WiFi and Cellular Handoff

1
Wi-Fi and Cellular Handoff

• Sowjanya Talasila
• Shilpa Pamidimukkala
• Sravanthi Yalamanchili

2
Agenda

• Cellular Networks
• WLAN
• Vertical Handoff
• Fixed Mobile Convergence
• Introduction to HTN
• HTN working
• Performance
• Introduction to UMA
• UMA specifications
• UMA technology

3
Cellular Networks

• Wide coverage (km range)
• Large number of users
• Low speeds (in Kbps)
• High deployment costs

4
Wireless LANs

• High Inexpensive to set up
• Speeds up to 108 Mbps
• Low coverage
• Small number of users

5
Vertical Handoff

• Vertical handoff is a technique that allows a
  mobile user to roam between different networks
  and access technologies ,in a manner that is
  transparent to the applications and users ,
  without disrupting connectivity.

6
Benefits of Vertical Handoff

• Simultaneous use of different access networks and
  technologies.
• Seamless transfer of connection between different
  networks and access technologies.

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Motivations
Mobility
Vehicle
3G
2G
Complementary performance
Vertical handover
Walk
WLAN
Fix
LAN
Data rate
Mbit/s
0.1
2
50
1000
Mobility vs. Throughput for communication systems
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Combining both WLAN and Cellular

• Combine advantages of cellular networks and Wi-Fi
  hotspots
• Higher bandwidth
• Extended coverage
• Inexpensive
• Large number of users

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Goals of Vertical Handoff

• Low handoff latency
• Power saving
• Low bandwidth overhead

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Vertical Handoff Procedure - Mobile Downward
CDMA cellular card activate
11
Vertical Handoff Procedure- Mobile Upward
check beacon and activate WLAN card
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Handoff Decision

• Radio link characteristic
• Application traffic classes

13
Fixed Mobile Convergence

• Fixed mobile convergence (FMC) solutions enable
  seamless handoff of calls and call features
  across wireline (Wi-Fi or 802.11) and wireless
  (cellular) networks .
• FMC solutions available today enable wireline
  carriers to recapture lost revenue and
  subscribers by extending mobility into the
  enterprise while keeping wireless minutes on the
  wireline network.

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Contd..

• These solutions use dual-mode handsets to
  seamlessly roam between Wi-Fi and cellular
  networks and provide users with one set of
  business telephony features, one phone number,
  and one user interface.

15
FMC
16
FMC Approaches

• Two approaches to Fixed Mobile Convergence
• Handoff Trigger Node(HTN)
• Unlicensed Multiple Access(UMA)

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Handoff Trigger Node
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Handoff Trigger Node (HTN)

• A simple WiFi handoff trigger node can be
  installed in the WLAN/cellular transition region
  and generates link layer triggers which cause the
  initiation of the vertical handoff process.

19
HTN

• Two solutions for inter-working of WLAN/ Cellular
  
• Tight-coupling
• Integrates WLAN hotspot into cellular
  infrastructure.
• WiFi operate as a slave to cellular coverage
  cell.
• Loosely-coupling
• No such close relation between the networks and
  allows many network operators and service
  providers to operate in the same market.

20
HTN (contd..)

• When roaming inside a WiFi hotspot, a dual mode
  MS uses IEEE 802.11 layer 2 roaming procedures.
• When the receive signal strength indication
  (RSSI) drops consistently below a certain
  threshold, MS scans for the new access point (AP)
  using standard IEEE 802.11 procedures.

21
Without HTN
22
HTN (contd..)

• The latency associated with the above can be
  significant and includes components such as BS
  searching and higher layer signaling functions.
• Existing WiFi/cellular transition coverage areas
  are highly site specific.

23
Using HTN

• HTN can be installed in the WLAN/cellular
  transition region, generate link layer triggers
  which cause the initiation of the vertical
  handoff process.
• HTN does not function as an access point but as a
  regular data station with enhanced capabilities.

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HTN (contd..)

• During a successful vertical handoff, the MS is
  assigned capacity in the cellular system.
• In a tightly-coupled WIFI/cellular design it is
  possible to reserve capacity for WiFi-cellular
  handoffs, so that call dropping probability is
  acceptably low.
• In loosely- coupled BS may not be able to
  distinguish WiFi-cellular handoff from new call
  request.

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Handoff Trigger Node (HTN)
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How HTN works

• HTN acts as a simple WiFi end station and
  associates with the closest AP i.e. AP3 in fig
  just as normal IEEE 802.11 station.
• HTN then continuously scans IEEE 802.11channel
  corresponding to the coverage area of AP3.
• The scanning that is performed is done in
  promiscuous mode, i.e. normal HTN MAC filtering
  is disabled and it intercepts and listens to all
  the station transmissions.

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How HTN works (contd..)

• The packets that are received are then filtered
  at higher protocol layers for active voice
  connections.
• The objective of this is to identify, if possible
  , all active voice connections that are with in
  the range of the HTN.
• When the HTN is installed, it is configured with
  a site-specific receive signal strength
  indication (RSSI) threshold, denoted by yhot.

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How HTN works (contd..)

• When an end station is detected HTN station
  scanning, whose RSSI exceeds yHOT, a
  HO_TRIGGER_CMD is sent to the MS in question.
• HTN must extract the MS MAC address from the
  scanned packets and use this information to send
  a trigger command to the station in question.
• Once the mobile station receives the
  HO_TRIGGER_CMD, it initiates the vertical handoff
  procedure.

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How HTN works (contd..)

• This includes having the MS turn on its cellular
  radio prior to setting up the vertical handoff.
• A handoff Trigger Node can easily perform handoff
  trigger in mulitichannel/multi-AP coverage
  situations simply by serially scanning on the
  various channels of interest.

30
HTN Performance
Here are some of the results obtained from a
stimulation of HTN design using the below table.
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Performance (contd..)

• In the result there is a comparison between
• LHO- legacy handoff case.
• HOT-Handoff triggering case.

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Handoff Dropping Probability

• This is the probability that a call with at least
  one handoff attempt from the WLAN to the cellular
  system is dropped.
• This is computed by the total number of stations
  that have at least one handoff request.

33
Handoff Dropping Probability
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Cellular Time Fraction

• This is the average fraction of time that a call
  which has stared inside the WiFi hotspot, spends
  being served by the cellular system.

35
Cellular Time Fraction
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Mean Vertical Handoff Deadline

• This is the average time the MS has to complete a
  vertical handoff after its first handoff attempt.

37
Mean Vertical Handoff Deadline
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False vertical Handoff Rate

• This is the false alarm rate ,i.e. the rate at
  which unnecessary vertical handoffs are
  triggered.
• This is obtained by computing the fraction of
  vertical handoffs that occur which are
  unnecessary because the MS completes its call
  before leaving the WiFi coverage area.

39
False vertical Handoff Rate
40

• Result
• An important function provided by the HTN is to
  significantly reduce the call dropping rate even
  when there is very little collaboration between
  the cellular and WLAN hotspot providers.

41
UMA
42
What is UMA?

• Unlicensed Mobile Access
• UMA establishes a standard for seamless hand-off
  and roaming between a cellular network and fixed
  IP-based wireless networks
• UMA is an extension of GSM/GPRS mobile services.

43
UMA (Unlicensed Mobile Access)

• UMA lets mobile operators deliver voice, data and
  IMS/SIP(IP Multi media Subsystem /Session
  Initiated Protocol) applications to mobile phones
  on Wi-Fi access network.

44
UMA Protocols

• UMA is on top of it at the transport layer (Layer
  4) and has its own set of control protocols .
• Limits IP packet Delivery??

45
UNC

• The UMA specification is based around UNC.
• What is UNC???
• A UMA Network Controller (UNC) acts as a
  virtual base station,
• providing handoff
• between cellular
• and Wi-Fi networks.

46
How UMA Technology Works

• A mobile subscriber with a UMA-enabled, dual-mode
  handset moves within range of an unlicensed
  wireless network to which the handset is allowed
  to connect.
• Upon connecting, the handset contacts the UMA
  Network Controller (UNC) over the broadband IP
  access network to be authenticated and authorized
  to access GSM voice and GPRS data services via
  the unlicensed wireless network.

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(No Transcript)
48
(Contd..)

• If approved, the subscribers current location
  information stored in the core network is
  updated, and from that point on all mobile voice
  and data traffic is routed to the handset via the
  Unlicensed Mobile Access Network (UMAN) rather
  than the cellular radio access network (RAN).

49
ROAMING

• When a UMA-enabled subscriber moves outside the
  range of an unlicensed wireless network to which
  they are connected, the UNC and handset
  facilitate roaming back to the licensed outdoor
  network. This roaming process is completely
  transparent to the subscriber.

50
HANDOVER

• Handover in
• The mobile station moves from macro network to a
  UMAN.
• Handover out
• The mobile station moves from UMAN to macro
  network.
• Handover UMA
• The mobile station moves with in a UMAN or from
  UMAN to UMAN.

51
(No Transcript)
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Handoff Specifications

• Subject to mode selection, UMA shall support
  seamless handover in and handover out ,provided
  the following conditions are true
• The mobile station stays within the limits of
  service (pedestrian state of motion)
• The mobile station remains during the time of
  handover within the coverage of both the networks

53
(Contd)

• UMA shall manage bandwidth during handover
  between macro network and UMAN.
• UMA shall produce seamles handover if
• If the MS stays with in the coverage limit
• If the MS remains during the time of handover
  with in the coverage of UMAN.
• Selection of APs and Macro-UMAN.

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(No Transcript)
55
Security in UMA

• UMA does not mandate any security mechanism,
  but can coexist with those available, such WPA,
  WPA2, or WEP.
• (WPA
  WEP???)
• WEP (wired equivalent privacy)
• WPA? Temporal Key Integrity Protocol (TKIP)

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Security in UMA

• UMA service providers to terminate tunnels while
  concurrently providing advanced security and
  routing functions. This allows service providers
  to deploy a single platform that can support IMS
  termination as well as additional security
  services such as firewalls, Denial of Service
  (DoS) attack prevention and Virtual Private
  Networks (VPNs).

57
Advantages Availability Pricing

• UMA could be used to provide better in-building
  coverage for customers who don't get a good
  cellular signal in some areas, including
  basements.
• It enables service providers to deliver voice at
  a lower cost when handsets are within range of an
  unlicensed wireless network.

58
Issues

• If a customer doesn't have a wireless network
  already in the house, a wireless access point
  would be needed in addition to a broadband link
  (ATA).
• The most expensive and technologically
  challenging component of UMA solution is the
  Wi-Fi and cellular handset, because of
  battery-life limitations, cost, and size

59
Contd..

• UMA cannot guarantee the quality of a voice call
  or the throughput of a data connection and
  traffic prioritization with QoS can significantly
  improve performance, especially in a residential
  environment where traffic is likely to be less
  heavy than in the enterprise.
• (fixed line divisions )

60
Conclusion

• As a growing number of handsets incorporate Wi-Fi
  , users will be able to take advantage of the
  proliferation of Wi-Fi WLANS- both in private and
  public enviro mants to route lower cost VoIP
  calls.

61
References

• IEEE White Paper Handoff Trigger Nodes for
  Hybrid IEEE 802.11 WLAN/Cellular Networks.
• http//telephonyonline.com/wireless/news/fixed_mob
  ile_convergence_021805/
• http//www.wirelessweek.com/article/CA626287.html?
  spacedescDepartments http//www.rimroad.com/artic
  les/2004/9/2004-9-8-Cellular-to-WLAN.html
• http//www.umatechnology.org/technology/index.htm
  
• http//www.semiconductors.philips.com/news/content
  /file_1137.html http//wifinetnews.com/archives/00
  4825.html

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Questions?

• What is FMC and its two approaches?
• Solution Refer to slide 13 and 16 .
• What are the two solutions for inter-working of
  WLAN/ Cellular and which is preferred?
• Solution Refer to slide 19 and 24 .
• What are UMA handoff specifications?
• Solution Refer to slide 52 .