ISDN Datasheet, PDF (10/14 Pages) Texas Instruments – ISDN Basic Rate Interface Software for the HPC16400E High Performance Data Communications Microcontroller

2 0 Functional Description (Continued)
The Layer 3 Controller Task supports all the Network Layer
Peer-to-Peer messages defined in the CCITT Specification
Q 931 i e
 Call Establishment and Clearing Messages
ALERT
Alerting
2 4 2 3 Call Status And Notification
The Network can request the status of a network connec-
tion at any time via the USER INFO NOTIFY and STATUS
Commands The information includes Service Validation
and Channel Configuration
CALL PROC
Call Proceeding
2 4 2 4 Layer 3 Protocol Execption Management
CONN
CONN ACK
INFO
PROG
SETUP
Connect
Connect Acknowledge
Information
Progress
Setup
The Layer 3 Controller is responsible for handling excep-
tions to the Network Control Protocol The primary Layer 3
Controller Task protocol exception is the expiry of the Layer
3 timer Such an exception requires the retransmission of
the particular command and may prompt a message to the
Management Entity Task
SETUP ACK
Setup Acknowledge
2 4 2 5 Timer Support
DISC
Disconnect
The Layer 3 Controller supports the following system timers
REL
Release
REL COM
Release Complete
 Call Suspension and Resumption Messages
RESUME
Resume
RESUME ACK Resume Acknowledge
RESUME REJ Resume Reject
SUSPEND
Suspend
te ^{SUSPEND ACK Suspend Acknowledge}
SUSPEND REJ Suspend Reject
 Miscellaneous Messages
NOTIFY
Notify
STATUS
Status
STATUS EN
Status Enquiry
le ^USERINFO
User Information
2 4 2 1 Call Establishment And Clearing
The Layer 3 Controller Task’s primary responsibility is to
establish and clear user network connections on available
bearer channel facilties The Q 931 CCITT Specifications
include Call Establishment and Clearing of both circuit-
switched and packet-switched calls Initially the HPC ISDN
o _{Software Package only supports circuit-switched call proce-}
dures on Basic Rate Interface (BRI) Bearer Channels The
Layer 3 Controller Task is responsible for Call Reference
assignment and maintenance The Layer 3 Controller Task
s ^{supports Call Establishment using both the Overlap and}
Non-Overlap (enbloc) addressing modes
The procedure for establishing and clearing network con-
nections is defined in CCITT Specification Q 931 It is impor-
tant to note that the Layer 3 Controller Task maintains an
b ^{associated state block for each network connection Primi-}
tive mail messages arriving at the Layer 3 Controller Task
will be interrogated to determine which network connection
is to receive the mail The mail message is processed de-
pending on the state of the network connection This pro-
cessing typically includes the transmission of a Primitive to
another Layer Task and the appropriate update of the net-
O ^{work connection state block}
per CCITT Specification Q 931
T303 SETUP ACK Timer
T305 DISCONNECT ACK Timer
T308 RELEASE ACK Timer
T313 CONNECT ACK Timer
2 4 2 6 SDL Updates
The Layer 3 Controller Task very closely follows the SDL
procedures illlustrated in CCITT Specification Q 931 with a
few enhancements These enhancements are listed here
and fully defined in the Software User’s Manual
a Three new SDL States have been added to accommo-
date establishing the Data Link corresponding to a partic-
ular CES The new states are
 IDLESTATE
 RELEASEWAIT
 ESTABLISHWAIT
b The Q 931 NULLSTATE SDL now accepts a new com-
mand CCBROADCASTRESP This command is sent
from the Call Control Task to allow transistion from the
NULLSTATE(0) to the CALLPRESENT State(6) during a
Network Originated call via the Broadcast mechanism
2 5 APPLICATION TASKS
The Application Tasks are very dependent on both the ter-
minal equipment configuration and the far-end Network En-
tity software implementation The HPC ISDN Software
Package includes two sample Application Tasks the Dem-
onstration Call Control Task and the Management Entity
Task Both of these tasks can be replaced or updated when
ported to a particular application These tasks are included
in the HPC ISDN Software Package primarily to verify the
operation of the OSI Layer Protocol Tasks and the HPC
Device Drivers
2 5 1 Demonstration Call Control Task
The Demonstration Call Control Task is closely coupled to
the specific facilities of an application The interaction be-
tween the Layer 3 Controller Task and Call Control is de-
fined in CCITT Specification Q 931 In the HPC ISDN Appli-
2 4 2 2 Call Suspension And Resumption
cation the Call Control Task communicates with the Layer 3
Call Suspension (SUSPEND) requires that the Bearer Chan-
nel facility and the Call Reference for a call be temporarily
relinquished The network connection is left intact but in the
suspend state The RESUME command reactivates the call
by obtaining a Bearer Channel facility and establishing a
new Call Reference The Suspend function is somewhat
Controller Task and the Tracer Task The availability of two
circuit switched voice bearer channels is simulated in the
Call Control Task The Call Control Task sends standard
Terminal Equipment prompts and messages to the Tracer
Task where they are displayed on a UART driven CRT The
Call Control Task has the following responsibilities
analogous to the call HOLD feature
 B Channel Resource Management
9