BNETDocs
S>C 0x25 SID_PING
Message Id:0x25
Message Name:SID_PING
Direction:Server to Client
Used By:Diablo II, Diablo II Lord of Destruction
Diablo Retail, Diablo Shareware
Starcraft Japanese, Starcraft Broodwar
Starcraft Shareware, Starcraft Original
Warcraft II BNE, Warcraft III The Frozen Throne
Warcraft III Reign of Chaos
Format:

(UINT32) Ping Value

Remarks

Used to calculate Client's ping. The received UINT32 should be sent directly back to Battle.net.

The ping displayed when in chat can be artificially inflated by delaying before sending this packet, or deflated by responding before requested. Ping can be set to -1 (Strictly speaking, 0xFFFFFFFF, since ping is unsigned) by not responding to this packet at all.

The received UINT32 is not what determines your ping, but it is actually a cookie for the Battle.net server. You should never change the UINT32.

Comments
Caaaaarrrrlll

On Starcraft Broodwar, I theorize that this is sent by the server if you never send any data back to Battle.net when Battle.net expects you to. How I theorize this? I debugged Starcraft, and made it 'Pause'. I resumed it and Battle.net had sent SID_PING multiple times. It never sent SID_PING ever again until I paused for about 10-20 seconds then resumed.

If you do not send any data back to Battle.net after a certain period of time, but Battle.net knows you WERE sending data, Battle.net will send this packet to you.