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ME60 V800R010C10SPC500 Hardware Description

This is ME60 V800R010C10SPC500 Hardware Description
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Signal Flow on the Data Plane

Signal Flow on the Data Plane

The data plane processes and forwards data packets at a high speed. The signal flow in the data plane is primarily service data signals.

Signals on the data plane flow through a physical link, an uplink board, an SFU, a downlink board, and another physical link.

Figure 6-3 illustrates the processing and forwarding of a signal flow on the data plane.

Figure 6-3 Processing and forwarding of a signal flow on the data plane


The processing and forwarding of a signal flow on the different uplink board and downlink board may differ. For more information, see "Overall QoS Process" in the HUAWEI ME60 Multiservice Control Gateway Feature Description - QoS.

The processing of an incoming signal flow is as follows:
  1. An uplink physical interface card (PIC) provides an inbound interface for a signal flow. Optical and electrical signals transmitted along a physical link enter the uplink PIC. The PIC obtains the physical layer clock frequency and performs data layer link protocol negotiation. Then the PIC encapsulates packets into Ethernet frames and sends the frames to the uplink NP.
    A PIC can receive high-speed services, such as packet over synchronous digital hierarchy (SDH)/synchronous optical network (SONET) (POS) and Ethernet packets and low-sped services, such as asynchronous transfer mode (ATM), time division multiplexing (TDM), and Point-to-Point Protocol (PPP) packets. Services before they are encapsulated are not described here.
  2. The uplink NP searches a forwarding table for an outbound interface for the signal flow. The processing is as follows:
    1. Inbound interface processing: Upon receipt of the signal flow, the inbound interface of the NP parses the data link layer protocol carried in the packets and obtains the packet types.
    2. Traffic classification: The uplink NP prioritized packets, performs traffic classification, and re-marks them.
    3. Packet forwarding based on the forwarding table: The uplink NP searches for forwarding entries based on destination MAC addresses, destination IP addresses, and MPLS labels and obtains outbound interface names or next-hop IP addresses contained in matching entries.
      Data packets are classified as Layer 2 MAC address-based packets, Layer 2.5 MPLS label-based packets, and Layer 3 IP address-based packets. The processing module on the inbound interface identifies packet types and searches forwarding tables based on these types so that the outbound interface names or next-hop IP addresses for all types of packets can be found.
    4. Traffic policing: The uplink NP limits the rate at which incoming packets are sent based on the committed access rate (CAR) parameters configured on the inbound interface or those configured in the incoming traffic classification profile. If the forwarding behavior is to discard packets, the uplink NP discards them before performing the CAR function.
  3. The uplink traffic management (TM) chip processes the signal flow as follows:
    • Congestion management and avoidance: The uplink TM monitors network resource usage. If traffic congestion worsens, the uplink TM discards packets and adjusts traffic to relieve network overload.
    • Traffic shaping: If traffic congestion occurs, the uplink TM caches packets in queues and uses a specific scheduling algorithm to prioritize packets before forwarding them.
    After the uplink TM processes packets using QoS functions, it sends them to the uplink flexible interface card (FIC).
  4. The uplink FIC fragments the signal flows. The SFU switches packets based on a fixed cell length. Before packets are sent to the SFU, the uplink FIC fragments the packets that are longer than the fixed cell length. The upstream FIC encapsulates the fragments into cells before sending them to the SFU.

The SFU switches data between LPUs. Upon receipt of the cells, the SFU caches and schedules them before sending them to the switching unit. The switching unit balances the cells using multiple switching planes, which improves the fault tolerance capability. The switching unit sends data packets through outbound interfaces to a downlink board.

The processing of an outgoing signal flow is as follows:
  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.
    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:
    1. The downstream NP obtains data link layer encapsulation information and encapsulates packets. The encapsulation process varies according to packet types. For example:
      • For Layer 2 802.1q-in-802.1q (QinQ) packets, the downlink NP adds a virtual local area network (VLAN) tag to each packet.
      • For MPLS packets, the downlink NP adds an MPLS label to each packet.
      • For IP packets, the downlink NP searches for Address Resolution Protocol (ARP) entries and adds MAC addresses mapped to ARP entries to the packets.
    2. The flow processing module performs traffic classification and re-marks packets based on priorities configured on outbound interfaces.
    3. 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.
    4. 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.
      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.
    5. 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.
Updated: 2019-01-04

Document ID: EDOC1100059474

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