Vertical Handover

Nawshad Rehan Rasha1014052020

INTRODUCTION

What is handover?

Changing the point of connection while communicating

Why is handover needed?

Mobility

User preferences

What is the objective?

Handover procedure without a users notice

”break before make”

Hard Handover

Old connection is broken before a new connection is activated

Primarily used in FDMA and TDMA systems (e.g. GSM)

Different frequency ranges used in adjacent cells to minimize the interference

When to perform hard handover?

E.g. based on measurements of the signal quality

Different schemes to avoid unnecessary handovers

”make before break”

Soft Handover

New connection is activated before the old is broken

Used in UMTS to improve the signal quality

Uplink and downlink signals may be combined for better signal

A mobile may in UMTS spend a large part of the connection time in soft handover

Better connection reliability

Horizontal Handover

Horizontal handover is when a mobile terminal changes its point of connection within the same type of network

E.g. from a cell to another in GSM

E.g. from an access point to another in WiFi

Reasons for handover

Worse signal quality or loss of signal

Traffic load balancing

Cost

BSC

BS1 BS2 BS3

BSC

BS1 BS2 BS3

BSC

BS1 BS2 BS3

Horizontal Handoff

AP AP

BSSBSS

Internet

6

Vertical Handover

Vertical handover is when a mobile terminal changes its point of connection in a different type of network

E.g. from a wired Ethernet connection to an access point in WiFi

E.g. from an access point in WiFi to a cell in UMTS

Reasons for handover

Worse signal quality or loss of signal

Performance requirements (bandwidth)

Cost

Power consumption

Vertical Handover

Ethernet

WiFi

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Vertical Handover

In order to sustain connection and service in heterogeneous wireless environment, vertical handover is necessary. Now-a-days research focus is to optimize vertical handover so that optimized and application specific handover can be made possible.

Vertical handover refers to automatic switching the communication/data session from one technology to the other.

Vertical handover may be referred to a process of transferring call connected to a network/data session from one channel connected in a cell to the core network of another.

Vertical Handoff

WCDMA

WLAN

APBS

Internet

Vertical Handover Strategies

9

BSC

BS1 BS2 BS3

1. Connect to BS1 and start conversation2. Moving out of BS1’s coverage – connect to BS23. Moving out of BS2’s coverage – connect to BS34. Conversation ended – still within BS3’s coverage

Ethernet

WiFi

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

Ethernet

WiFi

UMTS

1. Wired connection at the working desk2. Moving indoor3. Moving outdoor4. Moving into a hot-spot

Difference between Vertical/Horizontal Handover

Vertical Handover

Horizontal Handover

Access Technology Changed Not

changed

QoS Parameters May be changed Not

changed

IP Address Changed Changed

Network Interface May be change Not

Changed

Network Connection More than on connections Single

connection

12

Handoff Metrics

Horizontal HO – mainly use received (RSS) to decide the handoff…

But Vertical HO? RSS?Offered bandwidth? Price?Power consumption?Speed? ….

14

Why Vertical Handover

Cost/Capacity/Coverage…..

If a laptop might be able to use both a high speed wireless LAN and a cellular technology for Internet access.

Wireless LAN connections generally provide higher speeds

benefit of utilizing the higher bandwidth and lower cost

Cellular technologies generally provide more ubiquitous coverage.

better mobility support and larger coverage

The laptop user might want to use a wireless LAN connection whenever one is available, and to 'fail over' to a cellular connection when the wireless LAN is unavailable.

Vertical Handover decision

As incorrect handoff decision may degrade the quality of service

even break off current communication

Decision depending upon multi-parameter handoff metrics.

Challenges in Vertical Handover

Multi-mode devices

Power consumption

QoS

Available capacity

Security

Timing

The business model

Session continuity

Input Parameters for VHD

Available Bandwidth (BAV)

Speed of mobile terminal (VMT )

Number of Users (UN)

Received Signal Strength (RSS)

Battery Level (BL)

Cost of operation (C)

Traffic Type ( TT )

Vertical Handoff Process

Three main phases:

Initiation: mobile terminal (or network controller) must know which wireless networks are reachable.

Decision: selection, through a VHO algorithm, of the access point, on the basis of proper performance metrics (RSSI, network connection time, available bw, power consumption, cost, security level, user preferences)

Execution: signaling operations to re-establish connection and carry out data transfer .

It handles all the connections in same manner. When all

TCP/IP connection automatically transfers from one interface

to another, in this situation only one wireless interface (the best

one) is used at that moment.

The second limitation of vertical handover is that vertical

handover need the same network interface. All the wireless

interfaces must be used as part of the same Mobile IP and DNS

infrastructure because mobile nodes and peers must be able to

reach the Mobile IP and DNS server.

20

LIMITATIONS OF VERTICAL HANDOVER

Thank you.