Telecommunications network components fall into logical or physical elements'

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Course 1
Components of the Telecommunications Networks
Telecommunications network components fall into
logical or physical elements. A logical element
is a Software-Defined Network (SDN) or voice
Virtual Private Network (VPN) feature or
capability. Switching systems have evolved into
the use of external signaling systems to set up
and tear down the call. These external physical
and logical components formulate the basis of a
network element. A physical element is the
actual switching element, such as the link or the
matrices used internally. A network is made up
of a unique sequence of logical elements
implemented by physical elements.
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Communications Network Architectures
Any communications network is based on an
architecture planned to make the interconnection
work and to add the necessary features and
functions. The Public Switched Telephone Network
(PSTN) evolved using a five-level hierarchy to
switch calls across the country or the globe.
The dynamic nonhierarchical routing protocol
(DNHR) reduced the rigidity of the network
protocols which were transparent to the user, but
the operator certainly had to manage the
operation and maintenance of the PSTN. Open
Systems Interconnect (OSI) model led to an open
communication architecture. Unfortunately this is
too expensive and offers little return on
investment (ROI) to the manufacturing community.
An alternative to the open architecture was an
open de facto standard such as the TCP/IP
architecture.
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For the TCP/IP architecture the openness was too
much for many managers to handle. Finally, the
TCP/IP model has become one of the most widely
implemented standards. The packet-based
technological model assumes that all data traffic
is the same and can be dealt with equally. The
emergence of this packet-based architecture
changes when we add real-time applications such
as voice, video, and audio needs
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The Movement toward Fiberoptic Networks

• A transmission link transports information from
  one location to another in a usable and
  understandable format. The three functional
  attributes of this link are
• Capacity
• Condition
• Quality of Service
• The copper-based network limits opportunities.
• The transmission distances associated with the
  subscriber loop limit the amount of bandwidth
  available over twisted wire pair roughly to the
  rate of 1.5 Mbps.
• The current switched-star architecture runs at
  least one dedicated twisted pair from the central
  office to each customer's door without any
  intermediate locations available to unbundle the
  transport segment.
• This involves a lot of the innovation desired by
  the end user.

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• The fiber-based networks offer many more
  opportunities by improving
• the local access network,
• the central office nodes at remote sites (these
  nodes serve as flexibility points where signals
  can be switched or multiplexed to the appropriate
  destination).
• The bandwidth limitations of a fiber system are
  not due to the intrinsic properties of the fiber,
  but the limitations of the switching,
  multiplexing, and transmission equipment
  connected to the fiber.

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Digital Transfer Systems
The switching and multiplexing techniques are
all digital. The Synchronous Transfer Mode (STM)
technique is currently used for switching and
multiplexing these digital signals. The
Synchronous Digital Hierarchy (SDH) is the future
of the synchronous transmission. Itd escribes a
family of broadband digital transport signals
operating in 50 Mbps increments. The
Asynchronous Transfer Mode (ATM) is the preferred
method of transporting at the data link layer.
ATM uses the best of packet switching and routing
techniques to carry information signals,
regardless of the desired bandwidth, over one
high-speed switching fabric. Using fixed-length
cells, the information is processed at higher
speeds, reducing some of the original latency in
the network.
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In time-division multiplexing (TDM), timing is
crucial. In ATM, statistical time-division
multiplexing (STDM) timing is used, so the timing
is less crucial at the data link layer. ATM will
use a combined switching and multiplexing service
at the cell level. Continued use of SDH
multiplexers will combine and separate SDH
signals carrying ATM cells. What distinguishes
ATM from a synchronous approach is that
subscribers have the ability to customize their
use of the bandwidth without being constrained to
the channel data rates. The key attribute of the
ATM switch, which could facilitate more
modularity, is the bandwidth flexibility. Because
each information signal is segmented into cells,
switching is performed in much smaller
increments.
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TELECOMMUNICATIONS SYSTEMS What Constitutes a
Telecommunications System?
Because at the beginning on the communication
network there was transmitted only voice, for
transmitting data they had to make it look like
voice. For voice communications the phone
companies installed a thin wire (26-gauge) to
most customers whose locations were within a km
or two from the central office. At the
demarcation point, they installed the least
expensive termination device, satisfying the
standard two-wire unshielded twisted pair
communications infrastructure. When the data
communications industry began during the late
1950s, the telephone companies began to charge an
inordinate amount of money to accommodate this
different service.
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Because the local provider owns the wires from
the outside world to the entrance of the
customer's building it is now under constant
attack from the wireless providers offering
satellite service, local multipoint distribution
services (LMDS), and multichannel multipoint
distribution services (MMDS). Moreover, the
Community Antenna Television (CATV) companies
have installed coaxial cable or fiber offering
the interconnection to business and residential
consumers alike.
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A Topology of Connections Is Used
In the local loop, the topological layout of the
wires has traditionally been a single-wire pair
or multiple pairs of wires strung to the
customer's location. For other types of
services, such as digital circuits and
connections, require two pairs. The use of a
single or dual pair of wires has been the norm.
More recently, the local providers have been
installing a four-pair (eight wires) connection
to the customer location. The end user can use
separate voice lines, fax lines, and separate
data communications hookups. Each of these
requires a two-wire interface from the LEC. Or
if a CATV provider has the technology installed,
the end user can get a single coax (or fiber) to
satisfy the voice, fax, data, and high-speed
Internet access on a single interface. This
topology is a dedicated local connection of one
or more pairs from the telephone provider to the
customer location or a shared coax from the CATV
supplier. This is called a star and/or shared
star-bus configuration.
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The telephone company connection to the customer
originates from a centralized point called a
central office (CO). The provider at this point
might be using a either a star or a ring
configuration. The star/ring or star/bus
combinations constitute the bulk of the
networking topologies today. The telephone
companies have begun to see a shift in their
traffic over the past few years. 1996 marked the
first year that as much data was carried on the
network as voice.
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The Local Loop
Each subscriber or customer is delivered at least
one pair of wires per telephone line. If the
number of users demanding telephone service
exceeds the number of pairs available, a
Telcompany might offer the service on a party
line or shared set of wires. This is the
connection at the local portion of the
network. From there, the local connectivity must
be extended out to other locations
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The Telecommunications Network
A layered hierarchy of office connections was
designed around a five-level architecture. Each
of these layers was designed around the concept
of call completion. The offices were connected
together with wires of various types called
trunks -twisted pairs of wire, coaxial cables,
radio (microwave), or fiber optics. Light-based
systems, however, are limited in their use by
telephone companies. Fiber is still the
preferred medium from a carrier's perspective.