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Showing posts with label Emergency. Show all posts
Showing posts with label Emergency. Show all posts

Wednesday, 15 May 2013

Access Class Barring in LTE using System Information Block Type 2


As per 3GPP TS 22.011 (Service accessibility):

All UEs are members of one out of ten randomly allocated mobile populations, defined as Access Classes (AC) 0 to 9. The population number is stored in the SIM/USIM. In addition, UEs may be members of one or more out of 5 special categories (Access Classes 11 to 15), also held in the SIM/USIM. These are allocated to specific high priority users as follows. (The enumeration is not meant as a priority sequence):
Class 15 - PLMN Staff;
 -"-  14 - Emergency Services;
 -"-  13 - Public Utilities (e.g. water/gas suppliers);
 -"-  12 - Security Services;
 -"-  11 - For PLMN Use.

Now, in case of an overload situation like emergency or congestion, the network may want to reduce the access overload in the cell. To reduce the access from the UE, the network modifies the SIB2 (SystemInformationBlockType2) that contains access barring related parameters as shown below:




For regular users with AC 0 – 9, their access is controlled by ac-BarringFactor and ac-BarringTime. The UE generates a random number
– “Rand” generated by the UE has to pass the “persistent” test in order for the UE to access. By setting ac-BarringFactor to a lower value, the access from regular user is restricted (UE must generate a “rand” that is lower than the threshold in order to access) while priority users with AC 11 – 15 can access without any restriction

For users initiating emergency calls (AC 10) their access is controlled by ac-BarringForEmergency – boolean value: barring or not

For UEs with AC 11- 15, their access is controlled by ac-BarringForSpecialAC - boolean value: barring or not.


The network (E-UTRAN) shall be able to support access control based on the type of access attempt (i.e. mobile originating data or mobile originating signalling), in which indications to the UEs are broadcasted to guide the behaviour of UE. E-UTRAN shall be able to form combinations of access control based on the type of access attempt e.g. mobile originating and mobile terminating, mobile originating, or location registration.  The ‘mean duration of access control’ and the barring rate are broadcasted for each type of access attempt (i.e. mobile originating data or mobile originating signalling).

Another type of Access Control is the Service Specific Access Control (SSAC) that we have seen here before. SSAC is used to apply independent access control for telephony services (MMTEL) for mobile originating session requests from idle-mode.

Access control for CSFB provides a mechanism to prohibit UEs to access E-UTRAN to perform CSFB. It minimizes service availability degradation (i.e. radio resource shortage, congestion of fallback network) caused by mass simultaneous mobile originating requests for CSFB and increases the availability of the E-UTRAN resources for UEs accessing other services.  When an operator determines that it is appropriate to apply access control for CSFB, the network may broadcast necessary information to provide access control for CSFB for each class to UEs in a specific area. The network shall be able to separately apply access control for CSFB, SSAC and enhanced Access control on E-UTRAN.

Finally, we have the Extended Access Barring (EAB) that I have already described here before.

Thursday, 16 August 2012

3GPP SA1 Release 11 Standardisation Trends

Wednesday, 9 March 2011

ETWS detailed in LTE and UMTS

Its been couple of years since the introductory post on 3GPP Earthquake and Tsunami Warning service (ETWS). The following is more detailed post on ETWS from the NTT Docomo technical journal.

3GPP Release 8 accepted the standard technical specification for warning message distribution platform such as Area Mail, which adopts pioneering technology for faster distribution, in order to fulfil the requirements concerning the distribution of emergency information e.g. earthquakes, tsunamis and so on in LTE/EPC. The standard specifies the delivery of emergency information in two levels. The Primary Notification contains the minimum, most urgently required information such as “An earthquake occurred”; the Secondary Notification includes supplementary information not contained in the Primary Notification, such as seismic intensity, epicentre, and so on. This separation allows implementation of excellent information distribution platforms that can achieve the theoretically fastest speed of the warning distribution.

The purpose of the ETWS is to broadcast emergency information such as earthquake warnings provided by a local or national governments to many mobile terminals as quickly as possible by making use of the characteristic of the widespread mobile communication networks.

The ETWS, in the same way as Area Mail, detects the initial slight tremor of an earthquake, the Primary Wave (P wave - The first tremor of an earthquake to arrive at a location), and sends a warning message that an earthquake is about to happen to the mobile terminals in the affected area. ETWS can deliver the first notification to mobile terminals in the shortest theoretical time possible in a mobile communication system (about four seconds after receiving the emergency information from the local or national government), which is specified as a requirement by 3GPP.

The biggest difference between Area Mail and the ETWS is the disaster notification method (Figure 1). Earthquake warnings in Area Mail have a fixed-length message configuration that notifies of an earthquake. ETWS, on the other hand, achieves distribution of the highest priority information in the shortest time by separating out the minimum information that is needed with the most urgency, such as “Earthquake about to happen,” for the fastest possible distribution as a Primary Notification; other supplementary information (seismic intensity, epicentre, etc.) is then distributed in a Secondary Notification. This distinction thus implements a flexible information distribution platform that prioritizes information distribution according to urgency.

The Primary Notification contains only simple patterned disaster information, such as “Earthquake.” When a mobile terminal receives a Primary Notification, it produces a pre-set alert sound and displays pre-determined text on the screen according to the message content to notify users of the danger. The types of disaster that a Primary Notification can inform about are specified as “Earthquake,” “Tsunami,” “Tsunami + Earthquake,” “Test” and “Other,” regardless of the type of radio access.

The Secondary Notification contains the same kind of message as does the existing Area Mail service, which is, for example, textual information distributed from the network to the mobile terminal to inform of the epicentre, seismic intensity and other such information. That message also contains, in addition to text, a Message Identifier and Serial Number that identifies the type of disaster.

A major feature of the ETWS is compatibility with international roaming. Through standardization, mobile terminals that can receive ETWS can receive local emergency information when in other countries if the local network provides the ETWS service. These services are provided in a manner that is common to all types of radio access (3G, LTE, etc.).

Network Architecture

The ETWS platform is designed based on the Cell Broadcast Service (CBS). The ETWS network architecture is shown in Figure 2. Fig. 2 also shows the architecture for 3G network to highlight the features differences between LTE and 3G.

In the ETWS architecture for 3G, a Cell Broadcast Centre (CBC), which is the information distribution server, is directly connected to the 3G Radio Network Controller (RNC). The CBC is also connected to the Cell Broadcast Entity (CBE), which distributes information from the Meteorological Agency and other such sources.

In an LTE radio access network, however, the eNodeB (eNB) is directly connected to the core network, and eNB does not have a centralized radio control function as the one provided by the RNC of 3G. Accordingly, if the same network configuration as used for 3G were to be adopted, the number of eNB connected to the CBC would increase and add to the load on the CBC. To overcome that issue, ETWS for LTE adopts a hierarchical architecture in which the CBC is connected to a Mobility Management Entity (MME).

The MME, which acts as a concentrator node, is connected to a number of eNBs. This architecture gives advantages to the network, such as reducing the load in the CBC and reducing the processing time, and, thus preventing delay in distribution.

Message Distribution Area

In the 3G ETWS and Area Mail systems, the distribution area can be specified only in cell units, which creates the issue of huge distribution area database in CBC. In LTE ETWS, however, the distribution area is specified in three different granularities (Figure 3). This allows the operator to perform area planning according to the characteristic of the warning/emergency occasions, e.g. notice of an earthquake with a certain magnitude needs to be distributed in a certain width of area, thus allowing efficient and more flexible broadcast of the warning message.

1) Cell Level Distribution Area: The CBC designates the cell-level distribution areas by sending a list of cell IDs. The emergency information is broadcasted only to the designated cells. Although this area designation has the advantage of being able to pinpoint broadcast distribution to particular areas, it necessitates a large processing load in the network node (CBC, MME and eNB) especially when the list is long.

2) TA Level Distribution Area: In this case, the distribution area is designated as a list of Tracking Area Identities (TAIs). TAI is an identifier of a Tracking Area (TA), which is an LTE mobility management area. The warning message broadcast goes out to all of the cells in the TAIs. This area designation has the advantage of less processing load when the warning message has to be broadcast to relatively wide areas.

3) EA Level Distribution Area: The Emergency Area (EA) can be freely defined by the operator. An EA ID can be assigned to each cell, and the warning message can be broadcasted to the relevant EA only. The EA can be larger than a cell and is independent of the TA. EA is a unit of mobility management. EA thus allows flexible design for optimization of the distribution area for the affected area according to the type of disaster.




Message Distribution

The method of distributing emergency information to LTE radio networks is shown in Figure 4. When the CBC receives a request for emergency information distribution from CBE, it creates the text to be sent to the terminals and specifies the distribution area from the information in the request message (Fig. 4 (1) (2)).

Next, the CBC sends a Write-Replace Warning Request message to the MME of the specified area. This message contains information such as disaster type, warning message text, message distribution area, Primary Notification information, etc. (Fig. 4 (3)). When the MME receives this message, it sends a response message to the CBC to notify that the message was correctly received. The CBC then notifies the CBE that the distribution request was received and the processing has begun (Fig. 4 (4) (5)). At the same time, the MME checks the distribution area information in the received message (Fig. 4 (6)) and, if a TAI list is included, it sends the Write-Replace Warning Request message only to the eNB that belong to the TAI in the list (Fig. 4 (7)). If the TAI list is not included, the message is sent to all of the eNB to which the MME is connected.

When the eNB receives the Write-Replace Warning Request message from the MME, it determines the message distribution area based on the information included in the Write-Replace Warning Request message (Fig. 4 (8)) and starts the broadcast (Fig. 4 (9) (10)). The following describes how the eNB processes each of the specified information elements.

1) Disaster Type Information (Message Identifier/Serial Number): If an on-going broadcast of a warning message exists, this information is used by the eNB to decide whether it shall discard the newly received message or overwrite the ongoing warning message broadcast with the newly received one. Specifically, if the received request message has the same type as the message currently being broadcasted, the received request message is discarded. If the type is different from the message currently being broadcast, the received request message shall overwrite the ongoing broadcast message and the new warning message is immediately broadcasted.

2) Message Distribution Area (Warning Area List): When a list of cells has been specified as the distribution area, the eNB scans the list for cells that it serves and starts warning message broadcast to those cells. If the message distribution area is a list of TAIs, the eNB scans the list for TAIs that it serves and starts the broadcast to the cells included in those TAIs. In the same way, if the distribution area is specified as an EA (or list of EAs), the eNB scans the EA ID list for EA IDs that it serves and starts the broadcast to the cells included in the EA ID.

If the received Write-Replace Warning Request message does not contain distribution area information, the eNB broadcasts the warning message to all of the cells it serves.

3) Primary Notification Information: If Primary Notification information indication exists, that information is mapped to a radio channel that is defined for the broadcast of Primary Notification.

4) Message Text: The eNB determines whether or not there is message text and thus whether or not a Secondary Notification needs to be broadcasted. If message text exists, that text is mapped to a radio channel that is defined for the broadcast of Secondary Notification. The Secondary Notification is broadcast according to the transmission intervals and number of transmissions specified by the CBC. Upon the completion of a broadcast, the eNB returns the result to the MME (Fig. 4 (11)).


Radio Function Specifications

Overview : In the previous Area Mail service, only mobile terminals in the standby state (RRC_IDLE) could receive emergency information, but in ETWS, emergency information can be received also by mobile terminals in the connected state (RRC_CONNECTED), and hence the information can be delivered to a broader range of users. In LTE, when delivering emergency information to mobile terminals, the eNB sends a bit in the paging message to notify that emergency information is to be sent (ETWS indication), and sends the emergency information itself as system information broadcast. In 3G, on the other hand, the emergency information is sent through the paging message and CBS messages.

Message Distribution method for LTE: When the eNB begins transmission of the emergency information, a paging message in which the ETWS indication is set is sent to the mobile terminal. ETWS-compatible terminals, whether in standby or connected, try to receive a paging message at least once per default paging cycle, whose value is specified by the system information broadcast and can be set to 320 ms, 640 ms, 1.28 s or 2.56 s according to the 3GPP specifications. If a paging message that contains an ETWS indication is received, the terminal begins receiving the system information broadcast that contains the emergency information. The paging message that has the ETWS indication set is sent out repeatedly at every paging opportunity, thus increasing the reception probability at the mobile terminal.

The ETWS message itself is sent as system information broadcast. Specifically, the Primary Notification is sent as the Warning Type in System Information Block Type 10 (SIB10) and the Secondary Notification is sent as a Warning Message in SIB11. By repeated sending of SIB10 and SIB11 (at an interval that can be set to 80 ms, 160 ms, 320 ms, 640 ms, 1.28 s, 2.56 s, or 5.12 s according to the 3GPP specifications), the probability of the information being received at the residing mobile terminal can be increased. In addition, the SIB10 and SIB11 scheduling information is included in SIB1 issued at 80-ms intervals, so mobile terminals that receive the ETWS indication try to receive SIB10 and SIB11 after first having received the SIB1. By checking the disaster type information (Message Identifier and Serial Number) contained in SIB10 and SIB11, the mobile terminal can prevent the receiving of multiple messages that contain the same emergency information.

3G Message Distribution Method: For faster information delivery and increased range of target uers in 3G also, the CBS message distribution control used in Area Mail was enhanced. An overview of the 3G radio system is shown in Figure 5.

In the Area Mail system, a Common Traffic Channel (CTCH) logical channel is set up in the radio link, and emergency information distribution is implemented by sending CBS messages over that channel. To inform the mobile terminals that the CTCH logical channel has been set up, the RNC orders the base station (BTS) to set the CTCH Indicator information element in the system information broadcast to TRUE, and transmits the paging message indicating a change in the system information broadcast to the mobile terminals. When the mobile terminal receives the CTCH Indicator, it begins monitoring the CTCH logical channel and can receive CBS messages.

In ETWS, by including the Warning Type in the paging message indicating a change in the system information broadcast, processing for a pop-up display and alert sound processing (Primary Notification) at the mobile terminals according to the Warning Type can be executed in parallel to the processing at the mobile terminals to start receiving the CBS messages. This enhancement allows users whose terminals are in the connected state (RRC_CONNECTED) to also receive emergency information. In the previous system, it was not possible for these users to receive emergency information. Also including disaster type information (Message Identifier and Serial Number) in this paging message makes it possible to prevent receiving multiple messages containing the same emergency information at the mobile terminal.

More detailed information (Secondary Notification) is provided in CBS messages in the same way as in the conventional Area Mail system, thus achieving an architecture that is common to ETWS users and Area Mail users.

Monday, 14 February 2011

Non-Voice Emergency Services (NOVES)

Its been a while we talked about SMS for Emergency purposes and eCall. A new study item in 3GPP has looked at non-voice alternatives for Emergency purposes.

Picture Source: Dailymail

The following is from the recent 4G Americas report entitled: 4G Mobile Broadband Evolution: 3GPP Release-10 and Beyond:

Non-verbal communications such as text messaging and instant messaging via wireless devices has been very successful and continues to expand. Many of the consumers assume that they can utilize these types of non-verbal communications as mechanisms to communicate with emergency services whenever emergency assistance is required. Such mechanisms currently do not exist. The Emergency Services community has a desire to have multimedia emergency services supported with the same general characteristics as emergency voice calls.

Currently, service requirements for emergency calls (with or without the IP Multimedia Core Network) are limited to voice media. The Non-Voice Emergency Services (NOVES) is intended to be an end-to-end citizen to authority communications. NOVES could support the following examples of non-verbal communications to an emergency services network:
1. Text messages from citizen to emergency services
2. Session-based and session-less instant messaging type sessions with emergency services
3. Multimedia (e.g., pictures, video clips) transfer to emergency services either during or after other communications with emergency services.
4. Real-time video session with emergency services

In addition, to support the general public, this capability would facilitate emergency communications to emergency services by individuals with special needs (e.g., hearing impaired citizens).

The objectives of this study include the following questions for NOVES with media other than or in addition to voice:
1. What are the requirements for NOVES?
2. What are the security, reliability, and priority handling requirements for NOVES?
3. How is the appropriate recipient emergency services system (e.g., PSAP) determined?
4. What are the implications due to roaming?
5. Are there any implications to hand over between access networks?
6. Are there any implications due to the subscriber crossing a PSAP boundary during NOVES communications (e.g., subsequent text messages should go to the same PSAP)?
7. Do multiple communication streams (e.g., voice, text, video emergency services) need to be associated together?
8. What types of “call-back” capabilities are required?
9. What are the load impacts of NOVES in the case of a large scale emergency event or malicious use?

NOVES will be applicable to GPRS (GERAN, UTRAN) and to EPS (GERAN, UTRAN, E-UTRAN and non-3GPP). The content may be transmitted between the subscribers and the emergency services which might bring new security issues. Therefore, the security impacts need to be studied.

You can spend your weekend reading the 3GPP Study Item TR 22.871: Study on Non-Voice Emergency Services (Release 11).

A word of caution, the name NOVES may be changed in future as Emergency agencies in Europe have an objection to the name. See here and here.

Tuesday, 8 February 2011

VoLTE: Semi-Persistent Scheduling (SPS) and TTI Bundling

The following is from the recently released 4G Americas paper '4G Mobile Broadband Evolution: 3GPP Release-10 and beyond:

With the support of emergency and location services in Rel-9, interest in Voice over LTE (VoLTE) has increased. This is because the Rel-9 enhancements to support e911 were the last step to enable VoLTE (at least in countries that mandate e911) since the Rel-8 specifications already included the key LTE features required to support good coverage, high capacity/quality VoLTE. There are two main features in Rel-8 that focus on the coverage, capacity and quality of VoLTE: Semi-Persistent Scheduling (SPS) and TTI Bundling.

SPS is a feature that significantly reduces control channel overhead for applications that require persistent radio resource allocations such as VoIP. In LTE, both the DL and UL are fully scheduled since the DL and UL traffic channels are dynamically shared channels. This means that the physical DL control channel (PDCCH) must provide access grant information to indicate which users should decode the physical DL shared channel (PDSCH) in each subframe and which users are allowed to transmit on the physical UL shared channel (PUSCH) in each subframe. Without SPS, every DL or UL physical resource block (PRB) allocation must be granted via an access grant message on the PDCCH. This is sufficient for most bursty best effort types of applications which generally have large packet sizes and thus typically only a few users must be scheduled each subframe. However, for applications that require persistent allocations of small packets (i.e. VoIP), the access grant control channel overhead can be greatly reduced with SPS.

SPS therefore introduces a persistent PRB allocation that a user should expect on the DL or can transmit on the UL. There are many different ways in which SPS can setup persistent allocations, and Figure below shows one way appropriate for VoLTE. Note that speech codecs typically generate a speech packet every 20 ms. In LTE, the HARQ interlace time is 8 ms which means retransmissions of PRBs that have failed to be decoded can occur every 8 ms. Figure below shows an example where a maximum of five total transmissions (initial transmission plus four retransmissions) is assumed for each 20 ms speech packet with two parallel HARQ processes. This figure clearly shows that every 20 ms a new “first transmission” of a new speech packet is sent. This example does require an additional 20 ms of buffering in the receiver to allow for four retransmissions, but this is generally viewed as a good tradeoff to maximize capacity/coverage (compared to only sending a maximum of two retransmissions).

The example in Figure above can be applied to both the DL and UL and note that as long as there are speech packets arriving (i.e. a talk spurt) at the transmitter, the SPS PRBs would be dedicated to the user. Once speech packets stop arriving (i.e. silence period), these PRB resources can be re-assigned to other users. When the user begins talking again, a new SPS set of PRBs would be assigned for the duration of the new talkspurt. Note that dynamic scheduling of best effort data can occur on top of SPS, but the SPS allocations would take precedent over any scheduling conflicts.


TTI bundling is another feature in Rel-8 that optimizes the UL coverage for VoLTE. LTE defined 1 ms subframes as the Transmission Time Interval (TTI) which means scheduling occurs every 1 ms. Small TTIs are good for reducing round trip latency, but do introduce challenges for UL VoIP coverage. This is because on the UL, the maximum coverage is realized when a user sends a single PRB spanning 180 kHz of tones. By using a single 180 kHz wide PRB on the UL, the user transmit power/Hz is maximized. This is critical on the UL since the user transmit power is limited, so maximizing the power/Hz improves coverage. The issue is that since the HARQ interlace time is 8 ms, the subframe utilization is very low (1/8). In other words, 7/8 of the time the user is not transmitting. Therefore, users in poor coverage areas could be transmitting more power when a concept termed TTI bundling (explained in the next paragraph) is deployed.

While it’s true that one fix to the problem is to just initiate several parallel HARQ processes to fill in more of the 7/8 idle time, this approach adds significant IP overhead since each HARQ process requires its own IP header. Therefore, TTI bundling was introduced in Rel-8 which combined four subframes spanning 4 ms. This allowed for a single IP header over a bundled 4 ms TTI that greatly improved the subframe utilization (from 1/8 to 1/2) and thus the coverage (by more than 3 dB).

Martin Sauter puts it in a simpler way in his blog as follows: The purpose of TTI Bundling is to improve cell edge coverage and in-house reception for voice. When the base station detects that the mobile can't increase it's transmission power and reception is getting worse it can instruct the device to activate TTI bundling and send the same packet but with different error detection and correction bits in 2, 3 or even 4 consecutive transmit time intervals. The advantage over sending the packet in a single TTI and then detecting that it wasn't received correctly which in turn would lead to one or more retransmissions is that it saves a lot of signaling overhead. Latency is also reduced as no waiting time is required between the retransmissions. In case the bundle is not received correctly, it is repeated in the same way as an ordinary transmission of a packet. Holma and Toskala anticipate a 4dB cell edge gain for VoIP with this feature which is quite a lot. For details how the feature is implemented have a look at 3GPP TS 36.321.

A whitepaper explaining the concepts of TTI Bundling is available on Slideshare here.

Monday, 7 February 2011

'EU-Alert' in Release-11

In the recently concluded 3GPP CT-50 in Istanbul, EU-Alert was adopted as part of Rel-11. The EU-Alert is introduced under Public Warning System (PWS) in parallel with Earthquake and Tsunami Warning System (ETWS).

PWS was introduced in Rel-9 and I blogged about it here. ETWS has been around since Rel-8 and was blogged here.

In fact EU-Alert is sent as part of the Cell Broadcast Message (CBS) using new identifiers. For more details see 3GPP TS 23.401.

The following is an old video from CHORIST project, which was instrumental in providing details of working of this EU-Alert system.




Also Read: Commercial Mobile Alert System (CMAS) here.

Thursday, 20 January 2011

eMPS: Enhanced Multimedia Priority Service in Release-10 and beyond


The response to emergency situations (e.g., floods, hurricanes, earthquakes, terrorist attacks) depends on the communication capabilities of public networks. In most cases, emergency responders use private radio systems to aid in the logistics of providing critically needed restoration services. However, certain government and emergency management officials and other authorised users have to rely on public network services when the communication capability of the serving network may be impaired, for example due to congestion or partial network infrastructure outages, perhaps due to a direct or indirect result of the emergency situation.

Multimedia Priority Service, supported by the 3GPP system set of services and features, is one element creating the ability to deliver calls or complete sessions of a high priority nature from mobile to mobile networks, mobile to fixed networks, and fixed to mobile networks.

Requirements for the Multimedia Priority Service (MPS) have been specified in TS 22.153 for the 3GPP Release-9

The intention of MPS is to enable National Security/Emergency Preparedness (NS/EP) users (herein called Service Users) to make priority calls/sessions using the public networks during network congestion conditions. Service Users are the government-authorized personnel, emergency management officials and/or other authorized users. Effective disaster response and management rely on the Service User’s ability to communicate during congestion conditions. Service Users are expected to receive priority treatment, in support of mission critical multimedia communications.

LTE/EPC Release 9 supports IMS-based voice call origination by a Service User and voice call termination to a Service User with priority. However, mechanisms for completing a call with priority do not exist for call delivery to a regular user for a priority call originated by a Service User. MPS enhancements are needed to support priority treatment for Release 10 and beyond for call termination and for the support of packet data and multimedia services.

MPS will provide broadband IP-based multimedia services (IMS-based and non-IMS-based) over wireless networks in support of voice, video, and data services. Network support for MPS will require end-to-end priority treatment in call/session origination/termination including the Non Access Stratum (NAS) and Access Stratum (AS) signaling establishment procedures at originating/terminating network side as well as resource allocation in the core and radio networks for bearers. The MPS will also require end-to-end priority treatment in case of roaming if supported by the visiting network and if the roaming user is authorized to receive priority service.

MPS requirement is already achieved in the 3G circuit-switched network. Therefore, if the network supports CS Fallback, it is necessary to provide at least the same capability as 3G circuit switched-network in order not to degrade the level of voice service. In CS Fallback, UE initiates the fallback procedures over the LTE as specified in TS 23.272 when UE decides to use the CS voice service for mobile originating and mobile terminating calls. To achieve priority handling of CS Fallback, NAS and AS signaling establishment procedures, common for both IP-based multimedia services and CS Fallback, shall be treated in a prioritized way.

In Release-10, for LTE/EPC, the following mechanisms will be specified.
  • Mechanisms to allocate resources for signaling and media with priority based on subscribed priority or based on priority indicated by service signaling.
  • For a terminating IMS session over LTE, a mechanism for the network to detect priority of the session and treat it with priority.
In Release-10, for CS Fallback, the following mechanism will be specified:
  • A mechanism to properly handle the priority terminating voice call and enable the target UE to establish the AS and NAS connection to fall-back to the GERAN/UTRAN/1xRTT.
For more information, see:

3GPP TR 23.854: Enhancements for Multimedia Priority Service (Release 10)

3GPP TS 22.153: Multimedia priority service (Release 10)

Thursday, 4 November 2010

Emergency Calls in LTE/SAE Release-9


From a 3GPP presentation by Hannu Hietalahti:

Emergency calls in LTE

Regulatory requirement of emergency calls is supported in Rel-9 for LTE:
1. Detection of emergency numbers in UE
2. Indication and prioritisation of emergency calls
3. Location services, both for routing and user location data for PSAP (Public Safety Answering Point)
4. Callback is possible, but processed as normal call without exceptions

UE matches digits dialledby the user with list of known emergency numbers
1. Emergency number list in the UE is common for CS and PS domain use
2. Default 112 and 911, USIM pre-configuration, downloaded in MM procedure
3. In case of match, the UE shall initiate the call as an emergency call

In IMS emergency calls the UE translates dialled number into emergency service URN
1. Service URN with a top-level service type of "sos" as specified in RFC5031
2. Additionally, sub-service type can be added to indicate emergency category if information on the type of emergency service is known (fire, ambulance, police,…)

P-CSCF (Proxy - Call Session Control Function) must also be prepared to detect emergency call if the UE is not aware of local emergency call
1. This is backup for those cases when the (roaming) UE does not have full information of all local emergency call numbers and initiates a normal call
2. From EPC perspective, it will be a normal PDN connection

Benefit of location information
1. P-CSCF discovers the regionally correct PSAP to take the emergency call
2. PSAP gets information on the precise user location


Related Posts:

Thursday, 7 October 2010

Locating Wireless Devices Where GPS May Not Be Available

Some of you may have read my earlier posts on stealing spectrum via Femtocells and using Femtocells abroad illegally. This presentation tries to answer one such problem on how do you find the location where GPS cannot be used. This could also be used in case of Cognitive Radios. See my old blog entry here.

Thursday, 30 September 2010

RF Pattern Matching adopted in 3GPP Release-10

RF Pattern Matching is now a recognized unique location method in standards that provides carriers and OEMs with the ability to offer high accuracy location-based services that traditionally haven’t been available with low-accuracy Cell-ID based technologies. RF Pattern Matching will be incorporated into Release 10 of the 3G UMTS specifications, expected to become final in late 2010 or early 2011. This will also set the stage for opportunities to incorporate RF Pattern Matching into LTE and other future air interfaces.


“The decision to incorporate RF Pattern Matching into the 3G UMTS specifications is needed for all service providers wanting to provide the highest-SLA option for LBS as it gives them more credible options for public safety and commercial applications,” said Manlio Allegra, president and chief executive officer at Polaris Wireless. “This level of LBS accuracy will create an improved user experience for wireless customers, which ultimately generates additional revenue streams for carriers and other enterprises offering LBS applications.”


Polaris WLS™ is a patent-protected implementation of RF Pattern Matching, which provides the best network-based location performance in urban and indoor settings and is a perfect complement to A-GPS, enabling a best-in-class hybrid solution. Polaris’ WLS™ works without the RF Pattern Matching definition in standards, but standardization through 3GPP allows for future performance enhancements and provides flexibility for the solution and carrier implementations. Polaris’s current WLS products will continue to operate within existing standards.


By being included in the 3G UMTS standard, Polaris’ location technology has received further validation as one of the most accurate in the world. Polaris will now be considered a preferred provider to Tier 1 carriers and infrastructure vendors who want to add a high accuracy location solution to their technology mix that meets the new 3GPP standard.


The FCC is currently considering new E911 Phase II regulations that would improve indoor location capabilities for first responders. Using RF Pattern Matching, Polaris’ WLS™ software solution enables carriers and OEMs to be prepared to meet these new FCC requirements with little or no investment in new infrastructure or hardware.

RF Pattern Matching Discussion document presented in 3GPP is embedded below:


Thursday, 15 July 2010

Mobile Phones 'Ad-Hoc Networks'

Picture Source: Daily Telegraph

Couple of years back I blogged about MCN and ODMA concept. Another variation of this idea is now in news again.

From the Daily Telegraph:

Australian scientists have created a mobile phone that can make and receive calls in parts of the world that would normally have no reception.

The phones contain a built-in mini-tower that allows them to connect to other phones via Wi-Fi and create their own network.

Researchers at South Australia's Flinders University devised the phones to work in the event of a natural disaster or terrorist attack when normal mobile phone services had been cut off.
Dr Paul Gardiner-Stephen said the phones had been tested successfully in the remote Outback where mobiles cannot pick up a signal.

"There was absolutely no infrastructure or support for the telephones so they were acting entirely on their own to carry the calls," he said.

The phones are unlikely to replace existing mobile systems, but could be combined to create fail-safe communication.

"One of our dreams is that every phone will come out with this one day so that if there is a disaster anywhere in the world everyone's phones will then switch over to this mode as a fallback," Dr Gardiner-Stephen said.

"When the infrastructure is knocked out we still provide good service while the traditional mobile phone network provides no service."

At the moment, the signal between phones is limited to a few hundred yards, but the team hopes to expand the range in the future.


I dont see them becoming reality for quite some time to come but its an interesting concept.

This is not the first time this idea is being proposed. As I have discussed, ODMA was intended to do something similar but did not take off. MANET's are other areas that have been worked on for quite some time and you can find good ideas and journal papers. There is also this paper talking about Ad-Hoc networks for mobiles using Bluetooth.

In fact going many years back, Iridium idea was launched with something similar in mind. I remember reading jornal papers back in 1996 that mentioned that Iridium phones will work like landline phones when you are in your house and will work as cellular when out of house and in an area with cellular coverage. If there is no cellular coverage then it will rely on Satellite communication. Of-course in those days nobody thought data usage will become this popular and so it was focussed on voice. Still I cannot see this happening for many years to come.

Thursday, 3 June 2010

Quick preview of 3GPP Release-11 Features and Study items


Release 11 Features

Advanced IP Interconnection of Services

The objective is to specify the technical requirements for carrier grade inter-operator IP Interconnection of Services for the support of Multimedia services provided by IMS and for legacy voice PTSN/PLMN services transported over IP infrastructure (e.g. VoIP). These technical requirements should cover the new interconnect models developed by GSMA (i.e. the IPX interconnect model) and take into account interconnect models between national operators (including transit functionality) and peering based business trunking. Any new requirements identified should not overlap with requirements already defined by other bodies (e.g. GSMA, ETSI TISPAN). Specifically the work will cover:

• Service level aspects for direct IP inter-connection between Operators, service level aspects for national transit IP interconnect and service level aspects for next generation corporate network IP interconnect (peer-to-peer business trunking).
• Service layer aspects for interconnection of voice services (e.g. toll-free, premium rate and emergency calls).
• Service level aspects for IP Interconnection (service control and user plane aspects) between Operators and 3rd party Application Providers.

To ensure that requirements are identified for the Stage 2 & 3 work to identify relevant existing specifications, initiate enhancements and the development of the new specifications as necessary.


Release 11 Studies

Study on IMS based Peer-to-Peer Content Distribution Services

The objectives are to study IMS based content distribution services with the following aspects:

- Identifying the user cases to describe how users, operators and service providers will benefit by using/deploying IMS based content distribution services. such as with the improvement of Peer-to-Peer technology. The following shall be considered:
- Mobile access only (e.g. UTRAN, E-UTRAN, I-WLAN);
- Fixed access only (e.g. xDSL, LAN);- Fixed and mobile convergence scenarios;
- Identifying service aspects where IMS network improvements are needed to cater for content distributed services for above accesses;
- Evaluating possible impacts and improvements on network when IMS based content distribution services are deployed;
- Identifying QoS, mobility, charging and security related requirements in the case of content distribution services on IMS;
- Identifying potential copyright issues;


Study on Non Voice Emergency Services

The Non Voice Emergency Services could support the following examples of non-verbal communications to an emergency services network:

1. Text messages from citizen to emergency services
2. Session based and session-less instant messaging type sessions with emergency services
3. Multi-media (e.g., pictures, video clips) transfer to emergency services either during or after other communications with emergency services.
4. Real-time video session with emergency services

In addition to support the general public, this capability would facilitate emergency communications to emergency services by individuals with special needs (e.g., hearing impaired citizens).

The objectives of this study include the following questions for Non Voice Emergency Services with media other than or in addition to voice:

1. What are the requirements for Non Voice Emergency Services?
2. What are the security, reliability, and priority handling requirements for Non Voice Emergency Services?
3. How is the appropriate recipient emergency services system (e.g., PSAP) determined?
4. Are there any implications due to roaming?
5. Are there any implications to hand-over between access networks
6. Are there any implications due to the subscriber crossing a PSAP boundary during Non Voice Emergency Services communications (e.g., subsequent text messages should go to the same PSAP)?
7. Do multiple communication streams (e.g., voice, text, video emergency services) need to be associated together?
8. What types of “call-back” capabilities are required?9. Investigate the load impact of Non Voice Emergency Services in the case of a large scale emergency event or malicious use.

Non Voice Emergency Services will be applicable to GPRS (GERAN, UTRAN) and to EPS (GERAN, UTRAN, E-UTRAN and non-3GPP).


Study on UICC/USIM enhancements

The intent of this study item is to identify use cases and requirements enabling Mobile Network Operators to distribute new services based on the USIM, to improve the customer experience and ease the portability and customisation of operator-owned and customer-owned settings from one device to another (such as APN and other 3G Notebook settings, graphical user interface, MNO brand, Connection Manager settings,…), and help in reducing operation costs and radio resources usage.


Objectives of this study item are:

-To identify use cases and requirements for new USIM
-based services taking into account the GSMA Smart SIM deliverables;
- To identify use cases and requirements for the USIM used inside terminals with specialised functionalities (e.g. radio modems, 3G Notebook terminals) taking into account the GSMA 3GNBK deliverables;
- To identify use cases and requirements to drive the evolution from the traditional USAT to a multimedia USIM toolkit support, with a particular aim to the Smart Card Web Server;


Study on Alternatives to E.164 for Machine-Type Communications

M2M demand is forecast to grow from 50M connections to over 200M by 2013. A large number of these services are today deployed over circuit-switched GSM architectures and require E.164 MSISDNs although such services do not require "dialable" numbers, and generally do not communicate with each other by human interaction.


Without technical alternative to using public numbering resources as addresses, and considering the current forecasts and pending applications for numbers made to numbering plan administration agencies, there is a significant risk that some national numbering/dialling plans will run out of numbers in the near future, which would impact not only these M2M services but also the GSM/UMTS service providers in general.


The Objective is to determine an alternative to identify individual devices and route messages between those devices. Requirements for this alternative include:

- Effectively identify addressing method to be used for end point devices
- Effectively route messaging between those devices
- Support multiple methods for delivering messages, as defined by 22.368
- Support land-based and wireless connectivity
- Make use of IP-based network architectures
- Addressing/identifiers must support mobility and roaming- support on high speed packet
-switched networks when available and on circuit-switched networks
- Consider if there are security issues associated with any alternatives

Thursday, 11 February 2010

UICC and USIM in 3GPP Release 8 and Release 9


In good old days of GSM, SIM was physical card with GSM "application" (GSM 11.11)

In the brave new world of 3G+, UICC is the physical card with basic logical functionality (based on 3GPP TS 31.101) and USIM is 3G application on a UICC (3GPP TS 31.102). The UICC can contain multiple applications like the SIM (for GSM), USIM and ISIM (for IMS). There is an interesting Telenor presentation on current and future of UICC which may be worth the read. See references below.

UICC was originally known as "UMTS IC card". The incorporation of the ETSI UMTS activities into the more global perspective of 3GPP required a change of this name. As a result this was changed to "Universal Integrated Circuit Card". Similarly USIM (UMTS Subscriber Identity Module) changed to Universal Subscriber Identity Module.

The following is from the 3G Americas Whitepaper on Mobile Broadband:

UICC (3GPP TS 31.101) remains the trusted operator anchor in the user domain for LTE/SAE, leading to evolved applications and security on the UICC. With the completion of Rel-8 features, the UICC now plays significant roles within the network.

Some of the Rel-8 achievements from standards (ETSI, 3GPP) are in the following areas:

USIM (TS 31.102)
With Rel-8, all USIM features have been updated to support LTE and new features to better support non-3GPP access systems, mobility management, and emergency situations have been adopted.

The USIM is mandatory for the authentication and secure access to EPC even for non-3GPP access systems. 3GPP has approved some important features in the USIM to enable efficient network selection mechanisms. With the addition of CDMA2000 and HRPD access technologies into the PLMN, the USIM PLMN lists now enable roaming selection among CDMA, UMTS, and LTE access systems.

Taking advantage of its high security, USIM now stores mobility management parameters for SAE/LTE. Critical information like location information or EPS security context is to be stored in USIM rather than the device.

USIM in LTE networks is not just a matter of digital security but also physical safety. The USIM now stores the ICE (In Case of Emergency) user information, which is now standardized. This feature allows first responders (police, firefighters, and emergency medical staff) to retrieve medical information such as blood type, allergies, and emergency contacts, even if the subscriber lies unconscious.

3GPP has also approved the storage of the eCall parameters in USIM. When activated, the eCall system establishes a voice connection with the emergency services and sends critical data including time, location, and vehicle identification, to speed up response times by emergency services. ECalls can be generated manually by vehicle occupants or automatically by in-vehicle sensors.

TOOLKIT FEATURES IMPROVEMENT (TS 31.111)
New toolkit features have been added in Rel-8 for the support of NFC, M2M, OMA-DS, DM and to enhance coverage information.

The contactless interface has now been completely integrated with the UICC to enable NFC use cases where UICC applications proactively trigger contactless interfaces.

Toolkit features have been updated for terminals with limited capabilities (e.g. datacard or M2M wireless modules). These features will be notably beneficial in the M2M market where terminals often lack a screen or a keyboard.

UICC applications will now be able to trigger OMA-DM and DS sessions to enable easier device support and data synchronization operations, as well as interact in DVB networks.

Toolkit features have been enriched to help operators in their network deployments, particularly with LTE. A toolkit event has been added to inform a UICC application of a network rejection, such as a registration attempt failure. This feature will provide important information to operators about network coverage. Additionally, a UICC proactive command now allows the reporting of the signal strength measurement from an LTE base station.

CONTACT MANAGER
Rel-8 defined a multimedia phone book (3GPP TS 31.220) for the USIM based on OMA-DS and its corresponding JavaCard API (3GPP TS 31.221).

REMOTE MANAGEMENT EVOLUTION (TS 31.115 AND TS 31.116)
With IP sessions becoming prominent, an additional capability to multiplex the remote application and file management over a single CAT_TP link in a BIP session has been completed. Remote sessions to update the UICC now benefit from additional flexibility and security with the latest addition of the AES algorithm rather than a simple DES algorithm.

CONFIDENTIAL APPLICATION MANAGEMENT IN UICC FOR THIRD PARTIES
The security model in the UICC has been improved to allow the hosting of confidential (e.g. third party) applications. This enhancement was necessary to support new business models arising in the marketplace, with third party MVNOs, M-Payment and Mobile TV applications. These new features notably enable UICC memory rental, remote secure management of this memory and its content by the third party vendor, and support new business models supported by the Trusted Service Manager concept.

SECURE CHANNEL BETWEEN THE UICC AND TERMINAL
A secure channel solution has been specified that enables a trusted and secure communication between the UICC and the terminal. The secure channel is also available between two applications residing respectively on the UICC and on the terminal. The secure channel is applicable to both ISO and USB interfaces.

RELEASE 9 ENHANCEMENTS: UICC: ENABLING M2M AND FEMTOCELLS
The role of femtocell USIM is increasing in provisioning information for Home eNodeB, the 3GPP name for femtocell. USIMs inside handsets provide a simple and automatic access to femtocells based on operator and user-controlled Closed Subscriber Group list.

Work is ongoing in 3GPP for the discovery of surrounding femtocells using toolkit commands. Contrarily to macro base stations deployed by network operators, a femtocell location is out of the control of the operator since a subscriber can purchase a Home eNodeB and plug it anywhere at any time. A solution based on USIM toolkit feature will allow the operator to identify the femtocells serving a given subscriber. Operators will be able to adapt their services based on the femtocells available.

The upcoming releases will develop and capitalize on the IP layer for UICC remote application management (RAM) over HTTP or HTTPS. The network can also send a push message to UICC to initiate a communication using TCP protocol.

Additional guidance is also expected from the future releases with regards to the M2M dedicated form factor for the UICC that is currently under discussion to accommodate environments with temperature or mechanical constraints surpassing those currently specified by the 3GPP standard.

Some work is also expected to complete the picture of a full IP UICC integrated in IP-enabled terminal with the migration of services over EEM/USB and the capability for the UICC to register on multicast based services (such as mobile TV).

Further Reading:

Monday, 28 September 2009

Paging Permission with Access Control (PPAC) Study in Release 8

A new feature that was studied part of 3GPP Release 8 was PPAC (Paging Permission with Access Control). The aim of this feature was that in an emergency situation, the network can get congested and as a result all access is barred except for emergency services. This can cause problem when the user requires to be contacted but is unreachable.

Lets take Case 1: Disaster risk management office in government calls to emergency responder within disaster areas in order to supply temporary service to the disaster areas.

This should not be a problem because the emergency responder is an authorised user with higher priority of access class and will be able to make and receive calls in the disaster area.



Case2: Ambulance attendant reaches a rescue site in the disaster area but cannot find the person who asked for help originally because of unexpected destruction. The attendant should be able to call him/her in order to make sure where he/she is.

Case3: Firefighter is at a scene of fire of high-rise apartment in the disaster area and calls to a person who asked for help in order to give out directives on the evacuation.


These scenarios as such are no problem except when there is congestion on the receiving side. In that case either the emergency attendant or the risk management office should be able to get in touch and establish the call.

In technical terms, the people like emergency attendants and disaster risk management office attendants are called authorised users and the ordinary people who need help are known as unauthorised users.

It should also be possible to make a small duration call between unauthorised users so people can check each others safety. This can be controlled by changing the permission of different access class for small durations so that people can trigger calls for small duration.

The study found that eMLPP (Enhanced Multi-Level Precedence and Pre-emption) that is already available since GSM days can resolve the problem of prioritisation in resource allocation. A new capability will be required to allow UEs with indications from the network to perform location registration and respond to a paging request even though it is under access class barring conditions to complete certain classes of calls or messages (e.g. calls from emergency personnel, …).


This new capability will be available probably when Release 9 is finalised in December this year.


As far as understanding this eMLPP is concerned, the following book has quite a lot of details on this topic. If you can get hold of it then do go through it.

Preferential Emergency Communications: From Telecommunications to the Internet (The Springer International Series in Engineering and Computer Science)

Here is the google books link for that.




Tuesday, 22 September 2009

SMS for Emergency Services

I blogged few months back about SMS for emergency services in USA now the same is being tried in UK.

Ofcom is trialling a new system to let deaf people access 999 services using text messaging.

The system lets users who can’t speak send a text message to emergency services. Their text is received by 999 assistants and read out to fire, police or other emergency service. A reply is also sent back via SMS.

The trial kicked off earlier this month, with Ofcom asking people to register to test the service. As the trial will use actual emergency messages, it needs enough people to register to get a good feel for how the system is working as most won’t actually have cause to use it.

To register, text “register” to 999; anyone not registered will not be able to use the service.
Ofcom noted that users shouldn’t assume their message has been received until they’ve received a reply, and that anyone sending hoax messages will be prosecuted.


If the trial goes well, the texting system could be in place as early as next year, Ofcom said. It’s being supported by the major telecoms companies, as well as emergency services and the Royal National Institute for Deaf People (RNID).

SMS to the emergency website here.

Wednesday, 26 August 2009

Europe makes 'eCall' high priority



The European Commission has made a final call to the European governments to speed up the implementation of the 'eCall' technology that uses cellular networks to automatically alert emergency services when a road accident occurs.

Currently, the deployment of eCall is voluntary and is not being used in any EU country. The Commission warns, in a policy document, that if no significant progress is made in rolling out the system by the end of 2009 it could propose regulatory measures to make it mandatory.

The Commission has presented a policy document with a strategy for introducing an affordable in-car emergency call system in all new vehicles across Europe by 2014, starting next year. Triggered automatically, if the passengers cannot do so, eCall is claimed to be able to save up to 2,500 lives per year in the EU when fully deployed and reduce severity of injuries by 10 to 15%.




Implementing eCall needs the full collaboration of the car and telecoms industries, as well as national administrations in all EU countries who must ensure that their emergency services are equipped to handle eCalls.

Although the technology is ready and common EU-wide standards have been agreed by industry, six EU countries ( Denmark, France, Ireland, Latvia, Malta and the UK) are still not ready to commit, due to cost related concerns.

Preparing phone networks and emergency services for the roll out of eCall in cars across Europe has the full support of the European Parliament and 15 EU countries who have signed the eCall Memorandum of Understanding (Austria, Cyprus, Czech Republic, Estonia, Finland, Germany, Greece, Italy, Lithuania, Portugal, Slovakia, Slovenia, Spain, the Netherlands and Sweden) and three other European countries (Iceland, Norway and Switzerland) .

Another six countries (Belgium, Bulgaria, Hungary, Luxembourg, Romania and Poland) support eCall and are willing to sign the agreement in due time.


Before making eCall fully operational across the EU, countries must agree common standards and guidelines for harmonised deployment of the system and perform field tests putting it into practice (pilots have been launched in some EU countries, including Finland, Czech Republic, Germany, Austria, Italy, The Netherlands). Through its Competitiveness and Innovation Programme the Commission may financially support such pilots, as well as public awareness campaigns about how the technology works.

Road accidents cost the EU economy more than EUR160 billion a year. Equipping all cars in the EU with the eCall system could save EUR26 billion annually while the system' is estimated to cost less than EUR100 per car. Introducing this device will not only benefit consumers, but also businesses by enabling the car and telecoms industries to offer new upgraded applications and services (like digital tachographs or electronic tolls) based on eCall to be installed in all vehicles and use satellite positioning technology.

Wednesday, 17 June 2009

SMS: Information, MisInformation, Emergency and Spam


The other day someone pointed out that the number of SMS send per day globally is 2 Trillion. I said, surely this cant be true. The population of the world is somewhere around 7 Billion mark. If we assume that everyone uses the phone and sends 1 message per day than that is still 7 Billion messages, 2 Trillion cant possibly be true.

According to a post earlier, 1 Trillion messages were sent in 2008, compared to 363 Billion in 2007. Thats between 3 and 3.5 Billion per day. We may have to wait probably just couple of years before we see 1 Trillion messages per day (assuming the Networks can cope with this amount of SMS's). The reason for sharp rise in the number would be due to various factors.

The first reason being Spam. China is already facing SMS Spam problems. Its becoming such a nuisance that the operators are considering limiting the number of SMS to a max. of 200 messages per hour and 1000 per day. On holidays, 500 and 2000 respectively. I am not sure if Spammers use phones, rather there are many websites allowing bulk messaging facilities. Many companies are also offering power texting facilities that allows big bundles for minimal pricing. The average price being 1 cent per SMS or even cheaper.

Another reason that we should not forget is the introduction of many QWERTY phones that is making life of texters easier. There is some debate as to whether its having good or bad impact on the teens but I think its the health problems we should be worried about more than anything else. Its just matter of time when you get a new phone, there will be a caution note saying: "Caution: Text messaging can seriously harm your health. It can cause sore thumbs, cause sleeping disorders, anxiety and in some cases depression. Please click on I Accept if you would like to use it at your own risk" :)

Deciphering teen text messages is an art in itself. I blogged about it earlier but things change faster than you can anticipate. LG have launched a DTXTR service that can help you decipher your teen text messages. I tried few codes and it failed miserably. I suppose for these kinds of services, one more thing you need is to know the location of the users. Same code word can mean different thing in different countries/states. Webopedia has a very detailed list of these abbreviations.

Finally, I have always wondered why emergency services dont allow SMS. If I am in a bank being robbed, its safer to send a text rather than call and speak to an operator. Good news is that, its already being tested in the US. This should complement the eCall feature in future.

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