Why must endpoints manage conversions between bytes sent and received TSNs sent and received in SCTP congestion control?

Question

As stated in RFC 3286:

"...endpoints must manage the conversion between bytes sent and received and TSNs sent and received, since TSN is per chunk rather than per byte".

How does this affect the congestion control algortihm?

Answer 1

There are two reasons: 1. Pragmatically, RFC 3286 refers RFC 2581 for most of the congestion control, and it works in bytes. 2. Practically, and this is a stronger reason, there needs to be a buffer assigned at each end and these would be hard to define in terms of TSNs (chunks) since these are variably size. This would either mean over-allocating space in the buffer e.g. 64K * TSNs, or using a dynamically allocated list. The former is wasteful of space, the latter relatively slow.

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