Electronic – square wave carrier signal

T-carrier describes both an electrical specification as well as the data layer. DS specifies only the data layer. There is a lot of crossover between the two naming schemes though. For example, any T1 you order from a telco today will almost certainly be a DS1 over HDSL or HDSL2; it's never a "real" T1, but everyone just calls it a T1.

A DS1 contains 24 or 32 64kbps channels. A DS2 contains 4 DS1s, along with some "slop bits" so that the individual DS1s don't have to be synchronized to each other. A DS3 contains 7 DS2s, or 28 DS1s. You will never find a technical paper saying that a DS2 contains 4 T1s because the electrical specification is irrelevant; only the signal description, the DS-spec, is used.

First of all, it is important to distinguish between different layers of networking. A well-implemented RF stack is made up of different layers that provide what is called orthogonality between functionality. This means that you can distinguish the function of each 'layer' in the stack exclusively. For instance, a typical RF networking stack may look like:

• Bottom layer: the (analogue) RF transceiver that just carries a signal on top of some carrier frequency and radiates it out or amplifies it in from an antenna
• Next layer: the binary encoding layer, that decides how data transmitted and received should be interpreted (i.e. little/big endian, ECC, encryption)
• Next layer: protocol layer. This interprets the data as data, commands, etc.
• etc.
• Last layer: application layer. This takes the data and does something useful with it.

In your example, there is of course some possibility that a sent RF signal gets bounced back and received as data again. A well-written stack will have in its protocol some kind of way to distinguish between packets that are, and data that isn't aimed at that specific device. For instance a header in the protocol layer that says 'from: node1, to: node2'. For instance USB 2.0 works this way: all devices on a hub controller receive all data, but only those devices with the right address will do something with it.

However, I should also note that your example is very unlikely to happen. For all but the most advanced transceivers it is not possible to send and receive at the same frequency at the same time. And when you bounce those signals around in a building or even in the direct neighborhood of your transceiver, they still move at the speed of light and will - for the timescale of a transceiver - arrive instantaneously back. If they do not, the most likely event would simply be some kind of interference pattern and not something strong enough to be interpreted as data. Most transceivers use slightly different carrier frequencies for simultaneous transmit and receive, just so they can more easily distinguish between the two. If they even have simultaneous (full-duplex) tranasmit and receive capabilities - this is a relatively new feature in consumer RF implementations.