4.6.2

4.6.2 End-to-end transit delay

The purpose of the End-to-end transit delay information element is to request and indicate the nominal maximum permissible transit delay applicable on a per call basis to that virtual call.

The End-to-end transit delay information element is coded as shown in Figure 4-38 and Table 4-28.

The maximum length of this information element is 11 octets.

Bits
8	7	6	5	4	3	2	1	Octets
	End-to-end transit delay Information element identifier
0	1	0	0	0	0	1	0	1
Length of end-to-end transit delay contents								2
0 ext.	Spare					Cumulative transit delay value		3
0 ext.	0	0	0	0	0	Cumulative transit delay value		3
0 ext.	Cumulative transit delay value (cont.)							3a
1 ext.	Cumulative transit delay value (cont.)							3b
0 ext.	Spare					Requested end-to-end transit delay value		4*
0 ext.	0	0	0	0	0	Requested end-to-end transit delay value		(Note 1)
0 ext.	Requested end-to-end transit delay value (cont.)							4a*
1 ext.	Requested end-to-end transit delay value (cont.)							4b*
0 ext.	Spare					Maximum end-to-end transit delay value		5* (Note 2)
0 ext.	0	0	0	0	0	Maximum end-to-end transit delay value		5* (Note 2)
0 ext.	Maximum transit delay value (cont.)							5a*
1 ext.	Maximum transit delay value (cont.)							5b*
NOTES 1. Octets 4, 4a and 4b are optional. If present, these octets are always interpreted as Requested end-to-end transit delay. 2. Octets 5, 5a and 5b are optional. If present, octets 4, 4a and 4b must also be present.

Figure 4-38/Q.931

End-to-end transit delay information element

Table 4-28/Q.931

End-to-end transit delay information element

Cumulative transit delay value [octet 3 (bits 1-2) octets 3a and 3b]

Cumulative transit delay value binary encoded in milliseconds. Bit 2 of octet 3 is the highest order bit and bit 1 of octet 3b is the lowest order bit. The cumulative transit delay value occupies 16 bits total.

Requested end-to-end transit delay value [octet 4 (bits 1-2) octets 4a and 4b]

Requested end-to-end transit delay value binary encoded in milliseconds. Bit 2 of octet 4 is the highest order bit and bit 1 of octet 4b is the lowest order bit. The requested end-to-end transit delay value occupies 16 bits total.

Maximum end-to-end transit delay value [octet 5 (bits 1-2) octets 5a and 5b]

Maximum end-to-end transit delay value binary encoded in milliseconds. Bit 2 of octet 5 is the highest order bit and bit 1 of octet 5b is the lowest order bit. The maximum end-to-end transit delay value occupies 16 bits total.

Note - For a Recommendation X.31 type of access to an ISDN the procedures only apply in the notification phase at the terminating exchange. At the terminating exchange, if the End-to-End Transit Delay facility is present in the X.25 [5] incoming call request packet, the contents should be copied into End-to-end transit delay information element as follows:

i) The cumulative transit delay field (octets 3 and 4) of the X.25 end-to-end transit delay facility should be copied into octets 3, 3a and 3b. The bit order should be preserved as described above in the description.

ii) If octets 5 and 6 are present in the Recommendation X.25 end-to-end transit delay facility, they should be interpreted as the requested end-to-end transit delay value. The value present should be copied into octets 4, 4a and 4b. The bit order should be preserved as described above in the description.

iii) If octets 7 and 8 are present in the Recommendation X.25 end-to-end transit delay facility, the value present is the minimum end-to-end transit delay allowed. Octets 7 and 8 should be copied into octets 5, 5a and 5b. The bit order should be preserved as described above in the description.