[[overview]]
== Overview


[[intro_overview]]
=== About OsmoHNBGW

OsmoHNBGW implements the Home NodeB Gateway function in the 3G network architecture.  It serves 
as a gateway between the classic 3G core network (CN) domain with its IuCS and IuPS interface
and the femtocell based RAN.

A typical 3G network consisting of Osmocom components is illustrated in the following
diagram:

[[fig-3g]]
.Typical 3G network architecture used with OsmoHNBGW
[graphviz]
----
digraph G {
  rankdir = LR;

  UE [label="UE\n(3G phone)"]
  PBX [label="PBX\nAsterisk, FreeSwitch,\nKamailio, Yate, ..."]

  subgraph cluster_msc_mgw {
    style=dotted
    MSC
    MGW1 [label="MGW"]
    MSC -> MGW1 [label="MGCP",constraint=false]
  }

  subgraph cluster_hnbgw_mgw_upf {
    style=dotted
    MGW3 [label="MGW"]
    UPF
    HNBGW [label=HNBGW,style=bold]
    HNBGW -> MGW3 [label="MGCP",constraint=false]
    HNBGW -> UPF [label="PFCP",constraint=false]
  }

  hNodeB [shape="box",label="hNodeB\n(3G femto cell)"]

  MSC -> HLR [label="\nGSUP",style=bold]
  SGSN -> HLR [label="GSUP",style="dashed,bold"]
  UE -> hNodeB [label="Uu",style=bold]
  UE -> hNodeB [style="dashed,bold"]
  hNodeB -> HNBGW [label="Iuh",style="bold"]
  STP2 [label="STP\n(SCCP/M3UA)"]
  HNBGW -> STP2 -> SGSN [label="IuPS",style="dashed,bold"]
  HNBGW -> STP2 -> MSC [label="IuCS",style="bold"]
  SGSN -> GGSN [label="GTP-C",style="dashed,bold"]
  hNodeB -> UPF -> GGSN [label="GTP-U(3G)",style="dashed"]
  GGSN -> internet [label="tun",style="dashed"]

  hNodeB -> MGW3 [label="IuUP/RTP",constraint=false]
  MGW3 -> MGW1 [label="IuUP/RTP"]

  MSC -> SIPConnector [label="MNCC socket",style=bold]

  SIPConnector -> PBX [label="SIP",style=bold]
  MGW1 -> PBX [label="RTP"]

  A, B, C, D [style="invisible"]
  A -> B [label="data (PS)",style="dashed"]
  C -> D [label="voice/SMS/USSD (CS)"]

}
----


The HNB-GW performs a translation interface between the IuCS/IuPS interfaces on the one hand
side, and the Iuh interface on the or ther hand:

----
                      Iuh                         IuCS/IuPS
                                                  +----+----+
                                                  | CC | MM |
NAS                   +----+----+            .  . +----+----+
Non-Access Stratum    | CC | MM |         .       | RANAP   |
- - - - - - - - - - - +----+----+-------+         +---------+
                      | RANAP   |       |    H    | SCCP    |
Access Stratum        +---------+ HNBAP |    N    +---------+
                      | RUA     |       |    B    | M3UA    |
                      +---------+-------+    -    +---------+
                      |        SCTP     |    G    | SCTP    |
                      +-----------------+    W    +---------+
                      |        IP       |         | IP      |
                      +-----------------+         +---------+
----

On the femtocell (Home NodeB) side, OsmoHNBGW implements the Iuh interface as specified by 3GPP.

=== The Iuh interface

Iuh consists of the following sub-layers:

- HNBAP (Home NodeB Application Part)
- RUA (RANAP User Adaptation, between RANAP and SCTP
