Transcript Document

• PSTN
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Public switched telephone network - PSTN operators
The task of building the networks and
selling services to customers fell to the
network operators. The first company to
be incorporated to provide PSTN services
was the Bell Telephone Company in the
United States.
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Telecommunications in Bangladesh - PSTN
Bangladesh Telecommunications
Company Limited (former BTTB)- Now
having the largest PSTN subscriber
base..
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Telecommunications in Bangladesh - PSTN
The number of PSTN subscribers in
Bangladesh as of February 2009 was 1.372
million.
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Voice over IP - PSTN integration
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The Media VoIP Gateway connects the
digital media stream, so as to
complete creating the path for voice
as well as data media. It includes the
interface for connecting the standard
PSTN networks with the ATM and
Inter Protocol networks. The Ethernet
interfaces are also included in the
modern systems, which are specially
designed to link calls that are passed
via the VoIP.
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Voice over IP - PSTN integration
1
Most VoIP implementations support E.164
to allow calls to be routed to and from
VoIP subscribers and the PSTN/PLMN
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Voice over IP - PSTN integration
Echo can also be an issue for PSTN
integration. Common causes of echo
include impedance mismatches in analog
circuitry and acoustic coupling of the
transmit and receive signal at the receiving
end.
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PSTN
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Originally a network of fixed-line analog
signal|analog telephone systems, the
PSTN is almost entirely Digital data|digital
in its core and includes mobile
phone|mobile as well as landline#Fixed
phone|fixed telephones.
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PSTN
The technical operation of the PSTN
adheres to the standards created by the
ITU-T. These standards allow different
networks in different countries to
interconnection|interconnect
seamlessly. The E.163 and E.164
standards provide a single global
address space for telephone numbers.
The combination of the interconnected
networks and the single numbering plan
make it possible for any phone in the
world to dial any other phone.
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PSTN - History
However, a bell was added soon for
signaling, and then a switch hook, and
telephones took advantage of the exchange
principle already employed in telegraph
networks. Each telephone was wired to a
local telephone exchange, and the
exchanges were wired together with
trunking|trunks. Networks were connected in
a hierarchical manner until they spanned
cities, countries, continents and oceans. This
was the beginning of the PSTN, though the
term was not used for many decades.
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PSTN - History
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The growth of the PSTN meant that traffic
engineering (telecommunications)|traffic
engineering techniques needed to be
deployed to deliver quality of service (QoS)
guarantees for the users. The work of Agner
Krarup Erlang|A. K. Erlang established the
mathematical foundations of methods
required to determine the capacity
requirements and configuration of equipment
and the number of personnel required to
deliver a specific level of service.
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PSTN - History
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In the 1970s the telecommunications
industry began implementing packet
switched network data services using
the X.25 protocol transported over
much of the end-to-end equipment as
was already in use in the PSTN.
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PSTN - History
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Several large private telephone networks
are not linked to the PSTN, usually for
military purposes. There are also private
networks run by large companies which
are linked to the PSTN only through
limited Gateway
(telecommunications)|gateways, like a
large private branch exchange (PBX).
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PSTN - PSTN operators
The task of building the networks and
selling services to customers fell to the
telephone company|network operators.
The first company to be incorporated to
provide PSTN services was the Bell
Telephone Company in the United States.
1
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PSTN - Regulation
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In most countries, the central government
has a regulatory agency|regulator
dedicated to monitoring the provision of
PSTN services in that country. Their tasks
may be for example to ensure that end
customers are not over-charged for
services where monopolies may exist.
They may also regulate the prices charged
between the operators to
interconnection|carry each other's traffic.
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PSTN - Network topology
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The PSTN network architecture had to
evolve over the years to support
increasing numbers of subscribers,
calls, connections to other countries,
direct dialing and so on. The model
developed by the United States and
Canada was adopted by other nations,
with adaptations for local markets.
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PSTN - Digital channels
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The call is switched using a ISUP|call set
up protocol (usually ISUP) between the
telephone exchanges under an overall
routing in the PSTN|routing strategy.
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PSTN - Digital channels
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The call is carried over the PSTN using a
64 kbit/s channel, originally designed by
Bell Labs. The name given to this channel
is Digital Signal 0 (DS0). The DS0 circuit
is the basic granularity of circuit switching
in a telephone exchange. A DS0 is also
known as a timeslot because DS0s are
aggregated in time-division multiplexing
(TDM) equipment to form higher capacity
communication links.
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PSTN - Impact on IP standards
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Voice quality over PSTN networks was
used as the benchmark for the
development of the
Telecommunications Industry
Association's TIA-TSB-116 standard on
voice-quality recommendations for IP
telephony, to determine acceptable
levels of audio delay and echo.
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Internet telephony - PSTN integration
1
Most VoIP implementations support E.164
to allow calls to be routed to and from
VoIP subscribers and the PSTN/PLMN
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Internet telephony - PSTN integration
Echo can also be an issue for PSTN
integration.Packetcable Implementation
P557– Jeff Riddel– ISBN 1-58705-181-8
[http://books.google.com/books?id=8CNBbrx
ytcACpg=PA557lpg=PA557dq=PSTN+gatew
ay+VOIP+impedance+mismatch Google
Books Preview] Common causes of echo
include Impedance matching|impedance
mismatches in analog circuitry and acoustic
coupling of the transmit and receive signal at
the receiving end.
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IP Multimedia Subsystem - PSTN Gateways
A PSTN/CS gateway interfaces with
PSTN Circuit switching|circuit switched
(CS) networks. For signalling, CS
networks use ISDN User Part (ISUP) (or
Bearer Independent Call Control|BICC)
over Message Transfer Part (MTP),
while IMS uses SIP over IP. For media,
CS networks use Pulse-code
modulation (PCM), while IMS uses Realtime Transport Protocol (RTP).
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IP Multimedia Subsystem - PSTN Gateways
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* A Media Gateway (MGW) interfaces with
the media plane of the CS network, by
converting between Real-time Transport
Protocol|RTP and PCM. It can also
transcode when the codecs don't match
(e.g., IMS might use Adaptive MultiRate|AMR, PSTN might use G.711).
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Routing in the PSTN
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'Routing in the PSTN' is the process
used to route Telephone|telephone
calls across the public switched
telephone network. This process is the
same whether the call is made between
two phones in the same locality, or
across two different continents.
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Routing in the PSTN - Relationship between exchanges and operators
The PSTN is not a fully mesh
networking|meshed network with every
operator connected to every other - that
would be both impractical and inefficient.
Therefore calls may be routed through
intermediate operator networks before
they reach their Destination routing|final
destination. One of the major problems in
PSTN routing is determining how to route
this call in the most cost effective and
timely manner.
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Teletraffic engineering - In PSTN architectures
The traffic measurement
(telecommunications)|measurement of
traffic in a public switched telephone
network (PSTN) allows network operators
to determine and maintain the quality of
service (QoS) and in particular the grade
of service (GoS) that they promise their
subscribers. The Network
Performance|performance of a network
depends on whether all origin-destination
pairs are receiving a satisfactory service.
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Teletraffic engineering - In PSTN architectures
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Exchanges in the PSTN make use of
trunking concepts to help minimize the
cost of the equipment to the operator.
Modern switches generally have full
availability and do not make use of
grading concepts.
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Teletraffic engineering - In PSTN architectures
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A very important component in PSTNs is
the Signalling System No. 7|SS7 network
used to route signalling traffic. As a
supporting network, it carries all the
signalling messages necessary to set up,
break down or provide extra services. The
signalling enables the PSTN control the
manner in which traffic is teletraffic
routing|routed from one location to
another..
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Internet phone - PSTN integration
Echo can also be an issue for PSTN
integration. Common causes of echo
include Impedance
matching|impedance mismatches in
analog circuitry and acoustic
coupling of the transmit and receive
signal at the receiving end.
1
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BeoCom - BeoLine PSTN and BeoLine ISDN
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The Mark 1 BeoLine can support up to
six BeoCom handsets of different types
(provided that the BeoLine software has
been brought sufficiently up-todate).[http://www.beoworld.org/prod_d
etails.asp?pid=1234] Beoworld site
description of Mark 1 PSTN base The
Mark 2 BeoLine can support eight
BeoCom handsets, but only those of
recent
manufacture.[http://www.beoworld.org/
prod_details.asp?pid=1235] Beoworld
site description of Mark 2 PSTN base
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