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In a full-duplex system, both users can communicate at the same time. A telephone is the most common example of a full-duplex system because both users can speak and be heard at the same time on each end. Some types of full-duplexing methods are: Time-division duplex (TDD) Frequency-division duplex (FDD) Echo cancellation
For example, a walkie-talkie or a DECT phone or so-called TDD 4G or 5G phones requires only a single frequency for bidirectional communication, while a cell phone in the so-called FDD mode is a full-duplex device, and generally requires two frequencies to carry the two simultaneous voice channels, one in each direction.
Asynchronous response mode is an HDLC addition [1] for use over full-duplex links. While retaining the primary/secondary distinction, it allows the secondary to transmit at any time. Thus, there must be some other mechanism to ensure that multiple secondaries do not try to transmit at the same time (or only one secondary).
Transmitting and receiving on exactly the same frequency at exactly the same time has multiple purposes. In-band full duplex can potentially double spectral efficiency. It permits true full duplex operation where only a single frequency is available. And it enables “listen while talking” operation (see cognitive radio, below).
In a very simple example, a switch with three ports A, B, and C has a normal node connected to port A while ports B and C are connected to each other in a loop. All ports have the same link speed and run in full duplex mode. Now, when a broadcast frame enters the switch through port A, this frame is forwarded to all ports but the source port, i ...
This may happen, for example, if one is configured for autonegotiation while the other one has a fixed mode of operation that is full duplex (no autonegotiation). In such conditions, the autonegotiation device correctly detects the speed of operation but is unable to correctly detect the duplex mode.
The aggregate bit rate for both uplink and downlink is 8 Gbit/s in Full Duplex (FDX) mode and 4 Gbit/s in Time Division Duplexing (TDD) mode. Full Duplex mode is available on coaxial cables and Category 5 cables, and Time Division Duplexing mode is available on telephone lines.
Other topics associated with the physical layer include: bit rate; point-to-point, multipoint or point-to-multipoint line configuration; physical network topology, for example bus, ring, mesh or star network; serial or parallel communication; simplex, half duplex or full duplex transmission mode; and autonegotiation [15]