Information Technology Reference
of its input links, encodes them, and then forwards the information via multicasting or
broadcasting . Using this scheme, the network capacity can be enhanced. For the purpose
of data recovery, p -cycle will be used to deliver the combinations of data units to destination.
The 1+N protection against single link failures has three steps that are detailed as follows:
A. The p_Cycle Construction and Node Assignment Procedure to Cycles
First, a full p -cycle is found. The basic idea for receiving a second copy of data by a node
is to receive the signal via opposite directions; therefore, a full p -cycle is divided into two
unidirectional half p -cycles in opposite directions. These two p -cycles do not pass through the
same links, but must pass through the nodes in the same order. Then, two classes of
communication nodes should be selected in such a way that a node in one class communicates
with a node in another class. The sequence of nodes in each class is arbitrarily selected.
Nodes in one class have counter-clockwise direction and in another class have clockwise
direction. One of the two half p -cycles is a clockwise half p -cycle, and the other is a counter-
clockwise half p -cycle. They are used as follows:
A half p -cycle in the clockwise direction: On this half cycle, every node in each
class generates data units, encodes, and then transmits them. These encoded data are
decoded and removed by the corresponding receiver in two classes.
A half p -cycle in the counter-clockwise direction: Data units received on the primary
working paths in each class are encoded and transmitted by the nodes in every class.
The encoded data units are decoded and removed by the corresponding transmitters
in each class.
Note that encoding and decoding operations are simple module 2 addition operations
applied on data units that are transmitted and received on the same cycles. Transmissions take
place in rounds, i.e., encoded and transmitted data units on the p -cycle must belong to the
same round. A round can be started by one node, and then followed by other nodes. All nodes
in each class must keep track of the round number.
B. Encoding Operations
For every node in each class the network encoding operation is executed as:
The node will add the following data units to the signal received on the clockwise
Data unit generated by one node.
Data unit received on the primary path from a node on another class.
The node will add the following data units to the signal received on counter-
clockwise direction and will transmit the result on the outgoing link in the counter-
Data units transmitted in an earlier round.
Data units received on the primary path from a node in another class.