VoIP AND MOBILITY

VoIP AND MOBILITY

Vishnu Kanipakam

VoIP and Mobility 2

Contents… Introduction Issues -DSR -AMR -UPSD Conclusion References

VoIP and Mobility 3

VoIP and Mobility… 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

VoIP and Mobility 4

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 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 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


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.


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.


Proposed solution…


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).


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.


Regional Cell Division using Triangle unit…


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.


Region Organizing by Regional CellDivision…


Directional Cell Sectoring…


The DSRR Decision…


Experiment and Result analysis… Initial Shadow.Reg DSR


Conclusion… 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.


ISSUE…2 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???


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.


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.


Adaptive Multi Rate system for Voice over IP…


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.


Examples…


Selective Redundancy… 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.


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.


Partial Redundancy…


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.


Experiment…


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


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.


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???


An 802.11-based VoIP over WLAN System…


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.


Contd… 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.


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.


Frame exchange sequence of UPSD


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.


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.


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.


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.


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.


Average Duty Cycle of Voics STAs…Voice only…


Average Duty Cycle of Voice STAs(Voice+Data)…


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 & Voice+Data)

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


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 service:Mobile IP and SIP,” IEEE Wireless Communication,Oct. 2002.


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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