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The LMI protocol provides operational support for the User Network Interface (UNI). Originally defined by the Frame Relay Forum in 1990, it since has been adopted by ANSI and the ITU-T. The LMI is a polling protocol between the FRAD and the network that verifies the existence and availability of the PVC, as well as the integrity of the UNI link.
As a shared network designed for intensive data communications, Frame Relay is subject to congestion. Indeed, it is designed for congestion as a natural occurrence which serves to reduce the overall cost of the network. Congestion management is addressed through the following parameters, specified in an addendum to ANSI T1.606 [11-3], [11-8], and [11-9]:
The costs of Frame Relay vary widely among equipment manufacturers and carriers. It is clear, however, that Frame Relay is highly cost-effective for building mesh networks at > 56 Kbps. The equipment cost is that of the FRAD, which can be standalone, or can be built under the skin of a bridge or router. A DSU/CSU also is included in the device. In addition to the cost of the FRAD, the carriers charges typically include some combination of port charge (bandwidth-sensitive), access line (bandwidth- and distance-sensitive), Committed Information Rate (CIR) and burst size (Bc) (time-sensitive).
Frame Relay networks traditionally have been priced on a case-by-case basis. In consideration of the widespread popularity of the service, however, the FCC in October 1995 classified Frame Relay as a basic service. This reclassification required that the RBOCs, AT&T, MCI, and Sprint file tariffs. The publishing of Frame Relay rates allows smaller users to comparison-shop, simplifying the process and likely reducing their costs. Lager users, on the other hand lose some bargaining power. Significantly, the FCC has taken a position which will likely extend to other fast packet services in the future [11-11] and [11-12].
Prices have swung up and down since the FCC decision as competitors seek to develop their strategies. AT&T 512 Kbps PVCs are priced at $1,037; with 512 Kbps ports at $1,370 [11-13] and [11-14]. In the highly-competitive Frame Relay market, mesh networking that can be accomplished at costs which can be as little as 50% of the cost of a comparable FT-1 network [11-15]. Further, costs can be mitigated to some extent through the use of compression devices such as those offered by Telephone Company Systems, Inc. These devices allow transmission at a lower port speed and CIR through the recognition of patterns within data frames intended for as multicasting, or transmission to multiple addresses [11-16].
Frame Relay via VSATs is now offered by Orion Atlantic LP through its VISN (Virtual Integrated Sky Network) to sites in Europe and the eastern two-thirds of the U.S. Priced at $2,000 to $5,000 per month, VISN claims to be 35% to 40% less costly than it cabled counterparts [11-17].
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