Intel IXP1200 manual IP Lookup Table, ATM to Ethernet Processing Steps

IXP1200 Network Processor Family ATM OC-3/12/Ethernet IP Router Example Design

syndrome is updated appropriately. The VC Table Entry also contains an AAL type field. Currently, this example design supports only classical IP over ATM, where the AAL type can be either 0 or 5. A value of 0 indicates that the VC is not open, so any cell received on that VC is immediately discarded.

The LLC/SNAP field specifies the protocol type. Currently, the only valid value is 0x AA AA 03 00 00 00 08 00 (classical IP over ATM). While this implementation consumes and produces just one valid LLC/SNAP pattern, this pattern is not hard-coded. The LLC/SNAP bits are included in the IP route table entry, as well as the VC lookup table. This is to make it easy to modify the design, not only support a different LLC/SNAP pattern, but also to be able to support different valid patterns for each VC.

2.4.1.2IP Lookup Table

Each PDU contains an IP header in its first cell. Therefore, a single IP lookup is performed for each PDU, regardless of the number of cells in the PDU.

Figure 10. ATM to Ethernet Processing Steps

SDRAM

Check CRC

Packet Buffer

ATM PDU on Rx Port

on AAL-5 PDU

Cell N

7

(40 Bytes)

Ethernet PDU on Tx Port

1

Receive

Cell 1

ATM Cell

If end of PDU

Transmit 10

(48 Bytes)

ATM

LLC

IP

Payload

ATM

PAD

CLP

UU

LEN

CRC

MPKT

Hdr

Hdr

Hdr

Hdr

5

Cell 0

(48 Bytes)

		Move		Ether
6		payload		Hdr
Check		to buffer		IP Payload
length
8		7
Strip	Check
AAL-5	CRC
trailer				Build MPKT,
	IP look-up		9
3				add Ethernet
IP	on first cell			header on first
	Route Table			MPKT
Lookup
IP	Port	Port	Enet
Address	type	number	header
VC Lookup Table Entry			4 Locate buffer & offset

		VPI/VCI	AAL	LLC/SNAP	Buffer	Buffer base	CRC-32
VC Look-up check	2		type	header	offset	address	Residue
LLC/SNAP header

on first cell

A9638-01

18 Application Note

Modified on: 3/20/02,