MT92220BG Zarlink Semiconductor, MT92220BG Datasheet - Page 58

• Manufacturer Part Number: MT92220BG
• Description: Description = 1023 Channel Voice Over IP/AAL2 Processor ;; Package Type = Epbga ;; No. Of Pins = 608
• Manufacturer: Zarlink Semiconductor

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When the correct node associated with the packet is found, the post-search confirmation structure will indicate what
course of action to take concerning the packet. It may indicate to route the packet to the Packet Disassembly, to the
RX CPU buffer or onto network port A or B. It may also indicate that another look-up needs to be performed, this
time using a different look-up profile. The process then begins anew using the new profile
Other look-ups can take place in the binary tree: for example, ELAN-IDs contained in LANE v2 packets can be
looked up, along with the Flow Table Pointer. A CRC will be performed on the fields, a 60-bit key will be generated,
and a post-search entry will be obtained. This entry can be used to modify the Flow Table Pointer and the parsing of
the packet will then continue with the new pointer.
MPOA tags and MPLS labels can also be searched for in the binary tree and post-search structures: apart from
modifying the Flow Table Pointer, these searches are also used to identify the nature of the protocol above MPOA
or MPLS. When packets are first assembled in the AAL5 reassembly structure, the nature of the protocols above
these two are tagged in the fields MPLS_IP and MPOA_IP. When an MPOA or MPLS header is found in the packet
and the nature of the following protocol has not been established, this header is looked-up along with the Flow
Table Pointer. The resulting structure will identify the following protocol and may also change the Flow Table
Pointer. The packet analysis then strips the MPOA or MPLS header off and continues the binary tree search with
the following protocol.
To demonstrate the operation of this system, here is a simulation of the arrival of a packet in the packet identifier
module. The packet arrives from RX link A and is an IPv6 voice packet carrying UDP and RTP. When parsed by the
look-up module, its version number is established (6) and its IP header is searched until the protocol being carried
(UDP) is found. The packet is then classified as an IP/UDP packet and routed using the default note which points to
the Initial Search Structure for that type of packet, in this occurrence the structure at address 1200h.
The Initial Search Structure indicates that a binary tree search should be performed using a default profile #5. The
profile entry is consulted and it indicates which fields should be used in the binary tree search through a series of
mask fields. The mask fields depend on the default configuration of the packet type: for an IPv6 packet with UDP,
the default headers are the Source and Destination IP address, Source and Destination UDP port and RTP
Header CRC key
Profile
LA
RA
First Post-Search
Confirmation
Structure Address
+C
+0
+4
+8
LA [20] RA [20]
Field
b31
b30
b29
b28
b27
Bits 55:48 represent a CRC-8 of the initial identification key. Bits 47:32 represent a
CRC-16 of that same key, and bits 31:0 represent a CRC-32 of that same key.
Profile number being used to perform packet search. The profile number and header CRC
key, between them, represent the 60-bit identification key used to search for the packet.
Address of left node below the current node. The left node will contain an identification
key that is smaller than the current one.
Address of right node below the current node. The right node will contain an identification
key that is larger than the current one.
Indicates the address of the post-search confirmation structure that will be used to route
this packet if it matches the identification key.
b26
Profile
Left Address [19:4]
b25
b24
b23
b22
Table 18 - Fields and Description
b21
b20
Figure 31 - Binary Tree Node
b19
Zarlink Semiconductor Inc.
Header CRC Key [31:0]
b18
b17
b16
b15
First Post-Search Confirmation Structure Address [24:7]
b14
Header CRC Key [55:32]
Description
b13
b12
b11
b10
Right Address [19:4]
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0