Practical TCP/IP and Ethernet Networking- P12: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter | Networking fundamentals 37 node in a predefined order and as such it is an example of a point-to-point system. Nodes are arranged in a closed loop so that the initiating node is the last one to receive a packet. As a physical topology a ring describes a network in which each node is connected to exactly two other nodes. Information traverses a one-way path so that a node receives packets from exactly one node and transmits them to exactly one other node. A message packet travels around the ring until it returns to the node that originally sent it. In a ring topology each node can act as a repeater boosting the signal before sending it on. Each node checks whether the message packet s destination node matches its address. When the packet reaches its destination the destination node accepts the message then sends it back to the sender to acknowledge receipt. As you will see later in this chapter since ring topologies use token passing to control access to the network the token is returned to sender with the acknowledgment. The sender then releases the token to the next node on the network. If this node has nothing to say the node passes the token on to the next node and so on. When the token reaches a node with a packet to send that node sends its packet. Physical ring networks are rare because this topology has considerable disadvantages compared to a more practical star-wired ring hybrid which is described later. Figure Ring topology Ring topology advantages A physical ring topology has minimal cable requirements No wiring center or closet is needed The message can be automatically acknowledged Each node can regenerate the signal Ring topology disadvantages If any node goes down the entire ring goes down Diagnosis troubleshooting fault isolation is difficult because communication is only one-way Adding or removing nodes disrupts the network There will be a limit on the distance between nodes As well as these three main topologies some of the more important .
