Already today there are many issues with SMS flooding the networks and causing
service outages due to congestion. Most operators have begun offloading their SMS
traffic to a specialized packet network so that flooding does not impact the rest of the
network. This is because in traditional networks SMS is carried through the SS7 signaling
network, and congesting the SS7 network prevents calls from being connected.
Events such as American Idol in the U.S. and Pop Idol in the UK have created
huge amounts of bursty SMS traffic that easily congests the messaging network, and
operators have taken measures to engineer the network with this in mind. However,
in the IMS the messaging is carried by SIP through the same network used to connect
sessions.
It may be worthwhile to investigate an offload process for messaging to get this traffic
off of the SIP network onto a specialized network, much like what is done today to
offload SMS from the SS7 network (and onto SMPP, a dedicated messaging network).
Another form of attack may be by sending a large volume of REGISTER messages
into a network, containing the incorrect subscriber credentials. This would overload the
S-CSCF and force a number of error responses to be sent in response, not to mention
that any device that was already registered could be de-registered. When this occurs,
the device will then attempt to register again, causing congestion at the S-CSCF.
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