cx28224 Mindspeed Technologies, cx28224 Datasheet - Page 18

• Manufacturer Part Number: cx28224
• Description: Cx28224/5/9 Inverse Multiplexing For The Atm Ima Family
• Manufacturer: Mindspeed Technologies

Introduction to IMA
1.1.1
Figure 1-3. IMA Frame; Length = 16; Number of links = 3
1-4
This cell will be in
Link 0
Link 1
Link 2
the next frame
Incoming data from the ATM layer (which doesn't
know that the data is being split into frames)
ATM
x
ATM
36
IMA Framing
Data output into an IMA frame
ATM
15
ATM payload;
cell x in the sequence
34
F
F
ATM
35
ATM
ATM
ATM
14
The IMA protocol employs a simple frame structure as shown in
consists of a single IMA overhead cell (ICP) and M – 1 ATM layer cells, where M is
the IMA frame length. Valid frame lengths are 32, 64, 128 (default), or 256. This
example shows a group composed of three links and an IMA frame length of 16. (An
invalid frame length of 16 is used for brevity, the default frame length is 128.)
Since the ATM layer data rate is often less than the bandwidth available across the
links in the IMA group, the IMA engine generates IMA Filler cells when no ATM
layer cells are available. (The IMA Filler cells perform the same basic function as Idle
cells in a non-IMA ATM system and are discarded by the IMA receiver.)
The IMA frame rate is intentionally set slightly below the available payload
bandwidth of the IMA link. To allow for timing differences between the links in a
group, the IMA standard requires that the system insert an extra ICP cell every 2049
31
32
33
ATM
34
ATM
ATM
ATM
13
28
29
30
ATM
33
ATM
ATM
ATM
12
25
26
27
ATM
Mindspeed Technologies
32
ATM
ATM
11
23
24
F
...
ATM
ATM
10
21
22
F
ICP
Delay between the cells arrival at
n
Always at least 1 ICP cell per frame
the IMA device results in Filler
1 IMA frame
ATM
ATM
19
20
9
F
This link selected as the Timing Reference
Link, (TRL), thus first ICP starts at 0.
M = 16
IMA control Protocol Cell
IFSN = n
ATM
ATM
ATM
5
ICP
17
18
8
3
cells being inserted
ATM
ATM
ATM
ATM
4
14
15
16
7
ATM
ATM
3
13
6
F
F
ATM
ATM
ATM
™
2
ICP
11
12
5
3
ATM
ATM
ATM
10
4
8
9
ATM
1
ATM
ATM
3
F
6
7
ATM
F
0
ATM
ATM
ATM
2
3
4
5
ATM
Filler cell
ATM
Figure
x
1
F
F
2
CX28224/5/9 Data Sheet
This cell was in the
previous frame
ATM
ATM
ICP
0
3
0
1
28229-DSH-001-D
1-3. It
500027_067