Towfique 063382056


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Towfique 063382056

  1. 1. Prepared by: Name-Towfiqul Islam Student ID-063382056 Course Number-ETE-605 Prepared for: Dr. Mashiur Rahman Report On: Integration of IP Telephony In PSTN Environment
  2. 2. Integration of IP Telephony in P.S.T.N. Environment 1.1 PSTN network evolution history: 1.1.1 Invention of Telephone System: As known to all, DR. Alexander Graham Bell is the father of earliest version of telephone system. After his invention for a long period telephone system has been supported merely by manual switching. After that period machine switching and programmed switching were successively followed. The first automatic dialing system was patented in 1891 by a Cansas City undertaker. The first coin tel phone was e installed in Hatford, Connecticut in 1900.Party lines were soon developed to lower cost of telephone. With the development of automatic dialing technology, almost 80% telephone of the world was automatic phone by the end of 1950s. 1.1.2 From analog to digital transformation: There are two principal means by which telephone signals are transmitted: analog or digital. As the electronic current that transmits the voice is actually imitating the voice behavior, it has various shapes; while the digital system transmits only on or off-two binary states. In the early days of telephone history, the switching system was controlled by analog switches. As technology had advanced enough by the late 1970s where 100% Digital Systems were being developed for use in the telephone industry. Digital systems sample the analog signal and handle telephone calls internally as binary digits, then convert them back to analog to be compatible with regular telephones. This again made the switch smaller and more reliable. It also allowed new technologies to be added faster by using modular techniques (adding systems to the original system without complete redesign/reinstallation) and by using advanced computer software. 1.1.3 Emergence of “time -switching ”: While traditionally, telephone switches connected physical circuits, modern telephone switches use a combination of space and time division switching. In other words, each voice channel is represented by a time slot(say 1 or 2) on a physical wire pair ( A or B).In order to connect two voice channels (say A1 and B2) together, the telephone switch interchanges information between A1 and B2.It switches both the time slot and physical connection. To do this, it exchanges data between the time slots and connections 8000 times per seconds, under control of digital logic that cycle through electronic lists of the current connections. Using both types of switching makes a modern switch far smaller than either a space or time switch could be by itself. The structure of a switch is an odd number layer of smaller, simpler sub switches, interconnected by a web of wires that goes from each sub switch, to a set of the next layers of sub switches. In most designs, a physical switching layer will alternate with a time switching layer. The layers are symmetric, because every call is symmetric (there is a connection in both directions) A space division sub switch uses digital multiplexers controlled by a cyclic memory. This takes physical space for the wiring. A time division sub switch reads a complete cycle of time slots into a memory and then writes it out in a different order, also under control of a cyclic computer memory. This causes some delay in the signal. The above mentioned discussion very briefly describes how a Circuit Switch based PSTN system works. 1.1.4 Future of Circuit Switch based PSTN technology: In 1970’s the telecom industry conceived that digital services would follow much the same pattern as voice services and conceived a vision of end to end circuit switch based technology known as B-ISDN. But the B-version technology has been overtaken by disruptive technology of Internet. Many experts believe that the long term future of PSTN will be just one of the applications of Internet.
  3. 3. 1.2.1 Development of IP Network from a historical perspective: Until 1990, all efforts were concentrated on the development of voice service over legacy telecommunication network. Afterwards an effort was successful to send data, voice and video over a single line by introducing Integrated Services Digital Network technology. A separate packet switched based data network was evolved only for transmission of data. But ISDN is a circuit switched digital network and DSL variants are packet-switched data services over laid on the PSTN. Telephone systems have been slowly adopting the “IP” (Internet Protocol) technology over the last decade’s .Early experiments proved that voice can be converted to digital packets and sent over the internet. The packets would be collected and converted back to analog voice. The quality of the calls was not great but it showed that it could be done. The major problem was packet loss which is common with TCP/IP connections. By the early 2000’s IP telephony had improved. Using classes of service, reliable connections could be obtained and packets loss reduced to minimum levels. Business systems started using VOIP technology in their PABX. Development of network • The 1 st generation Fixed-line network -Analog switching • The 2 nd generation Fixed-line network -TDM and digital switching • The 3 rd generation Fixed-line network -Based on IP network and soft switch 3G Technology Service: Voice/Data/ Mult 1G 2G imedia Service: Voice Service: Voice Device: soft switch ,data Device: Manual Device: Digital Switch Switch/ Router, Application Connection, step switch server, SHLR, etc. Crossbar Switch, Analog Service Development in network evolution Service evolution(tone service-) PSTN tone/data-) data/multi-media service plays pointy) Data All in IP evolution Network Circuit switching-) packet switching-) All in IP PLMN Broad Separation of service and transportation band access 1990 1995 Multi-service 2000 2010 Multi protocol Simple Integration
  4. 4. 2.1. Integration of IP in PSTN domain: 2.1.1 Critical Evaluation of existing network: At present PSTN network exists for voice communication and packet network exists for data network. A critical review of the two networks is given below: PSTN Network : Voice is real time, delay-sensitive in nature. Here the communication is connection oriented Advantages and disadvantages: PSTN offers highest quality of speech (high intelligibility).It is also reliable because of no delay, no traffic loss. It also provides rich telecom features. PSTN has the disadvantage that it offers fixed bandwidth; bandwidth remains idle if there is no traffic. PSTN is not basically engineered for long holding of a call such as internet call. Data network : It is mainly designed for data traffic. Data is rate-sensitive, on-real in nature. Data communication is connectionless. Advantages and disadvantages Data network supports variable bandwidth facilities to integrate data, voice and video. It provides true end to end delivery of IP packets. Data network is subjected to delay and jitter. It is vulnerable to packet loss 2.1.2 Dynamic behavior of existing market players : Following changes are being observed in existing networks: • Data traffic is increasing faster than voice • Terminals are becoming more intelligent • Network is becoming more passive 2.1.3. Changes in customer demands : • Requirement of higher bandwidth • Integrated access for voice, data and video • Requirement of variety of sophisticated services, multimedia, web conferencing • Requirement of guaranteed quality of service and low price. 2.1.4 Changes in network operators requirements : • New revenue streams generation for new opportunities • Rapid service provisioning • Open interface to support multiple vendors • Reduced capital expense for future expansion
  5. 5. 2.1.5 March towards NGN: With the sustainable growth of data services, the current network framework is evolving to Data Networks. Therefore, both the traditional telecom carriers relying mainly on voice services and the emerging data network carriers pay much attention to the new generation Telecom Network that converges voice, video, data and integrates the PSTN circuit switching with packet switching technology. The network integration oriented soft switch architecture is a total solution of the new generation multimedia services. It implements the interconnection of various service networks including PSTN/ISDN, PLMN, IN and Internet etc.By optimizing the network architecture, it realizes network integration, and more important, the service integration, thus enabling the inheritance of rich service functions of the traditional Circuit Switching Network, meanwhile providing new services that are hard to be implemented in the traditional networks all over the new- generation networks. 2.1.6 Reasons to choose NGN as a means to integrate IP in PSTN domain: At present, two totally independent networks exist: the PSTN network and data network, which provide the voice service and basic data service respectively. Network separation and isolation of operation and maintenance have been keeping the costs on a high level and furthermore, a network cannot provide complicated convergence services, although network convergence has been an inevitable trend. Since a traditional voice network is a closed network with monopolized resources, it has become a common understanding in the telecom industry that the packet network with the advantages such as open architecture, low costs and large scale, will replace the PSTN to become the basic frame of the next generation of convergence networks and the construction of the next generation of networks will be based on current packet networks. 2.1.7 Considerations for converged networks: It is necessary for carriers to consider resource utilization and investment protection during construction of future networks. On one hand, carrier should trace the latest technologies; and on the other hand, they should try to utilize existing technologies and resources. Thus, carriers can provide users with large numbers of services economically and rapidly to make the highest profits, without the need of large-scale network alteration. The solution of smooth transition from existing networks to the new generation of networks is the key to the problem. The soft switch solution based on soft switch technology is just a mainstream solution to smooth network evolution. 3.1 Architecture of Soft Switch Solution: Hierarchical models are adopted for the soft switch based converged network .The entire network can be divided into four layers: Service Layer, Control Layer, Core (Transport Layer) and Edge Access Layer.
  6. 6. Soft switch Traditional Network Network Service Service Call control Call control Transportati on Transportati on APPLICATIO N SERVER IN MULTIMEDIA Management MENT OSA/PARL A SNMP ST SS7 SS SS ACCE H248 ATM/MPLS CORE SS TDM NETWORK GATE MGW MGC WAY/ PLMN P PSTN BROADBAND ACCESS MEDIA SERVER H323/SIP ARCHITECTURE SIP/H323
  7. 7. 3.1.1 Edge Access Layer: The edge access layer refers to various access gateways and new types of access terminal devices related to the current network. It implements inter working with the existing various types of communication networks and provides access of various communication terminals (eg., the DTMF phone, SIP phone, PC phone visual terminal and intelligent terminal ) to the IP core layer. 3.1.2 The Core Layer: The Core (Transport) Layer refers to a packet switching network composed of backbone transmission equipment such as IP router or broadband ATM switch, which is the bearer basis of a soft switch network. 3.1.3 The Control Layer: The Control Layer refers to soft switch control units, which completes integrated control processing functions such as call processing control, access protocol adaptation, and interconnection and inter working and provides an application support platform for the entire network. 3.1.4 The Application Layer: The Application Layer provides a network with various applications and services, client-oriented integrated intelligent services and service customization. 3.1.5 Interface and relation between layers : Standard interfaces are used between layers. Under the control of core equipment (i.e., the soft switch control equipment) and based on division of labor and cooperation of work, the related NE equipment implements various service functions of the system. In soft switch architecture, the soft switch control equipment is the core, which is independent of the bottom- layer bearer protocols and implements functions such as call control, media gateway access control, resource allocation, protocol processing, routing, routing, authentication and accounting. The soft switch control equipment can provide all basic call services, supplementary services and point-to-point multimedia services a PSTN can provide. Furthermore, with the cooperation of the service layer equipment (SCP) and application server, the equipment also can provide users with traditional intelligent services, value-added IP services, diverse third-party value added services and new intelligent services. 3.1.6 NGN elements: Soft Switch: • Provides the intelligence and call control and the signaling for the NGN • Control of media gateways • Bridges the traditional TDM and voice over packet networks • Communication with various networks (SS7, BICC, SIP-T, H.248, INAP etc) • Support of billing /accounting by providing call details • Control of subscriber feature capabilities
  8. 8. Media gateways: • Terminates voice calls from the TDM, compress and pocketsize the voice data, and delivers the compressed voice packets to the packet network • Supports VOIP functionality as well as all other bearer connections such as fax over IP • Controlled by the soft switch using an IP protocol such as H: 248 • Can be located remotely from the soft switch or can be co- located with it. Packet network: The core connectivity layer is a packet based network that shall provide the voice traffic bearer connectivity between the gateways and the soft switch. 3.1.7 Protocols of NGN: The main advantage of NGN over conventional circuit switch is that NGN are layered structure with open protocols between layer to layer and also between the elements of the same layer. A summary of the protocols are presented below: Layer/ Elements Protocols Soft Switch-TGW H.248/MGCP Soft Switch-IAD/AG H.248/MGCP Soft Switch-IP Phone SIP Soft Switch-Soft Switch SIP-T/BICC SS7-IP network Sigtran Soft Switch-Application Parley/SIP Server Soft Switch-AAA Server RADIUS Soft Switch Routing Server LDAP Routing Server- Routing TRIP Server Soft Switch- Signaling M3UA/SCTP gateway Soft Switch-Gatekeeper or H.323 H.323 gateway Signaling gateway-IN INAP Signaling gateway-SS7 TUP/ISUP Soft Switch-NMS SNMP 4.1. Integration of IP in PSTN domain- existing practices: 4.1.1 Replacement of Tandem Exchange: Before discussing on Tandem Excha nge replacement we must first provide a simplified architecture of a PSTN system. In the given figure we have provided a very simplified architecture of a PSTN system. In this system if a subscriber from exchange 1 wants to make a call to a subscriber of exchange 3 it must pass through tandem exchange A. In the PSTN system in addition to tandem exchange, TAX (Trunk automated exchange) and ITX (International trunk exchange) are used to carry voice traffic between inter-district and inter- country calls .For tandem replacement, trunking gateway, signaling gateway and media gate controller together will replace the tandem switch. The local exchange will be connected trunking gateway by TDM
  9. 9. link and the TGW will be the interface of PSTN and NGN. In this way the huge installation of cable network of PSTN system as well as local exchanges are retained. Thus it is a cost efficient gradual replacement of outdated circuit switches. Exchange Exchange Exchange Exchange A2 A1 B3 B1 Exchange Tandem Tandem Exchange A3 Exchange A Exchange B B2 Tandem Exchange C Exchange Exchange C3 C1 Exchange C2 Existing Structure of PSTN system Tandem replacement solution
  10. 10. 4.1.2 Bangladesh Context- special reference to network of BTTB: While Bangladesh is struggling to meet the demand of providing basic telecommunication services, question can be raised whether we should implement NGN projects. In Bangladesh, BTTB is the major PSTN operator. Still it has a huge number of unmet subscriber demands .So there is argument that BTTB should concentrate on PSTN business. But BTTB also provides data and internet service and it has also installed a nationwide data network. In the present scenario BTTB has to maintain separate networks for voice and data. Converging these networks will reduce the cost of mantling two separate networks. One important thing to add is that manufacturers of conventional switches are gradually closing the production of pure circuit- switch equipment and shifting to produce NGN equipment. The hybrid type solution to have old PSTN exchanges with conventional fixed phone at lower levels and IP backbone at core should be an appropriate choice. This will also allow BTTB to use the benefit derived from information super highway connectivity through submarine cable. Meanwhile as an interim arrangement to offer value added service BTTB has installed fixed intelligent network platform. This can be considered as an intermediate arrangement to offer many rich services before adopting full scale NGN. The newly introduced Intelligent Layer system (Computer and data base system) TCP/IP IN Separates service control function From switching function Signaling Layer (CCS7&TCP/IP Conversion The existing network Resources CCS7 Switch & Transmission Layer 4.1.3. General rules to be followed for migration: • Migration from traditional network infrastructure should be carried with the strategy so that past investment is protected. • Established operators have to find some ways to provide the customers with sophisticated services till the conversion to full scale NGN. • Migration should follow the speed so that established operators can compete the new operators to retain their customers. • Formulate an integrated management of legacy exchanges and the NGN soft switches in order to smoothly route increasing amount of traffic on NGN.
  11. 11. References: 1. International Telecommunication Union (ITU): NGN 2004 Project description-version 3”, February, 2004. 2. Organization for Economic Co-operation and Development (OECD): Next Generation Network Development in OECD Countries, Document No. DSTI/ICCP/TISP(2004)4/FINAL, January, 2005 3. Geok-Leng, Dr. Tan: Are you ready for the Next Generation Network (NGN)?APEC Telecommunications and Information Working group 29th meeting, Hong Kong, March 2004. 4. Feit, Sidnie : TCP/IP : Architecture, Protocols and Implementation, McGraw- Hill,Inc.,1993 5. ZXSS10 SS1 Training Materials, ZTE University,Dameisha,Yantian District, Shenzen,P.R. China 6. Teletech, a journal of BCS Telecom Samity, Vol. XIV, May 2005 7. Wikipedia on Next Generation Network 8. Technical Documents of Huawei Technologies Co. Ltd. about N.G.N.