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Uses of a DAA in VoIP Systems rD


									    VoIP Service Provider Strategies Drive Differing CPE Product Architectures
                               By Mark Thompson
                             Silicon Laboratories Inc.

As voice over IP gains momentum as a mainstream form of consumer and enterprise
communication, service providers are gathering customer feedback, learning lessons from
current generation customer premise equipment (CPE) products and using that
knowledge to refine next generation products to improve the VoIP experience. Cable
companies, telephone companies who provide ADSL service (incumbent local exchange
carriers, or ILECS) and non-incumbent VoIP start-ups that do not provide broadband
service are all utilizing different strategies to win the same customers, impacting the
design of VoIP CPE equipment.

VoIP Start-Ups
In the past few years, numerous companies were created that intended to compete with
ILECs by providing telephone service to consumers and businesses without relying on
the existing ILEC networks. The strategy of these new start-ups is to offer VoIP service
to consumers and businesses over existing broadband connections. The broadband
connection can be cable, copper or wireless from any provider. The ILECs are unable to
charge any fees to these start-ups because there is no leasing of lines or equipment

When a VoIP service provider gets a new customer, a terminal adaptor (TA) is usually
sent to the customer to enable the VoIP service. This device is simply a bridge between a
standard analog telephone and the digital broadband network. One function of the TA is
to act like a telephone central office to any analog phone and provide all normal functions
consumers expect for telephones, including powering and ringing the phone, converting
analog signals to digital and vice versa. Typically a subscriber line interface circuit (SLIC)
and a codec provide these functions. Today SLICs and codecs can be purchased as
separate ICs or as a single, monolithic CMOS IC. Another function of a TA is to interface
to a LAN port such as Ethernet. This enables the user of an analog telephone to
communicate to the outside world over the packet data network. A diagram of a TA is
shown in Figure 1.

                                                                      SLIC/Codec                 RJ11
      Network Processor                  Voice DSP
                                                                      SLIC/Codec                 RJ11

                                                                    Magnetics                    RJ45
                                        Ethernet Switch
                                                                     Magnetics                   RJ45

Figure 1: Diagram of a typical TA.
Because VoIP is becoming more prevalent throughout the world, equipment
manufacturers want to capture economies of scale by building globally-compliant
products that function equally in all regions. To accomplish this, the manufacturer has to
pay careful attention to the compliance of the SLIC to global telephony specifications.
Fixed function, standalone SLICs that might have been used in early generation products
require multiple external discrete components to be changed when different country
telephony specifications need to be met. Newer products that combine a CMOS SLIC and
codec into a single IC allow for greater software programmability, enabling a single
design that adjusts to different telephony specifications but does not change any external
components. With this solution, VoIP service providers have a globally-compliant
solution that allows customers to take their equipment wherever they travel.

Another trend in TAs that also applies to the entire VoIP industry is the desire to
differentiate the VoIP offering from standard telephony service provided by the RBOCs.
The primary differentiating factors for VoIP to date have been increased features
included in the standard offering and lower pricing. One additional way to differentiate
VoIP service from standard POTS service is to offer wideband telephony. Standard
POTS telephones are inherently limited in frequency response to a 200 Hzto 4 kHz
bandwidth. While the human ear can theoretically hear from 20 Hz to 20 kHz, most
people have come to accept this frequency response limitation of the telephone system.
However, by offering a wider frequency response, VoIP service providers can offer a
better sounding telephone system that offers more realistic sounding voice and music for
users. The standard wideband offering increases the frequency response of a telephone
call to 50 Hz to 7 kHz, which provides a much richer fidelity experience for the user.
Now VoIP service providers can claim to improve the user experience, providing further
incentive for consumers and businesses to switch to VoIP service.

While TAs are commonly used today, IP telephones are also becoming common. An IP
phone is a digital telephone that does not need a SLIC. Analog inputs are immediately
converted to digital data, and all normal functions of a telephone are performed digitally
from a central processor.

VoIP startups such as Vonage and 8x8 were the first to introduce VoIP service to
consumers on a wide scale. They currently have the majority of market share in many
parts of the world, including the US.

Cable companies
Recently, cable companies have gotten aggressive in rolling out VoIP services. The
primary reason for this lies in the central strategy of cable companies: to completely
eliminate ILECs. By offering traditional cable video, data services (cable broadband) and
voice telephony services, cable companies can provide the “triple play” of services. Cable
companies have been providing video and broadband data services long enough to
establish an adequate reputation of reliability for both. In establishing the IP-based
system to support broadband data services, cable companies have built an infrastructure
that is readily usable for voice services, albeit in a different way from traditional ILECs.
The biggest challenge facing cable companies today is the need to establish the same
reputation for reliability and quality of standard telephone services while using their IP-
based infrastructure.

Similar to VoIP startups described above, many cable companies are using TAs as they
offer VoIP services. This allows a cable company to avoid disruption of its established
video and data services by trying to combine multiple functions into one set of hardware.
However, as VoIP becomes mainstream, voice-enabled cable modems will become the
de-facto standard. A diagram of a voice-enabled cable modem is shown in Figure 2.

                                                                 SLIC/Codec             RJ11
  DOCSIS Cable                      Voice DSP
  Modem and
  Network Processor                                              SLIC/Codec             RJ11

                                                               Magnetics                RJ45
                                   Ethernet Switch
                                                               Magnetics                RJ45

                         Cable Tuner            Coax

Figure 2: Block diagram of a voice-enabled cable modem.

As voice-enabled cable modems are used more widely, certain trends can be observed.
One obvious trend is the desire for cost-reduced TAs and voice-enabled cable modems.
Much like VoIP service provider startups, cable companies typically provide the user
with the hardware and do not require the user to purchase a voice-enabled cable modem.
Achieving the lowest cost hardware possible is tantamount to increasing profitability.
Another trend for cable companies is the use of battery backup in cable modems. To
achieve a reputation for quality and reliability, cable companies must ensure that their
telephones will operate during a power outage. Many of the largest cable modem
manufacturers today offer versions of their products with the option of having one or
more batteries installed to provide uninterrupted telephony service for many hours
without power.

Along with this is the trend towards lower power electronic components. Battery backup
is only useful as long as the battery stays charged; if the components of the voice-enabled
cable modem drain the backup battery too quickly, consumers will be dissatisfied. While
power can be reduced in the digital components of the system by continuing to shrink the
process geometry, architectural innovations must be achieved to lower the power in the
heavily analog SLIC and codec devices.

Typical SLIC and codec systems require at least three battery supplies: one 3 V or 5 V
supply for the codec, one high-voltage supply for the SLIC to provide voltage to ring a
phone and a third medium voltage supply to provide enough headroom for proper audio
transmission over a reasonable length line. The voltage levels of the two SLIC supplies
are traditionally fixed for standalone, non-programmable SLICs. This can lead to
significant amounts of power being wasted because the voltage level of these fixed
supplies must be designed to operate correctly on the worst case load and loop length
possible. However, in most cases, users won’t have a worst case load and loop length on
their telephone line, so the excess power that is designed into the system is then wasted
and dissipated as heat. This can present a large drain on any battery backup system, thus
shortening the amount of time the system will operate during a power outage. One
solution for this is to use a tracking battery supply.

In products that integrate a CMOS SLIC and codec into one supply, a dc/dc power supply
controller can also be integrated into this IC to provide the necessary battery voltages to
ring a phone and transmit audio on the line. Tracking battery supplies sense how much
voltage is needed for the actual line that is being used and adjusts the battery supply to
that voltage and no more. This significantly minimizes the amount of power that is
wasted while the phone is off-hook. By using a tracking battery supply integrated into the
SLIC/codec device, battery backup times can be increased, maximizing the amount of
time phone service will be available during a power outage.

Incumbent local exchange carriers (ILECs)
ILECs throughout the world have the most to lose when it comes to VoIP services.
Standard telephony service has traditionally been implemented using switched networks,
and the large investments that the ILECs have in these existing networks drive them to
utilize them as much as possible. ILECs have been the last to implement VoIP services
for this reason. However, ILECs have been watching the number of telephone lines
deployed decline for several years now, and have finally decided that to keep their
customer base, they need to attempt to match the triple play offering from cable
companies. In the short term, ILECs are partnering with satellite television providers to
achieve the triple-play package. Longer term, ILECs are attempting to build out an
optical fiber infrastructure to the home or neighborhood in order to provide video
services directly. Interestingly, although ILECs already offer switched-network based
telephony services, offering VoIP service for telephony has also become an important
requirement. ILECs are positioning VoIP as an add-on to traditional POTS services. They
expect their customers to pay for a standard POTS land-line for local calls, and then to
pay for a VoIP plan for certain long-distance calls. This way, the ILECs continue to
utilize their investment in their existing switched networks, but also fend off the
onslaught of startup VoIP service providers and cable companies by offering VoIP
service to lower the cost of long distance calls.

Similar to cable companies, ILECs often use TAs to implement VoIP services quickly
without disrupting existing setups. However, since ILECs utilize ADSL to achieve
broadband service, it is inevitable that voice-enabled ADSL modems will become the de-
facto standard hardware used by ILECs around the world. This is already the case in
Japan where VoIP service has been offered for some time by Yahoo Broadband and
others. A diagram of a voice-enabled ADSL modem is shown in Figure 3.
                                                               SLIC/Codec              RJ11
 ADSL Modem and                    Voice DSP
 Network Processor
                                                               SLIC/Codec             RJ11

                                                              Magnetics               RJ45
                                  Ethernet Switch
                                                              Magnetics               RJ45

                        ADSL AFE              RJ11

Figure 3: Block diagram of a voice-enabled ADSL modem.

ILECs have an advantage over VoIP startups and cable companies by having the
reliability and dependability of their switched networks for telephony service. Consumers,
particularly in the US and Europe, are used to the telephones in their homes working
virtually 100 percent of the time, even if the power has gone out or the weather is bad.
Also, because of the dedicated connection that is formed in a switched network between
two calling parties, there is usually very little delay or echo in a conversation. IP-based
networks were designed to carry data, not real-time voice, and voice packets can actually
be received out of order and need reassembling. These types of phenomenon can produce
longer delay times or even echoes during a conversation. While the quality of VoIP calls
today has greatly improved over early VoIP service offerings, it still has yet to achieve
the consistency of quality that the standard switched network has. This reputation for
quality service can be exploited by an ILEC by offering standard telephony with VoIP as
an added service, whereas a cable company or VoIP startup can only offer VoIP and have
yet to prove that reliable telephony service can be delivered.

When examining the hardware used by ILECs to provide VoIP service, several
distinctions can be made when compared to other VoIP service providers. As expected,
ILECs are also seeking the lowest cost solution, as TAs and voice-enabled ADSL
modems are provided to users without additional fees. However, these products do not
have battery backup capability like voice-enabled cable modems do because this is
already provided through a standard telephone line. Thus, if the VoIP service is
unavailable, consumers will not be without telephone service. Reducing the power of the
CPE equipment is still important from a global energy consumption perspective, so a
tracking battery supply is preferred for the SLIC function. Wideband audio support is
also desired by ILECs, not because they want to compete against their standard telephony
offering, but because of the need to compete with cable companies and VoIP startups.

Perhaps the biggest difference in CPE between ILECs and other companies is the
existence of one or more direct access arrangements (DAAs) in the CPE equipment.
DAAs are being designed into TAs and VoDSL modems to provide a marriage of old and
new – standard telephone service and VoIP. Thus, these VoIP products have both a
digital interface to a packet-based network and a telephone line interface to the traditional
switched network operated by the local telephone company. This functionality provides a
number of benefits to consumers.

What is a DAA?
A DAA is a telephone line interface that terminates a traditional twisted-pair telephone
line and imitates an analog phone in applications such as analog modems, fax machines,
telephones and answering machines. The DAA electrically isolates the phone line and
central office (CO) equipment from the CPE, which makes it less likely that failure of
one would permanently affect the other. The DAA is also important in enabling various
features such as caller ID, ring detection and numerical dialing. In a VoIP box, the DAA
can connect a user to the switched network to make a standard telephone call, or it can
also convert a telephone call from a digital packet-based data network to an analog signal
over the local switched network, and vice versa. DAAs must meet the electrical
specifications dictated by the regulatory authority in the country of service. Products
must be tested and certified to meet each country’s specifications before being shipped
into the target country.

Consumer Benefits of a DAA in a VoIP CPE Product
Integrating a DAA into a VoIP CPE product provides a number of ease-of-use and
security benefits to the consumer. For example, DAAs provide backup standard
telephone service if the broadband service becomes inoperable or overly congested. It can
also provide a failover connection to the switched network during a power outage.
Telephone company COs provide battery backup power that allows the telephones in
residences to continue to operate even though the power has gone out.

Access to the switched network is also important for emergency, or “911”, call routing
with location services and for compatibility with residential alarm systems. If someone is
placing an emergency call, it is imperative that this call go through with no disruptions or
degradation of service. Many consumers prefer that the CPE detect if an emergency call
is being placed and route that call through the DAA in the CPE to the switched network
instead of over the IP network. Authorities in the US can determine the exact location of
a calling party placing a 911 call on the switched network, but this is not always the case
with a VoIP call since an individual can select a VoIP telephone number in one of many
areas in the world, regardless of where that individual resides. Some VoIP services allow
a subscriber to register their physical location upon signing up with the service, and if the
subscriber does not move locations, will allow the VoIP service provider to route a 911
call to emergency services and report a physical location for that number. However, since
VoIP equipment is portable and can be connected to any broadband network, a physical
location on file at the VoIP service provider for a given telephone number may not be
accurate. Thus, it is virtually impossible for authorities to guarantee they will know from
where a VoIP emergency call is being placed. It has also been reported that many
residential alarm systems don’t operate correctly with a VoIP system. So if a consumer
wants to keep their alarm system working, they will have to keep their standard telephone
line connection in addition to VoIP service. ILECs see this as a positive, while VoIP
startups and cable companies do not.

A DAA also provides the ability to set up a VoIP call server enabling low-cost long
distance phone calls to one or more locations. If an individual wants to make regular calls
to a particular area code, VoIP can be used to call from anywhere in the world to a call
server capable of receiving the packet-based phone calls. Once the call is accepted at the
call server location, the call can be completed using local telephone rates over the
switched network, which requires a DAA interface. If a private data network is used,
these VoIP calls could potentially be free of charge, although the cost of maintaining a
dedicated data network would be required.

Voice-enabled broadband products used by the telephone companies will utilize DAAs to
achieve the ability to offer both IP and traditional phone services. In these cases, certain
DAA features are important:
   - On-hook intrusion detection – to help determine if another parallel handset has
       picked up
   - Type I and II caller ID capability
   - Polarity reversal detection – important for CID service in certain parts of the
   - Global compliance – enables the creation of one CPE to ship anywhere in the
       world. This is important for helping CPE manufacturers limit the number of
       designs and SKUs they carry. This is typically only found in a silicon DAA such
       as the Si3050 voice DAA offered by Silicon Laboratories.
   - High surge protection – the CPE has multiple functions, typically having a higher
       dollar content than just a telephone. Thus, it’s important that the DAA be very
       robust to high voltage surges, such as those experienced from lightning storms, to
       reduce product returns.
   - A high degree of software programmability to respond to varying requirements in
       world regions, as well as changing regulatory specs. This also allows CPEs to be
       field upgradeable.

A Marriage of Technologies
Ultimately, whatever the consumer values most will determine if VoIP startups, ILECs or
cable companies have the upper hand. Cable companies have made satellite TVs
susceptibility to rainstorms a central part of their advertising campaigns as a means to
convince consumers that cable TV is more reliable than satellite TV. Ironically, cable
companies are now forced to offer voice services on a technology that is less reliable than
that offered by the ILECs, who are partnered with satellite TV companies. In order to
exploit this advantage of reliability in voice services, ILECs will start to utilize DAAs
more and more in their CPE equipment as they marry the reliability of switched network
services with the low-cost of IP-based services. Since IP-based voice services require a
broadband network connection, this also gives the ILECs a chance to sell their ADSL
service. The end goal for the ILECs is to increase the amount billed to the consumer by
offering a broader array of services than has been provided in the past. This way, the
consumer is willing to pay more for the increased value they are receiving. While this
requires the ILECs to continue to invest in the infrastructure required to provide ADSL
service over the existing telephone lines, the alternative of losing customers to VoIP
startups or cable companies is much worse.

While the consumer always has the choice to pick and choose individually their voice,
video and data services, bundled pricing and single billing in the future will offer
consumers an overall better value if they receive all three services from one provider (or
provider partnership, in the case of VoIP startups or ILECs partnering with satellite TV
providers). If a consumer just wants the lowest cost VoIP service and doesn’t mind
getting multiple bills for different services, then a VoIP startup is the likely choice. If a
consumer values reliable voice service, then receiving voice, video and data services
from an ILEC (plus satellite TV provider) would be the logical choice. If the consumer
wants to avoid any type of outage of TV service during a rainstorm, then receiving voice,
video, and data services from the local cable company would be best. Ultimately, having
multiple types of companies providing these services will benefit the consumer by
lowering prices and spurring innovation.

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