The document discusses EPC CUPS (Control and User Plane Separation) architecture in 3GPP releases. Some key points: 1) EPC CUPS was introduced in Release 14 to separate control and user plane functions for more flexible scaling and deployment. 2) CUPS introduces new Sxa, Sxb, and Sxc interfaces between control and user plane functions of SGW, PGW, and TDF. 3) The separation allows independent scaling of control and user plane resources to better handle increases in data traffic.

1. EPC CUPS
Architecture
Prepared: Hemraj Kumar
Senior 5G Technology Consultant

2. 2
EPC Core

3. Enhanced Packet Core (EPC)
13
Overall control of the UE within the LTE architecture is handled by the core network.
The core network (also known as EPC in SAE) is also responsible for establishing the
bearers.
The main components of the EPC are:
§ PDN Gateway (P-GW)
§ Serving Gateway (S-GW)
§ Mobility Management Entity (MME)
E-UTRAN Enhanced Packet Core (EPC)

4. EPC Entities Function
4

5. 5
EPC CUPS Architecture

6. CUPS Overview
6
CUPS architecture for EPC was first introduced in 3GPP release 14. All earlier EPC
specification follows NON-CUPS architecture. CUPS introduce 3 new interfaces, Sxa,
Sxb and Sxc between the CP and UP functions of the SGW, PGW, and TDF
respectively.
Control-/User Plane Separation (CUPS) in mobile networks refer to the complete
separation between control plane functions (which take care of the user connection
management, as well as defining QoS policies, performing user authentication, etc.)
and user plane functions (which deal with data traffic forwarding).
The main motivation for CUPS is to make user plane functions scale independently,
allowing operators for a more flexible deployment and dimensioning of the network.
For instance, if data traffic increases, more data plane nodes can be added without
affecting the control plane functions.
The Application protocol (AP) generates control signal and the CP encapsulates the
signal bearers used to transmit control signals from the gNB to the UE.
The UP provides the data bearers used to carry UE data from the DN to the UE using
the GTP-U. The principle of CUPS supports the SDN technology which is already
adopted in the 5GCN utilizing a service-based architecture.

7. EPC Control and User Plane Separation (CUPS)
7
§ 5G Core Network inherits control and
user plane separation (CUPS)
architecture from 3GPP Release 14.
§ In 4G EPC, S/PGWs are decomposed
to S/PGW-C and S/PGW-U to provide
an efficient scaling of services
independently.
MME
SGSN-C
SGSN-
U
RNC
E-
UTRA
N
SGW-
C
SGW-
U
PGW-
C
PGW-
U
SGSN-
U
ePDG-
U
SaMOG-
U
3GGP
AAA
HSS
SGSN-C
ePDG-
C
SaMOG-
C
PCRF
OCS
CG/BS
Operator
Services
S1
1
S4-C
S4-U
S1-
U
S12
Sxa Sxb
S5-U/S8-U
S5-C/S8-C
Gn-
C
Gn-U
S2b-U
S2b-C
S2a-C
S2a-U
S6b
Gx
Gy
Gz/Bp
SGi

8. CUPS Architecture Principles
8
EPC w/o CUPS
EPC with CUPS
CUPS introduces 3 new
interfaces, Sxa, Sxb and
Sxc between the CP and
UP functions of the SGW,
PGW and TDF
respectively.

9. Principles of CUPS
9
The CP function terminates the Control Plane protocols: GTP-C, Diameter (Gx, Gy, Gz).
A CP function can interface multiple UP functions, and a UP function can be shared
by multiple CP functions.
An UE is served by a single SGW-CP but multiple SGW-UPs can be selected for
different PDN connections. A user plane data packet may traverse multiple UP
functions.
The CP function controls the processing of the packets in the UP function by
provisioning a set of rules in Sx sessions, i.e. Packet Detection Rules for packets
inspection, Forwarding Action Rules for packets handling (e.g. forward, duplicate,
buffer, drop), Qos Enforcement Rules to enforce QoS policing on the packets, Usage
Reporting Rules for measuring the traffic usage.
All the 3GPP features impacting the UP function (PCC, Charging, Lawful Interception,
etc) are supported, while the UP function is designed as much as possible 3GPP
agnostic. For example, the UPF is not aware of bearer concept.
Charging and Usage Monitoring are supported by instructing the UP function to
measure and report traffic usage, using Usage Reporting Rule(s). No impact is
expected to OFCS, OCS and the PCRF.
The CP or UP function is responsible for GTP-u F-TEID allocation.
A legacy SGW, PGW and TDF can be replaced by a split node without effecting
connected legacy nodes.

10. Advantage and Disadvantage of CUPS
10
Advantage of CUPS :
§ Reducing Latency on application service, e.g. by selecting User plane nodes which
are closer to the RAN or more appropriate for the intended UE usage type without
increasing the number of control plane nodes.
§ Supporting Increase of Data Traffic, by enabling to add user plane nodes without
changing the number of SGW-C, PGW-C and TDF-C in the network.
§ Locating and Scaling the CP and UP resources of the EPC nodes independently.
§ Independent evolution of the CP and UP functions.
§ Enabling Software Defined Networking to deliver user plane data more efficiently.
Disadvantage of CUPS
§ The major disadvantages of CUPS is that it introduces complexity, standardization of
interfaces between CP and UP and high cost of operation which may result in
deployment delays .

11. EPC without CUPS
11
Data Network
(e.g. operator
or Internet)
LTE UE
S
1
-
M
M
E
S1-U SGi
eNB P-GW
MME
LTE Uu
GW (SGW/PGW) Function : Vertically integrated control plane (CP) and user plane (UP)
function.
CP function of GWs : proposed separately for each GW.
Expensive customized of GWs and high expansion costs as user traffic increase.
Unlimited scalability of GWs and high expansion costs as user traffic increase.
Centralized deployment of all GWs.
S-GW
S11
S5
§ MME : Mobility Management Entity.
§ S-GW : Serving Gateway
§ P-GW : PDN Gateway
§ PDN : Packet Data Network.
EPC
E-UTRAN

12. EPC with CUPS
12
Data Network
(e.g. operator
or Internet)
LTE UE
S1-M
M
E
eNB
EPC NAS
MME
LTE Uu
GW functions : separated into CP and UP functions.
CP functions of GWs : processed centrally .
Inexpensive commodity hardware based architecture.
Scaling CP and UP functions independently (Enabling to add
Only GW_Us independently as user traffic increased.)
Enabling flexible deployment of GW-Us (closer to RAN) to reduce latency.
Independent evolution of CP and UP function.
SGW
CP
SGW
UP
PGW
CP
PGW
UP
S11 S5-C
S5-U
Sxa
Sxb
Note : CUPS introduce 3 new interfaces, Sxa, Sxb and Sxc between the CP and UP
functions of the SGW, PGW, and TDF respectively.
Control Plane
SGi
User Plane

13. EPC with CUPS
13
Data Network
(e.g. operator
or Internet)
LTE UE
S1-U SGi
Gx Rx
Sx
SGW/
PGW UP
SGW/
PGW CP
PCRF
EPC NAS
S11
HSS
S6a
MME
S10
LTE RRC
LTE PDCP
LTE Uu
S5
 SGW/PGW-CP(GW-C) : Gateway Control Plane
 SGW/PGW-UP(GW-U) : Gateway User Plane
 BBU : Baseband Unit (or DU : Digital Unit )
 RRH : Remote Radio Head (or RU : Radio Unit)
eNB
E-UTRAN
Control Plane
User Plane
EPC
Note : In this architecture ,control plane & user plane of GWs (SGW + PGW) are separated .

14. EN-DC Core Architecture
14
Data Network
(e.g. operator
or Internet)
S1-MME
S1-U SGi
Gx Rx
Sx
SGW/
PGW UP
SGW/
PGW CP
PCRF
S11
HSS
S6a
MME
S10
S5
Enables early introduction of NR
through connectivity Option 3
UE anchored to network over LTE/EPC
control plane
Wide area coverage through LTE with
NR as capacity boost
LTE CP + UP
NR UP
eNB
gNB
LTE RAN
NR RAN
S1-U
X2-C X2-U
LTE + NR UE