Sequence controlled service and COP-1

Sequence Controlled Service:
1. Purpose:

• Ensures reliable, in-order delivery of telecommands
• Provides acknowledgment mechanism
• Handles retransmission of lost commands
• Maintains sequence counting

2. Key Features:

• Sequence numbering of frames
• Positive/negative acknowledgments
• Timeout mechanisms
• Frame acceptance and rejection rules

COP-1(Communications Operation Procedure-1) Protocol:
1. Basic Operation:

• Used in uplink (ground to space)
• Implements "go-back-n" retransmission strategy
• Maintains frame sequence numbering (N(S))
• Uses Frame Acceptance and Reporting Mechanism (FARM) on spacecraft

2. States and Operations:

• Active State: Normal transmission
• Retransmit State: When errors occur
• Initial State: During initialization
• Wait State: Waiting for acknowledgment

3. Key Mechanisms:

• Sliding window protocol
• Automatic retransmission on timeout
• Sequence number verification
• Status reporting

4. Error Recovery:

• Handles lost commands
• Manages duplicate commands
• Recovers from sequence errors
• Provides status verification

COP-1 sequence

1. Initial Setup:

• Ground station initializes Frame Sequence Number (N(S))
• Spacecraft initializes Receiver Frame Sequence Number (V(R))
• Both sides synchronize their counters

2. Normal Command Transmission:

Ground Station                    Spacecraft
     |                                |
     |-- TC Frame (N(S)=1) --------->|  Check N(S)
     |                                |  Store command
     |<-------- Accept/Acknowledge ---|
     |                                |
     |-- TC Frame (N(S)=2) --------->|  Check N(S)
     |                                |  Store command
     |<-------- Accept/Acknowledge ---|

3. Error Recovery Scenario:

Ground Station                    Spacecraft
     |                                |
     |-- TC Frame (N(S)=3) --X       |  Frame lost
     |         Timeout               |
     |                               |
     |-- TC Frame (N(S)=3) --------->|  Receive retry
     |                               |  Process frame
     |<-------- Accept/Acknowledge --|

4. Status Check and Recovery:

• Ground can request status from spacecraft
• Spacecraft reports current V(R)
• Ground can retransmit from any point if needed

5. Frame Processing Rules:

• Accept if N(S) = V(R)
• Reject if N(S) ≠ V(R)
• Increment V(R) after acceptance
• Report status when requested

6. Window Operation:

• Ground maintains sliding window
• Only sends frames within window
• Waits for acknowledgment before advancing
• Typical window size is configurable

7. Special Operations:

• UNLOCK command for resynchronization
• SET V(R) for counter reset
• CLCW (Command Link Control Word) for status reporting

COP-1 go-back-n

In COP-1's "go-back-n" protocol, the ground station can send multiple CLTUs before receiving acknowledgments from the spacecraft.

1. Window Operation:

Ground Station                    Spacecraft
     |                                |
     |-- CLTU (N(S)=1) ------------->|
     |-- CLTU (N(S)=2) ------------->|
     |-- CLTU (N(S)=3) ------------->|
     |-- CLTU (N(S)=4) ----X         | Frame 4 lost
     |-- CLTU (N(S)=5) ------------->|
     |                                |
     |<---- CLCW (expecting N(S)=4) -| Spacecraft reports gap
     |                                |
     |-- CLTU (N(S)=4) ------------->| Retransmit from 4
     |-- CLTU (N(S)=5) ------------->|

2. Key Parameters:

• Window size: Number of unacknowledged CLTUs allowed
• Usually configurable based on mission needs
• Common window sizes: 1 to 8 frames

3. Error Recovery:

• When error detected, ground retransmits from the failed frame
• All frames after the failed one must be retransmitted
• Hence "go-back-n" name (goes back to frame n)

4. Flow Control:

• Ground station tracks window limits
• Stops sending when window is full
• Resumes after receiving acknowledgments
• Uses CLCW for status monitoring

This approach provides efficient transmission while maintaining reliability through the retransmission mechanism.