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FRAME RELAY

Introduction

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. Today, it is used over a

variety of other network interfaces as well. Frame 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. The following two techniques are used

in packet-switching technology:

Variable-length packets

Statistical multiplexing

Variable-length packets are used for more efficient and flexible data transfers. These

packets are switched between the various segments in the network until the destination isreached.

Statistical multiplexing techniques control network access in a packet-switched network.The advantage of this technique is that it accommodates more flexibility and more

efficient use of bandwidth. Most of todays popular LANs, such as Ethernet and TokenRing, are packet-switched networks.

Frame Relay often is described as a streamlined version of X.25, offering fewer of therobust capabilities, such as windowing and retransmission of last data that are offered in

X.25. This is because Frame Relay typically operates over WAN facilities that offer more

reliable connection services and a higher degree of reliability than the facilities availableduring the late 1970s and early 1980s that served as the common platforms for X.25

WANs. As mentioned earlier, Frame Relay is strictly a Layer 2 protocol suite, whereas

X.25 provides services at Layer 3 (the network layer) as well. This enables Frame Relayto offer higher performance and greater transmission efficiency than X.25, and makesFrame Relay suitable for current WAN applications, such as LAN interconnection.

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Frame Relay Standardization

Initial proposals for the standardization of Frame Relay were presented to the

Consultative Committee on International Telephone and Telegraph (CCITT) in 1984.Because of lack of interoperability and lackof complete standardization, however, Frame

Relay did not experience significant deployment during the late 1980s.A major

development in Frame Relays history occurred in 1990 when Cisco, Digital EquipmentCorporation Initial proposals for the standardization of Frame Relay were presented to

the Consultative Committee (DEC), Northern Telecom, and StrataCom formed a

consortium to focus on Frame Relay technology development. This consortiumdeveloped a specification that conformed to the basic Frame Relay protocol that was

being discussed in CCITT, but it extended the protocol with features that provide

additional capabilities for complex internetworking environments. These Frame Relay

extensions are referred to collectively as the Local Management Interface (LMI).

Since the consortiums specification was developed and published, many vendors haveannounced their support of this extended Frame Relay definition. ANSI and CCITT have

subsequently standardized their own variations of the original LMI specification, andthese standardized specifications now are more commonly used than the original version.

Internationally, Frame Relay was standardized by the International Telecommunication

UnionTelecommunications Standards Section (ITU-T). In the United States, FrameRelay is an American National Standards Institute (ANSI) standard.

Why was Frame Relay Developed?

From the beginning, frame relay was embraced enthusiastically by users because it wasdeveloped in response to a clear market need, namely the need for high speed, high

performance transmission. Frame relay technology also made cost-effective use of

widespread digital facilities and inexpensive processing power found in end user devices.Developed by and for data communications users, frame relay was simply the right

technology at the right time. Let's explore the network trends that contributed to the

development of frame relay.As the 1980's came to a close, several trends combined to create a demand for and enable

higher speed transmission across the wide area network:

The change from primarily text to graphics interaction

The increase in "bursty" traffic applications

Intelligent end-user devices (PCs, workstations, X-Windows terminals) with increasedcomputing power

The proliferation of LANs and client/server computing Widespread digital networks

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Need 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. Since peak bandwidthrequirements for graphics were substantially higher than for text transactions, increased

bandwidth and throughput were clearly needed if response time expectations were to bemet.

Dynamic Bandwidth Requirements

This type of LAN user required high bandwidth in bursts, followed by periods of idle

time. "Bursty" traffic, as we call it, is well-suited for statistical sharing of bandwidth,

which is a characteristic of frame relay technology.

Smarter Attached DevicesAs networking requirements were changing, computing power was changing as well.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 andcorrection. This meant that the wide area network could be relieved of the burden of

application layer protocol processing another perfect fit for frame relay. End-user

equipment was becoming more sophisticated in its ability to recognize errors and

retransmit packets at the same time as digital facilities were reducing error rates withinthe network. In addition, industry-standard high layer protocols, such as TCP/IP, added

intelligence to end-user devices. Without the overhead associated with error detection and

correction, frame relay could offer higher throughput than other connectivity solutions,such as X.25.

Higher Performance

More LANs in general and Internet Protocol (IP) LANs in specific fueled the need to

internetwork LANs across the wide area network, another factor that drove the growth of

public frame relay services. Some users tried to solve the internetworking challenge bysimply hooking LAN bridges or routers together with dedicated lines. This approach

worked for simple networks, but as complexity increased, the drawbacks became

apparent: higher transmission costs, lower reliability, limited network management and

diagnostics, and hidden inefficiencies. It soon became apparent that a better approach toLAN internetworking was to connect bridges and routers into a reliable, manageable

WAN backbone designed to make the best use of facilities and offer the high

performance users demanded. Frame relay technology offered distinct advantages for thewide area network. First, it was a more efficient WAN protocol than IP, using only five

bytes of overhead versus 20 for IP. In addition, frame relay was easily switched. IP

switching was not widely available in the WAN, and IP routing added unnecessarydelays and consumed more bandwidth in the network.

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Widespread Digital Facilities

As the public telecommunications infrastructure migrated from analog facilities to high

quality digital facilities, bandwidth availability increased and error rates decreased. The

error-correcting capabilities of X.25 and SNA, which were developed to cope with the

inherent errors of analog lines, were no longer necessary in digital wide area networks.

Frame Relay Devices

Devices attached to a Frame Relay WAN fall into the following two general categories:

Data terminal equipment (DTE)

Data circuit-terminating equipment (DCE)

DTEs generally are considered to be terminating equipment for a specific network andtypically are located on the premises of a customer. In fact, they may be owned by the

customer. Examples of DTE devices are terminals, personal computers, routers, and

bridges.

DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to

provide clocking and switching services in a network, which are the devices that actually

transmit data through the WAN. In most cases, these are packet switches. Figure 1 showsthe relationship between the two categories of devices.

FIG-1 DCE generally reside in carrier operated WAN

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The connection between a DTE device and a DCE device consists of both a physical

layer component and a link layer component. The physical component defines the

mechanical, electrical, functional, and procedural specifications for the connection

between the devices. One of the most commonly used physical layer interface

specifications is the recommended standard (RS)-232 specification. The link layercomponent defines the protocol that establishes the connection between the DTE device,

such as a router, and the DCE device, such as a switch. This chapter examines acommonly utilized protocol specification used in WAN networking: the Frame Relay

protocol.

Frame Relay Virtual Circuits

Frame Relay provides connection-oriented data link layer communication. This means

that a defined communication exists between each pair of devices and that theseconnections are associated with a connection identifier. This service is implemented by

using a Frame Relay virtual circuit, which is a logical connection created between two

data terminal equipment (DTE) devices across a Frame Relay packet-switched network(PSN).

Virtual circuits provide a bidirectional communication path from one DTE device to

another and are uniquely identified by a data-link connection identifier (DLCI). Anumber of virtual circuits can be multiplexed into a single physical circuit for

transmission across the network. This capability often can reduce the equipment and

network complexity required to connect multiple DTE devices. A virtual circuit can passthrough any number of intermediate DCE devices (switches) located within the Frame

Relay PSN. Frame Relay virtual circuits fall into two categories: switched virtual circuits(SVCs) and permanent virtual circuits (PVCs).

Switched Virtual Circuits

Switched virtual circuits (SVCs) are temporary connections used in situations requiring

only sporadic data transfer between DTE devices across the Frame Relay network. Acommunication session across an SVC consists of the following four operational states:

Call setupThe virtual circuit between two Frame Relay DTE devices is established.

Data transferData is transmitted between the DTE devices over the virtual circuit.

IdleThe connection between DTE devices is still active, but no data is transferred. If

an SVC remains in an idle state for a defined period of time, the call can be terminated.

Call terminationThe virtual circuit between DTE devices is terminated.

After the virtual circuit is terminated, the DTE devices must establish a new SVC if there

is additional data to be exchanged. It is expected that SVCs will be established,

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maintained, and terminated using the same signaling protocols used in ISDN. Few

manufacturers of Frame Relay DCE equipment support switched virtual circuit

connections. Therefore, their actual deployment is minimal in todays Frame Relay

networks. Previously not widely supported by Frame Relay equipment, SVCs are now the

norm. Companies have found that SVCs save money in the end because the circuit is notopen all the time.

Permanent Virtual CircuitsPermanent virtual circuits (PVCs) are permanently established connections that are usedfor frequent and consistent data transfers between DTE devices across the Frame Relay

network. Communication across PVC does not require the call setup and termination

states that are used with SVCs. PVCs always operate in one of the following twooperational states:

Data transferData is transmitted between the DTE devices over the virtual circuit.

IdleThe connection between DTE devices is active, but no data is transferred. UnlikeSVCs, PVCs will not be terminated under any circumstances when in an idle state.

DTE devices can begin transferring data whenever they are ready because the circuit is

permanently established.

Data-Link Connection IdentifierFrame Relay virtual circuits are identified by data-link connection identifiers (DLCIs).

DLCI values typically are assigned by the Frame Relay service provider (for example, the

telephone company). Frame Relay DLCIs have local significance, which means that theirvalues are unique in the LAN, but not necessarily in the Frame Relay WAN.

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FIG-2 ASingle Frame Relay Virtual Circuit Can Be Assigned Different DLCIs on

Each End of a VC

Congestion-Control Mechanisms

Frame Relay reduces network overhead by implementing simple congestion-notificationmechanisms rather than explicit, per-virtual-circuit flow control. Frame Relay typically is

implemented on reliable network media, so data integrity is not sacrificed because flow

control can be left to higher-layer protocols. Frame Relay implements two congestion-notification mechanisms:

Forward-explicit congestion notification (FECN)

Backward-explicit congestion notification (BECN)

FECN and BECN each is controlled by a single bit contained in the Frame Relay frame

header. The Frame Relay frame header also contains a Discard Eligibility (DE) bit, whichis used to identify less important traffic that can be dropped during periods of congestion.

The FECN bitis part of the Address field in the Frame Relay frame header. The FECNmechanism is initiated when a DTE device sends Frame Relay frames into the network. If

the network is congested, DCE devices (switches) set the value of the frames FECN bit

to 1. When the frames reach the destination DTE device, the Address field (with theFECN bit set) indicates that the frame experienced congestion in the path from source to

destination. The DTE device can relay this information to a higher-layer protocol for

processing. Depending on the implementation, flow control may be initiated, or the

indication may be ignored.

The BECN bitis part of the Address field in the Frame Relay frame header. DCE devices

set the value of the BECN bit to 1 in frames traveling in the opposite direction of frameswith their FECN bit set. This informs the receiving DTE device that a particular path

through the network is congested. The DTE device then can relay this information to a

higher-layer protocol for processing. Depending on the implementation, flow-controlmay be initiated, or the indication may be ignored.

Frame Relay Discard Eligibility

The Discard Eligibility (DE) bitis used to indicate that a frame has lower importancethan other frames. The DE bit is part of the Address field in the Frame Relay frame

header. DTE devices can set the value of the DE bit of a frame to 1 to indicate that the

frame has lower importance than other frames. When the network becomes congested,

DCE devices will discard frames with the DE bit set before discarding those that do not.This reduces the likelihood of critical data being dropped by Frame Relay DCE devices

during periods of congestion.

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Frame Relay Error Checking

Frame Relay uses a common error-checking mechanism known as the cyclic redundancycheck (CRC). The CRC compares two calculated values to determine whether errorsoccurred during the transmission from source to destination. Frame Relay reduces

network overhead by implementing error checking rather than error correction. Frame

Relay typically is implemented on reliable network media, so data integrity is notsacrificed because error correction can be left to higher-layer protocols running on top of

Frame Relay

.

Frame Relay Local Management Interface

The Local Management Interface (LMI) is a set of enhancements to the basic Frame

Relay specification. The LMI was developed in 1990 by Cisco Systems, StrataCom,

Northern Telecom, and Digital Equipment Corporation. It offers a number of features(called extensions) for managing complex internetworks. Key Frame Relay LMI

extensions include global addressing, virtual circuit status messages, and multicasting.

The LMI global addressingextension gives Frame Relay data-link connection identifier

(DLCI) values global rather than local significance. DLCI values become DTE addresses

that are unique in the Frame Relay WAN. The global addressing extension addsfunctionality and manageability to Frame Relay internetworks. Individual network

interfaces and the end nodes attached to them, for example, can be identified by using

standard address-resolution and discovery techniques. In addition, the entire Frame Relaynetwork appears to be a typical LAN to routers on its periphery.

LMI virtual circuit status messages provide communication and synchronization between

Frame Relay DTE and DCE devices. These messages are used to periodically report onthe status of PVCs, which prevents data from being sent into black holes (that is, over

PVCs that no longer exist).

The LMI multicastingextension allows multicast groups to be assigned. Multicasting

saves bandwidth by allowing routing updates and address-resolution messages to be sent

only to specific groups of routers. The extension also transmits reports on the status ofmulticast groups in update messages.

Frame Relay Network Implementation

A common private Frame Relay network implementation is to equip a T1 multiplexerwith both Frame Relay and non-Frame Relay interfaces. Frame Relay traffic is forwarded

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out the Frame Relay interface and onto the data network. Non-Frame Relay traffic is

forwarded to the appropriate application or service, such as a private branch exchange

(PBX) for telephone service or to a video-teleconferencing application.

A typical Frame Relay network consists of a number of DTE devices, such as routers,connected to remote ports on multiplexer equipment via traditional point-to-point

services such as T1, fractional T1, or 56-Kb circuits. An example of a simple FrameRelay network is shown figure 3.

FIG-3 A Simple Frame Relay Network Connects Various Devices to DifferentServices over a WAN

The majority of Frame Relay networks deployed today is provisioned by service

Providers that intend to offer transmission services to customers. This is often referred toas a public Frame Relay service. Frame Relay is implemented in both public carrier-

provided networks and in private enterprise networks. The following section examines

the two methodologies for deploying Frame Relay.

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Public Carrier-Provided Networks

In public carrier-provided Frame Relay networks, the Frame Relay switching equipment

is located in the central offices of a telecommunications carrier. Subscribers are charged

based on their network use but are relieved from administering and maintaining the

Frame Relay network equipment and service. Generally, the DCE equipment also isowned by the telecommunications provider. DCE equipment either will be customer-

owned or perhaps will be owned by the telecommunications provider as a service to the

customer. The majority of todays Frame Relay networks are public carrier-providednetworks.

Private Enterprise Networks

More frequently, organizations worldwide are deploying private Frame Relay networks.In private Frame Relay networks, the administration and maintenance of the network are

the responsibilities of the enterprise (a private company). All the equipment, including

the switching equipment, is owned by the customer.

Frame Relay Frame FormatsTo understand much of the functionality of Frame Relay, it is helpful to understand the

structure of the Frame Relay frame. Figure 4 depicts the basic format of the Frame Relayframe.

Flags indicate the beginning and end of the frame. Three primary components make upthe Frame Relay frame: the header and address area, the user-data portion, and the frame

check sequence (FCS). The address area, which is 2 bytes in length, is comprised of 10

bits representing the actual circuit identifier and 6 bits of fields related to congestionmanagement. This identifier commonly is referred to as the data-link connection

identifier (DLCI). Each of these is discussed in the descriptions that follow.

Standard Frame Relay Frame

The following descriptions summarize the basic Frame Relay frame fields illustrated inFigure 4.

FlagsDelimits the beginning and end of the frame. The value of this field is always

the same andis represented either as the hexadecimal number 7E or as the binary number 01111110.

AddressContains the following information:

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- DLCIThe 10-bit DLCI is the essence of the Frame Relay header. This value

represents the virtual connection between the DTE device and the switch. Each virtual

connection that is multiplexed onto the physical channel will be represented by a unique

DLCI. The DLCI values have local significance only, which means that they are unique

only to the physical channel on which they reside. Therefore, devices at opposite ends ofa connection can use different DLCI, values to refer to the same virtual connection.

Standard Frame Relay frames consist of the fields illustrated in Figure 4.

Extended Address (EA)The EA is used to indicate whether the byte in which the EA

value is 1 is the last addressing field. If the value is 1, then the current byte is determined

to be the last DLCI octet. Although current Frame Relay implementations all use a two-octet DLCI, this capability does allow longer DLCIs to be used in the future. The eighth

bit of each byte of the Address field is used to indicate the EA.

C/RThe C/R is the bit that follows the most significant DLCI byte in the Addressfield. The C/R bit is not currently defined.

Congestion ControlThis consists of the 3 bits that control the Frame Relay

congestion-notification mechanisms. These are the FECN, BECN, and DE bits, which arethe last 3 bits in the Address field.

Forward-explicit congestion notification (FECN) is a single-bit field that can be set to a

value of 1 by a switch to indicate to an end DTE device, such as a router, that congestion

was experienced in the direction of the frame transmission from source to destination.The primary benefit of the use of the FECN and BECN fields is the capability of higher-

layer protocols to react intelligently to these congestion indicators. Today, DECnet and

OSI are the only higher-layer protocols that implement these capabilities.

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Backward-explicit congestion notification (BECN) is a single-bit field that, when set to a

value of 1 by switch, indicates that congestion was experienced in the network in the

direction opposite of the frame transmission from source to destination.

Discard eligibility (DE) is set by the DTE device, such as a router, to indicate that themarked frame is of lesser importance relative to other frames being transmitted. Frames

that are marked as discard eligible should be discarded before other frames in a

congested network. This allows for a basic prioritization mechanism in Frame Relaynetworks.

DataContains encapsulated upper-layer data. Each frame in this variable-length field

includes a user data or payload field that will vary in length up to 16,000 octets. This

field serves to transport the higher-layer protocol packet (PDU) through a Frame Relaynetwork.

Frame Check SequenceEnsures the integrity of transmitted data. This value iscomputed by the source device and verified by the receiver to ensure integrity oftransmission.

Frame Relay: The Right Mix of TechnologyFrame relay combines the statistical multiplexing and port sharing features of X.25 withthe high speed and low delay characteristics of TDM circuit switching. Defined as a

"packet mode" service, frame relay organizes data into individually addressed units

known as frames rather than placing it into fixed time slots. This gives frame relay

statistical multiplexing and port sharing characteristics. Unlike X.25, frame relay

completely eliminates all Layer 3 processing. (See Figure 2.) Only a few Layer 2functions, the so-called "core aspects," are used, such as checking for a valid, error-free

frame but not requesting retransmission if an error is found. Thus, many protocolfunctions already performed at higher levels, such as sequence numbers, window

rotation, acknowledgments and supervisory frames, are not duplicated within the frame

relay network.

Stripping these functions out of frame relay dramatically increases throughput (i.e., the

number of frames processed per second for a given hardware cost), since each framerequires much less processing. For the same reason, frame relay delay is lower than X.25

delay, although it is higher than TDM delay, which does no processing.

In order to remove this functionality from the frame relay network, end devices must

ensure error-free end-to-end transmission of data. Fortunately, most devices, especiallythose attached to LANs, have the intelligence and processing power to perform this

function

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Fig5: Open Systems Interconnection (OSI) Model

.Table 1 summarizes the characteristics of TDM circuit switching,

packet switching and frame relay

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Frame relay uses a variable length framing structure, which, depending on user data,

ranges from a few to more than a thousand characters. This feature, similar to X.25, isessential for interoperability with LANs and other synchronous data traffic, which

requires variable frame size. It also means that traffic delays (although always lower than

X.25) will vary, depending on frame size. Some traffic types do not tolerate delay well,

especially variable delay. However, frame relay technology has been adapted to carryeven delay-sensitive traffic, such as voice.

ADVANTAGES OF FRAME RELAY

The success of a new technology is often dependent upon compellingeconomic reasons

for implementation. In the years since its inception, users of frame relay have found that

it provides a number of benefits over alternative technologies:

1. Lower cost of ownership

2. Well-established and widely-adopted standards that allow open architecture and plug-

and-play service implementation3. Low overhead, combined with high reliability

4. Network scalability, flexibility and disaster recovery

5. Interworking with other new services and applications, such as ATM

Cost of Ownership

Frame relay provides users a lower cost of ownership than competing

technologies for a number of reasons: It supports multiple user applications, such as TCP/IP, NetBIOS, SNA and voice,

eliminating multiple private lines to support different applications at a single site.

It allows multiple users at a location to access a single circuit and frame relay port, andit efficiently uses bandwidth, thanks to its statistical multiplexing capability.

Because only a single access circuit and port are required for each site, tremendous

savings are often realized in recurring costs of transmission facilities. Customers realize a significant reduction in hardware, such as the number of router

cards and DSU/CSUs required, reducing up-front costs and on-going maintenance costs

when compared with point-to-point technologies.

Standards

Well established, widely-adopted standards are key to equipment interoperability andefficient use of capital acquisition funds. With frame relay, users can relax knowing thatframe relay standards are in place both in the United States and around the world. This

ensures that equipment and services provided today will be functional for the long run,

with constantly evolving standards to support new applications and to meet dynamicmarket place needs

.

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Low Overhead and High Reliability

By using only two to five bytes of overhead, frame relay makes efficient use of each

frame. This means that more of the frame relay bandwidth is used for sending user data

and less for overhead. Bandwidth utilization of frame relay is nearly equivalent toleased lines and better than numerous other technologies, such as X.25 or IP switching.

When the effects are spread over a large network with numerous sites, results improveexponentially:

Simplified switching means less delay.

Statistical multiplexing leads to more efficient bandwidth use. Low overhead means bandwidth is used only for user data, not for data transport.

Network Scalability, Flexibility and Disaster Recovery

To the end user, a frame relay network appears straightforward: one user simply connectsdirectly 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 because of thisstructure, frame relay is more easily scalable than a fixed point-to-point network. Thismeans 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 lendsitself equally well to the provision of alternate routes to disaster recovery sites, which are,

in many cases, transparent to the end user.

Interoperability with New Applications and Services

Compared with using 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 new directions of existing networks, for example,SNA migration to APPN. In 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 theappropriate technology without stranding existing network equipment.

APPLICATIONS OF FRAME RELAY

Initially, frame relay gained acceptance as a means to provide end users with a solution

for LAN-to-LAN connections and to meet other data connectivity requirements. Frame

relay's compelling benefit is that it lowers the cost of ownership comparedto competing technologies: Frame relay supports multiple user applications, such as TCP/ IP, NetBIOS, SNA and

voice and thus eliminates the need for multiple private line facilities supporting different

applications at a single site. Because it statistically multiplexes, frame relay allows multiple users at a location to

access a single circuit and frame relay port, making efficient use of the bandwidth.

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Since only a single access circuit and port are required for each user site, users often

realize tremendoussavings in the cost of transmission facilities. Customers realize a significant reduction in the number of router cards and DSU/CSUs

required, reducing up-front costs as well as ongoing maintenance compared with point-

to-point technologies.

Application #1: Meshed LAN Peer-to-Peer Networking

In a traditional solution for LAN or client/server networking across a WAN, meshed

network implementations can be costly. Since private line pricing is distance sensitive,the price of the network increases as geographic dispersion increases. Changes in

network design normally require physical reconfigurations in addition to software

changes, which increases the time to administer the changes. (See Figure 11.)

Frame Relay for LAN or Client/ServerBy moving to frame relay for LAN or client/server applications, additional VCs betweenlocations can be provisioned for minimal incremental cost. Most public frame relay

pricing is distance insensitive. Virtual connections are software configurable. Changes to

VCs can be done relatively quickly. This makes frame relay ideal for meshedconfigurations. (See figure 12.)

Figure 11: Traditional Solution for LAN or Client/Server Networking

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Figure 12: Frame Relay Solution for LAN or Client/Server Networking

Application #2: SNA over Frame Relay

Over the past few years there has been a migration of legacy traffic, such as BSC (binarysynchronous communications) and Systems Network Architecture (SNA), from low

speed leased lines onto frame relay services. Ratified standards from the Internet

Engineering Task Force (IETF) and the Frame Relay forum enable the encapsulation of

multiple protocols, including SNA, over frame relay networks. Together, they provide astandard method of combining SNA and LAN traffic on a single frame relay link. This

enables FRADs and routers, which provide network connectivity, to handle time-

sensitive SNA and bursty LAN traffic simultaneously.

The integration of legacy and LAN-to-LAN traffic provides network administrators with

a more efficient, flexible and costeffective network as well as a number of other benefits: Simplify the network

Leverage investment in capital equipment

Move in SNAs stated direction, with migration strategies to distributed and peer-to-peer enterprise networks

Dramatically lower line costs a potential of 30 to 40 percent compared to dedicated

links

Provide up to a 40 percent increase in network utilization through frame relays

multiprotocol support Experience no disruption of operations integrity and control of the network are

sustained with NetView and SNMP management Offer high performance networking for Advanced Peer-to-Peer Networking (APPN)

Let's explore a few of these benefits. SNA installations have expanded their use of frame

relay because it is a mature, proven and stable technology. Moreover, users can leverageexisting capital equipment and maintain existing network management

practices.

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Frame relay can be integrated into SNA networks with little or no disruption. Users may

migrate to frame relay without any changes to Front End Processor (FEP) hardware or

software, SNA naming or network topologies. Frame relay allows the familiar NetViewtools and practices to be maintained, so there is no need to retool network operations or

retrain operations staff. This allows users to migrate at their own pace to multi-vendor

enterprise network management such as SNMP. Because frame relay is consistent withSNA's stated direction, end users have the comfort of adopting a migration strategy to

distributed and peer-to-peer enterprise networks to advance and optimize their SNA

network. Users benefit from improved response times and session availability with higherperformance than the original multidrop network. A typical frame relay SNA application

will illustrate these benefits.

Frame Relay in a Banking Application

In a large bank with many branch locations, SNA and BSC devices are co-located with

LANs, resulting in parallel branch networks and high monthly WAN costs. (See

Figure13.) Consolidating traffic on frame relay customer premise

Figure 13: Parallel SNA, BSC, Alarm, and LAN Branch networks

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Consolidating traffic on frame relay customer premise equipment (CPE) combines serial

protocol networks and LAN networks in each branch. The CPE provides an integration of

legacy devices typically found at a branch with emerging devices that support

client/server applications. How does it work? The frame relay CPE consolidates SNA/

SDLC (Synchronous Data Link Control) and BSC data and LAN data onto the framerelay based WAN. This eliminates multiple single protocol leased lines connecting the

branch to its host resources. It also exploits the advantages of the higher performanceLAN internetwork to consolidate serial and LAN traffic, compared with low speed

analog leased-line networks. The result is better performance, greater reliability and

lower costs. Because one frame relay access line can be used to reach he same number ofsites as multiple leased lines, the amount of networking equipment may be reduced.

Monthly telecommunications charges are also reduced and the network is simplified.

Other benefits include efficient bandwidth utilization, predictable and consistent response

times, enhanced session reliability and simplified network topologies andtroubleshooting. For example, a BSC-to-frame relay conversion can be performed by the

frame relay CPE for BSC Automated Teller Machine locations that are supported by anSNA host at the data center. This leverages the banks investment in capital equipment.(See Figure 14.)

Figure 14: Consolidated Bank Network

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SNA over Frame Relay Pays

Frame relay enables mission-critical SNA networks to improve performance and reduce

operating costs. These savings are available because frame relay meets the response time,

availability and management requirements of mission-critical applications.

If you're interested in the details of how frame relay can be used as a replacement forSDLC point-to-point networks and how FRF.3.1 provides interoperability, take a look at

the SNA section in the advanced trail.

Application #3: Voice Over Frame Relay (VoFR)

Today, non-traditional uses for frame relay are beginning to emerge. One new

application, voice over frame relay (VoFR), offers telecommunication and network

managers the opportunity to consolidate voice and voice-band data (e.g., fax and analog

modems) with data services over the frame relay network. (See Figure 15.)

In migrating leased line networks to frame relay, many network administrators found a

cost-effective solution for their data needs. However, since many leased-line networks

also carried voice, a solution was needed to address corporate voice requirements. Withthe ratification of FRF.11, a standard was established for frame relay voice transport.

Among other things, FRF.11 defines standards for how vendor equipment interoperates

for the transport of voice across a carrier's public frame relay network.

Maximizing Frame Relay NetworksFRF.11 enables vendors to develop standards-based equipment and services that

interoperate. It also enables network managers seeking to reduce communications costsand maximize their frame relay network to consider VoFR as an option to standard

voice services. In some cases, users may find they have excess bandwidth in their frame

relay network that could efficiently support voice traffic. Other telecommunicationsmanagers may find that the incremental cost of additional frame relay bandwidth for

voice traffic may be more cost-effective than standard voice services offered by local or

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long distance carriers. VoFR can provide end users with a cost effective option for voice

traffic transport needs between company locations. For instance, the network manager

may integrate some voice channels and serial data over a frame relay connection between

a branch office and corporate headquarters. By combining the voice and data traffic on a

frame relay connection already in place, the user has the potential to obtain cost-effectiveintracompany calling and efficient use of the network bandwidth. Because it does not

significantly increase network architecture, link speeds or CIR, the integration of voice,fax and data traffic over a single access link provides a viable option for network

managers and adds to the growing list of new and non-traditional applications for frame

relay. Users are finding that frame relay offers another significant advantage: the abilityto interwork with other advanced services, such as ATM

.

Application #4: Frame Relay-to-ATM Interworking

Frame Relay/ATM Interworking is a viable solution that provides users with low costaccess to high speed networks. Ratified by both the ATM and Frame Relay Forums, theFrame Relay/ATM PVC Interworking Implementation Agreements (IAs) provide a

standards-based solution for interworking between existing or new frame relay networks

and ATM networks without any changes to end user or network devices. Why do userswant to interwork frame relay and ATM? While frame relay is well suited for many

applications including LAN internetworking, SNA migration and remote access, other

applications, such as broadcast video and server farm support, may be better suited for

ATM networks. Users are also interested in interworking frame relay and ATM networksto protect their capital investment in existing frame relay networks and to support

planned migrations from frame relay to ATM. Frame Relay/ATM SVC Interworking IAs

are currently being developed.

Frame Relay-to-ATM Interworking Standards

There are two Frame Relay/ATM Interworking IAs for PVCs, eachencompassing two

different types of interworking. The first one, Frame Relay/ATM Network Interworkingfor PVCs (FRF.5) allows network administrators to scale the backbone beyond the 45

Mbps trunks supported by frame relay. In other words, it provides the standards for ATM

to become a high speed backbone for frame relay PVC users. The second one, Frame

Relay/ ATM Service Interworking for PVCs (FRF.8) defines the standard for frame relayPVC and ATM PVC end users or systems to communicate seamlessly. Frame

Relay/ATM Network Interworking for PVCs can be thought of as encapsulation while

Frame Relay/ATM Service Interworking for PVCs is translational between the twoprotocols. Let's take a closer look at each standard.

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Frame Relay/ATM Network Interworking for PVCs

Frame Relay/ATM Network Interworking allows Frame Relay end-user or networking

devices such as FRADs or routers to communicate with each other via an ATM network

employed as the backbone. For example, SNA terminal users connected to FRADs inbranch offices communicate with frame relay-attached IBM 3745 Communications

Controllers located in corporate headquarters locations using a high speed ATM networkas the backbone.

Figure 16: Frame Relay/ATM Network Interworking

The frame relay devices interact as if they are using frame relay for the entire connectionwithout knowing that an ATM networks in the middle. An ATM backbone connecting

multiple frame delay networks can provide scalfor a large number of locations and end

user devices, without requiring hanges to the devices themselves.

Frame Relay/ATM Service Interworking for PVCs

Frame Relay/ATM Service Interworking enables communication between an ATM andframe relay network or end user devices. Frame Relay/ATM Service Interworking allows

existing frame relay devices in the remote branch offices to communicate with end users

at headquarters who are using ATM-based applications. By enabling existing devices to

access new ATM-based applications, Frame Relay/ATM Service Interworking protects

the investment in existing equipment. This promotes the decoupling of client and serversides of the network, allowing each to use the resources that best meet bandwidth

requirements and budget constraints, ability and high speed support

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Figure 16: Frame Relay/ATM Network Interworking

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