TIPOS DE FURGONETAS CAMPERIZABLES

The abstraction of calls, devices, and connections is illustrated graphically using a notation based on simple symbols. This graphical notation allows the depiction of both a specific situation in a telephone system at a moment in time, or a whole scenario involving a sequence of activities. Much the way that standard musical notation allows composers, arrangers, and musicians to easily describe and interpret a piece of music, this graphical notation allows material of an equally complicated nature—the activity inside a telephone system—to be easily and precisely communicated. This notation is used in standards documents, product documentation, and telephony reference materials to explain how certain telephone system functions behave. It is also used by those developing CT solutions in order to plan and troubleshoot their implementations.

Calls are represented as circles as shown in Figure 3-17. In order to make reference to a specific call, the calls are labeled with the letter "C" followed by a number.

Figure 3-17 Symbol for calls

Devices are represented as rectangles, as shown in Figure 3-18. They generally are labeled with the letter "D" followed by a number, so that different devices can be explicitly

referenced.

Figure 3-18 Symbol for devices

Connections represent the relationship between a call and a device. They are represented graphically as a line between a device and call, as shown in Figure 3-19. Connections do not require explicit labels because they can be uniquely identified by making reference to the labels for the device and the call (in that order) that they associate. Figure 3-19 shows two devices, D1 and D2, connected to call C1 with connections D1C1 and D2C1 respectively.

Figure 3-19

Symbolic representation of connections

Figures 3-20, 3-21, and 3-22 illustrate the use of this notation in a number of typical examples. In the first example, call C1 has two connections D1C1 and D3C1. The second example shows a multi-device call in which D1, D2, and D3 are all participating in call C2 using connections D1C2, D2C2, and D3C2 respectively. The last example shows call C3 in the process of being set up or cleared, as it is associated only with connection D4C3.

Figure 3-20 Two-device call

Figure 3-21 Three-way call

Figure 3-22 Single device in a call

3.5.1 Representing Directional Connections

Figure 3-23 shows how unidirectional connections are represented in graphical notation. By default, connections are bidirectional. If a particular connection is unidirectional, this is indicated by placing an arrowhead in the appropriate direction.

Figure 3-23 Directional connections

Asymmetric communication, where the data rate in one direction is different from the other, is abstracted as two separate calls consisting of unidirectional connections. In Figure 3-24, call C1 could be a high-speed data call, while call C2 could be a low-speed data call.

Figure 3-24

Asymmetric communication

If all the connections associated with a call are bidirectional, as shown in Figure 3-25, each device in the call receives a media stream representing a mix of the media streams from all of the other participants. Examples of calls involving unidirectional connections are shown in Figures 3-26 and 3-27.

Figure 3-25

Point-to-point and multi-point calls

In a scenario involving silent participation (as shown in Figure 3-26), the connection to the device which is only listening (D3C3) has an arrowhead to indicate that it is unidirectional towards the listening device (D3).

Figure 3-27 illustrates two scenarios involving unidirectional streams away from a device. In the first example, device D3 is delivering an announcement to an active call ("Please insert another 25¢ to continue

Figure 3-26

Multi-point with unidirectional stream towards device

this call" for example). All the other connections in the call are bidirectional and all hear the announcement. The second scenario involves broadcasting where all of the connections are unidirectional. One device, D3 in this case, is delivering a speech while the other devices listen so D3C4 is unidirectional from the device. D1 and D2 are not able to provide any media stream data to the call so their connections (D1C4 and D2C4) are unidirectional towards their devices.

Figure 3-27

Multi-point with unidirectional stream away from device

3.5.2 Connection State Representation

In graphical notation, connection states are represented by placing symbols over the line representing the appropriate connection. The symbols for the states are:

• 'a' representing alerting

• 'c' representing connected

• 'f' representing fail

• 'h' representing hold

• 'i' representing initiated

• 'n' representing null

• 'q' representing queued

If a particular connection is in the null state, meaning that it doesn't actually exist, the line representing the connection is generally omitted from the diagram altogether.

Figure 3-28 shows an example of how these symbols are used in graphical notation.

Figure 3-28

Connection state representation

In this example, call C1 has two connections: D1C1 and D2C1. Connection D1C1 is in the

connected state, indicating that it is active and that media streams are flowing. Connection D1C2 is in the fail state. A likely reason for the situation depicted in the example is that device D1 tried to place a call to device D2 but D2 was busy, so the attempt to connect to D2 failed. In this case, Device D1 probably would be receiving busy tone from the call.