H.323 Gatekeeper

For IP Office 4.0+ systems these settings have been moved to the System | LAN1 and if appropriate System | LAN2 tabs.

H.323 VoIP phones must register with a gatekeeper in order to send and receive H.323 calls. The gatekeeper then controls permission for the phone to make or accept calls.

IP Office can act as the gatekeeper for H.323 phones. For full details relating to Avaya H.323 phones refer to the IP Office IP Phone Installation Manual. For non-Avaya H.323 devices, entry of an IP End-Points license is required.

System \| H.323 Gatekeeper
Control Unit	SOE , IP403 , IP406 V1 , IP406 V2 , IP412 , IP500 .
Software Level	1.0 to 3.2.
Mergeable	.

•	Auto-create Extn: Default = On When this option is on, an extension entry is automatically created for H.323 phones registering themselves with the IP Office as their gatekeeper.

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RTP Port Number Range: Software level = 3.0+.
For each VoIP call, a receive port for incoming Real Time Protocol (RTP) traffic is selected from a defined range of possible ports, using the even numbers in that range. The Real Time Control Protocol (RTCP) traffic for the same call uses the RTP port number plus 1, that is the odd numbers. For IP Office control units and Avaya H.323 IP phones, the default port range used is 49152 to 53246. On some installations, it may be a requirement to change or restrict the port range used. It is recommended that only port numbers between 49152 and 65535 are used, that being the range defined by the Internet Assigned Numbers Authority (IANA) for dynamic usage.

•	Port Range (maximum): Default = 53246. Range = 2048 to 65534. This sets the upper limit for the RTP port numbers used by the IP Office. The gap between the minimum and the maximum must be at least 1024.

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DiffServ Settings
When transporting voice over low speed links it is possible for normal data packets (1500 byte packets) to prevent or delay voice packets (typically 67 or 31 bytes) from getting across the link. This can cause unacceptable speech quality. Therefore it is important that all traffic routers and switches in a network to have some form of Quality of Service mechanism (QoS). QoS routers are essential to ensure low speech latency and to maintain sufficient audible quality.

IP Office supports the DiffServ (RFC2474) QoS mechanism. This uses a Type of Service (ToS) field in the IP packet header. The IP Office uses this field to prioritize voice and voice signaling packets on its WAN interfaces. Note that the IP Office does not perform QoS for its Ethernet ports including the WAN Ethernet port on the Small Office Edition.

The hex and decimal entry fields for the following values are linked, the hex value being equal to the decimal multiplied by 4.

•	DSCP (Hex): Default = B8 (Hex)/46 (decimal), Range = 00 to FC (Hex)/0 to 63 (decimal) The DiffServ Code Point (DSCP) setting applied to VoIP calls. For correct operation, especially over WAN links, the same value should be set at both ends.

•	DSCP Mask (Hex): Default = FC (Hex)/63 (decimal), Range = 00 to FC (Hex)/0 to 63 (decimal) Allows a mask to be applied to packets for the DSCP value.

•	SIG DSCP (Hex): Default = 88 (Hex)/34 (decimal), Range = 00 to FC (Hex)/0 to 63 (decimal) This setting is used to prioritize VoIP call signaling.

•	Site Specific Option Number (SSON): Default = 176, Range 128 to 254. Sets the site specific option number (SSON) used by the IP Office's internal DHCP server. This should match the SSON used by 4600 and 5600 Series IP phones to request installation settings.