Frame relay is
becoming the transmission technology of choice
for wide area network (WAN) users worldwide who
are looking for a WAN technology that is low
cost, fast, flexible, and standards based.
Vendors and carriers have both reported growth
rates of 350% from 1994 to 1995.
ADDING VOICE TO DATA NETWORK
Optimized for data traffic,
frame relay’s explosive growth has been driven
predominantly by local area network (LAN)
internetworking, SNA migration, and remote
access. As customers continue to express
interest in frame relay, vendors and customers
are pushing for other applications and traffic
to run over a frame relay network.
In 1995 the first generation
of equipment was introduced that supported voice
over frame relay. These offerings met with
moderate acceptance due largely to a lack of
standards and lack of support. A year later, new
vendors have begun supporting voice over frame
relay and a new wave of customers has emerged
who want to realize the financial benefit of
incorporating voice/fax along with data into
their frame relay networks.
The second generation of
equipment does a better job of addressing the
quality issues associated with voice
compression. Additional buffer space to help
with jitter, coupled with more advanced
compression algorithms and better prioritization
schemes, have alleviated some of the issues.
However, there is still a lack of standards. As
of this writing, this lack of standards makes
all voice-over-frame relay (VOF) offerings
proprietary solutions and, consequently, an
issue for many end users.
In the 1990s, when the
corporate world is downsizing and rightsizing,
the prospect of lowering monthly
telecommunications infrastructure costs is
economically very attractive to many businesses.
In many cases the cost issues are paramount, but
there are other issues to be addressed as
well—among them, ongoing infrastructure
requirements, business continuity, and network
management. A brief discussion of when it may be
appropriate to incorporate voice into the data
network will address many of these issues.
Business Perspective on
Frame relay today provides
primary connectivity for LAN-to-LAN and IBM SNA/SDLC
(System Network Architecture/synchronous data
link control) connectivity, accounting for
almost 95% of current network utilization.
Unfortunately, many users of frame relay
technology have yet to recognize the full
economic advantage of its architecture.
voice over frame and potentially eliminating a
major portion of the network is financially
attractive. In fact, with the latest compression
techniques it can cost as little as half a cent
per minute. However, users must consider that if
the frame relay link is lost, then both voice
and data communication is now lost and a remote
site is potentially without any communications.
Business continuity and
application criticality must be considered. Many
dial backup solutions may be
applicable—integrated services digital network
(ISDN), in many cases, or plain old telephone
service, for example. In addition, for truly
critical sites, users should consider multiple
access paths for the cable into the building.
Network Management. Network
management must also be considered when users
look to combine multiple networks into one. The
combination of voice/fax/data over the same
physical link elevates the need for a robust
network management system and for working with a
carrier who provides valuable network
information. Some carriers are expanding this
part of their business and are offering access
to their network management data.
The best candidates for voice
over frame relay today are customers with
existing frame relay data networks whose data
requirements are a few DS0s, allowing them to
take a relatively simple approach of looking at
the equipment costs and the additional DS0 cost
for adding voice.
For many of the carriers,
combining voice traffic over the frame relay
network presents issues of pricing as well as
CARRIER SERVICE OFFERINGS
AND IMPACT ON VOICE AND DATA DELIVERY
For public network frame relay
service, many carriers have chosen a cautious
approach to promoting and supporting VOF
technology. This is due primarily to concerns
about guaranteeing quality of service (QOS)
specifications associated with voice traffic.
Of those carriers that offer
support for VOF (see Exhibit 1), they are
typically discussing tariffing data link
connection identifiers (DLCIs) for voice to
ensure acceptable delay. This would enable voice
to travel alone on a dedicated virtual circuit,
minimizing or eliminating many of the problems.
(Note: The majority of carriers, as of this
writing, do not provide voice over frame relay
as a service offering. Many of the carriers have
announced plans for voice over frame relay
service, but do not have definitive service
Many leading switch vendors
offer the ability to support different levels of
QOS for voice using different DLCIs. As these
devices become more prevalent and intelligent,
the carriers will be able to provide
higher-quality service, and users will gain more
One challenge for end-user
companies that have many sites is the
interoperability between the carriers. The
network-to-network interface (NNI) agreement
covers the very basics and does not address
voice issues and some network management issues.
Today, few carrier-based frame
relay offerings support all the traditional
voice applications, including interconnecting
private branch exchanges (PBXs), use of
off-premises extensions (OPX), and private line
auto ringdown (PLAR). When available, such
offerings can make frame relay networks an
attractive option for everything from tying
together telecommuters into a virtual office to
linking the branch office and regional office
locations. In this implementation, the home or
small branch office can be connected with a
single pipe that provides voice communications
integrated with the office PBX and voice mail,
as well as integrated data communications with
the office network and host computers.
This configuration often
creates an easier frame relay design and
implementation because the end stations are
typically homes back to a central office
location. This means advanced functionality
requirements of frame relay, such as switched
virtual circuit (SVC) support for voice, are not
required, as all voice calls need to be first
routed to the office PBX.