IEEE 1355

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IEEE 1355, also known as Heterogeneous Interconnect (HIC), is a data communication standard designed to connect many inexpensive devices with a simple, low‑cost network. It uses a switched, point‑to‑point approach and can mix different kinds of media and speeds while sharing a common network logic. The goal is to be easy to implement in hardware, with little software, and to scale to large networks without needing very high transmission speeds.

How it works
- The network is a collection of two‑way, point‑to‑point links that can be wired or fiber. Each link is part of a larger switching network.
- Packets travel using wormhole routing: the first data byte directs the packet to its next hop, and each router passes the rest of the packet to the next link without inspecting the contents.
- Flow control is built into every link so receivers can tell senders to pause if needed. When a link is idle, it sends NULL characters to keep the connection synchronized.
- A packet has a defined start and end, and the first bytes describe the destination so hardware can route it quickly without buffering the whole packet.
- The system is designed to work with other networks (like IP or ATM) but does not depend on them for data transfers or switching.

Media and speeds (the “slices”)
IEEE 1355 defines several media types, called slices, to cover different price points and distance needs:
- DS-SE (Data and Strobe, Single‑Ended): the cheapest electrical option, up to about 200 Mbps and very short range (around 1 meter inside instruments).
- DS-DE (Data and Strobe, Differential): better noise immunity, up to about 200 Mbps over longer electrical runs (tens of meters).
- TS-FO (Three of Six Fiber Optical): inexpensive fiber option using plastic fibers, supporting around 200 Mbps up to a few hundred meters.
- HS-SE (High Speed, Single‑Ended): the fast electrical option, up to about 1 Gbps over short distances (a few meters).
- HS-FO (High Speed Fiber Optical): high‑speed fiber links up to about 1 Gbps over distances up to several kilometers, using various fiber types.
- HS-FO variants extend range and performance with different fiber types and connectors.

Key ideas behind the design
- The network is designed to be simple in hardware. No complex software is required to route data; a switching node handles routing with straightforward logic.
- It supports long and short cable types and even fiber, with standardized connectors and “half‑twist” cables to simplify wiring.
- The coding schemes (including 8B/12B at high speeds in some slices) help ensure reliable clocking and error detection without heavy protocol overhead.
- SpaceWire, a derivative used in space instruments, follows the same fundamental concepts but with adaptations for vacuum, vibration, and lightweight connectors.

Why it matters
- IEEE 1355 aims to be a low‑cost, scalable way to connect many devices in scientific labs, instruments, and control systems.
- It emphasizes reliability and straightforward implementation, which appeals to engineers who want robust data links without complex software.
- The standard’s flexible “slice” approach lets designers pick the right mix of price, speed, and distance for a given application, while still participating in a common network framework.

In practice, IEEE 1355 has found use in scientific instrumentation and research environments and has inspired SpaceWire, a widely used standard for space missions.