Mobile Phone Technology

Handover and handoff are different words for the same idea.

The basics of mobile phone technology is that when a client is moving through the network, they wish to be continuously connected to a network. As mobile phone technology is based on a cell architecture, whilst moving through the network the client will move away from the influence of one cell and nearer to the influence of another cell. At some point the client will be moved oner from one cell to another.

If the client is alive, connected to the network, but not sending or receiving a call or data then the handover is unnoticed by the subscriber. If the subscriber is sending data and a handover occurs then one or more packets could be lost. This would just involve re-transmission and realistically unnoticed by the client. If a client is mid phone call (or mid real-time data transfer) there is potential for the call or data to be lost and hence a break in the transmission.

We can classify handover as either hard handover or soft handover

• Soft Handover - this is seamless handover where the phone and network realise the phone is moving away from the current cell and there is a more powerful cell on the same network. The network will move the phone from one eNodeB to an adjacent eNodeB on the same network. A soft handover is the preferred method of swapping from one part of a network to another.
• Hard Handover - this is called break before make handover, meaning that the current connection is cut prior to the new connection made. Perhaps this is where the client has come to the edge of the current network and has to change network. The client is moved from one network provider to another (where network roaming is allowed) or from one generation to another (4G to 2G).

There are a number of different reasons and types of handover :

• A subscriber moves nearer to another mast (eNodeB) still controlled by the same MSC (Mobile Switching Centre).
• A subscriber moves out of range of a mast run by one MME (Mobile Management Entity) and within range of a second MME.
• An eNodeB or MME is getting busy and the network tries to balance the demand by moving subscribers to another ENodeB or MME
• A subscriber on a 4G network wishes to make a call and does not have access to VO-LTE, a switch will be made to a 2G network.
• Whilst (international) roaming, a stronger network comes into range. For example if holidaying in France, a client will be moved from one French mobile operator to another.
• Within the UK, if we had internal roaming, then a change of network would involve a hard handover