THE BASIC GUIDE TO
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Chapter Four |
No discussion of frame relay would be complete without mentioning standards. This chapter will discuss frame relay standards — those that currently exist and how they developed. We'll also acquaint you with the Frame Relay Forum and the Implementation Agreements the Forum develops to ensure frame relay interoperability.
Basic Trail: Go!
The basic trail will discuss the development of ANSI and ITU standards for frame relay. This section also gives an overview of the Frame Relay Forum and lists the current Implementation Agreements.
There is no Advanced Trail in this chapter.
View Points :
Table 2: Frame relay standards Go
Table 3: List of frame relay Implementation Agreements (IAs) Go
Shortcut: Go!
The shortcut summarizes current frame relay standards and the work of the Frame Relay Forum.
How Did Frame Relay Standards Develop?
The remarkable degree of industry consensus about the need for frame relay to supplement existing switching technologies resulted in rapid development of industry standards. There are two major standards organizations which are active in this area:
To understand how frame relay standards developed, we need to go back to 1988. That year, ITU-T (then called CCITT) approved Recommendation I.122, "Framework for additional packet mode bearer services."
I.122 was part of a series of ISDN-related specifications. ISDN developers had been using a protocol known as Link Access Protocol - D channel (LAPD) to carry the signaling information on the "D channel" of ISDN. (LAPD is defined in ITU Recommendation Q.921.)
Developers recognized that LAPD had characteristics that could be very useful in other applications. One of these characteristics is that it has provisions for multiplexing virtual circuits at level 2, the frame level (instead of level 3, the packet level as in X.25). Therefore, I.122 was written to provide a general framework outlining how such a protocol might be used in applications other than ISDN signaling.
At that point, rapid progress began, led by an ANSI committee known as T1S1, under the auspices of the Exchange Carrier Standards Association (ECSA). This work resulted in a set of standards defining frame relay very clearly and completely. The principal frame relay standards are shown in Table 2.
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Description
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ANSI Standard
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Status
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ITU Standard
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Status
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Service Description
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T1.606
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Standard
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I.233
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Approved
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Core Aspects
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T1.618 (previously known as T1.6ca)
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Standard
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Q.922 Annex A
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Approved
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Access Signaling
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T1.617 (previously known as T1.6fr)
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Standard
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Q.933
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Approved
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T1.606 was approved early in 1990. Thanks to the hard work of the ANSI committee, coupled with a clear mandate from the market, the remaining ANSI standards sped through the stages of the standards process to receive complete approval in 1991.
Frame Relay Standards
The fast pace of frame relay standards work at ANSI was matched by an outstanding degree of cooperation and consensus in the international arena. As a result, the ITU-T recommendations for frame relay are in alignment with the ANSI standards and have also moved rapidly through the approval process. (Authors' note: although we refer to ANSI standards throughout this book, most of the discussion applies equally to the ITU-T standards.)
Interoperability and Standards Compliance
With the number of options in the standards and the range of design choices faced by vendors, what does it mean to a customer interested in interoperability?
Minimum requirements: Basic Data Handling
In order to achieve interoperability, frame relay network equipment must comply with the basic data transport method specified in the ANSI standard, which states that frame relay takes place using the DLCI in the two-byte frame relay header. This subject is covered in Chapter 2. With that relatively simple requirement met, there is interoperability. The remaining requirements determine how well the network performs and whether it can be managed.
Required for real-world networks: Interface signaling
The interface control mechanisms described in Chapter 3 are optional. Data flows without them, and ignoring them are not a violation of the standard.
In real networks, however, you may find interface signaling essential to ensure that the network operates with adequate performance. Otherwise, there is no way for a network to control congestion. This means that as the traffic increases, network throughput may decrease. And throughput may continue to decrease as congestion is further exacerbated by more discards and retransmissions.
The Frame Relay Forum
The Frame Relay Forum is a non-profit organization dedicated to promoting the acceptance and implementation of frame relay based on national and international standards. Established in 1991, the Forum now has more than 300 member companies worldwide.
The Forum develops and approves Implementation Agreements (IAs) to ensure frame relay interoperability and facilitates the development of standard protocol conformance tests for various protocols. Since the earliest frame relay IAs, additional features, such as multicast, multiprotocol encapsulation and switched virtual circuit signaling, have been defined in subsequent IAs to increase the capabilities of frame relay.
Work by the Frame Relay Forum has resulted in the completion of several implementation agreements, which are listed in Table 3. Work on implementation agreements and standards is ongoing to add enhancements and broaden the applications for frame relay.
An updated listing of IAs can be found on the Frame Relay Forum web site at <<www.frforum.com>> and in the Forum's quarterly newsletters.
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FRF.1.1
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User-to-Network (UNI) Implementation Agreement
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FRF.2.1
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Frame Relay Network-to-Network (NNI) Implementation Agreement
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FRF.3.1
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Multiprotocol Encapsulation Implementation Agreement (MEI)
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FRF.4
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Switched Virtual Circuit Implementation Agreement
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FRF.5
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Frame Relay/ATM PVC Network Interworking Implementation Agreement
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FRF.6
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Frame Relay Service Customer Network Management Implementation Agreement (MIB)
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FRF.7
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Frame Relay PVC Multicast Service and Protocol Description Implementation Agreement
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FRF.8
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Frame Relay/ATM PVC Service Interworking Implementation Agreement
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FRF.9
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Data Compression over Frame Relay Implementation Agreement
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FRF.10
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Frame Relay Network-to-Network Interface SVC Implementation Agreement
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FRF.11
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Voice over Frame Relay Implementation Agreement
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FRF.12
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Frame Relay Fragmentation Implementation Agreement
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There are two major standards organizations:
The initial frame relay standard was approved in 1990 by ANSI, and the remaining standards were approved by 1991. ITU recommendations for frame relay are in alignment with the ANSI standards.
In order to achieve interoperability, frame relay network equipment must comply with the basic data transport method specified in the ANSI standard, which states that frame relay takes place using the DLCI in the two-byte frame relay header.
Although interface control mechanisms are optional, they are essential to ensure that the network operates with adequate performance.
The Frame Relay Forum is a non-profit organization dedicated to promoting the acceptance and implementation of frame relay based on national and international standards.
The Forum develops and approves Implementation Agreements (IAs) to ensure frame relay interoperability. Since the earliest frame relay IAs, additional features, such as multicast, multiprotocol encapsulation and switched virtual circuit signaling, have been defined to increase the capabilities of frame relay.
END CHAPTER FOUR.
GO TO CHAPTER FIVE
