OSI/AS Configuration and Management Manual

OSI/AS Subsystem Description
OSI/AS Configuration and Management Manual—424119-001
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NSP Process: X25AM
NSP Process: X25AM
X25AM manages a connection through an internal subdevice. The TSP process adds
subdevices to X25AM using internal names that are different from those used by the
upper layers. Subdevices are added at connection time; each subdevice is assigned a
unique logical channel number (LCN) for each connection. X25AM acts as the service
provider for the TSP process, and provides services to the Network Layer.
Downward Information Flow
X25AM accepts primitives from the TSP process in file-system calls such as READ,
WRITE, and CONTROL. The following PTrace example shows a CONTROL request to
subdevice number 1. This is a subdevice that TSP has opened:
X25AM is responsible for establishing the connection, managing the circuit, and
sending and receiving data in packets in accordance with the X.25 protocol.
The following PTrace example shows an incoming call request (formatted) packet:
The incoming call request packet in the preceding sample trace was received from
X25AMs level 2, which is an LAPB protocol. All X.25 packets are transferred to and
from the Data Link Layer as LAPB information frames. The following PTrace example
shows an LAPB information frame:
Upward Information Flow
X25AM receives incoming packets and returns them to the TSP process in file-system
calls. When the subdevice detects an error, it returns an error code, such as error 140.
State Machine
The X.25 protocol is described in the CCITT X.25 1980 and 1984 recommendations.
The state tables specified for Layer 2 and Layer 3 ensure that data is transferred reliably
between networks.
02:48:44:270 >000.010 #31 L4^LCB^In
SDN #001/%001
Control LCB 77BF P1-6 %144000 %000026 %000000 %000013 %000020 %000000
02:48:44:600 >000.000 #43 L3 Pkt In
SDN #000/%000 LEN #0024 GFI(0001) MOD8 LGN/LCN $0FE
Call^req
000: 10FE 0BCC 4083 3311 1101 4083 3322 2201
008: 0343 0202 0000 0000
02:48:44:600 >000.000 #39 LAPB In
A/C($012E) DCE IFRAME P=0 N(S)=7 N(R)=1
000: 012E 10FE 0BCC 4083 3311 1101 4083 3322
008: 2201 0343 0202 0000 0000