tcp/ip sockets

https://docs.microsoft.com/ru-ru/dotnet/framework/network-programming/asynchronous-server-socket-example

https://docs.microsoft.com/ru-ru/dotnet/api/system.net.sockets.tcplistener?view=netframework-4.8#definition

https://docs.microsoft.com/ru-ru/dotnet/framework/network-programming/using-an-asynchronous-server-socket

https://www.winsocketdotnetworkprogramming.com/clientserversocketnetworkcommunication8o.html

https://habr.com/ru/post/327574/

TcpClient Class 
https://docs.microsoft.com/ru-ru/dotnet/api/system.net.sockets.tcpclient?view=netframework-4.8

TcpClient
https://metanit.com/sharp/net/4.1.php

https://professorweb.ru/my/csharp/web/level4/4_2.php

http://zetcode.com/csharp/tcpclient/

https://wm-help.net/lib/b/book/656723049/312

http://streletzcoder.ru/obmen-dannyimi-po-seti-v-c-protokol-tcp/

http://www.java2s.com/Code/CSharp/Network/TcpClientSample.htm

https://www.codeproject.com/Articles/1415/Introduction-to-TCP-client-server-in-C

https://stackoverflow.com/questions/3609280/sending-and-receiving-data-over-a-network-using-tcpclient

https://blog.stephencleary.com/2009/04/tcpip-net-sockets-faq.html

https://www.winsocketdotnetworkprogramming.com/clientserversocketnetworkcommunication8q.html

Example
https://stackoverflow.com/questions/43140949/tcplistener-send-heartbeat-every-5-seconds-and-read-message-from-client-async

https://stackoverflow.com/questions/865987/do-i-need-to-heartbeat-to-keep-a-tcp-connection-open

https://stackoverflow.com/questions/495922/what-is-the-best-way-to-implement-a-heartbeat-in-c-to-check-for-socket-connect

https://stackoverflow.com/questions/10281622/how-to-check-the-connection-state-of-a-tcp-server-socket-with-tcp-client-in-vb

https://stackoverflow.com/questions/3121598/tcpclient-communication-with-server-to-keep-alive-connection-in-c

NetworkStream

https://docs.microsoft.com/ru-ru/dotnet/api/system.net.sockets.networkstream?view=netframework-4.8#properties

NetworkStream.ReadTimeout

https://docs.microsoft.com/ru-ru/dotnet/api/system.net.sockets.networkstream.readtimeout?view=netframework-4.8#System_Net_Sockets_NetworkStream_ReadTimeout