Transmission Sequence Numbers (TSNs) are 32-bit sequence numbers used internally by the Stream Control Transmission Protocol (SCTP). Each unit of user data in an SCTP packet is associated with a TSN, allowing the receiving endpoint to acknowledge its receipt.
FAQ: Transmission Sequence Numbers in SCTP
Transmission Sequence Numbers, or TSNs for short, are commonly used within the Stream Control Transmission Protocol (SCTP) to ensure the reliable delivery of data packets. To help provide a better understanding of TSNs, we’ve put together some frequently asked questions.
What are Transmission Sequence Numbers (TSNs)?
TSNs are 32-bit sequence numbers that are used within SCTP to keep track of data packets being sent and received. Each individual packet of data that is being transmitted will have a TSN associated with it. The TSN helps to ensure the complete delivery of data packets, even if some packets become lost or delayed along the way.
How do Transmission Sequence Numbers help with data delivery?
When SCTP sends a packet containing user data, it will assign each data unit (or “chunk”) a unique TSN. This TSN is then included in the packet header, along with other essential information. When the receiving SCTP endpoint receives the packet, it can then use the TSN to determine which data units have been received and which are still outstanding.
This allows the receiving endpoint to acknowledge the receipt of the data units by sending an acknowledgment packet back to the sending endpoint. The sending endpoint can then determine which data units have been successfully delivered and which may require retransmission.
What happens if a TSN becomes lost or delayed?
Even with the use of TSNs, it’s possible for data packets to become lost or delayed during transmission. When this occurs, SCTP provides a mechanism for detecting and recovering from missing or out-of-order packets.
If a TSN acknowledgement isn’t received within a certain time frame, SCTP will automatically retransmit the missing packets. If packets arrive out of order, SCTP will properly order them before delivering them to the receiving application.
Transmission Sequence Numbers (TSNs) are an important component of SCTP that help ensure the reliable delivery of data packets. By assigning each data unit a unique TSN, SCTP can keep track of which packets have been delivered and which still require delivery. This helps to ensure that all data packets are properly received, even if some become lost or delayed during transmission.