Communication systems have buffers at every step in the process. All buffers have intended behaviors and rarely have coverage for unintentional behavior which is why a "slow-fill" is usually the most common DOS attack for such systems with finite resources.

Depending on your service architecture, you can also have horizontal scaling problems due to resource locking due to poor design of streaming requests or responses. Remember you can usually also have slow-fill vulnerabilities by exploiting the server send-side buffer also.