CODEWITHSUNDEEP
network-programmingtcp
user1202136
user1202136

Reputation: 11547

How many bytes can be sent in first TCP window?

I read somewhere (but cannot find the source anymore) that there is a certain maximum number of bytes that can be sent in the first TCP window. Sending more data requires ACK from the receiver, hence another round-trip. To reduce website latency, all above-the-fold content, including HTTP reply headers, should be less than this number of bytes.

Can anybody remember what the maximum number of bytes in the first TCP window is and how it is calculated?

Upvotes: 0

Views: 185

Answers (1)

Slava Bacherikov
Slava Bacherikov

Reputation: 2066

This is regulated by initial tcp congestion window (initcwnd). This parameter determines how many segments (MSS) could be sent without waiting for ACK at first phase of slow start. Currently recommended value for most workloads is 10, but some old systems still using 4. Also note, used window size depends on clients receive window too, so if some client will advertise receive window lower than your initial congestion window, it will be used this receive window as limit.

For more info, refer to this page.

Upvotes: 1

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