system directly inspired by the nerve fibers that transport muscle movements, external sensorial stimuli, and neural communication signals to and from the brain. The latter are inspired by the capillaries, which are the smallest blood vessels inside the human body. Capillaries connect arterioles and venules and their main function is to interchange chemicals and nutrients between the blood and the surrounding tissues. The feasibility and practicality of these systems still needs to be investigated, but they can serve as a starting point for future bio-inspired nanocommunication systems.

Last but not least, we proposed and studied in Gregori and Akyildiz4 a molecule transport technique using two different types of carrier entities, namely, flagellated bacteria and catalytic nanomotors. On the one hand, the flagellated bacteria are able to carry DNA messages introduced inside their cytoplasm. When set free in the environment, the carrier bacteria are headed to the receiver, which is continuously releasing bacteria attractant particles. Upon contact with the receiver, the bacteria release the DNA message to the destination. On the other hand, the catalytic nanomotors are defined as particles that are able to propel themselves and small objects. Nanomotors can be loaded with DNA molecules and their propagation can be guided using preestablished magnetic paths from the emitter to the receiver. Nanomotors can also compose a raft and transport the DNA message through a chemotactic process. The propagation of information by means of guided bacteria or catalytic nanomotors is relatively very slow (in the order of a few millimeters per hour), but the amount of information that can be transmitted in a single DNA strand makes the achievable information rate relatively high (up to several kilobits per second). All these results require us to rethink well-established concepts in communication and network theory.

 

Developing Nanonetworking Protocols Nanonetworks are systems composed by interconnected nanomachines that communicate by following spe-

While there is
still a long way
to go before a
fully functional
nanomachine is
realized, we believe
hardware-oriented
research and
communication-
focused
investigations
will benefit from
being conducted
in parallel from
an early stage.

cific protocols. These protocols must address various issues not only common to conventional networks, but also arising from the peculiarities of the different nanocommunication options. For this, several features required in any communication network, such as Medium Access Control (MAC) mechanisms, addressing schemes, or information routing techniques, must be designed in light of the properties of the aforementioned nanocommunication paradigms

Terahertz nanonetworks. The Terahertz Band provides a very large transmission bandwidth. On the one hand, this can be used to support very high-speed communication among nano-devices. On the other hand, a very large bandwidth enables new channel access techniques, which can ease the tasks of the MAC protocol. For example, when using femtosecond-long pulses for communication among nano-devices, 2 the chances of having a collision between different nanomachines‘ transmissions are almost nonexistent. As a result, very simple MAC protocols can be used. For instance, nanomachines can just transmit whenever they have some information ready and then they just wait for an acknowledgment. New ways to verify the integrity of the message that has been transmitted and to accordingly inform the transmitter will be necessary. In addition, in light of the capabilities of nanomachines, new coding schemes and error correction mechanisms will have to be developed. When it comes to addressing and routing, it will also be the capabilities of nanomachines what will determine what is possible and what is not. For example, it seems unfeasible to assign a unique ID to every component of a nanonetwork. Alternatively, by exploiting again the nature of pulse-based communications, we think that nanomachines will have a notion of the distances among them, which can be used for addressing and routing purposes. At the same time, in our vision, we believe that in some applications it will not be necessary to uniquely identify every nanomachine, but it will be enough by just classifying the nanomachines according to their internal status, for example, the sensing readings.