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What is Software Architecture AN-RAX?

Software architecture is completely modular. It comprises of entities that operate in a layered environment, with physical, data link and network layers, to support the communication between AN-RAX and LE. Most of the entities use an FSM based approach. The coding is done in the C language. The entire software runs on the ARC card. The other processor-based card in the system is the RTC card. The software for this card is reused from the RAX product.

• SOFTWARE ENTITIES
  

  Maintaining modularity, the architecture has been conceived as comprising of two major modules: the V5 Module and the AN Module.

V5 MODULE
This comprises of entities/processes which handle the V5 protocol towards the Local Exchange(LE).

• i) Core Protocols
  It consists of the processes for PSTN protocol (PSTNT), CONTROL protocol (CPT), Bearer Channel Connection (BCC), LINK CONTROL protocol (LCP), and PROTECTION protocol (PPT).
• ii) System Management /Access Initialisation Task (AIT) It consists of the system level general management and the layer 3 management for the V5 protocols.

AN MODULE
This comprises of entities/processes which handle the product-related features.

• Maintenance Software / Fail-Safe Task (FST)
  It implements strategies for providing fail-safe services to the ANRAX subscribers.
• Man-Machine Interface / Operation Administration Task (OAT)
  The user interface is provided through an RS232 interface. The MMI provides an interface for the user to configure the V5 interface and perform the maintenance functions on subscriber ports and V5 links.
• Port tester Task (PTT)
  This process handles the RTC (tester card) communication protocols and port testing.
• SPC Interface Task (SPT)
  This process handles the interrupts and subscriber events reported by SPC/ISP card from the line side. It also handles the ring cadence and metering pulse feeding.
• Layer 2 management/Data Link Protocol Task (DLPT)
  Manages the data link entity. It also acts as a message parser and distributor for the ANRAX system for a message received on V5 links and IPCP links. The functionality regarding the management of V5 links is shared with the protection protocol entity.
• Data Link Entity/Data Link Control Task (DLCT)
  It implements the data link layer functionality for both: V5 protocol and Interprocessor communication within ANRAX. It handles the error correction and ensures reliable communication over physical channels.
• Driver/Serial Communication Control Task (SCCT) It is the interface between the Data Link Entity and Communication channel.
• Real-time Operating System (XRTS)
  The operating system is real-time, based upon Xinu Operating System (Xinu Real-Time OS).
• Database Task (DBT)
  This process takes care of maintaining and updating the V5, system and port related data in both active and standby ARCs. Any status change in the active card is immediately updated to standby.
• Software Architecture AN-RAX Software Architectur
• e AN-RAX

• MESSAGES AND THEIR FLOW IN V5 PROTOCOL Software Architecture AN-RAX
  • V5 Messages
    As we know, V5 protocol is `message-based’, i.e., any information between LE and AN is exchanged through messages available in different protocols. The list of messages available in different protocols is given below.

  Software Architecture AN-RAX, Software Architecture AN-RAX

• PSTN Protocol

i) Establish

ii) Establish Ack

iii) Signal

iv) Signal Ack

v) Status

vi) Status Enquiry

vii) Disconnect

viii) Disconnect Complete

• Control Protocol

i) Port Control

ii) Port Control Ack

iii) Common Control

iv) Common Control Ack

• BCC Protocol

i) Allocation

ii) Allocation Complete

iii) Allocation Reject

iv) De-allocation

v) De-allocation Comp

vi) De-allocation Reject

vii) Audit

viii) Audit Complete

ix) Protocol Error

• Link Control Protocol

i) Link Control

ii) Link Control Ack

• Protection Protocol

i) Switch Over Request

ii) Switch Over Ack

iii) Switch Over Com

iv) Switch Over Reject

v) Protocol Error

vi) Reset SN Com

vii) Reset SN Ack

• Message Flow
  Message flow between AN and LE is explained in a sec. 5.4.7.1 & 5.4.7.2 with the help of examples. Further, message flows in different call scenario is given at the end of this chapter.
  • Call Initiated From LE
    On receiving a call request from the network for a particular AN port, LE feeds call routing tone to calling subscriber and proceed to get a bearer channel for this call by sending an ALLOCATION message to AN and starts a timer. After getting an ALLOCATION COMPLETE message from AN, LE sends an ESTABLISH message to AN with a cadenced ringing parameter to connect the ring to the user port and starts a timer. AN sends ESTABLISH ACK message and calls enter into the ringing phase.
    In case AN subscriber has a caller-id feature in which directory number of calling subscriber is to be sent to the user’s equipment, LE shall send ESTABLISH message to AN without a cadenced ringing parameter. LE shall send the digits in-band and thereafter send a SIGNAL message with Cadenced Ringing to AN to connect the ring to the user port. The call enters into the conversation phase when the answer is received from the AN subscriber, the answer should be communicated across the V5 interface by sending SIGNAL (Off Hook) message to the other end.

Various subscriber features can be initiated by the subscriber by doing Hook Switch Flash when the call is in the conversation phase.
If the release of the call is initiated from LE, parking tone should be fed to AN subscriber, parking tone timer shall be run at LE and disconnection from AN subscriber be awaited. AN subscriber disconnects before the expiry of parking tone timer, this indication comes in the form of SIGNAL (On Hook) message across the V5 interface. Call clearing is started by sending DEALLOCATION message and on getting DEALLOCATION COMPLETE, PSTN protocol is cleared by DISCONNECTION / DISCONNECTION COMPLETE message.

• • Call Initiated From AN
    AN on detecting an origination from the user port should send ESTABLISH message to LE. LE shall send ESTABLISH ACK message in response, gets a bearer channel by ALLOCATION/ALLOCATION COMPLETE and connect dial tone to the channel. When the answer is received from the PSTN subscriber, the call will enter into the conversation phase. For AN originated calls from subscribers with the home metering facility, metering pulses shall be reported to AN in the form of SIGNAL (Meter Pulse) message over the V5 interface.