On LTE Roaming ...

The IP eXchange (IPX) is used for data when the users roam between different networks. GPRS Roaming eXchange (GRX) is a service within IPX. One of the main areas of discussion within the LTE World Summit 2012 in the Signalling Focus day was roaming on LTE. Different vendors have different proposals and solutions; couple of them are as follows:

Interesting to see that iBasis has proposed LTE Signalling eXchange (LSX) as a way forward.

A presentation from Acme Packet (for an earlier conference) has interesting VoLTE roaming options proposal.

Finally, while everyone was focussing on LTE-LTE roaming, only Diametriq was looking at LTE-LTE/3G/2G Roaming. The relevant part of their presentation is embedded below.

Diameter and LTE Roaming

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Happy to hear more on this topic if anyone else wants to contribute. Please feel free to add comments.

Roaming with the IP eXchange (IPX)

From Wikipedia:

Traditionally, voice traffic interconnection between different operators has utilized the international SS7/TDM networks. However, lately the all-IP paradigm with VoIP is being rapidly introduced by different operators in various forms, such as IMS. In order to minimize the number of conversions between packet-switched voice and circuit-switched voice there is a clear need to deploy an IP based NNI (Network-to-Network Interface) and therefore an IP based interconnection network.

It is also evident that a large number of IP based services (such as Presence or IM) simply cannot be interconnected using a SS7/TDM network, further increasing the need for evolution into an IP based interconnection network.

Since the year 2000 GSM operators have been using GRX (GPRS Roaming Exchange) network for routing the IP based commercial roaming traffic between visited and home operators. Mainly 2.5G and 3G data roaming has been using GRX. GRX is a private IP network (separated from internet) consisting of multiple different GRX carriers that are connected to each other via peering points. However, GRX is limited only to GSM operator community and not all GRX's are capable of meeting the demands of real-time services.

Even though the GRX environment is not entirely suitable as a common IP network for interconnection and roaming, it offers a good starting point for the development of IPX. IPX development has been done in various GSM Association projects and working groups since 2004.

The following presentation is from LTE World Summit:

The IP Interconnect in VoLTE - Market & Technical requirements

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GPRS Roaming eXchange (GRX) for LTE/EPS Networks

The GSM Association (GSMA) has came to the realization that GPRS roaming based on bilateral relationships between individual GPRS operators is incredibly complex and expensive to maintain, in particular if the number of roaming partners is high. In fact, each operator will have to have N(N - 1) dedicated links to other operators (given that N is the global numbers of operators for which roaming should be supported). The GSMA has therefore recommended the use of a GPRS Roaming eXchange (GRX) for the Inter-PLMN GPRS roaming scenario.

The GRX is built on a private or public IP backbone and transports GPRS roaming traffic via the GTP between the visited and the home PLMN (Figure above). A GRX service provider has a network consisting of a set of routers and the links connecting to the GPRS networks. Moreover, the GRX network will have links connecting to other GRX nodes to support GRX peering between networks.

The GRX service provider acts as a hub, therefore allowing a GPRS operator to interconnect with each roaming partner without the need for any dedicated connections. This allows faster implementation of new roaming relations, faster time to market for new operators, and better scalability since an operator can start with low-capacity connections to the GRX and upgrade them depending on the bandwidth and quality requirements of the traffic. Other benefits of GRX are as follows:

Support of QoS: This aspect that will be very important for the GPRS services and, in particular, for the transition to 3G systems.

Security: The interconnection between the home operator and the visited operator uses the private GRX networks, hence does not require the overhead of maintaining expensive IPSEC tunnels over the public Internet.

DNS support: Through GRX it is possible to support a worldwide ".gprs" DNS root, where the various GRX operators will collaborate in managing the root and each operator's DNS servers will be connected to such roots to provide translation of DNS names specific to one operator.

In conclusion, GRX is introduced for GPRS roaming to facilitate the network operators for the interconnection between networks to support roaming and will play a very important role for the transition to third-generation systems.

In the LTE World Summit, Alex Sinclair, Chief Technology Officer, GSMA mentioned about the important role GRX will play in the LTE networks. The figure below are his views on GRX.

Diagram and Initial text Reference: IP in Wireless Networks By Basavaraj Patil, et al.

More information on GRX is available in GSM Association IR.34 document.