1.
Switched network cell assembly on the downstream FIC: The downstream FIC assembles
switched network cells into packets after switched network cells flow from the SFU to the
downlink FIC.
2.
Queuing and scheduling on the downlink TM: The downstream TM puts packets of the
signal flow in queues and schedules them based on the traffic shaping, policing, congestion
avoidance parameters. Then it sends the packets to the downstream NP.
NOTE
The downlink TM also replicates multicast packets before sending them through several outbound
interfaces.
3.
Forwarding table lookup and data layer link information query: The downlink NP obtains
data link layer encapsulation information, processes packets using a signal flow processing
module and outbound interface-specific processing modules. The processing is as follows:
a.
The downstream NP obtains data link layer encapsulation information and
encapsulates packets. The encapsulation process varies according to packet types. For
example:
l
For Layer 2 802.1q-in-802.1q (QinQ) packets, the downlink NP adds a virtual local
area network (VLAN) tag to each packet.
l
For MPLS packets, the downlink NP adds an MPLS label to each packet.
l
For IP packets, the downlink NP searches for Address Resolution Protocol (ARP)
entries and adds MAC addresses mapped to ARP entries to the packets.
b.
The flow processing module performs traffic classification and re-marks packets
based on priorities configured on outbound interfaces.
c.
The downstream NP limits the rate limit at which outgoing packets are sent based on
CAR parameters configured on the outbound interface or those in the outgoing traffic
classification profile.
d.
Host packets destined for the MPU are sent to an MPU, and packets to be forwarded
are sent to the outbound interface-specific processing modules.
NOTE
Due to limited CPU processing capability on an MPU, the limit on packets destined for the
CPU must be configured. This prevents attack or defective packets from being sent to the MPU
and causing high CPU usage, which improves device security. The packets are verified, and
only valid packets are sent to the CPU at a specified rate, which defends against attacks on the
CPU.
e.
The outbound interface-specific processing module adds a Layer 2 header to each
packet and forwards the packets to the downlink PIC.
4.
The downlink PIC converts data packets into optical and electrical signals and forwards
them through outbound interfaces connected to physical links.
2.4 Signal Flow on the Monitoring Plane
The monitoring plane monitors the system environment. If a fault occurs on a unit, the monitoring
plane isolates the fault to prevent it from affecting other units on the device. The control and
monitoring planes are working together to support the operation and maintenance of a device
and improve performance stability.
Both the control plane and monitoring plane consist of the system operation and maintenance
unit and the monitoring units on LPUs and an SFU. Inter-board communication is implemented
using the system backplane.
HUAWEI CX600-8/16/X3/X8/X16 Metro Service Platform
Hardware Description
2 Product Signal Flow Overview
Issue 03 (2013-11-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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