Abstract—
In this paper, the performance of two possible
switching schemes for ad hoc wireless networks, namely
reservation-based (RB) and non-reservation-based (NRB) is investigated.
It is shown that route reservation would be a scheme
of choice in a scenario where delay is a constraint, the network
is dense, and/or nodes move with moderate speed. However, a
non-reservation scheme is preferable in a scenario where the
network is sparse, there is heavy traffic load, nodes are static,
and/or delay is not a major concern.
I. INTRODUCTION
While it is obvious that transmission without route reservation
is suitable for a wired data network such as Internet, it
is not clear whether this is true in the case of ad hoc wireless
networks. To the best of our knowledge, this has not been
studied in the literature.
In this paper, we investigate the performance of two switching
paradigms: reservation-based (RB) and non-reservationbased
(NRB). In an NRB scheme, no reservation is required
before data transmission; data transmission can begin as soon
as a source discovers a route. This is the typical scheme used
for most of the protocols proposed in the literature [1]. In
contrast, in an RB scheme, a source reserves uniquely intermediate
nodes on a route for relaying its message. Intermediate
nodes agree to relay traffic of one source only while the route
is reserved. To the best of our knowledge, such a switching
scheme has never been considered in the literature.
Although a few analytical models which takes into account
delay and physical layer characteristics exist for NRB ad
hoc wireless networks [2–4], no analytical models have been
reported for RB schemes. In this paper, we quantify the
performance tradeoff between these two schemes in terms of
goodput, delay, and maximum tolerable node speed.
The remainder of this paper is organized as follows. In
Section II, we provide a description of RB and NRB schemes.
In Section III, we describe network models and assumptions
considered in this paper. Performance analysis of the two
switching schemes is presented in Section IV. We discuss
implications of our results in Section V. Finally, we conclude
the paper in Section VI.
II. THE TWO SWITCHING SCHEMES
A. Reservation-Based Switching
The principle of operation of an RB scheme is fairly
simple. Prior to data transmission, a source node reserves a
multi-hop route to the destination through a route discovery
process [5]. Once an intermediate node agrees to relay traffic
for a particular source in the network, it cannot initiate a
session or relay messages for any other source until the ongoing
session is over. The source node releases the route after
the session is terminated. We emphasize that this reservation
pertains to node processing but not to the shared common
radio channel. In other words, reservation of a multi-hop route
does not give any node an exclusive access to the shared radio
channel (in terms of frequency bands, time slots, or spreading
codes).
In order to evaluate the performance of an RB switching
scheme, we make the following assumptions.
• Each node in the network generates messages according
to a Poisson process with average arrival rate λm (dimension:
[msg/s]). While a node is acting as a relay, it still
generates its own messages, which are buffered for future
transmission.
• The message length Lm is exponentially distributed1 with
average value Lm (dimension: [b/msg]). Considering a
fixed transmission data rate Rb (dimension: [b/s]), the
message duration is therefore exponentially distributed
with mean value equal to Lm/Rb.
• Since intermediate nodes on a multi-hop route serve
only one source node at a time, simultaneously active
multi-hop routes are disjoint. In addition, given that
each multi-hop route has a certain average length, there
exists a maximum average number, denoted by Cs, of
simultaneously active routes (an expression for Cs will
be provided in Section IV-A.1).
• If the number of nodes wishing to activate a multi-hop
route is larger than Cs, then some nodes have to wait
before they can activate the route. The amount of time
that a node has to wait before it can activate a route will
be referred to as “access delay.”
• The route activation process can be described by a conceptual
“virtual request queue” which regulates requests
from all sources (see Fig. 1). In this sense, one can imagine
that the first message of the queue at each source node


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