Cisco XR 12000 Specifications download pdf (Page 39)

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Cisco XR 12000 Series Router SIP and SPA Software Configuration Guide, Release 3.2

Release 3.2, OL-6396-01, Rev.A1 January 9, 2006

Chapter 3 Overview of the Gigabit Ethernet SPAs

SPA Architecture

• Remote Monitoring (RMON)-MIB (RFC 1757)

• Cisco-class-based-QoS-MIB

• MPLS-related MIBs

• Ethernet MIB/RMON

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use

Cisco MIB Locator found at the following URL:

http://tools.cisco.com/ITDIT/MIBS/servlet/index

If Cisco MIB Locator does not support the MIB information that you need, you can also obtain a list of

supported MIBs and download MIBs from the Cisco MIBs page at the following URL:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

To access Cisco MIB Locator, you must have an account on Cisco.com. If you have forgotten or lost your

account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify

that your e-mail address is registered with Cisco.com. If the check is successful, account details with a

new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com

by following the directions found at this URL:

http://www.cisco.com/register

SPA Architecture

This section provides an overview of the architecture of the Gigabit Ethernet SPAs and describes the path

of a packet in the ingress and egress directions. Some of these areas of the architecture are referenced in

the SPA software and can be helpful to understand when troubleshooting or interpreting some of the SPA

CLI and show command output.

Every incoming and outgoing packet on the Gigabit Ethernet SPAs goes through the physical (PHY) SFP

optics, Media Access Control (MAC), and ASIC devices.

Path of a Packet in the Ingress Direction

The following steps describe the path of an ingress packet through the Gigabit Ethernet SPAs:

1. The PHY SFP optics device receives incoming frames on a per-port basis from one of the laser optic

interface connectors.

2. The PHY laser optics device processes the frame and sends it over the XAUI path to the MAC

device.

3. The MAC device receives the frame, strips the CRCs, and sends the packet via the SPI 4.2 bus to the

ASIC.

4. The ASIC takes the packet from the MAC devices and classifies the ethernet information. CAM

lookups based on etype, port, VLAN, and source and destination address information determine

whether the packet is dropped or forwarded to the SPA interface. If the packet is forwarded to the

SPA interface, an 8-byte SHIM header that is used for additional downstream packet processing is

propounded to the packet.

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Cisco XR 12000 Specifications Page 39