VoIP Mobility

1
VoIP Mobility

• Pavan Kundhavaram

2
Contents

• Introduction.
• VoIP Mobility.
• Issues.
• Conclusion.
• References.

3
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.

4
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.

5
VoIP Mobility

• Mobility include
• Terminal Mobility.
• User Mobility.
• Service Mobility.

6
Issues

• Optimizing the Handover Delay .
• Mobility Management for VoIP Traffic.
• VoIP Seamless Handover.

7
Issue1Optimizing Handover Delay

• The support of IP-based real time services in the
  next-generation 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.

8
Issue1 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 .

9
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.

10
Simple Model for Analysis
11
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 MNs home network and the
  CN is thc.

12
Assumptions

• tsltth.
• In MIPv4 FACoA instead of CCoA is used therefore
  MNs 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.

13
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 .

14
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 .

15
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.

16
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 t 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)t .

17
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)

18
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.

19
Back-off interval timer
20
Retransmission Probability

• The probability of retransmission q is the
  probability of a
• transaction having failed
• The probability of having a retransmission of
  Solicitation is
• q 1- ((1 - p)k1k2 )

21
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

22
contd..
Tt(i)MIP 1/1 - qNm (1 - q) (D (k - 1)t
) (1 - q)q(Tr(1) D (k -
1)t ) (1 - q)q2 (3Tr(1) D
(k - 1)t) (1 -
q)qNm-1 ((2Nm-1 - 1)Tr(1) D
(k - 1)t ) D (k - 1)t - Tr(1)
((1 - q)(1 - (2q)Nm))/(1 - qNm)(1 -
2q)) Tr(1)
23
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).

24
MIPv6 Handover Delay

• MIPv6 average handoff delay is as follows
• TtMIPv6 Tt(RSol) Tt(RAdv) 2trf
• 2trh 2trc 2Tt(BU)
  2Tt(BA).
• where trc is the delay between the RAN and the CN
  trc tmc - tmr.

where trc is the delay between the RAN and the CN
trc tmc - tmr).
25
Numerical Results
26
Disruption time vs. FER
27
Issue2 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.

28
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.

29
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.

30
SolutionDMA 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.

31
IDMP Architecture
32
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 MNs 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.

33
Elements of DMA Architecture
34
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.

35
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.

36
Signal Flow of VoIP Mobility
37
Issue3VoIP 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,

38
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.

39
SolutionVPN 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.

40
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.

41
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.

42
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.

43
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 (gt 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.

44
Seamless Handover Architecture
45
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.

46
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.

47
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.

48
Message flows During Handover
49
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.
  
  
  
  
  

50
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. 6675, October 2002.