Is There Any JavaScript Tcp Soket Library for PHP Like Signalr with .Net

C# Tcp Server - HTML5 Websocket communication

WebSockets are not plain TCP sockets, but an socket-like layer inside an HTTP(s) connection. What you see here is the HTTP request of the client with the request to upgrade the HTTP connection to a WebSocket connection.
If you don't want to use existing WebSocket libraries you have to implement the protocol yourself, that is first implement a minimal web server (RFC2616) and then put the WebSocket layer on top (RFC6455).

SignalR - only works with localhost

Solved it by running the program as administrator.

In what situations would AJAX long/short polling be preferred over HTML5 WebSockets?

WebSockets is ~~definitely the future~~ now.

Long polling is a dirty workaround to prevent creating connections for each request like AJAX does - but long polling was created when WebSockets didn't exist. Now due to WebSockets,
long polling is ~~going away~~ no more.

WebRTC allows for peer-to-peer communication.

I recommend learning WebSockets.

Comparison:

of different communication techniques on the web

AJAX - request → response. Creates a connection to the server, sends request headers with optional data, gets a response from the server, and closes the connection.
Supported in all major browsers.
Long poll - request → wait → response. Creates a connection to the server like AJAX does, but maintains a keep-alive connection open for some time (not long though). During connection, the open client can receive data from the server. The client has to reconnect periodically after the connection is closed, due to timeouts or data eof. On server side it is still treated like an HTTP request, same as AJAX, except the answer on request will happen now or some time in the future, defined by the application logic.
support chart (full) | wikipedia
WebSockets - client ↔ server. Create a TCP connection to the server, and keep it open as long as needed. The server or client can easily close the connection. The client goes through an HTTP compatible handshake process. If it succeeds, then the server and client can exchange data in both directions at any time. It is efficient if the application requires frequent data exchange in both ways. WebSockets do have data framing that includes masking for each message sent from client to server, so data is simply encrypted.
support chart (very good) | wikipedia
WebRTC - peer ↔ peer. Transport to establish communication between clients and is transport-agnostic, so it can use UDP, TCP or even more abstract layers. This is generally used for high volume data transfer, such as video/audio streaming, where reliability is secondary and a few frames or reduction in quality progression can be sacrificed in favour of response time and, at least, some data transfer. Both sides (peers) can push data to each other independently. While it can be used totally independent from any centralised servers, it still requires some way of exchanging endPoints data, where in most cases developers still use centralised servers to "link" peers. This is required only to exchange essential data for establishing a connection, after which a centralised server is not required.
support chart (medium) | wikipedia
Server-Sent Events - client ← server. Client establishes persistent and long-term connection to server. Only the server can send data to a client. If the client wants to send data to the server, it would require the use of another technology/protocol to do so. This protocol is HTTP compatible and simple to implement in most server-side platforms. This is a preferable protocol to be used instead of Long Polling. support chart (good, except IE) | wikipedia

Advantages:

The main advantage of WebSockets server-side, is that it is not an HTTP request (after handshake), but a proper message based communication protocol. This enables you to achieve huge performance and architecture advantages. For example, in node.js, you can share the same memory for different socket connections, so they can each access shared variables. Therefore, you don't need to use a database as an exchange point in the middle (like with AJAX or Long Polling with a language like PHP).
You can store data in RAM, or even republish between sockets straight away.

Security considerations

People are often concerned about the security of WebSockets. The reality is that it makes little difference or even puts WebSockets as better option. First of all, with AJAX, there is a higher chance of MITM, as each request is a new TCP connection that is traversing through internet infrastructure. With WebSockets, once it's connected it is far more challenging to intercept in between, with additionally enforced frame masking when data is streamed from client to server as well as additional compression, which requires more effort to probe data. All modern protocols support both: HTTP and HTTPS (encrypted).

P.S.

Remember that WebSockets generally have a very different approach of logic for networking, more like real-time games had all this time, and not like http.

Modifying an existing duplex WCF service to use with JavaScript

I am one of the guys behind XSockets.NET. I can help you with this one I hope.
XSockets has a "external" API that you can use from WCF (or anything else talking TCP/IP and .NET) to send messages to the XSockets server. The server will then pass the messages (pub/sub pattern) to the client(s) and vice versa.

So, there will be almost no changes to your WCF.

Just tell me if you need an example, and I will provide one for you. Just send me an email on uffe at xsockets dot net and we can take it from there.

EDIT: Created a example on howto boost your WCF to realtime. It´s on GitHub: Boost WCF to RealTime

Regards
Uffe, Team XSockets