How Does a Token Ring Work
Below is a MRR and PLR article in category Computers Technology -> subcategory Communications.
How Does a Token Ring Work
Overview
Token Ring is a type of local area network (LAN) technology developed in the 1960s by IBM’s Olof Söderblom. Its initial patents were credited in 1981, and IBM actively promoted it in the early 1980s. Token Ring’s architecture relied on active multi-station access units (MSAUs) and the IBM Structured Cabling System. The Institute of Electrical and Electronics Engineers (IEEE) later standardized it as IEEE 802.5. Although it saw early success, the rise of Ethernet and new cabling standards in the early 1990s led to its decline. Despite aggressive marketing efforts by IBM to revive it, Token Ring couldn't compete with Ethernet's cost-effectiveness. Today, IBM no longer supports Token Ring technology.
Brief History
In its early development, IBM tested the Token Ring at 4 Mbit/s in 1985, eventually achieving 16 Mbit/s by 1989. Apollo Computer introduced their Apollo Token Ring (ATR) at 12 Mbit/s in 1981, and Proteon launched the ProNet-10 Token Ring at 10 Mbit/s in 1984. Notably, IBM’s version was incompatible with those from Apollo and Proteon.
How Token Ring Works
Token Ring networks arrange stations in a ring topology. A control token circulates within this ring, allowing stations to transmit data. Visualize it as a star with loops radiating from the central station to surrounding hubs, using IBM Type-1 shielded twisted pair cables. However, these cables were bulky, requiring significant space and featuring complex connectors.
Token Ring operates at the data link layer (DLL) of the OSI model, utilizing a three-byte token to manage access across stations. A station acquires the token to transmit data, passing it along to its downstream neighbor. IEEE 802.5 initially standardized speeds of 4 Mbit/s and 16 Mbit/s. Eventually, speeds expanded to 100 Mbit/s and even 1000 Mbit/s by 2001, though these weren't widely adopted.
Despite early perceptions of Token Ring's superiority over Ethernet, testing revealed otherwise. Ethernet's advancements in speed and switching capabilities made it more reliable and efficient, leading to Token Ring's obsolescence.
Inserting a Station into a Token Ring
To incorporate a station into a Token Ring network, a five-phase insertion process is required:
1. Lobe Check (Phase 0): The station conducts a lobe media check, sending and receiving 2000 test frames wrapped at the MSAU to ensure error-free transmission.
2. Physical Insertion (Phase 1): The station sends a 5-volt signal to the MSAU, opening the relay.
3. Address Verification (Phase 2): The station sends MAC frames to its own MAC address in the Token Ring frame's destination field. If the frames return correctly, the station participates in a ring poll process every seven seconds, fully integrating into the MAC management functions.
4. Participating in Ring Poll (Phase 3): The station identifies its Nearest Active Upstream Neighbor (NAUN). Downstream neighbors are updated with its address, completing a new ring map.
5. Requesting Initialization (Phase 4): Finally, the station requests configuration from the parameter server through a special address known as the Token Ring bridge.
In summary, while Token Ring was once a pioneering technology, it was eventually eclipsed by Ethernet's advancements in speed and efficiency.
You can find the original non-AI version of this article here: How Does a Token Ring Work.
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