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home / developersection / interviews / what are the different transport protocols signalr can use for communication?
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Utpal Vishwas
Utpal Vishwas

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I am Utpal Vishwas from Uttar Pradesh. Have completed my B. Tech. course from MNNIT campus Prayagraj in 2022. I have good knowledge of computer networking.

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Utpal Vishwas
Utpal Vishwas 21 May 2025
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SignalR supports multiple transport protocols to enable real-time communication between the server and clients. It automatically selects the best available transport based on the client and server capabilities and network conditions.

Here are the main transport protocols SignalR can use:

1. WebSockets

  • Description: A full-duplex, persistent connection over a single TCP socket.
  • When used: If both client and server support it, SignalR will prefer WebSockets because it is the most efficient and lowest latency transport.
  • Advantages: Low overhead, bidirectional communication, real-time updates.
  • Support: Modern browsers, ASP.NET Core servers.

2. Server-Sent Events (SSE)

  • Description: A unidirectional connection where the server can push events/messages to the client over HTTP.
  • When used: If WebSockets are not available but the client supports SSE (mainly modern browsers except IE).
  • Advantages: Simple to implement, works well for streaming data from server to client.
  • Limitations: Only server-to-client communication; client cannot send messages over the same connection (SignalR handles this separately).

3. Long Polling

  • Description: The client sends a request to the server, and the server holds the request open until it has data to send or a timeout occurs. Then the client immediately sends a new request, effectively simulating a continuous connection.
  • When used: As a fallback when WebSockets and SSE are not available (older browsers, restrictive networks).
  • Advantages: Works on nearly all browsers and network setups.
  • Disadvantages: Higher latency and more overhead than WebSockets and SSE.

Transport Selection Summary

Transport Client Support Server Support Direction Preferred?
WebSockets Modern browsers Yes (ASP.NET Core) Bidirectional Yes (if available)
Server-Sent Events Modern browsers (not IE) Yes Server-to-client Yes (fallback)
Long Polling All browsers Yes Bidirectional (via repeated requests) Last fallback

SignalR’s ability to automatically negotiate and fallback between these transports makes it very robust and compatible with a wide range of client environments.

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