N-GEN
Communications Web-based Seminars ©NGCS
Seminar - An Overview of Communications Technologies
Seminar - An Overview of Communications Technologies
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Module 11 - The PSTN Evolution and Convergence Slide 1 of 45 ________________ Objectives: This module provides an introduction to the telecommunications communications industry and its evolution, telecommunications networks and underlying technological trends, and the services offered by the telecommunications carriers. The telecommunications industry continues to change and to adjust to the new economic reality, as telecommunications carriers continue to look for ways to reduce cost and improve the bottom line. In order to reduce costs, new technologies will be embraced. The installed base of “legacy” interfaces will not however change quickly, as most customers will adapt only when it is convenient for them. To increase their acceptance and adoption, new technologies must support legacy interfaces. The public switched telephone network (PSTN), a provider of Plain Old Telephone Services (POTS), evolved as the market demand grew for new services. POTS has included in its portfolio a multitude of services including high-speed data, Internet, entertainment along with voice - the prime quality service. The evolution to the PSTN has been forced by the wireless, satellite and cable companies, which are taking a chunk of the voice-market share from the wired services. The network, which was primarily designed for voice communications has no choice other than to migrate to an infrastructure to support multi-media applications. The network is transforming itself from circuit-switched, analogue transmission to packet-switched, digital transmission to transport real-time and non-real-time traffic. The PSTN evolution can be seen in its Core Network, Edge
Network and Distribution Network segments. All three segments have in many
circumstances migrated from copper wire to optical fiber. The switching
infrastructure is migrating from analogue voice based switches to Media Gateway
based switches. The PSTN of the future will support analogue voice, Internet voice, Video, TV and on-line Games services. The Public Switched Telephone Network (PSTN) The network with time-division multiplex design accommodated a single application, uncompressed voice. The network was engineered to deliver 99.9994 percent up time, low latency and jitter, highly scalable call routing. The control and the message signals used the same path. In the next phase of the network evolution, control signals were separated from the message signals using Common Control Signals (CCS #7) infrastructure, to provide value-added voice services such as voice messaging and caller ID. The PSTN provides voice access services in 64-K bps (DS-0) increments. The 64-K bps voice-streams are aggregated by digital cross connect systems in to a 1.544 M bps stream or a 45 M bps stream to class 5 switches. Class 5 switches terminate the customer local loops. The Class 5 switches communicate with access and toll tandem switches to route calls across the telephone network to destination Class 5 switches. The rapid growth of the Internet and distributed processing
traffic in the late 1980s and early 1990s had a major impact on the PSTN. Voice
users experienced busy signals due to extra-long Internet calls. The telephone carriers tried in vain to solve this problem
by investing in additional PSTN capacity. The bursty characteristics and bandwidth demands of data
transmission are not suited to the circuit-switched design of the PSTN and its value-add features. Packet-switched networks were well suited to
accommodate the rapid growth and handle the bursty nature of data applications
more efficiently than the PSTN’s fixed DS-0 architecture. Carriers quickly
concentrated their efforts on data-centric architectures and constructed frame
relay, ATM, and IP networks. Most of the data networks used ATM as a core
network technology. Data Networks Data networks got their start by using the PSTN
facilities. In the late 1970s and early 1980s dataphone services used the PSTN
facilities, to make a connection, to setup a link between sender and receiver,
then transmit data by using datasets, which converted the computer data into
an analogue format for transmission over the PSTN facilities. The PSTN dedicated
facilities were also used for high-speed data connections. The high-speed
analogue data
transmission was having problems with the poor quality of the local loops, which
gave rise to end-to-end digital transmission. Telephone carriers deployed many
facilities networks and packet networks to support customer demand. Early 1990
saw growth in the LAN-to-LAN interconnection market. Carriers started deploying
packet-centric networks using frame relay, ATM and SONET technologies. A Series of Overlay Networks The Carriers used the PSTN for voice, packet networks for data transmission and started deploying IP-based networks to meet the Internet demand, which resulted in carriers supporting a large number of overlay networks. The explosive growth of data traffic also forced carriers to expand constantly their data network infrastructures. It reached the point where carriers were spending considerable capital in the data backbone networks. With the size and scope of packet networks approaching that of the PSTN, carriers started looking for ways to converge voice, data and video traffic.
Carriers wanted to move voice services to packet networks both
to reduce internal costs and to provide value-added and cost-effective services
in an increasingly competitive environment, As the PSTN was not designed to
carry data efficiently, data networks were not designed to provide voice
services at the quality telephony users had come to expect. Most networks
utilize best-effort delivery techniques and pay little attention to ensuring the
low delay and consistent delivery times required by voice applications. Carriers
deployed networks to provide voice services over frame relay and ATM networks. The computer and communications industry has been very
successful in using IP technology to provide voice and video services, along with
data, in a Local Area Network (LAN) environment. IP networks were competing with
the frame relay and ATM networks to support multi-media traffic. Carriers
started paying more attention to IP networks. A converged architecture makes use of existing investments in
infrastructures (corporate network, the Internet, the PSTN and ATM core network)
and uses convergent switches to support interfaces with the existing
networks. A convergent solution will forward both voice and data traffic from
digital subscriber line access multiplexers, integrated access devices, and
service access multiplexers to the PSTN, the Internet, and other data networks. Next-Generation PSTN The
PSTN of the future will use Media Gateways to accommodate the multi-media
applications. The central assumption of the PSTN was network-based computing
power and a dumb end system. The next-generation system will adopt the strategy
where by intelligence will be distributed in the network and the end-points.
This will be achieved by implementing IP-based telephony, which requires a shift
in services at the network perimeter and the integration of signaling
protocols like H.323, SIP and MGCP in to the existing PSTN infrastructure. The MGCP requires the end system to be controlled by a network
server while as H.323 and SIP allow the use of servers – gatekeepers and
proxy/redirect servers – but also enable two end systems to contact directly,
without help of a third party. The preferred solution from the carrier’s point
of view is storing the programs implementing services in relatively few servers
rather than millions of endpoints. The Class5 switches will be modified to include a Media
Gateway function. Many telephone equipment manufacturers have started
developing Softswitch, a next-generation version of Class5 switch. Softswitches
are available from Nortel Networks and Lucent Technologies. This module will cover: 1.0 The POTS network infrastructure 2.0 The PSTN evolution to Intelligent Network 3.0 Common Control Signaling 4.0 IN 5.0 AIN 6.0 The PSTN Core network evolution and convergence 7.0 The PSTN Edge network evolution 8.0 The PSTN Distribution network evolution 9.0 Customer Premise Equipment (Telephone Set, Key systems and PABX) Evolution 10.0 IP-PABX System ________________
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