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Out of curiosity, how much data is actually sent when establishing a connection to a port (using Java sockets). Is it the size of a Socket object? SocketConnection object?
Your understanding of TCP network connections seems to conflate them with electrical circuits. (Understandable, given your background.)
From a physical standpoint, there’s no such thing as a connection, only data packets. Through the TCP protocol, two devices agree to establish a logical (that is, software) connection. A connection is established by a client first sending data to the remote host (SYN), the server sending data back to the client (SYN-ACK), and the client sending a final acknowledgement (ACK). All of this negotation necessarily consumes bandwidth, and when you terminate a connection, you must negotiate a completely new connection to begin sending data again.
For example, I’ll connect from my machine to a local web server, 192.168.1.2:80.
First, my machine sends a TCP SYN. This sends 66 bytes over the wire: (headers deliniated with
|)The first 14 bytes are the Ethernet frame, specifying that this packet’s destination MAC address. This will typically be an upstream router, but in this case, the server happens to be on the same switch, so it’s the machine’s MAC address, 00:24:8c:a9:4c:b4. The source (my) MAC follows, along with the payload type (IP, 0x0800). The next 20 bytes are the IPv4 headers, followed by 32 bytes of TCP headers.
The server responds with a 62-byte SYN-ACK:
Again, 14 bytes of Ethernet headers, 20 bytes of IP headers, and 28 bytes of TCP headers. I send an ACK:
14 + 20 + 20 = 54 bytes over the wire (this is the smallest possible TCP packet size, by the way – the SYN and SYN-ACK packets were larger because they included options).
This adds up to 182 bytes over the wire to establish a connection; now I can begin sending actual data to the server:
14 Ethernet + 20 IP + 20 TCP + data, in this case HTTP.
So we can see that it costs ~182 bytes to establish a TCP connection, and an additional 162-216 bytes to terminate a TCP connection (depending on whether a 4-way FIN ACK FIN ACK or more common 3-way FIN FIN-ACK ACK termination handshake is used), adding up to nearly 400 bytes to “pulse” a connection by disconnecting and reconnecting.
Compared to the 55 bytes you’d use to send one byte of data over an already established connection, this is obviously wasteful.
What you want to do is establish one connection and then send data as-needed. If you’re really bandwidth constrained, you could use UDP (which requires no handshaking at all and has an overhead of only 14 Ethernet + 20 IP + 8 UDP bytes per packet), but then you face the problem of using an unreliable transport, and having to handle lost packets on your own.