Enterasys Networks CSX6000 - Manual (Page 250)

USER’S GUIDE
250 CyberSWITCH
X.25 R ELIABILITY , W INDOWS , AND A CKNOWLEDGMENT
X.25 S EQUENCE N UMBER R ANGE
The type of sequence numbers to be used for X.25; regular or extended. Extended sequence
numbering allows for packets to be assigned sequence numbers from 0-127 (modulo 128),
as opposed to 0-7 (modulo 8). The default value is modulo 8.
M AXIMUM W INDOW S IZE
This is the largest possible window size to be supported on any virtual circuit. The window
size is the number of frames that a DTE can send without receiving an acknowledgment.
SVCs that support window size negotiation will never allow the agreed upon window size
to exceed this value. Using modulo 128, the DTEs can send up to 127 frames without
receiving an acknowledgment. Using modulo 8, the DTEs can send up to 7 frames without
receiving an acknowledgment. The default value for both modulo 8 and modulo 128 is 2.
M AXIMUM P ACKET S IZE
This value is used to determine the maximum packet size that the system will support for
X.25 connections. When packet size negotiation is performed on SVCs, this value will be
used as the upper bound. The default maximum packet size is 128 bytes.
X.25 Q UALITY - OF -S ERVICE F ACILITIES
The X.25 Quality-of-Service Facilities apply only to SVCs. The first three configuration elements are
for SVCs that support negotiation.
M AXIMUM T HROUGHPUT C LASS
This value is used to determine the maximum throughput class that the system will
support for X.25 connections. Throughput describes the maximum amount of data that can
be sent through the network, when the network is operating at saturation. Factors
influencing throughput are line speeds, window sizes, and the number of active sessions
in the network. When throughput class negotiation is performed on SVCs, this value will
be used as the upper bound. The default value is 19,200 BPS.
F LOW C ONTROL N EGOTIATION
This configuration element specifies whether Flow Control Negotiation is to be supported
for SVCs (negotiation is not performed on PVCs). If Flow control negotiation is supported
for SVCs, the window and packet sizes can be negotiated between DTEs on a per-call basis.
As a default, this facility is not supported.
T HROUGHPUT C LASS N EGOTIATION
This configuration element specifies whether Throughput Class Negotiation is to be
supported for SVCs (negotiation is not performed on PVCs). This facility allows the
throughput rates to be negotiated between DTEs on a per-call basis. As a default, this
facility is not supported.
Note: The next 6 items configured for the X.25 Quality of Service Facilities are the non-
standard default parameters for SVCs that do not support negotiation. These pa-
rameters are used on SVCs that do not use the standard X.25 values, but also do
not support any facility negotiation.