X25AM Programming Manual

Introduction
X25AM Programming Manual—527201-001
1-15
Packet-Layer Subscription Parameters
Window Frame Size (k)
The variable “k” refers to the window frame size, that is, the number of I-frames that
can be sent without being acknowledged. This is also called frame buffering. The
available values are generally from 1 to 7. HP recommends using the network value.
X25AM does not support values greater than 7. X25AM supports LAPB-Extended,
which may allow a value greater than 7, depending on your network.
Packet-Layer Subscription Parameters
Packet-layer subscription parameters include delivery bit modification, extended packet
sequencing, PVC and SVC logical channels, and nonstandard defaults.
Delivery (D) Bit Modification
This facility can be used but is generally not useful, as X25AM does not normally wait
for window rotation before signaling to the application that a WRITE has completed.
Applications using the D bit procedure must use PTP mode 2 to set the D bit in data
packets. PTP mode 2 applications can also negotiate the use of the D bit. X25AM
always rotates the window as soon as possible when a data packet is received with the
D bit set to one.
Extended Packet Sequencing
X25AM can be configured for modulo 8 or modulo 128 packet sequence numbering.
Logical Channels for PVCs and SVCs
X25AM supports up to 510 logical channels. These channels can be used for any
combination of PVCs and SVCs, up to the maximum supported for that RVU. All logical
channels used for SVCs must be one-way incoming, one-way outgoing, or two-way
channels.
Nonstandard Default Packet Size
X25AM can be configured for nonstandard packet sizes of 16 to 4096 bytes. Refer to
Per Call Facilities on page 1-16.
Nonstandard Default Throughput Class
The default throughput class for X25AM is 4. A system generation program X25AM
modifier (THRUPUT) can be used to specify a different class. X25AM subdevices can
be configured to negotiate throughput on a per call basis. Refer to Per Call Facilities on
page 1-16.