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MX Series Router As PGW-U

Overview

Junos Multi-Access User Plane can function as a standalone PGW user plane (PGW-U) in a single MX router. As Figure 1 shows, Juniper’s MX PGW-U interoperates with a third-party PGW-C through a the Sxb interface and one or more Juniper or third-party SGW-Us over one or more S5/8-U interfaces.

Figure 1: MX Series SGW-U and PGW-U in the CUPS Wireless Network ArchitectureMX Series SGW-U and PGW-U in the CUPS Wireless Network Architecture

The MX PGW-U supports the following CUPS interfaces:

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

  • S5/8-U—The S5/8-U interface is the data path between an SGW-U and a PGW-U.

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

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

  • Session management support:

    • Resource management for bearer resources

    • IP address and TEID assignment for GTP-U packets (IP address is allocated by the PGW-C and TEID-U is allocated by the PGW-U)

    • Packet forwarding

  • UE mobility support:

    • Sending of "end marker" after switching the path to target node

  • Accounting per UE and bearer (volume accounting only)

  • Lawful intercept

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

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

    • Encodes/decodes GTP-U packets. The anchor PFE interface decodes GTP-U packets from SGW-Us and forwards them to the core network and encodes IPv4 packets from the core network and forwards them to SGW-Us.

    • 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 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 PGW-C

  • At least one ingress interface-This is the S5/8-U interface in the CUPS architecture. The ingress interface is a physical interface that does the following:

    • Forwards GTP-U packets between the anchor PFE and the designated SGW-U

  • 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 PGW-U

As Figure 2 shows, a standard setup of an MX router as an PGW-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 PGW-U Standard setup for MX router as PGW-U
  • The ingress line card provides the S5/8-U interface, connecting to the SGW-U.

  • 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 PGW-U functionality. We show separate line cards here for simplicity and recommended setup.

To configure an MX router as an PGW-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 PGW-U.

  1. Define the SGi interface. This interface is on the egress line card.
  2. Define the Sxb interface, which connects to the PGW-C. This interface is on the ingress line card.
  3. Define the S5/8-U interface, which connects to the SGW-U. 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 PGW-Cs, define the local address under the control-plane-peers stanza for each PGW-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 PGW-U.

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

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

  2. Configure the connection to the core network peers (SGW-Us) through the S5/8-U interface.
  3. Define the interfaces that will provide the anchor PFE functionality.

Firewall Configuration

Define input and output firewall filters that discard all packets except GTP packets at the S1-U and S5/8-U interfaces.

Note:

For GTP-U path management, the filter must work in enhanced mode.

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 and discard all others: