Vertical Handover Nawshad Rehan Rasha

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

Horizontal Handoff AP BSS 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

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 AP BS Internet Vertical Handover Strategies 9

BSC BS1BS2BS3 1. Connect to BS1 and start conversation2. Moving out of BS1’s coverage – connect to BS2 3. Moving out of BS2’s coverage – connect to BS34. Conversation ended – still within BS3’s coverage

Ethernet 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.

Network Coverage WPAN WLANWMANWWANSatellite Bluetooth RFID WiFi IEEE WiMAX IEEE GSM/GPRS UMTS GPS GALILEO Wireless Personal Area Network – In a person’s proximityWireless Local Area Network – Home, Hotel, AirportWireless Metropolitan Area Network – City wide Wireless Wide Area Network – Regional, Cellular systemsSatellite – Worldwide coverage

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

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