Wi-Fi and Cellular Handoff

Sowjanya Talasila

Shilpa Pamidimukkala

Sravanthi Yalamanchili

Agenda

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

Simultaneous use of different access networks and technologies.

Seamless transfer of connection between different networks and access technologies.

Motivations

3G2G WLANLAN

Data rateMbit/s0.1 2 50 1000

Mobility

Vehicle

Walk

Fix

Complementary performance

Mobility vs. Throughput for communication systems

Vertical handover

Combining both WLAN and Cellular Combine advantages of cellular networks and

Wi-Fi hotspots

Higher bandwidth Extended coverage Inexpensive Large number of users

Goals of Vertical Handoff

Low handoff latency

Power saving

Low bandwidth overhead

Vertical Handoff Procedure - Mobile Downward

CDMA cellularcard activate

Vertical Handoff Procedure- Mobile Upward

check beaconand activateWLAN card

Handoff Decision

Radio link characteristic Application traffic classes

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.

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.

FMC

FMC Approaches

Two approaches to Fixed Mobile Convergence

Handoff Trigger Node(HTN)

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 Tight-coupling Integrates WLAN hotspot into cellular infrastructure.

WiFi operate as a slave to cellular coverage cell.

Loosely-couplingNo such close relation between the networks and allows

many network operators and service providers to operate in the same market.

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.

Without HTN

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.

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.

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.

Handoff Trigger Node (HTN)

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.

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.

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.

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.

HTN Performance

Here are some of the results obtained from a stimulation of HTN design using the below table.

Performance (contd..)

In the result there is a comparison between

LHO- legacy handoff case.

HOT-Handoff triggering case.

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.

Handoff Dropping Probability

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.

Cellular Time Fraction

Mean Vertical Handoff Deadline 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

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)

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

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

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 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.

(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

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.

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

(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.

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)

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).

Security in UMA

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.

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

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 )

Contd..

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.

References

IEEE White Paper: Handoff Trigger Nodes for Hybrid IEEE 802.11 WLAN/Cellular Networks.

http://telephonyonline.com/wireless/news/fixed_mobile_convergence_021805/

http://www.wirelessweek.com/article/CA626287.html?spacedesc=Departments http://www.rimroad.com/articles/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/004825.html

What is FMC and it’s 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 .

Questions?