TR TSY 000793 : ISSUE 1 REV 1

1 INTRODUCTION
    1.1 Purpose
    1.2 Scope
    1.3 The Layer 2 Model
    1.4 ISDN D-Channel Services
          1.4.1 USER DEVICE ADDRESSING SERVICES
          1.4.2 DATA LINK LAYER SERVICE
    1.5 Reference Architecture
          1.5.1 LAYER 1 ARCHITECTURES
          1.5.2 LAYER 2 ARCHITECTURES
          1.5.3 LAYER 2 TERMINATIONS IN A LOCAL AREA NETWORK
    1.6 Related Documents
    1.7 Organization of This Document
    1.8 Requirements conventions
2 FRAME STRUCTURE
    2.1 Numbering conventions
    2.2 Frame Format Types
          2.2.1 TYPE I FRAME FORMAT
          2.2.2 TYPE U FRAME FORMAT
          2.2.3 TYPE S FRAME FORMAT
    2.3 Frame Field Types
          2.3.1 FLAGS
          2.3.2 ADDRESS
                  2.3.2.1 Address Field Extension Bit
                  2.3.2.2 Command/Response Field Bit
                  2.3.2.3 Service Access Point Identifier
                  2.3.2.4 Terminal Endpoint Identifier
          2.3.3 FRAME CHECK SEQUENCE
          2.3.4 CONTROL FIELD
                  2.3.4.1 N(S) Sub-field
                  2.3.4.2 N(R) Sub-field
                  2.3.4.3 Poll/Final Sub-field
                  2.3.4.4 Supervisory Function Sub-field
                  2.3.4.5 Reserved Sub-field
                  2.3.4.6 Modifier Sub-field
          2.3.5 INFORMATION FIELD
    2.4 State Variables
          2.4.1 SEND STATE VARIABLE V(S)
          2.4.2 ACKNOWLEDGE STATE VARIABLE V(A)
          2.4.3 RECEIVE STATE VARIABLE V(R)
          2.4.4 RECOVERY STATE VARIABLE V(M)
    2.5 Frame Coding and Decoding
          2.5.1 ZERO-BIT STUFFING AND REMOVAL (TRANSPARENCY)
          2.5.2 FCS PROCESSING
          2.5.3 FRAME TYPE DECODING AND OCTET COUNTS
          2.5.4 ADDRESS DECODING
    2.6 Invalid Frames
          2.6.1 FRAME DELIMITING
                  2.6.1.1 Idle Codes
                  2.6.1.2 Flag Detection and Processing
                  2.6.1.3 Abort Code
          2.6.2 ZERO-BIT DECODING
          2.6.3 FCS CALCULATION
          2.6.4 VALID FRAME LENGTH
          2.6.5 VALID FRAME TYPE CHECK
          2.6.6 ADDRESS FIELD CHECK
          2.6.7 DLCI CHECK
                  2.6.7.1 Currently Active
                  2.6.7.2 Change to Active
                  2.6.7.3 Deactivate
3 COMMANDS AND RESPONSES
    3.1 Type I Command
    3.2 Type U Commands and Responses
          3.2.1 SET ASYNCHRONOUS BALANCED MODE EXTENDED
                  COMMAND
                  3.2.1.1 SABME Transmitted by SPCS
                  3.2.1.2 SPCS Receives SABME
          3.2.2 DISCONNECT COMMAND
                  3.2.2.1 SPCS Receives DISC
                  3.2.2.2 DISC Transmitted by SPCS
          3.2.3 UNNUMBERED INFORMATION COMMAND
                  3.2.3.1 Identity Request
                  3.2.3.2 Identity Assigned
                  3.2.3.3 Identity Denied
                  3.2.3.4 Identity Check Request
                  3.2.3.5 Identity Check Response
                  3.2.3.6 Identity Remove
                  3.2.3.7 Identity Verify
          3.2.4 UNNUMBERED ACKNOWLEDGMENT RESPONSE
          3.2.5 DISCONNECTED MODE RESPONSE
          3.2.6 FRAME REJECT RESPONSE
                  3.2.6.1 SPCS Receives FRMR
                  3.2.6.2 SPCS Transmits FRMR
          3.2.7 EXCHANGE IDENTIFICATION COMMAND/RESPONSE
                  3.2.7.1 XID format and Protocol
                  3.2.7.2 Automatic Notification
    3.3 Type S Commands/Responses
          3.3.1 RECEIVE READY COMMAND/RESPONSE
          3.3.2 REJECT COMMAND/RESPONSE
          3.3.3 RECEIVE NOT READY COMMAND/RESPONSE
4 EXCHANGE OF INFORMATION
    4.1 Unacknowledged Frame Transfer
    4.2 Acknowledged Frame Transfer
          4.2.1 INITIATING MULTIPLE FRAME OPERATION
                  4.2.1.1 SPCS Requests Multiple Frame
                            Operations
                  4.2.1.2 User Requests Multiple Frame
                            Operations
                  4.2.1.3 Checking Subscription Limits
                  4.2.1.4 Establishment Procedures
          4.2.2 INFORMATION TRANSFER DURING MULTIPLE FRAME
                  OPERATIONS
                  4.2.2.1 Transmitting I Frames
                  4.2.2.2 Receiving I Frames
                  4.2.2.3 Sending and Receiving
                            Acknowledgments
                  4.2.2.4 Receiving REJ Frames
                  4.2.2.5 Receiving RNR Frames
                  4.2.2.6 Polls
                  4.2.2.7 Link Controller Own Receiver
                            Busy Condition
                  4.2.2.8 T200 Expiration
                  4.2.2.9 Clearing Timer Recovery
          4.2.3 TERMINATION OF MULTIPLE FRAME OPERATION
                  4.2.3.1 T200 Expiration
                  4.2.3.2 T203 Expiration
                  4.2.3.3 TEI Removal
                  4.2.3.4 Layer 1 Failure
                  4.2.3.5 User-Transmitted DISC
                  4.2.3.6 User-Transmitted FRMR
          4.2.4 TEI ASSIGNED STATE
          4.2.5 LINK MONITOR FUNCTION
                  4.2.5.1 Start Timer T203
                  4.2.5.2 Stop Timer T203
                  4.2.5.3 Expiration of timer T203
5 DATA LINK CONNECTION IDENTIFIER (DLCI) MANAGEMENT
    5.1 Active DLCI Table
    5.2 SPCS TEI Management
          5.2.1 TEI Assignment Procedures
                  5.2.1.1 Identity Request
                  5.2.1.2 Identity Assigned
                  5.2.1.3 Identity Denied
          5.2.2 TEI Check Procedure
                  5.2.2.1 Query for a Specific TEI Value
                  5.2.2.2 Query for Redundant TEIs
                  5.2.2.3 Query to Perform a TEI Audit
          5.2.3 TEI Removal
          5.2.4 TEI Identity Verify
6 ERROR DETECTION AND RECOVERY
    6.1 N(S) Sequence Error
    6.2 N(R) Sequence Error
    6.3 Lost Transmitted Frames
    6.4 Frame Rejection
    6.5 Unsolicited Response Frames
7 THE SPCS LAYER 2 SYSTEM
    7.1 Specification and Description Language
          7.1.1 Layer 2 as a System
          7.1.2 States
          7.1.3 Queues
                  7.1.3.1 Awaiting Transmission Queue
                  7.1.3.2 Awaiting Acknowledgment Queue
                  7.1.3.3 Other layer 2 System Queues
    7.2 The Layer 3 Interface
          7.2.1 Call Control Abort Signal
          7.2.2 Call Control Abort Mapping Function
                  7.2.2.1 Inability to Begin Message
                            Transmissions
                  7.2.2.2 Interruption of Message
                            Transmissions
                  7.2.2.3 Failure to Recover from Timer
                            Expirations
                  7.2.2.4 Time-in-Queue Fault
          7.2.3 Model of the Interlayer Controller
    7.3 The Layer 1 Interface
          7.3.1 Status Commands
          7.3.2 Model of the Channel Controller
          7.3.3 Control of User Access
                  7.3.3.1 Link Access Authorization States
                  7.3.3.2 Changes in Link Access
                            Authorization
                  7.3.3.3 Updating Subscription Counters
    7.4 The Signaling Address Controller
    7.5 The Link Controllers
8 SERVICES
    8.1 ISDN Exchange Access Signaling Service
          8.1.1 Number of Signaling Links (nsl)
          8.1.2 Fixed Link Option (flo)
          8.1.3 Dynamic Links (dyn)
          8.1.4 Packet Links (pal)
          8.1.5 Signaling Parameter Negotiation (spn)
          8.1.6 Diagnostic Error Signaling (des)
          8.1.7 Automatic Notification (anot)
    8.2 Timers
          8.2.1 Timer T200
          8.2.2 Timer T201
          8.2.3 Timer T203
          8.2.4 Timer TM20
    8.3 Counters
          8.3.1 Retry Counter (RC) and N200
          8.3.2 Octet Counter (OC) and N201
          8.3.3 Number of Outstanding I Frames (OI) and k
          8.3.4 Number of links (nnol) and Number of
                  Signaling Links
          8.3.5 Number of User-Assigned Call
          8.3.6 - 8.3.9
9 REFERENCES

Describes Bellcores view of the generic requirements for a local Stored Program Controlled Switch (SPCS). SPCS is capable of offering data link layer (Layer 2) user access to an ISDN on the D-Channel of a Basic or Primary rate interface. Each ISDN exchange access interface requires a D-Channel on which SPCS gives priority to voice and data call control signaling. The SPCS D-Channel is functionally organized into layers, consisting of the physical layer (Layer 1), the data link layer (Layer 2), and the network layer (Layer 3). This document focuses on generic SPCS requirements for the D-Channel and Layer 2 only.