Cisco ASR 1000 Configuration Guide

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Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide
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Chapter 6 Overview of the ATM SPAs
SPA Architecture
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SPA Architecture
This section provides an overview of the data path for the ATM SPAs, for use in troubleshooting and
monitoring.
Figure 6-1 shows the data path for ATM traffic as it travels between the ATM optical
connectors on the front panel of the ATM SPA to the backplane connector that connects the SPA to the
SIP.
Figure 6-1 ATM SPA Data Architecture
Note LFI processing is not supported on the Cisco ASR 1000 Series Routers.
Path of Cells in the Ingress Direction
The following steps describe the path of an ingress cell as it is received from the ATM network and
converted to a data packet before transmission through the SIP to the router’s processors for switching,
routing, or further processing:
1. The SONET/SDH framer device receives incoming cells on a per-port basis from the SPA’s optical
circuitry. The actual number of optical ports depends on the model of ATM SPA on the Cisco ASR
1000 Series Routers.
2. The SONET/SDH framer removes the SONET overhead information, performs any necessary clock
and data recovery, and processes any SONET/SDH alarms that might be present. The framer then
extracts the 53-byte ATM cells from the data stream and forwards each cell to the ATM segmentation
and reassembly (SAR) engine using one channel per physical port supported by the SPA.
ATM Optics
SONET
ATM Cells Cells/Packets
SONET/SDH
Framer
ATM
SAR
SRAM/
SDRAM
FPGA
and
SPA Bus
Packets
SPA
Connector
SDRAM
To
Host
From
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Cisco ASR 1000 Specifications

General

Brand	Cisco
Model	ASR 1000
Category	Network Router
Language	English