Specifications

TD 92326GB
2009-03-10 / Ver. E
Installation and Operation Manual
VoIP Gateway
166
Tunnelling must be disabled in the VoIP Gateway definitions for any equipment, see
section 19.1.3 H.323 Interop Tweaks on page 136.
The following ports have to be released in both directions:
- Tcp: destination port 80 (http), any source port (for configuration).
- Tcp: Destination port 1720 (h.225), any source port (for VoIP calls). We recommend
releasing ports 1721, 1722, 1723, etc. The number of ports to be released result
from the number of connections and the administrator should do this, as required.
- Udp: destination port >= 2050, source port 5004 and 5005 (RTP) (for VoIP calls)
If the RAS protocol is to be used (recommended) the following ports also need to be
released.
- Udp: Destination port 1718 and 1719
- Udp: Source port 1719 (for RAS and h.225)
- Udp: Source port 5004 and 5005 (for RTP)
- In the configuration all RAS-Gateways must be set to “Register as gateway” mode,
the Remote gatekeeper IP address must be entered and the “Disable dynamic
signalling port” must be activated. In the Signalling Port field, the port (1720, 1721,
1722, 1723, etc.) for the “GWnn interface” must be entered.
- If the fax service is used, Udp: source port 5006 must also be released, as after
establishing a connection, it switches to T.38.
The number of ports to be released cannot be restricted if the VoIP Gateway has to
communicate with third party products. In that case all ports to and from the VoIP
Gateway must be released.
Note: If the RAS protocol is not used the QSIG tunnelling is not possible. This can lead to
performance limitations. For example, in a scenario where two locations with PBXs are
linked, no additional features can be transmitted.
• The VoIP Gateway is located in front of the firewall, which means that the data stream
does not need to pass the firewall. Bear in mind however, that in this case it is not
possible to establish voice connections from within your network to the VoIP Gateway.
It will not be not possible to operate across the firewall if your network is operated in NAT
mode and the product you are using does not support “H.323 NAT”.
B.2 VoIP and heavily loaded WAN Links
The voice quality can be affected if voice data is transmitted over heavily loaded, narrow
band WAN links and the links no longer can ensure adequate transmission quality. See the
tables under section Voice coding on page 137, and Packet size on page 138.
Prioritisation of voice data on the WAN links can help and this can usually be achieved by
the routers used.
Direct use can be made of the “Prioritisation of H.323 voice data” function, if it is
supported by your router.
If your router is able to use the “IP type of service” (TOS) field for prioritisation, you can
use this function. By default he VoIP Gateway sets the TOS field to 0x10 for all IP packets
that it transmits. This value can be changed as required.
If this is not the case, you can use the function “Prioritisation according to source/
destination address”, if available. In this way, data packets from and to the VoIP Gateway
are prioritized. This in effect corresponds to the prioritisation of voice data as above.
Tip: Hexadecimal, octal or decimal values can be entered; the entries 0x10, 020 and 16
are all equivalent. Remember that the same value should be set in the TOS field for
all devices.