Download VOIP AND MOBILITY

VoIP AND MOBILITY
Vishnu Kanipakam
Contents…
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Introduction
Issues
-DSR
-AMR
-UPSD
Conclusion
References
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VoIP and Mobility…
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VoIP…Voice over Internet Protocol.
Enables people to use the Internet as the
transmission medium for telephone calls
by sending voice data in packets using IP
rather than by traditional circuit
transmissions of the PSTN.
Voice over IP traffic might be deployed on
any IP network
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Contd…
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Incoming phone calls can be automatically routed
to your VoIP phone, regardless of where you are
connected to the network.
Call center agents using VoIP phones can work
from anywhere with a sufficiently fast Internet
connection.
A user can make and receive phone calls,no
matter…where he is present on the globe.
VoIP phones can integrate with other services
available over the Internet, including video
conversation, message or data file exchange in
parallel with the conversation, audio
conferencing, managing address books.
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ISSUE…1
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How can we reduce interdomain handoff
delay and disruption time in voip service
(mobile/wireless environments)???
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Can we process message exchange
between nodes within the intra domain in
the interdomain environment???
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DSR…
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Directional Shadow registration is a new
approach for seamless VoIP services.
Prevent unnecessary traffic by shadow
registration at neighboring cells with a
high probability of handoff.
DSR is established security association
(SA) between the MN and AAA server
(AAAF) in neighboring domain before the
actual handoff occurs.
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Contd…
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DSR includes technique and algorithmfor
organizing DSRR (DSR Region) that
reduces disruption and unnecessary
traffic.
A cell division scheme, DSRR can sense
the optimal time for handoff through
Regional Cell Division and applied
Direction Vector (DV) obtained through
Directional Cell Sectoring.
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Introduction…
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Shadow Registration, which registers prior
to handoff, registers at n neighboring cells
(denoted by AAAFn).
Shadow Registration uses the Randomwalk model, in which the probability for
MN to move to neighboring cells is equal.
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AIM…
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To reduce the interdomain handoff delay
and disruption time in VoIP service in
Mobile environments.
To minimize the number of neighboring
domains to register caused by
regional/directional cell filtering.
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Mobile computing architecture
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Description…
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The mobile computing system consists of
the fixed/wireless network, MN, BS, and
FN (Fixed Node).
The BS with radio interface was linked to
the IP network that is a fixed network.
One cell is a logical or geographical area
managed by a BS.
The MN can move while connecting to the
network.
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Contd…
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The MN should have radio communication
with the BS of the cell where it stays in
order to communicate with other MNs or
fixed nodes.
The system has to be designed
considering the user's mobility.
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Proposed solution…
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Contd…
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A hexagonal cell model which is divided
into a geographical unit managed by one
BS.
The X-Y coordinate system is showing the
allocation identification (ID) of each cell.
A cell is selected at random to starting
point(0,0).
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Contd…
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The cell is a hexagonal with center (that
is, ID) (Xc, Yc) and radius (that is,length
of a side of triangle) R.
Cells that adjoin for cell (Xc, Yc) have an
ID value that is increased or decreased by
each 1 on X axis and Y axis.
This ID is used by discernment value of
each cell.
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Regional Cell Division using Triangle
unit…
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Contd…
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To find HoR (Handoff Region), STR
(Shadow Trigger Region), and NRR (None
Registration Region) from the Cell
Boundary and Handoff Start Boundary.
Threshold becomes shortest distance
between the Handoff Start Boundary and
Cell Boundary.
Threshold is used to control the accuracy
of handoff, and affects the estimate of
handoff time and the number of DSRR
generated.
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Region Organizing by Regional Cell
Division…
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Directional Cell Sectoring…
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The DSRR Decision…
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Experiment and Result analysis…
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Initial
Shadow.Reg
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DSR
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Conclusion…
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A shadow trigger region (STR) that judges
registration availability, a None
Registration Region (NRR) that filters
registration are composed.
Direction Vector: Reflects MN’s moving
direction to decide minimal Shadow
Registration Region.
DSR adapt to arbitrary cell topologies in
which the number of neighboring base
stations at different locations may vary.
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ISSUE…2
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Can we reduce packet losses (which
causes degradation of the synthesized
speech) ???
At the same time, can we take care of
bandwidth used by the voice stream???
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FEC…
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In VoIP packet losses cause degradation of the
synthesized speech.
The distortions may propagate over several consecutive
frames since predictors in the codec exploit inter-frame
correlations to gain coding efficiency.
To reduce the effects of packet loss Forward Error
Correction (FEC) that adds redundant information to
voice packets can be used.
FEC can reduce the effects of packet loss, it will
increase the amount of bandwidth used by the voice
stream, which is not desirable.
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Packet loss…
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The major cause for speech quality degradation in IPnetworks is packet loss.
Packet loss usually occurs in routers due to
congestion.
Packets may also be dropped in the application, if
they are received too late to be useful.
While voice traffic can tolerate some amount of packet
loss, a loss rate of a few percent may he harmful to
the speech quality.
The amount of packet loss that can he tolerated
depends on the robustness of the used coding
algorithm.
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Adaptive Multi Rate system for Voice
over IP…
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Redundant Packets…
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Sender based mechanisms for recovering from
packet loss can be classified as retransmissionbased techniques and Forward Error Correction
(FEC) techniques.
For delay sensitive real-time applications, such
as telephony, FEC-techniques are dominant
because packet losses can he recovered without
time-consuming retransmission.
FEC-techniques transmit the speech
parameters in two or more consecutive packets.
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Examples…
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Selective Redundancy…
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For low packet loss rates (<2%), packet losses
during stationary speech segments are normally
concealed well with a conventional Error
Concealment Unit (ECU).
Problems with intelligibility occur when onset
frames or non-stationary frames are lost.
To maintain the intelligibility, it is possible to
enable redundancy only for these sensitive
frames, i.e. important frames are transmitted
twice while the remaining frames are only
transmitted once.
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Parameter Interpolation…
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Conventional ECUs extrapolate speech
codec parameters from the previous frame
in case of packet loss.
The parameters in the AMR codec that
may be interpolated are LSF parameters,
pitch lag and gain factors.
Pitch lags on the other hand are well
behaved during steady-state voiced
segments.
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Partial Redundancy…
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Principle…
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To transmit a given amount of the most
important coded speech bits redundant
information as redundant information.
The amount of partial redundancy may
depend on the potential gain for the
decoded speech as well on the channel
quality.
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Experiment…
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Network Adaptation…
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The horizontal bars are proposed working ranges
for the different configurations.
The arrow is a suggested adaptation path that
shows which configuration to use depending on
the packet loss rate.
The packet loss rate is reported to the encoder
via a feedback channel from the decoder
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Conclusion…
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AMR codec is a suitable choice for voice
over IP.
The adaptive capabilities allows for
maximizing the quality of service for all
network conditions, without increasing the
bit-rate significantly.
For packet loss rates below 1%,a high rate
mode should be selected to maximize the
basic speech coder quality and vice-versa.
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ISSUE 3…
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Can power consumption be managed in an
effective manner for VoIP over wireless
LAN applications???
If yes,what are those mechanismsand how
can we implement them???
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An 802.11-based VoIP over WLAN
System…
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Introduction…
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Wireless LAN (WLAN) systems providing
broadband wireless access have
experienced a spectacular rise in
popularity in recent years.
Power consumption of a hand-held device
can be managed.
In order to deliver competitive talk time
with a digital cordless or cellular device,
power conservation during an active voice
call becomes necessary.
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Contd…
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Power-efficient operation via transmit
power control and physical layer rate
adaptation for systems are some of the
mechanisms…but, they are very complex
to implement.
Unscheduled Power Save Delivery (UPSD)
in combination with the eDCA mechanism
is ideally suited for power management.
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Unscheduled Power Save Delivery…
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UPSD is an option that the STA can choose via
proper signaling.
To define an unscheduled service period, which
are contiguous periods of time during which a
STA is expected to be awake.
If a station establishes a downlink flow and
specifies UPSD power management, then the
station requests and the AP should deliver
buffered frames associated with that flow during
an unscheduled service period.
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Frame exchange sequence of UPSD
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Functioning…
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A STA initiates an unscheduled service period by
transmitting a trigger frame, where a trigger
frame is defined as a data frame associated with
an uplink flow having UPSD enabled.
After the AP acknowledges the trigger frame, it
should prepare to transmit the frames in its UPSD
power save buffer addressed to the triggering
STA.
UPSD is well suited to support bi-directional
frame exchanges between a voice STA and its AP.
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Behavior at the AP Operating UPSD…
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All UPSD-capable APs are required to maintain a
UPSD status for each admitted downlink flow.
When a STA is inactive mode, all frames destined
to that STA should be transmitted immediately,
according to the eDCA channel access
procedures.
There are two types of power-save buffers in a
UPSD-capable AP: the legacy PS buffer and the
UPSD buffer.
The legacy buffer is used to buffer downlink
frames belonging to flows using legacy power
management.
The UPSD buffer isused for UPSD flows.
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Contd…
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Upon receiving and acknowledging a
trigger frame the AP starts an
unscheduled service period.
During the unscheduled service period,
the AP should attempt to deliver all the
buffered UPSD downlink frames addressed
to the STA transmitting the trigger.
The AP should also have an aging function
to delete pending traffic when it is
buffered for an excessive amount of time.
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Behavior at a non-AP QSTA Operating
UPSD…
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A STA initiating an unscheduled service
period shall remain awake until the AP
indicates that the end of the unscheduled
service period has arrived.
A bi-directional flow is considered best
suited for using UPSD.
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Contd…
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In the absence of uplink data flow using
UPSD, a STA should create an artificial
uplink trigger flow using UPSD if the STA
establishes downlink flows using UPSD.
The STA wakes up periodically and sends
an empty frame to initiate unscheduled
service periods to retrieve buffered
downlink frames from the UPSD buffer.
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Average Duty Cycle of Voics STAs…
Voice only…
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Average Duty Cycle of Voice STAs
(Voice+Data)…
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Conclusion
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UPSD is a more efficient power
management mechanism than the legacy
power save procedure specified in 802.11.
UPSD delivers lower duty cycle and higher
system capacity in both the scenarios
(Voice only & Voice+Data)
At present, UPSD is one of the best power
management mechanism suitable for
implementing VoIP services over WLAN.
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References…
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T. Wilson, et al., “Normative Text for Unscheduled
eDCA Power Management,” Submission to 802.11
TGe group, doc 11-03-0698-00-000e, September,
2003.
D. Qiao, S. Choi, A. Soomro, and K. G. Shin,
“Energy-efficient PCF operation of IEEE 802.11a
Wireless LAN”, IEEE INFOCOM 2002.
IEEE Standard 802.11e, “Media Access Control
(MAC)Enhancements for Quality of Service
(QoS),” Draft 6.0, December2003
Ted Tackyoung Kwon, Mario Gerla, and Sajal
Das,Subir Das, “Mobility Management for VoIP
service:Mobile IP and SIP,” IEEE Wireless
Communication,Oct. 2002.
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References…
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E. Gustafsson, A. Jonsson, and C. Perkins,
“Mobile IP Regional Registration,” Internet Draft,
Sept. 2001.
IETF RFC 3267, J.Sjoberg et al.,” RTP Payload
format and file storage format for the adaptive
multi-rate ( AMR )and Adaptive Multi-rate
Wideband (AMR-WB) audio codecs,” 2002.
J.Wang and J.D.Gibson, ”Parameter interpolation
to enhance the frame erasure to CELP coders in
packet networks,” Proceedings ICASSP 2001, May
2001.
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Any questions???
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