Transcript Wi-Fi and Cellular Handoff

Wi-Fi and Cellular Handoff
Sowjanya Talasila
Shilpa Pamidimukkala
Sravanthi Yalamanchili
Agenda
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Cellular Networks
WLAN
Vertical Handoff
Fixed Mobile Convergence
Introduction to HTN
HTN working
Performance
Introduction to UMA
UMA specifications
UMA technology
Cellular Networks
•Wide coverage (km range)
•Large number of users
•Low speeds (in Kbps)
•High deployment costs
Wireless LANs
•High Inexpensive to set up
•Speeds up to 108 Mbps
•Low coverage
•Small number of users
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.
Benefits of Vertical Handoff
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Simultaneous use of different access
networks and technologies.
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Seamless transfer of connection between
different networks and access technologies.
Motivations
Mobility
Vehicle
Complementary performance
Walk
2G
3G
Vertical handover
WLAN
Fix
LAN
0.1
2
50
Mobility vs. Throughput for communication systems
1000
Data rate
Mbit/s
Combining both WLAN and Cellular
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Combine advantages of cellular networks and
Wi-Fi hotspots
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Higher bandwidth
Extended coverage
Inexpensive
Large number of users
Goals of Vertical Handoff
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Low handoff latency
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Power saving
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Low bandwidth overhead
Vertical Handoff Procedure
- Mobile Downward
CDMA cellular
card activate
Vertical Handoff Procedure
- Mobile Upward
check beacon
and activate
WLAN card
Handoff Decision
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Radio link characteristic
Application traffic classes
Fixed Mobile Convergence
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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.
Contd..
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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.
FMC
FMC Approaches
Two approaches to Fixed Mobile Convergence
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Handoff Trigger Node(HTN)
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Unlicensed Multiple Access(UMA)
Handoff Trigger Node
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.
HTN
Two solutions for inter-working of WLAN/ Cellular
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Tight-coupling
Integrates WLAN hotspot into cellular infrastructure.
WiFi operate as a slave to cellular coverage cell.
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Loosely-coupling
No such close relation between the networks and allows
many network operators and service providers to
operate in the same market.
HTN (contd..)
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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.
Without HTN
HTN (contd..)
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The latency associated with the above can be
significant and includes components such as BS
searching and higher layer signaling functions.
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Existing WiFi/cellular transition coverage areas
are highly site specific.
Using HTN
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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.
HTN (contd..)
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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.
Handoff Trigger Node (HTN)
How HTN works
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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.
How HTN works (contd..)
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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.
How HTN works (contd..)
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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.
How HTN works (contd..)
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This includes having the MS turn on its cellular
radio prior to setting up the vertical handoff.
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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.
HTN Performance
Here are some of the results obtained from a stimulation of HTN
design using the below table.
Performance (contd..)
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In the result there is a comparison between
LHO- legacy handoff case.
HOT-Handoff triggering case.
Handoff Dropping Probability
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This is the probability that a call with at least one
handoff attempt from the WLAN to the cellular
system is dropped.
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This is computed by the total number of stations
that have at least one handoff request.
Handoff Dropping Probability
Cellular Time Fraction
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This is the average fraction of time that a call
which has stared inside the WiFi hotspot,
spends being served by the cellular system.
Cellular Time Fraction
Mean Vertical Handoff Deadline
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This is the average time the MS has to
complete a vertical handoff after its first
handoff attempt.
Mean Vertical Handoff Deadline
False vertical Handoff Rate
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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.
False vertical Handoff Rate
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.
UMA
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.
UMA (Unlicensed Mobile Access)
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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.
UMA Protocols
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UMA is on top of it at the transport layer
(Layer 4) and has its own set of control
protocols .
Limits IP packet Delivery??
UNC
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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.
How UMA Technology Works
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A mobile subscriber with a UMA-enabled, dualmode handset moves within range of an
unlicensed wireless network to which the handset
is allowed to connect.
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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.
(Contd..)
If approved, the subscriber’s 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).
ROAMING
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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.
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.
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Handoff Specifications
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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
(Contd…)
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UMA shall manage bandwidth during handover
between macro network and UMAN.
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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.
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Selection of APs and Macro-UMAN.
Security in UMA
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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)
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).
Advantages
Availability &Pricing
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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.
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It enables service providers to deliver voice at a
lower cost when handsets are within range of an
unlicensed wireless network.
Issues
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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).
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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
Contd..
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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 )
Conclusion
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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.
References
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IEEE White Paper: Handoff Trigger Nodes for Hybrid IEEE 802.11
WLAN/Cellular Networks.
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http://telephonyonline.com/wireless/news/fixed_mobile_convergenc
e_021805/
http://www.wirelessweek.com/article/CA626287.html?spacedesc=De
partments http://www.rimroad.com/articles/2004/9/2004-9-8-Cellularto-WLAN.html
http://www.umatechnology.org/technology/index.htm
http://www.semiconductors.philips.com/news/content/file_1137.html
http://wifinetnews.com/archives/004825.html
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Questions?
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What is FMC and it’s two approaches?
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What are the two solutions for inter-working of
WLAN/ Cellular and which is preferred?
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Solution: Refer to slide 13 and 16 .
Solution: Refer to slide 19 and 24 .
What are UMA handoff specifications?
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Solution: Refer to slide 52 .