The question "What is MMS in TCP?" is a bit misleading because MMS (Manufacturing Message Specification) isn't directly in TCP. Instead, MMS is an application layer protocol that often uses TCP as its transport protocol. Let's clarify what each of these is and how they relate:
Understanding the Components
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TCP (Transmission Control Protocol): TCP is a fundamental protocol within the Internet Protocol Suite (TCP/IP). It provides reliable, ordered, and error-checked delivery of a stream of data between applications. Think of TCP as the reliable delivery truck for your data, ensuring everything arrives intact and in the correct sequence.
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MMS (Manufacturing Message Specification): MMS is an application layer protocol specifically designed for industrial automation systems, as described in the reference. It defines a standard set of messages for exchanging data between devices, such as programmable logic controllers (PLCs), robots, and other manufacturing equipment. It's like a universal language for these industrial devices to talk to each other.
How MMS Uses TCP
MMS relies on TCP/IP as its foundation. This means that when industrial devices communicate using MMS, the actual data transmission occurs over TCP connections. This is crucial because MMS applications often require dependable data exchange, and TCP's error-checking and reliable delivery features meet those needs.
Here's a breakdown of how they work together:
- Application Layer (MMS): MMS applications on devices create messages according to the MMS standard. These messages include requests for data, instructions, and other information pertinent to industrial control.
- Transport Layer (TCP): MMS passes these messages to the TCP layer. TCP then manages the reliable transmission of this data across the network by breaking it into smaller packets and ensuring that these packets reach their destination in the correct order.
- Network Layer (IP): Below TCP, the IP layer handles the routing of the data across different networks.
- Physical Layer: Finally, the data is physically transmitted over the network infrastructure (e.g., Ethernet cables).
Key Points
- MMS is NOT part of TCP: MMS is an application protocol built on top of TCP, not integrated within it.
- TCP Enables MMS Communication: TCP's reliable data transfer makes it suitable as a transport layer for the industrial needs of MMS.
- MMS Standardizes Industrial Data: MMS defines a specific way for industrial devices to communicate, standardizing various functions within manufacturing applications.
- Reliability is Crucial: The use of TCP in MMS ensures data is delivered correctly and in order, vital for industrial applications.
Example
Imagine a scenario where a supervisory control and data acquisition (SCADA) system needs to read data from a PLC.
- The SCADA system sends an MMS request to the PLC via a TCP connection.
- The PLC receives the request, processes it, and sends the data back using MMS over the same TCP connection.
- TCP ensures this data reaches the SCADA system reliably.
In Simple Terms
Think of it like sending a package. MMS is the specific label and content instructions for the package, while TCP is the reliable postal service that ensures it gets delivered intact and in the right order.
