Connecting just two IP networks–for example, an enterprise to a service provider (SP) or two SPs to each other–is no walk in the park. The edge requirements fall into five categories: security, service reach, service assurance, revenue and profit protection, and regulatory compliance (for example, e911 and lawful intercept). This is where session border controllers (SBCs) come into the picture. They are the source and destination of all signaling messages and media streams coming into and leaving a provider’s network.
Acme Packet ( www.acmepacket.com) would seem to be the SBC market leader if the recent IPO is a reliable benchmark. They decompose the term in the following way:
• Session: Any real-time, interactive voice, video, or multimedia communication using a layer 5 IP signaling protocol such as SIP.
• Border: Any IP-IP network border such as those between SPs and customers or between SPs.
• Control: Functions that provide security to protect the service infrastructure and customer/supplier identities, and service assurance to guarantee SLAs.
All three categories are important, but security comes first because trust has flowed out of today’s IP window.
Companies and individuals use firewalls with network address translation (NAT) to protect their IP networks, but firewalls only let traffic in that has been requested from the inside. That’s fine for the
Web, e-mail, IM, and other services, but it’s a serious roadblock for peer-to-peer communications. Inbound signaling and media will be blocked because the firewall sees this traffic as a security threat.
SBCs, however, support a NAT traversal feature that removes the roadblock without compromising security. And it does so without the addition of on-site hardware, new software, or changes to the firewall confi guration.
ture. This company is the largest provider of federation-based interconnection services. Currently it provides ENUM and peering services to more than 300 VoIP operators in more than 20 countries. Those large SPs also employ XConnect’s facility.
The basic concept is simple: the various session border controllers exchange traffic with XConnect’s SBCs rather than each other. But in practice the facilitator must create a circle of trust. Here are some examples:
• Simplify interoperability by normalizing the protocols.
• Insulate SPs from the need to re-certify when one or more upgrade their system.
• Provide an efficient way of exchanging numbering data.
• Enable peering policies since not every SP will want to peer with every other SP.
• Leverage the ability to address security issues at a central point in the network.
• Provide reporting, monitoring, and settlement information.
• Provide QoS assurances.
ENUM ENUM is yet another meaningless acronym, but it’s critical to the future of IP communications. Nominum (www. nominum.com) defines it as a collection of IP-based tech-
Large SPs that exchange a lot of traf- Figure 1: The Stratus solution is deployed as an SS7 signaling gateway fic may decide to peer on a bilateral between different networks. As illustrated, it performs protocol conversion basis for various technical and com- between the main legacy protocols and SIP. mercial reasons. For example, they establish a common electronic numbering (ENUM) database. ENUM is way of mapping regular phone numbers to IP addresses (more information on this in the next section). And rather than invoice each other at the end of the month, they might decide to go for a settle-ment-free agreement.
There are, however, several hundred service providers that offer a VoIP service, so there is a clear need for an easy way to facilitate multinational peering. This is where XConnect ( www.xconnect.com) enters the pic-
nologies designed to optimize the mapping of the global PSTN into domain names. ENUM is based on the domain name system (DNS) used in IP networks to map domain names like www.vonmag.com to IP addresses and vice versa.
DNS is a massively scalable, global database maintained in servers around the world, and at the end of 2005 there were around 85 million names. But this figure will increase dramatically due to VoIP and other IP services. For example, worldwide there are more than three
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