Packet Data

Service Options

SO33 can add a Forward Supplemental Channel for downlink data. Reverse data still uses the reverse fundamental channel; R-SCH is not implemented yet.

F-SCH Capacity

These are downlink RLP payload capacities before PPP/IP/TCP overhead and retransmissions. The session count assumes no other traffic users on the carrier; each packet session still consumes one F-FCH plus one F-SCH allocation.

Session Flow

Session Establishment

Simple IP vs Mobile IPv4

Simple IP is the default. In that flow, the handset includes the IPCP IP-Address option, usually IP=0.0.0.0, and the PDSN NAKs with the assigned pool address. Once the handset requests that assigned address and ACKs the PDSN’s IPCP request, IPCP opens and IP forwarding starts.

Mobile IPv4 support is disabled unless pdsn.packet.mobile_ip.enabled is set. When enabled, it is selected only if the handset opens IPCP without an IP-Address option. The PDSN may ACK a DNS-only IPCP request, then enters a registration-pending state instead of forwarding user traffic. It sends a Mobile IPv4 Agent Advertisement and accepts a Registration Request on UDP/434; only a successful Registration Reply makes the packet session active.

The implementation rejects the RFC 2290 IPCP Mobile IPv4 option. Mobile IPv4 registration happens as IP packets over PPP after IPCP opens. The current auth_mode is insecure, intended for local and/or testing use with handsets that send MN-HA/MN-AAA material the local PDSN does not validate yet.

PPP Session Resume

The PDSN keeps an open PPP/LCP/IPCP session cache per device identity. The key uses IMSI and ESN when both are known, otherwise whichever identity is available. When a packet traffic channel closes, the radio-side RLP state is discarded, but an open PPP state can remain cached for pdsn.ppp_session_timeout_secs.

If the same mobile opens another packet traffic channel before that timeout, the new channel still performs a fresh RLP sync. After RLP reaches data transfer, the PDSN restores the cached LCP/IPCP state and resumes IP transfer without renegotiating PPP. If the cache is missing or expired, the session follows the normal RLP -> LCP -> IPCP flow.

Cached PPP sessions keep their mobile IP allocation reserved so the resumed session receives the same peer IP. Expired cached sessions are reaped periodically and release their IP allocation.

PCF / PDSN Split

The BSC reaches packet-data control through a PcfClient boundary. The integrated cdma-nib runtime currently wires that boundary to a gRPC-backed client pointed at the packet service on 127.0.0.1:17021. The packet service owns the session path before delegating payload bytes to TUN, FOU, or FOU-TCP transport.

Real standards packet-core separation is still TODO: replace the local packet service path with BSC ↔ PCF A8/A9 transport and PCF ↔ PDSN A10/A11 transport. The FOU and FOU-TCP options are IP offload paths behind the current packet service; they are not the standards A10 GRE bearer.

Duplicate Service Connect Completion handling is idempotent. If the mobile retransmits completion during setup, the BSC does not leak an extra packet session. The PCF queues pending A11 registrations per packet session while the PDSN-side transport comes up, then drains them after activation. If an existing packet traffic channel is converted to voice, the BSC closes the old packet session after voice service connects.

IP Routing

Transport modes: TUN (local kernel interface, requires root), FOU (UDP tunnel), or FOU-TCP (TCP relay path).

The default DNS points mobiles at the packet gateway resolver. In the compose stack, that resolver serves the local speed test at http://speed/ and http://speed.local.1xbts.org/.

See Packet Data Setup for FOU configuration.

Configuration

{
  "packet_grpc_listen_addr": "127.0.0.1:17021",
  "ppp_session_timeout_secs": 1800,
  "packet": {
    "transport": "fou_tcp",
    "fou_remote": "127.0.0.1:17012",
    "fou_local_port": 17011,
    "gateway_ip": "10.55.0.1",
    "primary_dns": "10.55.0.1",
    "secondary_dns": "10.55.0.1",
    "enable_vj_compression_default": false,
    "mobile_ip": {
      "enabled": false,
      "fa_address": "10.55.0.1",
      "home_agent_address": "10.55.0.1",
      "advertisement_count": 3,
      "advertisement_lifetime_secs": 9000,
      "registration_lifetime_secs": 1200,
      "auth_mode": "insecure",
      "home_address_pool": null
    }
  }
}

enable_vj_compression_default controls whether the PDSN asks mobiles to send Van Jacobson TCP/IP header-compressed PPP packets. Leave it false unless you are testing a handset that handles VJ reliably; mobiles can still request VJ themselves for downlink compression.

mobile_ip.enabled controls Mobile IPv4 registration. Sprint handsets are known to require this when they complete IPCP without taking a Simple IP address. Leave it false for the normal Simple IP path. When enabled, registration_lifetime_secs must be lower than ppp_session_timeout_secs, and auth_mode currently accepts only "insecure".

F-SCH is controlled from bsc.json:

{
  "traffic_assignment": {
    "enable_f_sch": true,
    "f_sch_rate_bps": 153600
  }
}

Valid F-SCH rates are 19200, 38400, 76800, and 153600. 9600 is the fundamental-channel data rate and is not valid for f_sch_rate_bps.

The configured rate is currently a global packet-data policy: every eligible SO33 packet session gets the same F-SCH rate. Future burstable SCH support is planned, where the BSC can allocate and release supplemental channels dynamically based on traffic demand.

Dashboard

The /packets page shows active sessions, assigned IPs, RLP statistics, PPP state, and throughput.

Live session events

PDSN publishes session bind/unbind events to the aggregated event bus. Subscribe to EVENT_SOURCE_PDSN on events.v1.EventService to receive a PacketSessionBound when a mobile acquires an IP and a PacketSessionUnbound when the session is torn down:

grpcurl -plaintext -d '{"source_filter":["EVENT_SOURCE_PDSN"]}' \
  localhost:17023 events.v1.EventService/ListenEvents

See gRPC API → EventService for the full event schema.