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Service Interworking
Service Interworking
In Service Interworking, the ATM port connected to a Frame Relay port does not need to be aware that
it is connected to an interworking function. However, in Network Interworking, the ATM device does
need to be aware that it is connected to an interworking function.
The ATM device uses a standard service specific convergence sublayer, instead of using the Frame Relay
FR-SSCS (see Figure 22-4).
The Frame Relay service user does not implement any ATM specific procedures, and the ATM service
user does not need to provide any Frame Relay specific functions. All translational (mapping functions)
are performed by the intermediate IWF.
The ATM endpoints may be any ATM UNI/NNI interface supported by the MGX 8220 or MGX 8800,
such as BXM and AUSM. Translation between the Frame Relay and ATM protocols is performed in
accordance with RFC 1490 and RFC 1483.
Figure 22-4 Frame Relay to ATM Service Interworking Detail
B - CPE
Upper
layers
CPCS
SAR
ATM
Physical
Frame Relay CPE connected to B-ISDN CPE
Networking Interworking
In Network Interworking, in most cases, the source and destination ports are Frame Relay ports, and the
interworking function is performed at both ends of the connection as shown in Part A of Figure 22-5.
If a Frame Relay port is connected across an ATM network to an ATM device, network interworking
requires that the ATM device recognize that it is connected to an interworking function (Frame Relay,
in this case). The ATM device must then exercise the appropriate service specific convergence sublayer
(SSCS), in this case the Frame Relay service specific convergence sublayer (FR-SSCS) as shown in
Part B of Figure 22-5.
Cisco BPX 8600 Series Installation and Configuration
22-4
BPX
ASI
BNI
ATM
ATM
Physical
Physical
ATM T3/E3
ATM T3/E3
(feeder trunk)
ATM NW
Chapter 22
Configuring Frame Relay to ATM Network and Service Interworking
MGX 8220
BNM
ATM
ATM T3/E3
Physical
Physical
(feeder trunk)
AXIS shelf
BNM
RFC 1483 RFC 1490
Null SSCS
AAL-5
ATM
ATM
Physical
Physical
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
B - CPE
AUSM
Upper
layers
CPCS
SAR
ATM
ATM
Physical
ATM T1/E1
FRSM
FR CPE
Upper
layers
Q.922
Q.922
Physical
Physical
Frame Relay
Narrowband NW
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