Beyond the Border: Differentiating IPX Services with Value-Added Features

Guest Room

Beyond the Border: Differentiating IPX Services with Value-Added Features

This article originally appeared in the October 2010 issue of INTERNET TELEPHONY

VoIP traffic has been growing exponentially in recent years, as both enterprises and consumers increase their adoption of IP services. To keep pace with the demand, both fixed and mobile service providers steadily are steadily migrating their core networks from TDM to IP. Examples can be found in enterprises that are transitioning from legacy PBXs to IP PBXs. 

Organizations are also connecting to service provider networks with SIP trunks to transport both voice and data over a single IP connections. In addition, mobile operators that are deploying LTE (News - Alert) (News - Alert) must use IP in their core networks, both for voice and data. Finally, popular over-the-top (OTT) services, such as Skype (News - Alert), are driving a surge in VoIP traffic.

The result is that VoIP traffic definitely will definitely continue its rapid growth in fixed and mobile networks for several years.

The across-the-board migration to IP has highlighted IP Interconnect interconnect networks and several forums are now defining the IP interconnect architecture.  The most prominent of these— – the GSM Association’s IPX project— – divides the interconnect into two distinct layers: the IP layer and the service-aware Layer. The key to operating IP interconnect between service provider networks successfully is the service-aware multilateral interconnect mode of IPX.

IPX is critical for enabling end-to-end rich communication suite (RCS) services between service providers because interoperability is key to the successful, widespread adoption of RCS, or any mass-market service. E-mail’s early days illustrate the importance of interoperability. Early e-mail systems were proprietary and users could only communicate with people within the same system, which drastically limited its usefulness as a communications tool. Only when e-mail became interoperable and universal did usage take off, making e-mail the foundation for daily communications for everyone around the world. Similarly, social networking, IM, presence, HD voice, video conferencing, video share, file share and multimedia collaboration must work seamlessly across multiple operators to stimulate mass adoption.

Service-aware (News - Alert) IPX can play an important role in driving interoperability between service provider networks by transparently processing or interworking these services when needed. Further, IPX can add valuable functionality for interworking some variations in signaling, media or version of the implemented standards. While service providers focus on implementing and deploying services, an IPX provider (IPX-P) ensures that interconnect points are enabled, tested, and activated -- – and then provides interworking of services as needed. Following this model, each service provider works with a single IPX provider IPX-P while each IPX provider works with multiple service providers.  This allows services to interoperate faster across heterogeneous (fixed/mobile/cable) networks.  For example, a smartphone from one mobile operator can communicate/interact through an IPX network with an integrated access device (IAD) that is supplied by a cable operator on the other side of the globe.

IPX also helps expand the addressable market for over-the-top (OTT) services, which have grown exponentially in VoIP minutes due to applications such as Skype (News - Alert). According to Skype’s S1 IPO filing in August of 2010, it has 560 million registered users with 124 million users who are active each month.  Of those users, 8.1 million pay an average of $96 per year for the service, primarily for SkypeOut.  This is a VoIP service that connects the users to landline and mobile networks. To help connect Skype users on different networks, the IPX also provides useful interworking functions, such as transcoding Skype’s HD SILK codec to AMR-WB for a GSM handset across the globe, or enabling connectivity between a Skype user and a public switched telephone network (PSTN).

As the critical interconnection between different networks, a comprehensive IPX implementation must support the following features: Security – Denial of Service (DoS) protection; ACL;  policing and encryption; quality of sService (QoS) – TOS bit marking of packets;  CAC – Call admission based on an agreed SLA;  Billing and Settlements – Generation of CDRs and infrastructure for settlements; interoperability tools - SIP mMessage mManipulation; and  (SMM) SIP or media profiles. 

IPX Value-Added Features

In addition to these basic border features, IPX providers can accelerate adoption of IP interconnect among several heterogeneous VoIP islands by providing some session-aware value-added services.  These services can be divided into three broad categories: 1) signaling interworking, 2) media transcoding, and 3) centralized routing and policy.

BICC Support – Many legacy MSCs that are currently deployed do not support SIP-I but do support BICC over IP.  An IPX can support BICC to SIP-I interconnectivity, which enables the large pool of mobile operators with legacy MSCs to interwork with IP networks.

SIP-I to SIP-I Interworking – SIP-I is the signaling protocol of choice for carrier interconnect and is defined by the International Telecommunication Union (ITU) in Q.1912.5 profile C.  When carrying international calls, however, switches may include various international flavors of ISUP in SIP-I.  The IPX must be able to interwork these variations of ISUP and deliver the desired version of ISUP to each peer. 

Transcoding – By transcoding from one form of HD codec to another form of HD codec (example:like from SILK to 722.2), or from one wireless codec to another (example: like from AMR to EVRC), the IPX can interconnect heterogeneous networks.  Video codec transcoding or transrating is an extension of this IPX capability. 

Transport Interworking – The IPX can interwork various network and transport layers for enabling traffic between multiple peers, including UDP (News - Alert) (News - Alert)/TCP/SCTP, IPv4/IPv6, TLS/IPSec, RTP/RTSP, and so on.

ENUM Enablement– ENUM started many years ago in IETF as a public translation database of end- user service addresses.  More recently it has become a technique for improving inter-carrier routing.  The GSMA (News - Alert) (News - Alert) Pathfinder is an example of such usage.  IPX providers can deploy a centralized routing engine using ENUM, which lets the members of the IPX provider federation populate their address information into the routing engine through standardized interfaces. Using this technology enables IPX providers to add new members quickly and provide an easy way of integrating their new routes into the federation.

Centralized Network Routing and Policy – The IPX network needs a centralized router and policy engine that provides one centralized routing database for all interconnection points.  The IPX provider should be able to route traffic efficiently using the most economically suitable route based on the QoS and pricing agreements with all peers.  The centralized routing and policy engine should be able to use a variety of SIP parameters and headers as well as the information from the ENUM database to route the traffic for various services.


As all fixed and mobile networks migrate to IP to support the proliferation of IP applications, services and devices, the role of IP interconnect is quickly growing beyond basic border control. An IPX provider can leverage its capabilities for value-added signaling interworking, media transcoding, routing and addressing to support its customers’ service velocity, business growth and service usage across disparate networks worldwide.To learn more, visit TMCnet's subscriber page.