> Focus > Full Story
Relay For Wider Reach
competitive business markets continue to shape the very
nature of how we communicate. As the computing environment
changes from a host-centric model to a network-centric model,
corporations are redistributing network processing and utilizing
the increased intelligence of network endpoints. New protocols
and communication methods are taking advantage of this competitive
potential, creating new demands for faster and more effective
networks. Frame Relay is here to meet these demands.
Is Frame Relay?
Frame Relay is a high-performance WAN protocol that operates
at the physical and data link layers of the OSI reference
model. Frame Relay originally was designed for use across
Integrated Services Digital Network (ISDN) interfaces.
put, Frame Relay is a way of sending information over a
Wide Area Network (WAN) by dividing the information into
frames or packets. Each frame has an address that the network
uses to determine the destination of the frame. The frames
travel through a series of switches within the Frame Relay
network and arrive at their destination.
with the definition is the explanation of its functionality.
Frame Relay is simply a programmed software located at the
telephone company designed to provide more efficient, digital
connections from one point to another. It is an emerging
technology, which will provide a faster, and cost-effective
method for accomplishing your computer networking.
Relay is an example of a packet-switched technology. Packet-switched
networks enable end stations to dynamically share the network
medium and the available bandwidth.
Let's explore the network trends that contributed to the
development of Frame Relay.
For Increased Speed
Today, rapid storage and retrieval of images for interactive
applications is as common as transmitting full screens of
text was in the 1970s and 1980s. Early graphics applications
users who were accustomed to rapid information transfer
over their LANs expected similar response times when transmitting
data over the wide area network. Since peak bandwidth requirements
for graphics were substantially higher than for text transactions,
increased bandwidth and throughput were clearly required
if response time expectations were to be met.
A typical LAN user followed a certain pattern in functioning
which varied from high bandwidth bursts to periods of idle
time "Bursty" traffic, as we call it, which is
well-suited for statistical sharing of bandwidth, a characteristic
of the Frame Relay technology.
Decreasing cost of processing power resulted in the proliferation
of intelligent PCs and powerful workstations and servers,
all connected by LANs. These new end-user devices also offered
the possibility of performing protocol processing, such
as error detection and correction. This meant that the Wide
Area Network could be relieved of the burden of application
layer protocol processing--another perfect fit for Frame
More LANs in general and Internet Protocol (IP) LANs in
specific fuelled the need to internetwork LANs across the
Wide Area Network, another factor that drove the growth
of public Frame Relay services.
The Frame Relay Forum has been instrumental in developing
implementation agreements between its members to drive forward
the early adoption of the Frame Relay protocol. To enable
successful operation with both private and public Frame
Relay networks, routers must conform to all the core standards
of the Frame Relay protocol. These standards define the
structure of the LAPD frame used by the Frame Relay protocol
and are a basis for the addressing structure between the
router and the network. In addition, the router requires
information about the virtual connections provisioned by
the Frame Relay service. This is achieved by signaling the
User to Network Interface (UNI). All the major standards
bodies have implementations for the UNI standard
CCITT I.233.1 [ Replaces I.122 ] ( T1.606 )
Frame Mode Bearer Services--Architectural Framework
2. CCITT Q.922 (ANSI T1.618) ISDN Data link Layer Specification
for Frame Mode Bearer Services--Core Aspects of Frame Protocol
3. CCITT Q.933 (T1.617) ISDN Frame Mode Bearer Services
Signaling Description--Signaling Specification for FRBS
does Frame Relay work?
Similar to X.25, Frame Relay uses the concept of Virtual
Circuits (VCs) to provide maximum bandwidth utilization
and connectivity flexibility. A physical Frame Relay port
can have multiple Virtual Circuits, each connecting to a
different destination port. Unlike TDM (Time Division Multiplexing),
where each application is assigned its own channel, such
that idle bandwidth cannot be used, Virtual Circuits belonging
to the same physical port can share all the available bandwidth
so that applications can borrow from the unused idle bandwidth
for a short duration to accommodate traffic burst.
further optimize efficiency, Frame Relay takes advantage
of the improvements in quality of digital transmission facility
by using only the bottom two OSI (Open Systems Interconnection)
protocol layers, rather than three as in the case of the
X.25 protocol. (OSI is the international standard that defines
an open systems connection by standardizing the interface
for each layer; this assures the compatibility of multi-vendor
hardware and software systems). By restricting its use to
Layers 1 and 2, Frame Relay performs error detection only,
whereas X.25 performs both error detection and retransmission.
Frame Relay leaves retransmission up to the intelligent
devices at each end of the network.
the event of errors, Fame Relay simply drops bad frames
to reduce overhead and enable greater throughput. Congestion
is handled through vendor implementation of the congestion
management techniques described in the Frame Relay standards.
Standards-compliant congestion management means that, even
during congestion, each end user device has guaranteed access
to a defined amount of bandwidth.
Relay also provides tremendous flexibility in terms of the
types of devices that can be connected to the network. Because
it is protocol transparent above Layer 2, the data link
layer, most types of traffic can ride over a Fame Relay
network without realizing that Fame Relay is being used.
Because it is an access technique, Frame Relay is concerned
only with the network interface; protocols determine the
transfer of information on and off the WAN.
Frame Relay technology is based on the concept of using
Virtual Circuits (VCs). VCs are two-way, software-defined
data paths between two ports that act as private line replacements
in the network. While today there are two types of Frame
Relay connections, Switched Virtual Circuits (SVCs) and
Permanent Virtual Circuits (PVCs), PVCs were the original
service offering. As a result, PVCs were more commonly used,
but SVC products and services are growing in popularity.
Of Frame Relay
Frame Relay networks are made up of Frame Relay access equipment,
Frame Relay switching equipment, and public frame relay
Relay access equipment is the customer premises equipment
(CPE) that uses Frame Relay to send information across the
wide area. Access equipment may be bridges, routers, hosts,
packet switches, specialized Frame Relay "PADs"
or any other similar devices.
Relay switching equipment comprises devices that are responsible
for transporting the Frame Relay compliant information offered
by the access equipment. Switching equipment may be T1/E1multiplexers,
packet switches, or any specialized Frame Relay switching
equipment that implements the standard interface and is
capable of switching and routing information received in
Frame Relay format.
service providers (carriers) offer Frame Relay services
by deploying Frame Relay switching equipment. Both Frame
Relay access equipment and private Frame Relay switching
equipment may be connected to services provided by a carrier.
The service provider maintains access to the network via
the standard Frame Relay interface and charges for the use
of the service.
Of Frame Relay
Here are some of the benefits that Frame Relay offers.
When using a private Frame Relay network, statistically
multiplexed traffic from multiple sources over private backbone
networks can reduce the number of circuits and corresponding
cost of bandwidth in the wide area. Public Frame Relay services
almost universally save money when compared with the equivalent
service provided by dedicated leased lines.
Frame relay provides multiple logical connections within
a single physical connection, access costs are also reduced.
Equipment costs may be lowered by reducing the number of
port connections required to access the network. For remote
access devices, access line charges can be lowered by reducing
the number of physical circuits needed to reach the networks.
Performance With Reduced Network Complexity
Both by reducing the amount of processing (as compared to
X.25) and by efficiently utilizing high-speed digital transmission
lines, Frame Relay can improve performance and response
times of applications.
Relay reduces the complexity of the physical network without
disrupting higher-level network functions. In fact, as discussed
earlier, it actually utilizes the existence of these higher
layer protocols to its advantage. It provides a common network
transport for multiple traffic types while maintaining transparency
to higher level protocols unique to the individual traffic
types. The frames contain addressing information that enables
the network to route them to the proper destination.
With New Applications And Services
As compared with point-to-point leased lines, Frame Relay
suits meshed networks and hub and spoke networks equally
well. This means that Frame Relay easily accommodates new
applications and future expansions of existing networks,
for example, SNA migration to APPN.
addition, Frame Relay standards have been developed to interwork
with newly evolving services such as ATM. As new applications
emerge and/or bandwidth requirements increase, networks
can gracefully migrate to the appropriate technology without
stranding existing network equipment.
Scalability, Flexibility And Disaster Recovery
To the end user, a Frame Relay network appears straightforward:
one user simply connects directly to the Frame Relay cloud.
A Frame Relay network is based on virtual circuits, which
may be meshed, or point-to-point, and these links may be
permanent or switched.
of this structure, Frame Relay is more easily scalable than
a fixed point-to-point network. This means that additions
and changes in a network are transparent to end users, giving
telecommunications managers the flexibility to modify network
topologies easily and scale networks as applications grow
and sites are added. This inherent flexibility lends itself
equally well to the provision of alternate routes to disaster
recovery sites, which are, in many cases, transparent to
the end user.
The Frame Relay Service
Today, Frame Relay is available worldwide from a large number
of domestic and international carriers. These carrier services
vary according to the capabilities of the platform on which
the network is provisioned. It is important to understand
the issues of Frame Relay service provisioning before committing
to one particular service.
Relay is a frame switched statistical multiplexed technology
that provisions more bandwidth at the access layer (i.e.
Frame Relay ports to the end users routers) than in the
backbone. Thus the carrier then relies upon the statistically
bursty nature of LAN interconnect traffic not to have too
many coincidental bursts and congest the backbone network.
However, the ratio of carrier access bandwidth to backbone
bandwidth or 'overbooking' dictates the ability of the service
to handle LAN bursts without becoming congested. Some carriers
leave as much as 20 per cent of the trunk capacity free
for data bursts while others overbook by as much as thirty
times in order to gain backbone trunk efficiency.
it is important to understand the carriers' overbooking
strategy within their Frame Relay network in order to select
the service with the best potential for carrying "bursty"
also varies depending upon the carrier. There are many different
methods of tariffing a Frame Relay service, however, most
services are tariffed on a flat rate or fixed CIR (Committed
Information Rate) basis. The tariff for the CIR will depend
on size (i.e. 256 Kbps and 512 Kbps) and geographical distance.
In addition, there are port charges for each Frame Relay
port provisioned. Most likely, tariff structures will eventually
move away from fixed CIR billing towards a usage based system
in line with the implementation of SVC services.
performance of the service is extremely important. It is
essential that a high performance router is matched with
an appropriate service. Additionally, it is important to
ensure that switching performance nodal delay information
is available from any prospective carrier. Remember that
performance is also affected by the overbooking and congestion
susceptibility of the network.
of Frame Relay
Originally Frame Relay was used predominantly for LAN interconnection.
However, recent developments in various standards bodies
have broadened its use to support delay-sensitive applications
such as Voice over Frame Relay.
manufacturing, bank and finance are only a few of the industries
now benefiting from Frame Relay's ability to provide affordable
and efficient connectivity between many sites. Besides,
the bandwidth sharing qualities of Frame Relay make it an
attractive alternative to leased lines. Service providers
also benefit because the efficient use of bandwidth enables
them to support a larger customer base.
most popular Frame Relay application provides companies
with LAN to LAN communication. This allows companies to
integrate their information systems in order to have employees
throughout the enterprise to access specific information
residing on a LAN somewhere in the enterprise. The devices
on the LANs can communicate over the Frame Relay network
regardless of their native protocol.
example, native protocols that can traverse Frame Relay
networks include SNA, DECnet, IPX, TCP/IP, and AppleTalk.
Therefore, Frame Relay has the ability to make the users
perceive that the entire company is on one large LAN. Application
software such as groupware, e-mail, document sharing, database
and many other LAN applications can utilize Frame Relay
Frame Relay is a technology that can create a robust wide
area networking fabric that integrates information systems
together to form an enterprise network. It is an affordable
and capable service for supporting today's bandwidth intensive
applications as well as those residing on legacy systems.
Because logical connections are defined in software, it
is easy to manage moves, changes, additions, and deletions
of logical connections. Systems analysts should consider
the use of Frame Relay for corporate applications that incorporate
information systems at more than one location because of
the technical, financial and logistical advantages of the
of Frame Relay
cost of ownership.
and widely adopted standards that allow open architecture
and plug-n-play service implementation.
overhead combined with high reliability.
of Frame Relay
Relay offers users the ability to improve performance (response
time) and reduce transmission costs dramatically for a number
of important network applications. However in order to be
effective, Frame Relay requires that two conditions be met:
The end devices must be running an intelligent higher layer
2. The transmission lines must be virtually error-free.
of the major applications of frame relay:
LAN Peer to Peer Networking
Network Architecture over Frame Relay
over Frame Relay (VoFR)
Relay to A