chapter39

Lack of Carrier Agreements
IP networks are today a loose confederation of agreements among carriers.
A carrier-class VoIP network cannot depend on a service provider’s decision
whether to carry transit traffic. This, in turn, means that international division of
revenue processes must be developed. Competing carriers must deal promptly
with impairments and failures and must cooperate to ensure that service is not
affected by the structure of the interface points of diverse networks.
Carrier and Regulator Inertia
The existing PSTN infrastructure works well, represents a considerable investment,
and is maintained and managed by workers that lack the skills to manage an
all IP infrastructure. ILECs, in particular, will retain what they have until it is
functionally obsolete or competitive pressures force them to change. Numerous
other forces resist change. Congress is subject to numerous pressures that affect
the shape telecommunications will take, and money is at the root of it. Cash-rich
companies such as the ILECs have the ability to inject huge amounts of money to
purchase influence and they have been successful in this endeavor.
The regulatory framework is based on conventional telephone technology as
are the structure of taxes and fees and these tend to change slowly. Much of the
economies of VoIP in the U.S. today result from Congress’ reluctance to burden IP
with the fees, restrictions, and taxes that it loads on the conventional telephone
industry. Access charges, USF fees, excise taxes, and myriad state and local taxes,
not to mention carriers’ miscellaneous fees complicate the picture. Moreover,
regulations are inconsistent. LEC cable pairs are subject to unbundled access
regulations, but new fiber investments are not. Cable companies can prohibit
other carriers from using their access facilities and have both the ability and the
motivation to exclude other providers from using them for VoIP. All of this creates
an atmosphere in which progress is impeded because there is little assurance that
the rules will not change.
Reliability and Availability
IP networks are inherently robust with their ability to route around failures, but
router convergence time is too lengthy for real-time applications. Operational
changes such as hardware and software upgrades and configuration changes cannot
be done in real time with many router platforms. The solution requires a new
generation of routers and protocols, which will be slow to propagate themselves
through the network.
Compliance Issues
Making VoIP comply with E-911 and CALEA is a major unresolved problem.
Many countries censor Web content, block access to certain sites, or monitor access
to parts of the Internet. These requirements are incompatible with using the
Internet as a reliable communications channel.
Interworking between the PSTN and IP
Until the transition to an all-IP infrastructure is complete, communication
between the two networks is required. This requires gateways, signaling, addressing,
and numerous other complexities that must be transparent to the users. Much
work remains to be done to make the interface with the PSTN seamless.
THE IPsphere INITIATIVE
Many of the changes necessary to make VoIP equivalent to the PSTN require
voluntary or compulsory adherence to centralized authority, a concept that is anathema
to the Internet community. If we conclude that the Internet in its present state is
not an appropriate vehicle for isochronous traffic, then the solution may be an overlay
network that is designed to provide the elements missing from the Internet: QoS,
predictability, end-to-end management, security, and carrier interconnections with
division of revenues or settlement process. Such a network would not be accessible
from the public Internet and would provide the benefits of IP without subjecting its
subscribers to the chaotic conditions that prevail on the Internet today.
An initiative known as the IPsphere, previously known as the Infranet is
underway to create such a network. Equipment manufacturers and carriers are
not unanimous in their support of the IPsphere and there is no assurance that
such a network will happen. The goal of IPsphere is to deliver performance over
a virtual network that is predictable, flexible, and secure so subscribers can entrust
mission-critical information to it. At the edge of the IPsphere is a barrier that
requires customers to authenticate themselves before admission.
The IPsphere requires communication between the subscriber’s application
and the network to enable the application to request the level of security, quality,
and bandwidth it needs. Costs would be based on what the application needs, in
contrast to the Internet where the cost is independent of the application. Since no
single provider can guarantee worldwide connectivity, connections are needed
between networks so providers can communicate levels of service and security
when handing off traffic. In addition, accounting mechanisms are needed to
enable carriers to bill each other for carrying traffic.
CONVERGENCE APPLICATION ISSUES
The motivation for the converged network in the enterprise network can be
summed up in one word: productivity, both of personnel and capital. In the public
network the motivation is also clear. For consumers it is saving money and getting
enhanced services. For service providers it is the opportunity to make money. It
will be many years before the technology has advanced to the point of replacing the
PSTN for more than a narrow spectrum of users, but the obstacles will gradually
be surmounted.
VoIP in the Public Network
At this stage of development, the ways of implementing VoIP are many and varied.
From a residential or small business user’s standpoint the ideal would be to connect
a VoIP telephone into a wired or wireless LAN, assign it a telephone number, and
use it as if it were a wired phone. The reality, however, is considerably different.
Several companies have jumped onto the VoIP bandwagon and by the time this is
published, many more would have joined the fray. IDC estimates that by 2008 some
14 million customers worldwide will subscribe to VoIP services. In this section we
briefly discuss the alternative configurations and some of the considerations in
selecting them. The services they offer are changing, however, so it is best to refer
to the vendor’s description on its Web page before relying on this discussion.
Computer-to-Computer Services
Representative services include Pulver, Skype, and Dialpad. These services
generally cannot be reached from the PSTN because the user does not have an
E.164 number. In the process of registering with the service provider, the user
obtains an address that is valid within that network. Calls within the network can
be made to others who have registered and are online.
The telephone instrument is usually a softphone and client, which can be
downloaded without cost. These services usually do not carry a monthly fee,
although some offer off-net prepaid packages. PC-to-PC calling is free. Calls that
hop off to a wireline phone carry a charge that is usually much lower than small
users can obtain, but may not be much of a saving for large users. The greatest
savings are on international calls. Features include buddy lists, redial, and running
account balance.
Firewalls and NAT generally do not bother these types of service because
nothing identifies the call as a voice call. To place or receive calls the user logs onto
the provider’s Web service, so the session looks to the network like any other Web
connection.
Computer to PSTN Services
Representative services include AT&T CallVantage, Vonage, Net2Phone, and
Go2Call. A major difference between these and computer-to-computer services is
the provision of an E.164 number, which enables the IP phone to be called as if it
were a wireline phone. Since the service provider controls the design, the portion
of the call that uses the Internet is under its control, so the service provider can
control the quality. The architecture is invisible to the customer, so there is no way
to evaluate the service in advance except to try it.
Some products permit or require the use of a VoIP terminal adapter, which
connects an analog phone to the network. Some will work with downloaded softphone
products. In most cases existing numbers can be ported to the IP service, and
the IP phone is not tied to a physical location. This means it can be transported to
another place and operate as it does from the primary location. Vonage offers a virtual
number in certain local calling areas. This permits someone with a landline telephone
to make a local call, which is transported to the destination across the Internet.
Most of these services carry a monthly rate, which may include unlimited
domestic calling. The rates are generally lower than LEC phones, and may include
a package of special features that the LEC charges for. Voice mail is typically available,
with message retrieval from either telephone or browser. Voice mail messages
can also be forwarded as e-mail attachments. Other typical features include
caller ID, call forwarding, call logging, do-not-disturb, conferencing, and locate
service.
The service has much in common with cell phone service. Most users will
not give up their PSTN phone, but it is a good solution for a second line. The
service has several downsides that must be considered, not the least of which is
lack of compatibility with E-911. In addition, it does not work through power
failures. If the line is to be used as an additional line throughout the house or
business, the adapter must be wired in place, which defeats the easy portability.
Finally, the service is not as simple to set up as buying a telephone and plugging
it in. The author’s experience with AT&T CallVantage is a case in point. After
several hours of attempting to make it work through Comcast cable, the AT&T
technician gave up concluding that Comcast’s routers were blocking the service.
TDM over IP (TDMoIP) Multiplexers
Several manufacturers provide TDMoIP multiplexers for applications such
as the one shown in Figure 39-1. Here, the company has an Ethernet connection
between sites and T1/E1 compatible PBX and key systems. The IP multiplexers connect
to the CPE devices with TDM and to the Ethernet switches with 100Base-T,
sharing the bandwidth between sites with data. The multiplexers shown use T1
on both ends, but they could just as easily use analog trunks, in which case the
connection would typically be FXS/FXO. The TDM frames are encapsulated into
IP packets that are transported over the fast Ethernet ports. The ToS bits of the
packets are set to classify the packets as high priority.
TDMoIP provides a circuit-emulation service, also called pseudowire, that
is transparent to protocols and signaling. The multiplexer repeats the contents
of each channel to the other end. The IETF PWE3 Working Group is working
on protocol standards that are in draft form as this book is published, so products
are likely to be proprietary. Typically, the payload of each channel connects to a
48-octet ATM cell, which does not have the 5-octet header. These are encapsulated
into IP frames in some multiple. As the number of TDM octets per frame increases
throughput increases because of lower packet overhead, but the effects of frame
loss are more severe.
Compared to VoIP gateways, TDMoIP multiplexers have lower latency, so
the circuit quality is likely to be better, provided packet loss is not excessive. As
with VoIP gateways, the multiplexers compensate for packet loss by repeating the
contents of the previous packet. The multiplexer transmits channel timeslots
whether they are empty or not, so from this standpoint it is less bandwidthefficient
than VoIP. The impact of this is generally irrelevant, however, because a
TDMoIP multiplexer is not used where bandwidth is restricted. For example, it
would not be usable over the Internet. Some products support fractional T1/E1 so
vacant channels are not transmitted.
VoIP Business Applications
VoIP has four principal categories of applications in the enterprise network:
_ Branch office. Since the branch office is already equipped with a router
or FRAD, adding voice may be a natural outgrowth of the existing
network. For distant branch offices, the existing frame relay network
may be used. For local branches, it may be feasible to replace off-premise
extensions with VoIP.
_ Telecommuting. Similar in architecture to the branch office, telecommuters
may use VoIP to provide a voice and data connection to the main office.
_ Toll bypass. Carrying long distance traffic for next to nothing is attractive,
particularly when the distances are great. The ability to send large
quantities of fax messages, which tend not to be time sensitive, over
the Internet, can be particularly attractive.
_ Web-enabled call center. Callers can browse the company’s Web page
by computer, and then click an icon to talk to a live agent. Costs are
reduced and customer convenience is enhanced.