12-6 Cisco BPX 8600 Series Reference
Networking Interworking
The frame relay to ATM networking interworking function is available as follows:
• IPX switch frame relay (shelf/feeder) to IPX switch frame relay (either routing node or
shelf/feeder).
• MGX 8220 frame relay to MGX 8220 frame relay.
• MGX 8220 frame relay to IPX switch frame relay (either routing node or shelf/feeder).
• IPX switch frame relay (either routing node or shelf/feeder) to BPX switch or MGX 8220 ATM
port.
• MGX 8220 frame relay to BPX switch or MGX 8220 ATM port.
• In the items listed above, an IGX switch can be substituted for each instance of an IPX switch.
On the IPX switch, interworking is performed by the AIT card, and on the IGX switch by the BTM
card. A simplified example of the connection paths is shown in Figure 12-6. In interworking, the AIT
card receives FastPackets from the FRP, rebuilds the frames, and converts between frames and ATM
cells. Data is removed from one package and placed in the other. Congestion information from the
header is mapped to the new package. This processing by the AIT trunk card is called Complex
Gateway. AIT trunk cards are required on every BPX switch to IPX switch hop in a Frame Relay to
ATM connection’s path.
Figure 12-6 ATF Connections, Simplified Example
The cells within the frame are expected to possess the standard ATM Access Interface cell header.
The traffic is assumed to have AAL-5 PDUs, and will not function properly otherwise (framing
errors will result). Within the AAL-5 PDUs, the data must be packaged in standard frame relay
frames, one frame per PDU (with respect to the AAL-5 layer).
The UPC and ForeSight algorithms are applied according to their configured values. The cell
headers are converted into the proprietary Cisco WAN switching STI format before entering the
network. The cells are delivered to their destination according to the configured route of the
connection. Cells can be lost due to congestion.
S5241
SV
+
NMS
ATM
(T3/E3
Feeder
trunk
ATM
(T3/E3
Frame
Relay (T1)
Feeder
trunk
Some typical ATF connection paths shown:
BNI
BPX HubIGX Shelf
BNI
FRM
UXM
Crosspt
switch
ATM
(T3/E3
ASI
BPX
BNI
Crosspt
switch
AXIS
shelf
Frame
Relay
(T1)
Frame
Relay (T1)
Frame
Relay (T1)
(pvc2)
(pvc3)
IGX
UXM
FRM
Router
ATM
(T3/E3/
OC-3
ATM
(T3/E3/
OC-3
(pvc1)
(pvc3)
CPE
Frame
Relay (T1)
(pvc1)
(pvc2)
Router
