You are driving and talking on the phone. The call does not drop when you leave one cell and enter another. That is handoff — transferring a call between cells without disconnection. The network monitors your signal. When it weakens, it finds a stronger cell and switches the call. The process takes milliseconds.

Handoff comes in two types. Hard handoff breaks the connection before making the new one. It is used in early systems and some digital networks. Soft handoff makes the new connection before breaking the old one. CDMA networks use soft handoff. It is more reliable but uses more resources.

Handoff types

• Hard: break before make
• Soft: make before break
• Horizontal: between cells of same network
• Vertical: between different networks, like Wi-Fi to cellular

Handoff is invisible when it works. You do not notice it. When it fails, the call drops. Engineers design networks with overlapping coverage to make handoff reliable. The transition between cells is one of the most complex parts of mobile networking.