IP exchange

For Novell’s IPX protocol see Internetwork Packet Exchange

Introduction

IPX (IP eXchange) is a telecommunication roaming and interconnection network designed to for the purpose of exchanging IP based traffic between the customers of separate mobile and fixed operators as well as other service providers (such as ISP) via IP based Network-to-Network Interface. IPX is developed by GSM Association.

For the avoidance of a doubt, IPX is not aimed to replace or compete with internet in any way. IPX just offers an alternative option for the operators specifically aimed to solve the different inter-operator traffic scenarios. Aim of IPX is to provide interoperability of IP based services between all types of operators & service providers with a commercial framework that enable all parties in the interworking value chain to receive a commercial return.

As typical for also in the other interconnection environments, the IPX network itself is invisible to the normal end-user. I.e. users don’t have to worry or care about IPX per se. For example, a normal web browsing performed by the end-user is not in the scope of IPX. Thus, IPX is relevant only for the operators / service providers serving the end-user. However, the general availability of interconnection is an important aspect also for the end-users. So for example if Mr. Smith-Smythe-Smith wants to connect with Mr. Putey using some operator offered service and the users happen to be served by different operators, interconnection needs to take place.

It should be noted that IP Exchange is not in any way related to the Novell’s Interwork Packet Exchange, thus IPX does not utilize IPX.

Background

Traditionally the voice traffic interconnection between the different operators has utilized the international SS7/TDM networks. However, lately the paradigm of “All IP” with VoIP is being rapidly introduced by different operators in various forms, such as IMS. Thus, 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 the 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 was not designed for all the requirements of interconnection network offering real-time services.

Even though the existing GRX environment was not 100% suitable for a common roaming and interconnection IP network, it offered a good starting point for the IPX development. This development was handled by various projects and working groups within GSM Association from the year 2004 onwards.

Need for private backbone

IP based interconnection could be handled with internet, since internet natively offers the required global connectivity and obviously supports IP protocol. However, there some issues when using internet for this particular purpose.

As Alex Sinclair of GSMA put it “The open Internet is a wonderful thing, but when it comes to providing a guaranteed quality of service, particularly for time-critical services, there is still a long way to go”.

It should be noted that naturally operators & other service providers are free to choose which interconnection option to use. It is also possible to utilize multiple different options at the same time (even though this will lead to increased complexity).

Architecture

IPX architecture consists of different IPX providers connecting together via IPX peering point for traffic exchange.

Both signaling (such as SIP) and media (such as RTP) are transported via IPX network between the participating operators & service providers.

A typical end-to-end path of traffic in an interconnection scenario where the Bob is sending some kind of traffic towards the Alice is illustrated in the sophisticated figure below:

+--IPX Provider1<--(NNI)--Operator1<--(UNI)--Bob

|

X

|

+-->IPX Provider2--(NNI)-->Operator2--(UNI)-->Alice

X is a peering point where IPX Provider1 and IPX Provider2 exchange traffic

IPX offers two major modes of interconnection:

Bilateral
Multilateral

Bilateral means the traditional model of two operators bilaterally writing an interconnection contract prior to setting up a connection to each other themselves. Multilateral on the other hand means that the IPX provider to some extend takes care of both handling the contract and connectivity set-up on behalf of the operators. Setting up bilateral interconnection contracts & connections with tens/hundreds of other operators can be a major burden. Therefore the multilateral option, which allows an operator to open multiple connections by making a single contract and single technical connection with the IPX provider, makes interconnection deployment easier and faster.

IPX service will be provided by a number of international IP carriers, such as Belgacom, France Telecom, Telecom Italia and TeliaSonera. These companies function as IPX Providers towards the operators & other service providers that are able to choose which IPX Provider they would like to use in order to access the IPX network.

Key principles

Openness - open to any fixed operator, mobile operator or other service provider (such as ISP or cable operator) willing to adopt the necessary common IPX technical and commercial principles and sign in
Quality - support for QoS ensured by usage of combination of technical features in the network and an enforceable contract model among all the players involved (end-to-end Service Level Agreements)
Cascading payments – the cascading responsibility in IPX means each party is responsible for the performance of the next party in the transit chain. Because all participants make this commitment, the financial benefits of providing the service are cascaded through the value chain, enabling all involved to receive a commercial return for their participation
Efficient connectivity - operator connecting to IPX can choose a multilateral interconnection mode where one interconnection contract opens interconnection partners
IP network - supporting natively IP based protocols (such as SIP, RTP, GTP, SMTP, SIGTRAN etc)
Security - completely separated from the public internet, both logically and physically. IPX is not addressable nor visible from the internet
Global reach - not restricted to a certain geographical area
Compliant with the existing specifications & recommendations – no need to upgrade e.g. 3GPP compliant IMS core system due to introducing IPX based Network-to-Network Interface (NNI)
Deals only with the NNI related issues, i.e. User-to-Network Interface (UNI) is completely out of scope for IPX
Common technical specifications such as IR.34 used end-to-end
IPX covers both interconnection and roaming scenarios
Service provided by a variety of competing international IP carriers all connected to each other via dedicated IPX peering points

Status

Principles of IPX have been tested within GSMA a number of times using various hands-on activities. For example SIP Trial tested IP based NNI with numerous IMS based services from the 2004 onwards, while Pre-commercial Implementation trials have been ongoing since April 2007 focusing especially on PS voice service.

According to GSMA press release in February 2008 successful IPX trials are run and a number of international carriers are preparing to rollout the service.

References

GSMA IR.34 - Inter-Service Provider IP Backbone Guidelines
GSMA IR.40 - Guidelines for IPv4 Addressing and AS Numbering for GRX/IPX Network Infrastructure and User Terminals
GSMA IR.65 - IMS Roaming & Interworking Guidelines
GSMA IR.67 - DNS Guidelines for Operators
GSMA IR.77 - Inter-Operator IP Backbone Security Requirements

External links

GSMA IP Interworking – a collection of different IPX related material