Page 27 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1

the tags, routing should also facilitate higher-level op- the accumulated route. (Any node which receives the
erations, e.g., searching for a particular object, such as RREQ and knows the route to the destination, can cre-
other associated/related tags in the network (e.g., for ate an RREP by appending the known route to the
all the tags that were in close contact with a tag carried accumulated route in the RREQ and forwarding the
by an infected individual); querying to identify all the RREP back to the source node through reversing the
objects with certain attributes or certain historical val- accumulated route.) Unfortunately, the above process
ues, thus creating “communities of interest” among ob- will not work in a BTTN, because many links are uni-
jects to facilitate interactions and information exchange directional only, thus reversing the route will create an
among such member objects, etc. infeasible path. First, we note that our route discov-
ery operates between a source tag and a community of
As an example of an approach to routing in BTTN, we tags, rather than a single destination node. Second, a
now briefly discuss how to address two of the specific new RREQ/RREP process could be introduced, where
challenges of routing in BTTN: (a) routing scalability in a message Forward Route Request (FREQ) is broadcast
a densely-deployed network and (b) route discovery in by the source and propagates (with route accumulation).
the presence of unidirectional links in the network. When the FREQ is received by any member of the com-

In a massively deployed network, such as is envisioned munity of tags, such a node now becomes the destination
for IoT applications, it is difficult to discover whether node. The destination node, upon receipt of the FREQ,
a particular tag is reachable by another tag. To com- initiates a new Backwards Route Request (BREQ), by
bat this problem, the tags can establish loose associa- appending the forward route from the FREQ and broad-
tions, creating communities of interest – a collection of casting the BREQ back to the source. When the BREQ
related objects, which are interspersed by other objects arrives at the source, it now contains both, the forward
in the network. For example, all books in a library by and the backward routes, where the routes in the two
a particular author could be an example of a commu- directions are not necessarily the same. The source then
nity of interest. In this way, as further explained below, creates an RREP message with the backward route and
rather than routing a message to a particular book (i.e., uses the forward route to send the RREP to the desti-
a particular tag), a message is anycasted to the “com- nation.
munity of books by the author,” rather than unicasted
to a specific tag. Routing in the network is then per- 5. APPLICATIONS OF BTTNS
formed based on the attributes of a community. When In this section, we first explain a fundamental operation
a node moves away or changes its attributes, it removes of two tagged objects that will facilitate many applica-
itself from the particular community of interest. Once tions based on object interactions, then we describe an
a message is delivered to any member of a community application that involves human interactions, and finally
of interest (i.e., anycasted), based on the attribute of we list a number of possible applications of BTTNs.
the community, the member will then share the message
with all the other members of its community through 5.1 Object interactions
intra-community routes. In other words, we proposed a
two-level distributed routing hierarchy, where each tag By object interaction we mean exchange of information
maintains a route to some members of its community between two objects with attached tags that are in the
of interest, so that delivery to a particular member of a proximity of each other and that is used for some pur-
community of interest requires only delivery to one (i.e., pose. For example, tagged objects can localize them-
any) member of the community. The notion of commu- selves relative to one another or even in an absolute
nities of interest addresses a major challenge in routing sense if some tagged objects serve as anchors, that is,
in the network of tags – routing scalability. Instead of their locations are known. Tagged objects can also track
discovering routing paths between every pair of tags in other tagged objects in their neighborhood.
the network, routing within only a much smaller com-
munity of tags is needed. The central problem here is the estimation of distances
between communicating tags. One technique for dis-
We now discuss the second challenge – discovering rout- tance estimation is based on multiphase backscattering,
ing paths in unidirectional graphs. One approach to where a tag changes the phase offset of the signal that is
path discovery in ad hoc networks and sensor networks being backscattered in a systematic manner [23]. Sup-
is through broadcasting Route Request Query (RREQ), pose there are two tags, Tag 1 and Tag 2, where Tag
which is a message sent from the source node to the des- 1 acts as Tx tag with different phases. It can readily
tination node. As the RREQ propagates through the be shown that the square of the estimated amplitude
network, the nodes append their ID to the message, un- of the Rx Tag 2 at the output of the envelope detector
til the message reaches the destination. The destination is a sinusoid that is a function of the used phase offsets
extracts the accumulated route in the RREQ and cre- and a fixed parameter that carries information about the
ates the Route Reply Message (RREP), which is then distance between the two tags. When the roles of Tag
forwarded back to the source node through reversing 1 and Tag 2 are reversed, i.e., Tag 1 receives and Tag

© International Telecommunication Union, 2020 7