Configured to auto mode, an LTE modem will fall back to 3G/2G in bad signal conditions. When it falls back (hands over to 2G or 3G), does it need to make a new PPP dialup connection?
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In case of LTE, "fall back" mechanisms pop up in Inter-RAT handover with legacy systems as :
- SRVCC - Incase of legacy system offering only CS voice services
- CSFB - CS voice calls via legacy RATs in scenarios where IMS services were not deployed
The SRVCC enables the handover of the VoIP calls based on PS to a CS based voice call in legacy network and the UE will be able to continue with the call after handover as it would transfer the PS bearer into a CS bearer. However, CSFB involves a CS call establishment procedure at the HO execution phase.
Karthik Balaguru
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No, it doesn't need to make a new connection. It should maintain the IP connection during handover.
Description of handovers here. The behaviour expected from the network and the handset is defined by 3GPP in their specification TS 23.009.
user1725145
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That depends on what we mean by "fall back". It's somewhat carrier specific, but there are two classes of fallback.
Fallback on the Radio Only
In this case, the device falls back to 3G (HSPA or EvDO for example), but we remain in the IMS core. In this case, everything is the same, you will see no connection state change.
Fallback to the legacy network
In this case, the device loses its LTE/IMS connection. For some networks, it falls back to HSPA, others back to its CDMA roots. In this case, you DROP your connection to the IMS core and LTE and fall back to the legacy network, as if you had disconnected and reconnected. In fact, you may disconnect. At this point you will see a new PPP session.
user500123
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