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Bluetooth is used for a lot of devices that send data in one direction: keyboards, mice, headphones. If it was designed for that, I would think that it was originally specified to only send data in one direction. Is that true?

Note that I am not talking about sending acknowledgments back to the sender (which is necessary for data transmission). You could have two channels, to support bi-directional exchange, but I am not asking that. There could be later versions of the specification that provide two-way exchange, but I am not asking that either. I am asking: Was the basic Bluetooth protocol itself designed to transmit data in one direction?

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I think the specific answer to your question lies in the history of the Bluetooth protocol. Here's what I found:

  • Bluetooth was created in 1994, and is used to exchange data over short distances. The protocol is managed by Bluetooth Special Interest Group. IEEE standardized it as 802.15.1, but they no longer maintain it. So your answers lie with the Bluetooth SIG.

  • BISG is made up of over 30,000 Tech and TCOM companies, and a network of patents. To find the original uses of bluetooth, I'd use google's patent search and take a look at some old tech.

Here's a patent from 2001, using Bluetooth to modify network IP:

That article mentions first establishing a bluetooth connection, then both sending and receiving data/indicators from the connected device.

While each implementation has specific requirements that are detailed in the Bluetooth specification, the Bluetooth core system architecture has many consistent elements. The system includes an RF transceiver, baseband and protocol stacks that enable devices to connect and exchange a variety of classes of data.

Since the core spec maintains consistent design, and that design includes a transceiver, it leads me to believe Bluetooth was always designed to both send and receive.

----- UPDATE -----

Two-way comm is called a Full-duplex transmission. It means data can be transmitted in both directions on a signal carrier at the same time.

Here is the Bluetooth 1.0 spec, released in 1999. It's the first official release of Bluetooth.

Bluetooth is a short-range radio link intended to replace the cable(s) connecting portable and/or fixed electronic devices. Key features are robustness, low complexity, low power, and low cost.

Bluetooth operates in the unlicensed ISM band at 2.4 GHz. A frequency hop transceiver is applied to combat interference and fading. A shaped, binary FM modulation is applied to minimize transceiver complexity. The symbol rate is 1 Ms/s. A slotted channel is applied with a nominal slot length of 625 µs. For full duplex transmission, a Time-Division Duplex (TDD) scheme is used. On the channel, information is exchanged through packets. Each packet is transmitted on a different hop frequency. A packet nominally covers a single slot, but can be extended to cover up to five slots.

In its first official release, Bluetooth supported FDT.

Digger further (pg42) - a piconet (2 or more connected BT devices) follows the master-slave protocol. Only a single device can be the master of the piconet, which broadcasts out to the slaves. Only the master can be active in that channel, but slaves are allowed to respond to the master device. So devices can ping and expect a response.

I forget where I read (think Flow Control section), but they mentioned that implementation is key and Bluetooth is pretty much agnostic of the flow control between devices. It is just generally a better implementation to broadcast from one end of the devices because synchronous packets may need to buffer between endpoints (thus getting corrupted).

So while most implementation of bluetooth is one-way in practice (speaker, headphones, etc) - Bluetooth technology was built to support both flows of communication.

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  • \$\begingroup\$ I am looking, but either I am a dullard or it doesn't specifically say. The Spec site says it was conceived as a replacement for RS-232 cables, and is good for applications like streaming audio. Streaming audio is one-way, and as far as I am concerned, mice and keyboards and headphones are also. So, that means...? \$\endgroup\$
    – user56384
    May 17, 2017 at 15:47
  • \$\begingroup\$ @nocomprende And RS-232 was bidirectional, so... \$\endgroup\$ May 17, 2017 at 15:58
  • \$\begingroup\$ @StainlessSteelRat but I never heard of anyone using RS-232 to run headphones, or input-only devices like a mouse or keyboard. Since that is most of the use cases I have seen for Bluetooth, it seems a bit like swatting flies with a hammer. My assumption was that it evolved first as a one-way protocol. \$\endgroup\$
    – user56384
    May 17, 2017 at 17:49
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The inventor of Bluetooth on where wireless is going next

The inventor of Bluetooth, Jaap Haartsen, while working with Ericsson, started laying the foundation for Bluetooth in 1994. He states:

I was asked to come up with a system that was wireless, digital and should be able to support both voice and data. I got a kind of blank sheet, and just made it.

When I explained Bluetooth to people, I said it was a walkie-talkie done on a world-scale, because all of the devices could potentially talk with each other.

It took them 3 years to develop lower level (physical layer and data-link layer). Ericsson started it to differentiate themselves from other mobile phone manufacturers, but realized they could not bring it to market. They wanted to implement the Bluetooth protocol in a single chip, without any external component, which was unrealistic at the time. So they went looking for partners. And the Bluetooth SIG was formed in 1998.


It is clear, Jaap Haartsen is talking implementing the lower 2 levels of the 7 layer OSI networking protocol. The companies of Bluetooth SIG would not be interested in one direction communications. And more importantly, you are ignoring the complexity of such a task.

No. Bluetooth was bi-directional from the outset.

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  • \$\begingroup\$ Ok. I just wonder why so many one-way devices use it? \$\endgroup\$
    – user56384
    May 18, 2017 at 0:54
  • \$\begingroup\$ That depends on the application. The goal is to eliminate wires. \$\endgroup\$ May 18, 2017 at 0:58
  • \$\begingroup\$ So, a piece of wire is basically zero cost, but we spend years and millions to bridge that distance with custom designed chips, software, batteries, connectors to charge the batteries... Then it comes out cheaper than the piece of wire! Sometimes I think humans are either stupid or lazy or arrogant. Maybe all 3? We will probably get to the moon before we solve mass transit. \$\endgroup\$
    – user56384
    May 18, 2017 at 1:02
  • \$\begingroup\$ A piece of wire is not zero cost. Take a look at the rats nest behind most computers. Every time I buy something, I get a power cable. I have a box of 20+ power cables. Everything is a trade off. \$\endgroup\$ May 18, 2017 at 1:09
  • \$\begingroup\$ I would feel better about the accelerating use of RF to solve all of our "modern problems" if most people knew anything about it at all. I remember when early cell phones came out and people learned that there was no encryption, etc and anyone with a cheap scanner could listen in. Yeah, you are effectively shouting your "private" conversation! Duh! Radio is the only thing in the universe which we can control that travels. Period. If that was well known, ok, then we can make real decisions. Ignorant people cannot make decisions. \$\endgroup\$
    – user56384
    May 18, 2017 at 11:54

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