EPS NETWORK ARCHITECTURE

In one of my series, i have discussed the 3GPP system evolution at a glance and highlighted how the technology has evolved, today we are going to look at the EPS Network Architecture and understand what different elements & interfaces do, before we can move forward to the signaling procedures.

LOGICAL CONNECTIVITY & INTERFACES:

I also recall i highlighted the compositions of the EPS in one of my series but i will repeat myself for clarity's sake: The Evolved Packet System (EPS) consists of 3 parts as shown above:

1). UE i.e. The User Equipment.

2). LTE Subsystem i.e. The Access Network

3).  SAE i.e. System Architecture Evolution. (This is the Evolved Packet Core), recall in the Past i was using the word PS alot, now i change to EPC but it generically mean the same, PS is 2G/3G & 4G we evlove and call it the EPC.(Not a big issue anyway, i will break it down)

NE'S INVOLVED:
1). P-GW: Packet Data Network Gateway (Previously called GGSN)

2). S-GW: Serving Gateway (Previously SGSN, Forwarding Function)

3). HSS: Home Subscriber Server (Previously called HLR)

4). MME: Mobility Management Entity (Previously SGSN, Signaling Function)

5). PCRF: Policy & Charging Rules Function (Same as before)

6). eNODEB: evolved NodeB

7). UE: User Equipment

FUNCTIONS OF NE'S:

MME:

• Tracking Area List Management.
• S-GW & P-GW selection.
• SGSN selection for 2G/3G Handovers.
• Non Access Stratum Signaling & Security.
• Bearer Management.  etc

S-GW:

• Anchor Point for different 3GPP access Networks.
• Packet routing and transfer.
• Local Mobility anchor point for inter e-NodeB Handovers. etc

P-GW:

• IP address Allocation to UE's.
• Packet Filtering.
• UL/DL rate enforcement based on APN-AMBR
• DL rate enforcement based on GBR. etc

HSS:

• Subscriber Authentication & Registration & downloading user profiles into MME
• Provides Barring Services.
• Provides restrictions over Access Network Types etc

PCRF:

• Same as before, i discuss PCC alot so i will not reapeat this because i think there is some concept clarity about PCRF function now.

INTERFACE PROTOCOLS:

1). S1MME - S1AP

2). S1-U - GTP-U (V1)

3). S6 - Diameter

4). S11 - GTP-C (V2)

5). S5/S8 - GTP-C (V2)

6). Gx/Gxc - Diameter

7). Gi - Radius

In the Next Edition, we will discuss what each interface does.