Skip to content

SINTRAN III Deep Dive: Architecture, Scheduling, and Network Operations

A Comprehensive Technical Guide for System Architects and Advanced Operators

Table of Contents

  1. SINTRAN III Architecture Overview
  2. Interrupt System and Hardware Levels
  3. Process Scheduling and Execution
  4. ND-500/ND-100 Dual Processor Architecture
  5. Memory Management and Page Tables
  6. Complete System Setup and Configuration
  7. Process and Performance Monitoring
  8. COSMOS and XMSG Network Architecture
  9. HDLC Configuration and Setup
  10. Network Debugging and Troubleshooting

SINTRAN III Architecture Overview

High-Level System Architecture

graph TB
    subgraph "Hardware Levels (ND-100 CPU)"
        L15[Level 15: Unused]
        L14[Level 14: Internal Interrupts<br/>Power Fail, Page Fault, MPV]
        L13[Level 13: Real-Time Clock]
        L12[Level 12: Input Devices]
        L11[Level 11: Mass Storage]
        L10[Level 10: Output Devices]
        L9-6[Levels 9-6: Unused]
        L5[Level 5: XMSG Communication]
        L4[Level 4: INBT/OUTBT<br/>Byte I/O]
        L3[Level 3: Monitor Kernel<br/>Segment/Time/I/O Management]
        L2[Level 2: Unused]
        L1[Level 1: RT Programs<br/>Background Processor]
        L0[Level 0: Idle DUMMY]
    end

    subgraph "Page Tables"
        PT0[Page Table 0<br/>SINTRAN Resident<br/>SINTRAN Swapping<br/>Window Pages]
        PT1[Page Table 1<br/>RT Programs<br/>RTCOMMON]
        PT2[Page Table 2/3<br/>Background Users<br/>Special Applications]
    end

    subgraph "Protection Rings"
        R2[Ring 2: System]
        R1[Ring 1: Shared]
        R0[Ring 0: User]
    end

    L14 --> L3
    L13 --> L3
    L12 --> L11
    L11 --> L10
    L10 --> L4
    L4 --> L3
    L3 --> L1
    L1 --> L0

    PT0 -.Memory Mapping.-> R2
    PT1 -.Memory Mapping.-> R1
    PT2 -.Memory Mapping.-> R0

System Components Interaction

graph LR
    subgraph "User Space"
        U1[User Programs]
        U2[Application Programs]
    end

    subgraph "RT Programs Level 1"
        BAK[BAKxx<br/>Background Terminals]
        BCH[BCHxx<br/>Batch Processors]
        TAD[TADxx<br/>Network TADs]
        RWRT[RWRTxx<br/>I/O Drivers]
        CUSTOM[User RT Programs]
    end

    subgraph "Monitor Level 3"
        KERNEL[SINTRAN Kernel]
        SEGMENT[Segment Manager]
        FILESYS[File System]
        TIMER[Time Manager]
    end

    subgraph "Device Drivers Levels 10-13"
        DISK[Disk Drivers L11]
        INPUT[Input Drivers L12]
        OUTPUT[Output Drivers L10]
        CLOCK[Clock Driver L13]
    end

    U1 --> BAK
    U2 --> BAK
    BAK --> KERNEL
    BCH --> KERNEL
    TAD --> KERNEL
    KERNEL --> SEGMENT
    KERNEL --> FILESYS
    KERNEL --> TIMER
    KERNEL --> RWRT
    RWRT --> DISK
    RWRT --> INPUT
    RWRT --> OUTPUT
    CLOCK --> TIMER

Interrupt System and Hardware Levels

ND-100 Interrupt Architecture

SINTRAN III's efficiency stems from using the ND-100's 16 hardware interrupt levels. Each level has its own complete register set, enabling context switches in only 0.9 microseconds.

graph TD
    subgraph "Priority Interrupt System"
        PIE[PIE Register<br/>Priority Interrupt Enable<br/>16 bits - Program controlled]
        PID[PID Register<br/>Priority Interrupt Detect<br/>16 bits - HW/SW controlled]
    end

    subgraph "Interrupt Determination"
        AND[AND Operation]
        HIGHEST[Highest Priority<br/>Level Selection]
    end

    subgraph "Internal Interrupt Enable"
        IIE[IIE Register<br/>Bits for specific interrupts:<br/>POW MC MPV PF II Z PI IOX PTY MOR]
    end

    PIE --> AND
    PID --> AND
    AND --> HIGHEST
    IIE -.Controls Level 14.-> PID

    HIGHEST --> ACTIVE[Active Interrupt Level]

Interrupt Level Allocation

Level Function Priority Usage
15 Unused Highest Reserved
14 Internal Interrupts Very High Monitor calls, Page faults, Memory violations, Power fail
13 Real-Time Clock High System timing, Time-slicing
12 Input Devices High Terminal input, Card readers
11 Mass Storage High Disk I/O operations
10 Output Devices Medium-High Printers, Terminal output
9-6 Unused Medium Available for expansion
5 XMSG Medium Network message passing
4 Byte I/O (INBT/OUTBT) Medium-Low Character-level terminal I/O
3 SINTRAN Monitor Low-Medium Kernel, Segment mgmt, File system
2 Unused Low Reserved
1 RT Programs Very Low Background processor, All RT programs
0 Idle Lowest DUMMY idle process

Internal Interrupt Types (Level 14)

graph TB
    L14[Level 14 Activated]

    L14 --> IIC[IIC Register<br/>4-bit Interrupt Code<br/>Identifies Source]

    IIC --> MC[Bit 1: Monitor Call<br/>User→System transition]
    IIC --> MPV[Bit 2: Memory Protect Violation<br/>Ring/Permission violation]
    IIC --> PF[Bit 3: Page Fault<br/>Page not in memory]
    IIC --> II[Bit 4: Illegal Instruction]
    IIC --> Z[Bit 5: Error Indicator]
    IIC --> PI[Bit 6: Privileged Instruction<br/>User tried system instruction]
    IIC --> IOX[Bit 7: IOX Error<br/>No device response]
    IIC --> PTY[Bit 8: Memory Parity Error]
    IIC --> MOR[Bit 9: Memory Out of Range]
    IIC --> POW[Bit 10: Power Fail Interrupt]

    MC --> L3A[Processed by Monitor<br/>Level 3]
    MPV --> L3A
    PF --> L3A
    II --> RTERR[RTERR RT Program<br/>Error logging]
    Z --> RTERR
    PI --> RTERR
    IOX --> RTERR
    PTY --> RTERR
    MOR --> RTERR
    POW --> PWRFAIL[Power Fail Handler<br/>Save state, Battery mode]

Process Scheduling and Execution

RT Program Scheduling

RT programs on Level 1 use a priority-based execution queue. Unlike time-sharing background programs, RT programs have priority levels and run until they voluntarily wait or are preempted by higher-priority RTs.

graph TB
    subgraph "RT Execution Queue (Level 1)"
        direction TB
        DUMMY[DUMMY - Priority 0<br/>Idle Process<br/>ALWAYS READY]

        subgraph "System RT Programs"
            STSIN[STSIN<br/>System Initialization]
            RWRT[RWRTxx<br/>I/O Drivers]
            TIMRT[TIMRT<br/>Device Timeouts]
            RTERR[RTERR<br/>Error Handler]
            FIXRT[FIXRT<br/>Segment Fixing]
        end

        subgraph "Background Management RT"
            BAK[BAKxx<br/>Terminal Backgrounds]
            BCH[BCHxx<br/>Batch Processors]
            TAD[TADxx<br/>Network TADs]
        end

        subgraph "Application RT"
            XROUT[XROUT<br/>XMSG Routing]
            XTRACE[XTRACE<br/>XMSG Tracing]
            SIBAS[SIBAS<br/>Database<br/>User RT Program]
        end
    end

    subgraph "Time Slicer (RTSLI)"
        RTSLI[RTSLI RT Program<br/>Adjusts Background Priorities<br/>Every Time Slice]
    end

    subgraph "Clock Interrupt"
        CLK[Level 13 Clock<br/>100-200 Hz]
    end

    CLK -.Triggers.-> RTSLI
    RTSLI -.Modifies.-> BAK
    RTSLI -.Modifies.-> BCH

    SIBAS -.Higher Priority.-> BAK
    BAK -.Higher Priority.-> DUMMY
    BCH -.Same/Lower Priority.-> BAK
    RWRT -.Higher Priority.-> SIBAS

Priority Levels in RT Programs

graph LR
    subgraph "Priority Hierarchy"
        P0["Priority 0<br/>DUMMY<br/>(Idle)"]
        P1["Priority 1-10<br/>Background BAKxx<br/>Time-sliced"]
        P2["Priority 11-50<br/>Batch BCHxx<br/>Lower than interactive"]
        P3["Priority 51-100<br/>User RT<br/>Database, Custom"]
        P4["Priority 101-150<br/>System RT<br/>I/O, Timing"]
        P5["Priority 151-200<br/>Critical RT<br/>Emergency only"]
    end

    P0 --> |Preempted by| P1
    P1 --> |Preempted by| P2
    P2 --> |Preempted by| P3
    P3 --> |Preempted by| P4
    P4 --> |Preempted by| P5

Background Process Time-Slicing

sequenceDiagram
    participant CLK as Clock (L13)
    participant RTSLI as RTSLI Time Slicer
    participant BAK1 as BAK01 (Pri 10)
    participant BAK2 as BAK38 (Pri 5)
    participant BAK3 as BAK39 (Pri 10)
    participant DUMMY as DUMMY (Pri 0)

    Note over CLK: Every 0.02 seconds
    CLK->>RTSLI: Clock interrupt
    activate RTSLI

    Note over RTSLI: Rotate priorities
    RTSLI->>BAK1: Priority 10→5
    RTSLI->>BAK2: Priority 5→10
    RTSLI->>BAK3: Priority 10→10 (unchanged)

    deactivate RTSLI

    Note over BAK2: Now highest priority
    BAK2->>BAK2: Executes until next slice

    Note over CLK: Next time slice
    CLK->>RTSLI: Clock interrupt
    activate RTSLI

    RTSLI->>BAK1: Priority 5→10
    RTSLI->>BAK2: Priority 10→5

    deactivate RTSLI

    Note over BAK1,BAK3: Now both priority 10
    BAK1->>BAK1: Executes (round-robin)
    BAK3->>BAK3: Then executes

State Transitions for RT Programs

stateDiagram-v2
    [*] --> PASSIVE: @START command

    PASSIVE --> READY: RT activated<br/>(signal received)

    READY --> EXECUTING: Highest priority<br/>in queue

    EXECUTING --> READY: Preempted by<br/>higher priority RT

    EXECUTING --> RTWAIT: Waiting for:<br/>• I/O completion<br/>• Semaphore<br/>• Message<br/>• Event

    RTWAIT --> READY: Event occurred<br/>Resource available

    EXECUTING --> PASSIVE: Program completed<br/>@ABORT command

    PASSIVE --> [*]: @DELETE command

    note right of EXECUTING
        On Level 1
        Can be interrupted by
        Levels 3-15
    end note

    note right of RTWAIT
        Removed from
        execution queue
        Not consuming CPU
    end note

ND-500/ND-100 Dual Processor Architecture

The ND-500 system uses a unique dual-processor architecture where the ND-100 acts as a "front-end" processor handling I/O and system management, while the ND-500 CPU performs computational tasks.

Architecture Overview

graph TB
    subgraph "ND-100 Front-End Processor"
        direction TB

        subgraph "ND-100 Memory"
            MEM100[ND-100 RAM<br/>SINTRAN Kernel<br/>RT Programs<br/>I/O Buffers]
        end

        subgraph "ND-100 Functions"
            SINT[SINTRAN III<br/>Operating System]
            IO[I/O Management<br/>All Devices]
            SWAP100[ND-100 Swapper<br/>Segment Management]
            N500MON[ND-500 Monitor<br/>Runs in ND-100]
        end

        MEM100 --> SINT
        MEM100 --> IO
        MEM100 --> SWAP100
        MEM100 --> N500MON
    end

    subgraph "Shared Memory"
        SHARED[Shared RAM<br/>Process Communication<br/>Data Transfer<br/>Mailboxes]
    end

    subgraph "ND-500 Main Processor"
        direction TB

        subgraph "ND-500 Memory"
            MEM500[ND-500 RAM<br/>User Processes<br/>Application Data<br/>Computational Space]
        end

        subgraph "ND-500 Functions"
            PROC[User Processes<br/>Computational Tasks]
            SWAP500[ND-500 Swapper<br/>Runs in ND-500]
            FORTRAN[FORTRAN Runtime<br/>Numerical Code]
        end

        MEM500 --> PROC
        MEM500 --> SWAP500
        MEM500 --> FORTRAN
    end

    subgraph "I/O Devices"
        DISK[Disk Controllers]
        TERM[Terminals]
        TAPE[Magnetic Tape]
        NET[Network Interfaces]
    end

    N500MON <-->|Commands &<br/>Status| PROC
    N500MON <-->|Data| SHARED
    PROC <-->|Data| SHARED

    IO <--> DISK
    IO <--> TERM
    IO <--> TAPE
    IO <--> NET

    SWAP100 <--> DISK
    SWAP500 <--> DISK

Process Execution Flow

sequenceDiagram
    participant USER as User Terminal
    participant BAK as BAK38 (ND-100)
    participant MON as ND-500 Monitor
    participant PROC as ND-500 Process
    participant SWAP as ND-500 Swapper
    participant DISK as Disk System

    USER->>BAK: @FORTRAN<br/>Execute program
    activate BAK

    BAK->>MON: Request ND-500<br/>process creation
    activate MON

    MON->>PROC: Allocate process<br/>Load program
    activate PROC

    Note over PROC: Check if program<br/>in ND-500 memory

    alt Program not in memory
        PROC->>SWAP: Page fault<br/>Request segments
        activate SWAP
        SWAP->>DISK: Read program pages
        DISK-->>SWAP: Program data
        SWAP-->>PROC: Pages loaded
        deactivate SWAP
    end

    Note over PROC: Execute program<br/>(in ND-500 CPU)

    PROC->>PROC: Computation

    alt Program needs I/O
        PROC->>MON: I/O request
        MON->>BAK: Forward request
        BAK->>DISK: Perform I/O<br/>(ND-100 handles)
        DISK-->>BAK: Data
        BAK-->>MON: I/O complete
        MON-->>PROC: Resume
    end

    PROC-->>MON: Program complete
    deactivate PROC
    MON-->>BAK: Results
    deactivate MON
    BAK-->>USER: Output
    deactivate BAK

Memory Allocation Between ND-100 and ND-500

graph TB
    subgraph "Total Physical Memory"
        TOTALMEM[Total RAM<br/>e.g., 8 MB]
    end

    subgraph "ND-100 Allocation"
        direction TB
        SINTRAN[SINTRAN Kernel<br/>~512 KB Fixed]
        SEG100[Segment Files<br/>for ND-100 Swapping<br/>Configurable]
        RTPROG[RT Programs<br/>~256 KB]
        BUFFER[I/O Buffers<br/>~128 KB]
    end

    subgraph "ND-500 Allocation"
        direction TB
        SWAP500[ND-500 Swap Area<br/>Configurable]
        PROC500[Active ND-500<br/>Process Pages<br/>Dynamic]
    end

    subgraph "Configuration Commands"
        GIVE[GIVE-N500-PAGES<br/>Transfer to ND-500]
        TAKE[TAKE-N500-PAGES<br/>Transfer to ND-100]
    end

    TOTALMEM --> SINTRAN
    TOTALMEM --> SEG100
    TOTALMEM --> RTPROG
    TOTALMEM --> BUFFER
    TOTALMEM --> SWAP500
    TOTALMEM --> PROC500

    GIVE -.Moves Memory.-> PROC500
    TAKE -.Moves Memory.-> SEG100

Key Differences: ND-100 vs ND-500 Execution

Aspect ND-100 ND-500
CPU Type ND-100/CX 16-bit ND-500 32-bit
Word Size 16 bits 32 bits
Interrupts 16 hardware levels None (polling)
I/O System Direct device access Via ND-100 monitor calls
Swapping Segment-based (SINTRAN) Page-based (ND-500 Monitor)
Scheduling Priority + time-slice Priority-based
Primary Use OS, RT, I/O, Management Computation, Applications
Idle Overhead ~5-10% (interrupts) Near 0%

Memory Management and Page Tables

Page Table Organization

graph TB
    subgraph "64K Logical Address Space"
        direction LR
        TOP[Top 256 locations<br/>Page Tables 0-3]
        USER[User Space<br/>0-65279]
    end

    subgraph "Page Table 0 (SINTRAN)"
        PT0_0[Page 0-15<br/>SINTRAN Kernel<br/>Ring 2<br/>Core Resident]
        PT0_1[Page 16-29<br/>SINTRAN Swappable<br/>Ring 2]
        PT0_2[Page 30-33<br/>Window Pages<br/>Ring 2<br/>Dynamic Mapping]
        PT0_3[Page 34-37<br/>System Segments<br/>Ring 2]
    end

    subgraph "Page Table 1 (RT Programs)"
        PT1_0[Page 0-n<br/>RT Program Code<br/>Ring 1]
        PT1_1[Page n+1-m<br/>RT Program Data<br/>Ring 1]
        PT1_2[Page m+1-33<br/>RTCOMMON<br/>Ring 1<br/>Shared RT Data]
        PT1_3[Page 34-37<br/>RT File Segment<br/>Ring 1]
    end

    subgraph "Page Table 2 (Background)"
        PT2_0[Page 0-31<br/>User Program<br/>Ring 0]
        PT2_1[Page 32-33<br/>User Data<br/>Ring 0]
        PT2_2[Page 34-37<br/>System Segments<br/>Ring 2<br/>Monitor Calls]
    end

    subgraph "Page Table 3 (Special)"
        PT3[Large Applications<br/>Special Programs<br/>64K Address Space]
    end

    TOP -.Contains.-> PT0_0
    TOP -.Contains.-> PT1_0
    TOP -.Contains.-> PT2_0
    TOP -.Contains.-> PT3

Page Index Table Entry Format

graph LR
    subgraph "16-bit Page Table Entry"
        direction TB
        B15[Bit 15<br/>FPM<br/>Fetch Permitted]
        B14[Bit 14<br/>WPM<br/>Write Permitted]
        B13[Bit 13<br/>RPM<br/>Read Permitted]
        B12[Bit 12<br/>WIP<br/>Written In Page]
        B11[Bit 11<br/>AIP<br/>Accessed In Page]
        B10_0[Bits 10-0<br/>Physical Page<br/>Address<br/>(0-2047)]
    end

    B15 --> FETCH{Fetch?}
    B14 --> WRITE{Write?}
    B13 --> READ{Read?}

    FETCH -->|No| MPV1[MPV Interrupt]
    WRITE -->|No| MPV2[MPV Interrupt]
    READ -->|No| MPV3[MPV Interrupt]

    B12 --> DIRTY[Page Modified<br/>Must write to disk]
    B11 --> USED[Page Referenced<br/>For LRU algorithm]

    B10_0 --> PHYS[Physical<br/>Page 0-2047]

Segment vs Page Management

graph TB
    subgraph "Segment Structure"
        SEG[Segment<br/>Logical Unit]

        SEG --> PSEG[Program Segment<br/>:PSEG<br/>Code]
        SEG --> DSEG[Data Segment<br/>:DSEG<br/>Variables]
        SEG --> BOTH[Combined<br/>Code + Data]
    end

    subgraph "Page Mapping"
        PSEG --> P1[Page 0<br/>1 KB]
        PSEG --> P2[Page 1<br/>1 KB]
        PSEG --> P3[Page 2<br/>1 KB]
        PSEG --> PN[Page n<br/>1 KB]

        DSEG --> D1[Page 0<br/>1 KB]
        DSEG --> D2[Page 1<br/>1 KB]
    end

    subgraph "Paging Strategies"
        P1 --> NON[Non-Demand Paging<br/>Load all pages at once<br/>Fast, Guaranteed timing<br/>For RT programs]

        D1 --> DEMAND[Demand Paging<br/>Load page on reference<br/>Slower, Less memory<br/>For background programs]
    end

Complete System Setup and Configuration

Initial System Generation Workflow

flowchart TD
    START([New ND-500 System]) --> HARDWARE[Hardware Setup<br/>• Install cabinets<br/>• Connect peripherals<br/>• Set battery switches<br/>• Power on]

    HARDWARE --> BOOTFLOPPY[Boot from Floppy<br/>• Insert SINTRAN diskette<br/>• STOP + MCL buttons<br/>• LOAD button]

    BOOTFLOPPY --> FIRSTBOOT{First Boot?}

    FIRSTBOOT -->|Yes| NODIR[NO MAIN DIRECTORY<br/>message appears]
    FIRSTBOOT -->|No| WARMSTART[Warm Start<br/>Skip to configuration]

    NODIR --> CREATEDIR[CREATE-DIRECTORY<br/>• Name: PACK-ONE<br/>• Device: DISC-70MB-1<br/>• Unit: 0<br/>• Bit-file: default]

    CREATEDIR --> ENTERDIR[@ENTER-DIRECTORY<br/>PACK-ONE]

    ENTERDIR --> CREATESYS[@CREATE-USER SYSTEM]

    CREATESYS --> LOGOUT1[@LOGOUT<br/>Exit to re-login]

    LOGOUT1 --> LOGIN1[ENTER SYSTEM:<br/>PASSWORD: <blank>]

    LOGIN1 --> PASSWD[@CHANGE-PASSWORD<br/>Set SYSTEM password]

    PASSWD --> SPACE[@GIVE-USER-SPACE<br/>SYSTEM 15000<br/>~29MB for install]

    SPACE --> FILEACCESS[@SET-INITIAL-FILE-ACCESS<br/>R,RWA,RWAD<br/>@SET-DEFAULT-FILE-ACCESS]

    FILEACCESS --> USERS[Create Standard Users<br/>• RT<br/>• SCRATCH<br/>• UTILITY<br/>• PROGRAM-FILES<br/>• BPUN-FILES<br/>• FLOPPY-USER]

    USERS --> ND500USERS{ND-500<br/>System?}

    ND500USERS -->|Yes| ADD500[Create ND-500 Users<br/>• DOMAINS<br/>• N502-MICRO-TEST]
    ND500USERS -->|No| SYSFILES

    ADD500 --> SYSFILES[Create System Files<br/>• SINTRAN:DATA<br/>• SEGFILE:DATA<br/>• SWAP-FILE-x:SWAP<br/>• LOAD-MODE:BATC<br/>• MAILBOX:DATA]

    SYSFILES --> INSTALL[Install Software<br/>• Copy from floppies<br/>• Compilers<br/>• Utilities<br/>• Applications]

    INSTALL --> CONFIGURE[Configure SINTRAN<br/>• S3-CONFIGURATION<br/>• Terminals<br/>• Devices<br/>• Network (if applicable)]

    CONFIGURE --> LOADMODE[Edit LOAD-MODE<br/>• Auto-start programs<br/>• Set defaults<br/>• Configure hardware]

    LOADMODE --> COLDSTART[Cold Start<br/>STOP+MCL+LOAD]

    COLDSTART --> TEST[Test System<br/>• Login users<br/>• Run programs<br/>• Check devices]

    TEST --> VERIFY{All<br/>Working?}

    VERIFY -->|No| DEBUG[Debug Issues<br/>• Check logs<br/>• @TERMINAL-STATUS<br/>• @LIST-RT-PROGRAMS]
    DEBUG --> VERIFY

    VERIFY -->|Yes| COMPLETE([System Ready<br/>for Production])

    WARMSTART --> TEST

Configuration File Structure

graph TB
    subgraph "System Configuration Files"
        direction TB

        S3CNFG[S3-CONFIGURATION:CNFG<br/>Binary configuration<br/>Terminal types, Device mappings]
        S3PROG[S3-CONFIGURATION:PROG<br/>Configuration program<br/>Interactive setup]

        LOADMODE[LOAD-MODE:BATC<br/>Startup batch file<br/>Commands run at boot]

        DUMP[DUMP-REENTRANT:MODE<br/>Mode file for<br/>backup procedures]

        DOMAINS[STANDARD-DOMAINS:MODE<br/>ND-500 domain setup]
    end

    subgraph "User Configuration"
        USERDIR[User Directories<br/>Home directories<br/>File access rights]

        PASSWORDS[Password File<br/>User authentication<br/>Protected by SYSTEM]
    end

    subgraph "Network Configuration (if COSMOS)"
        COSMOS[COSMOS Config<br/>Network topology<br/>Computer names]

        XMSG[XMSG Setup<br/>Message routing<br/>Port assignments]

        HDLC[HDLC Parameters<br/>Line protocols<br/>Physical connections]
    end

    S3PROG -.Modifies.-> S3CNFG
    LOADMODE -.Executes at.-> BOOT[System Boot]
    DOMAINS -.Loaded by.-> LOADMODE

LOAD-MODE File Example

sequenceDiagram
    participant BOOT as System Boot
    participant LM as LOAD-MODE:BATC
    participant SINT as SINTRAN
    participant RT as RT Programs
    participant N500 as ND-500 Monitor

    BOOT->>LM: Execute LOAD-MODE
    activate LM

    LM->>SINT: ENTER SYSTEM <password>
    SINT-->>LM: Authenticated

    LM->>SINT: @SET-ERROR-DEVICE 2
    Note over SINT: Console printer = error device

    LM->>SINT: @CREATE-TERMINAL 1,38,39,...
    Note over SINT: Define available terminals

    LM->>RT: @START IMPORTANT-RT
    Note over RT: User RT programs start

    alt ND-500 System
        LM->>N500: @ND-500-MONITOR
        activate N500
        LM->>N500: GIVE-N500-PAGES 2000
        Note over N500: Allocate 2000 pages to ND-500
        LM->>N500: START-SWAPPER
        LM->>N500: EXIT
        deactivate N500
    end

    LM->>SINT: @START-SPOOLING LINE-PRINTER
    Note over SINT: Enable print spooling

    alt COSMOS Enabled
        LM->>RT: @START-XMSG
        Note over RT: Network message system
        LM->>SINT: @COSMOS-ADMINISTRATOR
        Note over SINT: Network management
    end

    LM->>SINT: @SET-AVAILABLE
    Note over SINT: Allow user logins

    deactivate LM

    SINT-->>BOOT: System Ready

Terminal Configuration Commands

# In S3-CONFIGURATION program
*S3-CONFIGURATION

# Define console terminal
FUNCTION: CREATE-TERMINAL
LOGICAL UNIT NO: 1
TERMINAL TYPE: 15         # Tandberg TDV 2200
DEVICE: 8                 # Device number
UNIT: 0                   # Unit number
INPUT SPEED: 9600
OUTPUT SPEED: 9600

# Define user terminals
FUNCTION: CREATE-TERMINAL
LOGICAL UNIT NO: 38
TERMINAL TYPE: 15
DEVICE: 8
UNIT: 1
INPUT SPEED: 9600
OUTPUT SPEED: 9600

# Repeat for terminals 39, 40, etc.

# Save configuration
FUNCTION: GENERATE-SYSTEM
OUTPUT FILE: (SYSTEM)S3-CONFIGURATION:CNFG

# Exit
FUNCTION: EXIT

Process and Performance Monitoring

Monitoring Tools Overview

graph TB
    subgraph "ND-100 Monitoring Tools"
        RTLOG[RT-PROGRAM-LOG<br/>• CPU usage by RT<br/>• I/O statistics<br/>• Swapping activity]

        PROGLOG[PROGRAM-LOG<br/>• Individual program profiling<br/>• Execution time<br/>• Resource usage]

        HIST[HISTOGRAM<br/>• CPU distribution<br/>• Memory usage<br/>• Address space analysis]

        SYSHIST[SYSTEM-HISTOGRAM<br/>• Hardware level activity<br/>• Interrupt overhead<br/>• System efficiency]

        TIMEUSED[TIME-USED<br/>• Per-program CPU time<br/>• Background programs<br/>• Does NOT include OS overhead]
    end

    subgraph "ND-500 Monitoring Tools"
        PROCLOG[PROCESS-LOG<br/>• ND-500 process activity<br/>• CPU distribution<br/>• Memory usage]

        MCLOG[MONITORCALL-LOG<br/>• ND-500 monitor calls<br/>• I/O requests<br/>• System call frequency]

        SWAPLOG[SWAPPING-LOG<br/>• ND-500 page swapping<br/>• Swap performance<br/>• Memory pressure]

        EXECQ[LIST-EXECUTION-QUEUE<br/>• Active ND-500 processes<br/>• Priorities<br/>• Status]
    end

    subgraph "Real-Time Monitoring"
        TERMSTAT[@TERMINAL-STATUS<br/>• Active users<br/>• CPU minutes<br/>• Current command]

        RTPROG[@LIST-RT-PROGRAMS<br/>• All RT programs<br/>• Status<br/>• RT descriptors]

        WHOIS[@WHO-IS-ON<br/>• Logged-in users<br/>• Login time<br/>• Terminal numbers]
    end

RT-PROGRAM-LOG Output Analysis

graph LR
    subgraph "RT-PROGRAM-LOG Metrics"
        direction TB

        CPU[CPU %<br/>Time in RT execution<br/>vs idle time]

        SWAP[SWAP %<br/>Time swapping<br/>ND-100 segments]

        FILES[FILES %<br/>Time in file I/O<br/>Includes ND-500 swap]

        DISK[DISK %<br/>Total disk activity<br/>SWAP + FILES]

        LEVEL[Level Distribution<br/>% time at each<br/>interrupt level]
    end

    subgraph "Interpretation"
        CPU --> CPUBOUND{CPU > 80%?}
        CPUBOUND -->|Yes| CPUISSUE[CPU Bound<br/>Need faster CPU<br/>or optimization]
        CPUBOUND -->|No| CPUOK[CPU OK]

        SWAP --> SWAPBOUND{SWAP > 30%?}
        SWAPBOUND -->|Yes| MEMISSUE[Memory Bound<br/>Need more RAM<br/>or reduce load]
        SWAPBOUND -->|No| MEMOK[Memory OK]

        DISK --> DISKBOUND{DISK > 50%?}
        DISKBOUND -->|Yes| IOISSUE[I/O Bound<br/>Need faster disk<br/>or more controllers]
        DISKBOUND -->|No| IOOK[I/O OK]
    end

Example Monitoring Session

sequenceDiagram
    participant OPR as Operator
    participant SINT as SINTRAN
    participant RTLOG as RT-PROGRAM-LOG
    participant N500 as ND-500 Monitor

    OPR->>SINT: @RT-PROGRAM-LOG
    activate SINT
    SINT->>RTLOG: Start logging
    activate RTLOG

    OPR->>RTLOG: RT-NAME: -J
    Note over RTLOG: -J = all system

    OPR->>RTLOG: INTERVAL: 10
    Note over RTLOG: Report every 10 seconds

    OPR->>RTLOG: DURATION: 600
    Note over RTLOG: Run for 10 minutes

    OPR->>RTLOG: DEVICE: TERMINAL
    Note over RTLOG: Output to terminal

    loop Every 10 seconds
        RTLOG-->>OPR: CPU: 45% SWAP: 5% FILES: 10% DISK: 15%
    end

    deactivate RTLOG
    deactivate SINT

    Note over OPR: Check ND-500 if applicable

    OPR->>SINT: @ND-500-MONITOR
    activate SINT
    SINT->>N500: Enter monitor
    activate N500

    OPR->>N500: PROCESS-LOG
    N500-->>OPR: Process statistics

    OPR->>N500: LIST-EXECUTION-QUEUE
    N500-->>OPR: Active processes:<br/>Proc 1: Pri 100, CPU 45s<br/>Proc 2: Pri 50, CPU 12s

    OPR->>N500: EXIT
    deactivate N500
    deactivate SINT

System Performance Diagnosis Flowchart

flowchart TD
    START([Performance Issue]) --> RTLOG[Run RT-PROGRAM-LOG<br/>10-minute sample]

    RTLOG --> CHECKCPU{CPU > 80%?}

    CHECKCPU -->|Yes| ND500{ND-500<br/>System?}
    CHECKCPU -->|No| CHECKSWAP

    ND500 -->|Yes| WHICH[Check which CPU:<br/>RT-PROGRAM-LOG = ND-100<br/>PROCESS-LOG = ND-500]
    ND500 -->|No| CPU100[ND-100 CPU Bound<br/>Solutions:<br/>• Faster ND-100<br/>• Buffered terminals<br/>• Reduce RT programs]

    WHICH --> PROCLOG{ND-500<br/>High?}
    PROCLOG -->|Yes| CPU500[ND-500 CPU Bound<br/>Solutions:<br/>• Faster ND-500 CPU<br/>• AX vector option<br/>• Optimize programs]
    PROCLOG -->|No| CPU100

    CHECKSWAP{SWAP > 30%?} -->|Yes| MEM100[ND-100 Memory Bound<br/>Solutions:<br/>• Add RAM<br/>• GIVE-N500-PAGES<br/>• Reduce backgrounds]
    CHECKSWAP -->|No| CHECKFILES

    CHECKFILES{FILES > 40%?} -->|Yes| SWAPLOG[Run SWAPPING-LOG<br/>Check ND-500 swap]
    CHECKFILES -->|No| IDLE[System Healthy<br/>Adequate resources]

    SWAPLOG --> SWAP500{ND-500<br/>Swapping?}
    SWAP500 -->|Yes| MEM500[ND-500 Memory Bound<br/>Solutions:<br/>• Add RAM<br/>• TAKE-N500-PAGES<br/>• Fix critical pages<br/>• Reduce processes]
    SWAP500 -->|No| DISKIO[Disk I/O Bound<br/>Solutions:<br/>• Faster disks<br/>• Multiple controllers<br/>• Separate swap/data<br/>• More disk cache]

    CPU100 --> IMPLEMENT[Implement Solutions]
    CPU500 --> IMPLEMENT
    MEM100 --> IMPLEMENT
    MEM500 --> IMPLEMENT
    DISKIO --> IMPLEMENT

    IMPLEMENT --> RETEST[Re-test after<br/>changes]

    RETEST --> BETTER{Improved?}
    BETTER -->|Yes| DONE([Monitor Regularly])
    BETTER -->|No| START

    IDLE --> DONE

COSMOS and XMSG Network Architecture

COSMOS Network Layers

graph TB
    subgraph "Application Layer"
        APP1[File Transfer<br/>Remote File Access]
        APP2[Terminal Access<br/>Connect-To]
        APP3[Mail System<br/>Message Passing]
        APP4[Custom Applications]
    end

    subgraph "COSMOS Layer"
        COSMOS[COSMOS Services<br/>• TAD Management<br/>• Connection Control<br/>• Routing]

        CT[Connect-To Service<br/>Remote login<br/>Session management]

        FS[File Server<br/>FSART (Administrator)<br/>RTRFA (Access)]
    end

    subgraph "XMSG Layer (Message Passing)"
        XROUT[XROUT RT Program<br/>• Message routing<br/>• Computer naming<br/>• Port management]

        XTRACE[XTRACE RT Program<br/>• Message logging<br/>• Debugging<br/>• Traffic analysis]

        XMSG[XMSG API<br/>Send/Receive calls<br/>Port allocation]
    end

    subgraph "Transport Layer"
        HDLC[HDLC Protocol<br/>High-Level Data Link<br/>Frame transmission]

        DRIVER[Line Drivers<br/>RS-232, V.24<br/>Modem control]
    end

    subgraph "Physical Layer"
        SERIAL[Serial Lines<br/>Synchronous/Async<br/>Point-to-point]

        MODEM[Modems<br/>Long distance<br/>Dial-up/Leased]
    end

    APP1 --> COSMOS
    APP2 --> CT
    APP3 --> COSMOS
    APP4 --> COSMOS

    COSMOS --> XROUT
    CT --> XROUT
    FS --> XROUT

    XROUT --> XMSG
    XTRACE -.Monitors.-> XROUT

    XMSG --> HDLC
    HDLC --> DRIVER
    DRIVER --> SERIAL
    SERIAL --> MODEM

XMSG Port and Message Architecture

graph LR
    subgraph "Computer A"
        direction TB
        A_APP[Application]
        A_PORT1[Local Port 1001]
        A_PORT2[Local Port 1002]
        A_XROUT[XROUT<br/>Routing Table]
        A_HDLC[HDLC Line 0]
    end

    subgraph "Network"
        LINE1[HDLC Line<br/>Computer A ↔ B]
        LINE2[HDLC Line<br/>Computer B ↔ C]
    end

    subgraph "Computer B (Hub)"
        direction TB
        B_HDLC1[HDLC Line 0]
        B_HDLC2[HDLC Line 1]
        B_XROUT[XROUT<br/>Routing Table<br/>Routes A ↔ C]
        B_PORT[Local Port 2001]
        B_APP[Local Application]
    end

    subgraph "Computer C"
        direction TB
        C_HDLC[HDLC Line 0]
        C_XROUT[XROUT<br/>Routing Table]
        C_PORT1[Local Port 3001]
        C_PORT2[Local Port 3002]
        C_APP[Application]
    end

    A_APP -.Uses.-> A_PORT1
    A_PORT1 --> A_XROUT
    A_XROUT --> A_HDLC
    A_HDLC --> LINE1

    LINE1 --> B_HDLC1
    B_HDLC1 --> B_XROUT
    B_XROUT --> B_HDLC2
    B_HDLC2 --> LINE2

    LINE2 --> C_HDLC
    C_HDLC --> C_XROUT
    C_XROUT --> C_PORT1
    C_PORT1 -.Delivers to.-> C_APP

    B_XROUT -.Also serves.-> B_PORT
    B_PORT -.Local.-> B_APP

XMSG Message Flow

sequenceDiagram
    participant APP_A as Application A<br/>(Computer ALPHA)
    participant XMSG_A as XMSG on ALPHA
    participant XROUT_A as XROUT on ALPHA
    participant HDLC_A as HDLC Line
    participant HDLC_B as HDLC Line
    participant XROUT_B as XROUT on BETA
    participant XMSG_B as XMSG on BETA
    participant APP_B as Application B<br/>(Computer BETA)

    Note over APP_A: Want to send message<br/>to BETA:3001

    APP_A->>XMSG_A: XMSEND<br/>Dest: BETA:3001<br/>Source: LOCAL:1001<br/>Data: "Hello"

    XMSG_A->>XROUT_A: Route message<br/>Destination: BETA

    Note over XROUT_A: Check routing table<br/>BETA via HDLC Line 0

    XROUT_A->>HDLC_A: Transmit frame<br/>Header + Data

    HDLC_A->>HDLC_B: Physical transmission<br/>CRC check, ACK

    HDLC_B->>XROUT_B: Frame received<br/>Destination: LOCAL:3001

    XROUT_B->>XMSG_B: Deliver to port 3001

    XMSG_B->>APP_B: XMRECV<br/>Data available

    APP_B-->>XMSG_B: Read data: "Hello"

    Note over APP_B: Process message

    APP_B->>XMSG_B: XMSEND<br/>Reply to ALPHA:1001<br/>Data: "Acknowledged"

    Note over XMSG_B,HDLC_A: Reverse path

    HDLC_A->>XROUT_A: Reply received
    XROUT_A->>XMSG_A: Deliver to port 1001
    XMSG_A->>APP_A: XMRECV<br/>Reply available

HDLC Configuration and Setup

HDLC Physical Connection

graph TB
    subgraph "Computer ALPHA"
        CPU_A[ND-100 CPU]
        COMM_A[Communication Board<br/>ND-3231 or 3232]
        MODEM_A[Modem/DCE<br/>or Direct]
    end

    subgraph "Physical Medium"
        CABLE[RS-232 Cable<br/>or<br/>Leased Line]
    end

    subgraph "Computer BETA"
        MODEM_B[Modem/DCE<br/>or Direct]
        COMM_B[Communication Board<br/>ND-3231 or 3232]
        CPU_B[ND-100 CPU]
    end

    CPU_A <--> COMM_A
    COMM_A <-->|TXD, RXD<br/>RTS, CTS<br/>DTR, DSR| MODEM_A
    MODEM_A <-->|Electrical Signals| CABLE
    CABLE <--> MODEM_B
    MODEM_B <-->|TXD, RXD<br/>RTS, CTS<br/>DTR, DSR| COMM_B
    COMM_B <--> CPU_B

HDLC Configuration Commands

Setting up HDLC Line (in SINTRAN Service Program):

# Enter SINTRAN Service Program
@SINTRAN-SERVICE-PROGRAM

# Create HDLC line device
FUNCTION: CREATE-DEVICE
DEVICE-NAME: HDLC
DEVICE-NUMBER: 40           # Device number for HDLC controller
UNIT-NUMBER: 0              # First HDLC line
TYPE: HDLC

# Configure HDLC parameters
FUNCTION: SET-HDLC-PARAMETERS
DEVICE: 40
UNIT: 0
SPEED: 9600                 # Baud rate: 1200, 2400, 4800, 9600, 19200
MODE: NRM                   # Normal Response Mode (or ABM for Async Balanced)
WINDOW-SIZE: 7              # Number of frames before ACK (1-7)
FRAME-SIZE: 256             # Maximum frame size in bytes
TIMEOUT: 5                  # Seconds before retransmission
RETRIES: 10                 # Number of retries before failure

# Set line protocol
FUNCTION: SET-LINE-PROTOCOL
DEVICE: 40
UNIT: 0
PROTOCOL: HDLC-LAP-B        # HDLC LAP-B variant

# Configure modem control
FUNCTION: SET-MODEM-CONTROL
DEVICE: 40
UNIT: 0
DTR: ON                     # Data Terminal Ready
RTS: ON                     # Request To Send
MODE: ORIGINATE             # or ANSWER for receiving end

# Save configuration
FUNCTION: GENERATE-SYSTEM

# Exit
FUNCTION: EXIT

COSMOS Network Setup

Initializing COSMOS Network:

# Start XMSG (prerequisite for COSMOS)
@START-XMSG

# Configure computer name
@XMSG-SERVICE-PROGRAM
FUNCTION: SET-COMPUTER-NAME
COMPUTER-NAME: ALPHA        # This computer's network name
FUNCTION: EXIT

# Add routing table entries
@XMSG-SERVICE-PROGRAM
FUNCTION: ADD-ROUTE
DESTINATION-COMPUTER: BETA
LINE-NUMBER: 0              # HDLC line 0
FUNCTION: ADD-ROUTE
DESTINATION-COMPUTER: GAMMA
LINE-NUMBER: 0              # Via BETA (routing)
VIA-COMPUTER: BETA
FUNCTION: EXIT

# Start COSMOS Administrator
@COSMOS-ADMINISTRATOR

# Configure TAD (Terminal Access Device) pool
FUNCTION: CREATE-TAD-POOL
NUMBER-OF-TADS: 16          # Support up to 16 remote users
FIRST-TAD-NUMBER: 768       # Starting terminal number
FUNCTION: EXIT

# Enable file server (optional)
@FILE-SERVER-ADMINISTRATOR
FUNCTION: START-FILE-SERVER
FUNCTION: EXIT

HDLC Operational States

stateDiagram-v2
    [*] --> DISCONNECTED: Power on/<br/>Line created

    DISCONNECTED --> SETUP: SETUP frame sent

    SETUP --> CONNECTED: UA (Ack) received

    CONNECTED --> INFORMATION: Ready to<br/>transfer data

    INFORMATION --> INFORMATION: I-frames exchanged<br/>RR (Receive Ready) ACKs

    INFORMATION --> BUSY: RNR (Receive Not Ready)<br/>Remote buffer full

    BUSY --> INFORMATION: RR received<br/>Remote ready again

    INFORMATION --> DISCONNECT: DISC frame sent<br/>Normal termination

    DISCONNECT --> DISCONNECTED: UA received

    INFORMATION --> ERROR: Timeout<br/>Bad CRC<br/>Invalid frame

    ERROR --> RETRY: Retransmit frame

    RETRY --> INFORMATION: Successful

    RETRY --> DISCONNECTED: Max retries<br/>exceeded

    note right of INFORMATION
        Normal operation
        I-frames with data
        Sequence numbers
        ACKs via RR frames
    end note

    note right of ERROR
        Error recovery:
        - Retransmit
        - REJ (Reject)
        - SABM (reset)
    end note

HDLC Frame Structure

graph LR
    subgraph "HDLC Frame"
        FLAG1[Flag<br/>01111110<br/>1 byte]
        ADDR[Address<br/>Station ID<br/>1 byte]
        CTRL[Control<br/>Frame type<br/>Sequence nos<br/>1 byte]
        INFO[Information<br/>User data<br/>0-256 bytes]
        FCS[FCS<br/>CRC-16<br/>2 bytes]
        FLAG2[Flag<br/>01111110<br/>1 byte]
    end

    FLAG1 --> ADDR
    ADDR --> CTRL
    CTRL --> INFO
    INFO --> FCS
    FCS --> FLAG2

Frame Types:

graph TB
    FRAME[HDLC Frame Types]

    FRAME --> IFRAME[I-Frame<br/>Information<br/>Contains user data<br/>Sequence numbers]

    FRAME --> SFRAME[S-Frame<br/>Supervisory<br/>Flow control<br/>ACKs]

    FRAME --> UFRAME[U-Frame<br/>Unnumbered<br/>Link setup<br/>Disconnect]

    SFRAME --> RR[RR<br/>Receive Ready<br/>ACK + Ready]
    SFRAME --> RNR[RNR<br/>Receive Not Ready<br/>ACK + Busy]
    SFRAME --> REJ[REJ<br/>Reject<br/>Request retransmit]

    UFRAME --> SABM[SABM<br/>Set Async Balanced<br/>Initialize link]
    UFRAME --> DISC[DISC<br/>Disconnect<br/>Terminate link]
    UFRAME --> UA[UA<br/>Unnumbered ACK<br/>Acknowledge U-frame]

Network Debugging and Troubleshooting

XMSG Debugging Commands

Enabling XMSG Tracing:

# Method 1: Start XTRACE RT program
@START XTRACE

# XTRACE automatically logs all XMSG activity
# Output goes to file or terminal

# Method 2: Enable debug print in File Transfer
@FILE-TRANSFER
FT: DEBUGPRINT-ON

# Now all XMSG calls are displayed:
# XMSEND: TO=BETA:3001 FROM=ALPHA:1001 LEN=64
# XMRECV: FROM=BETA:3001 TO=ALPHA:1001 LEN=32

# Transfer a file to see traffic
FT: COPY-TO-REMOTE
...

# Disable debug
FT: DEBUGPRINT-OFF
FT: EXIT

# Method 3: XMSG Service Program logging
@XMSG-SERVICE-PROGRAM
FUNCTION: SET-DEBUG-LEVEL
LEVEL: 3                    # 0=off, 1=errors, 2=warnings, 3=all
LOG-FILE: (SYSTEM)XMSG-LOG:DATA
FUNCTION: EXIT

XMSG Trace Output Analysis

sequenceDiagram
    participant TRACE as XTRACE RT
    participant APP as Application
    participant XMSG as XMSG Layer
    participant HDLC as HDLC Layer

    Note over TRACE: Intercepts all XMSG calls

    APP->>XMSG: XMSEND call
    XMSG-->>TRACE: Log: SEND<br/>Dest=BETA:3001<br/>Src=ALPHA:1001<br/>Len=128

    XMSG->>HDLC: Frame transmission
    HDLC-->>TRACE: Log: HDLC<br/>Line=0<br/>Frame=I,Seq=5<br/>Len=140

    Note over HDLC: Wait for ACK

    HDLC->>XMSG: ACK received
    XMSG-->>TRACE: Log: ACK<br/>Line=0<br/>Seq=5

    Note over TRACE: Timestamps all events

    HDLC->>XMSG: Data received
    XMSG-->>TRACE: Log: RECV<br/>From=BETA:3001<br/>To=ALPHA:1001<br/>Len=64

    XMSG->>APP: XMRECV delivers
    APP-->>TRACE: Log: DELIVERED<br/>Port=1001<br/>Status=OK

Example XTRACE Output:

TIME     EVENT     DETAILS
========================================
10:23:15 XMSEND    TO=BETA:3001 FROM=ALPHA:1001 LEN=128 DATA=...
10:23:15 HDLC-TX   LINE=0 FRAME=I SEQ=5 ACK=3 LEN=140
10:23:15 HDLC-ACK  LINE=0 SEQ=5 RTT=12ms
10:23:16 HDLC-RX   LINE=0 FRAME=I SEQ=4 ACK=5 LEN=76
10:23:16 XMRECV    FROM=BETA:3001 TO=ALPHA:1001 LEN=64
10:23:16 DELIVER   PORT=1001 STATUS=OK QUEUED=0

HDLC Line Debugging

Checking HDLC Line Status:

# SINTRAN Service Program
@SINTRAN-SERVICE-PROGRAM

# Display line status
FUNCTION: LIST-HDLC-STATUS
DEVICE: 40

# Example output:
# UNIT  STATE      TX-FRAMES  RX-FRAMES  ERRORS  RETRANS  TIMEOUTS
# 0     CONNECTED  1523       1487       0       0        0
# 1     DISCONN    0          0          0       0        0

# Detailed statistics
FUNCTION: DISPLAY-LINE-STATISTICS
DEVICE: 40
UNIT: 0

# Output:
# CRC Errors: 0
# Frame Errors: 0
# Overruns: 0
# Underruns: 0
# Timeouts: 0
# Retransmissions: 0
# Current Window: 7
# Queue Depth: 0

# Reset error counters
FUNCTION: RESET-STATISTICS
DEVICE: 40
UNIT: 0

HDLC Troubleshooting Flowchart

flowchart TD
    START([HDLC Link Problem]) --> CHECK[Check Physical]

    CHECK --> CABLE{Cables<br/>Connected?}
    CABLE -->|No| FIXCABLE[Connect cables<br/>Check pinout]
    CABLE -->|Yes| MODEM

    FIXCABLE --> MODEM

    MODEM{Modem<br/>Lights OK?}
    MODEM -->|No| CHECKMODEM[• Check power<br/>• Check DTR/DSR<br/>• Check carrier]
    MODEM -->|Yes| SINTSTATUS

    CHECKMODEM --> SINTSTATUS

    SINTSTATUS[Check SINTRAN<br/>@SINTRAN-SERVICE-PROGRAM<br/>LIST-HDLC-STATUS]

    SINTSTATUS --> STATE{Line<br/>State?}

    STATE -->|DISCONNECTED| NOLINK[No Link Established<br/>Check:<br/>• HDLC parameters match<br/>• Both ends configured<br/>• Speeds match<br/>• Protocol compatibility]

    STATE -->|CONNECTED| ERRORS{Errors<br/>Count?}

    ERRORS -->|High| ERRTYPE{Error<br/>Type?}

    ERRTYPE -->|CRC Errors| BADLINE[Line Quality Issue<br/>• Bad cable<br/>• Interference<br/>• Speed too high<br/>• Reduce speed]

    ERRTYPE -->|Timeouts| TIMING[Timing Issue<br/>• Increase timeout<br/>• Reduce window size<br/>• Check latency<br/>• Modem delay]

    ERRTYPE -->|Overruns| BUFFER[Buffer Problem<br/>• CPU overloaded<br/>• Reduce traffic<br/>• Check RT priority<br/>• More memory]

    ERRORS -->|Low| XMSG[Check XMSG Layer<br/>@XMSG-SERVICE-PROGRAM<br/>LIST-ROUTES]

    XMSG --> ROUTE{Routing<br/>Correct?}

    ROUTE -->|No| FIXROUTE[Add/Fix Routes<br/>ADD-ROUTE<br/>Check computer names]

    ROUTE -->|Yes| TRACE[Enable Tracing<br/>@START XTRACE<br/>or DEBUGPRINT-ON]

    TRACE --> MONITOR[Monitor Traffic<br/>Look for:<br/>• Messages sent?<br/>• ACKs received?<br/>• Where failing?]

    MONITOR --> APPISSUE{Application<br/>Problem?}

    APPISSUE -->|Yes| FIXAPP[Debug Application<br/>Check port numbers<br/>Check addresses]

    APPISSUE -->|No| COSMOSCHECK[Check COSMOS<br/>@TADADM<br/>@COSMOS-ADMIN]

    NOLINK --> RETRY[Reset Link<br/>DISCONNECT-LINE<br/>CONNECT-LINE]

    BADLINE --> RETRY
    TIMING --> RETRY
    BUFFER --> RETRY

    RETRY --> RETEST{Working?}
    RETEST -->|Yes| DONE([Problem Solved])
    RETEST -->|No| ESCALATE([Contact<br/>ND Support])

    FIXROUTE --> RETEST
    FIXAPP --> RETEST

    COSMOSCHECK --> TADOK{TADs<br/>Available?}
    TADOK -->|No| CREATETAD[CREATE-TAD-POOL]
    TADOK -->|Yes| DONE

    CREATETAD --> DONE

Common HDLC Error Messages and Solutions

graph TB
    subgraph "Error Messages"
        E1[HDLC TIMEOUT<br/>LINE 0]
        E2[HDLC CRC ERROR<br/>LINE 0]
        E3[HDLC DISCONNECT<br/>LINE 0]
        E4[HDLC OVERRUN<br/>LINE 0]
        E5[XMSG NO ROUTE<br/>TO BETA]
        E6[XMSG PORT BUSY<br/>3001]
    end

    subgraph "Causes and Solutions"
        E1 --> T1[Timeout Causes:<br/>• Remote not responding<br/>• Line delay too high<br/>• Heavy traffic]
        T1 --> S1[Solutions:<br/>• Increase timeout value<br/>• Check remote system<br/>• Reduce window size]

        E2 --> T2[CRC Causes:<br/>• Noisy line<br/>• Bad cable<br/>• Interference<br/>• Speed mismatch]
        T2 --> S2[Solutions:<br/>• Check cable quality<br/>• Reduce speed<br/>• Shield cables<br/>• Check connectors]

        E3 --> T3[Disconnect Causes:<br/>• Remote shutdown<br/>• Modem carrier loss<br/>• Line failure]
        T3 --> S3[Solutions:<br/>• Check remote system<br/>• Verify modem connection<br/>• Test line continuity]

        E4 --> T4[Overrun Causes:<br/>• CPU too slow<br/>• Buffer overflow<br/>• High interrupt load]
        T4 --> S4[Solutions:<br/>• Reduce traffic<br/>• Increase buffer size<br/>• Optimize RT priorities]

        E5 --> T5[No Route Causes:<br/>• Routing table incomplete<br/>• Computer name wrong<br/>• XMSG not started]
        T5 --> S5[Solutions:<br/>• ADD-ROUTE command<br/>• Check computer names<br/>• @START-XMSG]

        E6 --> T6[Port Busy Causes:<br/>• Application crash<br/>• Port not released<br/>• Duplicate allocation]
        T6 --> S6[Solutions:<br/>• Restart application<br/>• Check RT programs<br/>• Use different port]
    end

COSMOS Debugging Session Example

sequenceDiagram
    participant OPR as Operator
    participant SINT as SINTRAN
    participant XMSG as XMSG Service
    participant XTRACE as XTRACE
    participant HDLC as HDLC Line

    Note over OPR: User reports: "Can't connect to BETA"

    OPR->>SINT: @XMSG-SERVICE-PROGRAM
    activate SINT

    OPR->>SINT: LIST-ROUTES
    SINT-->>OPR: BETA: Line 0, Status OK

    OPR->>SINT: LIST-COMPUTER-NAMES
    SINT-->>OPR: LOCAL: ALPHA<br/>REMOTE: BETA, GAMMA

    OPR->>SINT: EXIT
    deactivate SINT

    OPR->>SINT: @SINTRAN-SERVICE-PROGRAM
    activate SINT

    OPR->>SINT: LIST-HDLC-STATUS 40
    SINT-->>OPR: Unit 0: CONNECTED<br/>TX: 523, RX: 487<br/>Errors: 15 CRC

    Note over OPR: CRC errors - line quality issue

    OPR->>SINT: DISPLAY-LINE-STATISTICS 40 0
    SINT-->>OPR: CRC Errors: 15<br/>Retransmissions: 8<br/>Timeouts: 2

    deactivate SINT

    Note over OPR: Start detailed tracing

    OPR->>XTRACE: @START XTRACE
    activate XTRACE

    OPR->>SINT: @CONNECT-TO BETA
    activate SINT

    SINT->>XMSG: XMSEND to BETA:CT-PORT
    XMSG-->>XTRACE: LOG: SEND BETA:101 LEN=32

    XMSG->>HDLC: Transmit frame
    HDLC-->>XTRACE: LOG: HDLC-TX Line=0 Seq=50

    Note over HDLC: Wait...timeout

    HDLC-->>XTRACE: LOG: TIMEOUT Seq=50<br/>Retransmitting

    HDLC->>HDLC: Retransmit frame
    HDLC-->>XTRACE: LOG: HDLC-TX Line=0 Seq=50 (retry)

    Note over HDLC: ACK received

    HDLC-->>XTRACE: LOG: HDLC-ACK Seq=50 RTT=250ms

    Note over OPR: High RTT - line delay

    deactivate SINT
    deactivate XTRACE

    Note over OPR: Solution: Increase timeout<br/>Reduce speed if errors continue

Comprehensive Monitoring Commands Reference

Quick Command Reference

Command Purpose Example
System Status
@WHO-IS-ON List logged-in users @WHO-IS-ON
@TERMINAL-STATUS Detailed terminal info @TERMINAL-STATUS,,
@LIST-RT-PROGRAMS All RT programs @LIST-RT-PROGRAMS,,
@LIST-OPEN-FILES User's open files @LIST-OPEN-FILES
@LIST-RTOPEN-FILES RT-open files @LIST-RTOPEN-FILES,,
Performance
@RT-PROGRAM-LOG ND-100 performance Interactive command
@PROGRAM-LOG Individual program profile Interactive command
@HISTOGRAM CPU distribution Interactive command
@SYSTEM-HISTOGRAM Hardware levels Interactive command
ND-500 Specific
@ND-500-MONITOR Enter ND-500 monitor @ND-500-MONITOR
PROCESS-STATUS ND-500 processes In ND-500 monitor
PROCESS-LOG ND-500 performance In ND-500 monitor
LIST-EXECUTION-QUEUE Process queue In ND-500 monitor
Network
@TADADM COSMOS TAD status @TADADM
@XMSG-SERVICE-PROGRAM XMSG configuration Interactive command
@START XTRACE Enable XMSG tracing @START XTRACE
HDLC
@SINTRAN-SERVICE-PROGRAM Configure HDLC Interactive command
LIST-HDLC-STATUS Line status In service program
DISPLAY-LINE-STATISTICS Detailed stats In service program

Best Practices Summary

System Setup

  1. Always backup before configuration changes
  2. Test commands manually before adding to LOAD-MODE
  3. Document all changes in comments
  4. Use descriptive names for users, files, directories
  5. Set appropriate passwords for SYSTEM and RT users

Performance Monitoring

  1. Establish baselines - know normal system behavior
  2. Monitor regularly - don't wait for problems
  3. Check all layers - hardware, OS, application
  4. Correlate metrics - CPU + memory + I/O
  5. Keep logs - historical data helps diagnosis

Network Operations

  1. Verify physical before software debugging
  2. Enable tracing only when debugging (performance impact)
  3. Match parameters on both ends of HDLC links
  4. Use routing tables correctly
  5. Monitor error counters regularly

Troubleshooting

  1. Work bottom-up - physical → link → network → application
  2. Check one thing at a time
  3. Document findings for future reference
  4. Use systematic approach - flowcharts, checklists
  5. Know when to escalate - don't waste time guessing

Appendix: System Architecture Summary

Complete SINTRAN III Stack

graph TB
    subgraph "User Applications"
        USERAPP[User Programs<br/>FORTRAN, COBOL<br/>Custom Applications]
    end

    subgraph "Application Services"
        COSMOS[COSMOS<br/>Network Services]
        SIBAS[SIBAS<br/>Database]
        NOTIS[NOTIS<br/>Office Suite]
    end

    subgraph "RT Program Layer (Level 1)"
        BAK[Background<br/>Terminals]
        XROUT[XMSG<br/>Messaging]
        RTCUSTOM[Custom RT<br/>Programs]
    end

    subgraph "SINTRAN Monitor (Level 3)"
        KERNEL[System Kernel]
        FILESYS[File System]
        SEGMENT[Segment Manager]
    end

    subgraph "Device Drivers (Levels 10-13)"
        DISKDRV[Disk Drivers]
        TERMDRV[Terminal I/O]
        NETDRV[Network Drivers]
    end

    subgraph "Hardware"
        CPU[ND-100/ND-500<br/>Processors]
        MEM[Memory<br/>Management]
        DEVICES[Peripherals<br/>Disk, Terminal, Network]
    end

    USERAPP --> COSMOS
    USERAPP --> SIBAS
    COSMOS --> XROUT
    SIBAS --> RTCUSTOM
    NOTIS --> BAK

    BAK --> KERNEL
    XROUT --> KERNEL
    RTCUSTOM --> KERNEL

    KERNEL --> FILESYS
    KERNEL --> SEGMENT
    KERNEL --> DISKDRV
    KERNEL --> TERMDRV
    KERNEL --> NETDRV

    DISKDRV --> CPU
    TERMDRV --> CPU
    NETDRV --> CPU

    CPU --> MEM
    CPU --> DEVICES

    SEGMENT --> MEM
    FILESYS --> DISKDRV

Document Version: 2.0 Date: 2025-11-18 Purpose: Deep technical guide for SINTRAN III system architects and advanced operators

Related Documents: - SINTRAN-Operations-Guide.md (Basic operations) - ND-30.003.007 EN SINTRAN III System Supervisor - ND-60.062.01D EN SINTRAN III System Documentation - ND-30.049.1 EN SINTRAN III Tuning Guide