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I am not sure if this is the right forum to ask this question. So please forgive my ignorance.

I build an Android app which sent UDP packets to my server and the server sent a reply. But I noticed something strange. I bought a 20 MB internet package. After a while, the bandwidth of that package finished. So I could not browser or use internet from my mobile.

But I noticed something strange. My android app was still sending UDP packets to my server. My server was also sending the reply but the response was not reaching my android phone's app. I got interested and started sending a lot of UDP packets to the server. The server was receiving all of those packets and response was getting lost.

I would like to know why this is happening. Should the ISP not have blocked this? I am very curious about this topic. Can anyone explain why this is happening or give me any good link to understand in details why this is happening?

Al-Alamin
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    What do you mean, "_the bandwidth of that package finished_?" The bandwidth is the maximum number of bits per second that can be transferred over a link. – Ron Maupin Nov 22 '17 at 18:23

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UDP is connectionless and apparently, your ISP only blocks the data downlink to your phone when the data plan is exhausted. TCP can't work this way because ACK packets need to flow back but UDP doesn't care.

Zac67
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  • I guessed that ISP has blocked the downlink connection. But wouldn't it be more beneficial to the ISP if the blocked uplink connection? I mean then then downlink would have blocked automatically because of NAT. – Al-Alamin Dec 05 '17 at 05:17
  • The ISP probably can't block the uplink as easily. I mean, how are they going to stop your phone from transmitting data? Yes, they could drop those frames. But that would not save them any bandwidth where it matters at the cell tower. – Timmy Brolin Jul 30 '20 at 12:23