telecom overview part 1a

8/8/2019 Telecom Overview Part 1a

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TELECOM OVERVIEW


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SWITCHING (PSTN, TDM, NGN, VOIP)


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CIRCUIT SWITCHING AND PACKET SWITCHING

PSTN uses circuit switching to transmit voice data whereas VoIP usespacket-switching to do so.

The difference in the way these two types of switching work is thething that made VoIP so different and successful.

To understand switching, you need to realize that the network inplace between two communicating persons is a complex field of

, .

Consider a person in Pakistan having a phone conversation withanother person on the other side of the globe, say in the US.

There are a large number of routers, switches and other kinds ofdevices that take the data transmitted during the communication

from one end to the other.


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CIRCUIT SWITCHINGCIRCUIT SWITCHINGCIRCUIT SWITCHINGCIRCUIT SWITCHING VSVSVSVS PACKET SWITCHINGPACKET SWITCHINGPACKET SWITCHINGPACKET SWITCHING


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CIRCUIT SWITCHINGCIRCUIT SWITCHINGCIRCUIT SWITCHINGCIRCUIT SWITCHING VSVSVSVS PACKET SWITCHINGPACKET SWITCHINGPACKET SWITCHINGPACKET SWITCHING


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TDM SWITCHING

Time Division Multiplexing (TDM) Switching is a type of digital multiplexing where twoor more channels are derived from a selected frequency spectrum.

In circuit switched networks such as that of the Public Switched Telephone Network(PSTN) there is the need to transmit multiple users' calls across the sametransmission line.

This is done by TDM switching and is distinguished from packet switching by the fact- .

TSM switching allows the switches to create multiple channels on the line allowingfor multiple users to use the same medium.

A typical voice signal will have a bandwidth of 64kbps, TDM will multiplex the voicesignal into a TDM frame.

With multiple voice samples there will be multiple frames which will require a higherbandwidth than that of 64kbps, the bandwidth of the system will need to be enoughto hold n voice frames, so the bandwidth will need to be n *64kbps.

TDM Switching systems typically multiplex 24, 32 or more channels on the same lineas standard. North America uses 24 channel TDM frames, whereas Europe uses 32channel TDM frames.


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TELEPHONE LINE BANDWIDTHTELEPHONE LINE BANDWIDTHTELEPHONE LINE BANDWIDTHTELEPHONE LINE BANDWIDTH


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T1 VS E1

T-carrier is the generic designator for any of severaldigitally multiplexed telecommunications carrier systemsoriginally developed by Bell Labs and used in NorthAmerica, Japan, and South Korea.

The basic unit of the T-carrier system is the DS0, which,

used for one voice circuit.

The E-carrier system, where 'E' stands for European, isincompatible with the T-carrier (though cross compliant

cards exist) and is used in most locations outside ofNorth America, Japan, and Korea. It typically uses theE1 line rate and the E3 line rate.


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T1 VS E1

Telephone system nominal voiceband (including guardband)is 4,000 Hz, the required digital sampling rate is 8,000 Hz

(see Nyquist rate). Since each T1 frame contains 1 byte of voice data for each

of the 24 channels, that system needs then 8,000 frameser second to maintain those 24 simultaneous voice

channels. Because each frame of a T1 is 193 bits in length (24

channels X 8 bits per channel + 1 framing bit = 193 bits),8,000 frames per second is multiplied by 193 bits to yield a

transfer rate of 1.544 Mbit/s (8,000 X 193 = 1,544,000). Similarly, E1=8 x 8000 x 32 = 2,048,000 (2.048 Mb/s)


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NGN (NEXT GENERATION NETWORK)

NGN is a packet-basednetwork able to provide

Telecommunication Services and able to makeuse of multiple broadband, QoSenabledtransport technologies and in which service-

related unctions are independent romunderlying transport- related technologies.

It enables unfettered access for users and

networks to competing service providersand/or services of their choice.


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NGN


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NGN ARCHITECTURE


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TRANSMISSION MEDIA Copper

Straight

Twisted Pair Shielded

Unshielded

Coaxial

Multimode Singlemode

Wireless

GSM

CDMS Wi-Fi

Wimax

Satellite


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DROP WIRE

Wire suitable for extending an

open wire or cable pair from apole or cable terminal to a

building.


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STP VS UTP


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COAXIAL CABLE Coaxial cable, or coax, has a single, solid

copper core, which is wrapped in a dielectric, a

copper outer conductor, and a PVC covering.

The outer conductor can be woven mesh or

solid copper.

Two t es of coax are thicknet and thinnet. Thicknet, also referred to as

attachment unit interface (AUI) cable, is thick and inflexible and is installedin a physical bus configuration, either for end station connections or in

building risers to connect LANs on different floors. A 15-pin amphenol type

connector is used with thicknet.

Thinnet is more flexible than thicknet and the terminator used in the BNC.

Thinnet is often used to daisy chain workstations or nodes to form either

physical buses or rings.

Coaxial cables inflexibility and relatively high cost are making it a less

desirable choice than twisted pair wiring.


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UNDERSEA COPPER CABLES: 1901


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OPTICAL FIBER

Optical fiber carries much more information than conventionalcopper wire and is in general not subject to electromagnetic

interference and the need to retransmit signals. Most telephone company long-distance lines are now made of optical

fiber.

Transmission over an optical fiber cable requires repeaters at.

The glass fiber requires more protection within an outer cable thancopper.

For these reasons and because the installation of any new cabling islabor-intensive, few communities have installed optical fiber cables

from the phone company's branch office to local customers (knownas local loops).

A type of fiber known as single mode fiber is used for longerdistances; multimode fiber is used for shorter distances.


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SINGLEMODE VS MULTIMODE FIBERCharacteristicCharacteristicCharacteristicCharacteristic Single ModeSingle ModeSingle ModeSingle Mode Multi ModeMulti ModeMulti ModeMulti Mode

Diameter 10 um 50-60 um

Applications LAN and Small Distance (Data Comm) Long Distance (Telecom)

Cost Cheaper Expensive

Attenuation High Low

Light Rays Single Multiple


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SUBMARINE FIBER CABLE


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WIRELESS MEDIA


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WIRELESS TECHNOLOGIES


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TRANSMISSION TECHNOLOGIES

PDH

SDH

DWDM

Metro Ethernet


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PDH


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SDH Software ControlSoftware ControlSoftware ControlSoftware Control allows extensive use of intelligent network management software

for high flexibility, fast and easy re-configurability, and efficient networkmanagement.

Survivability.Survivability.Survivability.Survivability. With SDH, ring networks become practicable and their use enablesautomatic reconfiguration and traffic rerouting when a link is damaged. End-to-endmonitoring will allow full management and maintenance of the whole network.

Efficient drop and insert.Efficient drop and insert.Efficient drop and insert.Efficient drop and insert. SDH allows simple and efficient cross-connect without fullhierarchical multi lexin or de-multi lexin . A sin le E1 2.048Mbit s tail can bedropped or inserted with relative ease even on Gbit/s links.

StandardisationStandardisationStandardisationStandardisation enables the interconnection of equipment from different suppliersthrough support of common digital and optical standards and interfaces.

Robustness and resilienceRobustness and resilienceRobustness and resilienceRobustness and resilience of installed networks is increased.

Equipment size and operating costsEquipment size and operating costsEquipment size and operating costsEquipment size and operating costs are reduced by removing the need for banks ofmultiplexers and de-multiplexers. Follow-on maintenance costs are also reduced.

Backwards compatiblyBackwards compatiblyBackwards compatiblyBackwards compatibly will enable SDH links to support PDH traffic. Future proof.Future proof.Future proof.Future proof. SDH forms the basis, in partnership with ATM (asynchronous transfer

mode), of broad-band transmission, otherwise known as B-ISDN or the precursor ofthis service in the form of Switched Multimegabit Data Service, (SMDS).


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SDH SDH is a standard technology for synchronous data transmission on optical

media.

It is the international equivalent of SONET. Both technologies provide faster and less expensive network

interconnection than traditional PDH equipment.

In digital telephone transmission, "synchronous" means the bits from onecall are carried within one transmission frame.

"Plesiochronous" means "almost (but not) synchronous," or a call that mustbe extracted from more than one transmission frame.

SDH uses the following Synchronous Transport Modules (STM) and rates:

STM-1 (155 Mb/s),

STM-4 (622 Mbps),

STM-16 (2.5 Gbps), and STM-64 (10 Gbps).


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SONET VS SDH


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telecom overview part 1a

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