In certain network topologies, a small control message that is passed from one station to another to grant the right to transmit data is known as what?

Introduction / Context:
Some local area network technologies use special control messages to regulate when each station is allowed to send data. Instead of allowing every device to transmit whenever it wants, they circulate a unique control packet that grants temporary permission to transmit. This approach helps prevent collisions and ensures orderly access to the shared medium. The control packet used in these systems has a specific name that appears often in networking textbooks and exam questions.

Given Data / Assumptions:

• The question refers to a small message passed between stations in a network.
• This message is used to control which station has the right to transmit data.
• Options include token, byte, word, ring and frame header.
• We assume a token passing network such as a token ring or token bus topology.

Concept / Approach:
In token passing networks, a special control frame called a token circulates continuously among all stations. When a station receives the token, it gains the right to transmit data for a limited time or a limited amount of information. After finishing, it releases the token so that it can pass to the next station. This mechanism avoids collisions because only the station holding the token can send data at a given moment. The token itself is a small message, often with a simple format, whose main purpose is to grant or relinquish the transmission privilege. Therefore, the correct term for this control message is token.

Step-by-Step Solution:

Verification / Alternative check:
Networking references describe token passing as an access method where a unique token travels around the network. Standards for token ring networks, such as IEEE 802.5, define the structure of the token frame and explain how stations use it to gain access to the medium. The term token is repeatedly used for the small control message that grants this right. Byte, word and frame header are generic data structure terms and do not specifically name the access control message. The word ring describes the physical or logical topology rather than the message. These descriptions confirm that token is the correct answer.

Why Other Options Are Wrong:

• Byte: A unit of data, usually eight bits, but not a specific control message for access rights.
• Word: A processor dependent group of bits representing a data unit, not a network control frame.
• Ring: Refers to the logical or physical layout of some networks, not to the message passed around.
• Frame header: Part of any data frame that contains addressing and control information, but not specifically the special access control message used in token passing schemes.

Common Pitfalls:
Some learners may confuse the term token with general words like frame or header because they know that network communication uses frames. The key is to remember that token has a special meaning in token passing access methods and always refers to the small control frame granting transmission rights. Visualising a ring of computers passing a token from one to the next can help fix this concept in your mind. When an exam question mentions a small message passed between stations to control access, token should immediately stand out as the correct choice.

Final Answer:
In token passing networks, the small control message used to pass the right to transmit is called a Token.