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../../principles/sharing.rst:636
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While the basic principles of the Token Ring are simple, there are several subtle implementation details that add complexity to Token Ring networks. To understand these details let us analyze the operation of a Token Ring interface on a station. A Token Ring interface serves three different purposes. Like other LAN interfaces, it must be able to send and receive frames. In addition, a Token Ring interface is part of the ring, and as such, it must be able to forward the electrical signal that passes on the ring even when its station is powered off.
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../../principles/transport.rst:707
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Three-way handshake : recovery from duplicates `CR` and `CA`
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../../glossary.rst:95
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Open Systems Interconnection. A set of networking standards developed by :term:`ISO` including the 7 layers OSI reference model.
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../../principles/dv.rst:70
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Assume that router `A` is the first to send its distance vector `[A=0]`.
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../../principles/sharing.rst:638
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When powered-on, Token Ring interfaces operate in two different modes : `listen` and `transmit`. When operating in `listen` mode, a Token Ring interface receives an electrical signal from its upstream neighbor on the ring, introduces a delay equal to the transmission time of one bit on the ring and regenerates the signal before sending it to its downstream neighbor on the ring.
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../../principles/transport.rst:711
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Data transfer
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../../glossary.rst:141
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OSPF
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`B` and `D` process the received distance vector and update their routing table with a route towards `A`.
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../../principles/sharing.rst:640
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The first problem faced by a Token Ring network is that as the token represents the authorization to transmit, it must continuously travel on the ring when no data frame is being transmitted. Let us assume that a token has been produced and sent on the ring by one station. In Token Ring networks, the token is a 24 bits frame whose structure is shown below.
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../../principles/transport.rst:713
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Now that the transport connection has been established, it can be used to transfer data. To ensure a reliable delivery of the data, the transport protocol will include sliding windows, retransmission timers and `go-back-n` or `selective repeat`. However, we cannot simply reuse the techniques from the datalink because a transport protocol needs to deal with more types of errors than a reliable protocol in datalink layer. The first difference between the two layers is the transport layer must face with more variable delays. In the datalink layer, when two hosts are connected by a link, the transmission delay or the round-trip-time over the link is almost fixed. In a network that can span the globe, the delays and the round-trip-times can vary significantly on a per packet basis. This variability can be caused by two factors. First, packets sent through a network do not necessarily follow the same path to reach their destination. Second, some packets may be queued in the buffers of routers when the load is high and these queuing delays can lead to increased end-to-end delays. A second difference between the datalink layer and the transport layer is that a network does not always deliver packets in sequence. This implies that packets may be reordered by the network. Furthermore, the network may sometimes duplicate packets. The last issue that needs to be dealt with in the transport layer is the transmission of large SDUs. In the datalink layer, reliable protocols transmit small frames. Applications could generate SDUs that are much larger than the maximum size of a packet in the network layer. The transport layer needs to include mechanisms to fragment and reassemble these large SDUs.
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../../glossary.rst:143
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Open Shortest Path First. A link-state intradomain routing protocol that is often used in enterprise and ISP networks. OSPF is defined in and :rfc:`2328` and :rfc:`5340`
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`D` sends its distance vector `[D=0,A=1]` to `A` and `E`. `E` can now reach `A` and `D`.
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../../principles/reliability.rst:435 • ../../principles/reliability.rst:452
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../../principles/sharing.rst:649
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802.5 token format
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../../principles/transport.rst:715
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To deal with all these characteristics of the network layer, we need to adapt the techniques that we have introduced in the datalink layer.
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../../glossary.rst:57
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packet
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`C` sends its distance vector `[C=0]` to `B` and `E`
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