3.6	Recommendation I.335



ISDN ROUTING PRINCIPLES

















































































	It should be noted that the user specifies only the service required. The network allocates the resources to set up a 
connection of the specific

type as necessary to support the requested service. For certain services, additional network functions, e.g. additional lower 
layer function and/or higher layer functions, may be required as depicted in Figure 1/I.335. For examples of such cases 
refer to Recommendation I.310.  





































	Figure 2/I.335 shows the general relationship between telecommunication services and ISDN connection types. It also 
shows in general the association with the actual realization of a service provision (call) by the establishment of a connection 
through the selection of a route.  









-    an appropriate association between the selected functional grouping in         terms of a physical realization, i.e. the 
network allocates the set of         connection elements necessary to realize the appropriate connection type.  

	The concept of connection type describes network capabilities using the attribute technique. One of these attributes is 
known as "Information (Transfer Susceptance". Some other attributes (e.g. "Connection Control Protocol") describe the sig-
nalling capabilities.  









































	-	CCITT No. 6 signalling







Figure 3/I.335 shows the relationship between recommendations relating to routing











































































































	m)	Time of day



	Because of varying traffic distributions during a 24 hours period, it maybe advantageous to change the call routing 
arrangements dependant of time of day.  4.	Generic performance parameters



	Nine generic primary performance parameters are listed below. These have been developed as a result of the matrix 
approach described in AnnexA. These parameters may be used in developing specific QOS and NP parameters:



	-	Access speed



	-	Access accuracy



	-	Access dependability



	-	Information transfer speed



	-	Information transfer accuracy



	-	Information transfer dependability



	-	Disengagement speed



	-	Disengagement accuracy



	-	Disengagement dependability



	Section 3.4.2 defines derived performance parameters in addition to primary parameters. Derived performance parame-
ters are determined utilizing a function of the primary performance parameter values. Recommendation G.821 defines one 
such function, which identifies transitions between available and unavailable states based on a threshold for severely errored 
seconds. The generic derived performance parameter associated with such a function is availability.



	Examples of specific primary and derived performance parameters for bearer service QOS and those for circuit-switched 
and packet-switched NP are provided in AnnexB.