1xBTS 1xBTS

Connections & Data Path

With a UATI-keyed session in place (see Sessions & UATI), a device can open a traffic connection, move IP traffic over HRPD streams, and reach the same PCF/PDSN packet core that 1x packet data uses. This page covers the connection setup, the data path, and how 1x and HRPD coexist.

Opening a traffic connection

Once the AT has a UATI, it can request an active traffic connection:

  1. The AT sends ConnectionRequest and RouteUpdate.
  2. The AN sends TrafficChannelAssignment.
  3. The AT starts reverse pilot, RRI, and DRC in RTCMAC Setup state.
  4. The AN acquires the reverse traffic channel and sends RTCAck.
  5. The AT sends TrafficChannelComplete.

That RTCAck step is load-bearing. In the HRPD specs, TrafficChannelComplete is sent only after the AT receives RTCAck and the reverse traffic MAC reports LinkAcquired. This is why 1xBTS treats timely reverse pilot/DRC acquisition and RTCAck scheduling as part of connection setup, not as optional diagnostics.

Streams

HRPD separates signaling from packet data with streams:

  • Stream 0 carries Default Signaling, including reliable setup messages and acknowledgements.
  • Stream 1/2/3 can carry Default Packet Application data. 1xBTS uses the default packet stream path for PPP/IP traffic.

Moving user data

On the forward link, the AT reports a DRC value. The scheduler chooses a matching physical packet size and transmits on the Forward Traffic Channel, with H-ARQ feedback from the AT’s reverse ACK channel. On the reverse link, the AN decodes pilot, RRI, DRC, ACK, and data, then feeds signaling and packet bytes back into the AN session logic.

The packet-core bridge

For IP service, the HRPD packet stream is bridged to the packet core:

  1. The AN opens A8 toward the PCF.
  2. The PCF registers the packet session with the PDSN over A11.
  3. A10 carries the keyed-GRE bearer between PCF and PDSN.
  4. The PDSN runs PPP LCP/IPCP and assigns the device an IP address.

In a normal single-host 1xBTS setup these are separate logical interfaces inside the stack, even when the processes are co-located.

1x and HRPD together

The 1x and HRPD radio paths are intentionally separate. A 1x SO7/SO33 packet session is assigned by the BSC on a 1x traffic channel; an EV-DO packet session is assigned by the HRPD AN on the HRPD traffic channel. Both converge at the PCF/PDSN packet core. Hybrid-device coordination uses A21 so the 1x BSC and HRPD AN can correlate identities, suppress duplicate paging, and cross-page an HRPD-attached device for 1x services.

See also