 messages are difficult to reconcile within a single network. Data More efficient than circuit switching traffic tends to be bursty, consuming large volumes of Disadvantages bandwidth for occasional, short intervals, whereas voice traffic is predictable and requires a steady, low-delay, Performance drops when many users share the same network As far as communication networks are concerned, the notion of switching began with circuit switching. The Table 3.1-1 A comparison table on circuit switching VS packet telephone (or telegraph) company provided an electrical switching. path that allowed my instrument to connect to yours, perhaps with an operator plugging a connector into Circuit Packet a jack. The telephone company first combined (or switching switching multiplexed) multiple calls on a single physical circuit Dedicated "copper" path using Frequency Division Multiplexing (FDM). You can think of these discrete calling paths as the first virtual Bandwidth available Fixed Dynamic circuits in the sense that there was no longer a Potentially wasted one-to-one ratio between phone calls and wires (or in- bandwidth sulators on the utility pole). Store-and-forward transmission Frame switching Each packet follows the same route FDM turned out to be insufficiently scalable for the Call setup Required Not required demands of telephony. So, in the early 1960s the phone companies began digitizing voice signals and multiplexing When can congestion occur? At setup time On every packet them in the time domain using TDM. Charging Per minute Per packet For example, with TDM a T1 line interleaves 24 phone calls among successive time slots within 1 frame, Data and voice traffic CHAPTER 3.1 Figure 3.1-1 Circuit switching. which consists of 193 bits. Bit 1 through bit 8 are dedi- of outbreaks of Internet fever in many countries, it is still cated to channel 1, bit 9 through bit 16 are dedicated to heavily relied on in much of the world. Packets on an channel 2, and SO on, until bit 185 through bit 192 are X.25 network aren't slotted