IXP1200 Network Processor Family ATM OC-3/12/Ethernet IP Router Example Design
8Application Note
Modified on: 3/20/02,

1.2.1 Supported / Not Implemented Functions

The following identifies the ATM, Ethernet, and StrongARM supported functions, as well as those
functions that are not supported.
The majority of RFC1812 router va l idations are performed in the layer 3 forwarding code running
on the microengines, while rare case exception packets are sent to the StrongARM core control
plane for validation and processing. No processing code on the StrongARM core is currently
implemented. Refer to the document "IXP1200 Network Processor RFC 1812 Compliant Layer 3
Forwarding Example Design Implementation Details" for further information.
This example design can be configured to run in three different hardware/software configurations
(see the README.TXT file for further information):
1.3 Background

1.3.1 Ethernet, IP and AAL5 Protocol Processing

Figure 1 identifies how this design processes Ethernet, IP, and AAL5 protocols., Reading from top
to bottom, Ethernet packets go through the LLC/SNAP Encapsulation, followed by segmentation
into ATM AAL5 cells. Reading from bottom to top, it also shows the reverse process, in which
AAL5 cells are reassembled into Ethernet packets.
ATM Support Ethernet Support StrongARM Core
Processing Hooks NOT Implemented
1xOC-12 port or up to
4xOC-3 ports (full-duplex).
Segmentation and Re-
assembly (SAR).
ATM Adaptation Layer 5
(AAL5 with CRC-32).
IP over ATM LLC/SNAP
Encapsulation.
Routing from ATM to
Ethernet ports based on IP.
Unspecified Bit Rate
(UBR).
Full ATM VC name space.
16K Virtual Circuits (VC)
simultaneously in use.
Up to 8 100Mbps
Ethernet ports (full
duplex).
Routing from
Ethernet to ATM
ports based on IP.
RFC1812 compliance.
AAL5 Protocol data units
(PDUs) for signaling,
(ILMI, LECS, PNNI, CIP)
forwarded to the
StrongARM core.
Control Plane processing.
ATM Traffic shaping.
ATM ARP support.
Configuration Description
One ATM OC-12 port and eight
100Mbps Ethernet ports For use with the IXP1240/1250, which uses hardware CRC capability.
Four ATM OC-3 ports and eight
100Mbps Ethernet ports S imilar to the above configuration (requires the IXP1240/50), except that
it uses four OC-3 ports.
Two ATM OC-3 ports and four
100Mbps Ethernet ports
For use with the IXP1200 (which does not have hardware CRC
capability). Instead, CRC computation is performed by two microengines
(thus the reduced data rates).