network address (CEi may be required). The switching network may support an APi, but then used according to the layer APi method 3. Socket route: This type of route requires both a network address and an APi. The switching network supports the layer-element APi method. 4. Link route: both global, switched and socket routes imply some kind of routing in the common element. Routes may, however, be realized just as point-to-point hosting networks, in which case no hosting network address is needed (other parameters may, however, be required in an REdef). Such routes are called link route. 5. Physical route: a physical route belongs to a logical network that interfaces a physical-media stratum. It requires neither an REi nor an REdef. Criterion 3: routes that are established on-demand are drawn with dotted lines, all other routes with solid lines. Note that this distinction may be used both for global routes, socket routes and switched routes. On-demand route, i.e., it must be requested by the logical network that uses it before it can be used Semi-permanent or permanent route, i.e., it need not be requested before used. The route may be established by management actions, or represent a route in a datagram switching network Fig. 3.18 Route symbols that identify the permanency of a route Criterion 4: routes that comprise more than one channel are drawn with double lines, as the example in Fig. 3.19. If nw1 type is BRA a LAPD route, realized by a BRA agent layer. The route contains 127 point-to-point connections Fig. 3.19 Route symbol for routes with multiple connections/channels 3.3 Route Properties and Symbols The symbol can be annotated with the number of connections or channels in the route. Normally, all channels in a multiple-channel route are identical. When such a route is used, data to be sent or received must be identified as to which channel it belongs. Methods that are used differ between synchronous and asynchronous routes: In synchronous routes, channels are identified by their position in the frames of t