Allworx 24X Manual de usuario descargar pdf (Pagina 18)

VoIP White Paper

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Revised: February 8, 2007

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9 Allworx Solves the SIP NAT Problem

Using VoIP protocols with NAT/Firewalls can be a big headache, unless you are using Allworx equipment.

Allworx products are designed to work together – automatically discovering networking topology between end-

points and adjusting all VoIP negotiations accordingly. Allworx products are able to do this even when third-

party firewalls are involved in the path, but this requires the use of Allworx IP phones or servers at the

associated end points. Non-Allworx end-points may not support all the necessary mechanisms to make this

possible.

Generally speaking, the primary requirement is for each Allworx server to have its WAN port connected directly

to the Internet at a publicly routable IP address. The Allworx server does NOT have to be the primary data

NAT/Firewall for the LAN; it must have a publicly routable WAN connection in parallel with an existing firewall.

Note: First introduced with Allworx server software Release 5.2, many times it is now also possible to place

the Allworx server behind a 3rd party NAT/Firewall. New advanced features were added in Release 5.2

to allow remote VoIP connectivity with a properly configured 3rd party firewall. See the admin manual

for details.

Remote end-points (such as Allworx IP phones) on a LAN can typically be behind any single NAT/Firewall,

whether it is an Allworx server acting as the firewall or any third-party NAT/Firewall product. InSciTek

specifically tests Cisco/Linksys™ and Sonicwall™ products as base verification reference points of typical

firewalls. Since InSciTek doesn’t control the implementation of third-party products, it can’t guarantee proper

operation, but would expect proper operation with most firewalls, including the ones InSciTek tested.

• Ensure the Local Area Network (LAN) is free of legacy hubs or repeaters and coaxial cable network

segments. A completely modernized network with fully 10/100 switched Ethernet infrastructures is ideal.

• Minimize the number of Ethernet switches installed in the closet. Daisy-chaining together small switches

to add more ports also adds latency and increases traffic flow bottlenecks. Installing one 48-port switch is

much better than installing four 12-port switches.

• Group all VoIP devices onto the same Ethernet switch, if possible.

• There is usually no need for queuing capable switches or routers on the LAN. Both Allworx and VoIP

phones employ sliding packet buffers that mask the modest packet loss and jitter (variable delay)

associated with busy LAN networks. Managed routers and switches are only concerns in large enterprise

networks.

• Don’t bother with a VLAN setup on the network switches unless the customer’s LAN is very large or users

are extremely heavy data users. In these cases, the Allworx should be configured as a LAN host and a

voice VLAN should be built on a separate switch to handle telephony traffic.

The simpler the site, the better the above tips will work. Things start to break down when network data traffic is

regularly very heavy and the network is getting overloaded, or the site has onsite routers to direct traffic

between more than one local subnet. If voice traffic is going to flow through those routers along with data,

significant attention to QoS topics will be required to ensure proper operation 100 percent of the time. Although

a full discussion of this case is beyond the scope of this paper, the next section talks about QoS issues over a

WAN and addresses some of the issues involved.

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Allworx 24X Manual de usuario Pagina 18