 Namaste, Welcome to the video lecture on GSM Speech Coding, Authentication and Security. Learning Outcome. At the end of this session, students will be able to explain speech coding. Students will be able to analyze authentication and security in GSM. These are the contents of video lecture. To send a voice across a radio network, we have to turn our voice into a digital signal. The speech signal is compressed using an algorithm known as RPE LPC algorithm, that is nothing but regular pulse-excited linear predictive coder. Before starting the GSM speech coding, authentication and security topic, pause the video for two minutes and list all steps which are involved in digital signal transmission. You can pause video for two minutes and list out all the process or all the steps which are involved in digital signal transmission. I think two minutes are over. GSM transmission process involves following steps. First step is analog to digital conversion, then converted data is segmented and speech is coded. Then next process is called speech coding, channel coding, inter-living, cyphering that is encryption process, bus formation and modulation and transmission. In essence, data from previous data samples are used to predict the current data samples. Each data sample is then encoded, which is a sum of bits representing the coefficients of the linear combination of previous sample. And an encoded form of difference between the predicted and actual sample speech is converted into 60-bit packet with duration of 20 millisecond. Speech coder output bits are ordered into selected group for error protection. This can be divided into three classes. Based on the importance of the bits, from the given packet of 260-bit information or following division is taken place. First class that is class 1abit. This group includes 50 bits most sensitive to the bit errors. Next class is called class 1b. This includes 132 bits moderately sensitive to bit errors and third group is called class 2, which involves or which includes 78 bits least sensitive to bit errors. Class 1a that is 50 bits are protected by three bits by using CRC method that is cyclic redundancy check. Class 1a which includes 50 bits and 3 CRC bits, 189 bits block which includes 53 bits from class 1a and 132 bits of class 1b, which all add together to form 189-bit packet. And next step is these 189-bit packet is then error protected by convolution with rate of 0.5 or we can say with half rate and with the length of 5. Resulting 189 bits are converted into 378 bits by using convolution method. Now the last group that is least important bits which is also called class 3 bits which includes 78 bits are unprotected and are appended to existing sequence to produce 456 bits in 20 millisecond. We can observe how 260 bits are converted into 456 bits. First the 260 bits packet are converted into three groups that is class 1a, class 1b and class 2 and then by using error protection these bits are converted into 456-bit packet. We can observe speech coding process distribution of 260-bit speech data in 50, 132 and 78 bits and further how these 50, 132 and 78 bits are error protected and converted to form 456-bit packet. Now next step which involved in data transmission interleaving of user traffic data. The purpose of interleaving user traffic data is to improve the signal quality by distributing the effects of fading among several mobile subscribers receiving data simultaneously from base stations. The user traffic data of 456 bits are interleaved into transmitted normal burst in blocks of 57 bits plus 1 plaque bit means the 456-bit data is distributed in 58-bit block, 456-bit encoded data divided into 857-bit sub block forming speech frame. The speech data are encrypted 114 bits at a time assembled into time slot and modulated for transmission. Next step is packets of signaling channel. The number of signaling or control channels are used to determine how traffic data are in the network. Signaling channel employing the normal burst use 184 signaling bits in 20ms duration. Further these bits are coded with 40 additional parity check bits and 4 tail bits to form 228-bit block, further 228-bit block is then coded with convolution encoder with the same rate which was previously used. We can say it is used as a half rate convolution packets of data traffic 192 bits user data plus 48-bit signaling data with 4 tail bits which results in 244-bit packet encoded with half rate convolution encoder punctured coding to eliminate duplicate bits resulting coded data packet is of 456 bits. Now next step of data transmission which is called channel coding for traffic or control data. Traffic data is processed in blocks of 240 bits every 20ms traffic data is processed in blocks of 240 bits every 20ms. For the actual supported data rates of 9.6kbps, 4.8kbps and 2.4kbps each block is augmented by 4 tail bits. Trim code is used to produce a block of 244 into 2 that means 488 bits. The 488 bits are spread over 22 bus first and 22nd bus carry 6 bits, 2nd and 21st bus carries 12 bits, 3rd and 20th bus carry 18 bits, 4th through 19th bus carry 24 bits each. Authentication and security in GSM. The two security goals of GSM are to provide an infrastructure which protects access to the mobile services and to prevent any information from being disclosed. In other words, GSM aims to prevent fraudulent phone use and to provide privacy for both parties to provide security. First is authentication and register users, second one secure data transfer, then subscriber identity protection, then mobile phones are inoperable without SIM chip. Next one is duplicate SIMs on network are not permitted and last one keys are securely stored. Authentication and security which includes GSM divides security on three different levels. Each level provides the mechanism for anonymity, authentication, confidentiality or integrity. On the lowest level of security GSM provides authentication and anonymity for the user through the SIM card. The SIM chip serves as the identification of the user. Billing and authentication are verified through the SIM chip. The second layer of security identifies the location of the user and reveals the incoming caller's name to the receiver so the receiver can choose whether or not to accept the call. The third layer encrypts any data travelling between the two users with the data encrypted and connection secure integrity and confidentiality is provided. As we can see the authentication process in GSM involves two segments, MS and network and it needs supporting data like IMSA number and key. Let us discuss the authentication process in detail. A cell phone call placed on a GSM network goes through the two steps. Any mobile device must first be authenticated before any data transmission can begin Being successful authentication a private key KC is generated and data is exchanged. Authentication is done through a challenge and response mechanism. The base station initially sends a random 128 bit number R to the mobile device using A3 encryption with input key KI from the SIM and the random number R a 32 bit encrypted number SRS is generated. The mobile device then sends generated number back to the network to validation. The network itself knows the mobile device KI that is input key and can thus compare the value it generated to the value the mobile device generated. Authentication is successful if mobile numbers are identical. These are references. Thank you.