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26 | June 2008 |
The mobile WiMAX interoperability challenge
The architecture of a typical mobile WiMAX
WiMAX network architecture
network comprises MSs (mobile stations), which sit
at the network edge and are responsible for over-
Access Service Network
the-air transmission.
R2 Network (CSN)
Further into the network, the ASN interfaces
the BTS and the all-IP core network—the CSN.
Typically the ASN includes numerous BTSs with
one or more ASN gateway. The ASN manages
radio resources, MS access, mobility, security and
ASN Gateway
QoS. It acts as a relay for the CSN for IP address
allocation and AAA (authorisation, authentication,
accounting) functions. The ASN gateway hosts the
mobile IP Foreign Agent (FA).
The CSN performs core network functions,
including policy and admission control, IP address
allocation, billing and settlement. It hosts the
mobile IP home agent (HA), the IP and AAA
servers, and PSTN and VoIP gateways. The CSN is
ASN Gateway
also responsible for interworking with non-WiMAX
networks (eg, 3G, DSL) and for roaming through
Other Operator’s
links to other CSNs.
Source: Senza Fili Consulting
The mere presence of profile B is irksome for a proprietary starting point but with some It might be argued from dyed in the wool
vendors backing profile C, not least because Mo- commitment in the future to move to a certified profile B vendors that the R6 standard is not
torola deploys WiMAX equipment based on it. version at some point,” he says. sufficiently developed to build interoperable kit
Of the WiMAX equipment suppliers, Motorola, The Irish Broadband CTO does not, however, to. It’s not a view held by Markku Hollström,
according to Market Intelligence Centre (MIC), entirely rule out using profile B kit. “It could be, who heads up WiMAX product management
had the highest WiMAX subscriber base at the over the next six months, we might start with a at Nokia Siemens Networks. “It’s true that the
end of 2007 with a 52 per cent market share. profile B because that is the fastest way to get to management protocol [on R6] is not yet fully
This makes it more difficult for the independent market,” he says. “That could be something we specified, but that’s not really an issue for op-
vendors to expand, which fuels their dislike of would deploy for a pilot but it wouldn’t be some- erators in my view,” he says. “The management
profile B. (Motorola could not provide a spokes- thing that we would want to build our future protocols of GSM and WCDMA networks, for
person for this article to confirm whether or not architecture on.” example, are drafted at a roughly similar level.”
it has a roadmap for profile C.) To serve smaller and fixed WiMAX deploy- WiChorus CEO Jalil is equally supportive of
“Profile B is a misnomer, since it does not de- ments, some BTS vendors may also see a ben- the specification. “By going through a few IOTs,
fine any interface between the BTS and the ASN efit in not using the full R6 specification. As a we have learned that under profile C, R6 interop-
gateway,” says WiChorus’ Jalil. “In essence, it of- larger ASN gateway can be cost prohibitive for erability is straightforward,” he says. “An average
fers a loophole that can be exploited by vendors smaller operators, independent BTS vendors R6 IOT between and ASN gateway and BTS
that want to pursue proprietary solutions. Hope- may look, says Aptilo’s Ward, “for a structure in takes three to four weeks.”
fully, the WiMAX Forum will eliminate profile B, which commodity [off-the-shelf] routers can Despite the apparent ease of R6 interoper-
as it is bad for the industry as a whole.” be used to handle the network routing of the ability, NSN does not intend to confirm any
Jalil outlines a scenario where carriers that want user data and interconnect that data path to interoperable BTS and ASN gateway partners to
to leverage micro and pico cell architectures—in the Internet”. This would avoid the expense of a its profile C equipment until next year.
addition to macro cell base stations—are disad- larger ASN gateway, but the BTS would not be
vantaged in a profile B environment. “Without a R6 compliant. More features, more IOT
base station interface, operators will not be able to Ideally, says Ward, the small BTSs should be Between the ASN gateway and the CSN, Aptilo’s
leverage these types of multi-vendor solutions,” he able to scale up if the operator goes to 802.16e Ward says much interoperability progress has
says. “One of the promises of WiMAX has been to and expands the number of features on the net- been made using the R3 interface, especially
deliver an alternative to the traditionally closed and work—such as encryption, authentication, key when it comes to establishing basic services.
relatively expensive 2G/3G architectures. Profile B generation and quality of service—all of which “By using our basic AAA features in the
flies in the face of this goal.” require an ASN gateway. “There are examples CSN it is fairly easy to determine whether the
Irish Broadband’s Stacey nevertheless sees of vendors offering forward-compatible base user is post-paid or pre-paid, which services
movement from profile B to profile C among station infrastructure to accommodate ASN he is entitled to use, and to generate the keys
suppliers. “Some profile B vendors are offering gateways based on the R6 interface,” he says. for encryption,” says Ward. “Where there is
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