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MX Series Router As SAEGW-U

Overview

Junos Multi-Access User Plane can function as a combined SGW user plane (SGW-U) and PGW user plane (PGW-U) in a single MX series router. The combined SGW-U/PGW-U is referred to as a SAEGW-U (System Architecture Evolution Gateway-User Plane). As Figure 1 shows, Juniper’s MX SAEGW-U interoperates with a third-party SAEGW-C through a combined Sxa/Sxb interface.

Figure 1: MX Series SAEGW-U in the CUPS Wireless Network ArchitectureMX Series SAEGW-U in the CUPS Wireless Network Architecture

The MX SAEGW-U supports the following CUPS interfaces:

  • Combined Sxa/Sxb—Packet Forwarding Control Protocol (PFCP) enables communication on the Sxa/Sxb interface between the SAEGW-C and SAEGW-U. PFCP encodes TLV messages for transport over UDP/IP. The Sxa/Sxb interface can also transport user data packets (GTP-U based) between the user plane and control plane. SAEGW-U runs PFCP as the control protocol with the third-party SAEGW-C to set up data paths for wireless subscribers.

  • S1-U—The S1-U interface is the data path between an eNodeB and the SAEGW-U. Application data packets from end-user equipment are encapsulated over GTP. For upstream packets, SAEGW-U is responsible for GTP tunnel termination and forwarding the user packets to the core. For downstream packets from core, SAEGW-U adds the GTP header and forwards to eNodeB(s). The data plane of SAEGW-U handles IP packets encapsulated in GTP-U from/ to eNodeBs that arrive for the mobile subscribers and performs routing to/from the external Internet.

  • SGi—Interface to the core Internet, supporting IPv4.

The MX SAEGW-U as the user plane provides the following functionality:

  • Subscriber tunnel encapsulations (GTP-U)

  • Packet routing and forwarding

  • Bandwidth policing based on rules defined by the SAEGW-C

  • Layer 3 policy enforcement based on policies defined by the SAEGW-C

  • Statistics gathering and reporting for accounting and customer billing purposes

  • Lawful intercept

Junos Multi-Access User Plane provides purely the SAEGW-U in the form of an MX router that interacts with a third-party SAEGW-C. The MX router, functioning as an SAEGW-U, receives instructions from the SAEGW-C through the Sxa/Sxb interface using PFCP. Based on those instructions, the MX routing engine manages SAEGW-U sessions and programs data paths in the anchor PFEs. For the MX router to function as an SAEGW-U, it must contain the following minimum elements:

  • At least one anchor PFE interface–An anchor PFE interface is a line card interface that has no physical interface connection, but rather provides the core processing of data traffic by doing the following:

    • Encoding/decoding of GTP-U packets. The anchor PFE interface decodes GTP-U packets from eNodeBs and forwards them to the core network and encodes IPv4 packets from the core network and forwards them to eNodeBs.

    • Enforces class of service and firewall filter rules on subscriber sessions

    • Collects statistics on data usage for charging/accounting purpose

  • At least one signalling/control interface-This is the Sxa/Sxb interface in the CUPS architecture. The signalling/control interface is a physical interface that does the following:

    • Sends/receives PFCP packets to/from the SAEGW-C

  • At least one ingress interface-This is the S1-U interface in the CUPS architecture. The ingress interface is a physical interface that does the following:

    • Forwards GTP-U packets between eNodeBs and the anchor PFE

  • At least one egress interface-This is the SGi interface in the CUPS architecture. The egress interface is a physical interface that does the following:

    • Forwards IPv4 packets between the anchor PFE and the core network

Note:

You can configure all four interface types on the same line card, as long as that line card supports all of the interface types. See Table 1 for a list of line card support by interface type.

Configuring an MX Router as an SAEGW-U

As Figure 2 shows, a standard setup of an MX router as an SAEGW-U includes an ingress line card, and egress line card, and a recommended two anchor PFE line cards operating redundantly.

Figure 2: Standard setup for MX router as SAEGW-U Standard setup for MX router as SAEGW-U
  • The ingress line card provides the S1-U interface, connecting to the radio access network (RAN), and the combined Sxa/Sxb interface, connecting to the SAEGW-C.

  • The anchor PFE line cards provide the core processing of data traffic through internal pfe- interfaces. At least one anchor PFE card is required, but two are recommended to provide redundancy.

  • The egress line card provides the SGi interface, connecting to the core Internet.

  • You can configure all of this functionality on a single line card as long as that line card supports all of the SAEGW-U functionality. We show separate line cards here for simplicity and recommended setup.

To configure an MX router as an SAEGW-U, perform the following configuration procedures in the listed order:

DDoS Attack Protection Configuration

Define DDoS attack protection for PFCP protocol traffic.

  1. Configure protection for the PFCP protocol.
  2. Configure GTP path management protection.

GRES Configuration

The graceful Routing Engine switchover (GRES) feature in Junos OS enables a router with redundant Routing Engines to continue forwarding packets, even if one Routing Engine fails. GRES preserves interface and kernel information. Traffic is not interrupted.

Configure Graceful Restart (GRES).

Chassis Configuration for the Anchor PFE Line Cards

Define each Packet Forwarding Engine (PFE) on each anchor PFE line card as an anchor interface.

  1. Enable enhanced IP network services.
  2. Configure slots for anchor PFE processing.

Interface Configuration

Configure the interfaces needed for the SAEGW-U.

  1. Define the SGi interface. This interface is on the egress line card.
  2. Define the Sx interface, which connects to the SAEGW-C. This interface is on the ingress line card.
  3. Define the S1-U interface, which connects to the access network. This interface is on the ingress line card and is set to admit only GTP packets.
  4. Define the UPF local address and Mobile Edge interface.
    Note:

    If you are connecting to multiple SAEGW-Cs, define the local address under the control-plane-peers stanza for each SAEGW-C rather than define a single loopback address.

    Note:

    mif.0 is used in the default inet.0 routing instance. Junos OS creates a default APN with inet.0 as the routing instance. If you want to configure other routing instances, you must create mif interfaces with unit numbers other than 0.

  5. Assuming two anchor PFE linecards, each with two PFEs, define the anchor PFE interfaces.
    Note:

    You cannot mix primary and secondary anchor PFEs on the same MPC. An MPC can have only either primary anchor PFEs or secondary anchor PFEs.

    CAUTION:

    Changing the anchor PFE redundancy configuration once sessions are active kills all active sessions.

Mobile Edge Configuration

Once you’ve configured all of the necessary interfaces, you can configure the MX router to be a SAEGW-U.

  1. Configure the connection to the control plane, the SAEGW-C.
    Note:

    If you are connecting to multiple SAEGW-Cs, define the local address under the control-plane-peers stanza for each SAEGW-C. The loopback address, however, is still required for Lawful Intercept to function.

  2. Configure the connection to the access network through the S1-U interface.
  3. Define the interfaces that will provide the anchor PFE functionality.

Firewall Configuration

Define a firewall filter that discards all packets except GTP packets at the S1-U interface.

  1. Set the filter to enhanced mode.
  2. GTP packets are UDP packets that have a destination port of 2152. GTP prime packets have a destination port of 3386. Accept and count these packets:
  3. Discard all other packets: