Showing posts sorted by relevance for query DSAC. Sort by date Show all posts
Showing posts sorted by relevance for query DSAC. Sort by date Show all posts

Wednesday 27 May 2009

Service Specific Access Control (SSAC) in 3GPP Release 9


In an emergency situation, like Earthquake or Tsunami, degradation of quality of service may be experienced. Degradation in service availability and performance can be accepted in such situations, but mechanisms are desirable to minimize such degradation and maximize the efficiency of the remaining resources.

When Domain Specific Access Control (DSAC) mechanism was introduced for UMTS, the original motivation was to enable PS service continuation during congestion in CS Nodes in the case of major disaster like an Earthquake or a Tsunami.

In fact, the use case of DSAC in real UMTS deployment situation has been to apply access control separately on different types of services, such as voice and other packet-switched services.

For example, people’s psychological behaviour is to make a voice call in emergency situations and it is not likely to change. Hence, a mechanism will be needed to separately restrict voice calls and other services.

As EPS is a PS-Domain only system, DSAC access control does not apply.

The SSAC Technical Report (see Reference) identifies specific features useful when the network is subjected to decreased capacity and functionality. Considering the characteristics of voice and non-voice calls in EPS, requirements of the SSAC could be to restrict the voice calls and non-voice calls separately.

For a normal paid service there are QoS requirements. The provider can choose to shut down the service if the requirements cannot be met. In an emergency situation the most important thing is to keep communication channels uninterrupted, therefore the provider should preferably allow for a best effort (degradation of) service in preference to shutting the service down. During an emergency situation there should be a possibility for the service provider also to grant services, give extended credit to subscribers with accounts running empty. Under some circumstances (e.g. the terrorist attack in London on the 7 of July in 2005), overload access control may be invoked giving access only to authorities or a predefined set of users. It is up to national authorities to define and implement such schemes.

Reference: 3GPP TR 22.986 - Study on Service Specific Access Control

Wednesday 16 March 2011

Direct Communication between devices in case of disasters

Yesterday, a discussion started after I read this article on RCR Wireless News:

As in every major disaster, communications networks quickly showed their inherent weakness in times of greatest need. Japan's NTT Communications reported outages affecting Internet voice data that relies on IP-VPN technology.

In a brief statement, the operator apologized for the "trouble and inconvenience," following the string of earthquakes and significant aftershocks that rattled nerves and buildings throughout much of Japan. Some communication services are no longer available, NTT said, and telephone service, particularly long-distance service, is showing strain as well.

Service disruptions have been reported by all three of the major mobile operators in Japan, according to BusinessWeek.

This prompted me to ask on Twitter about which technologies are available that can help the mobile network cope with these problem.

Here are few approaches:

I blogged earlier about Multihop Cellular Networks (MCN) and ODMA. These technologies have their own limitations and problems and I have not heard of anything more about them being standardised or adopted.

Another post was on Ad-Hoc Networks that can be formed in case of failures resulting in Mobile devices being able to communicate directly without the need for network or base stations. The slight problem is that this approach replies on WiFi being available which may not always be the case.

A colleague suggested that in Tetra, Direct Mode of operation is available that is intended for situations like these. A presentation is embedded below:




Steven Crowley on twitter suggested that 802.16m has already started working in this direction. I got a related presentation on that which is embedded below:




Finally, Kit Kilgour mentioned about DSAC (Domain Specific Access Control) whose intention is to discontinue the voice service in emergency (to avoid congestion) but continue the packet domain normally. I have not looked at DSAC on this blog but in LTE instead Service Specific Access Control (SSAC) is used since LTE is PS only. See the blog entry here.

Please feel free to add any more information on this topic in the comments.