Samsung Ubigate iBG2016, Configuration Manual

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Ubigate iBG2016 Configuration Guide/Ed.00
© SAMSUNG Electronics Co., Ltd.
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Buffer Reservation for Interfaces
When a wan interface is created, a certain amount of queue buffers will be
reserved for it’s transmitting queue from the global buffer pool. Buffer
reservation is only done for wan interfaces and not GE interfaces because we
expect congestion and hence queue build-ups only on wan interfaces.
The number of buffers reserved for a wan interface’s queue is such that it
provides 15 msec of buffering for 100 byte packets at a rate equal to the
interface bandwidth. This amount of buffering is always guaranteed for a wan
interface. A wan interface can use more than its reserved amount of buffers by
borrowing queue buffers from the global pool if available. However, only the
portion allocated for transmit queues can be borrowed. Therefore it is not
possible for traffic, flooding a WAN interface, to consume all buffers and
starve other interfaces(including Ethernet) of receive buffers. The calculation
below shows how the number of reserved buffers is calculated for a WAN
interface.
MAX((NxBCR_BUFS_RED * Bc)/AVG_PKTSIZE_FOR_BUF_CALC, 20) +
(Bc/MIN_PKTSIZE_FOR_BUF_CALC)
Where,
The value of NxBCR_BUFS_RED is 3,
The value of _PKTSIZE_FOR_BUF_CALC is 100 bytes,
Bc is interface bandwidth proportional to scheduling interval(5 msec),
The value of MIN_PKTSIZE_FOR_BUF_CALC 64 bytes.
The first part of expression gives 15 msec worth of packet buffering, and
second part of expression gives extra buffers accounting for buffers which are
not freed right away after completing transmission of packet from the driver
queue.