July 1, 2004
VoIP Network Interconnection
By Justin J. Junkus, Telephony Editor
End-to-end telephone call completion often requires the use of multiple networks operated by two or more service providers. This month, we are going to discuss how cable voice over Internet protocol (VoIP) networks can be interconnected, and look at some real world solutions.
Interconnection of networks for completion of telephone calls also is known as origination-termination service. It can be accomplished in either or both of two modes: time division multiplexing (TDM) and native IP. Both are digital solutions.
TDM places the bits representing call information into fixed timeslots of a dedicated link between telephone switches, while native IP is a packet-switched solution, where the bits of call information are routed or switched as packets across interconnected packet networks. TDM is the way things have been done for circuit-switched telephony for a half century.
If a cable company has an agreement with a competitive local exchange (CLEC) or interexchange carrier (IXC) to provide interconnection to the PSTN, chances are TDM is part of the solution. Although carriers are moving toward native IP technology, there is a lot of TDM in telephone networks, and call information often must be converted from IP to TDM to complete a call. This conversion adds delays, and because TDM uses dedicated links, also can contribute to traffic bottlenecks.
Native IP interconnection is preferable for a telephone call that originates as VoIP; however, IP interconnection is evolving. The learning curve for native IP interconnection of VoIP calls began with enterprise private networks where cost savings outweighed quality concerns. As improved routing and switching protocols such as multiprotocol label switching (MPLS) became available, enterprise solutions were adapted to service provider needs.
In the hierarchical network model consisting of access, distribution and core layers, interconnection lives in the distribution and core network layers. In cable standards, our industry began with access issues and is working its way out toward the core layer.
The PacketCable 1.2 Architectural Framework Technical Report provides some general guidelines for interconnection of cable packet networks. This high- level view leaves a lot of leeway for vendor implementation, and the PacketCable certification process has not yet gone this deep into network hierarchy. Interconnection vendors, therefore, can claim compliance without much of a challenge.
Three telephony models
In practicality, the real world doesn't segment easily into vendors who specialize in pieces of the VoIP network hierarchy. Any vendor that has attained some mass beyond a single piece of hardware usually is trying to operate in any or all of the modes: trust me, don't worry, or plug me in.
"Trust me" describes a vendor's total solution for the service provider that wants to own and operate its network. "Don't worry" is the hosted VoIP solution, where the service provider owns the access piece, but purchases call processing and completion from the vendor, who owns and maintains the IP network. "Plug me in" is the mode for a vendor whose individual pieces of hardware or software comply with your standards and demonstrate some proof of interoperability with other vendors, such as having participated in PacketCable interoperability testing and certification.
For purposes of reviewing interconnection, this column will concentrate on the plug-me-in mode applied to the network interconnections required for long-distance and cross-provider VoIP calls. However, all of the vendors I interviewed were quick to note that origination and termination services were only part of their offerings. For them, interconnection is typically a wholesale service consisting of bulk minutes of call time. To differentiate themselves as value-added partners, most interconnection vendors also offer network-based services such as conferencing or calling cards.
At the National Cable Show and in subsequent interviews, I met with Callipso, Level 3 Communications and Volo Communications to learn how they differentiate themselves via VoIP network interconnection. I also touched base with Sonus Networks, which supplies some of the systems used by these vendors.
Callipso (www.callipso.com) was started in 1996 as a regional Internet service provider (ISP). It marketed interconnection and IP services to both enterprise and service-provider customers, using its own national network that runs platforms from both Lucent and Sonus. The Sonus platform is a relatively new addition to Callipso's network and is the enabler for native IP interconnection.
According to Callipso President Deb Lenart, since its inception, Callipso has invested over $120 million in 40 points of presence (POPs) across the United States, enabling it to cover 100 percent of the U.S. footprint with less hops than alternate interconnection services. "What makes us unique," says Lenart, "is that our network runs only VoIP, so we do not have to manage priorities for data and video, as well as voice." Also, Callipso has developed its own routing protocol, which it claims enables it to respond quicker to the changes in technology and customer needs.
Level 3 (www.level3.com) began operations about the same time as Callipso, but approached the market differently. Its original market was data network interconnection, although it has been working on VoIP solutions since 1998. Merle McNeal, Level 3 vice president of VoIP services, points out that the company developed its own Class 4 softswitch after it acquired XCOM, and helped develop the specifications for the session initiation protocol (SIP), which is emerging as a popular choice for IP multimedia applications. According to McNeal, "Level 3 operates the largest IP network in the U.S. It serves both voice and data interconnection customers and uses MPLS to prioritize voice over anything other than network control traffic."
McNeil stressed that one of the strengths of Level 3 is its local trunking capability. "We own 1.3 million local trunks across the U.S. When a cable operator decides to use our services for voice interconnection, chances are we already have facilities in place and are providing services to them for data." He noted that Level 3 pays close attention to route utilization to avoid service degradation. "If a route has more than 50 percent utilization, it will be augmented to avoid problems before they begin."
Volo Communications (www.volocommunications.com) is a relative new comer to the interconnection business. Founded in 2001 by Shawn Lewis, it operates 22 POPs across the United States and uses an MPLS-based backbone as the core network. When I asked Lewis what was unique about Volo, he said, "We have developed our own technology for our network. Since it is not purchased hardware, we can rapidly adapt to changes. Also, we don't compete with our customers for end-user business." In cable, Volo's target market for origination and termination services is the large operator. Lewis explains that this decision is based upon economics. "The hosted VoIP model works best for small-to-medium operators."
The bottom line for interconnection solutions (and VoIP in general) is choice. As more solutions hit the market, the technical decision-maker in your company needs to be proficient enough in networks and telephony to understand the tradeoffs or have a working relationship with a knowledgeable consultant who can help.
Justin J. Junkus is president of KnowledgeLink Inc. Email him at email@example.com.