Multi-Channel Multi-Interface Wireless Network Architecture

IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 07, 2014 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 30
Multi-Channel Multi-Interface Wireless Network Architecture
Ruchita Gupta1 R.N.Shukla2 Pooja Lohia3
1,2,3
Department of Electronic & Communication Engineering
1,2,3
Madan Mohan Malaviya University of Technology, Gorakhpur (U.P.)
Abstract— With the increase of usage of wireless networks
for purposes where the nodes are either stationary or
minimally mobile, focus is also on increasing the network
capacity of wireless networks. One such way is to use non-
overlapping multiple channels provided by 802.11 by using
multiple interfaces per node. Multiple non overlapped
channels exist in the 2.4 GHz and 5 GHz spectrum. Under
this scenario, several challenges need to be addressed before
all the available channels can be fully utilized.
Keywords: channel assignment, mac, network simulator,
routing protocol
I. INTRODUCTION
Wireless network technology, despite being extremely
useful in mobile communication and computing application,
suffers from low link-layer data rates. The 54 Mbps peak
link-layer data rate of IEEE 802.11a/g wireless LAN
interface stands no chance in front of huge bandwidths
provided by wired technologies. Moreover, overheads of
packet loss, packet errors, contention and packet headers,
drastically reduce the actual good put available to the
wireless network applications. The data rate also falls
quickly with increasing distance between signal source and
destination.
Interference from adjacent hops in a multi-hop
network further decreases the available bandwidth. Usage of
multiple channels thus removes both of the problems - it
extends the available bandwidth and removes the problem of
interference as now simultaneous communication is
established between adjacent hops on a non-overlapping
channel. it is now feasible to equip nodes with multiple
802.11 wireless interfaces. As we cannot equip the nodes
with an interface for every non overlapping channel due to
power consumption and size constraints, we need to devise
channel assignment algorithms which would switch the
interfaces from one channel to other albeit at the cost of
switching delay. Multi-radio and multi-channel architecture
has special usage is wireless mesh networks (WMN)[2]. In a
mesh network, nodes act as repeaters to transmit data from
nearby nodes to distant nodes in the network.
Their special utility is in case of providing
inexpensive last mile broadband internet connectivity. In
some cases the mesh may be serving as an extension to a
wired backbone, thus decreasing the need of a dense
physical wire network and hence the cost of maintenance
Introduction of mesh networks also calls for efforts in the
direction of increase in network capacity. Usage of mesh
networks as an extension to a wired backbone will lead to
surge in bandwidth-intensive applications like video-
sharing. Usage of multiple channels available in IEEE
802.11a/g standards offers a promising avenue in this
regard. the IEEE 802.11b/g standards and IEEE 802.11a
standard provide 3 and 12 nonoverlapped frequency
channels, respectively. Utilization of these multiple channels
effectively would increase the bandwidth substantially.
II. CHANNEL ASSIGNMENT
To utilize a greater number of channels with fewer NICs per
node we need the ability to switch a NIC between channels.
For example, if we have a single NIC per node in a network
of four nodes, and each node is fixed on the same channel,
the opportunity to use the other available channels is wasted.
We cannot fix the NIC to other channel, as then the nodes
on two different channels will be unable to communicate
with each other. Thus, we need a channel assignment
algorithm which coordinates between the nodes and
schedules assignment, and if necessary, switching of
channels among the NICs to utilize multiple channels. For
maximum benefit, such a channel assignment algorithm
needs to adhere to certain demands of the network. There
are a number of ways of approaching the channel-
assignment problem each with some issues[3].
A. Fixed Channel Assignment
One such way would be to use as many channels as the
number of NICs available per node i.e. if we have n number
of NICs on a node we fix them to n different channels. This
would lead to a very simplified scenario as we will just need
to manage simultaneous communications on multiple
channels. This is however not a optimal solution as it will
leave many channels unused and be inefficient, specially in
the case where the number of NICs is very less as compared
to the number of channels. Another approach would be to
fix NICs on different nodes to non-disjoint sets of different
channels. Thus each node will share atleast one different
channel with other nodes. This would balance the load on
different channels and utilize all channels effectively.
Though, this might simplify the protocol, a simple
assignment of channels might hamper network connectivity.
It might cause network partitioning i.e. disjoint sets of nodes
which have no connectivity between them (Fig.1), even if
nodes have multiple NICs.
Fig. 1: Fixed Channel Assignment leading to disjoint set
B. Dynamic Channel Assignment
Through this flexible approach, each node balances its load
over all channels in due course of time. However, this policy
will require frequent channel switching leading to switch
delays. Also it requires careful co-ordination between nodes
to ensure that two nodes which need to communicate have
alteast one of their interfaces use a common channel.

(IJSRD/Vol. 2/Issue 07/2014/009)
III. MULTI-CHANNEL MAC [4]
MMAC is a link-layer protocol for single interface networks
to utilize multiple channels. MMAC requires time
synchronization between nodes to coordinate channel
assignment. In MMAC time is divided into quantum units
called beacons. At the start of this beacon, each node is
forced to assign a common channel to its NIC. This ensures
connectivity between nodes and a chance for all nodes to
exchange information for further communication.
As soon as all nodes are on a common channel after a
random interval (to avoid contention) the node which has
data to transmit (SRC1) sends a ATIM packet to the
destination (DST1). The ATIM packet includes channel
information about the usage of channels in SRC1’s
neighborhood, termed as the Preferred
Channel List (PCL). On receiving this ATIM
packet, DST1 matches its own PCL and decides the least
used channel as communication medium and replies with an
ATIM-ACK packet containing the above information. The
transaction is confirmed by SRC1 by sending an ATIM-RES
packet. Meanwhile, the neighbors of SRC1 and DST1
update their PCL’s on hearing the conversation. Similarly,
other SRCDST pairs get ready for communication within
the stipulated ATIM window. After the ATIM window,
communication as decided earlier continues and data is sent
by SRC1 to DST1 on the pre-decided channel.
Simultaneously, other SRC-DST pairs do data transaction.
The communication stops as the beacon interval approaches
and all the nodes switch back to the common channel. Thus,
MMAC enables equal load distribution on all channels as
well as adequate opportunities for broadcast during the
ATIM window.
IV. ROUTING PROTOCOL
Although most routing protocols for single channel
assignment would work with proposed channel assignment
algorithms, they will not be optimal. In multiple channel
network, as opposed to single channel network, shortest-
path metric is not optimal. Hence, the challenge is to suggest
the best suitable metric for such networks. While deciding
the metric for such a case, we need to keep in mind the
switching delay, channel diversity and the conventional
resource usage i.e. the number of hops.
When we choose a route for a packet in a multiple
channel network, though it might be shorter than their paths,
it might include channel switching for a majority of hops on
its way. Switching of interfaces to different channels incurs
switching delay which should be minimized. At the same
time a node should transmit and receive on different
channels as this enables it to do so simultaneously,
increasing the throughput. Hence, a route where all nodes
receive and transmit on different channels should be
preferred[5]. However, total hops along the route also have a
weight age as there should not be inefficient use of
resources along the route.
V. NETWORK SIMULATOR
A network simulator is a software that simulates the network
without a netwowrk actually being present. Compared to the
cost and time involved in setting up an entire test bed
containing multiple networked computers, routers,
infrastructure, network simulators are relatively fast and
inexpensive. They allow testing of scenarios that might be
particularly difficult or expensive to simulate using real
hardware. Networking simulators are particularly useful in
allowing designers to test new networking protocols or
changes to existing protocols in a controlled and
reproducible environment. There are a wide variety of
network simulators, ranging from the very simple to the
very complex.
VI. NETWORK SIMULATOR- NS2[1]
NS2 is an open source simulator targeted for network
research. NS2 official release does not support multi-
channel wireless network environment. In the NS
implementation of wireless networks, the layers are defined
as:
 Routing- topmost layer
 Link Layer-either queue or send the packet
 ARP-address resolution
 Ifq- queueing
 MAC-MAC parameters and timers
 NetIF & Propagaton-Physical layer
 Channel – channel assignment and connectivity
A packet is passed from one layer to another by
calling recv() function of the layer UPSTREAM or
DOWNSTREAM. The neighbour nodes that will be
affected.
VII. MULTI-INTERFACE MULTI-CHANNEL EXTENSION
The Multi-Interface Multi-Channel extension of NS-2.29
now enables us to simulate such wireless network
environments in NS. Other simulators either do not provide
sufficient features or are not freely available. The extension
can serve as platform for performance evaluation of channel
assignment protocols and routing protocols developed for
such wireless environments. First we must generate the
topology as required i.e. the placement of the nodes in the
network[6]. Next we decide upon the traffic that we need to
simulate on the given topology. Given the traffic and
topology, the implementation of the protocol should assign
different channels to the network interfaces of the nodes and
also find routes for the traffic. The routing that is generated
using this protocol can then be generated in the form of a
script in the form of manual routing where we hardcode the
route that each traffic flow needs to take Thus, the
implementation can be any programming language with the
end result as a tcl script. Though the number of interfaces on
a node is 5, it can be increased by making changes in the NS
code. For protocols that require fewer number of interfaces,
the implementation can be done assuming the required
number of interfaces and rest of the interfaces can be
assigned a fixed channel that is never used. Unless an
interface is specifically instructed to be used in a particular
route it does not interfere with the performance[7]. The
network environment can be altered by changing the
network parameters available in NS.
VIII. CONCLUSION
Multi-interface multi-channel wireless algorithms are useful
for exploiting the wasted bandwidth available in the form of

(IJSRD/Vol. 2/Issue 07/2014/009)
orthogonal channels in the IEEE 802.11a/g interface.
Special routing protocols and channel assignment
algorithms are required for such network environments.
Wide usage of such networks would be a great boon to last-
mile internet connectivity and development of low-cost
wireless mesh networks where only a wired backbone is
used as a support. Extensive literature survey in this field
shows that though there have been many theoretical
advances in the field, there is lack of any real extensive
deployment. Most of the implementation on simulators like
Ns2 were either out of date or broken. The extension of NS
provides a framework on which other channel assignment
and routing algorithms for multi-channel multi-interface
networks can be implemented.
REFERENCES
[1] N. S. 2. http://www.isi.edu/nsnam/ns/.
[2] A. Raniwala and T. cker Chiueh. Architecture and
Algorithms for an IEEE 802.11-Based Multi-
Channel
[3] P. Kyasanur and N. H. Vaidya. Routing and
Interface Assignment in Multi-Channel Multi-
Interface Wireless
[4] C. Chereddi. Pradeep Kyasanur, Jungmin So and
N. H. Vaidya. Multi-Channel Mesh Networks:
Challenges and Protocols. IEEE Wireless
Communications, April 2006.
[5] P. Kyasanur and N. H. Vaidya. Capacity of Multi-
Channel Wireless Networks: Impact of Number of
Channels and Interfaces. ACM Mobicom, 2005.
[6] J. Padhye. R. Draves and B. Zill. Routing in Multi-
Radio, Multi-Hop Wireless Mesh Networks. ACM
Mobicom, 2004.
[7] Nitin H. Vaidya. Chandrakanth Chereddi, Pradeep
Kyasanur. Design and implementation of a
multichannel multi-nterface network. second
international workshop onMulti-hop ad hoc
networks: from theory to reality, May 2006.

Multi-Channel Multi-Interface Wireless Network Architecture

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Multi-Channel Multi-Interface Wireless Network Architecture