In this case the media is the space and the link between the two local offices is the Microwave link. The users from the left want to communicate the users on the right. They have to share the common media. This can be done in two ways: First, the users can take turns; each one periodically uses the microwave link for a short period of time. This time-sharing is known as Time division Multiplexing (TDM). | CSN200 Introduction to Telecommunications, Winter 2000 Lecture-28 Multiplexing Trunks and Multiplexing: What happens, when there is only one media available between two local offices, as shown below? ℡ ℡ ℡ ℡ Local Local ℡ Office Office ℡ ℡ ℡ ℡ ℡ In this case the media is the space and the link between the two local offices is the Microwave link. The users from the left want to communicate the users on the right. They have to share the common media. This can be done in two ways: First, the users can take turns; each one periodically uses the microwave link for a short period of time. This time-sharing is known as Time division Multiplexing (TDM). Second, the bandwidth of the microwave link can be divided among logical channels, with each user having exclusive possession of some frequency band. Think the microwave link as a wide road. The road is then divided into lanes and then each car is using their own lane. This sharing by frequency band is known as Frequency division Multiplexing (FDM). • Sharing one media by multiple users is known as multiplexing. If the number of users are high then in the TDM each users have to wait for a long time to get their turn and is not a very practical way of sharing the media. So, FDM is a better way of sharing the media. You could ask, why we are not establishing the same number of microwave links as the users. But are limited by the one media. The other microwave links have to use different frequency bands, again an example of FDM by the links. This problem of one media can be solved by using multiple copper cables or fiber optic strands. This is again impractical in terms of costs. Page 1 (7) CSN200 Introduction to Telecommunications, Winter 2000 Lecture-28 Multiplexing This problem of one media can be solved by transmitting copper cables or fiber optic strands. All these media have their band limitation, copper have the lowest. So we need lots of links and this is again impractical in terms of costs and some time
