Transcript VoIP Mobility

VoIP Mobility
Pavan Kundhavaram
Contents

Introduction.

VoIP Mobility.

Issues.

Conclusion.

References.
VoIP Introduction

VoIP is Voice Over IP.

VoIP is the routing of voice conversations over the
internet or any other IP-based network.

Voice Calls are transmitted over Packet switched
Network instead of Public Switched Telephone
Network(PSTN).

VoIP allows users to travel anywhere in the world
and still make and receive phone calls.
How It Works

VoIP converts the voice
signal from telephone into a
digital signal that travels
over the internet then
converts it back at the other
end .

A broadband connection is
required in order to place
VoIP call.
VoIP Mobility

Mobility include :

Terminal Mobility.

User Mobility.

Service Mobility.
Issues

Optimizing the Handover Delay .

Mobility Management for VoIP Traffic.

VoIP Seamless Handover.
Issue#1:Optimizing Handover Delay

The support of IP-based real time services in the nextgeneration systems require coupling of mobility with QOS.

Coupling host mobility and quality of service is one of main
challenges.

The mobile node can experience disruptions or intermittent
disconnections of on going real-time session due to
handovers.
Issue#1 contd..

The time or duration of such interruption is called disruption
time.

The handover delay is the time interval from when the
handover process starts to when the first data packet is
received by MN.

The handover delay can heavily affect the user satisfaction .
Proposed Solution

First step : Simple model that takes into account the delay
increases between the different entities involved in the
handover.

Second step: Considers FER of the wireless link and the
retransmissions strategies of the different protocols to
overcome the losses.
Simple Model for Analysis
Analysis contd..

the delay between the MN and the Radio Access Network
(RAN) is tmr.

the delay between the MN and the Access Router (AR)is ts.

the delay between the MN and the FA/MAP is tmf.

the delay between the MN and its HA is assumed to be th.

the delay between the MN and the CN is tmc.

the delay between the MN’s home network and the CN is thc.
Assumptions

ts<th.

In MIPv4 FACoA instead of CCoA is used therefore MN’s
incoming and outgoing traffic is relayed by the FA.

The MN sends regularly solicitations after leaving one network.

For each binding update (BU) message sent ,Binding
Acknowledge (BA) is expected to be received.

For MIPv6 registration we do not consider the time needed by
Duplicate Address Detection (DAD) process.
MIPv4 handoff

The MN detects the IP subnet by exchanging Agent
Solicitation and Agent Advertisement messages which takes
2tmf.

Then, the MN sends a MIP Registration Request to the HA and
gets a Registration Reply, which takes 2th.

At this MN starts receiving downlink packets.

The MIPv4 handoff takes 2tmf + 2th .
MIPv6 handoff

The MN detects the IP subnet by exchanging with AR Router
Solicitation and Router Advertisement messages that takes
2ts.

MN sends to HA a Binding Update and gets a Binding
Acknowledge that takes 2th.

Finally, the MN sends to the CH a Binding Update and gets a
Binding Acknowledge that takes 2tmc.

The MIPv6 handoff delay is 2ts + 2th + 2tmc .
Second Step Assumptions

A random error process.

An Agent/Router Advertisement is sent only if a Agent/Router
Solicitation has been previously received.

An Registration Reply/Binding Acknowledge is sent only if a
Registration Request/Binding Update has been received
previously.

Error correction mechanisms and processing /queuing times
are not considered here.
Second Step contd..

Probability of the frame being erroneous in the air link is p.

For k frames in MIP packet ,the packet loss rate is
(1 − (1 − p)k) .

We denote τ as the inter frame time. D as the frame
propagation delay through the RAN.

Propagation delay from MN to RAN for a MIP message is
D + (k − 1)τ .
Adaptive Retransmission timer

The retransmission timers for all the MIP-based protocols
follow the exponential back-off mechanism.

Tr(1) be the initial back-off timer.

The back-off timer upon the ith transmission Tr(i) doubles after
each retransmission
Tr(i) = 2 (i−1) · Tr(1)
contd..

the initial retransmission timer Tr(1) is a crucial
parameter which should be optimized

It should not be too short.

It should not be too long.

It is proportional to the transmission time of the
messages involved in the handover transaction.
Back-off interval timer
Retransmission Probability

The probability of retransmission q is the probability of a
transaction having failed

The probability of having a retransmission of Solicitation
q = 1− ((1 − p)k1+k2 )
is:
Average Handover Delay

Let Nm be the maximum number of transmissions.

The average delay for a successful transaction is the average
delay for successfully transmitting and receiving the
corresponding acknowledgement of an MIP message.

The average handover delay TtMIP is given as:
TtMIP = ∑ Tt(i)MIP
contd..
Tt(i)MIP =1/1 − qNm · [(1 − q) (D + (k − 1)τ )
+(1 − q)q(Tr(1) + D + (k − 1)τ )
+(1 − q)q2 · (3Tr(1) + D + (k − 1)τ) + · · ·
+(1 − q)qNm−1 · ((2Nm−1 − 1)Tr(1)
+D + (k − 1)τ )]
= D + (k − 1)τ − Tr(1) +
((1 − q)(1 − (2q)Nm))/(1 − qNm)(1 − 2q)) · Tr(1)
MIPv4 Handover Delay

MIPv4 average handover delay is
TtMIPv4 = Tt(AgSol) + Tt(AgAdv) + 2trf
+2trh + Tt(RegReq) + Tt(RegRep).
Where trf is the delay between the RAN and the FA
(trf =tmf − tmr) and trh is the delay between the RAN
and the HA (trh = th − tmr).
MIPv6 Handover Delay

MIPv6 average handoff delay is as follows:
TtMIPv6 = Tt(RSol) + Tt(RAdv) + 2trf
where trc is the delay between the
RAN and the CN trc =
+2trh
+ 2trc + 2Tt(BU) + 2Tt(BA).
tmc − tmr).
where trc is the delay between the RAN and
the CN trc = tmc − tmr.
Numerical Results
Disruption time vs. FER
Issue#2: Mobility Management for VoIP Traffic

IP based mobility management traditionally operate at the
network layer and provide basic connectivity to the MN as they
change their point of attachment.

MIP ensures ubiquitous connectivity by allowing MN to retain
its permanent home address(PHoA) and by tunneling packets
to temporarily care of address(CoA).

These solutions are necessary for VoIP application in dynamic
tactical battlefield networks.
Issue contd..

MIP potentially high update latency makes it
unsuitable for supporting seamless handoffs during
ongoing call.

SIP at application layer offers many advantages over
corresponding MIP but suffers a drawback of
absence of mobility management hierarchy.

SIP and MIP use flat hierarchy in which every change
in MN requires generation of global binding updates.

Updates incur high latency and make rapid handoffs
impossible.
Draw backs of Flat Architecture

On every change in subnet.

MN refreshes its configuration information (COA) .

Generate global bindings to update remote nodes with new COA.

In absence of hierarchy every update travel all the way to the
remote node.

Update process can have high latency because of
communication delay.

If there is packet loss latency becomes much higher at
intermediate hops.
Solution:DMA Architecture

The DMA Architecture is based on two-level mobility
management hierarchy.

IDMP is used as the protocol for managing mobility
within a domain.

The Mobility Agent(MA) is similar to MIP foreign Agent (FA)
excepts it resides higher in network hierarchy and acts as a
domain-wide point for packet redirection.

A Subnet Agent (SA) is similar to MIP FA and provides
subnet-specific mobility services.
IDMP Architecture
contd..





Under IDMP MN has two concurrent CoAs:

Global Care of Address(GCoA).

Local Care of Address (LCoA).
Packets from a remote CN are forwarded to the GCoA and are
intercepted by the MA.
The MA tunnels these packets to the MN’s current LCoA.
Global binding updates are generated only when the MN
changes domains and obtains a new GCoA,
This approach drastically reduces the global signaling load.
Elements of DMA Architecture
Dynamic technique

The DMA architecture defines a dynamic technique for
assigning an MA to an MN when it first moves into the domain.

The architecture assumes the presence of multiple MAs and
applies a load balancing technique for distributing the mobility
load across the multiple MAs.

A central node called the Mobility Server (MS) implements
different load balancing and MA-allocation strategies.
Contd..

The architecture also uses the Differentiated Services
framework to dynamically provision domain resources and
provide an MN QoS guarantees as it moves within the domain.

DMA requires MN to obtain a new LCoA if network mobility is
confined to single mobility domain.

A group of 200 soldiers communicating with 5CNs would
generate 1000 simultaneous global binding updates under flat
architecture but only 200 local updates under DMA approach.
Signal Flow of VoIP Mobility
Issue#3:VoIP Seamless Handover

The period from when the MN last receives data traffic via its
old IP subnet to when it receives it new IP subnet is handover
delay.

Delay is divided into four sub-delays:

Layer 1/Layer 2 radio link switching delay.

L2 access re-authentication delay.

IP layer binding delay.

Application layer authentication and registration delay,
Contd..

The Inter-AP handoff is reduced Inter-Access point protocol is
proposed.

L2 re-authentication delay could be reduced during inter-AP
roaming.

IP layer binding delay is due to allocation of dynamic IP
address via DHCP followed by routing path update to new AP.

DHCP delay in Mobile IP and application layer authentication
and registration delay in SIP mobility is a challenge.
Solution:VPN Technology

The MN is identified by its static private IP address regardless
of its current point of attachment to the subnets.

This allows the MN to use the same IP address during
handover.

When the mobile host hands off to any other AP the new AP
receives session information in advance hindering further
messages.

The delay of re-authentication for the MN is reduced.
Link Layer

The packet loss and end to end transmission delays can be
reduced.

MN moves from one subnet to another subnet without
interruption only if

MN should communicate simultaneously with multiple APs.

The network must duplicate and correctly merge the IP
flows from the CN to the MN through different APs.
Multi-Homing Concept

The multi-homing feature enables the MN to support seamless
handover by simultaneous binding of two different addresses.

The packets are multicast to MN and MIP agents without need
to tunnel packets to the NAR form the PAR as in Mobile IPv6
networks.

The packet loss is reduced during the handover.
Mobile Agent Technology

The MA is software component which can be transferred from
one network element to another while carrying on its status of
execution.

MA technology can diminish network traffic and can maintain
load balancing thus improving network performance specially
in mobile environment.

MA technology in VoIP services includes reducing control
packets, processing the SIM-based authentication via the VPN
tunnel at new location of attachment and secure packet
tranmission.
Mobile Agents to support seamless VoIP
service

Both IP layer binding delay and application layer authentication
and registration delay are major parts of the overall handover
delay.

The delay of IP address renewal (> 2s) has significant effect
on the overall handover performance.

The application layer authentication and registration delay is
harder to reduce than the DHCP delay and cannot be ignored
due to security consideration.
Seamless Handover Architecture
Solution Contd..

Layer 2 Tunneling Protocol (L2TP) VPN tunnels are
constructed between the L2TP Network Server (LNS) and all
L2TP Access Concentrators (LACs).

Service and authentication requests and data packets are
protected under IPSec tunnels while transmitted between the
MN and LNS.

They are further encapsulated into L2TP VPN tunnels during
transmission between the LNS and LAC.
contd..

The LNS function as a service proxy to forward the service
requests from the MN to the application server.

To minimize the DHCP delay, IP binding delay and application
layer authentication delay there are three techniques



VPN with a private static IP address.
Multi-homing.
Mobile Agent.
contd..

L2TP VPN can be implemented as an Intranet.

It can have the static private IP addresses assigned to its
private MNs regardless of their location.

The fast handover for Mobile IPv6 tries to minimize the period
of service disruption by the packet tunneling mechanisms
while performing network layer handover.

The multi-homing concept is used to minimize the disruption
time and packet loss ratio.
Message flows During Handover
Conclusion


The issues discussed above deal with the various VoIP protocols and
various standard both at the network layer and application layer.
In order to achieve transmission during roaming is a challenge and
this can be achieved with proper hand over of the signal to the next
BS.
References




Fathi, Chakraborty, Prasad .”Mobility management for VoIP:
Evaluation of Mobile IP-based protocols”.IEEE ,2005.
Misra ,Das,Anthony.”Hierarchical Mobility Management for VoIP
Traffic”.IEEE 2001.
Lin ,Shun Yang.” Mobile Intelligent Agent Technologies to
Support VoIP Seamless Mobility”.IEEE 2005 .
T. T. Kwon, M. Gerla, and S. Das, “Mobility Management for
VoIP service: Mobile IP vs. SIP,” IEEE Wireless
Communications, vol. 9, no. 5,pp. 66–75, October 2002.