Mobility and other wireless technologies
Moving devices must stay connected as they change access points and networks. Beyond Wi-Fi and cellular, Bluetooth, satellites, and low-power IoT networks fill other niches.
Degrees of mobility
Mobility ranges from a laptop moved between rooms on the same Wi-Fi network, to a phone roaming between Wi-Fi and cellular, to a device on a train crossing many cells while keeping active calls. The challenge is keeping connections alive when a device's point of attachment, and possibly its IP address, changes.
Handovers
A handover moves an active connection from one base station or access point to another. In cellular networks, the device measures signal strength from neighbouring cells and reports to the network, which decides when to hand over and prepares the target cell in advance, so traffic is redirected with minimal interruption. Within one Wi-Fi network, standards such as 802.11r speed up roaming between APs.
Home networks and roaming
Cellular networks track each subscriber's home network, which holds their records, and the visited network they currently use. When abroad, a phone attaches to a visited operator, which authenticates the subscriber via the home network; data may be routed back through the home network or broken out locally, affecting latency.
Mobility at the IP layer
TCP connections are identified by IP addresses and ports, so changing address normally breaks them. Mobile IP lets a device keep a permanent home address, with a home agent forwarding traffic to its current care-of address, but it saw limited deployment. In practice, cellular cores keep a device's IP address stable while it moves, and QUIC's connection IDs let connections survive address changes.
Bluetooth
Bluetooth, standardised as IEEE 802.15.1 and now maintained by the Bluetooth SIG, connects personal devices such as headphones, keyboards, and watches over short range in the 2.4 GHz band, using frequency hopping to avoid interference. Bluetooth Low Energy (BLE), introduced in 2010, supports small battery-powered devices such as fitness trackers and location beacons for years on a coin cell.
Low-power IoT networks
Internet of Things devices often need long battery life and long range at low data rates. Zigbee and Thread form low-power mesh networks in homes and buildings; LoRaWAN covers kilometres with tiny data rates for sensors in agriculture and cities; and cellular variants NB-IoT and LTE-M connect meters and trackers using licensed spectrum.
Satellite internet
Geostationary satellites, about 35,786 kilometres above the equator, give wide coverage but a round-trip time of at least about 480 milliseconds for a request and reply, since signals travel up and down twice. Low Earth orbit constellations, such as SpaceX's Starlink, orbit at roughly 550 kilometres, giving latencies of a few tens of milliseconds, but require thousands of satellites and frequent handovers between them.
Worked example
Minimum latency to a geostationary satellite: a request travels ground to satellite to ground, about 2 x 35,786 = 71,572 km, and the reply does the same, about 143,000 km in total. At the speed of light, 3 x 10^8 m/s, that takes about 0.48 seconds. A low Earth orbit satellite at 550 km makes the same four legs about 2,200 km, roughly 7 milliseconds, before ground-network delays are added.
Key takeaways
Mobility ranges from moving within one network to roaming across networks during active sessions. Handovers move connections between base stations, prepared by the network using device measurements; 802.11r speeds Wi-Fi roaming. Home networks authenticate roaming subscribers in visited networks. Changing IP addresses breaks TCP connections; Mobile IP saw little use, while cellular cores keep addresses stable and QUIC connection IDs survive changes. Bluetooth and BLE serve personal devices; Zigbee, Thread, LoRaWAN, NB-IoT, and LTE-M serve IoT. Geostationary satellites add about 480 ms round trips; low Earth orbit constellations such as Starlink reduce latency to tens of milliseconds.
Flashcard
Staying connected while moving
Check your understanding
Why does internet access through a geostationary satellite feel sluggish for interactive use, even with high bandwidth?