MT92220 Zarlink Semiconductor, MT92220 Datasheet - Page 63

• Manufacturer Part Number: MT92220
• Description: 1023 Channel Voice Over IP/AAL2 Processor
• Manufacturer: Zarlink Semiconductor

Data Sheet
7.0
This chapter describes the treatment of AAL2 CPS-packets and cells as they are transmitted and received from the
network.
7.1
Once AAL2 CPS-packets are assembled, they are shipped to the AAL2 cell assembly module, which is responsible
for the concatenation of separate AAL2 CPSCPS-packets into complete AAL2 cells. The AAL2 cell assembly
module then sends the cells to the TX link cell queues to be sent onto the network.
Each CPS-packet that is sent is accompanied by a descriptor. This descriptor contains a VC number, which is used
to point to an assembly structure. It also contains a time-out value: when the TDM pointer equals or exceeds this
value, the cell containing that CPS-packet must be transmitted, even if it is not complete. This time-out period is
measured in frames. If a CPS-packet's time-out value is equal to the current TDM pointer, then a cell will be
assembled immediately with the CPS-packet in it (i.e. instead of waiting until the end of the frame). This ensures
that some CPS-packets may be sent "alone" in cells. AAL2 cells can also be transmitted when enough bytes have
been accumulated on a single VC to send a complete cell, in other words 47 bytes.
TDM Pointer Send
PS
V
SN
Bytes in cell
+1C
+10
+14
+18
+C
+0
+4
+8
b31
Field
TX/RX AAL2 VC Treatment
TX AAL2 VC Treatment
b30
b29
b28
b27
b26
When the “Bytes in Cell” field is non-zero (i.e. bytes are pending transmission the
current cell), this field indicates at what time (in frames) must this cell be sent out in
order to avoid adding too much delay to the CPS-packets that are awaiting transmission.
This field is updated each time new CPS-packets is added to the current cell using the
packet’s CPS timer. This field should be initialized to zero by software.
Prevent scanning. When ‘1’, the scanning process is not allowed to send out a partially
fill cell due to the CPS timer of one of the packet within it. When ‘0’, scanning for cells
that are due for transmission occur normally for this VC.
Valid bit. When ‘0’, this structure is deemed invalid. All packets sent to it will be
discarded and scanning will not occur.
Sequence Number. This field represents the sequence number that will be sent in the
next cell. This field should be initialized to zero by software.
This field indicates how many bytes are awaiting transmission in the current cell. The
range is 0 to 46. This field should be initialized to zero by software.
TDM Pointer Send [13:0]
b25
b24
b23
b22
Table 20 - Fields and Description
b21
Figure 33 - TX AAL2 VC Structure
Cell Route
b20
ATM Header [31:0] / AAL2 VC Number [15:0]
b19
Zarlink Semiconductor Inc.
b18
Transmitted Byte Count [31:0]
Transmitted Cell Count [31:0]
b17
b16
b15
PS V
b14
Description
b13
b12
b11
b10
Pending Cell Handle [14:0]
b9
b8
b7
SN
b6
b5
b4
Bytes in Cell [5:0]
b3
b2
MT92220
b1
b0
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