[[bssgp]]
== BSS GPRS Protocol (BSSGP)

=== List of Messages

The following tables list the BSSGP messages used by OsmoPCU, grouped
by their level of compliance with 3GPP TS 08.18.

==== Messages Compliant With TS 08.18

.Messages compliant with TS 08.18
[options="header",cols="10%,10%,20%,35%,5%,20%"]
|===
| TS 08.18 § | type code (hex) | This document § | Message | <-/-> | Received/Sent by OsmoPCU
6+<| *RL and BSSGP SAP Messages:*
| 10.2.1 | 0x00 | <<dl_unit_data>> | DL-UNITDATA | <- | Received
| 10.2.2 | 0x01 | <<ul_unit_data>> | UL-UNITDATA | -> | Sent
| 10.2.3 | 0x02 | <<ra_capab>> | RA-CAPABILITY | <- | Received
6+<| *GMM SAP Messages:*
| 10.3.1 | 0x06 | <<paging_ps>> | PAGING PS | <- | Received
| 10.3.2 | 0x07 | <<paging_cs>> | PAGING CS | <- | Received
| 10.3.7 | 0x0c | <<susp_ack>> | SUSPEND-ACK | <- | Received
| 10.3.8 | 0x0d | <<susp_nack>> | SUSPEND-NACK | <- | Received
| 10.3.10 | 0x0f | <<res_ack>> | RESUME-ACK | <- | Received
| 10.3.11 | 0x10 | <<res_nack>> | RESUME-NACK | <- | Received
6+<| *NM SAP Messages:*
| 10.4.9 | 0x21 | <<block_ack>> | BVC-BLOCK-ACK | <- | Received
| 10.4.12 | 0x22 | <<bvc_reset>> | BVC-RESET | <-/-> | Received/Sent
| 10.4.13 | 0x23 | <<reset_ack>> | BVC-RESET-ACK | <- | Received
| 10.4.10 | 0x24 | <<bvc_unblock>> | BVC-UNBLOCK | -> | Sent
| 10.4.11 | 0x25 | <<unblock_ack>> | BVC-UNBLOCK-ACK | <- | Received
| 10.4.4 | 0x26 | <<flow_bvc>> | FLOW-CONTROL-BVC | -> | Sent
| 10.4.5 | 0x27 | <<flow_bvc_ack>> | FLOW-CONTROL-BVC-ACK | <- | Received
| 10.4.7 | 0x29 | <<flow_ms_ack>> | FLOW-CONTROL-MS-ACK | <- | Received
| 10.4.1 | 0x2a | <<flush_ll>> | FLUSH-LL | <- | Received
| 10.4.15 | 0x40 | <<invoke_trace>> | SGSN-INVOKE-TRACE | <- | Received
| 10.4.14 | 0x41 | <<bssgp_status>> | STATUS | <-/->  | Received/Sent
|===

==== Messages Specific to OsmoPCU

There are no OsmoPCU specific BSSGP messages.

[[not_impl]]
==== Messages Not Implemented by OsmoPCU

.3GPP TS 08.18 messages not implemented by OsmoPCU
[options="header",cols="10%,10%,80%"]
|===
| TS 08.18 § | type code (hex) | Message
3+<| *RL (relay) and BSSGP SAP Messages:*
| 10.2.4 | 0x03 | PTM-UNITDATA
3+<| *GMM (GPRS mobility management) SAP Messages:*
| 10.3.3 | 0x08 | RA-CAPABILITY-UPDATE
| 10.3.4 | 0x09 | RA-CAPABILITY-UPDATE-ACK
| 10.3.5 | 0x0a | RADIO-STATUS
| 10.3.6 | 0x0b | SUSPEND
| 10.3.9 | 0x0e | RESUME
3+<| *NM (network management) SAP Messages:*
| 10.4.8 | 0x20 | BVC-BLOCK
| 10.4.6 | 0x28 | FLOW-CONTROL-MS
| 10.4.2 | 0x2b | FLUSH-LL-ACK
| 10.4.3 | 0x2c | LLC-DISCARDED
3+<| *PFM (packet flow management) SAP Messages:*
| 10.4.16 | 0x50 | DOWNLOAD-BSS-PFC
| 10.4.17 | 0x51 | CREATE-BSS-PFC
| 10.4.18 | 0x52 | CREATE-BSS-PFC-ACK
| 10.4.19 | 0x53 | CREATE-BSS-PFC-NACK
| 10.4.20 | 0x54 | MODIFY-BSS-PFC
| 10.4.21 | 0x55 | MODIFY-BSS-PFC-ACK
| 10.4.22 | 0x56 | DELETE-BSS-PFC
| 10.4.23 | 0x57 | DELETE-BSS-PFC-ACK
|===


=== Details on Compliant BSSGP Messages

[[dl_unit_data]]
==== DL-UNITDATA

This message conforms to 3GPP TS 08.18 § 10.2.1, with the following
limitations:

* OsmoPCU does not support QoS
* all optional IEs except for IMSI and old TLLI are ignored.

._DL-UNITDATA_ IE limitations
[options="header",cols="10%,30%,60%"]
|===
| TS 08.18 § | IE Name | Handling
| 11.3.28 | QoS Profile | _ignored_
| 11.3.22 | MS Radio Access Capability | _ignored_
| 11.3.27 | Priority | _ignored_
| 11.3.11 | DRX Parameters | _ignored_
| 1.3.42 | PFI | _ignored_
| 11.3.19 | LSA Information | _ignored_
| 11.3.47 | Service UTRAN CCO | _ignored_
|===

[[ul_unit_data]]
==== UL-UNITDATA

This message conforms to 3GPP TS 08.18 § 10.2.2, with the following limitations:

* OsmoPCU does not send optional IEs - PFI (§ 12.3.42) and LSA
  Identifier List (§ 11.3.18).
* QoS Profile (§ 11.3.28) IE is always set to 0x04.

[[ra_capab]]
==== RA-CAPABILITY

This message is received and logged but ignored by OsmoPCU at the moment.

[[paging_ps]]
==== PAGING PS

This message conforms to 3GPP TS 08.18 § 10.3.1, with the following
limitations:

* only IMSI and P-TMSI are parsed by OsmoPCU.

._DL-UNITDATA_ IE limitations
[options="header",cols="10%,30%,60%"]
|===
| TS 08.18 § | IE Name | Handling
| 11.3.11 | DRX Parameters | _ignored_
| 11.3.6 | BVCI | _ignored_
| 11.3.17 | Location Are | _ignored_
| 11.3.31 | Routeing Area | _ignored_
| 11.3.3 | BSS Area Indication | _ignored_
| 11.3.42 | PFI | _ignored_
| 11.3.43 | ABQP | _ignored_
| 11.3.28 | QoS Profile | _ignored_
| 11.3.36 | P-TMSI | treated as mandatory (in case of absence paging with 0-length P-TMSI will be sent)
|===


[[paging_cs]]
==== PAGING CS

This message is received and logged but ignored by OsmoPCU at the
moment.

[[susp_ack]]
==== SUSPEND-ACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[susp_nack]]
==== SUSPEND-NACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[res_ack]]
==== RESUME-ACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[res_nack]]
==== RESUME-NACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[block_ack]]
==== BVC-BLOCK-ACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[bvc_reset]]
==== BVC-RESET

OsmoPCU never transmits optional Feature bitmap (3GPP TS 08.18 §
11.3.40) IE.

Receiving BVC RESET will cause OsmoPCU to respond with "Unknown BVCI"
status message.

[[reset_ack]]
==== BVC-RESET-ACK

This message conforms to 3GPP TS 08.18 § 10.4.13.

After receiving it OsmoPCU completes the RESET procedure for BVC
according to 3GPP TS 08.18 § 8.4.

[[unblock_ack]]
==== BVC-UNBLOCK-ACK

This message conforms to 3GPP TS 08.18 § 10.4.11.

After receiving it OsmoPCU completes the RESET procedure for BVC
according to 3GPP TS 08.18 § 8.3.

[[bvc_unblock]]
==== BVC-UNBLOCK

This message conforms to 3GPP TS 08.18 § 10.4.10 and is send by
OsmoPCU as part of UNBLOCK procedure described in 3GPP TS 08.18 § 8.3.

[[flow_ms_ack]]
==== FLOW-CONTROL-MS-ACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[flow_bvc_ack]]
==== FLOW-CONTROL-BVC-ACK

This message is received and logged but ignored by OsmoPCU at the
moment.

[[flow_bvc]]
==== FLOW-CONTROL-BVC

This message conforms to 3GPP TS 08.18 § 10.4.4, with the following
limitations:

* OsmoPCU does not support Current Bucket Level (CBL) feature so
  Bucket_Full Ratio (TS 08.18 § 11.3.46) IE is not transmitted as part
  of this message.

[[flush_ll]]
==== FLUSH-LL

This message is received and logged but ignored by OsmoPCU at the
moment.

[[invoke_trace]]
==== SGSN-INVOKE-TRACE

This message is received and logged but ignored by OsmoPCU at the
moment.

[[bssgp_status]]
==== STATUS

This message conforms to 3GPP TS 08.18 § 10.4.14.

=== Information Elements Overview

All of the IEs handled by OsmoPCU are listed below, with limitations
and additions to 3GPP TS 08.18 specified in more detail.

==== IEs Conforming to 3GPP TS 08.18

The following Information Elements are accepted by OsmoPCU. Not all
IEs are actually evaluated.

.IEs conforming to 3GPP TS 08.18
[options="header",cols="5%,10%,40%,5%,40%"]
|===
| tag (hex) | TS 08.18 § | IE name | <-/-> | Received/Sent by OsmoPCU
| 0x00 | 11.3.1 | Alignment Octets | <-/-> | Received/Sent
| 0x01 | 11.3.2 | Bmax default MS | -> | Sent
| 0x02 | 11.3.3 | BSS Area Indication | <- | Received
| 0x03 | 11.3.4 | Bucket Leak Rate | -> | Sent
| 0x04 | 11.3.6 | BVCI | <-/-> | Received/Sent
| 0x05 | 11.3.5 | BVC Bucket Size | -> | Sent
| 0x06 | 11.3.7 | BVC Measurement | -> | Sent
| 0x07 | 11.3.8 | Cause | <-/-> | Received/Sent
| 0x08 | 11.3.9 | Cell Identifier | -> | Sent
| 0x09 | 11.3.10 | Channel needed | <- | Received
| 0x0a | 11.3.11 | DRX Parameters | <- | Received
| 0x0b | 11.3.12 | eMLPP-Priority | <- | Received
| 0x0c | 11.3.13 | Flush Action | <- | Received
| 0x0d | 11.3.14 | IMSI | <-/-> | Received/Sent
| 0x0e | 11.3.15 | LLC-PDU | <-/-> | Received/Sent
| 0x0f | 11.3.16 | LLC Frames Discarded | -> | Sent
| 0x10 | 11.3.17 | Location Area | <- | Received
| 0x11 | 11.3.20 | Mobile Id | <- | Received
| 0x12 | 11.3.21 | MS Bucket Size | -> | Sent
| 0x13 | 11.3.22 | MS Radio Access Capability | <- | Received
| 0x14 | 11.3.23 | OMC Id | <- | Received
| 0x15 | 11.3.24 | PDU In Error | <-/-> | Received/Sent
| 0x16 | 11.3.25 | PDU Lifetime | <- | Received
| 0x17 | 11.3.27 | Priority | <- | Received
| 0x19 | 11.3.29 | Radio Cause | -> | Sent
| 0x1a | 11.3.30 | RA-Cap-UPD-Cause | -> | Sent
| 0x1b | 11.3.31 | Routeing Area | <-/-> | Received/Sent
| 0x1c | 11.3.32 | R_default_MS | -> | Sent
| 0x1d | 11.3.33 | Suspend Reference Number | <-/-> | Received/Sent
| 0x1e | 11.3.34 | Tag | <-/-> | Received/Sent
| 0x1f | 11.3.35 | TLLI | <-/-> | Received/Sent
| 0x20 | 11.3.36 | TMSI | <-/-> | Received/Sent
| 0x21 | 11.3.37 | Trace Reference | <- | Received
| 0x22 | 11.3.38 | Trace Type | <- | Received
| 0x23 | 11.3.39 | TransactionId | <- | Received
| 0x24 | 11.3.40 | Trigger Id | <- | Received
| 0x25 | 11.3.41 | Number of octets affected | -> | Sent
| 0x26 | 11.3.18 | LSA Identifier List | -> | Sent
| 0x27 | 11.3.19 | LSA Information | <- | Received
| 0x28 | 11.3.42 | Packet Flow Identifier | <-/-> | Received/Sent
| 0x3a | 11.3.43 | Aggregate BSS QoS Profile (ABQP) | <-/-> | Received/Sent
| 0x3b | 11.3.45 | Feature Bitmap | <-/-> | Received/Sent
| 0x3c | 11.3.46 | Bucket_Full Ratio | -> | Sent
| 0x3d | 11.3.47 | Service UTRAN CCO (Cell Change Order) | <- | Received
|===

==== IEs Not Conforming to 3GPP TS 08.18

.IEs not conforming to 3GPP TS 08.18
[options="header",cols="5%,10%,30%,55%"]
|===
| tag (hex) | TS 08.18 § | IE name | Description
| 0x18 | 11.3.28 | QoS Profile | Received value is ignored. Sent value is hard-coded to 0x4 (3 octets).
|===

==== Additional Attributes and Parameters

There are no OsmoPCU specific additional Attributes and Parameters.

=== Details on IEs

==== BSS Area Indication

This IE is ignored by OsmoPCU.

==== Bucket Leak Rate

The value used by OsmoPCU for this IE can be set through configuration
file or vty via "flow-control force-ms-leak-rate <1-6553500>" command.

==== BVC Bucket Size

The value used by OsmoPCU for this IE can be set through configuration file or vty via
"flow-control force-bvc-bucket-size <1-6553500>" command.

==== Channel needed

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<paging_cs>> for details.

==== DRX Parameters

This IE is ignored by OsmoPCU.

==== eMLPP-Priority

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<paging_cs>> for details.

==== Flush Action

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<flush_ll>> for details.

==== LLC Frames Discarded

This IE is not available because entire message which contains it
(LLC-DISCARDED) is not implemented by OsmoPCU - see for <<not_impl>>
details.

==== Location Area

This IE is ignored by OsmoPCU.

==== Mobile Id

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<invoke_trace>> for details.

==== MS Bucket Size

The value used by OsmoPCU for this IE can be set through configuration
file or vty via "flow-control force-ms-bucket-size <1-6553500>"
command.

==== MS Radio Access Capability

This IE is ignored by OsmoPCU.

==== OMC Id

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<invoke_trace>> for details.

==== Priority

This IE is ignored by OsmoPCU.

==== QoS Profile

No QoS is supported by OsmoPCU so this IE is ignored or safe default
used when mandatory.

==== Radio Cause

This IE is not available because entire message which contains it
(RADIO-STATUS) is not implemented by OsmoPCU - see for <<not_impl>>
details.

==== RA-Cap-UPD-Cause

This IE is not available because entire message which contains it
(RA-CAPABILITY-UPDATE-ACK) is not implemented by OsmoPCU - see for
<<not_impl>> details.

==== Routeing Area

This IE is ignored by OsmoPCU upon receiving.

The messages which might require this IE to be send are not
implemented by OsmoPCU - see for <<not_impl>> details.

==== Suspend Reference Number

This IE is ignored by OsmoPCU upon receiving.

The messages which might require this IE to be send are not
implemented by OsmoPCU - see for <<not_impl>> details.

==== Tag

This IE currently only used by OsmoPCU for Flow Control procedure (TS
08.18 § 8.2). In other cases it's either ignored or unavailable.

==== Trace Reference

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<invoke_trace>> for details.

==== Trace Type

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<invoke_trace>> for details.

==== TransactionId

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<invoke_trace>> for details.

==== Trigger Id

This IE is ignored because entire message which contains it is ignored
by OsmoPCU - see <<invoke_trace>> for details.

==== Number of octets affected

This IE is not available because the messages which contains it
(FLUSH-LL-ACK and LLC-DISCARDE) are not implemented by OsmoPCU - see
for <<not_impl>> details.

==== LSA Information

This IE is ignored by OsmoPCU.

==== LSA Identifier List

This IE is not implemented by OsmoPCU.

==== Packet Flow Identifier

This IE is ignored by OsmoPCU upon receiving.

The messages which might require this IE to be send are not
implemented by OsmoPCU - see for <<not_impl>> details.

==== Aggregate BSS QoS Profile (ABQP)

This IE is ignored by OsmoPCU upon receiving.

The messages which might require this IE to be send are not
implemented by OsmoPCU - see for <<not_impl>> details.

==== Feature Bitmap

This IE is not implemented by OsmoPCU.

This IE is ignored by OsmoPCU when received.

Absence of Feature Bitmap automatically disables optional features for
Network Service Entity (NSE) communicating with OsmoPCU.

==== Bucket_Full Ratio

This IE is not implemented by OsmoPCU.

==== Service UTRAN CCO (Cell Change Order)

This IE is ignored by OsmoPCU.

=== Gb BSSGP Initialization / PCU bring-up

The BSSGP initialization directly follows NS connection establishment
described in <<ns_init>>.

OsmoPCU allocates a BVC context for the BVCI given by OsmoBTS, which
in turn receives it from OpenBSC via OML procedures.

In addition to the BVCI identifying the OsmoPCU side of BSSGP
connection, there is also special BVCI which is accepted by OsmoPCU in
accordance with 3GPP TS 08.18 § 5.4.1: BVCI = 0 represents signaling data
between SGSN and PCU in contrast to PTP (Peer-To-Peer) user's data.

The mapping between BSSGP PDUs and signaling or PTP BVCIs is available
in 3GPP TS 08.18 Table 5.4.
