Add NB-IoT PDN content.

Apply changes from PR #1113 to v5.13.

Author: Amanda Butler

docs/reference/technology/connectivity/connectivity.md

@@ -48,7 +48,7 @@ Cellular coverage, load balancing and reliability are the responsibility of the
 
 The new cellular technologies, NB-IoT and CAT-M1, are designed for IoT devices. They offer some advantages, but there are also risks and costs.
 
-**Narrow-band-IoT** (NB-IoT) relies on a simple waveform and therefore requires the lowest power consumption of all the cellular methods. It also has fewer components and offers better signal penetration through walls (thanks to lower bitrates and better link budgets). NB-IoT requires country-specific chips because each country uses its own spectrum, which complicates production. It also causes problems with large transfers because of its reduced bandwidth.
+**Narrow-band-IoT** (NB-IoT) is a 3GPP standard for low-power wide area networks (LPWANs) specifically designed for low-cost, battery-powered IoT devices. The two network attach options for NB-IoT are network attach with and without packet data network (PDN). NB-IoT relies on a simple waveform and therefore requires the lowest power consumption of all the cellular methods. It also has fewer components and offers better signal penetration through walls (thanks to lower bitrates and better link budgets). NB-IoT requires country-specific chips because each country uses its own spectrum, which complicates production. It also causes problems with large transfers because of its reduced bandwidth.
 
 **CAT-M1** has a higher data rate than NB-IoT (closer to existing cellular behavior) but is not proven to be more power efficient. Any efficiency gains can be lost because of operator configurations.