Tài liệu ADSL Residential and SOHO Installations ppt

Previous Deployment Attempts Full-rate ADSL The initial ANSI T1.413 and ITU G.992.1 from the ITU G.dmt standards group full-rate ADSL standards stated that ADSL could enable the simultan

Asymmetric Digital Subscriber Line (ADSL) deployment to Residential and Small Office/Home Office

(SOHO) environments has accelerated the development of appropriate splitters and filters This

Application Note briefly reviews the history and status of these devices, and provides guidelines for

their selection and use in typical installations

Previous Deployment Attempts

Full-rate ADSL

The initial ANSI T1.413 and ITU G.992.1 (from the ITU G.dmt standards group) full-rate ADSL

standards stated that ADSL could enable the simultaneous transmission of analog voice and digital

data over ordinary copper wire To add high-speed data transmission, however, each subscriber line

would require the installation of a splitter at the Network Interface Device (NID) Figure 1 shows how

the voice channel was routed as usual through the existing POTS line while the ADSL channel was

distributed through new data wiring (such as Category 5) To separate the lower-frequency analog

voice channel at 300Hz~4kHz from the higher-frequency ADSL digital data channel at

25kHz~1.1MHz, the splitter would need to use simple passive high- and low-pass frequency filters

Splitters and Microfilters

ADSL Residential and SOHO Installations

Under this plan, ADSL data transmission required a truck roll by the service provider to install the splitter and new data wiring ADSL deployment was consequently viewed as being too costly and too complex

NID with Splitter Subscriber

line

POTS + ADSL

POTS

ADSL

FAX

ADSL modem

Figure 1 Use of Splitters with Full-rate ADSL

Figure 2 G.lite Splitterless ADSL Deployment

NID Subscriber

line

Shared:

- POTS

- ADSL POTS + ADSL

POTS + ADSL FAX

ADSL Modem

G.lite

Subsequently, the ITU G.lite standards group developed G.lite (G.992.2), an enhanced ADSL specification, which included new features to overcome these perceived barriers These features included:

• Reduced maximum data rate and frequency bandwidth, which lessens the likelihood of encountering problems with reflections or attenuation on the wiring

• Fast Retrain, which rapidly adjusts ADSL modems to the off-hook or on-hook conditions of analog telephones, modems, and FAX devices sharing the premises wiring

• G.handshake (G.hs) which enables G.lite modems to automatically negotiate the use of these features with the central office equipment (G.hs is also a feature of G.dmt)

Because of these enhancements, the G.lite-compliant solutions could be installed without the addition of either the external splitter or data wiring (Figure 2) The previous barriers to rapid deployment had been successfully surmounted The resulting installations were called "splitterless" or "no-truck-roll" deployments

Although the promise of G.lite is very appealing to service providers, occasional problems were still encountered between analog and ADSL digital devices sharing premises wiring:

• Nonlinear impedance of some analog telephones and other devices caused distortion of ADSL signals

• Audio noise in the voice channel was generated by down conversion from the ADSL signals, due to intermodulation distortion caused by the nonlinear impedances

• Rapid impedance changes of telephones and other analog devices as they switched between

"on-hook" and "off-hook" modes caused many data errors, and even the "fast retraining"

of ADSL modems was time consuming, usually requiring a large fraction of a second Interference could consequently occur between the voice and data signals, even though they were originally transmitted in very different frequency bands Estimates based on early deployments indicate that over half of customer premises have at least one telephony device causing interference

Internal microfilters, splitters, and distributed splitters have recently been developed for those cases They preserve the benefits of G.lite easy installation, while assuring that interference between voice and data channels will not be a problem The following sections of this Application Note explain the selection and application of these devices

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Internal Microsplitter

If the installation has only a single telephone and a single ADSL modem, then an internal microsplitter can be employed As shown in Figure 3, the user installs the microsplitter between the wall jack and the two devices

NID

Single POTS device

Microsplitter

Subscriber Line

POTS + ADSL

POTS POTS + ADSL

ADSL modem

High-frequency signals are directed to the ADSL modem, and low-frequency signals are directed to the telephone or other analog voice-channel device Since the high-frequency ADSL signals do not reach the telephone, there can be no distortion of the ADSL signal, any major impedance changes as the telephone switches between on-hook and off-hook modes, and no intermodulation distortion

Internal microsplitters are small, low cost devices that do not require a power source (Figure 4) They typically have three standard RJ-11 telephone jacks or plugs for easy connection by the subscriber to standard modular telephone wiring

Figure 3 Use of an Internal Microsplitter

PH ON E AD SL

PO TS /A DS

L S plitter

LIN E

Figure 4 Internal Microsplitter

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Internal microsplitters are an excellent solution for premises with only a single telephone jack or connection A single microsplitter, installed at the single telephone jack or connection, is needed for each residence In addition, many residences have a second telephone line with only one jack, often for a business telephone, FAX, or Internet connection through an analog modem The microsplitter is also a convenient solution for adding ADSL in these situations

Note that a single microsplitter is not adequate for the common situation where there is one ADSL modem, but several telephones, analog modems, or FAX devices (Figure 5) The other analog devices may still cause interference due to their connection to wiring shared with an ADSL modem

NID

Additional phones that can cause interference

Subscriber

line POTS + ADSL Microsplitter

POTS + ADSL

ADSL modem

Figure 5 Incorrect Deployment of an Internal Microsplitter

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Internal Microfilter

If the installation has several telephones or other analog devices, then an internal microfilter can be employed at each analog device that presents a problem (Figure 6)

NID Subscriber

line POTS + ADSL

POTS + ADSL

ADSL modem FAX

Microfilter Microfilter

Figure 6 Use of an Internal Microsplitter

Internal microfilters are small, passive (no power source needed), and very low cost devices (Figure 7) They typically have a standard RJ-11 telephone jack or plug on each end for easy connection by the subscriber to standard modular telephone wiring

Dual jacks

Plug and jack

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Since ADSL modems have built-in basic filtering to reject low-frequency voice-band and ringing signals, the internal microfilter technique has essentially the same result as the external or internal splitter method Each device only sees the signals in the appropriate frequency band As a result, none of the problems previously mentioned can occur

The use of internal microfilters has the additional advantage over the external splitter method in that all devices can share the premises wiring This allows the use of any telephone jack for analog

telephony devices, ADSL modems, or both No additional data wiring is required

Typically, up to five internal microfilters can be used at a single site Versions are available for North American standard wall-mount and desktop telephones

Internal Distributed Microsplitter

Internal microfilters, however, are limited Since the implementation of an internal microfilter is typically

a simple passive two-pole filter, its electrical performance is limited This leads to limitations on the number of filters, which may be used in a single installation, as well as limitations in the level of electrical isolation of frequency bands Estimates based on early deployments indicate that up to 25 percent of all premises will need stronger measures

To resolve these limitations for installations requiring multiple analog devices, a new generation of filters is being developed This new generation may provide up to five-pole filtering, as well as other advanced functions These filters are so sophisticated that they provide all the performance of external splitters But they do not require the truck roll or additional data wiring Consequently, they are often called "Distributed Microsplitters."

Distributed Microsplitters are used in exactly the same manner as Internal Microfilters (see Figure 6) However, they are slightly larger and a bit more expensive (Figure 8) Distributed Microsplitters should

be used for those installations where the largest number or most severely offending telephone devices are encountered

Figure 8 Distributed Microsplitter

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Recommended Selection and Application

Microsplitters

• Premises with single telephone jack or connection

• Second lines with a single telephone jack or connection

• One per premises

Microfilters

• Premises with multiple telephone jacks or connections used for telephony devices

• One per offending device, or more simply, one per telephony device

• No more than 5 microfilters per premises

Distributed Microsplitters

• Premises with numerous or severely offending telephony devices

• One per severely offending device; or more simply, one per telephony device

• No more than seven microfilters per premise

External Splitter

• Premises with numerous or severely offending telephony devices

• One per subscriber line

• No arbitrary limit on telephony devices per premises

ADC Filter and Splitter Products

ADC offers a family of filter and splitter products that provide a solution for the most commonly encountered environment and installation needs The family currently includes the following products:

Future ADC product releases include an internal wall-mount microfilter, internal European microfilter, and an internal “distributed microsplitter” microfilter (Contact your local ADC sales representative.)

ADC Telecommunications, Inc., P.O Box 1101, Minneapolis, Minnesota USA 55440-1101

Specifications published here are current as of the date of publication of this document Because we are continuously improving our products, ADC reserves the right to change specifications without prior notice At any time, you may verify product specifications by

Web Site: www.adc.com

From North America, Call Toll Free: 1-800-366-3891 • Outside of North America: +1-952-938-8080 Fax: +1-952-946-3292 For a complete listing of ADC's global sales office locations, please refer to our web site.

This document is intended for planning purposes only It therefore does not modify or supplement any ADC specifications, price quotes, or warranties relating to the products or services mentioned herein Data quoted in this document are based on typical DSL performance As such, this data cannot be considered applicable to any specific order or contract ADC cannot assume responisibility for any consequences resulting from the use of this documentation The information contained herein is subject to change at ADC’s discretion