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MX Series Router As SGW-U

Overview

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

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

  • S1-U—The S1-U interface is the data path between an eNodeB and the SGW-U. Application data packets from end-user equipment are encapsulated over GTP. For upstream packets, the SGW-U is responsible for forwarding GTP packets to the appropriate PGW-U. For downstream packets, SGW-U forwards GTP packets to eNodeB(s).

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

The MX SGW-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 SGW-C and TEID-U is allocated by the SGW-U)

    • Packet forwarding (GTP-U tunnel relay between S1-U and S5/8-U interfaces)

  • UE mobility support:

    • Forwarding of End Marker message (as long as user plane to source eNodeB exists)

      For UE mobility, the End Marker message is used to help packet ordering at the target eNodeB. The End Marker is sent by the SGW-U during handover when the UE moves to a new eNodeB but keeps the same SGW-U. The SGW-U sends the End Marker message to the original eNodeB across all S1-U tunnels corresponding to the UE session. The original eNodeB forwards the End Marker packets to the target eNodeB.

      If handover involves an SGW-U change as well, the PGW-U sends the End Marker message to the original SGW-U on all S5-U/S8-U tunnels corresponding to the UE session. The SWG-U in turn forwards all End Marker packets over corresponding S1-U tunnels to the original eNodeB, which forwards them to the target eNodeB.

    • Sending of End Marker message after switching the path to target eNodeB

    • Buffered packet forwarding

      When a UE enters ECM-IDLE or power saving mode, all downlink data packets destined for the UE are buffered at the SGW-U. The SGW-C provisions the SGW-U with one of the following behaviors:

      • Buffer packets without notifying the SGW-C upon arrival of the first downlink packet

      • Buffer packets with notifying SGW-C upon arrival of the first downlink packet

      • Drop packets

      No indication is sent to the SGW-C when the MX router as SGW-U is instructed to buffer but does not have available buffering queue space. The MX router as SGW-U discards packets until a queue becomes available. On the first packet, if First DL Packet notification is configured, the SGW-U notifies the SGW-C of the packet arrival. The MX router as SGW-U supports up to 1GB of active buffering on up to 100,000 bearers per anchor PFE.

  • Accounting per UE and bearer (volume accounting only)

  • Lawful intercept

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

  • At least one anchor PFE interface–An anchor PFE interface on the SGW-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:

    • Forwards GTP-U packets

    • 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 interface in the CUPS architecture. The signalling/control interface is a physical interface that does the following:

    • Sends/receives PFCP packets to/from the SGW-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 S5/8-U interface in the CUPS architecture. The egress interface is a physical interface that does the following:

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

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 for a list of line card support by interface type.

Configuring an MX Router as an SGW-U

As Figure 2 shows, a standard setup of an MX router as an SGW-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 SGW-U Standard setup for MX router as SGW-U
  • The ingress line card provides the S1-U interface, connecting to the radio access network (RAN), and the Sxa interface, connecting to the SGW-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 S5/8-U interface, connecting to the PGW-U.

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

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

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

  1. Configure the connection to the control plane, the SGW-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 access network through the S1-U interface.
  3. Configure the connection to the core network peers (PGW-Us) through the S5/8-U interface.
  4. 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: