Using Windows Messenger Voice and Video
使用 視窗信息 傳達語音與視瀕
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Will Windows Messenger voice and video real time communications work behind a residential home gateway that includes Network Address Translation (NAT) support? Until recently, I didn't think it would ever happen. I've been using developmental firmware and I've got really good news: Voice and video now work behind a NAT box in my home office with Windows XP Windows Messenger!
In the traditional world of residential/broadband gateways and NAT boxes, applications such as NetMeeting and many games depend on a fixed port and/or range of ports being available and usually can be accessed only after a manual configuration of ports, triggers, and DMZ zones. Windows Messenger is one of the first applications to take advantage of session initiation protocol (SIP), an emerging Internet Engineering Task Force (IETF) standard. When it comes to media streams for voice and video, SIP has the same problems behind a NAT box since voice and video are transmitted using the UDP protocol, not TCP. The port number of the end point PC will be wrong in the SIP headers due to the NAT. To fix this problem, Microsoft has implemented the Universal Plug and Play (UPnP) protocols in Windows XP, but that will only work if the NAT device also implements the UPnP protocol. (Without this support, voice and video using Windows Messenger will not work reliably behind a NAT device).
UPnP and the Networked Home
UPnP is a set of specifications that enable diverse devices to communicate with each other, announcing their presence and capabilities on a network and in the PC realm, allowing UPnP-enabled operating systems such as Windows XP and UPnP-enabled devices to recognize each other, communicate with each other, negotiate ports, and allow UPnP applications to work transparently with no configuration needed. In the simplest terms, UPnP devices broadcast their capabilities to all points on the network and allow authorized UPnP clients to act as control points. And, in the not-too-distant future, my networked UPnP alarm clock will turn the networked UPnP thermostat up on a wintry morning and turn on my networked coffee pot. Once a week, I'll send a shopping list of staples from my UPnP-networked refrigerator to my 802.11b-networked Pocket PC and when on the road, I'll probably be able to send instructions from my laptop to my UPnP personal video recorder to record a documentary I'd otherwise miss.
In tomorrow's world, UPnP devices will be embedded in many standard appliances such as TVs, microwave ovens, and HVAC systems and will be transparent to the entire range of networking mediums, including traditional cabled Ethernet, wireless 802.11 (a, b, g and whatever's next), HPNA, power line, Bluetooth, and 1384 or FireWire. Today, I've got a UPnP-enabled residential gateway and am seeing, for the first time, a small part of the home and home office of the future. It looks good indeed, and the best news is that you won't need a personal IT consultant to install it or keep it running.
Automatic Discovery and Setup
D–Link has released the UPnP firmware for their DI-804 router (or Internet gateway device in the new UPnP terminology) and it is available on their support site. I'm pleased to report that the firmware I'm using today is both UPnP enabled and SIP aware. To get the upgrade, visit D-Link Support and select firmware as a resource, then select DI-804 as a product, and then select PROM code and click the download button. I've been happily running Windows Messenger using voice and video behind this residential gateway device over my 802.11b wireless network. These devices are the best of all worlds. Older applications that still require manual opening of ports and special configurations can use the traditional and familiar manufacturer's interfaces. With UPnP-enabled applications such as Windows Messenger and UPnP-enabled home gateways, there's absolutely no configuration or intervention needed. It just works.
Installing a UPnP-enabled residential gateway couldn't be easier. Connect the uplink port to a cable or DSL modem and connect Ethernet clients to the internal LAN ports. Windows XP immediately discovers the presence of a UPnP residential gateway and configures it automatically. As with any other network connection, it is displayed in the Network Connections window; right-click the connection to display a menu that allows you to Enable/Disable the connection, view Status, or display the Internet Connection Properties dialog box. The image below shows the Status display.