1006  ISA 100.11A Protocol Stack and Comparison

1006.1 Introduction

This chapter explores the ISA 100.11A protocol stack architecture and provides a detailed comparison with WirelessHART. Understanding these differences is crucial for selecting the right industrial wireless standard for specific deployment requirements.

NoteLearning Objectives

By the end of this chapter, you will be able to:

  • Explain the ISA 100.11A layered protocol architecture
  • Understand the security key hierarchy and dual encryption approach
  • Compare ISA 100.11A and WirelessHART across all protocol layers
  • Identify the philosophical differences between the two standards
  • Make informed decisions about protocol selection for industrial applications

1006.2 Prerequisites

Before studying this chapter, you should be familiar with:

1006.3 Protocol Stack

1006.3.1 Layered Architecture

ISA 100.11A offers more flexibility than WirelessHART in upper layers:

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#E67E22', 'secondaryColor': '#16A085', 'tertiaryColor': '#7F8C8D'}}}%%
graph TB
    A[ISA 100.11A Protocol Stack] --> B[Application Layer]
    A --> C[Transport Layer]
    A --> D[Network Layer]
    A --> E[Data Link Layer]
    A --> F[Physical Layer]

    B --> B1[ISA 100 Application<br/>Tunneled Protocols:<br/>Modbus, HART, etc.]
    C --> C1[UDP<br/>End-to-End Security]
    D --> D1[IPv6 + 6LoWPAN<br/>Header Compression]
    E --> E1[IEEE 802.15.4 MAC<br/>TDMA + CSMA/CA<br/>Hop-by-Hop Security]
    F --> F1[IEEE 802.15.4 PHY<br/>2.4 GHz<br/>16 Channels]

    style A fill:#E67E22,stroke:#2C3E50,color:#fff
    style B fill:#2C3E50,stroke:#16A085,color:#fff
    style C fill:#16A085,stroke:#2C3E50,color:#fff
    style D fill:#16A085,stroke:#2C3E50,color:#fff
    style E fill:#2C3E50,stroke:#16A085,color:#fff
    style F fill:#7F8C8D,stroke:#2C3E50,color:#fff

Figure 1006.1: ISA 100.11A Protocol Stack with IPv6/6LoWPAN and Tunneled Industrial Protocols

{fig-alt=“ISA 100.11A protocol stack showing Application layer with tunneled protocols (Modbus, HART), Transport layer with UDP security, Network layer with IPv6/6LoWPAN compression, Data Link layer with IEEE 802.15.4 MAC using hybrid TDMA/CSMA and hop-by-hop security, Physical layer with 2.4 GHz IEEE 802.15.4”}

This variant directly compares the protocol stacks side-by-side:

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#E67E22', 'secondaryColor': '#16A085', 'tertiaryColor': '#7F8C8D', 'fontSize': '10px'}}}%%
graph TB
    subgraph ISA["ISA100.11a Stack"]
        IA["Application:<br/>Native + Tunneled<br/>(Modbus, HART, FF)"]
        IT["Transport:<br/>UDP"]
        IN["Network:<br/>IPv6 + 6LoWPAN"]
        IM["MAC:<br/>TDMA + CSMA/CA"]
        IP["PHY: IEEE 802.15.4<br/>2.4 GHz"]
        IA --> IT --> IN --> IM --> IP
    end

    subgraph WHART["WirelessHART Stack"]
        WA["Application:<br/>HART Commands Only"]
        WT["Transport:<br/>None (direct)"]
        WN["Network:<br/>Proprietary Graph Routing"]
        WM["MAC:<br/>TDMA Only"]
        WP["PHY: IEEE 802.15.4<br/>2.4 GHz"]
        WA --> WT --> WN --> WM --> WP
    end

    subgraph KEY["Key Differences"]
        K1["ISA: IPv6 = IT Integration"]
        K2["WHART: Graph = Determinism"]
        K3["ISA: CSMA = Flexibility"]
        K4["WHART: TDMA = Reliability"]
    end

    ISA --> KEY
    WHART --> KEY

    style ISA fill:#7F8C8D,stroke:#2C3E50,color:#fff
    style WHART fill:#16A085,stroke:#2C3E50,color:#fff
    style KEY fill:#2C3E50,stroke:#16A085,color:#fff

Both protocols share the same IEEE 802.15.4 PHY layer but diverge above that. ISA100.11a uses standard Internet protocols (IPv6/UDP), while WirelessHART uses proprietary optimized layers. The trade-off: IT compatibility vs proven industrial reliability.

1006.3.2 Security Architecture

Key Types: - Master Key: Long-term device credential - Session Keys: Per-device communication - DLL Keys: Data link layer encryption (hop-by-hop) - Network Keys: Network layer encryption (end-to-end)

Dual Security: - Data Link Layer encryption (hop-by-hop, like WirelessHART) - Transport Layer security (end-to-end, UDP/IPv6 layer)

1006.4 ISA 100.11A vs WirelessHART

1006.4.1 Comparison Table

Feature ISA 100.11A WirelessHART
Standard Body ISA HART Communication Foundation
International Std IEC 62734 IEC 62591
Physical Layer IEEE 802.15.4 (2.4 GHz) IEEE 802.15.4 (2.4 GHz)
MAC TDMA + CSMA/CA (hybrid) TDMA only
Network Layer IPv6 / 6LoWPAN Proprietary (graph routing)
Transport UDP / TCP (IPv6) Proprietary
Application Native + Tunneled HART commands only
Topology Star, mesh, hybrid Mesh
Flexibility High (multiple options) Moderate (optimized for HART)
Determinism Optional (TDMA mode) Always (TDMA only)
IT Integration Excellent (IPv6 standard) Moderate (proprietary above PHY)
Backward Compat Tunneled protocols HART devices
Market Focus Broad industrial Process automation (HART)
Adoption Moderate High (process automation)

1006.4.2 Philosophical Differences

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#E67E22', 'secondaryColor': '#16A085', 'tertiaryColor': '#7F8C8D'}}}%%
graph LR
    A[Design Philosophy] --> B[WirelessHART<br/>Specialized Industrial]
    A --> C[ISA 100.11A<br/>Flexible General]

    B --> B1[HART Backward Compatible<br/>Process Automation Focus]
    B --> B2[Proprietary Stack<br/>HART-7 Protocol]
    B --> B3[Fixed TDMA<br/>Deterministic Only]
    B --> B4[Source Routing<br/>Centralized]

    C --> C1[Internet Standards<br/>IPv6/6LoWPAN Native]
    C --> C2[Open Protocols<br/>Tunneling Support]
    C --> C3[TDMA + CSMA Hybrid<br/>Flexibility]
    C --> C4[Multiple Routing<br/>Graph + AODV]

    style A fill:#E67E22,stroke:#2C3E50,color:#fff
    style B fill:#2C3E50,stroke:#16A085,color:#fff
    style C fill:#16A085,stroke:#2C3E50,color:#fff

Figure 1006.2: WirelessHART vs ISA 100.11A Design Philosophy Comparison

{fig-alt=“Philosophical differences between WirelessHART (specialized for process automation with HART backward compatibility, proprietary stack, fixed TDMA) versus ISA 100.11A (flexible general-purpose with IPv6/6LoWPAN, open protocols, hybrid TDMA/CSMA, multiple routing options)”}

This variant presents the WirelessHART vs ISA 100.11A decision through a use-case flowchart - useful for engineers selecting the appropriate industrial wireless standard for specific plant requirements.

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#E67E22', 'secondaryColor': '#16A085', 'tertiaryColor': '#7F8C8D', 'fontSize': '11px'}}}%%
flowchart TD
    START["Industrial Wireless<br/>Project Requirements"]

    Q1{"Existing HART<br/>infrastructure?"}
    Q2{"Need to tunnel<br/>multiple protocols?<br/>(Modbus, Profibus)"}
    Q3{"IT/IPv6 integration<br/>required?"}
    Q4{"Need both TDMA<br/>and CSMA/CA?"}

    WHART["✅ WirelessHART<br/>━━━━━━━━━━<br/>• HART backward compatible<br/>• Proven 99.9%+ reliability<br/>• Large installed base<br/>• Simpler deployment<br/>━━━━━━━━━━<br/>Cost: $150-300/device"]

    ISA["✅ ISA 100.11A<br/>━━━━━━━━━━<br/>• IPv6/6LoWPAN native<br/>• Protocol tunneling<br/>• Flexible MAC modes<br/>• IT-friendly addressing<br/>━━━━━━━━━━<br/>Cost: $200-400/device"]

    BOTH["Consider Both:<br/>Dual-protocol gateways<br/>available ($2,500-5,000)"]

    START --> Q1
    Q1 -->|"Yes<br/>(HART devices)"| WHART
    Q1 -->|"No"| Q2

    Q2 -->|"Yes"| ISA
    Q2 -->|"No"| Q3

    Q3 -->|"Yes<br/>(Enterprise IT)"| ISA
    Q3 -->|"No"| Q4

    Q4 -->|"Yes<br/>(Mixed traffic)"| ISA
    Q4 -->|"No<br/>(Deterministic only)"| WHART

    WHART -.->|"Legacy + New"| BOTH
    ISA -.->|"Greenfield"| BOTH

    style START fill:#2C3E50,stroke:#16A085,color:#fff
    style Q1 fill:#16A085,stroke:#2C3E50,color:#fff
    style Q2 fill:#16A085,stroke:#2C3E50,color:#fff
    style Q3 fill:#16A085,stroke:#2C3E50,color:#fff
    style Q4 fill:#16A085,stroke:#2C3E50,color:#fff
    style WHART fill:#E67E22,stroke:#2C3E50,color:#fff
    style ISA fill:#E67E22,stroke:#2C3E50,color:#fff
    style BOTH fill:#7F8C8D,stroke:#2C3E50,color:#fff

Figure 1006.3: Decision flowchart for selecting between WirelessHART and ISA 100.11A based on plant requirements

{fig-alt=“Decision tree for industrial wireless protocol selection. If existing HART infrastructure exists, choose WirelessHART for backward compatibility. If need to tunnel multiple protocols like Modbus/Profibus, choose ISA 100.11A. If IT/IPv6 integration required, choose ISA 100.11A. If need mixed TDMA and CSMA/CA, choose ISA 100.11A. Otherwise choose WirelessHART for proven deterministic performance. Dual-protocol gateways available for brownfield plants with mixed requirements.”}

1006.5 Key Concepts

  • Hybrid MAC: Flexible medium access combining TDMA and CSMA/CA based on application needs
  • IPv6 / 6LoWPAN: Standard internet protocol stack integration instead of proprietary layers
  • Usage Classes: Different reliability/latency profiles (0-6) for diverse industrial applications
  • Multiple Transports: Support for UDP, TCP, and other protocols
  • CSMA/CA Option: For non-deterministic or monitoring applications without TDMA overhead
  • DLL & Network Encryption: Defense-in-depth security with hop-by-hop and end-to-end encryption
  • Flexibility over Optimization: Standard-based approach supporting multiple protocols and topologies

1006.6 Knowledge Check

Test your understanding of ISA 100.11a protocol stack and comparison.

Question 1: An ISA 100.11A backbone router receives a packet with compressed IPv6 header (7 bytes) destined for the enterprise network. What transformation occurs at the router?

Explanation: Backbone Routers and Gateways perform header transformation: (1) Incoming from 6LoWPAN network: Receive 6LoWPAN compressed packet with 7-byte header. (2) Decompression: Reconstruct full 40-byte IPv6 header from compressed representation. Addresses: fe80::1234 → 2001:db8:100::device:1234. (3) Forwarding: Send standard IPv6 packet to enterprise network. Reverse direction: (1) Receive standard IPv6 packet (40-byte header), (2) Compress using 6LoWPAN IPHC (40 → 7 bytes), (3) Forward to wireless network. This transparent adaptation allows ISA 100.11A sensors to appear as normal IPv6 hosts to the IT network, while conserving bandwidth on the constrained wireless side. The gateway/border router is the adaptation point between 6LoWPAN and standard IPv6.

Question 2: A pressure sensor publishes critical alarms (Usage Class 4: Alerting) that must reach the control room within 5 seconds with 99% reliability. The ISA 100.11A network has average latency of 80ms per hop. What is the maximum hop count to meet requirements?

Explanation: Usage Class 4 (Alerting) requirements: <5 seconds latency, 99% reliability. Seems relaxed, but must account for: (1) Average vs worst-case: 80ms average per hop. Worst-case with scheduling delay + jitter: 150-200ms per hop. (2) Retransmissions: 99% reliability means 1% loss rate. With 10 hops, cumulative success = 0.99^10 = 90.4% (below 99%). Need some retries. (3) Network congestion: Alerting packets may queue behind periodic data. (4) Practical limit: While 5000ms/200ms = 25 hops theoretically works, best practice is 5-10 hops maximum for alerting to maintain <1 second typical latency and >99.5% reliability with margin. Solution: Deploy routers to ensure critical sensors are within 5-7 hops of gateway. Use TDMA mode for alerting messages (not CSMA/CA) for deterministic latency.

Question 3: What is the main advantage of ISA 100.11a’s hybrid MAC over WirelessHART’s TDMA-only approach?

Explanation: ISA 100.11a supports both: TDMA (Time Division Multiple Access): Deterministic, scheduled timeslots. Use for control loops requiring guaranteed latency and high reliability. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance): Contention-based, more flexible. Use for monitoring and diagnostic applications where determinism is less critical. Benefits: Critical control loops can use TDMA for reliability, monitoring devices can use CSMA/CA for simplicity, mixed network: some devices TDMA, others CSMA/CA, application decides the appropriate mode. WirelessHART uses TDMA only—optimized but less flexible.

Question 4: An ISA 100.11A network has 4 key types: Master, Session, DLL, and Network keys. A packet travels from Sensor A → Router B → Router C → Gateway D. Which keys are used where?

Explanation: ISA 100.11A uses layered security (defense in depth): DLL (Data Link Layer) Keys provide hop-by-hop encryption—each wireless hop is encrypted/decrypted at intermediate routers. Packet encrypted at A with DLL key, decrypted at B, re-encrypted with different DLL key for B→C hop, etc. Routers can inspect packet headers for forwarding. Network Keys provide end-to-end encryption—payload encrypted at source A, stays encrypted through all hops, only decrypted at final destination D. Routers cannot inspect payload. Both can be used simultaneously: DLL protects each wireless hop, Network protects payload across entire path. Master keys are long-term credentials for device authentication during join. Session keys are derived per-device for specific communication sessions. This multi-layer approach provides security even if one key is compromised.

1006.8 Summary

ISA 100.11A’s protocol stack reflects its flexible, standards-based approach to industrial wireless:

  • The layered architecture includes Application (native + tunneled protocols), Transport (UDP), Network (IPv6/6LoWPAN), Data Link (IEEE 802.15.4 with TDMA/CSMA hybrid), and Physical layers
  • Security uses dual encryption with DLL keys for hop-by-hop protection and Network keys for end-to-end confidentiality, providing defense-in-depth
  • Compared to WirelessHART, ISA 100.11A offers IPv6 standard integration, protocol tunneling, flexible MAC modes, and multiple topology options
  • WirelessHART prioritizes determinism and HART ecosystem compatibility, while ISA 100.11A emphasizes flexibility and IT integration
  • Protocol selection depends on existing infrastructure (HART devices), multi-protocol needs, IT integration requirements, and determinism criticality
  • Both standards share IEEE 802.15.4 physical layer but diverge significantly in upper layers, making them incompatible without dual-protocol gateways

1006.9 What’s Next

Continue to ISA 100.11A Labs and Security to explore hands-on simulations, protocol tunneling examples, and comprehensive security key management.

1006.10 References

  • ISA100.11A-2011 Standard
  • IEC 62734: Industrial Networks - Wireless Communication Network and Communication Profiles
  • International Society of Automation: www.isa.org
  • ISA100 Wireless Compliance Institute