MARKC, thanks, great reading anf great lead for me to post>>>>> BTW, Nortel's 250 Switch is the equivalent of the SS7 and We GOT IT!
world VOIP
ISPs need to expand their switching setups to provide IN capabilities.
By Andres Llana
onsider these the salad days of voice over Internet protocol (VOIP). There's
no real regulatory control, and public VOIP providers aren't working under the
same "five-nines" reliability rigors traditional local exchange carriers (LECs) must
meet. VOIP providers are riding the crest of a technology wave that hasn't been
tested by the rigors of copper telephony. All that must change if Internet telephony
is going to become a competitive service offering.
Observers place the beginnings of VOIP to early 1995, when VocalTec
Communications (Northvale, N.J.) introduced its Internet Phone software, which
was designed to run on a 486/33 PC configured with a sound card, speakers,
microphone and modem. This development set the stage for the introduction of
similar products, including the WebPhone from NetSpeak Corp. (Boca Raton, Fla.),
VocalTec's Internet Phone, and the Internet Phone from Intel Corp. (Santa Clara,
Calif.). What moved PC-to-PC VOIP technology forward has been the development
of better sound cards, faster processors, higher speed modems and much better
compression.
At first, voice over the Internet was viewed as a hobbyist novelty; however, as
more workers migrated to home offices, VOIP represented a tremendous cost
savings. Users could bypass long distance carriers in favor of integrating their voice
and data requirements over a single line for a flat monthly Internet access fee.
In this environment, compatible software lets users conduct voice conversations
with each other. When the software is loaded on the end user's PC, it automatically
detects the user's sound card and modem. Setup procedures establish whether a call
will be full- or half duplex, and whether a static IP address or one that changes
every time the user signs on to the Internet is used. A codec algorithm is selected to
work with the onboard modem to compress the voice data into packets for
transmission over the Internet or a private IP network. These packets are sent to a
correspondent system, where they are disassembled and played back to the
recipient.
VOIP's evolution is rocketing forward with the emergence of fully configured,
gateway-based, phone-to-phone VOIP systems, which interface a company's private
branch exchange (PBX) or local area network (LAN) with outside callers across the
Internet.
Large corporations long accustomed to linking company locations using tie lines
with their PBXs, find that the same arrangement can be accomplished across the
Internet using a gateway-based VOIP environment (Figure 1). Here, gateway
software accepts voice traffic coming over LAN or PBX trunk lines, compresses it
and packetizes it for routing over the Internet to the recipient. Greater call volumes
can be accommodated, but all calls must originate and terminate on a proprietary
server for proper encoding and/or decoding. This strategy is being adopted by
corporate networks as a means of consolidating many levels of traffic.
A Gallup/Pitney Bowes survey reports that an average Fortune 500 company will
spend $15 million to $20 million annually on telecommunications, of which 36%
will be used to support fax traffic. According to other studies, there are more than
60 million fax machines worldwide, accounting for $80 billion per year in
telephone charges. By virtue of the market's dimension, these budgetary factors will
further influence the continued development and refinement of VOIP, as well as
and fax over IP (FOIP) products.
For example, gateways that support voice and fax over the Internet encourage
companies to consider the economies of placing more voice, fax and data traffic
over IP networks. For this reason, major corporate networks will provide the
greatest potential market for VOIP technology.
These changes in technology will place increasing pressure on Internet service
providers (ISPs) to differentiate their services by supporting VOIP traffic.
However, ensuring two-way voice communications over a packetized data network
is not an easy feat.
What's so different about voice?
In a typical Internet data transmission, the ISP for the most part validates the user's
ID and then routes the transmission to a specific data switch, where the call is
connected to the Internet and a session can begin. Voice calls must be handled in an
entirely different process.
To begin with, protocols have been developed to address multimedia
communications over packet networks which effect signal processing through the
public network. For example, the H.323 standard affects terminals and gateways,
while H.225 defines the means by which audio, video, data and associated controls
are coded and packetized for transport between H.323 terminals.
The H.225 protocol is intended for packetizing and synchronization of traffic over
the network with non-guaranteed quality of service (QoS). Consequently, to process
VOIP exchanges, the ISP must be in a position to handle a complex message stream
to route calls to their proper destination.
For these reasons, the ISP must assume a much different switching configuration,
taking on the posture of a service switching point (SSP) in the public network. This
is a major problem for many ISPs, because many cannot support functional SSP
termination. However, some ISPs have begun using a combination of gateway and
gatekeeper units to support call setup, packetization and routing functions to
transport voice calls across an IP network.
Although new to ISPs, gateways provide the interface between the public switched
telephone network (PSTN) and the IP network, and support the encoding/decoding
and packetization of information between the two networks. In addition, gateways
send and receive call signaling to and from the PSTN via multifrequency trunks,
integrated services digital network (ISDN) D channels, and so on. Gatekeepers act
on the signaling information to determine the switching/routing logic so they can
establish a communication path between IP networks and the PSTN. Gatekeepers
maintain lists of remote gatekeeper IP addresses, as well as the associated PSTN
dialing plan routing information.
With the evolution of the intelligent network (IN), however, these basic systems
may not be enough. For example, local number portability (LNP) is expected to
bring about a number of network changes-the least of which is the signaling
process, which will require an LNP database query for every ported subscriber
number. This will increase the number of signaling system 7 (SS7) links to
signaling points required to support these added database queries.
Expanding the fabric
ISPs will have to expand their switching fabric to support enhanced, SS7-type
operations, and in doing so will compete directly with other types of carriers. To
compete in this environment, ISPs will have to reconfigure their networks to
establish an Internet telephone service switching point (IT-SSP).
Figure 2 is an example of an IT-SSP providing the interface between the PSTN
and IP networks. By deploying an IT-SSP, VOIP calls can take advantage of IN
services using SS7 technology. In this setting, application of the SS7 standard
enables more advanced call handling.
The ISP in Figure 2 uses a MicroLegend Telecom Systems (Raleigh, N.C.)
VSP-SS7 switch configured with a number of gateway and gatekeeper units to
support SS7 intelligent call processing. The IT-SSP unit serves as a direct interface
to the local central office (CO) or network switching point, and the IN using SS7
trunking. In this example, an Internet user establishes a normal data connection with
his ISP. Once on the network, the user initiates a VOIP call (to 978/543-6768) that,
in reality, has been transported to another local CO. In this scenario, the end user
dials a portable number, which in turn relies on the SS7 intelligence embedded in
the network for LNP service.
The service provider's newly enhanced switching fabric would be able to recognize
that the number dialed was a ported number. In turn, a message on the internal
network of the ISP's IT-SSP would send an SS7 query to the serving signal transfer
point (STP) and service control point (SCP) database to determine the address of
the switching center that services the relocated number. This query would be
processed by the MicroLegend SS7 switch, which would cause the local (sending)
gateway to establish a route to the CO switch that serves this ported telephone
number.
The second local office, using the information sent from the STP, determines the
ported number being called and then sets up the call to the dialed number. When the
call has been completed, the SS7 signaling (message) process simplifies the call
tear-down process, freeing up the SS7 trunk.
Thus, the ISP can utilize SS7 messaging to transport any of its VOIP traffic directly
over the Internet or the SS7 network. The application of the SS7 switch provides
the ISP with a fully compliant SS7 intelligent switching solution to support all types
of VOIP calls. The switch provides the basic interface for an SS7 link, avoiding the
requirement to provision multiple H.323 gateway terminals with separate SS7
trunks.
The IT-SSP configuration gives ISPs other advantages. For example, an SS7
interconnection provides a more reliable PSTN interconnection, because SS7
message transfer part (MTP) routing provides automatic message routing and
retransmission to overcome network faults.
With the expanding application of LNP, an ISP will be able to support the added
database queries via the SS7 links to complete call processing. Without SS7's
enhanced call features, the ISP would be unable to support portable number calls.
This requirement is certain to expand with wider application of "portable" 800/888
numbers used by vendors for Internet online selling.
In addition, as Internet users begin to make use of calling card services, ISPs will be
able to support the SS7 calling card features needed to complete Internet calls
requiring such functionality. The application of a versatile signaling point (VSP)
SS7 switch will gain further importance to ISPs as international connections to
multiple networks require conversion of different SS7 protocol variants.
The other threats
It is only reasonable to assume that large businesses will take advantage of IP
networks to contain their telecom costs. In like manner, we can expect that ISPs will
take whatever steps are necessary for them to stay in business. To do this, ISPs will
have to adopt increasingly sophisticated switching fabrics (such as the IT-SSP) to
support SS7 call processing over IP networks.
The FCC has moved one step away from the president's hands-off policy for the
Internet by stating that it would charge access fees on a case-by-case basis for all
long distance calls completed over LEC networks. Considering the fact that the
Internet is worldwide, it is difficult to see how this policy can be enforced.
Major carriers have stepped up to the plate to defend their interests by becoming
ISPs. Therefore, the issue of access fees may soon pass, since the difference between
ISP and carrier may become to tough to tell.
Andres Llana is a consultant with the Vermont Studies
Group Inc. (King of Prussia, Pa.). Llana's
telecommunications career spans more than 40 years, and
he has authored numerous reports on disaster recovery,
new telecom systems and wireless technologies. Readers
may direct comments to anrespond@americasnetwork.com.
June 15, 1998 table of contents
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