TSN Transmission Sequence Number
Transmission Sequence Number (TSN) is a concept used in networking protocols, particularly in the context of the Stream Control Transmission Protocol (SCTP) and Time-Sensitive Networking (TSN). It serves as a unique identifier for data chunks or packets sent over a network, allowing the receiver to reassemble and process them in the correct order. In this explanation, we will focus on TSN's significance in SCTP and its role in ensuring reliable and ordered data transmission.
1. Introduction to SCTP
The Stream Control Transmission Protocol (SCTP) is a reliable, message-oriented transport protocol that operates at the transport layer of the OSI (Open Systems Interconnection) model. SCTP is designed to provide features such as message-oriented communication, multi-streaming, multi-homing, and congestion control, making it suitable for various applications, including real-time and time-sensitive communications.
2. The Role of TSN in SCTP
TSN is a fundamental aspect of SCTP and is used to address two critical requirements of the protocol:
2.1. Uniqueness: Each data chunk transmitted by SCTP is assigned a unique TSN. This uniqueness is essential to distinguish individual chunks from one another during transmission and reassembly at the receiving end.
2.2. Ordered Delivery: SCTP ensures ordered delivery of data chunks to the application layer at the receiver. TSNs play a significant role in achieving this by enabling the receiver to reconstruct the original message from the received data chunks based on their sequence numbers.
3. TSN Assignment and Management
When an SCTP association is established between two endpoints (sender and receiver), TSNs are assigned by the sender to each data chunk before transmission. The sender maintains a TSN counter, which increments as new data chunks are generated. As data chunks are transmitted, they are labeled with the current value of the TSN counter.
4. Handling of Out-of-Order and Lost Data Chunks
The receiver, upon receiving data chunks, examines their TSNs to determine their correct ordering. SCTP employs a sliding window mechanism to manage the received TSNs. The sliding window allows the receiver to reorder out-of-sequence data chunks and keep track of missing chunks.
If a data chunk with a TSN lower than the expected value arrives, it indicates that one or more data chunks have been lost in transit. The receiver can request retransmission of the missing data chunks using SCTP's selective acknowledgment (SACK) mechanism. The sender will then retransmit the requested data, ensuring reliable delivery.
5. Advantages of TSN in SCTP
The use of Transmission Sequence Numbers provides several advantages in SCTP-based communications:
5.1. Reliability: TSNs enable SCTP to guarantee reliable data transmission, as lost or out-of-order data chunks can be identified and retransmitted.
5.2. Ordered Delivery: TSNs ensure that data chunks are delivered to the receiving application layer in the correct order, maintaining the integrity of the transmitted message.
5.3. Flow Control: SCTP uses TSNs to manage flow control, allowing the receiver to control the rate at which data is sent by selectively acknowledging received data chunks.
5.4. Multi-Stream Support: TSNs are particularly useful in SCTP's multi-streaming feature, where data can be divided into multiple streams, and each stream has its own TSN space.
6. TSN in Time-Sensitive Networking (TSN)
In the context of Time-Sensitive Networking (TSN), TSN stands for Time-Sensitive Networking and does not refer to Transmission Sequence Number as in SCTP. TSN in TSN refers to a set of IEEE standards for Ethernet that enable deterministic communication and low-latency networking for time-critical applications.
7. Conclusion
Transmission Sequence Numbers (TSN) are integral to the reliable and ordered data transmission in SCTP. They provide unique identifiers to data chunks, enabling proper ordering and reassembly at the receiver's end. The use of TSNs ensures the integrity of data transmission, flow control, and support for various advanced features in SCTP, making it a suitable transport protocol for a wide range of applications, including real-time and time-sensitive communications.