| Internet-Draft | SCHC into 5G | July 2025 |
| Mokdad, et al. | Expires 8 January 2026 | [Page] |
This document describes a possible integration of Static Context Header Compression [RFC8724] into 5G networks.¶
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This document defines a solution for how Static Context Header Compression and fragmentation (SCHC) can be used in 5G. It proposes a new architecture that integrates SCHC within the 5G core network. This architecture can handle both full-IP flows and SCHC flows while ensuring compatibility with full-IP application servers, based on 3GPP specifications. The document also describes the SCHC parameters needed to support SCHC over the 5G architecture. (to be done)¶
+--------+ +--------+
| AUSF |-------------------| UDM |
+--------+ +--------+
\ / |
\ / |
\ / |
+-------------+ +-------------+
| AMF |-------| SMF |
+-------------+ +-------------+
/ | |
/ | |
/ | |
+-----+ +-----+ +-------+ +----------------+
| UE |-------| gNB |------------| UPF |-----------| Data Network |
+-----+ +-----+ +-------+ +----------------+
The 5G network architecture is illustrated in Figure 1 . Below is a brief explanation of the main components¶
The 5G system consists of the following main components¶
User Equipment (UE) It includes all devices that can connect to 5G networks, such as smartphones, IoT devices, etc.¶
Radio Access Network (RAN) It consists of new radio technologies responsible for wireless communication between the UE and the 5G core network. One of its main components is:¶
gNodeB (gNB) It represents the 5G node base station.¶
5G Core Network (5GC) It is a service-based architecture that comprises various network functions (NFs). These include:¶
+--------+ +--------+ +--------+
| NSSF | | AUSF |-----| UDM |
+--------+ +--------+ +--------+
\ | / |
\ | / |
\ | / |
+-------------+ +-------------+
| AMF |-------| SMF |
+-------------+ +-------------+
/ | |
/ | |
/ | |
+----------+ +-----+ +-------+ +----------------+
| UE |----| gNB |------------| UPF |-----------| Data Network |
| SCHC C/D | +-----+ +-------+ +----------------+
+----------+ |
+----------+
| SCHC C/D |
+----------+
The proposed solution is depicted in Figure 2. A modified User Plane Function (UPF), designated as SCHC-UPF and referred to as S-UPF, is introduced. The UPF is a key component of the 5G core network, responsible for routing and forwarding user data packets between the User Equipment (UE) and the Data Network (DN). The S-UPF handls SCHC compression and decompression processes. It is capable of redirecting packets from devices that support SCHC to the SCHC compression/decompression (C/D) unit.¶
+-----------+ +-----------+
| IP/Non-IP | | IP/Non-IP |
| (SCHC) | | (SCHC) |
+-----------+ +-----------+-----------+ +-----------+
| SDAP | | SDAP | GTP-U | | GTP-U |
+-----------+ +-----------+-----------+ +-----------+
| PDCP | | PDCP | UDP | | UDP |
+-----------+ +-----------+-----------+ +-----------+
| RLC | | RLC | IP | | IP |
+-----------+ +-----------+-----------+ +-----------+
| MAC | | MAC | L2 | | L2 |
+-----------+ +-----------+-----------+ +-----------+
| L1 | | PHY | L1 | | L1 |
+-----------+ <------> +-----------+-----------+ <------> +-----------+
UE gNB UPF
Radio Link N3
This subsection describes how endpoints can signal SCHC support during setup.¶
During Registration procedure¶
+-----+ +-----+ +-----+
| UE | | gNB | | AMF |
+--+--+ +--+--+ +--+--+
| | |
| Registration Request | |
| (5GMM Capability [SCHC]) | |
|============================>| |
| | |
| Selects AMF |
| | |
| | Registration Request |
| | (5GMM Capability [SCHC]) |
| |==========================>|
| | |
| | |
| Registration Accept |
| (5GS network feature support [SCHC]) |
|<========================================================|
| | |
| Registration Complete |
|========================================================>|
| | |
During PDU Session establishment procedure¶
+-----+ +-----+ +-----+ +-----+ +------+
| UE | | gNB | | AMF | | SMF | | S-UPF|
+--+--+ +--+--+ +--+--+ +--+--+ +--+---+
| | | | |
| PDU Session Establishment Request | |
| (5GSM Core Network Capability [SCHC]) | |
|==================================================>| |
| | | | |
| | | Selects S-UPF and |
| | | IP address |
| | | | |
| | | |N4 Session Establishment|
| | | | Request |
| | | |----------------------->|
| | | |N4 Session Establishment|
| | | | Response (TEID_UPF) |
| | | |<-----------------------|
| | | | |
| PDU Session Establishment Accept | |
| (5GSM Network feature support [SCHC]) | |
|<==================================================| |
| | | | |
| | N2 PDU Session | | |
| | Resourse setup | | |
| | response | | |
| |------------------->| | |
| | |Nsmf_PDUSession_ | |
| | | UpdateSMContext | |
| | | Request | |
| | |---------------->| |
| | | | N4 Session Modification|
| | | | Request |
| | | |----------------------->|
| | | | |
| | | | |
| | | | |
<-----------><------------------ Packet data flow ------------------------->
The SCHC C/D unit stores the contexts of many devices connected to the network. When a packet arrives, it must be recognized by the SCHC C/D in order to retrieve the appropriate device context. Therefore, the use of a unique identifier is essential. Among 5G identifiers, there is the Permanent Equipment Identifier (PEI), which identifies UEs capable of accessing a 3GPP network. What makes the PEI suitable for this use is that it is known by both the 5G operator and the device owner, and it is transmitted to the UPF during the PFCP association procedure.¶
This subsection presents how the S-UPF handle SCHC-compressed packets.¶
+-----+ +----- +--------+ +----+
| UE |---->| gNB | ---------> | S-UPF | -----------------> | DN |
+-----+ +-----+ +--------+ \ +----+
\ / /\ \---------------------------------\
\ / / \ \
+--------------------+/ +----------------------------------------\----------------------------+
| IP | | +---------------------+ \ |
| src: gNB addr | | | PFCP Session Look | \ |
| dest: UPF addr | | | Retrieve UE ID | \ |
+--------------------+ | +---------------------+ \ |
| UDP | | +---------------------------+ \ |
| Port number | | | Retrieve the UE identifier| +--------------------+ |
+--------------------+ | +---------------------------+ | IP | |
| GTP | | | +--------------------+ |
| TEID 2 | | +---------------------------+ | UDP | |
+--------------------+ | | SCHC D | +--------------------+ |
| SCHC Packet | | | Decompress using UE ID | | Payload | |
| +-------------+ | | | and find context |----> +--------------------+ |
| | Rule ID | | | +---------------------------+ |
| |-------------| | | \ / |
| | Residue | | | \ / |
| +-------------+ | | +--------------------+ |
+--------------------+ | | IP | |
| | src: gNB addr | |
| | dest: UPF addr | |
| +--------------------+ |
| | UDP | |
| | Port number | |
| +--------------------+ |
| | GTP | |
| | TEID 2 | |
| +--------------------+ |
| | +-------------+ | |
| | | IP | | |
| | +-------------+ | |
| | | UDP | | |
| | +-------------+ | |
| | | Payload | | |
| | +-------------+ | |
| +--------------------+ |
+---------------------------------------------------------------------+