog, digital AMPS (D - AMPS), global system for mobile communications (GSM), personal communications service (PCS), low - earth orbiting satellites (LEO), specialized mobile radio (SMR), and cellular digital packet data (CDPA). In the U.S., PCS is the dominant service with the large national PCS pro - viders being AT&T Wireless and Sprint PCS; most local Bells support their own cellu - TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. P UBLIC S WITCHED T ELEPHONE N ETWORK (PSTN) 29 lar networks. A service that runs well on one of these standards or networks may be of interest to the others as well; for example, the mobile “browser cell phone” merges desirable features that originated in separate networks. Figure 2 - 2: Connection Layers: Tower, MTSO Mobile Switch, PSTN Central Office The PSTN is based on circuit - switching technology that establishes and maintains a single end - to - end circuit for each call placed. The management of the calls requires the support of three primary functions: switching, transmission, and signalling. • Switching. This function handles automatic call routing by means of highly sophisticated computers such as the 4ESS switching machines. A national net - work has on the order of 100 such switches strategically located in major hubs. They were introduced in the mid - 1970’s and continue to be upgraded with state - of - the art switching technology. Today, a single 4ESS switch can handle upwards of 1.2 million calls per hour Transmission. These facilities are responsible for physical transport of the call’s information, in a manner that permits satisfactory recovery of the source signal. The technologies include fiber - optic cables, microwaves, radio relays, and satel - lite communications. Most of today’s traffic is carried over Synchronous Optical NETworks (SONET) and Dense Wave Division Multiplexing (DWDM) on fiber - optic cables. SONET operates at multiples of OC1(51.84 Mb/s) and the European equivalent ITU - T SDH operating at OC3 and above • Signalling. This function operates the out - of - band signalling which controls the flow of calls across the network and supports the enhanced telephony services such as toll - free calling including 800 service. We do not consider in - band sig - nalling TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 30 M IDDLEWARE N ETWORKS: C ONCEPT, D ESIGN AND D EPLOYMENT 2.1.1 Intelligent Network The PSTN is actually composed of two networks. The first is the switched network that carries the calls over circuits, and the second is data network that carries signalling. This signalling network benefits greatly from reliable digital transport and processing. They improve the efficiency of network management, while operating at much lower cost. The signalling network also enables new and enhanced services. At the heart of this network are the 4ESS switches and the SS7 protocol that form the modern Intelli - gent Network. In the mid-1970s, AT&T developed Signalling System 6 (SS6) for the old Bell System to automate calling - card validation, and remove the dependency on operators to handle this validation. It was the first use of new computer - controlled switching functions on an out - of - band secondary data network. The result was an all - in - one solution in which each switch also performed basic call processing and database processing for both ser - vices and control. These solutions were typically built and deployed by different ven - dors who used different approaches to the provisioning and operation of the switches. This required extensive and expensive coordination to synchronize and update both the software and the database contents in the entire network. Nevertheless, this enabled service providers to begin creating new services such as call forwarding. These services were custom built from scratch and required extensive patching to integrate into the existing systems. As a side note, even with the later move to IN/AIN, this practice of building vertically integrated systems continued until the early 1990s. In much the same way, the early history of Internet services followed the same model. Yet in both industries, the tele - communication and the Internet models for building, provisioning, and operating ser - vices relied on a shared common infrastructure mainly out of economic necessity. Ten years later, a faster and more capable Signalling System 7 (SS7) was developed as a layered protocol with signalling links of 64Kbs. Today it supports 1.54 megabit signal - ling links. This established a global standard based on Common Channel Interoffice Signalling architecture (CCIS), and was the beginning of the Intelligent Network (IN). With the introduction of SS7, services moved out of the switches and into Service Con - trol Points (SCP). The basic components of SS7 are the Signal Transfer Points, Service Control Points, and Service Switching Points, as shown in Figure 2 - 3. • STP – Signal Transfer Point STPs are signal transfer points which route queries between central office switches and databases in SCPs. These are packet switches that forward SS7 messages from SSPs to SCPs based on the destination address of the SCPs. TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. P UBLIC S WITCHED T ELEPHONE N ETWORK (PSTN) 31 Figure 2 - 3: SS7 components of an IN/AIN • SCP – Service Control Point SCPs are the databases that hold the call routing instructions and the enhanced services such as the network - based voice mail, or fax and IVR applications. • SSP – Service Switching Point SSPs enable central offices to initiate queries to databases and specialized com - puters. The model for the Intelligent Network was realized when the services moved from switches and into the SCPs, where these services could accept standardized messages. This standardization concept was well understood in the software industry, but it was not until the adaptation of SS7 and its common set of standardized messages that the model entered the telephone networks. The standard message and the well specified set of rules published by ITU - T and Bellcore created a very powerful platform on which to build the next generation of telephony services. 2.1.2 Private Branch Exchange, Key Systems, and Centrex Businesses using telephony services depend on the use of Private Branch Exchanges (PBX), key systems, or Centrex systems; they support voice mail, service call centers, speed dialing, redial, and other advanced voice services. All of these systems provide connectivity between the members of the supported organization and the connectivity to the PSTN. They differ in the location of the equipment and the ownership of that equipment. PBX and key systems are on - site privately owned systems. They differ mainly in the size with PBX supporting large organizations while key systems tend to support small businesses with only dozens of connections. Due to the large organizations supported by PBX, PBX’s are connected to the central offices with T1 or PRI ISDN trunks. How - ever, the big difference between the two lies in the control of the local telephones. PBX TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 32 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT grounds all calls and thus provides the dial tone to its organization. To call outside, an outside access code has to tell the PBX to route the call outside. The PBX then has ded - icated trunk lines connecting it to a central office. With a key system, the dial tone is provided by the central office. Centrex, in contrast to a PBX or key system, is located in the central office of a tele - phone company; the term is derived from the words central and exchange. The motiva - tion for a Centrex was for a large company to outsource its PBX services to the telephone company and save on the administrative and operational cost of managing their own PBXs. The first Centrex system was deployed in 1965 in Newark, New Jersey to support the Prudential Life Insurance Company. By 1982, according to a 1986 DataPro report, Centrex provided service to 70% of all business with over 1000 lines. Since the divestiture of 1984, the legislation made Centrex more applicable to both small and large businesses. It is insightful to note that the Intelligent Network and the Centrex/PBX systems are targeting the same requirements but from different sides of the spectrum. IN/AIN offers telephone companies the infrastructure on which to build in - network services focused primarily on home subscribers; while the latter offers local services and con - trol to organizations. As we explore next, the “new kid on the block (i.e., Internet) offers these customers a captivating wealth of services common to both the PSTN and data networks. 2.1.3 Services Spanning both the PSTN and the Internet Since the early days of data networks, many ventures have tried to interoperate ser - vices in the PSTN and the data networks. These span a spectrum from controlling tele - phone - based devices and services from Internet hosts, up through running large data and call centers in support of PSTN services. The results include Computer Telephony Integration (CTI) with Telephony APIs (e.g., TAPI/JTAPI/TSAPI) on one end, and car - rier - class interoperability efforts such as TINA, Java AIN (JAIN), and Parlay API on the other end. Several of these convergence technologies strive to decouple the upper - layer services from the specific supporting technologies, and we describe several challenges introduced through this realization. CTI and Telephony APIs Some of the key CTI applications include Integrated Voice Response (IVR), predictive dialing, “faxback”, call center management, and IP telephony, To address the growing demand by businesses to deploy CTI applications a number of competing standards developed. These include Lucent’s Pas - sageways, IBM’S CallPath, SunXTL, Microsoft’s TAPI, Sun’s JTAPI, and Nov - ell/Lucent’s TSAPI. As an example, Microsoft’s TAPI integrates multimedia stream control with legacy telephony and H.323 conferencing standard as part of its Windows platform. TAPI solutions use their COM API to inte - grate a TAPI Server, interoperating with a PBX or a PC modem for PSTN TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. P UBLIC S WITCHED T ELEPHONE N ETWORK (PSTN) 33 access or ATM/ISDN NIC for WAN access, with an LDAP directory and TAPI clients. TAPI uses RTP and RTCP for managing the synchronization and timing of its isochronous (i.e., fixed duration between events or sig - nals) packets. In October 1996, Sun developed Java Telephony API (JTAPI) in cooperation with IBM, Intel, Lucent, Nortel, and Novell in an effort to offer a Java - based open - specification for computer telephony standard. One of its goals was to bridge the gap between numerous proprietary, competing standards for CTI. With JTAPI, applications, regardless of the platform on which they were developed, are able to interoperate with JTAPI - compliant compo - nents built with the other standards. TINA (Telecommunication Information Network Architecture) In 1993, the TINA Consortium (TINA - C) was formed with 40 leading Telcos and software companies to cooperatively create a common architecture to address the communication industry’s growing difficulty with the delivery of new services, or adaptation to changes within the infrastructure. In 1997 TINA - C delivered a set of validated architectural specifications that inte - grated all management, development and control functions into a unified, logical software architecture supported by a single distributed computing platform, the Distributed Processing Environment (DPE). TINA’s DPE is based on OMG technology, CORBA, and extends CORBA to provide func - tions specific to telecommunication. TINA’s architecture is based on four principles, specifically: • Object - oriented analysis and design • Distribution • • Separation of concern These principles address the telecommunication industry’s requirements of interoperability, portability and reusability of software components, and achieves valuable independence from specific technologies. Creation and management of complex systems, formerly the burden of large vertically integrated corporations, can now be shared among different business stakeholders, such as consumers, service providers, and connectivity pro - viders. Decoupling of software components, and JAIN (Java APIs for Integrated Network) JAIN is a set of Intelligent Network (IN) specific APIs developed by Sun Microsystems for the Java platform. JAIN targets the integration of PSTN, wireless, and IP networks, and specifically aims at some of the incompati - bility between IN programs that use SS7. The JAIN APIs define interfaces for TCAP (SS7 database and switch interactions), ISUP (ISDN signalling) TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 34 M IDDLEWARE N ETWORKS: C ONCEPT, D ESIGN AND D EPLOYMENT and MAP (cellular processing); its classes also support Operations Admin - istration and Maintenance (OA&M) and Media Gateway Controller Proto - col (MGCP). These capabilities parallel JAIN support for IP voice protocols (H.323 and SIP). Together, they enable service development that is indepen - dent of the underlying communications stacks and implementations. At its core, the JAIN architecture defines a software component library, development tools, a service creation environment (SCE), and a carrier - grade service logic execution environment for building next - generation services for integrated PSTN, packet and wireless networks. Parlay API In May 1998, an industry consortium was formed to develop an open API standard that would allow 3rd party developers access to the Telcos’ switches and which would support new IP - based telephony services. The consortium was spearheaded by British Telecom given the discussions with the AT&T GeoPlex project, and now also includes DGM&S Telecom, Microsoft, Nortel Networks, Siemens, Ericsson, Cisco and others. The Par - lay API being standardized by the consortium would facilitate the inter - networking of IP networks with the PSTN while maintaining its integrity, performance and security. Parlay’s philosophy closely parallels the approach taken in the GeoPlex project at AT&T. Due to the close interoperation with PSTN, however, the architecture does not subscribe to all the design principles described in this book Specifically, it does not subscribe to the Routing Principle. The Parlay API supports registration, security, discovery, event notifica - tion, QA&M, charging and billing, logging and auditing, load and fault management, and offers service interfaces for services such as call control and messaging. Parlay - based applications are also intended to support TAPI - based appli - cations developed by enterprises. JAIN and Parlay APIs are complimentary and together will provide significant oppor - tunities to expand the access and breadth of services available. Java provides the com - mon mechanism that makes Parlay services available on the Internet. Parlay is a way to bring telecom models including security to the JAIN community, expanding the reach of the JAIN activity 2.2 Packet Networks This brings us to digital packet networks; these move data in small packets. Unlike the switched networks that dedicate a single circuit to a single session, these move many TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. P ACKET N ETWORKS 35 packets from many sessions over the same circuit simultaneously, The previous span - ning services (Section 2.1.3) anticipated many of these interrelated developments. Today with all the sophistication and complexity of the PSTN, many people perceive the telephone and the data networks as being two completely different technologies having little to do with each other. They perceive the use of modems to tunnel over POTS between our computers and the Internet as shown in Figure 2 - 4; or perhaps think of DSL or cable as offering direct broadband to the Internet through their ISP. Figure 2 - 4 Tunneling to an ISP over POTS to reach the Internet What many people do not realize is that parts of the PSTN have carried Internet traffic since the very beginning of digital signalling, and this rising trend builds upon the existing properties of the PSTN. Specifically: the underlying network technologies for carrying voice and data are the same. Their respective transport networks are there - fore merging into one network. In some cases the all - digital voice circuits even bridge the “last mile” into the subscriber’s business or home, thereby eliminating the remnant analog portion from their local loops. In other cases the customers retain analog equipment. Due to the mix of premises technologies, the differences in this mix can be handled at local switches and associated programs. These edge components distinguish between analog and digital traffic. The ingress network adjusts to each kind of traffic, and for PSTN service the source signals are transparent to the transport network. For example, transmission impairments (i.e., noise) present different challenges to analog and data signals. The classic case is echo on a two - wire connection. Only analog devices – such as the “black phone” – require echo cancellation to filter out the return signal inherent in the sharing of one wire - pair by both end points. The networks’ echo canceller removes the return signal that arrives after one round - trip delay time. Whereas echo cancellation removes unwanted signals from analog voice, it must be disabled during digital trans - mission. Digital signals have different characteristics than analog ones. Modem TEAM LinG - Live, Informative, Non-cost and Genuine! Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... (derived from the word archive) was an effort to archive the content of FTP sites using several Archie servers; the Wide-Area Information Server (WAIS) offered detailed document indices allowing keyword searches through the archived documents Gopher was a hierarchical menu-based system consisting of thousands of Gopher servers; it demonstrated the model for what the WWW would later generalize and improve... if private keys were improperly distributed Compliance with correct usage policies is one way to retain the benefits of the underlying technology, and the networking middleware can help ensure this compliance For example, the networking middleware can provide certified key-management services that a security-naive use may depend upon A second area of concern is interoperability with existing protocols... Internet, the innovation in the backbone is of distant concern Their online experience comes from the simple task of gaining access and maintaining TEAM LinG - Live, Informative, Non-cost and Genuine! 40 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT an acceptable performance of their connections to the Internet through their ISPs or enterprise LAN connections For most of them, the promise of rich... being deployed, but these were mostly large enterprise database solutions accessing large computer mainframes deployed outside the labs and campuses TEAM LinG - Live, Informative, Non-cost and Genuine! 42 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT Figure 2-6: Internet and Television access over Cable Even so, much activity centered around posting large collections of information online (see Figure...36 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT devices actively maximize the useful bandwidth through signal-specific adjustments adapting to various kinds of line-noise, including echo The network’s... At the same time, a hypertext technology was being standardized around SGML Tim merged the two into a new protocol called the Hypertext Transfer Protocol (HTTP) that utilized MIME and a newly designed document type definition (DTD) of SGML called Hypertext Markup Language (HTML) These innovations were used to create the web as a collection of HTTP servers that individually formed portals into the local... Tim’s WWW foundation was the single most important enabling factor for the industry, the catalyst that ignited the popularity of WWW happened at the TEAM LinG - Live, Informative, Non-cost and Genuine! 44 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT National Center for Supercomputing Applications (NCSA) at the University of Illinois There, graduate students developed a graphical browser called Mosaic... the notion of browser plug-ins Third party developers crafted browser-oriented services delivering complex information through a collage of content-oriented formats including device independent Portable Document Format (PDF), macromedia, and Virtual Reality Markup Language (VRML) This soon transformed into a general notion of dynamically varying presentations through browser-resident programs, automatically... longer the sole sources of Web information Proxies, which simply put, are HTTP relays with value-added functions, quickly became an integral part TEAM LinG - Live, Informative, Non-cost and Genuine! 46 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT of the Web Proxies supplement many server roles, while also adapting to many network configurations One role is that of security for enterprises, whereby... appealing interface called “*7” The user's guide and helper for this device was an animated figure named Duke, who later became Java's official mascot TEAM LinG - Live, Informative, Non-cost and Genuine! 48 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT The product was demonstrated around Sun and impressed important people like Scott McNealy and Bill Joy, but the next step was uncertain The fledgling . Informa - tion Server (WAIS) offered detailed document indices allowing keyword searches through the archived documents. Gopher was a hierarchical menu -. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 32 MIDDLEWARE NETWORKS: CONCEPT, DESIGN AND DEPLOYMENT grounds all calls and thus