4G Architecture

This page is just a collection of my research on 4G Network Architecture. Better information can be found (look at the end). Nonetheless enjoy reading !

The heart of 4G network is fully using IP. The name of this architecture is EPS for Evolved Packet System. It is split in many functions, some of them are :

• UE - User equipment : The end user system obviously 4G compatible. It is usually a cell phone, but it can be something else like, for example, a router with 4G antennas. UE are identified by a unique ID called IMEI whereas users are identified by the IMSI.
• eNodeB - The service provider antenna's. It's the border of wireless network.
• S-Gateway. A classic IP router, with some specific features for mobile networks.
• P-Gateway. A classic IP router. It's the border of the EPS and allow access to other IP networks called PDN.
• MME - Mobility management system. MME is part of the control plane. It register user position on the network, controls which P/G-Gateways user should use.
• HSS - Home Subscriber Server. Some kind of source of truth of the network. Stores user credentials. Mostly use Diameter protocol to interact with other functions. An open source HSS implementation written in Python: https://github.com/nickvsnetworking/pyhss

IMS is a system able to provide multimedia services on any IP networks. Therefore it is not specifically bound to 4G. It's architecture look similar to EPS (eventhoug it's older than EPS) on a point : it is split between data and control plane. Protocols used are mostly Diameter and SIP. Main functions are :

• P-CSCF : SIP proxy in front of internat users. Could for example, be right behind a P-GW from an EPS system.
• S-CSCF : Main SIP proxy.
• I-CSCF : SIP proxy connected to HSS (same function as the EPS).
• MMTEL : Telephony application server (B2BUA - Asterisk, GNU Bayonne 👌, Freeswitch, etc…).
• IBCF : SIP Proxy in front of another SIP network (IMS or not).
• MGCF : SIP Gateway in front of PSTN.

Multimedia data flows on trough other functions :

• ATGw
• Tr Gw
• MRF
• IM-MGw