Some questions about the MTU(Maximum Transmission Unit) about gamenetworkingsockets HOT 2 CLOSED

The constants you refer to are the largest message sizes, not packet sizes. For the actual MTU (max UDP packet size): The relevant constant is k_cbSteamNetworkingSocketsMaxUDPMsgLen, which is currently 1300. Any messages passed to the API larger than about 1200 bytes will be fragmented into multiple UDP packets by the API. (The difference since we need to save some room for headers and such.) We would never try to send a 512KB UDP packet; there are practically no places on the Internet where that would work.

As for sending a 512KB message: it's really only reasonable for a reliable message, where there is retransmission in the event of individual segment loss. And that constant has to do with buffering really, not fragmentation and packet loss. For unreliable, the practical limit is much lower without forward error correction. (Say 5-20 MTU's?) or else the effective message delivery rate will plummet, as you mention.

We currently don't have a configurable MTU, and don't do MTU discovery. I am aware that it is a theoretical problem and that there might be some routers or network devices out there that cannot handle a UDP packet with a 1300-byte payload, and might either drop it or fragment it. But in practice, using this code on Dota and CS:GO basically all over the world, this hasn't posed a problem, so I don't think the set of users affected by this is large. I don't think it's worth the complexity to the interface to either allow customization (which then needs to be exposed to the user somehow) or to do the discovery/negotiation.

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Thank you for your reply. I'm sorry that I misunderstand the const value's meaning.
PS: I am trying to use this lib on a moblie phone game. In the past, the game's network layer used the TCP/IP protocol. Although we have done some optimizations on upper level, we still suffer from the jitter of the Internet.So I want to try some UDP based protocol. I have written a C#-style wrapper and hope to use this lib in our game.

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