Switching network or matrix:
Major components of a switching system or an exchange office are the set of input and output circuits called inlets and outlets respectively. The primary function of a switching system is to establish an electrical path between a given inlet-outlet pair. The hardware used for establishing such a connection is called the switching matrix or the switching network. Figure 1 shows a model of a switching network with N inlets and M outlets.
Symmetric network: When the number of inlets equal to the number of outlets (N=M) in a switching network then it is called a symmetric network.
There are four types of connection can be established in a switching network as like below:
1. Local call connection between two subscribers in the same exchange
2. Outgoing call connection between a subscriber and an outgoing trunk, i.e to another exchange
3. Incoming call connection between an incoming trunk (from another exchange) and a local subscriber
4. Transit call connection between an incoming trunk and an outgoing trunk.
[ The links that run between the switching systems are called trunks and those that run to the subscriber premises are known as subscriber lines]
Floded network: When all the inlets/outlets are connected to subscriber lines in a switching network, it is called a floded network because the output lines are floded back to the input. The logical connections appears like below -
Non-floded network: When all the inlets/outlets are connected to the trunks ( links between exchanges ) in a switching network, it is called non-floded network. The logical connections appears like below -
In a folded network with N subscribers, there can be a maximum of N/2 simultaneous calls or information interchanges. The switching network may be designed to provide N/2 simultaneous switching paths, in which case the network is said to be non-blocking. In a non-blocking network, as long as a called subscriber is free, a calling subscriber will always be able to establish a connection to the called subscriber. In other words, a subscriber will not be denied a connection for want of switching resources. But, in general, it rarely happens that all the possible conversations take place simultaneously. It may, hence, be economical to design a switching network that has as many simultaneous switching paths as the average number of conversations expected. In this case, it may occasionally happen that when a subscriber requests a connection, there are no switching paths free in the network, and hence he is denied connection. In such an event, the subscriber is said to be blocked, and the switching network is called a blocking network. In a blocking network, the number of simultaneous switching paths is less than the maximum number of simultaneous conversations that can take place. The probability that a user may get blocked is called blocking probability.
Non-blocking network: When a calling subscriber always free to establish a connection ( doesn't matter on switching path or server ) in a network, it is called non-blocking network.
Blocking network: When a calling subscriber call is denied due to lack of switching paths or servers in a network, it is called blocking network.