22-06-2012, 01:06 PM
Energy-Efficient VoIP over Wireless LANs
INTRODUCTION
DUAL-MODE phones like the Apple iPhone and RIM
Blackberry are an emerging trend with both a cellular
and a Wireless LAN (WLAN) interface [1]. Apart from data
access, the WLAN interface can also be leveraged for
making Voice over Internet Protocol (VoIP) calls. This offers
two advantages over traditional calling over the cellular
interface: 1) calls over the Internet through WLANs are
more cost effective and 2) these calls are not affected by lack
of coverage of the cellular network in some indoor areas like
the office or home,1 or in certain outdoor areas.
BACKGROUND AND RELATED WORK
We begin this section by providing some background on
how energy wastage by time spent in the idle mode of the
WLAN interface can be minimized. Subsequently, we will
look at related work that saves energy in the idle mode
classified based on the type of traffic under consideration:
Non-VoIP traffic or VoIP traffic.
Saving Energy Consumed by WLAN Interface
The key idea of saving energy of the wireless interface is to
allow it to sleep as much as possible by reducing the time
spent in idle mode. There is typically about one order of
magnitude difference between the power consumption in
the idle and sleep states [9]. This is a difficult problem since
the radio may not know when exactly it has to wake up to
receive incoming packets and will lose them if it stays in the
sleep state. Other researchers have thus proposed schemes
that use multiradio solutions. The data and control channels
are separated, with the control channel generally using a
lower power, always active radio to wake up the higher
powered Wireless LAN radio (e.g., [9], [10], [11]).
PROBLEM DEFINITION
Based on the background provided in the earlier section, we
state the problem that needs to be solved in this section. We
begin by studying the latency components of a VoIP call
from an end-to-end perspective and then provide a more
formal problem statement.
Problem Statement
We will now define the problem we consider in more detail.
illustrates the possible packet arrival patterns for two
cases at the client—when it does not go to sleep at all, and
when it periodically goes to sleep. For simplicity, this
illustration and associated description assumes that only the
client is trying to save energy (we look at the case when both
ends try to save energy in Section 4.2). The packet receive
times when client is not using PSM is not a straight line
because the network latencies from peer to client are
variable.
INTRODUCTION
DUAL-MODE phones like the Apple iPhone and RIM
Blackberry are an emerging trend with both a cellular
and a Wireless LAN (WLAN) interface [1]. Apart from data
access, the WLAN interface can also be leveraged for
making Voice over Internet Protocol (VoIP) calls. This offers
two advantages over traditional calling over the cellular
interface: 1) calls over the Internet through WLANs are
more cost effective and 2) these calls are not affected by lack
of coverage of the cellular network in some indoor areas like
the office or home,1 or in certain outdoor areas.
BACKGROUND AND RELATED WORK
We begin this section by providing some background on
how energy wastage by time spent in the idle mode of the
WLAN interface can be minimized. Subsequently, we will
look at related work that saves energy in the idle mode
classified based on the type of traffic under consideration:
Non-VoIP traffic or VoIP traffic.
Saving Energy Consumed by WLAN Interface
The key idea of saving energy of the wireless interface is to
allow it to sleep as much as possible by reducing the time
spent in idle mode. There is typically about one order of
magnitude difference between the power consumption in
the idle and sleep states [9]. This is a difficult problem since
the radio may not know when exactly it has to wake up to
receive incoming packets and will lose them if it stays in the
sleep state. Other researchers have thus proposed schemes
that use multiradio solutions. The data and control channels
are separated, with the control channel generally using a
lower power, always active radio to wake up the higher
powered Wireless LAN radio (e.g., [9], [10], [11]).
PROBLEM DEFINITION
Based on the background provided in the earlier section, we
state the problem that needs to be solved in this section. We
begin by studying the latency components of a VoIP call
from an end-to-end perspective and then provide a more
formal problem statement.
Problem Statement
We will now define the problem we consider in more detail.
illustrates the possible packet arrival patterns for two
cases at the client—when it does not go to sleep at all, and
when it periodically goes to sleep. For simplicity, this
illustration and associated description assumes that only the
client is trying to save energy (we look at the case when both
ends try to save energy in Section 4.2). The packet receive
times when client is not using PSM is not a straight line
because the network latencies from peer to client are
variable.