VoIP

The Many Challenges of VoIP Peering

At ISPCON, one speaker explained why building a global VoIP network will be far more challenging than the stitching together of a global IP network through peering agreements.

by Alex Goldman ISP-Planet Managing Editor [October 21, 2005]

Chris Celeberti, director of advanced services at Sterling, Va.-based data clearinghouse operator Neustar began his ISPCON talk, QoS and Peering for VoIP/SIP Services, by reminding attendees that VoIP is far more than just IP.

He said that considerations in VoIP peering include:

• Latency
• Jitter
• Out of order delivery of packets
• Packet loss
• ENUM
• Security
• SPIT
• PSTN on/off ramp

Latency, Celeberti said, is affected by the network, the jitter buffer in the edge equipment, and by the CODEC used. CODECs offer a tradeoff: a higher bandwidth CODEC provides higher sound quality and lower latency but is less tolerant of packet loss.

As to packet loss, Celeberti warned attendees that their networks would be subject to higher standards. "In IP peering, a packet loss of one to three percent is okay, but even 1 percent is not acceptable for VoIP traffic."

Celeberti warned that more than one ENUM system is being developed. All-inclusive public ENUM systems are delayed by the involvement of numerous government bureaucracies. Private ENUM systems, for within a single corporation, for example, are easier to implement but are not necessarily compatible with other ENUM systems.

The SBC problem
When IP traffic is handed from one network to another, it is routed, eventually, to its destination. But, Celeberti said, VoIP networks have Session Border Controllers.

In IP peering, traffic going from network A to network C can go through network B. With SBCs, network B is not necessarily allowed to transit traffic between network A and network C.

There's a good reason to have SBCs. Celeberti said bluntly, "we must have security, or we'll have a mess."

Security is a key part of the fight against VoIP spam, known as Spam over Internet Telephony, or SPIT.

He noted that VoIP is still illegal in some large nations, including China and India. In Italy, he said, the government is not worried about VoIP, but Telecom Italia, the ILEC, has thousands of people reading e-mail, searching for threats from Al Qaeda

Other issues
For last mile VoIP routing, NAT transversal can be a problem. Many residential users have wireless or other routers, and business users are often behind a firewall, so a call cannot necessarily be sent to an IP address. There are mechanisms to solve the problem, but they don't make VoIP peering simpler.

In spite of all of this, there is some peering occurring through specialist organizations like London, England-based XConnect and New York, N.Y.-based Stealth Communications.

Celeberti warned that ISPs should eventually expect to pay for transit. "I do not believe we can sustain free peering," he said.

He added that some open source initiatives, such as Distributed Universal Number Discovery (DUNDi) may be useful for smaller ISPs but added, "I don't think DUNDi scales. I don't see SBC using it."

For many ISPs, there could be no greater endorsement of DUNDi.

—End