Multiplexing & Demultiplexing

• More to do with networking

• Used in many protocols - http2, quic, mptcp

What

• Multiplexing

  • taking several lines (requests) and merging them into one

  • reduce number of tcp connections

  • Done on client side

• Demultiplexing

  • is the reverse

  • taking one line which contains multiple messages/requests and spliting the out into separate requests

  • Done on the server side, thus each request can be handled separately

Example - Connection pooling

• Creation of multiple connections to a database, keep them hot never closed, and allow the code to use a free one instead of creating on the fly (which is expensive) or having one connection which leads to contention; and release it back to the pool for others to use when done.

  • If a new req comes in and needs a connection, but all the connections are used in the pool, it will be blocked until one is free

Why

• Common example of http1.1 and browsers, if a website needs to make several requests to different endpoints, it will need to make several unique tcp connections. But the browsers only allow a max of 6 tcp connections, so there will be some wait time.

  • Using Http 2, the reques is multiplex so can send multiple req in a single tcp connections (within reason)

Issues

• When the single multiplexed request is demultiplexed then it puts strain on the cpu