Dsl

About the Organization

Scom is a leading technology services provider, delivering business solutions to its principle customers. Scom delivers one of the industry's broadest portfolios of information technology and business process outsourcing services to customers in the industries. They are Different as they provide outstanding service, innovation and industry thought leadership.

As their customers' trusted business ally, Scom provides the best solutions for principles to maximize return on their Network investments. Its deep industry knowledge enables it to provide customers with innovative ideas that help them improve productivity and security. Scom deliver on its commitments, so customers can build strong relationships with their customers, achieve profitable growth and win in the marketplace.

Scom’s portfolio is built around innovative and dedicated offerings in maintenance and development, business process outsourcing, and infrastructure, including desktop services, hosting, storage and networking. We use our next-generation global delivery system to ensure high quality. This enables our customers to respond quickly to changing market dynamics and increase their competitiveness.

Scom is a 17-year-old IT Hardware, Networking, Customer Service oriented Company, headquartered at New Delhi. It has a pan-India presence through its own network of 26 offices. Business Partner to world famous Brands like HP, Lenovo, IBM for Computer Peripherals, PC, Consumer Electronics, and Enterprise Business. As far as Customer Service goes, Scom is Service Partner to topmost Telecommunications Brands in the country like Bharti Airtel Limited, HFCL Infotel Limited, and Reliance Communication Limited. It has built for itself a high credibility amongst its vast network and several million satisfied end users by offering value-for-money quality products supported by effective service and a consistent policy of transparent, fair and ethical dealings.

During the last 8 financial years, the company turnover has increased from INR 2 crore in 2001-02 to INR 10 crore in FY 2010. The company has also been recognized by Principles through various rankings and awards received over the years.

The company has a strong technical Department in Delhi which is well-equipped with modern facilities and highly qualified engineers looking after developing systems for improvment in value-added services , specifications, benchmarking, quality up-gradation in service industry and technology development etc. This activity ensures that state-of-the-art products are offered as per the latest global standards.

As part of its diversification plan, Scom has added new business feathers in its cap."Trading Financial Securities" and "Materials Management". Mr.Vivek Bajaj having 20 years of experience in Financial Service & Securities have accepted the challenge and has joined Scom as Director Finance. With his experience in the portfolio, Scom has become Business Partner to Edelwise. Mr.S.C.Sehgal, having a vast experience of 40 years in Materials Management, consultant to NTPC, PMI, APGENCO, Ex-Advisor to Zimbabwe Electricity Board, has joined Scom Board of Directors for the same challenge.

One of the most valuable assets of the company is its team of more than 500 employees with over 50000 man years of experience. The average age of a Scom employee is 7 years. Scom acknowledges the support and co-operation provided to the company by its dedicated and hardworking network of employees.

The vision of the company is to make itself a globally respected name and to improve the quality of services to the Customers and to provide a good working Environment and continuously upgrade skills of the employees.

Vision of the Organization:

"Without Vision, there's no Destination. Without Mission, there's no Purpose.Without Values, there are no Guiding Principles."

o "A Commitment to Excellence and Quality Services to our Customers and to provide a good Working Environment and to Continuously Upgrade Skills of the Staff through Training Programs."

o Customer Delight.o Seek Technology and Trade Leadership.o Work with Quality People.o Enhance Work Culture and Environment.o Optimize Resource Management.o To Offer Services that, Empower our Customers to take control of their Financial Goals.o We will be Ethical, Sincere & Fair with our Clients.o We will Provide Outstanding Services.o We will strive to achieve Innovative and Dedicated Offerings.o We will be committed to Optimize Resource Management.o We will be committed towards creating an Operational Culture based on the highest level

of Efficiency, Transparency, Team Work, Integrity and Common purpose".

Services offered:

o Telecommunication

Fiber and Copper Termination DSL broadband Land line Installation RF Installation

o Trading Financial Securitieso Office Automationo Materials Managemento Networking

PRI and Lease Line Installation WI-FI Installation

o Infocomm Trainingo Networking Surveillance

Flowchart of the process:

Partners:

Lenovo, hp, ibm, molex dlink, edelweiss, airtel, alcatel lucent

INTRODUCTION

DSL is a high-speed Internet service like cable Internet. DSL provides high-speed networking

using existing twisted-pair telephone lines to transport high-bandwidth data, such as multimedia

and video, to service subscribers with the assistance of a broadband modem technology. DSL

technology allows Internet and telephone service to work over the same phone line

simultaneously without requiring customers to disconnect either their voice or Internet

connections. The term xDSL covers a number of similar yet conflicting forms of DSL, including

ADSL, SDSL, HDSL, RADSL, and VDSL. xDSL is growing and getting significant attention

from customers and service providers because it promises to deliver high-bandwidth data rates to

dispersed locations with relatively small changes to the existing telecom infrastructure. [1] xDSL

provides dedicated, point-to-point, public network access services over copper wire on the local

area between a network service provider (NSP’s) central office and the customer site, or on local

loops created either within a building or a campus. DSL technology is attractive because it

requires little to no upgrading of the existing copper infrastructure that connects nearly all

populated locations in the world. In addition, DSL is inherently secure due to its point-to-point

nature.

DSL Internet services are used primarily in homes and small businesses. DSL Internet service

only works over a limited physical distance and remains unavailable in many areas where the

local telephone infrastructure does not support DSL technology. DSL technology theoretically

supports data rates of 8.448 Mbps, although typical rates are 1.544 Mbps or lower. Currently the

primary focus in xDSL is the development and deployment of ADSL and VDSL technologies

and architectures.

Overview:

Alexander Graham Bell and Samuel Morse, who developed the idea that data could be

transmitted through copper wire. they had no where they would actually lead. However, the

principles had been laid. The technological race is a fast-paced. Improvements and developments

are constantly being made. What once seemed to be amazing advances had became yesterday’s

news. Has DSL (Digital Subscriber Line) always moved at this speed?

Bell and Morse, were instrumental in developing a path for the ever-increasing volume of data

transmitted over the Internet. In the late 1980s, Joseph Lechleider, father of broadband

technologies demonstrated the possibility of sending broadband signals. He developed the idea

of asymmetry (the A in ADSL), which suggested that a higher rate of data could be sent in one

direction. Putting it simply, this was the beginning of the move from analog to digital.[2]

This was the time when ISDN was created as a first effort or this technology. Integrated Services

Digital Network, is a system of digital phone connections which allows voice and data to be

transmitted simultaneously. The result of this is that more data could be transmitted at the same

time, thus creating more speed. Bringing ISDN technology to bear throughout the telephone

network required an immense effort lasting more than a decade, consuming money and yielding

a service that, was too little. The ISDN specification, built to deliver digital data at the now-

unimpressive rate of 128 kbps, presumed brief data sessions with relatively slow transmission

speeds, and supporting mainly for digital phone calls. At that time we can say nothing was best

suited for the Internet, which scarcely existed as a consumer medium at the time of ISDN's

introduction, which now emerges as the central force behind the broadband revolution.

John Cioffi at Standard University’s Department of Electrical Engineering, developed DMT

(discrete multitone), a method of separating a DSL signal into 256 frequency bands or channels.

Cioffi founded a company called Amati, who, in 1993, designed equipment to perform this task.

And this equipment was dramatically better than its competitors in Bellcore testing and became

the most common standard. DSL technology turns the historical telephone network into a high-

speed broadband delivery instrument. In a way, DSL has revived a maturing business—that of

using the telephone network to carry phone calls.

DSL was designed mainly for video. ADSL was a favorite choice as it provides the high

downstream rates needed for streaming video. Video on Demand (VOD) was viewed as the next

generation service supporting the next generation network from telephone companies around the

world. Video on Demand was gave the telephone companies a way to compete with cable

television providers, and ADSL was the technology to make it possible. However, with few

exceptions, VOD has not proven to be as popular as was once predicted. Instead, the market for

DSL has emerged much differently than was once expected. It was started being used device to

access high-speed Internet on Personal Computers by corporate networks from residences and

remote offices. Now, this PC user market has captured the attention of both cable TV providers

and telephone companies, as both are furiously working to meet their needs.

The motivation of digital subscriber line technology was the Integrated Services Digital Network

(ISDN) specification proposed in 1984 by the CCITT (now ITU-T) as part of Recommendation

I.120, later reused as ISDN Digital Subscriber Line (IDSL). Employees at Bellcore (now

Telcordia Technologies) developed Asymmetric Digital Subscriber Line (ADSL) and filed a

patent in 1988[2] by placing wide-band digital signals above the existing baseband analog voice

signal carried between telephone company telephone exchanges and customers on conventional

twisted pair cabling facilities.[3] Consumer-oriented ADSL was designed to operate on existing

lines already conditioned for BRI ISDN services, which itself is a switched digital service (non-

IP), though most incumbent local exchange carriers (ILECs) provision Rate-Adaptive Digital

Subscriber Line (RADSL) to work on virtually any available copper pair facility—whether

conditioned for BRI or not. Engineers developed higher-speed DSL facilities such as High bit

rate Digital Subscriber Line (HDSL) and Symmetric Digital Subscriber Line (SDSL) to

provision traditional Digital Signal 1 (DS1) services over standard copper pair facilities.

A DSL circuit provides digital service. The underlying technology of transport across DSL

facilities uses high-frequency sinusoidal carrier wave modulation, which is an analog signal

transmission. A DSL circuit terminates at each end in a modem which modulates patterns of bits

into certain high-frequency impulses for transmission to the opposing modem. Signals received

from the far-end modem are demodulated to yield a corresponding bit pattern that the modem

retransmits, in digital form, to its interfaced equipment, such as a computer, router, switch, etc.

Unlike traditional dial-up modems, which modulate bits into signals in the 300–3400 Hz

baseband (voice service), DSL modems modulate frequencies from 4000 Hz to as high as

4 MHz. This frequency band separation enables DSL service and plain old telephone service

(POTS) to coexist on the same copper pair facility. Generally, higher bit rate transmissions

require a wider frequency band, though the ratio of bit rate to bandwidth are not linear due to

significant innovations in digital signal processing and digital modulation methods.

Early DSL service required a dedicated dry loop, but when the U.S. Federal Communications

Commission (FCC) required ILECs to lease their lines to competing DSL service providers,

shared-line DSL became available. Also known as DSL over Unbundled Network Element, this

unbundling of services allows a single subscriber to receive two separate services from two

separate providers on one cable pair. The DSL service provider's equipment is co-located in the

same central office (telephone exchange) as that of the ILEC supplying the customer's pre-

existing voice service. The subscriber's circuit is then rewired to interface with hardware

supplied by the ILEC which combines a DSL frequency and POTS frequency on a single copper

pair facility.

On the subscriber's end of the circuit, inline low-pass DSL filters (splitters) are installed on each

telephone to filter the high-frequency "hiss" that would otherwise be heard, but pass voice

(5 kHz and below) frequencies. Conversely, high-pass filters already incorporated in the circuitry

of DSL modems filter out voice frequencies. Although ADSL and RADSL modulations do not

use the voice-frequency band, nonlinear elements in the phone could otherwise generate audible

intermodulation and may impair the operation of the data modem in the absence of low-pass

filters.

TYPES OF DSL:

There are many variations of DSL, each aimed at particular markets, all designed to accomplish

the same basic goals. Several modulation technologies are used by various kinds of DSL,

although these are being standardized by the International Telecommunication Union (ITU ).

Different DSL modem makers are using either Discrete Multitone Technology (DMT ) or

Carrierless Amplitude Modulation ( CAP ). A third technology, known as Multiple Virtual Line

MVL is another possibility.

 ADSL :

ADSL, or Asymmetric DSL, is aimed at the residential consumer market. ADSL is called

"asymmetric" because most of its two-way or duplex bandwidth is devoted to the downstream

direction, sending data to the user.[3]ADSL provides higher data rates in the downstream

direction, from the central office to the end user, than in the upstream direction, from the end

user to the central office. Only a small portion of bandwidth is available for upstream requests.

However, most Internet and especially graphics or multi-media demanding Web data need large

downstream bandwidth, but user requests and responses are small and require little upstream

bandwidth. Using ADSL, up to 6.1 megabits per second of data can be sent downstream and up

to 640 Kbps upstream. The high downstream bandwidth means that your telephone line will be

able to bring motion video, audio, and 3-D images to your computer or hooked-in TV set. In

addition, a small portion of the downstream bandwidth can be devoted to voice rather data, and

you can hold phone conversations without requiring a separate line.[4]

CAPABILITY:

ADSL has ability to operate along with existing Plain Old Telephone Service (POTS) on a single

pair of wires without disruption. POTS is the basic service that provides all phone lines with

access to the Public Switched Telephone Network (PSTN). POTS provides the means for all

voice-band related applications and technologies, such as telephony, caller identification, call

waiting, analog facsimile, analog modem, etc...  

It can be also used without Splitters, G.lite or Universal ADSL and now also known as G.992.2

does not require a POTS splitter to be installed at the consumer's home or business. ADSL Lite

provides bandwidth downstream up to 1.5 Mbps and upstream up to 512 kbps. ADSL Lite

provides service up to a maximum range of 12,000 feet (about 2.0 miles) from the central office

Three information channels—a high-speed downstream channel, a medium-speed duplex

channel, and a basic telephone service channel are created when an ADSL modem is connected.

The basic telephone service channel is divided from the digital modem by filters, thus

guaranteeing uninterrupted basic telephone service, even if ADSL flops. The high-speed channel

ranges from 1.5 to 6.1 Mbps, and duplex rates range from 16 to 640 kbps. Each channel can be

sub multiplexed to form multiple lower-rate channels. ADSL modems provide data rates

consistent with North American T1 1.544 Mbps and European E1 2.048 Mbps digital hierarchies

(see Figure 15-2) and can be purchased with various speed ranges and capabilities. The

minimum configuration provides 1.5 or 2.0 Mbps downstream and a 16 kbps duplex channel;

others provide rates of 6.1 Mbps and 64 kbps duplex. Products with downstream rates up to 8

Mbps and duplex rates up to 640 kbps are available today ADSL modems accommodate

Asynchronous Transfer Mode (ATM) transport with variable rates and compensation for ATM

overhead, as well as IP protocols. Downstream data rates depend on a number of factors,

including the length of the copper line, its wire gauge, presence of bridged taps, and cross-

coupled interference. Line attenuation increases with line length and frequency and decreases as

wire diameter increases.

FREQUENCY ALLOCATION:

ADSL uses Frequency Division Multiplexing (FDM) to separate frequency bands, referred to as

the upstream and downstream bands. The upstream band is used for communication from the end

user to the telephone central office. The downstream band is used for communicating from the

central office to the end user. With standard ADSL (annex A), the band from 25.875 kHz to 138

kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream

communication.

Fig. Process of Frequency Division Multiplexing

Fig. Frequency Band for ADSL after modulation

Splitter: 

A "splitter" (which is a filter), one at the user end and one at the exchange end, separates the

telephony signal from the ADSL signal.  This means that telephone calls can be made at the

same time that data is being sent or received. A block diagram of the splitter is shown in the

following figure. One can see that it consists of low pass filter, which will extract the telephone

signal, and a high pass filter that extract the DSL signal. [5]  The DC component that is used for

transmitting the signal, have to be blocked to get only the high frequency signals.

Telephone network Telephone

ADSL

Fig. Splitter for ADSL

ADSL2

ADSL2 (ITU G.992.3 and G.992.4) adds new features and functionality targeted at improving

performance and interoperability and adds support for new applications and services. Among the

changes are improvements in ADSL's data rate, an increase in the distance ADSL can reach from

the local telephone exchange, dynamic data rate adaptation, better resistance to noise,

diagnostics, and a stand-by mode to save power. ADSL2 also reduces the initialisation time from

more than 10 seconds (as is required for ADSL) to less than 3 seconds. ADSL2 has the same

signal footprint as ADSL.

Low Pass Filter

High Pass FilterDC Blocking

Device

ADSL2+

ADSL2+ (ITU G.992.5) doubles the bandwidth used for downstream data transmission,

effectively doubling the maximum downstream data rates, and achieving rates of 20 Mbps on

telephone lines as long at 5,000 feet. ADSL2+ solutions will interoperate with ADSL and

ADSL2, as well as with ADSL2+. ADSL2+ will include all the feature and performance benefits

of ADSL2 while maintaining the capability to interoperate with legacy ADSL equipment

Limitation:

ADSL access is distance-sensitive. The connection speed depends on several factors:

Distance between the subscriber and the central office

Copper line wire gauge

Copper line wire speed increases with wire diameter because of the wire will have lower

resistance. With high frequency and small diameter the Skin Effect arises and limits the

distance since the signal gets attenuated because of the increased resistance. The skin

effect is the tendency of an alternating current (AC) to distribute itself within a conductor

so that the current density near the surface of the conductor is greater than that at its core.

That is, the electric current tends to flow at the "skin" of the conductor.

Presence of bridge taps - bridge taps are extensions, between the subscriber and the

central office, that extend service to other subscribers. Bridge taps may increase the

distance limit but slow down the access speed.

Crosstalk due to electromagnetic interference between wires.

HDSL:

HDSL (High bit-rate Digital Subscriber Line), one of the earliest forms of DSL, is used for

wideband digital transmission within a corporate site and between the telephone company and a

customer. It was the first DSL technology to use a higher frequency spectrum of copper, twisted

pair cables.[6] The main characteristic of HDSL is that it is symmetrical: an equal amount of

bandwidth is available in both directions. HDSL can carry as much on a single wire of twisted-

pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up

to 2.048 Mbps) in Europe over a somewhat longer range. The operating range of HDSL is

limited to 12,000 feet (3658.5 meters), so signal repeaters are installed to extend the service.

HDSL requires two twisted pairs, so it is deployed primarily for PBX network connections,

digital loop carrier systems, interexchange POPs, Internet servers, and private data networks.[7]

VDSL:

VDSL was developed to support exceptionally high-bandwidth applications such as High-

Definition Television (HDTV). VDSL is not as widely deployed as other forms of DSL service.

However, VDSL can achieve data rates up to approximately 51,840 Kbps, making it the fastest

available form of DSL. To perform at this speed, VDSL relies on fiber optic cabling. VDSL is

designed to work more as a business service that uses ATM internetworking rather than as a

consumer service that utilizes IP. VDSL supports both voice and data communication on the

same line, like other forms of DSL.

Also like most DSL technology, the performance of VDSL depends significantly on the physical

distance traversed by wires: Shorter distances mean faster networking. The technology was

originally named VADSL ('A' for asymmetric), but VDSL has now been improved and can

operate in either symmetric or asymmetric modes. VDSL, based on DMT, creates 247 virtual

channels within the available bandwidth. Each channel's integrity is monitored and data is

switched to an alternate channel when signals become degraded. In this way, data is constantly

shifted to the best route for transmitting or receiving data, making DMT a robust, albeit complex

technology.

As with other broadband technologies, end-user speeds will depend upon the distance of the feed

or loop to the local telephone company or telco office. Shorter distances afford faster rates, while

longer loops degrade signal and speed. One drawback of VDSL is that it requires a very short

loop of about 4000 feet (1219 meters), or three-quarters of a mile. However, another

complication can inadvertently create a solution for the distance problem: the complication of

fiber optic lines.

Many telcos are installing fiber optic lines in place of copper lines. If a stretch of line between

the customer and telco is fitted with fiber optic, VDSL signals get "lost in translation" converting

from analog (copper), to fiber optic (digital), and back to analog. A VDSL gateway device

installed at the junction box will translate the VDSL signals to pulses of light able to traverse the

fiber optic cable. Through this process, the distance barrier associated with copper wire and

VDSL is "bridged" or bypassed. When the telco receives the light impulses, it sends data back to

the junction box gateway, which converts the signal to forward along the copper wires a short

distance to the VDSL modem. In this scenario, distance is not a limiting factor.

Japan and Korea are by far the most ardent supporters of VDSL and have made widespread use

of it to date. Other countries have been slower to take up the technology, with only one or two

providers in each participating country.[8]

RADSL:

RADSL (Rate-Adaptive DSL) is an ADSL technology from Westell in which software is able to

determine the rate at which signals can be transmitted on a given customer phone line and adjust

the delivery rate accordingly. In RADSL the DSL modem adjusts the upstream bandwidth to

create a wider frequency band for the downstream traffic. Using this technique the line is more

tolerant of errors caused by noise and signal loss.As the frequency is adjusted, the upstream

bandwidth may be markedly decreased if there is a large amount of line noise or signal

degradation - this may reduce the upstream bit rate to as little as 64 kbit/s - the same speed as a

single ISDN B channel. Westell's FlexCap2 system uses RADSL to deliver from 640 Kbps to 2.2

Mbps downstream and from 272 Kbps to 1.088 Mbps upstream over an existing line.

SDSL:

SDSL (Symmetric DSL) is similar to HDSL with a single twisted-pair line, carrying 1.544 Mbps

(U.S. and Canada) or 2.048 Mbps (Europe) each direction on a duplex line. It's symmetric

because the data rate is the same in both directions. It is used primarily by small and medium

size enterprises (SMEs) to transmit and/or receive large volumes of data across the Internet at

very high speeds.  SDSL can transfer data at speeds of up to 3 Mbps (megabits per second) in

either direction.

Unlike other high-speed Internet technologies, SDSL does not require a sophisticated optical or

coaxial cable network to provide broadband Internet connectivity.  Instead, SDSL leverages the

standard twisted-pair copper wires that are used by conventional land-line telephones. 

Consequently, the cost of providing SDSL service is relatively inexpensive and service is now

available in many areas.

SDSL is well-suited to small and medium sized businesses and to consumers who require high

bandwidth but can't justify the cost of dedicated, expensive leased lines or frame-relay services.

UDSL:

UDSL (Unidirectional DSL) is a proposal from a European company. It's a unidirectional

version of HDSL. Uni-DSL was developed by Texas Instruments which would provide bit rates

of at least 200 Mbit/s in aggregate on the downstream and upstream paths. UDSL is backwards

compatible with all discrete multitone modulation (DMT) standards (ADSL, ADSL2, ADSL2+,

VDSL and VDSL2). Uni-DSL means "One DSL for universal service". It was marketed for

service providers as an affordable option to support all of their network requirements and

services in fiber to the node configurations.

A DSL Summary Table

DSL Type Description

Data Rate

Downstream;

Upstream

Distance Limit Application

IDSL

ISDN Digital

Subscriber

Line

128 Kbps18,000 feet on 24

gauge wire

Similar to the ISDN

BRI service but data

only (no voice on

the same line)

CDSL

Consumer

DSL

from Rockwell

1 Mbps downstream; less

upstream

18,000 feet on 24

gauge wire

Splitterless home

and small business

service; similar to

DSL Lite

DSL Lite

(same as

G.Lite)

"Splitterless"

DSL without

the "truck roll"

From 1.544 Mbps to 6 Mbps

downstream, depending on

the subscribed service

18,000 feet on 24

gauge wire

The standard ADSL;

sacrifices speed for

not having to install

a splitter at the user's

home or business

G.Lite

(same as

DSL Lite)

"Splitterless"

DSL without

the "truck roll"

From 1.544 Mbps to 6 Mbps

, depending on the

subscribed service

18,000 feet on 24

gauge wire

The standard ADSL;

sacrifices speed for

not having to install

a splitter at the user's

home or business

HDSL

High bit-rate

Digital

Subscriber

Line

1.544 Mbps duplex on two

twisted-pair lines;

2.048 Mbps duplex on three

twisted-pair lines

12,000 feet on 24

gauge wire

T1/E1 service

between server and

phone company or

within a company;

WAN, LAN, server

access

SDSLSymmetric

DSL

1.544 Mbps duplex (U.S.

and Canada); 2.048 Mbps

(Europe) on a single duplex

line downstream and

upstream

12,000 feet on 24

gauge wire

Same as for HDSL

but requiring only

one line of twisted-

pair

ADSL

Asymmetric

Digital

Subscriber

Line

1.544 to 6.1 Mbps

downstream;

16 to 640 Kbps upstream

1.544 Mbps at 18,000

feet;

2.048 Mbps at 16,000

feet;

6.312 Mpbs at 12,000

feet;

8.448 Mbps at 9,000

feet

Used for Internet

and Web access,

motion video, video

on demand, remote

LAN access

RADSL

Rate-Adaptive

DSL from

Westell

Adapted to the line, 640

Kbps to 2.2 Mbps

downstream; 272 Kbps to

1.088 Mbps upstream

Not provided Similar to ADSL

UDSL Unidirectional

DSL proposed

by a company

Not known Not known Similar to HDSL

in Europe

VDSL

Very high

Digital

Subscriber

Line

12.9 to 52.8 Mbps

downstream;

1.5 to 2.3 Mbps upstream;

1.6 Mbps to 2.3 Mbps

downstream

4,500 feet at 12.96

Mbps;

3,000 feet at 25.82

Mbps; 1,000 feet at

51.84 Mbps

ATM networks;

Fiber to the

Neighborhood

NETWORK ARCHITECTURE OF DSL

When the telephone network was originally developed, it was designed to carry voice traffic

only. Voice signals were designed to use only the first 4 kHz of the frequency spectrum of the

copper wires. Digital Subscriber Line (DSL) works by using part of the remaining frequencies on

the copper twisted pair to send and receive data traffic. DSL uses frequencies between 25 kHz -

1MHz. This extra bandwidth means DSL can send more data. Generally, access providers need

two pieces of hardware to effect Digital Subscriber Line (DSL) solutions that include both voice

and data elements-solutions that should have great appeal to the mass consumer market.

Providers will need to install special equipment and consumers will also have to install special

equipment to accommodate DSL. The table below details and gives short descriptions of

equipment that must be installed.

Provider

Equipment

Equipment Description

Plain Old Telephone

Service (POTS) Splitter

Enables analog voice services to be

carried simultaneously on the same line

as digital data services. Allows the

voice signal to be routed to the existing

voice switch.

DSL Modem DSL transmission unit that engages in

physical layer negotiations between the

remote location and the CO.

DSL Access Multiplexer

(DSLAM)

Aggregates DSL-based signals.

Element Management

System

Hardware and software that make

remote access and management

possible.

Consumer

Equipment

Network Interface Card

(NIC)

Electronic circuitry that connects a

workstation (computer) the network.

Works to transmit and receive

messages.

DSL Modem DSL transmission unit that engages in

physical layer negotiations between the

remote location and the CO.

Splitter Enables analog voice services to be

carried simultaneously on the same line

as digital data services. Allows the

voice signal to be routed to the existing

voice switch.

Network Interface Device

(NID)

Device wired between a telephone

protector and the interior customer

wiring to isolate customer equipment

from the network.

Table 1.5: Equipments Needed For DSL Provider and Consumer  

Fig. A network Architecture of DSL Network.

Internet Router:

An internet service provider is directly connected to internet cloud through internet routers, this

act as a server and switch and helps in providing access, hosting, and transiting. This helps in

communicating with many computers networks. When multiple routers are used in

interconnected networks, the routers exchange information about destination addresses, using a

dynamic routing protocol. Each router builds up a table listing the preferred routes between any

two systems on the interconnected networks. A router has interfaces for different physical types

of network connections, (such as copper cables, fiber optic, or wireless transmission). It also

contains firmware for different networking protocol standards. Each network interface uses this

specialized computer software to enable data packets to be forwarded from one protocol

transmission system to another. This router provide connectivity within enterprises, between

enterprises and the Internet, and between internet service providers (ISPs) networks. The largest

routers (such as the Cisco CRS-1 or Juniper T1600) interconnect the various ISPs, or may be

used in large enterprise networks. Smaller routers usually provide connectivity for typical home

and office networks. The routers determine where to send information from one computer to

another. The router provides the logical network termination. Common link access methods

include PPP over Ethernet (PPPoE), PPP over ATM (PPPoA) encapsulated sessions, bridged

ethernet over ATM or Frame Relay (RFC 1483/RFC 1490), or just plain ethernet. In the case of

ATM or Frame Relay based access, individual subscribers are identified by Virtual Circuit IDs.

Subscribers connected over ethernet-based remote access devices are usually identified by

VLAN IDs or MPLS tags.

fig. network diagram with routers.

Here in above figure you can see that a router is connected to the internet, and one end of router

is connected to ISP’s router at central office and other end is connected to modems or PRIs at

local exchange which are further connected to a PSTN in case of voice lines and for data lines

through MDF. An internet router keeps track of

Information on which connections lead to particular groups of addresses

Priorities for connections to be used

Rules for handling both routine and special cases of traffic

A router has two separate, but related, jobs:

It ensures that information doesn't go where it's not needed. This is crucial for keeping

large volumes of data from clogging the connections of "innocent bystanders."

It makes sure that information does make it to the intended destination.

In performing these two jobs, a router is extremely useful in dealing with two separate computer

networks. It joins the two networks, passing information from one to the other. It also protects

the networks from one another, preventing the traffic on one from unnecessarily spilling over to

the other. Regardless of how many networks are attached with the use of firewall for security, the

basic operation and function of the router remains the same. Since the Internet is one huge

network made up of tens of thousands of smaller networks, its use of routers is an absolute

necessity.

BRAS:

A broadband remote access server (BRAS, B-RAS or BBRAS) routes traffic to and from

broadband remote access devices such as digital subscriber line access multiplexers (DSLAM)

on an Internet service provider's (ISP) network. BRAS can also be referred to as a Broadband

Network Gateway (BNG). BRAS is used to provide network access to the devices connected

with it. It has these functions

It aggregates the circuits from one or more link access devices such as DSLAMs.

Provides layer 2 connectivity through either transparent bridging or PPP sessions over Ethernet

or ATM sessions.

Enforces quality of service (QoS) policies.

Provides layer 3 connectivity and routes IP traffic through an Internet service provider’s

backbone network to the Internet.

Access usually connects the customer or CPE (Customer Provided/Premise Equipment). Access

circuits are multiplexed, integrated, or aggregated to Edge routers.

At the Edge, a myriad of different protocols are combined by the carrier depending on their

architecture into Core protocols such as IP (Internet Protocol) or ATM (Asynchronous Transfer

Mode). In order to reduce the number and types of different routing and switching systems, the

next-generation Edge device is often called a BRAS (Broadband Remote access Aggregation

Server) or MSSS (Multi-Service Switching System). MSE (Multi-Service Edge) system provides

protocol conversion from Access protocols to one or more Core protocols. BRAS also provides

the interface to authentication, authorization and accounting systems.

BRAS in an exchange is directly connected to internet router and digital subscriber line access

multiplexer which is further connected to xDSL modem and MDF.[9]

DSLAM:

A digital subscriber line access multiplexer (DSLAM, often pronounced dee-slam) is a

network device, often located in the telephone exchanges of the telecommunications operators. It

connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital

communications channel using multiplexing techniques. The DSLAM equipment collects the

data from its many modem ports and aggregates their voice and data traffic into one complex

composite "signal" via multiplexing. Depending on its device architecture and setup, a DSLAM

aggregates the DSL lines over its Asynchronous Transfer Mode (ATM), frame relay, and/or

Internet Protocol network (i.e., an IP-DSLAM using PTM-TC [Packet Transfer Mode -

Transmission Convergence]) protocol(s) stack.

The aggregated traffic is then directed to a telco's backbone switch, via an access network (AN)

also called a Network Service Provider (NSP) at up to 10 Gbit/s data rates.

The DSLAM acts like a network switch since its functionality is at Layer 2 of the OSI model.

Therefore it cannot re-route traffic between multiple IP networks, only between ISP devices and

end-user connection points. The DSLAM traffic is switched to a Broadband Remote Access

Server where the end user traffic is then routed across the ISP network to the Internet. Customer-

premises equipment that interfaces well with the DSLAM to which it is connected may take

advantage of enhanced telephone voice and data line signaling features and the bandwidth

monitoring and compensation capabilities it supports.

A DSLAM may or may not be located in the telephone exchange, and may also serve multiple

data and voice customers within a neighborhood serving area interface, sometimes in

conjunction with a digital loop carrier. DSLAMs are also used by hotels, lodges, residential

neighborhoods, and other businesses operating their own private telephone exchange.

It synchronizes with a modem installed at customer end to provide data flow, it sync everytime a

modem is reset or powered. This is typically indicated by LEDs on the modem. Without sync,

nothing happens. The modem will establish a sync rate which is often throttled by the provider at

a predefined limit. This limit, or "cap", is at the provider's discretion and is part of the service

that is being provided. Your modem may well sync at a higher rate than the "cap", but your

speed will be limited to whatever "cap" the provider is enforcing. So while ADSL has an upward

theoretical limit of 8 Mbps, you will not see that speed -- unless of course your provider is

selling an 8 Mbps plan. Most plans are well below this

In addition to being a data switch and multiplexer, a DSLAM is also a large collection of

modems. Each modem on the aggregation card communicates with a single subscriber's DSL

modem. This modem functionality is integrated into the DSLAM itself instead of being done via

an external device like a traditional computer modem.

MDF:

To make possible for a subscriber to communicate with remaining subscribers, telephone of each

and every subscriber must be connected to the exchange. The function of Main Distribution

Frame is to provide a means for connecting customer’s telephone lines to the xdsl modem

installed at the exchange. Each subscriber is provided with a telephone number, and to ensure

that same telephone number connection is provided to the customer the telephone service

provider generates a MDF address, a technician uses that code to connect telephone line to the

xDSL modem through copper wires. MDF have ports coded alpha-numerically, for vertical it is

coded alphabetically and for horizontal it is coded numerically.

DSL Modem:

A DSL modem is a device that is used to connect a computer or router to a telephone circuit that

has a Digital Service Line (DSL). Using a Digital Subscriber Line Access Multiplexer

(DSLAM), the DSL modem modulates high-frequency tones for transmission. The DSL modem

will also receive and demodulate the transmissions from the DSLAM. Compared to analog dial-

up, DSL significantly increases the bandwidth between the user's computer and the Internet.

Download speeds are theoretically capable of reaching 10 Mbps and beyond, but telephone

companies often limit the speed and/or bandwidth capabilities to prevent Web Hosting.

However, DSL modems still transfer data at a rate which is typically 10 to 20 times that of a

voice-band modem. Furthermore, a single telephone line can be used for simultaneous voice and

data with DSL, while a voice-band modem does not allow for simultaneous voice traffic.

Because a single phone line commonly carries DSL and voice, DSL filters are used to separate

the two lines. DSL modems use frequencies from 25 kHz - 1MHz, in order not to interfere with

voice service (which is primarily located between 0-4kHz. Some DSL modems also manage the

connection for and sharing of the DSL service in a network, and in this case, the DSL modem

would be referenced as a DSL router or residential gateway.

Most DSL modems are external to the computer and wired to the computer's Ethernet port. Less

common are DSL modems that connect to a computers USB port. Internal DSL modems with

PCI interfaces are also available, however, they too are rare compared to DSL modems that use

an Ethernet port. Like many other computer technologies, DSL functions that have typically

been provided by multiple chips can be integrated onto one chip.

DSL modem Specifications:

Installation/setup for single user and multiple users

1. DSL modem

2. Mower supply for modem

3. Ethernet cable

4. Modem cable

ADSL Standards ANSIT1.413Issue2,

ITUG.992.1A/B(G.dmt),

ITUG.992.2(G.lite),

ITUG.992.3(ADSL2), ITU G.992.5

(ADSL2+)

Line Speeds Max. 24 mbps (downstream), max. 2 mbps

(upstream)

DSL line length Max. 5,5 km

Bridging modes PPPoE

ADSL 1 Screw-typ Terminal

LAN Ethernet, 10/100 mbps

Network strength 10-15m, decreases with increase in

distance

Power Supply 1 screw-typ Terminal. 9V

Wireless type 802.1 b+g

Extra Reset button to reset modem

Encryption Type TKIP/AES

Authentication WPA-PSK/WPA2-PSK

Gateway Static/Dynamic

5. Phone line filters

6. Phone line splitter

7. Modem instructions and safety guide

8. Modem installation guide

Steps to Follow:

Connect the Wire from Telephone network to the splitter, so that it can separate Data

Line and Voice.

Connect the Voice cable to Telephone and check if the line is active or not. If it is active

insert data line cable into DSL’s port where DSL is written, and supply power through

the adapter provided with modem.

Wait for synchronization with multiplexer at central office, this will take few minutes

after that green lights will glow in front of DSL for internet.

As now the modem is installed, we need to configure the modem, for that use Ethernet

cable to connect DSL with computer.

Open any browser and enter the IP Address of the modem in address bar. IP address of

almost all DSL modems are same (192.168.1.1), but Different manufacturers uses

different IP addresses. IP address is printed in back of the modem.

It will ask for username and password which is by default (admin/admin or

admin/password).

After you enter the password it will take you to the device’s homepage. Which contains

the information about your device eg. Firmware version, IP Address etc.

In case you are using a router then go to maintenance and click on firmware and upgrade

it by choosing a firmware file (RSA) you have in your hard drive or ask your service

provider for it. It deletes cashes.

Now for connecting with the internet go to interface setup, and check PPPoE in

encapsulation, then enter the username and password provided by your service provider.

Now you can use internet.

If you are using a wireless modem then go to Interface MenuWAN to configure

wireless network.

Here you have to enter a name for you wireless network, a password/key, authentication

type and encryption type.

Choose any of authentication type, it is better to choose WPA-PSK/WPA2-PSK.

You are provided with two encryption types which are both good, but better to choose

TKIP.

In SSID enter a desired name for your Wi-Fi.

Just below SSID enter Pass key for your network. And save and wait for few seconds and

close your browser.

Enable your Wi-Fi driver and enter the key and start browsing.

COMPARISON OF DSL TO OTHER TECHNOLOGY

CABLE MODEMS 1- to 2-mbps download/128- to 384-kbps upload, costs and monthly rates

AND DSL ADSL: 384-kbps to 9-mbps download/128-kbps upload

SDSL: 1.5-mbps download/upload

ISDL: Up to 144-kbps download/upload, cost and monthly rates

There are two types of cable modems. The most prevalent is the hybrid fiber/coax (HFC)

modem, which runs over HFC cable networks and offers theoretical download speeds from 3 to

30 megabits per second; however, real-world data indicate that speeds from 400 to 1440 kilobits

per second can be expected.

The other, older type is a one-way modem that runs over standard cable coaxial networks. These

modems offer up to 2 megabits per second download speeds, but they offer no upload capacity

because cable networks were not originally designed for two-way communication. With the

older system, in order to send out information over the Internet, a separate phone line, modem

and ISP are required. This one-way approach is being dumped as cable companies upgrade to

two-way infrastructure.

In order to offer the two-way service, the cable company must first upgrade your neighborhood

to hybrid fiber/coax cable lines. As of early 1999, only about 30% of the total cable lines in the

United States have been converted to HFC. One reason for the spotty availability of cable

modem service is that upgrading lines is very expensive. In addition, cable lines are not likely to

be located around office buildings and business parks, so high-bandwidth options for businesses

probably won't include cable.

Cable networks differ from DSL networks in their basic structure. With a cable modem, you are

sharing access to the Internet, unlike DSL which runs on a dedicated connection. Cable modem

service is set up like a local area network (LAN), making it possible for many users to share the

same bandwidth. The downside of shared access is security where experienced hackers may be

able to break into other computers on the same cable network in the neighborhood. Also, as more

users in a neighborhood send and receive information, it is possible that the available bandwidth

for individual users could shrink, slowing speeds similar to the rush hours on a city highway.

It is worth asking about content restrictions before purchasing the cable modem service. Some

cable systems would prefer that you use the cable TV service for watching video, so as to restrict

the amount of streaming video accessible with cable modem! One company is trying to require

cable modem subscribers to take its proprietary content. In other words, one would see what the

company wants him/her to see, and wouldn't be able to venture beyond that area to the whole

Internet. The Consumers Union and the Consumer Federation of America are attempting to stop

these practices by convincing the Federal Communications Commission that cable systems are

common carriers like phone networks. If successful, the FCC could legally prevent cable

companies from putting any restrictions on Internet access.

DSL Cable Modem

Pros Cons Pros Cons

DSL

(digital

subscriber

line) runs

over plain

old

telephone

service

(POTS)

lines.

Internet

traffic

travels on

Setup can be

difficult.

Most telephone

lines weren't run

with data traffic in

mind. Often, they're

not DSL-ready.

Although the

companies are

upgrading their

lines, they do it on

a block-by-block,

building-by-

Cable enters

your house

via the same

lines as cable

television.

The cable

company is

typically

your single

point of

contact for

all

provisioning

Less secure

than DSL.

Line shared

with others in

neighborhood

; speeds vary

accordingly.

Cable users

are on local

loops that

share

bandwidth;

more people

the same

line as

voice

signals; the

two are

separated

by filters

on your

telephone

jack.

Always on.

Far faster

than 56-

kbps dial-

up modem.

Better

security

than cable.

building basis.

Locating and fixing

individual

connectivity

problems can be

extremely difficult.

And since the line

owner and the DSL

service provider

may be separate

entities, finger

pointing is

common.

You need to be

within a certain

distance of the

central office (a

telephone switch)

or you can't get

service. The

distance allowed

varies, but

generally it's

15,000 to 18,000

feet. Insist on

knowing your

distance and the

company's

maximum service

distance. If your

case is borderline,

pursue other

options or wait

(preparing

the line),

installation,

and service.

More

widespread

than DSL.

Potentially

faster than

DSL.

Price break if

you get cable

TV service,

too.

joining your

loop means

less

throughput

available to

you.

until a central

office is closer.

Table 1.3: DSL Vs. Cable Modem

Satellite access

The most widely available high-bandwidth Internet access technology in a geographic sense is

Direct Broadcast Satellite (DBS), also known as Digital Satellite Service (DSS), a competitor to

cable television that 6.6 million Americans were using in 1998. As long as there is a clear line of

sight to the southern sky, a special type of Internet access through DBS service can de ordered.

DBS service requires a small dish (usually 18 to 21 inches across), mounted outdoors to receive

data sent from a stationary satellite. A recent test showed that DBS service providers can deliver

download speeds in the neighborhood of 350 kilobits per second.

The downside is that the competitively-priced services are receive-only, much like the one-way

cable modem setup. A phone line and modem are still needed to request information from the

Internet. Also, satellites are slow for Internet usage. Let's say you have a DBS Internet access

provider and you click a link to pull up a web page. Clicking that link is actually a request for

information that travels out on your phone line, through the ISP, through the normal paths on the

Internet, and is finally answered. The information you requested is then sent 22,300 miles up to

the satellite, and then back down 22,300 more miles to your DBS dish. Even at the speed of light,

this method of communication is slow enough to cause a noticeable lag between click and

response. This is not a big problem for downloads, but if you're a chat junkie, or you use the

Internet for a lot of live, two-way communications, DBS may not be the best choice for you.

Setup is a bit more of a hassle with DBS, too. Getting the DBS hardware to "talk" to your

computer is an issue, and satellites can have technical problems. Historically, they have been

very reliable, but when they quit working, there is no quick fix. It's possible that there's no

service for a while. One may be able to switch to another satellite, possibly requiring the

repositioning of dish and/or retuning satellite receiver.

One of the most well-known companies in DBS Internet access services is charging $179 - $229

for installation, and the dish and satellite modem together cost about $350. Monthly service rates

range from $20 for 25 hours per month of online usage, up to $110 for 200 hours per month.

Additional hours are billed at $1.99. (If you would like to receive DirecTV/USSB television with

your Internet access, you can pay $400 - $500 for a dish that can receive both data and television

signals. This cost includes the satellite modem, but the TV receiver will cost you more.)

1.2 ADVANTAGES AND DISADVANTAGES OF DSL

Network Access Provider Benefits

For the network access provider, the principal benefit of DSL is its ability to permit the rapid

flow of information while using the existing copper wire foundation. Therefore, access providers

do not need to install more copper or lay down miles of expensive fiber, as they would for other

potential solutions.

DSL also eliminates providers' need to constantly upgrade their pricey Class 5 switch

installations. If providers were to continue to provide data and voice services over the same

network, they would have to buy more switches to ensure a congestion-free network.

As widely reported, a typical voice call lasts about five minutes, compared to an average 30

minutes for an Internet call. This means that for every new Internet customer, the carrier would

need to provision six additional lines to guarantee the previous level of service availability to

Plain Old Telephone Service (POTS) users.

DSL bypasses the Class 5 switch for data-only calls, so access providers can accept more traffic

without investing in a huge switch upgrade. With DSL, voice and data paths are separated, which

means that providers can meet the burgeoning need for high-speed data services without

breaking their budgets. Furthermore, by keeping costs low, service providers can make money

off the traditionally low-margin business of providing Internet access.

User Benefits

DSL offers customers access to a range of information services they previously could not receive

through Internet communication. Users can experience high-speed Web browsing and can send

and receive large documents.

Another benefit is to use DSL's always-on capability to receive information, such as news, video

clips and stock quotes, that is pushed toward the user at the time it is generated, according to a

personalized profile, without the need for the user to dial-up.

Always-on capability will help turn the PC into an appliance, making it easier for the mass

consumer market to use. People will be able to walk to a PC and send e-mail, check for the latest

airfare promotion or download a promotional clip for a new movie - and they will be charged on

a usage basis, not a connect-time basis.

Consumers also may benefit by receiving all of their telephone-related services through a single

provider. Customers are buried under a monthly pile of bills from utility service companies. By

being able to receive voice and data services from one source-and paying for them through a

single bill-consumers will gain significant added value from their service provider. This one-stop

shopping will give providers an important means of differentiating their services from those of

competitors such as cable companies.

For the business customer, DSL represents a very compelling investment for several key reasons:

First, DSL provides a cost-effective way for telecommuters and branch offices to access

the corporate network, provisioned via secure virtual private network services.

Additionally, a DSL-based approach can improve the quality and reduce the cost of

communications among employees via videoconferencing. It also can improve

productivity by making intranet applications available to the distributed work force and

by creating a cost-effective communications channel with the corporation's partners via

extranets.

Finally, DSL can displace the costs associated with separate voice, data and video

networks.

To the business, though, a faster pipe does not represent a significant advantage if the service

provider cannot guarantee bandwidth on that pipe. The availability of different classes of

services and quality of service, provisioned at different prices, are essential requirements for the

business. The granularity of these service classes also will help the carrier market its services to

multiple tiers of customers, helping to accelerate the return on its overall investment.

Advantages

Fast - Modems are much faster than analog modems. Different varieties of DSL provide

different maximum speeds, from twice as fast to approximately 125 times faster than a

56.6K analog modem. The only speed limit with DSL is the speed of the Internet and all

the different computers attached to it. The speed can go up to 1.5Mbps.

Doesn’t tie up to phone line - DSL doesn't interfere with phone calls, even though it uses

regular phone line. This means that one can leave the Internet connection open and still

use the phone line for voice calls.

Always on - DSL connection is always available. No more traditional dialing-up

procedure is required and user doesn’t have to be worried being line-dropped while

browsing or downloading. One only need to set up the computer to check for new e-mail

or to browse through the internet.

Reliable - DSL is reliable said to be reliable since it runs on phone line and phone

company networks are among the most reliable in the world, experiencing only minutes

of downtime each year

DSL doesn't necessarily require new wiring; it can use the phone line you already have.

The company that offers DSL will usually provide the modem as part of the installation.

A router, along with a DSL modem, allows up to eight computers to access the Internet

over a single DSL line.

DSL provides the bandwidth you need for high-bandwidth applications. Streaming audio

and video will come across in real-time, rather than interrupted segments.

DSL offers reliable high-speed Internet connections that are far less expensive than other

options such as T1 lines.

DSL is flexible and scalable, ideal for growing business computer networks.

Enable users to work from home, listen to streaming audio or watch streaming video

while working on your computer.

Disadvantages

A DSL connection works better when user is closer to the provider's central office.

The connection is faster for receiving data than it is for sending data over the Internet.

The service is not available everywhere

SECURITY ISSUES

People are often surprised to discover that their DSL (or cable modem) connection is not

secure. If file sharing is turned on, for example, it's possible for someone out on the Internet

to easily hack into your computer and view or modify your files. DSL and cable modem

connections, despite advertising claims to the contrary, are often architected as "shared"

connections. The nature of your connection exposes you to significant danger if you don't

have protection. If you are connecting your network to the Internet via DSL or Cable

Modem, make sure you have a device or software that provides protection. If you have a

single computer, you either want to turn off file-sharing, or better yet, install a personal

firewall. McAfee, among other companies, offers personal firewall products.

ADDRESSING ISSUES

DSL accounts come with either a dynamically assigned TCP/IP address or static address(es).

Most low-cost accounts designed for home offices or very small businesses offer a single

dynamically assigned address. The benefit to the provider is that they can use a smaller pool of

addresses to support a larger number of users. Although these providers will claim that their DSL

service is "always on" the truth is that your connection, when idle, times out. Each time A user

wants to use the Internet after an idle timeout period, he will have to reconnect and obtain an IP

address. Granted, this may take a couple of seconds, but he's not really always on! A common

protocol used to provide your DSL connection and IP address in this scenario is the Point to

Point Protocol over Ethernet (PPPoE). The provider will give the subscribers PPPoE software for

their PC or Macintosh. Other software available on the Internet can also be used. With a

dynamically assigned address, it is more difficult to share a DSL account with multiple users on

the same LAN, although not impossible. It is also more difficult to host an email server, web site

or FTP site on DSL connection, although again, not impossible. Slightly more expensive

accounts come with at least one fixed IP address. With fixed addresses, it is easier to share the

DSL connection and host email and web servers.

Various manufacturers

NetGear

Motorola

TRENDnet

Linksys

Zoom

Cisco

Siemens

D-Link

Actiontec

Qwest

Integrated Services Digital Network:

ISDN stands for Integrated Services Digital Network. It is a design for a completely digital telephone/telecommunications network. It is designed to carry voice, data, images, video everything you could ever need.[10] It is also designed to provide a single interface (in terms of both hardware and communication protocols) for hooking up your phone, your fax machine, your computer, your videophone, your video-on-demand. ISDN is not restricted to public telephone networks alone; it may be transmitted via packet switched networks, telex, CATV networks, etc. With ISDN, voice and data are carried by bearer channels (B channels) occupying a bandwidth of 64 kb/s (bits per second). Some switches limit B channels to a capacity of 56 kb/s. A data channel (D channel) handles signaling at 16 kb/s or 64 kb/s, depending on the service type. Note that, in ISDN terminology, "k" means 1000 (103), not 1024 (210) as in many computer application.[11][12]

ISDN Configurations:

ISDN comes with two type of channels 'B' and 'D' channels. The B or 'bearer' channels are used to carry the payload data which may be voice and / or data, and the D or 'Delta' channel is intended for signalling and control, although it may also be used for data under some circumstances. There are two ISDN access levels (BRI and PRI) which can be provided using ISDN.[13]

BRI (Basic Rate Interface):

This consists of two B channels, each of which provides a bandwidth of 64 kbps under most

circumstances. One D channel with a bandwidth of 16 kbps is also provided. Together this

configuration is often referred to as 2B+D.[14]

The basic rate lines connect to the network using a standard twisted pair of copper wires. The

data can then be transmitted simultaneously in both directions to provide full duplex operation.

The data stream is carried as two B channels as mentioned above, each of which carry 64 kbps (8

k bytes per second). This data is interleaved with the D channel data and this is used for call

management: setting up, clearing down of calls, and some additional data to maintain

synchronization and monitoring of the line. To access BRI service, it is necessary to subscribe to

an ISDN phone line. Customer must be within 18000 feet (about 3.4 miles or 5.5 km) of the

telephone company central office for BRI service; beyond that, expensive repeater devices are

required, or ISDN service may not be available at all Customers will also need special equipment

to communicate with the phone company switch and with other ISDN devices.[15] These devices

include ISDN Terminal Adapters (sometimes called, incorrectly, "ISDN Modems") and ISDN

Routers.

The network end of the line is referred to as the 'Line Termination' (LT) while the user end acts

as a termination for the network and is referred to as the 'Network Termination' (NT). Within

Europe and Australia, the NT physically exists as a small connection box usually attached to a

wall etc, and it converts the two wire line (U interface) coming in from the network to four wires

(S/T interface or S bus).[16] The S/T interface allows up to eight items or 'terminal equipments to

be connected, although only two may be used at any time. The terminal equipments may be

telephones, computers, etc, and they are connected in what is termed a point to point

configuration. In Europe the ISDN line provides up to about 1 watt of power that enables the NT

to be run, and also enables a basic ISDN phone to be used for emergency calls. [17[18] In North

America a slightly different approach may be adopted in that the terminal equipment may be

directly connected to the network in a point to point configuration as this saves the cost of a

network termination unit, but it restricts the flexibility. Additionally power is not normally

provided.[19]

Primary Rate Interface:

PRI lines is intended for users with greater capacity requirements. This makes it much more

expensive, because of much higher data speeds and different wiring. It is a standardized

telecommunications service level within the Integrated Services Digital Network (ISDN)

specification for carrying multiple DS0 voice and data transmissions between a network and a

user. PRI is the standard for providing telecommunication services to offices. It is based on the

T-carrier (T1) line in the US and Canada, and the E-carrier (E1) line in Europe.[20]

European "E1" primary rate lines have 30 B-channels, one D-channel and a synchronization

channel (total 2.048 Mbit/s). American "T1" primary rate lines have 23 B-channels and one D-

channel (total 1.544 Mbit/s). Cheaper lines are often available that have some of the B-channels

disabled but are otherwise identical. Primary rate connections are presented to the user on four

wires - one pair for each direction.[21] They are usually 120 ohm "balanced" twisted pairs using

standard network cable, but older installations may use 75 ohm "unbalanced" coaxial cables.

Devices called "baluns" can convert between the two types.

Primary rate lines are mainly used to connect to a private branch exchange (PBX) in an office or

hotel. The PBX then typically provides many POTS telephone lines or basic rate ISDN lines to

the users. PRI is a local exchange access service which provides a high speed (T-1 or 1.5 Mbps)

direct digital connection. This connection provides customers access to voice and data services

such as WATS, 800 service, and circuit switched data on a single circuit, which eliminates the

need for individual dedicated circuits.[22] The access structure for the Primary Rate Interface is a

digital carrier system using time division multiplexing (TDM). In India this system is the E-1

carrier system. The channel structure on the primary rate is variable. Depending on the tariff and

the provisioning options, the PRI can contain B-channels, D-channels, and H-channels. In T-

carrier systems the PRI supports a 32-time-slot digital carrier system in which time slot 0 is used

for framing and synchronization, and time slot 16 is used for signaling. The other 30 time slots

are used as traffic carrying channels. T1 carrier has 24 time slots, which are assigned on an as-

needed basis for the various channel types.[23] The most common configuration is a 23B+D

configuration comprising 23 B-channels and one D-channel (for signaling). If multiple PRIs are

deployed to the same device, the D-channel of one PRI can provide signaling support for the B-

channels of another PRI. It is common to have at least 2 D-channels in such a group of PRI, but

the remaining PRIs can be deployed as 24B comprising 24 B-channels and no D-channel.

Features of a PRI[24]:

There is only one line physically terminating on the customer PBX but still a PRI line can

receive/send 30 calls simultaneously! A PRI line is end to end digital circuit.

It provides digital service integrating voice, data, video and packet switch data on a single

access loop.

Multi-channel, digital pipes supporting different services on separate channels.

A PRI (Primary Rate Interface) line is a form of ISDN (Integrated Services Digital

Network) line which is a telecommunication standard that enables traditional phone lines

to carry voice, data and video traffic, among others.[25]

A PRI circuit consists of two pairs of copper lines terminating on a modem from a service

provider premises to the customer premises. It uses multiplexing/de-multiplexing

techniques to carry more than one channel in a single circuit. There are two common

forms of PRI lines – E1 and T1. Each channel in a PRI line provides 64 Kbps for data

transmission.

A PRI line can connect to both Analog/Mixed EPABX systems and also the newer IP

PBX systems. A PRI Card / Interface might be required to terminate the PRI circuit on

the PBX.

A PRI line can also be used to connect two PBX systems thereby providing 30 channels

between them for interoperability.

Network Architecture:

Fig. Primary Rate Interface Architecture

In a PRI system at the local exchange optical fibers are used to carry the data and then it is connected to a switching device which has ports defined 1-24 for transmission and 26-52 for receiving. It also grants every user a specific identity depending on the port codes generated by

the service provider. A copper wire is used to connect the lines from PRI to a PRI modem. This modem is connected through copper wires from exchange to the receiver PRI modem installed at customer’s premises like hotels, banks and offices A PRI Card is used to connect PRI lines to IP PBX/ IP Telephony Server so that all the IP Phones/ Analog phones (extensions) can make outgoing calls or receive incoming calls using it.

In an Analog/IP PBX, one needs to procure a specialized PRI Card that fits into one of the empty slots of the PBX in order to connect the PRI Line. This Card is mostly proprietary to the specific PBX vendor. But with Soft-Switches (that run using standard server hardware), one can purchase a generic PRI Card to interface/ connect the PRI line.

The generic PRI Cards are generally vendor neutral and they are inserted into PCI 3.3V/ PCI 5V/ PCI Express (empty) Slots in the server. There are different PRI Cards for each type of PCI interface.

One PRI Card can have 1,2 or 4 Slots to connect to 1,2 or 4 PRI lines. Some PRI Cards come with echo cancellation modules (at extra cost) in order to reduce the echo generated when Digital Signals are converted to IP & vice versa. It is recommended to buy PRI Cards along with Echo Cancellation modules.[26]

As in DSL receiver and DSLAM sync to begin connection, here instead of DSLAM these two

modem synchronizes and provide connection. At the customer end a PBX or EPBAX is

connected to the PRI modem which is used to make multiple telephone connections. A PBX can

split 1 voice line into 30 different lines and thus customers could have 30 different numbers at

their offices. For internet routers are connected to the modem depending on area to be covered

and signal strength.

A PBX/EPABX allows more than one user to be on a telephone network, based on the idea that

not everybody uses their local phone extension at the same time. A PBX is typically installed in

offices and homes. The user will have more than one-telephone number which benefits the user

because the user will not have to pay for another separate line from the telephone companies.

Calls can be routed internally to the PBX. A PBX baud rate speed is usually about 9.6Kpbs. This

is not as fast as ISDN, as ISDN can be a guaranteed 64Kbps.

In a PBX environment you need to dial a prefix number to connect to the external public phone

network (this prefix number is programmed by the PBX). Once realizing that a prefix number is

dialed (it is the first integer in the phone number) the PBX knows that the caller wants to

communicate to an external number outside the PBX.

Advantages of PRI Lines:

If thirty separate analog trunks are taken instead of one PRI line

The cost of terminating all the thirty analog trunk lines becomes higher than terminating

one PRI line.

There would be thirty rentals to be paid instead of one consolidated lower rental for a

PRI line.

Some analog trunks might be used more (uneven distribution of calls) and some lines

may not have even crossed the free calls limit.

Terminating 30 analog trunks in a PBX also requires more free slots/cards than the one

slot usually occupied by one or even two PRI trunk cards.

1. Direct Inward Dialing: For each PRI line, the service provider would provide more

around 100-500 numbers which can be used by outsiders to call the extension directly,

instead of having to go through the PBX Auto-attendant.

2. Caller ID: Since all the extensions have their own number, this unique number will be

displayed in the phones that they are calling to. Some call centre applications are based

on the unique caller ID number for differentiation of services.

3. It is possible to offer both voice and data in the PRI line. Some service providers have

dynamic offerings where data is transmitted in all the channels that are free (not occupied

by voice) at that given point of time.

4. Call hunting (Where the call lands in any channel that is free, instead of the called

number specifically – For example, if there is one board number but a number of people

are calling in at the same time and still a channel is allocated to them .With analog lines,

if one number is busy, they need to call in another number manually) is possible by

default with a PRI connection, but for the analog trunks this facility needs to be extended

by the service provider and enabled on the PBX, involving additional cost at times.

5. PRI lines can be used for voice connectivity, data connectivity, video conferencing,

faxing, and all the above can be done simultaneously too (on different channels).

6. PRI lines are end-to-end digital lines and hence the clarity is much better than analog

trunk lines.

7. Since they are digital lines, PRI lines are more reliable and trouble shooting is also

easier with them. They are mostly on a fiber core ring and hence there is some

redundancy.

8. It is harder to tap into digital lines and listen to the conversations.

9. There are flexible billing options available with most of the PRI service providers. The

billing can be centralized or distributed (department wise, etc).

10. PRI lines take lesser time to establish calls then analog trunk lines.

11. Some service providers offer flexible plans where instead of the full 30 channels, they

provide and charge for only 20 channels etc. This makes PRI lines more economical for

smaller companies.

Disadvantages of PRI lines:

1. A PRI line is economical only if the minimum rental charged by the service provider

for a PRI line is more than the average value of calls with analog trunk lines every

month in an organization. Otherwise, the usage may not even cross the free call value

provided by the service provider for a PRI line.

2. A PRI line is not so economical for long distance/ international calling. An ITSP or

SIP trunk service provider who takes the calls over the internet might charge much lesser

for international long distance calls.

3. Inter branch communication between the branches is not free of cost with PRI lines

(Some PRI service providers provide this facility, but all your branches may need to have

PRI lines from the same service provider and there also might be a minimum revenue

commitment for the same). With VOIP systems, inter-branch communication can be done

over internet/ leased lines hence reducing the cost drastically.

4. The cost of a single PRI card to connect to your EPABX/ IP PBX is still very high.

Most of these cards are proprietary, meaning you can buy them only from your EPABX

vendor.

1. (http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/adsl.htm

2. Andrew R. Reichert, William J. Schirmer, Nicholas M. Esser, Bradley R. Nelson, Lauren T. May, Stewart C. Brown.

"System for communicating digital data on a standard office telephone system". US Patent 4,785,448. Filed February

23, 1987. Issued November 15, 1988.

3. http://webcache.googleusercontent.com/search?q=cache:tt_NpzRaIPcJ:www.pulsewan.com/data101/pdfs/

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11. http://searchenterprisewan.techtarget.com/definition/ISDN

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isdn.pdf+&hl=en&gl=in&pid=bl&srcid=ADGEESh-

l5rajupcorWXkSf9Zh515svFkP00GPyO2NJ9uigYup1gQBnXeky3naUWH34jvwuYKrhJraAS4fXcrcJTdNDlpiGHkWxGnyJ3Q

4CwPdNSlSerJ5Mo3LeiuUBEJUqXkzwgD1WX&sig=AHIEtbSKkaW2qL3I7FbHSIqu6JEzmNCUbw

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14. http://www.tij.co.jp/general/jp/docs/lit/getliterature.tsp?literatureNumber=snla018&fileType=pdf

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17. http://searchnetworking.techtarget.com/definition/Basic-Rate-Interface

18. http://www.linktionary.com/b/bri.html

19. http://www.tij.co.jp/general/jp/docs/lit/getliterature.tsp?literatureNumber=snla018&fileType=pdf

20. http://en.wikipedia.org/wiki/Primary_Rate_Interface

21. http://www.webopedia.com/TERM/P/PRI.html

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23. http://www.t1everywhere.com/isdn-pri.html

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%2Fpri.pdf&ei=DYohUPaXFsPhrAezloHABQ&usg=AFQjCNEmOeFsxClWaMWLs3vT5DO1Kvxzbw&sig2=U1KVl_0bLLw

hDduldnSBmw

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26. www.excitingip.com/2573/pri-cards-analog-interface-cards-connectivity-architecture-diagram-in-voip-ip-telephony/