MODBUS-GW Installation and Operation Manual — P/N LS10015-000NF-E:C2 4/30/2019 9
Bandwidth Calculation Product Overview
1.7 Bandwidth Calculation
Use the following information to calculate the network bandwidth MODBUS-GW usage requires and how it will impact the network.
1.7.1 Calculating the Bandwidth Requirement
• 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 MODBUS-GW network bandwidth requirement based on polling rate:
Bandwidth Requirement = (329 x (1000/polling rate in milliseconds) x 8) / (10
6
) Mbps
Table 1.1 Modbus 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
Table 1.2 Modbus 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
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