3Com SuperStack II PathBuilder S330 Reference Manual page 255

The interworking scheme shown in Figure 177 works as follows:
The application on the frame DTE passes its data through Q.922 core service
with the assumption that there is an end-to-end pipe to carry its data from its
end to the other DTE at the far end. The Q.922 core only sees a point-to-point
link to the next connection point; it has no knowledge about the type of
network behind the current link.
On the other end, the application residing in ATM DTE passes its data through
a NULL SSCS that sits on top of AAL5. What this ATM DTE sees is the ATM
network to which it is connected.
The PathBuilder S330/S310 switch sitting in the middle performs all the
required translation and management functions between these two networks,
implementing the stacks as indicated in Figure 177 and performing the
following key functions:
Translating from Q.922 Frame to ATM AAL5 PDU and from ATM AAL5 PDU
to Q.922
Performing Frame PVC management
Managing traffic
Handling congestion
Network Interworking Function
Figure 178 shows a PathBuilder S330/S310 switch providing Network
Interworking function between Frame Relay and ATM services.
Figure 178 Frame Relay/ATM Network Interworking Connection (FRF.5)
Frame
Relay
DTE
Frame
Frame
Relay
Relay
DTE
Network
Application
Q.922
DL Core DL Core
PHY
PathBuilder ATM
Network
S330/S310
FR-SSCS
Q.922
AAL 5
SAR
ATM
PHY PHY
Serial Interface
Frame
Relay
Network
PathBuilder
S330/S310
FR-SSCS
Q.922
AAL 5
DL Core
SAR
ATM
PHY PHY
247
Frame
Relay
DTE
Frame
Relay
DTE
Application
Q.922
DL Core
PHY