Cisco Systems Cisco 12008 manual Overview of the Cisco

Overview of the Cisco 12008

Once the forwarding decision has been made, the silicon queuing engine is notified by the forwarding processor, and the silicon queuing engine places the packet in the proper queue.

This partitioning between the Layer 2 switching accelerator and the forwarding processor blends the high throughput of hardware-accelerated forwarding with the flexibility of software-based routing.

•Silicon queuing engine—Each line card has two silicon queuing engines: receive and transmit. The receive engine moves packets from the burst buffer to the switch fabric, and the transmit engine moves packets from the switch fabric to the transmit interface.

When an incoming IP packet is clocked into the silicon queuing engine, the packet’s integrity is verified by a check of the CRC. Next, the silicon queuing engine transfers the IP packet to buffer memory and tells the Layer 3 switching accelerator the location of the IP packet.

Simultaneously, the silicon queuing engine is receiving forwarding information from the forwarding processor. The forwarding processor tells the silicon queuing engine the virtual output queue where the IP packet is to be placed.

Each virtual output queue represents an output destination (destination line card). This placement of the IP packets in a virtual output queue is based on the decision made by the forwarding processor. There is one virtual output queue for each line card, plus a dedicated virtual output queue for multicast service.

The transmit silicon queuing engine moves the packet from the switch fabric to the transmit buffer, and then to the transmit interface.

•Switch fabric interface—The switch fabric interface is the same 1.25-Gbps, full-duplex data path to the switching fabric that is used by the GRP. Once a packet is in the proper queue, the switch fabric interface issues a request to the master clock scheduler on the CSC. The scheduler issues a grant and transfers the packet across the switching fabric.

•Maintenance bus (MBus) module—A maintenance bus (MBus) module on the line card responds to requests from the master MBus module on the GRP. The MBus module on the line card reports temperature and voltage information to the master MBus module. In addition, the MBus module on the line card contains the ID-EEPROM, which stores the serial number, hardware revision level, and other information about the card.

Product Overview 1-59