|
FUNI was developed by the ATM Forum in
order to provide users with the ability to connect between
ATM networks and existing frame-based equipment (e.g., routers,
etc.). FUNI uses a T1/E1 interface and offers a relatively
easy and cost-effective method for users to take advantage
of ATM infrastructure or an ATM backbone, while not having
to replace existing equipment with more expensive ATM equipment.
The frame structure of FUNI is shown in
the following illustration:
FUNI PDU |
Flag |
FUNI header |
User SDU |
FUNI FCS |
Flag |
| |
2 |
1-n
(n<=4096) |
2
(up to 4) |
1 |
FUNI
frame structure |
The FUNI header is as follows
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
Frame address |
RSVD |
0 |
Frame address |
CN |
RSVD |
CLP |
1 |
FUNI header structure |
RSVD
Reserved bits for interface management.
These bits are set to 0 unless the frame is used for management.
Frame address
Octet 1, bits 6-3 are mapped
to the 4 LSBs of the VPI in the ATM cell header. The 4 MSBs
of the VPI are not coded in the address field. Octet 1, bits
8 and 7 and Octet 2 bits 8-5 are mapped to the six LSBs of
the VCI in the ATM cell header.
FCS
16 bit frame check sequence.
CN
Congestion notification. If the
PTI=01x in the last ATM cell composing the FUNI frame, the
CN is 1 for the FUNI frame, otherwise it is 0.
CLP
The network equipment copies
the CLP bit sent from the user equipment into the CLP bit of
all ATM cell headers constituting the FUNI frame. The CLP bit
from the network equipment to the user equipment is always
set to 0.
Interested in more details about testing
this protocol?
|
