VoIP AND MOBILITY

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VoIP AND MOBILITY

• Vishnu Kanipakam

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Contents

• Introduction
• Issues
• -DSR
• -AMR
• -UPSD
• Conclusion
• References

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VoIP and Mobility

• VoIPVoice 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

• 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
  matterwhere 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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ISSUE1

• How can we reduce interdomain handoff delay
  and disruption time in voip service
• (mobile/wireless environments)???
• Can we process message exchange between nodes
  within the intra domain in the interdomain
  environment???

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DSR

• 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

• 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

• Shadow Registration, which registers prior to
  handoff, registers at n neighboring cells
  (denoted by AAAFn).
• Shadow Registration uses the Random-walk model,
  in which the probability for MN to move to
  neighboring cells is equal.

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AIM

• 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

• 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

• 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

• 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

• 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

• 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 CellDivision
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Directional Cell Sectoring
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The DSRR Decision
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Experiment and Result analysis

• Initial Shadow.Reg DSR

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Conclusion

• A shadow trigger region (STR) that judges
  registration availability, a None Registration
  Region (NRR) that filters registration are
  composed.
• Direction Vector Reflects MNs 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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ISSUE2

• 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

• 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

• The major cause for speech quality degradation in
  IP-networks 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

• Sender based mechanisms for recovering from
  packet loss can be classified as
  retransmission-based 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

• For low packet loss rates (lt2), 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

• 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

• 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

• 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

• 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

• 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

• 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

• Power-efficient operation via transmit power
  control and physical layer rate adaptation for
  systems are some of the mechanismsbut, 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

• 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

• 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

• 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

• 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

• 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

• 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

• (VoiceData)

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Conclusion

• 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
  VoiceData)
• At present, UPSD is one of the best power
  management mechanism suitable for implementing
  VoIP services over WLAN.

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References

• 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
  serviceMobile IP and SIP, IEEE Wireless
  Communication,Oct. 2002.

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References

• 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???