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ForeRunner
ATM Switch Network Configuration Manual
Configuring FramePlus Modules
D.1 Frame Relay Overview
Serving as an interface between user and network equipment, Frame Relay provides a means
for statistically multiplexing many logical data channels (or virtual circuits) over a single
physical transmission link. Frame Relay is ideal for supporting multiple data streams because
it provides flexible and efficient utilization of available bandwidth.
D.1.1 Interworking Function (IWF)
When connecting an ATM Customer Premise Equipment (CPE) and a Frame Relay CPE, each
device has no knowledge that the distant device supports a different protocol. The FramePlus
network module performs a service interworking function (IWF) to terminate the respective
Frame Relay and ATM services and to perform appropriate interworking conversions before
transmitting the CPE information. IWF uses two different modes of operation to address
interoperability between upper layer user protocol encapsulation techniques on the FramePlus
network module: translation mode and transparent mode.
D.1.1.1 Translation Mode
When the two CPEs support different encapsulation protocols, a translation, or re-encapsula-
tion, must take place in the CPE payload portion of the cells that are being transmitted. Since
Frame Relay supports RFC 1490 encapsulation and ATM supports RFC 1483 encapsulation,
the information in the frames is converted to cells and vice versa.
D.1.1.2 Transparent Mode
When both CPEs support the same encapsulation protocol, there is no need for any translation
or re-encapsulation of the CPE payload portion of the cells that are being transmitted. There-
fore, the traffic is sent “transparently.” When the transparent method of IWF is used, there is a
mapping that occurs of each Frame Relay DLCI to an ATM VPI, VCI combination.
One example would be if proprietary encapsulation techniques are being used. A second
example would be if there is FR/CPE equipment at both edges of the network with ATM pro-
viding the transport, there would be no need for any translation.
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Страница 16: ...TOC 10 ForeRunner ATM Switch Network Configuration Manual Table of Contents ...
Страница 20: ...LOF 4 ForeRunner ATM Switch Network Configuration Manual List of Figures ...
Страница 22: ...LOT 2 ForeRunner ATM Switch Network Configuration Manual List of Tables ...
Страница 30: ...viii ForeRunner ATM Switch Network Configuration Manual Preface ...
Страница 144: ...3 58 ForeRunner ATM Switch Network Configuration Manual Configuring an Emulated LAN ...
Страница 180: ...6 12 ForeRunner ATM Switch Network Configuration Manual ATM Forum PNNI ...
Страница 220: ...9 6 ForeRunner ATM Switch Network Configuration Manual Configuring Timing ...
Страница 300: ...D 24 ForeRunner ATM Switch Network Configuration Manual Configuring FramePlus Modules ...
Страница 308: ...Acronyms 8 ForeRunner ATM Switch Network Configuration Manual Acronyms ...
Страница 346: ...Glossary 38 ForeRunner ATM Switch Network Configuration Manual Glossary ...
Страница 352: ...Index 6 ForeRunner ATM Switch Network Configuration Manual Index ...