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Ripple: A wireless token-passing protocol for multi-hop wireless mesh networks
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A wireless token-passing protocol for multi-hop wireless mesh networks
Abstract
This work presents a wireless token-passing protocol, named Ripple, for wireless mesh networks (WMNs). In contrast to existing random-access approaches, Ripple uses a decentralized controlled-access approach to protect nodes from unintentional packet collisions and maximize the spatial reuse. The performance of Ripple under an error-free wireless channel was investigated and the accuracy of the analysis was verified by simulation. Simulation results also indicated that Ripple achieved throughput, stability, and QoS enhancement than that of 802.11 DCF under a highly loaded situation
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IEEE COMMUNICATIONS LETTERS, VOL. 10, NO. 2, FEBRUARY 2006 123
Ripple: A Wireless Token-Passing Protocol for
Multi-hop Wireless Mesh Networks
Ray-Guang Cheng, Member, IEEE, Cun-Yi Wang, Li-Hung Liao, and Jen-Shun Yang, Member, IEEE
Abstract— This work presents a wireless token-passing pro-
tocol, named Ripple, for wireless mesh networks (WMNs). In
contrast to existing random-access approaches, Ripple uses a
decentralized controlled-access approach to protect nodes from
unintentional packet collisions and maximize the spatial reuse.
The performance of Ripple under an error-free wireless channel
was investigated and the accuracy of the analysis was verified by
simulation. Simulation results also indicated that Ripple achieved
throughput, stability, and QoS enhancement than that of 802.11
DCF under a highly loaded situation.
Index Terms— Medium access control, quality-of-service
(QoS), token-passing, wireless mesh network.
I. INTRODUCTION
ECENTLY, multi-hop wireless networks and proprietary
commercial systems have focused on a class of networks
termed ”mesh networks” [1]. Unlike mobile ad hoc networks
(MANETs), in which communication generally occurs be-
tween any pair of nodes through several mobile relaying
nodes, wireless mesh networks (WMNs) serve as access net-
works utilizing non-mobile relaying nodes to provide wireless
backbone services for nomadic users to access the wired
Internet. In such an environment, it is essential for all nodes
to support quality-of-service (QoS) transport in multi-hop
operation under a highly loaded situation. However, it has been
shown in [2]- [4] that IEEE 802.11 distributed coordination
function (DCF) is hard to fulfill these requirements.
Li et al. [2] found that ready-to-send/clear-to-send
(RTS/CTS) does not efficiently schedule transmissions in a
multi-hop chain. Although techniques such as multi-channel,
spatial-reuse, cut-through [3], or enhanced physical carrier
sensing [4] can improve the performance of 802.11 DCF, they
still rely on the random-access-based CSMA/CA mechanism
and thus, suffer from the same fairness problems, backoff
inefficiencies, and unavoidable high collision rate problems
under a highly loaded situation. A wireless token ring protocol
(WTRP) [5] has been proposed to eliminate the backoff
inefficiencies and the collision problems in a ring topology;
however, the network is underutilized since the spatial-reuse
is not adopted.
Manuscript received August 7, 2005. The editor coordinating the review of
this paper and approving it for publication was Prof. E. Baccarelli. This work
was supported in part by the National Science Council, Taiwan, under Contract
No. NSC 94-2219-E-011-005, and by the Computer and Communications
Research Laboratory, Industrial Technology Research Institute (CCL/ITRI),
Taiwan, under Project ID A341XSYB10.
R. G. Cheng, C. Y. Wang, and L. H. Liao are with the Dept.
of Electronic Engineering, National Taiwan University of Science
and Technology, Taiwan (e-mail: [email protected]; [email protected];
J. S. Yang is with the CCL/ITRI, Taiwan (e-mail: [email protected]).
Digital Object Identifier 10.1109/LCOMM.2006.02005.
This work presents a wireless token-passing protocol,
named Ripple, for WMNs. Unlike current random-access-
based approaches, Ripple adopts a controlled-access-based
approach to prevent nodes from inevitable collisions in WMN.
The rest of this work is structured as follows. The operation
of Ripple is described in Section II. Section III presents
the performance of Ripple. Conclusions are finally drawn in
Section IV.
IPPLE PROTOCOL
This work considers a WMN with a chain topology, where
nodes are equally spaced and radios of nodes that are not
neighbors do not interfere with each other [2]. The chain
topology can be easily generalized to be a tree topology
and both topologies are mainly used by the public WMN
deployment in Taipei city. Without losing generality, this
work concentrates on unidirectional downlink transmissions,
where packets are only sent from the root node (the node
that links to the wired Internet gateway) to a leaf node.
Bidirectional transmission is possible either with time-division
duplex using one channel or frequency-division duplex using
two individual channels. Li et al. proved that a node in
the chain topology may attain an optimal utilization of 1/3
by applying spatial-reuse [2]. They also predicted that, data
frames could be forwarded hop-by-hop without interfering
with each other if each node can properly schedule its frame
transmission interval. Under this optimal condition, the frame-
forwarding resembles ripples of water moving apart from a
central location, which is referred as ”ripple phenomenon”
herein. However, the optimal condition is hard to be realized
in WMN because the lack of a central coordinator and the
presence of hidden nodes and expose nodes [1] in WMN. The
objective of this work is to propose a wireless token-passing
protocol, named Ripple, to coordinate frame transmission for
nodes in WMN and thus, enable the ripple phenomenon.
Ripple uses six types of frames, called DATA, NULL, RTS,
CTS, ACK and Ready-To-Receive (RTR). The frame format
of RTS, CTS, DATA, NULL, and ACK are the same as
that defined in 802.11 except that Ripple only utilizes fixed-
duration DATA frames. An RTR frame has the same format
as CTS and is used by a node to request a DATA frame from
its upstream node. IFS
, the inter-frame-spaces (IFSs) of
RTR frame, is set as two SIFS plus the time needed to transmit
an RTS frame. The IFSs of the remaining frames are all set
as short-IFS (SIFS). Ripple modifies the data transmission
procedure of 802.11 DCF and employs RTS and RTR frames
as ”tokens.” A node is allowed send a DATA frame only if
it holds a token. The way to generate and circulate RTS and
1089-7798/06$20.00
2006 IEEE
Authorized licensed use limited to: National Taiwan Univ of Science and Technology. Downloaded on January 8, 2010 at 04:44 from IEEE Xplore. Restrictions apply.
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