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Serial Interface 219
HDLC/SDLC Mode
Transparent HDLC mode is used for point-to-point HDLC connections across the
ATM network. No service-based encapsulation other than AAL5 is needed. All
packets are terminated and SAR’d to a single VP/VC in the ATM network.
Transparent mode functionality is best implemented with a PRBS type of pattern
included in a sequence of frames. The TTC Firebird V.35 frame relay interface
provides that simple capability.
When using transparent HDLC mode, you set the following parameters:
n Minimum number of flags between HDLC frames
n CRC type
The PathBuilder S330/S310 will SAR AAL5 and map HDLC/SDLC frames onto an
ATM VCC. You could use the HDLC service for router to router and X.25 to X.25
links. You could use the SDLC service for IBM FID2 3270 SNA Peripheral or IBM
FID4 372X SNA Backbone.
Figure 160 shows HDLC/SDLC applications.
You should disable NRZI on the FEP (i.e., IBM 3745). NRZI is commonly used when
the FEP is connected to DSUs over a non-digital line. The PathBuilder S330 does
not require NRZI to be enabled.
Figure 160 HDLC/SDLC Applications
Frame Relay Mode
Frame relay mode is used to terminate a frame relay router, across the ATM
network, for example. This protocol mode converts the frame relay DLCI to a
VP/VC ATM connection.
A PathBuilder S330/S310 provides two interworking features to interconnect a
Frame relay network with an ATM network:
n Service Interworking
n Network Interworking
HDLC
X.25
FID 4
FID 2
3270
3
7
2
5
X.25
X.25
Host
3
7
2
5
X.25
P
AD
HDLC
FID 4
FID 2
SDLC
SDLC
S
N
A
PathBuilder
S330/S310
PathBuilder
S330/S310