26-05-2012, 11:36 AM
Supporting Efficient and Scalable Multicasting over Mobile Ad Hoc Networks
[attachment=23114]
INTRODUCTION
There are increasing interests and importance in supporting
group communications over Mobile Ad Hoc Networks
(MANETs). Example applications include the exchange of
messages among a group of soldiers in a battlefield, communications
among the firemen in a disaster area, and the support
of multimedia games and teleconferences. With a one-to-many
or many-to-many transmission pattern, multicast is an efficient
method to realize group communications. However, there is a
big challenge in enabling efficient multicasting over a MANET
whose topology may change constantly.
Conventional MANET multicast protocols [3]–[8], [28] can
be ascribed into two main categories, tree-based and meshbased.
However, due to the constant movement as well as
frequent network joining and leaving from individual nodes,
it is very difficult to maintain the tree structure using these
conventional tree-based protocols (e.g., MAODV [3], AMRIS
[4], MZRP [5], MZR [28]).
RELATED WORK
In this section, we first summarize the basic procedures
assumed in conventional multicast protocols, and then introduce
a few geographic multicast algorithms proposed in the
literature.
Conventional topology-based multicast protocols include
tree-based protocols (e.g., [3]–[5], [28]) and mesh-based protocols
(e.g., [6], [8]). Tree-based protocols construct a tree
structure for more efficient forwarding of packets to all the
group members. Mesh-based protocols expand a multicast
tree with additional paths which can be used to forward
packets when some of the links break. Although efforts were
made to develop more scalable topology-aware protocols [7],
the topology-based multicast protocols are generally difficult
to scale to a large network size, as the construction and
maintenance of the conventional tree or mesh structure involve
high control overhead over a dynamic network.
EFFICIENT GEOGRAPHIC MULTICAST PROTOCOL
In this section, we will describe the EGMP protocol in details.
We first give an overview of the protocol and introduce the
notations to be used in the rest of the paper in Section
3.1. In Sections 3.2 and 3.3, we present our designs for the
construction of zone structure and the zone-based geographic
forwarding. Finally, in Sections 3.4, 3.5 and 3.6, we introduce
our mechanisms for multicast tree creation, maintenance and
multicast packet delivery.
Neighbor Table Generation and Zone Leader
Election
For efficient management of states in a zone, a leader is
elected with minimum overhead. As a node employs periodic
BEACON broadcast to distribute its position in the underneath
geographic unicast routing [13], to facilitate leader election
and reduce overhead, EGMP simply inserts in the BEACON
message a flag indicating whether the sender is a zone leader.
With zone size r · rt=P
a broadcast message will be
received by all the nodes in the zone. To reduce the beaconing
overhead, instead of using fixed-interval beaconing, the
beaconing interval for the underneath unicast protocol will be
adaptive. A non-leader node will send a beacon every period of
Intvalmax or when it moves to a new zone. A zone leader has
to send out a beacon every period of Intvalmin to announce
its leadership role.
Zone-supported Geographic Forwarding
With a zone structure, the communication process includes
an intra-zone transmission and an inter-zone transmission. In
our zone-structure, as nodes from the same zone are within
each other’s transmission range and are aware of each other’s
location, only one transmission is required for intra-zone
communications. Transmissions between nodes in different
zones may be needed for the network-tier forwarding of
control messages and data packets. As the source and the
destination may be multiple hops away, to ensure reliable
transmissions, geographic unicasting is used with the packet
forwarding guided by the destination position. However, in
normal geographic unicast routing, location service is required
for the source to obtain the destination position.
[attachment=23114]
INTRODUCTION
There are increasing interests and importance in supporting
group communications over Mobile Ad Hoc Networks
(MANETs). Example applications include the exchange of
messages among a group of soldiers in a battlefield, communications
among the firemen in a disaster area, and the support
of multimedia games and teleconferences. With a one-to-many
or many-to-many transmission pattern, multicast is an efficient
method to realize group communications. However, there is a
big challenge in enabling efficient multicasting over a MANET
whose topology may change constantly.
Conventional MANET multicast protocols [3]–[8], [28] can
be ascribed into two main categories, tree-based and meshbased.
However, due to the constant movement as well as
frequent network joining and leaving from individual nodes,
it is very difficult to maintain the tree structure using these
conventional tree-based protocols (e.g., MAODV [3], AMRIS
[4], MZRP [5], MZR [28]).
RELATED WORK
In this section, we first summarize the basic procedures
assumed in conventional multicast protocols, and then introduce
a few geographic multicast algorithms proposed in the
literature.
Conventional topology-based multicast protocols include
tree-based protocols (e.g., [3]–[5], [28]) and mesh-based protocols
(e.g., [6], [8]). Tree-based protocols construct a tree
structure for more efficient forwarding of packets to all the
group members. Mesh-based protocols expand a multicast
tree with additional paths which can be used to forward
packets when some of the links break. Although efforts were
made to develop more scalable topology-aware protocols [7],
the topology-based multicast protocols are generally difficult
to scale to a large network size, as the construction and
maintenance of the conventional tree or mesh structure involve
high control overhead over a dynamic network.
EFFICIENT GEOGRAPHIC MULTICAST PROTOCOL
In this section, we will describe the EGMP protocol in details.
We first give an overview of the protocol and introduce the
notations to be used in the rest of the paper in Section
3.1. In Sections 3.2 and 3.3, we present our designs for the
construction of zone structure and the zone-based geographic
forwarding. Finally, in Sections 3.4, 3.5 and 3.6, we introduce
our mechanisms for multicast tree creation, maintenance and
multicast packet delivery.
Neighbor Table Generation and Zone Leader
Election
For efficient management of states in a zone, a leader is
elected with minimum overhead. As a node employs periodic
BEACON broadcast to distribute its position in the underneath
geographic unicast routing [13], to facilitate leader election
and reduce overhead, EGMP simply inserts in the BEACON
message a flag indicating whether the sender is a zone leader.
With zone size r · rt=P
a broadcast message will be
received by all the nodes in the zone. To reduce the beaconing
overhead, instead of using fixed-interval beaconing, the
beaconing interval for the underneath unicast protocol will be
adaptive. A non-leader node will send a beacon every period of
Intvalmax or when it moves to a new zone. A zone leader has
to send out a beacon every period of Intvalmin to announce
its leadership role.
Zone-supported Geographic Forwarding
With a zone structure, the communication process includes
an intra-zone transmission and an inter-zone transmission. In
our zone-structure, as nodes from the same zone are within
each other’s transmission range and are aware of each other’s
location, only one transmission is required for intra-zone
communications. Transmissions between nodes in different
zones may be needed for the network-tier forwarding of
control messages and data packets. As the source and the
destination may be multiple hops away, to ensure reliable
transmissions, geographic unicasting is used with the packet
forwarding guided by the destination position. However, in
normal geographic unicast routing, location service is required
for the source to obtain the destination position.