Primary Task Subsystems - Cisco ASR 5000 Series Administration Manual

Primary Task Subsystems

Primary Task Subsystems
The individual tasks that run on the CPUs are divided into subsystems. Following is a list of the primary
subsystems responsible for call session processing:
• System Initiation Task (SIT): This subsystem starts tasks and initializes the system. This includes
• High Availability Task (HAT): With the Recovery Control Task (RCT) subsystem, the HAT subsystem
• Recovery Control Task (RCT): This subsystem executes a recovery action for any failure that occurs
• Shared Configuration Task (SCT): This subsystem provides a facility to set, retrieve, and receive
• Resource Management (RM): This subsystem assigns resources, such as CPU loading and memory,
• Virtual Private Network (VPN): This subsystem manages the administrative and operational aspects
• Network Processing Unit (npusim on ASR 5500, and iftask or knpusim on VPC-DI and VPC-SI)
1 knpusim runs instead of iftask on VPC VMs that do not have Intel DPDK supported configurations.
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starting a set of initial tasks at system startup time (static tasks), and starting individual tasks on demand
at arbitrary times (dynamic tasks).
maintains the operational state of the system. HAT monitors the various software and hardware
components of the system. If there are unusual activities, such as the unexpected termination of another
task, the HAT subsystem takes a suitable course of action, such as triggering an event to the RCT
subsystem to take corrective action or to report the status. The primary function of the HAT task is to
minimize service impacts.
in the system. The RCT subsystem receives signals from the HAT subsystem (and in some cases from
the NPU subsystem) and determines what recovery actions are needed.
notification of system configuration parameters. The SCT is mainly responsible for storing configuration
data for the applications that run on the system.
The SCT subsystem runs only on the active management card and synchronizes the information it
contains with the SCT subsystem on the standby management card.
for every system task upon start-up. The RM subsystem monitors resource use to verify that allocations
are as specified. RM also monitors all sessions and communicates with the Session Controller to enforce
capacity licensing limits.
of all VPN-related entities in the system. The functions performed by the VPN subsystem include:
• Creating separate VPN contexts
• Starting the IP services within a VPN context
• Managing IP pools and subscriber IP addresses, and distributing the IP flow information within a
VPN context.
All IP operations within StarOS are done within specific VPN contexts. In general, packets are not
forwarded across different VPN contexts. The only exception currently is the Session subsystem.
This subsystem is responsible for the following:
• Using the database to match address and port numbers to destination tasks for fast-path forwarding
of dataframes
• Receiving and transmitting user data frames to/from various physical interfaces
• IP forwarding decisions (both unicast and multicast)
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