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
