Juniper Networks PWHT and Post-Weld Heat Treatment

Pseudowire headend termination (PWHT) is an innovative feature that connects subscribers directly to the BNG, making it possible to design robust active/standby or active/active solutions.

PWHT configurations combine transport and service logical interfaces of a pseudowire service interface (ps) onto one redundant logical tunnel interface (RLT) which also supports load balancing.

PWHT Configuration

MX series routers feature dual, internal NAND flash devices which store the primary Junos OS image. If this partition becomes corrupted, rebooting will switch over and use its backup image stored elsewhere in its root partition as soon as possible.

The chassis daemon maintains a static database containing maximum power requirements for various line cards, so when budgeting power for microinput cards (MICs), the chassis daemon checks that its worst-case power consumption won’t surpass this number; otherwise it disables or takes offline the associated port immediately and disconnects it if this proves impossible.

At system startup, power management allocates available power among host subsystem components and then powers on FPCs in accordance with their configured priorities until all FPCs are online or all available power to the chassis has been depleted. If any FPCs go offline during powerup or restart of their chassis, they won’t be powered back on until taken back online or restart of said chassis has taken place.

PWHT (pseudowire headend termination) connects an L2 dedicated circuit directly into an L3 service at the service node. PWHT can be configured on either transport or subscriber management service logical interface, depending on your topology. You may choose between anchoring it either with redundant logical tunnel (RLT), AS boundary router, route reflectors or any combination thereof based on your load-balancing configuration needs.

PWHT Management

The BNG pwht framework offers you the capability to implement a redundant transport and service logical interface (LTI) attached to a redundant logical tunnel (RLT). When configured in this mode, traffic is automatically load-balanced across all active member logical tunnel interfaces (lt). This approach may be utilized either for supporting dual homed EVPN-VPWS with multi-homed service PEs in metro aggregation networks or redundancy of single homed EVPN-VPWSs.

Junos OS maintains two pseudowire status codes for every SS-PW it participates in: local and remote pseudowire status codes. Each S-PE that receives and sends MPLS LDP label mapping messages increments their status code value accordingly; at the same time they provide each segment of an SS-PW with local pseudowire status code updates.

The chassis daemon process (chassisd) keeps track of how much power each MIC consumes by maintaining a static database. Junos OS relies on this information when budgeting power for these MICs when they power on. Furthermore, Junos OS doesn’t reevaluate maximum power that each MIC requires after reboot; when an FPC is removed from a chassis without its power being adjusted; although you can force chassisd to do so by making configuration changes through [edit chassis] hierarchy level and using commit command on commit command to commit any changes made at that level if desired.

PWHT Monitoring

Post-weld heat treatment (PWHT) is an essential process for stress relief and improving mechanical properties of welded materials. PWHT involves heating material to an appropriate temperature range for an appropriate duration, before cooling at an accelerated pace using proper equipment and facilities. PWHT helps ensure quality standards are met when welding welds together, thus avoiding distortion or cracking of welds during welding operations and producing quality finished material products.

PWHT can help reduce the hardness of welded material, making it easier to machine or form. There is, however, some concern that prolonged exposure could cause its welds to degrade over time due to oxidation and corrosion; so weld procedure qualification testing must take place on each material after PWHT to ensure that its results remain acceptable.

Junos OS Release 12.3 includes a new power management feature which allows you to limit how much chassis output power is allocated to Flexible PIC Concentrators (FPCs), thus preventing routers from powering on FPCs when insufficient power is available for normal boot and operation of these devices.

This feature can be especially helpful when configuring multiple vMX960 routers as a BNG and you wish to minimize the number of physical ports on each device. To activate it, configure the [edit chassis network-services] hierarchy of each device with an enable-fpc-power-management statement and ensure its presence there.

PWHT Troubleshooting

If you experience jitter or latency issues, first ensure the shaping rates on each constituent link are properly configured. If they aren’t, increase them until jitter and latency have dissipated; otherwise contact Juniper Networks Technical Assistance Center (JTAC) so they can diagnose the issue for you.

Pseudowire Headend Termination (PWHT) allows for seamless connection of an L2 dedicated circuit directly into an L3 service such as L3VPN or EVPN at its service node. PWHT includes both transport logical interface and subscriber management logical interface, with transport being either an LT or RLT anchor point and subscriber management being connected through RLT anchor points respectively.

ISSU downloads a software image for primary nodes that replaces existing software on routers, and in case it fails an error message is displayed with possible causes, including an inaccessible image file or routing engine failure that occurred during download.

Before configuring, the security policies on both engines must be aligned. If they don’t match, use the request security policies resync command to synchronize their settings if they differ significantly; note that this operation could take some time; additionally, your router could temporarily go offline during its execution.