LTE Traffic Flow inside IP Backbone

I have explained about EPS in several posted include each LTE interface for simple architecture. Example implement Cisco & Juniper L3 Switch for EPC and E-UTRAN, we can called that is IP Backbone (IPBB). The LTE traffic flow inside IP Backbone is simple. It can ping between node in virtual routing, example S11_VR virtual routing: MME can ping to SGW and vice versa. The previous example is very simple, only one node each, that is not reflect the live network, may be implemented for very simple lab. For expand network you can enable OSPF or MPLS inside IPBB as you need.

Before UE can access internet or VPN use LTE, there are some step will be happen. The simple step for traffic flow, I will divide it become 2, the EPS bearer and the access internet. The EPS bearer is reflect to control plane process and the access internet is user plane process (payload).

The simple definition of EPS Bearer is process UE to get signal and IP address. The access internet is generic process IP flow use TCP or UDP. Each interface between two node use different protocol. If you dump traffic between them you will see encapsulation/tunneling based on below description.

For example:
S11 interface use GTPv2-C protocol to transfer between MME and SGW. The GTPv2-C isn't native encapsulation based on OSI layer but tunneling in layer 4. Layer 3 is general IP flow and layer 2 is ethernet. Basicly GTP packet based on UDP for transfer. But GTP-C and GTP-U has different port for transfer, GTP-C use UDP 2123 and GTP-U use UDP 2152.

# The EPS Bearer #

UE ---- eNodeB
->Wireless interface

eNodeB ---- MME
->S1-MME interface (SCTP)

MME ---- HSS
->S6a interface (Diameter)

MME ---- SGW
->S11 interface (GTPv2-C)

SGW ---- PGW
->S5 interface (GTPv2-C)

# The Access Internet #

UE ==== eNodeB
=>Wireless interface

eNodeB ==== SGW
=>S1-U interface (GTPv1-U)

SGW ==== PGW
=>S5 interface (GTPv2-U)

PGW ==== Gateway to Internet/VPN/etc.
=>SGi interface (IP)