SIM card
The SIM card (from the English s ubscriber i Dentity m odule for "subscriber identity module") is a smart card , in a mobile phone is inserted and used to identify the user in the network. With it, mobile network providers provide subscribers with mobile telephone connections and data connections .
The SIM card is a small processor with memory (usually in ID-000 format, which is broken out of an ID-1 format card). The card can be protected against unauthorized use by a changeable PIN . With the help of the SIM card, the mobile equipment (usually the mobile phone) is assigned to a network and authenticated . For these purposes, which is on the SIM card IMSI stored, which in case of power search and booking into a wireless network is unencrypted and eavesdropping of mobile phone calls and narrowing down the location of the mobile phone allowed within a radio cell ( IMSI catcher ). Other number sequences and algorithms stored on the SIM card are used to encrypt the voice and signaling data ( ciphering ). The SIM is also used to store temporary, network-related data as well as preferred and blocked networks. In addition, a telephone and notebook, memory for short message service messages (SMS) and memory of the last phone numbers called can be integrated. SIM and mobile equipment together form the mobile station in the GSM .
Around 115 million SIM cards were in circulation in Germany in 2012.
technology
The SIM card is often delivered in the large ID-1 format (85.6 mm × 54 mm). The smaller ID-000 part (25 mm × 15 mm) can be broken out. Due to the ever smaller mobile devices, the small ID-000 format was introduced over time for D-Netz devices . There are now a large number of devices that use the even smaller micro-SIM instead. Many modern smartphones already use the smallest format, the nano-SIM .
A SIM toolkit makes it possible to store small programs on a SIM card, for example info services, with which current information about politics, sport, weather can be delivered. The mobile phone operators O₂ , T-Mobile and Vodafone use this to offer their Homezone service. With the help of the SIM toolkit, it is shown there whether the mobile phone is in the home zone . Functions such as topping up or checking your credit balance (with prepaid prepaid cards) are possible. The advantage of applications on the SIM card is that they can be used regardless of the device used (so the cell phone can be changed without any apparent change in functionality).
Various manufacturers are currently working on the development of a SIM card with larger storage space, similar to the well-known memory cards such as SD cards . This memory, up to now up to 128 GB , can be used freely for MP3 audio or other documents.
A technology is called SIM Access Profile , with which z. For example, in the car the SIM data of a mobile device equipped with Bluetooth can be read by a permanently installed device and the device itself establishes the radio connection. In this way, the data transmission through the permanently installed external antenna can be improved and the power consumption of the mobile phone can be reduced.
In dual SIM cell phones or with the help of dual SIM adapters , two or more SIM cards can be accommodated in one device, which are either active simultaneously (simultaneously) or alternatively (alternately) .
contacts
There are eight contact areas on a SIM card. Different cards vary in number and distribution, but only these eight contacts were specified with the following assignment:
| V cc - supply voltage | C1 | C5 | GND - ground | |
| Reset - Reset for SIM-CPU | C2 | C6 | V pp - programming voltage | |
| CLK - clock | C3 | C7 | I / O data | |
| reserved | C4 | C8 | reserved |
The operating voltage is supplied to the SIM card via V cc and GND. There are SIM cards with an operating voltage of 1.8 volts, 3 volts and, with the older generation of cards, 5 volts (see table types ). The respective voltage is printed on the SIM card in some cases (e.g. from Cellway provider).
If a SIM card with the wrong voltage is used in a mobile phone, error messages, crashes or unusually fast battery discharge can occur.
If a SIM card no longer reacts to requests from the mobile device, it can be restarted via the reset contact. The clock of the mobile device for the synchronization of the data transfer taking place via the I / O contact is transmitted via CLK.
The optional programming voltage V pp is only required during manufacture in order to initialize or delete the internal software of the card. The normal read and write processes on the user area of a SIM card (e.g. when used in a mobile device) manage without this voltage.
The two additional contact pins are reserved for currently rare eight-pin SIM cards, as they are to be used in future mobile devices - there are currently several competing designs for what these contacts are to be used for, among others. a. SIM cards with very high storage capacities are being discussed, which could be connected via a variant of the USB protocol. Other ideas concern special encryption functions or near field communication (NFC). Current European cell phones, however, still only use six-pin SIM cards.
circuit
The I / O unit regulates access to the SIM card. It is the interface between the CPU and the mobile device. The CPU is mainly used for memory management, but it can run small programs. The memory consists of a ROM , a RAM and an EEPROM . The operating system of the card is stored in the ROM. The brandings of the mobile phone companies are saved there (start logos). The RAM contains the data you are currently using; it is volatile. User data are stored in the EEPROM.
lifespan
SIM cards have a limited lifespan. With every erase-write cycle of the non-volatile card memory, for example during authentication in the network, the memory used ages. Originally, the manufacturers of the SIM chips guaranteed 100,000 such cycles. With current chips this value is 500,000 to a million. In order to defuse this process, the SIM manufacturers build protective mechanisms into the operating system .
Regardless of this, some older SIM cards are not recognized by current cell phones. One reason could be that the SIM card no longer works with the voltage provided by the device. Another reason could be that the device requires a USIM card .
ICCID
The ICCID (from the English I ntegrated C ircuit C ard ID entifier) is a unique identification number of the SIM card itself. Even with eSIM ICCID numbers are used for unique identification. These are stored on the card's ROM and are usually printed on the card itself.
The ICCID is defined by the E.118 standard of the International Telecommunication Union as the primary account number . The arrangement is based on ISO 7812 .
According to this standard, the number consists of three parts. The issuer identification number (IIN) (4-7 characters), the SIM number (typically 11-13 characters) and the check digit (1 character), the total length should be 19, other lengths (up to 22) occur. The check digit is calculated using the Luhn algorithm . The areas Issuer identification number (IIN) and SIM number can overlap.
The ETSI-GSM standard provides a memory of 10 bytes for this information on the SIM card. The digits are saved in BCD code , 2 digits per byte. This means that the maximum logical length is 20 characters.
| Issuer identification number (IIN) | SIM number | Check digit | |||
|---|---|---|---|---|---|
| length | 2 characters | 1-3 characters | 1-4 characters | typ. 11–13 characters | 1 character |
| Explanation | service | Country code defined by ITU-T recommendations E.164 | Cellular provider | The length is variable, but always the same length within the IIN. | Calculated on the basis of the remaining characters using the Luhn algorithm |
| Example 1 (length 20) |
for telecommunications : 89 |
for Switzerland : 41 |
for Swisscom : 01 |
0500 744 46 76 81 |
5 |
| Example 2 (length 19) |
for telecommunications : 89 |
for the Czech Republic : 420 |
for O2 Czech Republic : 20 |
390 2044 3988 |
5 |
The E.118 standard requires the publication of the list of all currently internationally assigned IIN codes; this is done twice a month on the ITU-T website. The ITU-T publishes complete lists with historical data, these are updated annually.
Formats
In the technical world, the hardware of the SIM card is called Universal Integrated Circuit Card or UICC for short.
Since the development of the UMTS standard by the European Telecommunications Standards Institute at the end of the 1990s, it has been assumed that mobile end devices will be smaller in the future or at least have less space inside and that SIM cards with a smaller size will therefore be required.
| SIM card | default | Form factor |
Dimensions in mm (inches) | ||
|---|---|---|---|---|---|
| length | width | thickness | |||
| Standard SIM (full-size) |
ISO / IEC 7810 : 2003, ID-1 | (1) FF | 85.60 (≈ 3 3 ⁄ 8 ) |
53.98 (≈ 2 1 ⁄ 8 ) |
0.76 (≈ 1 ⁄ 32 ) |
| Mini SIM | ISO / IEC 7810 : 2003, ID-000 | 2FF | 25.00 (≈1) |
15.00 (≈ 3 ⁄ 5 ) |
0.76 (≈ 1 ⁄ 32 ) |
| Micro SIM | ETSI TS 102 221 V9.0.0, Mini-UICC | 3FF | 15.00 (≈ 3 ⁄ 5 ) |
12.00 (≈ 1 ⁄ 2 ) |
0.76 (≈ 1 ⁄ 32 ) |
| Nano SIM | ETSI TS 102 221, TS 102 221 V11.0.0 | 4FF | 12.30 (≈ 1 ⁄ 2 ) |
8.80 (≈ 1 ⁄ 3 ) |
0.67 (≈ 1 ⁄ 40 ) |
| Embedded SIM | JEDEC Design Guide 4.8, SON-8 | - | 6.00 (≈ 1 ⁄ 4 ) |
5.00 (≈ 1 ⁄ 5 ) |
<1.00 (≈ 1 ⁄ 25 ) |
Full-size SIM
The first GSM devices had a slot for inserting SIM cards in credit card format. Often these SIM cards were inserted under the battery, as in the Sharp TQ-G700. Another example of such a device is the D-Netz mobile phone Siemens S3com from 1995. The design of the devices was at least as wide as a credit card.
Since the SIM chip did not take up such a large area, the significantly smaller UICC format was established as early as the late 1990s. This is why only a few devices with full-size SIMs came onto the market. In the early days, the UICC SIM card was punched out of the credit card-sized SIM card; later the mini-SIM cards could be broken out of the full-size SIM card. In the opposite case (in the case of a device with a SIM card the size of a credit card), the original card (from which the UICC SIM card was punched out or broken out) could usually be used as an adapter.
Mini SIM (UICC)
The mini SIM card ( 2FF abbreviation for “ Second Form Factor ”) is only 25 mm × 15 mm in size and just as thick as the full-size SIM.
SIM cards are sometimes still delivered in credit card format, but the mini-SIM is then already pre-cut so that it only has to be broken out at predetermined breaking points . In the beginning, the mini-SIM was not pre-punched in the full-size SIM that was delivered, which is why there were not only punching devices but also instructions for self-assembly (cut out with a template and scissors). In order to save material, the SIM card has often only been supplied in UICC format in a cardboard template since the mid-2010s.
Micro SIM (Mini UICC)
The micro SIM ( 3FF abbreviation for “ Third Form Factor ”) is 52% smaller than that of the mini SIM card. With the micro-SIM, the outer lengths are only 15 mm × 12 mm . As with the full-size SIM or mini-SIM, the thickness is 0.76 mm. As far as the technical data of the circuit is concerned, there are no differences.
With a special punching device, a full-size SIM or mini-SIM can be made into a micro-SIM.
One of the first devices to use a micro SIM card was the iPad in 2010, followed by the iPhone 4 . Nokia uses this card type, for example with the Nokia N9 or the Nokia Lumia 800 . Motorola uses micro SIM cards for the Motorola Droid Razr. Many other manufacturers have followed the trend and are now using micro-SIM cards in their smartphones.
Nano SIM
The Nano-SIM ( 4FF for " Fourth Form Factor ") is 40% smaller with 12.3 mm × 8.8 mm × 0.67 mm , but above all 12% thinner than a micro-SIM and should therefore be more spacious save in compact devices. Cards in nano-SIM format offer the same functionality as larger cards. The standard includes mechanical downward compatibility, which should allow simplified distribution.
Both Apple and Nokia initially wanted to standardize their version as the better one. In June 2012, the ETSI finally decided on Apple's design proposal. This is downward compatible with the micro-SIM cards already in use. The nano SIM card was launched on the market in September 2012 with the iPhone 5 . Many modern smartphones now offer a nano-SIM slot.
Although punching, as described for the micro SIM, to the nano SIM is described as not possible (because it is thinner), warned about it or not mentioned at all, there are numerous articles on the World Wide Web with instructions, cutting templates, Punching equipment and videos.
Cell phone providers warn against re-punching, and usually recommend re-ordering the SIM card for a fee.
SIM card adapter
The adaptation (reverse conversion) to the next larger format is possible using a special SIM adapter (except for the embedded SIM).
clipping
Many mini and micro SIMs have eight contact surfaces, two of which are only kept in reserve and are not connected. It is therefore possible to cut a standard SIM not only to the mini format, but also to the size of a micro or nano SIM. The most common mistake of such manual cuts is that the chips created create a connection between two or more contacts that damage or destroy the SIM when it is used for the first time.
Combi SIM
Many providers now supply combi SIM , hybrid SIM or also triple SIM cards in the mini format , from which a micro or nano SIM card can be broken out by pre-punching. Instead, some manufacturers supply nano SIM cards with adapter frames that make the nano format usable in devices for micro or mini SIM cards and thus combine all three sizes. In the case of adapter frames (not SIM adapters), the SIM card in the mobile phone can break out of the frame and, in the worst case, block the SIM slot.
embeddedSIM
The embeddedSIM (eSIM) replaces the classic physical SIM card. It is smaller than SIM cards, built directly into the device and cannot be physically exchanged. The information stored on it is provided using the procedures standardized by the GSM Association. The main advantage is the fact that the customer no longer has to be provided with a real chip card. Instead, the participant information can also be made available online, with the help of an existing Internet connection.
First devices such as Samsung's Smartwatch Gear S2, Apple Watch Cellular (from Series 3), and newer Apple iPhones use them.
NFC SIM
An NFC SIM is required to use the mobile payment functions. This has a second, completely separate and encrypted area (Secure Element) that only the bank has access to. The card receives the data for the bank function so that it is retained when the device is changed. It is also possible to save several bank cards on one NFC SIM. Externally, the cards do not differ from those without NFC. The cards are also available in the three sizes mini, micro and nano.
- Austria
The “digital bank card ” payment system was field-tested in Austria from June 2015 and has been offered by all major banks and the three major mobile phone providers since the beginning of 2016, but only for Android devices. It is necessary to exchange the SIM with the mobile phone provider; new customers have not yet been automatically equipped with NFC SIMs. The digital debit card can then be ordered from the house bank.
Types
The card type or generation type is, for example, on the GSM SIM
- at the end of the last line as the last 2 characters (Telekom, O 2 ) or
- at the front of the first line as the last 2 characters (e +) or
- at the end of the last line as the first character (Mobilcom) or also
- behind the 14-digit card ID.
| Type | network | Provider | Operating voltage |
Storage capacity (in bytes) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| phone book | Own numbers |
protected numbers |
Last elected |
Service numbers |
Expansion memory 1 - 3 |
SMS memory |
SMS parameters |
Skills memory |
||||
| F3 | D1 | Deutsche Telekom |
125 × 30 | 3 × 30 | 7 × 30 | 10 × 20 | n. v. | 10 × 13 1 × 13 n.v. |
10 × 176 | 2 × 40 | 2 × 14 | |
| H4 | D1 | Deutsche Telekom |
125 × 30 | 3 × 30 | 10 × 30 | 10 × 20 | n. v. | 10 × 13 1 × 13 n.v. |
15 × 176 | 2 × 40 | 2 × 14 | |
| N3 | D1 | Congstar, clear mobile |
230 × 30 | 4 × 30 | 10 × 30 | 10 × 30 | n. v. | n. v. | 20 × 176 | 2 × 40 | 3 × 15 | |
| C / WE | D1 | Congstar | 250 × 30 | 4 × 30 | 10 × 30 | 10 × 30 | n. v. | n. v. | 20 × 176 | 2 × 40 | 3 × 15 | |
| OT | D2 | Cellway, Mobilcom |
3 V | 255 × 31 | 4 × 31 | 50 × 31 | 10 × 20 | n. v. | 10 × 13 5 × 13 n.v. |
30 × 176 | 5 × 45 | 5 × 14 |
| G | D2 | 1 & 1 | 200 × 32 | 3 × 24 | 5 × 32 | 5 × 32 | n. v. | 20 × 13 2 × 13 n.a. |
20 × 176 | 3 × 46 | 3 × 15 | |
| VY | E2 | O 2 Germany | 250 × 30 | 3 × 30 | 30 × 30 | 10 × 30 | 10 × 30 | 10 × 13 3 × 13 3 × 13 |
20 × 176 | 3 × 44 | 10 × 15 | |
The abbreviation n.v. in table means that this memory area is not available on the SIM card.
For the telephone book, own numbers, protected numbers, last numbers dialed and service numbers with
- 32 bytes per storage space are 18 characters for the name
- 31 bytes per storage space are 17 characters for the name
- 30 bytes per storage space are 16 characters for the name
- 24 bytes per storage space are 10 characters for the name
- 20 bytes per storage space are 6 characters for the name
and for SMS parameters with
- 46 bytes per storage space are 18 characters for the name
- 45 bytes per storage space are 17 characters for the name
- 44 bytes per storage space are 16 characters for the name
- 40 bytes per storage space are 12 characters for the name
supported.
The number of bytes specified in the table does not automatically indicate the number of characters that can be stored on the SIM in this area. So z. B. Numbers stored in the so-called BCD code . Each of the digits only uses a nibble , which makes more effective use of the comparatively small memory space. Not every mobile phone can use the full available storage capacity.
The extended memory can be used freely by the operating system of the mobile phone, which means that the information stored there is not or incorrectly interpreted by another mobile phone. This memory area has been used by some devices, e.g. B. used to extend the number of characters for the name for the first entries (e.g. Siemens A60), for others to save a second telephone number.
Country specifics
On February 13, 2009, the German Federal Council approved a regulation by the Federal Ministry of Economics and Technology , according to which emergency calls ( 110 and 112 ) can no longer be dialed without a SIM card. Since emergency calls were made more and more frequently from cell phones without a card, only communication participants who could be identified by SIM cards should now have this option.
safety
New SIM cards have better security features than older SIM cards. For security reasons, all SIM cards that are over ten years old should be replaced with new SIM cards.
DES encryption
At the Black Hat 2013 and the OHM 2013, Karsten Nohl demonstrated that many cell phones still use SIM cards with DES encryption, which has long been considered unsafe . In Germany, the IT industry association Bitkom and the major telecommunications providers Deutsche Telekom , Telefónica , E-Plus -Gruppe and Vodafone reacted calmly, since the insecure DES encryption is no longer used.
Key theft
Based on published secret documents by whistleblower Edward Snowden , The Intercept reported in February 2015 that the National Security Agency and Government Communications Headquarters had stolen keys from Gemalto , the largest manufacturer of SIM cards, in 2010 . They are thus able to eavesdrop on a large part of global mobile communications, including voice messages and data, without being recognized. In one of the documents, the German company Giesecke & Devrient is named as the target.
USIM application
The USIM application enables the mobile station to better encrypt the calls, messages and data transmitted over the cellular network . The mobile station can better protect its authentication against the mobile operator thanks to the USIM application. For security reasons, SIM cards should be operated with the USIM application in all mobile stations. Mobile stations that do not support the USIM application should be replaced with newer devices for security reasons.
See also
- SIM lock
- Alternate Line Service
- IMEI serial number for the unique identification of mobile radio devices
- IMSI for the unique identification of network subscribers in GSM and UMTS cellular networks
- IMSI catcher for eavesdropping on cell phone customers
- Stealth Ping - also Silent SMS or Silent SMS for locating mobile devices or for creating movement profiles
- Cell-ID is a method of mobile positioning in the GSM cellular network.
Web links
- Specification of the Subscriber Identity Module - Mobile Equipment (SIM-ME) Interface
- Machine to Machine UICC (3GPP TS 102 671 version 9.0.0)
- Historical SIM cards. In: prepaid-wiki.de. Retrieved December 30, 2017 . More examples for German SIM cards.
Individual evidence
- ↑ Guide to data access, especially in the telecommunications sector. (PDF; 429 kB) Munich Public Prosecutor's Office, June 2011, accessed on December 5, 2011 .
- ↑ Stefan Krempl: 26C3: GSM hacking made easy. In: Heise News. Retrieved July 10, 2013 .
- ↑ Martin Wocher: Mobile discounter on the advance . In: Handelsblatt . No. 120 , June 26, 2013, ISSN 0017-7296 , p. 25 .
- ↑ [1]
- ↑ SIM cards also age
- ↑ anti tearing .
- ↑ ITU-T, ITU-T Recommendation E.118, The international telecommunication charge card, version history , revision "05/2006"
- ^ Digital cellular telecommunications system (Phase 2+); Specification of the Subscriber Identity Module -Mobile Equipment (SIM - ME) interface; (GSM 11.11) , Version 5.3.0, July 1996, Chapter 10.1.1 EF ICCID (ICC Identification) , page 51
- ↑ Operational Bulletin No. 1163 (1.I.2019) ( en-US ) www.itu.int. Retrieved January 5, 2019.
- ↑ List of issuer identifier numbers for the international telecommunication charge card (In accordance with Recommendation ITU-T E.118 (05/2006)) . International Telecommunication Union. 5th January 2015.
- ↑ New SIM card format for slimmer, smaller phones. ETSI, June 1, 2012, accessed June 3, 2012 .
- ↑ Siemens S3 com. In: chip.de. Retrieved January 5, 2018 .
- ↑ 1995 brings Siemens with the s3com. In: focus.de. Retrieved January 5, 2018 .
- ↑ The end of Siemens Mobile 10 years ago. In: inside-handy.de. Retrieved January 5, 2018 .
- ↑ a b c Apple wants to offer its own format for nano-SIM free of charge , March 30, 2012
- ↑ Nokia Austria - Nokia N9 - Technical Specifications. Nokia, accessed August 16, 2011 .
- ↑ New SIM card format for slimmer, smaller phones. ETSI, June 1, 2012, accessed June 3, 2012 .
- ↑ Compare iPad models. In: apple.com. Retrieved October 23, 2012 .
- ↑ callmobile faq. In: callmobile.de. Retrieved January 27, 2015 .
- ↑ Thomas Streitberger: SIM card cutting - instructions and template for download. (No longer available online.) In: www.sim-vorlage.download. Thomas Streitberger, archived from the original on September 17, 2016 ; accessed on September 17, 2016 .
- ↑ Flavio Trillo: Micro-SIM template: Download and instructions for cutting yourself Giga, January 30, 2014.
- ↑ Annika Demgen: This is how it works: SIM or micro SIM card cut to nano size netzwelt.de, November 3, 2012
- ↑ Frederik Niemeyer: Video: Cutting the Nano SIM - DIY - Tutorial. In: Chip.de. January 19, 2015, accessed June 2, 2018 . .
- ↑ SIM card formats mini, micro, nano. In: congstar.de. Retrieved January 27, 2015 .
- ↑ Sébastien Bonset: Cutting to a new format works. In: t3n magazine . September 18, 2012, accessed September 18, 2012 .
- ↑ eSIM Whitepaper - Section "How it Works" . GSM Association. Retrieved December 25, 2018.
- ↑ iPhone XS Specifications. Retrieved on October 3, 2018 (German).
- ↑ MWC 2016: Samsung's “Gear S2 Classic 3G” smartwatch opens the age of eSIM. In: heise online. Retrieved March 26, 2016 .
- ↑ Mobile ATM card .
- ↑ From June the mobile phone will become an ATM card , Futurezone.at on May 22, 2015.
- ↑ Delayed start of the ATM card on the cell phone , Futurezone.at on December 9, 2015.
- ↑ prepaid-wiki.de - T-Mobile SIM cards accessed on December 30, 2017
- ↑ prepaid-wiki.de - SIM cards O2 accessed on December 30, 2017
- ↑ prepaid-wiki.de - SIM cards E-Plus accessed on December 30, 2017
- ↑ SIM cards mobilcom. In: prepaid-wiki.de. Retrieved December 30, 2017 .
- ↑ ETSI Standard TS 100 977 V8.14.0. (PDF) European Telecommunications Standards Institute, p. Section 1.5.1, p. 96 ff. , Accessed on December 26, 2018 .
- ^ Federal Council printed paper 967/08. Retrieved on December 25, 2016 : “This ordinance serves this goal in conjunction with Section 108 of the TKG and makes it clear who of the parties is responsible for which areas. It also serves to implement Article 6 Paragraph 3 and Article 26 of Directive 2002/22 / EC of the European Parliament and of the Council of 7 March 2002 on universal service and user rights in electronic communications networks and services (Universal Service Directive, OJ EC L 108 of April 24, 2002 p. 51) and the Commission recommendation of July 25, 2003 on the transmission of information on the caller's location in electronic communications networks to emergency services with additional location information (OJ EC L 189 of July 29, 2003, p. 49). "
- ↑ Volker Briegleb: No emergency call without a SIM card. In: heise online. February 13, 2009, accessed June 3, 2012 .
- ↑ Christian Kirsch: ITU warns of the danger of SIM card hacking. heise Security, July 21, 2013, accessed on July 8, 2014 .
- ↑ Jürgen Schmidt: DES hack exposes millions of SIM cards. heise Security, July 21, 2013, accessed on July 8, 2014 .
- ↑ Rooting SIM cards | Security Research Labs. Security Research Labs, accessed July 9, 2014 .
- ↑ Is your cellular SIM card secure? Entrepreneur magazine Creditreform, July 24, 2014, accessed October 10, 2014 .
- ↑ The Great SIM Heist. The Intercept, February 19, 2015, accessed February 20, 2015 .
- ↑ DAPINO GAMMA CNE Presence and IPT keys. The Intercept, February 19, 2015, accessed February 28, 2015 .
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