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Frame Relay to ATM Network and Service Interworking 12-9
AIT/BTM Interworking and the ATM Protocol Stack
Figure 12-8 Protocol Stack Operation
S5242
FLAG
DLCI upper
DLCI lower
Q.922 Fr Rly PDU
FECN
Data field
BECN DE EA
CR EA
FLAG
87654321
VPI
HCF
00 = STI
5-byte
header
VPI
VCI
Congestion
control
(bursty
data)
Re-
served
CLP
(cell
loss
prior-
ity)
PTI
(payload type
indicator)
ATM PDU
(adds in 5-byte
header)
FFCI = ForeSight
forward
congestion
indicator
FFCI
Payload class
VCI
HEC
48 data byte
87654321
FLAGDLCI upper
DLCI lower
FR-SSCS PDU
CPCS PDU
SAR PDU
FECN
Data
AAL5 PDU payload
N byte (1-65535)
Length of user data
2 byte
CRC32
4 byte
PAD
0-47 byte
48-byte PDU 48-byte PDU 48-byte PDU
BECN DE EA
CR EA
Trailer
87654321
...........
...........
Physical
(line framing, coding,
physical interface, etc.)
53-byte
ATM cell
53-byte
ATM cell
53-byte
ATM cell