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248
A
B: P
B
PPENDIX
ATH
UILDER
Ethernet Interface
(10BASE-T or
10/100BASE-T)
S330/S310 M
A
ODULE AND
PPLICATION
In the interworking scheme shown in Figure 178, a Frame Relay DTE
communicates with the other Frame Relay DTEs through an ATM network. Note
that FR-SSCS is used in this configuration.
This interworking scheme works as follows:
The Frame Relay DTE at either end works exactly the same way as the Frame
Relay DTE in the Service Interworking configuration: it passes its data through
Q.922 core service, assuming that there is an end-to-end pipe to carry its data
from its end to the other DTE at the far end.
On the other end, the application resides in a Frame DTE instead of an ATM
DTE.
The PathBuilder S330/S310 switch performs all the required translation and
management functions between these two networks, implementing the stacks
as indicated in Figure 178 and performing the following key functions:
Translating from Q.922 Frame to FR-SSCS/ATM AAL5 PDU and from
FR-SSCS/ATM AAL5 PDU to Q.922 Frame
Supporting 2-octet—not 3-octet or 4-octet—FR header (10-bit DLCI)
Allowing you to configure DLCI to VPI/VCI mapping
Providing one-to-one mapping: maps one FR-SSCS DLCI (default FR-SSCS
DLCI (1022) or 16-991) for one FR DLCI to one ATM VPI/VCI. (The FR-SSCS
DLCI(s) for the two end systems should be configured to be the same.)
Providing many-to-one mapping (network interworking only): maps
multiple DLCIs to one ATM virtual circuit.
Managing traffic
Handling congestion
The Ethernet 10BASE-T port and optional 10/100BASE-T (PCI Ethernet) port on
the PathBuilder S330/S310 switch provide multiple connections to Ethernet
segments over ATM WAN.
When the Ethernet interface receives data from the LAN, any packets appearing
on the 10BASE-T or 10/100BASE-T port are checked for packet integrity and
stored in the shared memory area. The system then performs a bridge operation to
determine if the packet will be sent on to any other interface. See "Bridge
Operation" below for details.
If the packet is to go on the HDLC port, it is bridged directly after being
encapsulated properly for Frame Relay.
If the packet is to go on an ATM interface, the bridge determines the VCI
connection for the packet destination. The packet is then encapsulated
according to RFC 1483, and the descriptor is handed off to the SAR, together
with the associated ATM header descriptor. The SAR appends the AAL5
convergence sublayer to the packets and queues them according to the shaper
you specify for that connection. The packet is then segmented according to the
rate of the traffic descriptor, and the cells are sent to the CTX where ATM
switching and queueing is performed.
O
VERVIEW
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