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A
B: P
B
PPENDIX
ATH
Ethernet Interface
S330/S310 M
UILDER
ODULE AND
The PathBuilder S330/S310 performs all the required translation and
n
management functions between these two networks, implementing the stacks
as indicated in Figure 162 and performing the following key functions:
Translating from Q.922 Frame to FR-SSCS/ATM AAL5 PDU and from
n
FR-SSCS/ATM AAL5 PDU to Q.922 Frame
Supporting 2-octet—not 3-octet or 4-octet—FR header (10-bit DLCI)
n
Allowing you to configure DLCI to VPI/VCI mapping
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Providing one-to-one mapping: maps one FR-SSCS DLCI (default FR-SSCS
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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.)
Managing traffic
n
Handling congestion
n
The PathBuilder S330/S310 Ethernet LAN modules 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 ports 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
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encapsulated properly for Frame Relay.
If the packet is to go on an ATM interface, the bridge determines the VCI
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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.
The SAR contains 15 traffic shapers, each of which can be programmed for
sustained cell rate of transmission (SCR), peak cell rate (PCR), and maximum burst
size (MBS).
The traffic shapers work as follows:
The packet is segmented using a dual leaky buffer algorithm, whereby the cells
n
are transmitted from each connection in the shaper at an average rate until the
bucket of token fills up (a token is given to the connection at an average rate if
it has no cells to transmit at that moment).
The shaper then turns the burst mode on and transmits at the peak rate for a
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burst length. Note that the shaper serves every connection independently.
Cells received from the ATM WAN are switched via the CTX chip to the SAR
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queues. You can enable shaping on the SAR queues to slow down the
incoming traffic on the SAR.
A
O
PPLICATION
VERVIEW
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