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In order to increase the responsiveness and throughput for protocols that are happy to kill and reestablish connections such as HTTP does, “Port Bridge” is always multiplexing concurrent traffic that’s flowing between two parties on the same logical socket.

With Hybrid, all connections are first established through the Service Bus Relay and then our bits do a little “NAT dance” trying to figure out whether there’s a way to connect both parties with a direct socket – if that works the connection gets upgraded to the most direct connections in-flight.

Now you might say You are using a WCF ServiceContract? Isn’t that using SOAP and doesn’t that cause ginormous overhead? No, it doesn’t. We’re using the WCF binary encoder in session mode here. That’s about as efficient as you can get it on the wire with serialized data. The per-frame SOAP overhead for net.tcp with the binary encoder in session mode is in the order of 40-50 bytes per message because of dictionary-based metadata compression. The binary encoder also isn’t doing any base64 trickery but treats binary as binary – one byte is one byte. Port Bridge is using a default frame size of 64K (which gets filled up in high-volume streaming cases due to the built-in Nagling support) and so we’re looking at an overhead of far less than 0.1%. That’s not shabby.