In a bus topology you have a terminator which absorbs unused packet(noise).What happens in the case of a ring topology?
This assumes that you are speaking of token passing rings.
Most (all?) physical layer devices only accept packets addressed to them. In the early Ethernet days using COAX (10Base2, 10Base5) the terminator was used to prevent reflection of the data.
Most (all?) token passing ring technologies would re-generate the unchanged packet if the packet was not addressed to the PHY layer. A packet that traversed the entire network would be consumed by the sender.
In ring technologies the token controlled the ability to transmit new data.
In the case of other ring technologies, such as SONET, data is written into specific time-slots, so there is no token. Generally the time-slots have some fixed bandwidth associated with them, in the case of SONET it is an STS-1 or STM1.
This ring is not a real uninterrupted line like 10Base2-Ethernet, but every node is a terminator. It receives the packet on one side and sends it out again on the other side if it wasn't meant for this node. Otherwise, it justs send out the token again, without any data.
Additionally, there is a controller station that destroys packets after a certain time when no other node feels responsible for it.