Cisco, Microsoft will support and implement Interactive Connectivity Establishment (ICE) technology, which is a proposed IETF standard for allowing VoIP calls to traverse firewalls without compromising security. Listen in:Cisco's Cullen Jennings explains how ICE works and what it's killer application might be - and it's not straight voice over IP.Windows MediaMP3 (9.5MB)The two companies will support and implement Interactive Connectivity Establishment (ICE) technology, which is a proposed IETF standard for allowing VoIP calls to traverse firewalls without compromising security. At issue is network address translation (NAT ), which is one of the most basic methods for protecting client and other network-based devices behind a firewall. NAT distributes internal IP addresses to nodes and then translates the addresses to publicly routable IP addresses when traffic traverses the Internet. This can prevent a VoIP call from being set up because NAT makes each IP endpoint in a VoIP connection handshake seem unreachable to the other.Many companies have worked around NAT\/VoIP compatibility issues by tunneling IP voice traffic through VPN connections. This is common for remote users with softphone clients and laptops, who connect to a corporate IP PBX through a home firewall or a hotel broadband connection with a VPN link. Site-to-site VoIP setups also use tunneling, virtual LAN (VLAN ) segments over VPNs or point-to-point links to connect VoIP calls to offices protected via NAT firewalls.But some observers and standards crafters say such methods are stopgaps, and that VoIP connectivity should work as seamlessly across the Internet as browsing a Web site, sending e-mail or as in instant-messaging sessions.This is where ICE comes in. The technology works by discovering the internal IP address schemes of networks that the two VoIP endpoints are attached to, behind NAT firewalls. To do this, ICE uses existing protocols and IP address discovery mechanisms, such as Simple Traversal of UDP through NAT (STUN), Traversal Using Relay NAT (TURN) and Realm Specific IP. This requires servers that can accept STUN and TURN requests and broker these connections for VoIP devices, which are called initiators in the ICE model.STUN and TURN "by nature of their design, are difficult to operate through NAT," according to Jonathan Rosenberg, a Cisco engineer and author of the IETF Internet draft for ICE."ICE makes use of STUN and TURN, but uses them in a specific methodology, which avoids many of the pitfalls of using any one alone," Rosenberg writes in the ICE IETF draft proposal.The potential for any-to-any VoIP connectivity without impediment from NAT firewalls has strong promise for consumer VoIP technology, according to Don Proctor, senior vice president of the Voice Technology Group at Cisco. "Microsoft's and Cisco's endorsement of ICE standards bodes well for our mutual customers," he said in a statement. This is especially true considering that most home networks with broadband have Microsoft operating systems, are protected by broadband router\/NAT firewalls and connect to carrier networks with Cisco gear.For some companies that run their business phone systems on IP networks, the concepts behind ICE pose some security issues, and the problem ICE proposes to solve is not one that is very pressing for companies that use IP PBXs and IP phones."We run VoIP so that all of our traffic runs on our internal network," says Irving Tyler, CTO for Quaker Chemical, an industrial chemical manufacturer in Conshohocken, Pa. His firm uses Avaya IP phones, IP-enabled PBXs and Cisco switches and routers to connect users in the company's main office and satellite sales offices. Any VoIP calls made on the network run inside Quaker Chemical's firewall boundaries and over point-to-point WAN links. When calls leave the network, they're translated to digital public switch telephone network voice signals.The concept behind ICE - allowing IP communication devices to link with IP devices over the Internet, regardless of firewall configurations - might be a neat trick, but not an application his company is interested in now, Tyler says.Also, the methodology of ICE, in which behind-the-NAT IP addresses are discovered and shared among connecting parties, is something that businesses might be hesitant to explore."I could see people being leery about doing that," he says. If a carrier or VoIP vendor could provide security for such exchanges, "I think companies would be more likely to look into opening up their internal IP addresses."Proponents of the standard say the benefits of ICE will become more apparent when wide adoption of VoIP happens, and IP PBX installations become more mature. As more companies build security within network boundaries, ICE could play a role in simplifying voice-traffic management, says Cullen Jennings, a Cisco engineer.Like Quaker, most VoIP traffic in businesses runs behind the edge firewall. But "many enterprises are looking at deploying, or are already using, lots of NATs inside the network," he says. This could be a large company that shares one large network, but separates divisions or departments with internal firewalls for security, or IP address management.Branch offices sometime use NATs, so that devices can receive IP addresses from a local DHCP server, instead of a centralized source. ICE would help simplify VoIP connectivity in this case, as well, he adds.As for when ICE will show up in VoIP products, Jennings says this is a ways off."ICE is still a draft, not even an RFC yet, so no one can really say they support it," he says. "But [Cisco has] products that we are working on with a prestandard implementations of ICE."