Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   3) =====================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   4) The Linux kernel GTP tunneling module
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   5) =====================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   6) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   7) Documentation by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   8) 		 Harald Welte <laforge@gnumonks.org> and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   9) 		 Andreas Schultz <aschultz@tpip.net>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  10) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  11) In 'drivers/net/gtp.c' you are finding a kernel-level implementation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  12) of a GTP tunnel endpoint.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  13) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  14) What is GTP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  15) ===========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  16) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  17) GTP is the Generic Tunnel Protocol, which is a 3GPP protocol used for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  18) tunneling User-IP payload between a mobile station (phone, modem)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  19) and the interconnection between an external packet data network (such
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  20) as the internet).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  21) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  22) So when you start a 'data connection' from your mobile phone, the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  23) phone will use the control plane to signal for the establishment of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  24) such a tunnel between that external data network and the phone.  The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  25) tunnel endpoints thus reside on the phone and in the gateway.  All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  26) intermediate nodes just transport the encapsulated packet.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  27) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  28) The phone itself does not implement GTP but uses some other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  29) technology-dependent protocol stack for transmitting the user IP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  30) payload, such as LLC/SNDCP/RLC/MAC.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  31) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  32) At some network element inside the cellular operator infrastructure
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  33) (SGSN in case of GPRS/EGPRS or classic UMTS, hNodeB in case of a 3G
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  34) femtocell, eNodeB in case of 4G/LTE), the cellular protocol stacking
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  35) is translated into GTP *without breaking the end-to-end tunnel*.  So
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  36) intermediate nodes just perform some specific relay function.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  37) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  38) At some point the GTP packet ends up on the so-called GGSN (GSM/UMTS)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  39) or P-GW (LTE), which terminates the tunnel, decapsulates the packet
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  40) and forwards it onto an external packet data network.  This can be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  41) public internet, but can also be any private IP network (or even
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  42) theoretically some non-IP network like X.25).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  43) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  44) You can find the protocol specification in 3GPP TS 29.060, available
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  45) publicly via the 3GPP website at http://www.3gpp.org/DynaReport/29060.htm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  46) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  47) A direct PDF link to v13.6.0 is provided for convenience below:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  48) http://www.etsi.org/deliver/etsi_ts/129000_129099/129060/13.06.00_60/ts_129060v130600p.pdf
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  49) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  50) The Linux GTP tunnelling module
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  51) ===============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  52) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  53) The module implements the function of a tunnel endpoint, i.e. it is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  54) able to decapsulate tunneled IP packets in the uplink originated by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  55) the phone, and encapsulate raw IP packets received from the external
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  56) packet network in downlink towards the phone.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  57) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  58) It *only* implements the so-called 'user plane', carrying the User-IP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  59) payload, called GTP-U.  It does not implement the 'control plane',
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  60) which is a signaling protocol used for establishment and teardown of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  61) GTP tunnels (GTP-C).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  62) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  63) So in order to have a working GGSN/P-GW setup, you will need a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  64) userspace program that implements the GTP-C protocol and which then
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  65) uses the netlink interface provided by the GTP-U module in the kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  66) to configure the kernel module.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  67) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  68) This split architecture follows the tunneling modules of other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  69) protocols, e.g. PPPoE or L2TP, where you also run a userspace daemon
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  70) to handle the tunnel establishment, authentication etc. and only the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  71) data plane is accelerated inside the kernel.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  72) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  73) Don't be confused by terminology:  The GTP User Plane goes through
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  74) kernel accelerated path, while the GTP Control Plane goes to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  75) Userspace :)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  76) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  77) The official homepage of the module is at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  78) https://osmocom.org/projects/linux-kernel-gtp-u/wiki
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  79) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  80) Userspace Programs with Linux Kernel GTP-U support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  81) ==================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  82) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  83) At the time of this writing, there are at least two Free Software
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  84) implementations that implement GTP-C and can use the netlink interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  85) to make use of the Linux kernel GTP-U support:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  86) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  87) * OpenGGSN (classic 2G/3G GGSN in C):
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  88)   https://osmocom.org/projects/openggsn/wiki/OpenGGSN
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  89) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  90) * ergw (GGSN + P-GW in Erlang):
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  91)   https://github.com/travelping/ergw
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  92) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  93) Userspace Library / Command Line Utilities
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  94) ==========================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  95) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  96) There is a userspace library called 'libgtpnl' which is based on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  97) libmnl and which implements a C-language API towards the netlink
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  98) interface provided by the Kernel GTP module:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  99) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) http://git.osmocom.org/libgtpnl/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) Protocol Versions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) =================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) There are two different versions of GTP-U: v0 [GSM TS 09.60] and v1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) [3GPP TS 29.281].  Both are implemented in the Kernel GTP module.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) Version 0 is a legacy version, and deprecated from recent 3GPP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) specifications.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) GTP-U uses UDP for transporting PDUs.  The receiving UDP port is 2151
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) for GTPv1-U and 3386 for GTPv0-U.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) There are three versions of GTP-C: v0, v1, and v2.  As the kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) doesn't implement GTP-C, we don't have to worry about this.  It's the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) responsibility of the control plane implementation in userspace to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) implement that.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) IPv6
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) ====
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) The 3GPP specifications indicate either IPv4 or IPv6 can be used both
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) on the inner (user) IP layer, or on the outer (transport) layer.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) Unfortunately, the Kernel module currently supports IPv6 neither for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) the User IP payload, nor for the outer IP layer.  Patches or other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) Contributions to fix this are most welcome!
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) Mailing List
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) ============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) If you have questions regarding how to use the Kernel GTP module from
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) your own software, or want to contribute to the code, please use the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) osmocom-net-grps mailing list for related discussion. The list can be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) reached at osmocom-net-gprs@lists.osmocom.org and the mailman
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) interface for managing your subscription is at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) https://lists.osmocom.org/mailman/listinfo/osmocom-net-gprs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) Issue Tracker
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) =============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) The Osmocom project maintains an issue tracker for the Kernel GTP-U
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) module at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) https://osmocom.org/projects/linux-kernel-gtp-u/issues
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) History / Acknowledgements
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) ==========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) The Module was originally created in 2012 by Harald Welte, but never
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) completed.  Pablo came in to finish the mess Harald left behind.  But
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) doe to a lack of user interest, it never got merged.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) In 2015, Andreas Schultz came to the rescue and fixed lots more bugs,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) extended it with new features and finally pushed all of us to get it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) mainline, where it was merged in 4.7.0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) Architectural Details
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) =====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) Local GTP-U entity and tunnel identification
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) --------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) GTP-U uses UDP for transporting PDU's. The receiving UDP port is 2152
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) for GTPv1-U and 3386 for GTPv0-U.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) There is only one GTP-U entity (and therefor SGSN/GGSN/S-GW/PDN-GW
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) instance) per IP address. Tunnel Endpoint Identifier (TEID) are unique
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) per GTP-U entity.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) A specific tunnel is only defined by the destination entity. Since the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) destination port is constant, only the destination IP and TEID define
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) a tunnel. The source IP and Port have no meaning for the tunnel.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) Therefore:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175)   * when sending, the remote entity is defined by the remote IP and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176)     the tunnel endpoint id. The source IP and port have no meaning and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177)     can be changed at any time.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179)   * when receiving the local entity is defined by the local
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180)     destination IP and the tunnel endpoint id. The source IP and port
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181)     have no meaning and can change at any time.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) [3GPP TS 29.281] Section 4.3.0 defines this so::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185)   The TEID in the GTP-U header is used to de-multiplex traffic
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186)   incoming from remote tunnel endpoints so that it is delivered to the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187)   User plane entities in a way that allows multiplexing of different
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188)   users, different packet protocols and different QoS levels.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189)   Therefore no two remote GTP-U endpoints shall send traffic to a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190)   GTP-U protocol entity using the same TEID value except
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191)   for data forwarding as part of mobility procedures.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) The definition above only defines that two remote GTP-U endpoints
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) *should not* send to the same TEID, it *does not* forbid or exclude
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) such a scenario. In fact, the mentioned mobility procedures make it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) necessary that the GTP-U entity accepts traffic for TEIDs from
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) multiple or unknown peers.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) Therefore, the receiving side identifies tunnels exclusively based on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) TEIDs, not based on the source IP!
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) APN vs. Network Device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) ======================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) The GTP-U driver creates a Linux network device for each Gi/SGi
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) interface.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) [3GPP TS 29.281] calls the Gi/SGi reference point an interface. This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) may lead to the impression that the GGSN/P-GW can have only one such
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) interface.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) Correct is that the Gi/SGi reference point defines the interworking
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) between +the 3GPP packet domain (PDN) based on GTP-U tunnel and IP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) based networks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216) There is no provision in any of the 3GPP documents that limits the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) number of Gi/SGi interfaces implemented by a GGSN/P-GW.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) [3GPP TS 29.061] Section 11.3 makes it clear that the selection of a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) specific Gi/SGi interfaces is made through the Access Point Name
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) (APN)::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223)   2. each private network manages its own addressing. In general this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224)      will result in different private networks having overlapping
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225)      address ranges. A logically separate connection (e.g. an IP in IP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226)      tunnel or layer 2 virtual circuit) is used between the GGSN/P-GW
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227)      and each private network.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229)      In this case the IP address alone is not necessarily unique.  The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230)      pair of values, Access Point Name (APN) and IPv4 address and/or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231)      IPv6 prefixes, is unique.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233) In order to support the overlapping address range use case, each APN
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) is mapped to a separate Gi/SGi interface (network device).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) .. note::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238)    The Access Point Name is purely a control plane (GTP-C) concept.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239)    At the GTP-U level, only Tunnel Endpoint Identifiers are present in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240)    GTP-U packets and network devices are known
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242) Therefore for a given UE the mapping in IP to PDN network is:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244)   * network device + MS IP -> Peer IP + Peer TEID,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) and from PDN to IP network:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248)   * local GTP-U IP + TEID  -> network device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) Furthermore, before a received T-PDU is injected into the network
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) device the MS IP is checked against the IP recorded in PDP context.