Expand Configuration and Management Manual (G06.24+)

Tuning
Expand Configuration and Management Manual—523347-008
20-9
Packet Format
The values of fsm and pkt vary according to the oldest version of the Expand
subsystem at the originating and destination nodes, as shown in Table 20-2.
For example, if an application message of 500 bytes is sent from a G02 version of the
Expand subsystem to another G02 Expand node, the number of Expand packets
required is calculated as follows:
1 + $INT((500 + 95) / (256 - 64)) =
1 + $INT (595 / 192) =
1 + $INT (3.09) = 4
Packet Format
The Expand subsystem enforces a minimum value of 1024 bytes for the variable-
packet size (set with the PATHPACKETBYTES modifier). The default value for
PATHPACKETBYTES (1024 bytes) yields the same data-per-packet percentage as
nonextended packets with a frame size of 132 words.
Table 20-3 compares the data-per-packet percentages for nonextended packet
(L4EXTPACKETS_OFF modifier) and extended packet (L4EXTPACKETS_ON
modifier) header formats. An Expand network using a frame size of 132 words is
assumed.
Table 20-2. Message Header and Packet Header Overhead
Expand Version fsm (Bytes) pkt (Bytes)
C30.08 and earlier 53 16
C30.09 49 64
D10 89 16
D20 and later 95 64
Table 20-3. Data-Per-Packet Percentages
Packet
Header
Format
PATHPACKETBYTES
Modifier Value (Bytes)
Packet
Size
(Bytes)
Packet
Header
(Bytes)
Data
Portion
(Bytes)
Percentag
e
(Bytes)
Nonextended Any 256 16 240 93.75
Extended 0 256 64 192 75.00
Extended 1024 1024 64 960 93.75
Extended 4095 4095 64 4031 98.44
Note. The variable packet-size feature cannot be used with the L4EXTPACKETS_OFF
modifier.