Logical Interfaces - Cisco ASR 5000 Series Administration Manual

Understanding the Service Operation

Logical Interfaces

Prior to allowing the flow of user data, the port must be associated with a virtual circuit or tunnel called a logical
interface. A logical interface within the system is defined as the logical assignment of a virtual router instance that
provides higher-layer protocol transport, such as Layer 3 IP addressing. Interfaces are configured as part of the VPN
context and are independent from the physical port that will be used to bridge the virtual interfaces to the network.
Logical interfaces are assigned to IP addresses and are bound to a specific port during the configuration process. Logical
interfaces are also associated with services through bindings. Services are bound to an IP address that is configured for a
particular logical interface. When associated, the interface takes on the characteristics of the functions enabled by the
service. For example, if an interface is bound to a MME service, it will function as an S1-MME interface between the
MME service and the eNodeB. Services are defined later in this section.
There are several types of logical interfaces that must be configured to support the service as described below:
S1-MME Interface: This interface is the reference point for the control plane protocol between eNodeB and
MME. S1-MME uses S1- Application Protocol (S1-AP) over Stream Control Transmission Protocol (SCTP) as
the transport layer protocol for guaranteed delivery of signaling messages between MME and eNodeB (S1).
This is the interface used by the MME to communicate with eNodeBs on the same LTE Public Land Mobile
Network (PLMN). This interface serves as path for establishing and maintaining subscriber EPS bearer
contexts.
One or more S1-MME interfaces can be configured per system context. S1-MME interfaces are bound to ports
on either the Ethernet 10/100 or Ethernet 1000 Line Cards or on the four-port Quad Gig-E Line Card (QGLC).
S3 Interface: This is the interface used by the MME to communicate with SGSNs on the same Public PLMN for
interworking between GPRS/UMTS and LTE network access technology. This interface serves as both the
signalling and data path for establishing and maintaining subscriber EPS bearer contexts.
The MME communicates with SGSNs on the PLMN using the Evolved GPRS Tunnelling Protocol (e-GTP).
The signalling or control aspect of this protocol is referred to as the GTP Control Plane (GTP-C) while the
encapsulated user data traffic is referred to as the GTP User Plane (GTP-U).
One or more S3 interfaces can be configured per system context. S3 interfaces are bound to ports on either the
Ethernet 10/100 or Ethernet 1000 Line Cards or on the four-port Quad Gig-E Line Card (QGLC).
S6a Interface: This is the interface used by the MME to communicate with the Home Subscriber Server (HSS).
The HSS is responsible for transfer of subscription and authentication data for authenticating/authorizing user
access and EPS bearer context authentication. The MME communicates with the HSSs in the PLMN using
Diameter protocol.
One or more S6a interfaces can be configured per system context. S6a interfaces are bound to ports on either
the Ethernet 10/100 or Ethernet 1000 Line Cards or on the four-port Quad Gig-E Line Card (QGLC).
S10 Interface: This is the interface used by the MME to communicate with MME in same PLMN or on different
PLMNs. This interface is also used for MME relocation and MME to MME information transfer or handoff.
One or more S10 interfaces can be configured per system context. S10interfaces are bound to ports on either
the Ethernet 10/100 or Ethernet 1000 Line Cards or on the four-port Quad Gig-E Line Card (QGLC).
S11 Interface: This interface provides communication between MME and Serving Gateways (SGW) for
information transfer.
One or more S11 interfaces can be configured per system context. S11 interfaces are bound to ports on either
the Ethernet 10/100 or Ethernet 1000 Line Cards or on the four-port Quad Gig-E Line Card (QGLC).
S13 Interface: This interface provides communication between MME and Equipment Identity Register (EIR).
This interface is not supported in this release.
OL-22987-01
Cisco ASR 5000 Series Mobility Management Entity Administration Guide ▄
Terminology ▀
55