Cisco XR 12000 Specifications download pdf (Page 60)

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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 5 Overview of Packet over SONET SPAs

SPA Architecture

1-Port OC-192c/STM-64 POS/RPR XFP SPA Architecture

Figure 5-1 identifies the primary hardware devices that are part of the POS 1-Port OC-192c/STM-64

POS/RPR XFP SPA architecture.

Figure 5-1 1-Port OC-192c/STM-64 POS/RPR XFP SPA Architecture

In POS mode, every incoming and outgoing packet on the 1-Port OC-192c/STM-64 POS/RPR XFP SPA

goes through the SONET/SDH framer, and the SPI4.2 interface.

Path of a Packet in the Ingress Direction

The following steps describe the path of an ingress packet through the 1-Port OC-192c/STM-64

POS/RPR XFP SPA (see Figure 5-1):

1. The framer receives SONET/SDH streams from the XFP optics, extracts clocking and data, and

processes the section, line, and path overhead.

2. The framer extracts the POS frame payload and verifies the frame size and frame check sequence

(FCS).

3. The framer passes valid frames to the System Packet Level Interface 4.2 (SPI4.2) interface on the

SPA.

4. The SPI4.2 interface transfers frames to the host through the SPI4.2 bus for further processing and

switching.

Path of a Packet in the Egress Direction

The following steps describe the path of an egress packet through the 1-Port OC-192c/STM-64

POS/RPR XFP SPA (see Figure 5-1):

1. The host sends packets to the SPA using the SPI4.2 bus.

2. The SPA stores the data in the appropriate channel’s first-in first-out (FIFO) queue.

3. The SPA passes the packet to the framer.

4. The framer accepts the data and stores it in the appropriate channel queue.

5. The framer adds the FCS and SONET/SDH overhead.

6. The framer sends the data to the XFP optics for transmission onto the network.

SONET/SDH

Streams

Optics

Transceiver

SPI4.2 Bus

Packets

SONET/SDH

Framer

SPA

Connector

Host

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