CGW-MB Installation and Users’ Manual | P/N:LS10248-000HW-E | REV.G | JUL/31/2022
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Bandwidth Calculation
Modbus Communications
7.6 Bandwidth Calculation
Use the following information to calculate the network bandwidth CGW-MB usage
requires and how it will impact the network.
Requirements for the Calculation
•
One request and response pair requires 329 Bytes (66 + 263).
•
If a client is polling at one second intervals, then request and response are both
possible in one second.
•
A request and response pair creates network traffic of 329 Bytes per second (329 x 1).
•
In other words, a request and response pair creates network traffic of 2632 bits per
second (329 x 8).
•
Therefore, the network must be able to accommodate at least 0.0027 Mbps data flow.
•
Once every five seconds, an analog request adds a small amount of network traffic.
•
Formula for CGW-MB network bandwidth requirement based on polling rate:
Bandwidth Requirement
=
(329 x (1000/polling rate in milliseconds) x 8) / (10 ^ 6) Mbps
Table 7.2: Total Required Bandwidth
For TCP Request
Description
Bytes
Ethernet Header
14
IP Header
20
TCP Header
20
MBAP Header
7
Message—5 bytes Function code (1) + Start Address (2) + Quantity of Registers (2)
5
Total Bytes
66
For TCP Response
Description
Bytes
Ethernet Header
14
IP Header
20
TCP Header
20
MBAP Header
7
Message—Function code (1) + Byte Count (1) + Max 100 registers of each
2 Bytes (200)
202
Total Bytes
263