Networking – Why WiFi to Ethernet Sharing Doesn’t Halve Speed but Repeater Does?

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i have a TP link C6U Router which i am using as a repeater/extender WDS. I am using my 5G main router's wifi and extending that signal via TP link's router. My main router have a connection of 250Mbps. I have these scenarios

  1. When My mobile is directly connected to the main routers 5G Wifi connection i get 250Mbps full speed.'
  2. When my mobile is connected to main router and sharing the ethernet to PC via USB connection then still i get 250Mbps speed.
  3. When my TP link's router is connected to main router via WDS bridging of 5G connection, i am limited to nearby 120Mbps.

Note: I tested the mobile's connection the same place where my second router (TP link) is placed. And main router is in another room.

Best Answer

If your phone is talking to a wireless router there are two streams of traffic, one from your phone to the router and one from the router to the phone.

If your phone is talking to a repeater, the repeater is also talking to the wireless router. Now there are four streams of traffic:

  1. From the phone to the repeater
  2. From the repeater to the phone
  3. From the repeater to the wireless router
  4. From the wireless router to the repeater.

Streams 1 and 2 are mutually exclusive, as are 3 and 4. Basically, the repeater can be either sending or receiving on an interface, but not both sending and receiving in parallel. This is called half-duplex.

This is why by default a WiFi repeater halves the speed of your existing WiFi network. The repeater uses half of the bandwidth to transmit the signal and the other half for receiving. If you choose a WiFi repeater with mesh, you won't have this problem.

This is chiefly a problem of single band WiFi extenders, having only one transmit/receive, thus having to use the same 2.4 GHz band and the same channel to repeat the frame. This reduces the throughput to 50%. There are better WIFI extenders that are dual band and some even tri-band. These will get the frame from 2.4 GHz and simultaneously send it (with slight delay) out to the 5GHz band.

User @TomYan recommended this Wikipedia article: Wireless distribution system.

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