CHAPTER 3 FUNCTIONAL OUTLINE
PRELIMINARY
NEC confidential and Proprietary
58
3.2 ATM
Function
The
µ
PD98413 can map ATM cells into a SONET/SDH payload. The mapping of ATM cells into a SONET
payload is shown below.
Figure 3-14. Mapping of ATM cell
Figure 3-15 shows the format of the ATM cell (user network interface). An ATM cell consists of a 5-byte header
and 48-byte payload data. In the case of the user network interface (UNI), the header contains a GFC field (4 bits).
In the case of the network node interface (NNI), however, the corresponding field is defined as a VPI field that is 12
bits long.
Figure 3-15. Structure of ATM Cell
User network interface (UNI)
Network node interface (NNI)
CLP
8 7 6 5 4 3 2 1
HEC
VCI
PTI
GFC
VPI
VPI
Payload data
48 bytes
T
ransm
ission
se
q
uence
CLP
8 7 6 5 4 3 2 1
1
2
3
4
5
6
7
8
9
10
.
.
.
.
.
53
HEC
VCI
PTI
VPI
Header
Payload data
48 bytes
GFC: Generic flow control
PTI: Payload type identifier
VPI: Virtual path identifier
CLP: Cell loss priority
VCI: Virtual channel identifier
HEC: Header error control
SO H
POH
Fixed Stuff
Payload
ATM cell
ATM cell
ATM cell
ATM cell
Содержание NEASCOT-P65
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