GSM Unit (3G)
Both user plane data and control plane data is transferred over the UMTS air interface in so‐called _______
'channels'
Spreading and scrambling
*** Downlink: - Spreading: Addressing of different users, Controls the individual datarate for each user - Scrambling: Ensures consistent spectral distribution, Used by the mobile device to differentiate base stations ***Uplink: - Spreading: Controls the individual datarate for each user - Scrambling: Ensures consistent spectral distribution, Differentiates users, Removes the need for a timing advance by preserving the orthogonal nature of the codes necessary for soft handover
For very dense traffic areas, like streets in a downtown area
- A Node‐B microcell can be an alternative to a sectorized configuration. - A microcell is usually equipped with only a single transceiver that covers only a very small area, for example, several dozens of meters of a street. - As the necessary transmission power for such a small coverage area is very low, most network vendors have specialized micro Node‐Bs with very compact dimensions.
What is the The Radio Access Bearer (RAB)
- A description of the transmission channel between the network and a user. - The RAB is divided into the radio bearer on the air interface and the Iu bearer in the radio network (UTRAN)
Evolution of the air interface?
- According to Moore's law, the number of transistors in integrated circuits grows exponentially. Therefore, the processing power of today's processors used in mobile networks is in orders of magnitude more than that of the processors of the early GSM days. - This in turn enables the use of much more computing‐intensive air interface transmission methods that utilize the scarce bandwidth on the air interface more effectively than the comparatively simple GSM air interface.
The UTRAN is free to set these parameters as it sees fit; the standards merely contain examples ....
- As an example, for a voice call (service class conversational) it does not make much sense to repeat lost frames. - For other services, like web browsing, such behavior is beneficial as delay times are shorter if lost packets are only re-transmitted in the radio network instead of end to end.
Authentication, ciphering and integrity checking are performed _____
- Authentication, ciphering and integrity checking are performed independently for circuit‐switched and packet‐switched connections. - This is because the MSC handles circuit‐switched calls while the SGSN is responsible for packet sessions. - As these devices are independent they have to use different sets of authentication vectors and sequence numbers.
Explain the Access Stratum (AS)
- Contains all functionalities associated with the radio network ('the access') and the control of active connections between a user and the radio network. - Handover control, for example, for which the RNC is responsible in the UTRAN, is part of the AS.
Functions of RAB
- Data can be exchanged between a user and the network it is necessary to establish a RAB between them. - This channel is then used for both user and signaling data. - A RAB is always established by request of the MSC or SGSN
In Case of Emergency' (ICE) -
- Devices that implement this functionality allow the user to store information on the subscriber identity module (SIM) card that can be accessed in a standardized way in emergency situations where the user of the phone is unable to identify himself or to contact their relatives
In the uplink direction the scrambling code
- Each mobile device is assigned its own scrambling code. Therefore, each mobile device could theoretically use all codes of the code tree. - This means that in the uplink direction the system is not limited by the number of codes but by the maximum transmitting power of the mobile device and by the interference that is created by other mobile devices in the current and neighboring cells.
In the downlink direction the scrambling code
- Enable the mobile device to differentiate between base stations. This is necessary as all base stations of a network transmit on the same frequency. - In some cases mobile operators have bought a license for more than a single UMTS frequency - This was done to increase the capacity in densely populated areas and not as a means to make it easier for mobile devices to distinguish between different base stations.
The goal of the RRC connection setup is to _____
- Establish a temporary radio channel that can be used for signaling between the mobile device, the RNC and a core network node. - The RNC can choose either to assign a dedicated chan- nel (Cell‐DCH state) or to use the FACH (Cell‐FACH state) for the subsequent exchange of messages.
3GPP Release 8: LTE, Further HSPA Enhancements and Femtocells
- First, Release 8 introduced the successor of the UMTS radio network, the E‐UTRAN (UTRAN is a collective term for the network and equipment that connects mobile handsets to the public telephone network or the Internet), and the successor architecture of the core network, the EPC. - Together they are commonly known as LTE, although technically this is not quite correct. - To reach even higher data speeds, Release 8 introduces the aggregation of two adjacent UMTS carriers to get a total bandwidth of 10 MHz. - This is referred to as Dual‐Cell or Dual‐Carrier operation
3GPP Release 9: Digital Dividend and Dual‐Cell Improvements
- For UMTS, Release 9 brought a number of further speed enhancements in both uplink and downlink directions. - In the uplink direction, aggregation of two adjacent 5 MHz carriers has been specified in a similar way as in the downlink direction in the previous release.
Further enhancements of the CDMA standard were initially foreseen but at some point it was decided by network vendors and network operators that the 3GPP LTE system should become the common successor to UMTS and EV‐DO
- For this purpose, extensions in the LTE specifications were defined to have a standardized interface to the EV‐DO core network. - These enable dual‐mode devices to access both systems and to handover ongoing sessions between the two radio network technologies in a similar way to handover between UMTS and LTE.
What is the purpose of The OVSF Code Tree (Orthogonal Variable Spreading Factors)?
- If the spreading factor was also constant, all users of a cell would have to communicate with the network at the same speed. This is not desirable, as a single cell has to support many users with many different applications simultaneously - While some users may want to simply make voice calls, which require only a small bandwidth, other users might want to place video calls, watch some mobile TV (video streaming) or start a web‐surfing session. - All these services require much higher bandwidths, and thus using the same spreading factor for all connections is not practicable. - Therefore the OVSF Code Tree is used to provide variable data rates for supporting different bandwidth requirements in wideband code division multiple access (WCDMA) systems.
In practice today, mobile devices are either in _____
- In RRC idle state when not transferring any data or in Cell‐PCH or URA‐PCH state. - In these states, the mobile only listens to the PCH and only reestablishes a physical connection when it receives a Paging message or when new data packets arrive from applications running on the device
GSM, UMTS and other fixed and wireless communication systems differentiate between two kinds of data flow
- In UMTS, these are referred to as two different planes. Data flowing in the user plane is data which is directly and transparently exchanged between the users of a connection, such as voice data or IP packets. - The control plane is responsible for all signaling data exchanged between the users and the network. The control plane is thus used for signaling data to exchange messages for call establishment or messages, for example, for a location update
As different users are at different distances from a base station the signals take a different amount of time to arrive. How does that differ in the GSM model?
- In the GSM radio network this was solved by controlling the timing advance. - The use of a timing advance, however, is not possible in the UMTS radio network because of the soft handover state in which the mobile device communicates with several base stations at the same time
Once the MSC has received the CM Service Request message _____
- It verifies the identity of the subscriber via the attached TMSI or IMSI. - This is done in a challenge and response procedure similar to GSM.
For services like voice or video communication it is very important that ____
- Little or no interruption of the data stream occurs during a cell change - For these services, only the Cell‐DCH state can be used. In this state, the network constantly controls the quality of the connection and is able to redirect the connection to other cells if the subscriber is moving. - This procedure is called handover or handoff.
Another advantage of the dedicated approach is ___
- Mobile devices also do not have to be synchronized within a single cell and thus do not have to wait for their turn to send data. - This further reduces RTD times
Limitations of GSM
- New air interface modulation schemes like EDGE have since increased the speed to about 150-250 kbit/s per user in operational networks. - Therefore, further increase in transmission speed was difficult to achieve with the GSM air interface - Electronic interference. Because GSM uses a pulse-transmission technology, it is known to interfere with electronics like hearing aids. This electromagnetic interference is why certain places like airports, gas stations and hospitals require mobile phones be turned of - Bandwidth lag. When using GSM technologies, multiple users access the same bandwidth, sometimes resulting in considerable latency as more users join the network. - Limited rate of data transfer. GSM offers a somewhat limited data transfer rate. To achieve higher data rates, a user must switch to a device with more advanced forms of GSM. - Repeaters. GSM technologies require carriers to install repeaters to increase coverage.
3GPP Release 7: Even Faster HSPA and Continued Packet Connectivity
- One of the shortcomings of UMTS and HSPA is the high power consumption during transmission gaps, for example, between the downloads of two web pages. - Reducing power consumption and achieving a fast return to full active state have been the goals of Release 7 feature package referred to as Continuous Packet Connectivity (CPC) - In addition, 3GPP Release 7 once again increased the maximum possible data‐transfer speeds in the downlink direction with the introduction of: 1. the use of several antennas and Multiple Input Multiple Output (MIMO) transmission schemes; 2. 64‐Quadrature Amplitude Modulation (64‐QAM) The maximum speeds reached with these enhancements under ideal signal conditions are 21 Mbit/s with 64‐QAM modulation and 28 Mbit/s with MIMO.
For user data in the downlink direction _____
- One or more High‐Speed Physical Downlink Shared Channels (HS‐PDSCH) are used. - These can be shared between several users - Hence, it is possible to send data to several subscribers simultaneously or to increase the transmission speed for a single subscriber by bundling several HS‐PDSCH, where each uses a different code.
Cable and Asymmetric Digital Subscriber Line (ADSL) modems made an impact in 2002 -
- Reached the mass market and dramatically increased transmission speeds for end users. - With these technologies, transmission speeds of several megabits per second are easily achieved
3GPP Release 6: High‐Speed Uplink Packet Access (HSUPA)
- Referred to as High‐Speed Uplink Packet Access (HSUPA) in public, which enables uplink datarates of 2-3 Mbit/s for a single user under ideal conditions today. - HSUPA also increases the maximum number of users who can simulta- neously send data via the same cell and thus further reduced the overall cost of the network. - The combination of HSDPA and HSUPA is sometimes also referred to as HSPA
3GPP Release 99: The First UMTS Access Network Implementation
- Release 99 contains all the specifications for the first release of UMTS. - The main improvement of UMTS compared to GSM in this first step was the completely redesigned radio access network, which the UMTS standards refer to as the UMTS Terrestrial Radio Access Network (UTRAN) - Instead of using the time‐ and frequency‐ multiplexing methods of the GSM air interface, a new method called Wideband Code Division Multiple Access (WCDMA) was introduced.
The advantage of packet‐switched connections is that ________
- Resources are shared and used only while they are needed to transfer data. - In Release 99, however, air interface resources were not immediately freed once there was no more data to be transferred
Responsibilities of The Third Generation Partnership Project (3GPP)
- Responsible for evolving the GSM, UMTS, LTE and 5G wireless standards and refers to the different versions as 'Releases'. - Each 3GPP release of the specifications includes many new features for each of the radio access technologies mentioned, some large and some small
The FP is responsible for _______
- Responsible for the correct transmission and reception of user data over the Iub interface and transports user data frames in a format that the Node‐B can directly transform into a Uu (air interface) frame - The FP is also used for synchronization of the user data connection between the RNC and the Node‐B. - This is especially important for data transfer in the downlink direction, as the Node‐B has to send an air interface frame every 10, 20, 40 or 80 milliseconds to the mobile device - FP frames are also used to forward quality estimates from the Node‐B to the RNC. These help the RNC during the soft handover state of a dedicated connection to decide which Node‐B has delivered the best data frame for the connection
The network can decide to release the HSDPA connection after a period of time and put the subscriber into the Cell‐FACH state
- Save Power and the mobile device can still send and receive data, but the bandwidth is very small. - Nevertheless, this is quite acceptable as an HSDPA connection can be reestablished again very quickly, when required.
Explain Hard Handover
- Similar to GSM handover. - By receiving measurement results from the mobile device of the active connection and measurement results of the signal strength of the broadcast channel of the neighboring cells, the RNC is able to recognize if a neighboring cell is more suitable for the connection. - To redirect the call into the new cell, a number of preparatory measures have to be performed in the network before the handover is executed. - Once the new connection is in place, the mobile device receives a command over the current connection to change into the new cell. -The handover command contains, among other parameters, the frequency of the new cell and the new channelization and scrambling code to be used. - The mobile device then suspends the current connection and attempts to establish a connection in the new cell
An initial disadvantage of IP‐based links was
- That the transport protocol used on them, for example, Ethernet, was not synchronous and therefore could not be used by the base stations to synchronize themselves with the rest of the network. - As a consequence, protocol extensions had to be developed to enable recovery of a very precise clock signal from such links before they could be relied on as the only means to connect Node‐Bs to the RNCs.
On the physical layer, the E‐DCH is split into two channels.
- The Enhanced Dedicated Physical Data Channel (E‐DPDCH) is the main transport channel and is used for user data (IP frames carried over RLC/MAC‐frames) and layer 3 RRC signaling between the mobile device on the one side and the RNC on the other. - The Enhanced Dedicated Physical Control Channel (E‐DPCCH) is used for physical layer control information. For each E‐DPDCH frame, a control frame is sent on the E‐DPCCH to the Node‐B, which, most importantly, contains the 7‐bit Traffic Format Combination ID (TFCI).
What's another responsibility of Media Gateway (MGW)
- The MGW is also responsible for the transcoding of the user data for different transmission methods. - This way it is possible, for example, to receive voice calls via the GSM A‐interface via E‐1 64 kbit/s timeslots at the MSC MGW which will then convert the digital voice data stream onto a packet‐switched IP connection toward another MGW in the network
In contrast to the establishment of a channel in GSM...
- The MSC and SGSN do not specify the exact properties of the channel - Instead, the RAB establishment requests contain only a description of the required channel properties.
Explain the Non‐Access Stratum (NAS)
- The NAS contains all functionalities and protocols that are used directly between the mobile device (UE) and the core network. - These have no direct influence on the properties of the established RAB and its maintenance. - Furthermore, NAS protocols are transparent to the access network. - Functionalities like call control, mobility and session manage- ment, as well as supplementary services (e.g. SMS), which are controlled via the MSC and SGSN, are considered NAS functionalities.
During the E‐DCH establishment procedure ___
- The RNC informs the mobile device of the Transport Format Combination Set (TFCS) that can be used for the E‐DCH. - A TFCS is a list (set) of datarate combinations, coding schemes and puncturing patterns for different transport channels that can be mapped on to the physical channel
Explain the RNC
- The Radio Network Controller (RNC) is a governing element in the UMTS radio access network (UTRAN) and is responsible for controlling the Node Bs - All interfaces of the radio network are terminated by the RNC.
How has the speed increased with the 99 Release?
- The bandwidth of a single carrier was significantly increased compared to GSM, enabling a much faster data transfer than was previously possible. - This allowed a Release 99 UTRAN to send data with a speed of up to 384 kbit/s per user in the downlink direction and also up to 384 kbit/s in the uplink direction. - In the first few years, however, uplink speeds were limited to 64-128 kbit/s.
While on the mobile device the MAC‐e/es layers are combined
- The functionality is split on the network side between the Node‐B and the RNC. The lower‐layer MAC‐e functionality is implemented on the Node‐B in the network. - It is responsible for scheduling, which is further described below, and the retransmission (HARQ) of faulty frames.
What remains important is the TPC
- The idea behind the new slot format is to increase the number of bits to encode the TPC and decrease the number of pilot bits while the uplink channel is idle. - This way, additional redundancy is added to the TPC field - As a consequence, the transmission power for the control channel can be lowered without risking corruption of the information contained in the TPC.
To establish a circuit‐switched or packet‐switched connection _____
- The mobile device has to contact the network and request the establishment of a session. - The establishment of the user data bearer is then performed in several phases.
If a Paging message is received that contains the subscriber's International Mobile Subscriber Identity (IMSI) or Temporary Mobile Subscriber Identity (TMSI) ___
- The mobile device reacts and establishes a connection with the network - As the monitoring of the paging channel consumes some power, subscribers are split into a number of groups based on their IMSI (paging group)
If a circuit‐switched connection is established _____
- The mobile device sends a CM Service Request DTAP message over the established signaling connection to the RNC, which transparently forwards the message to the MSC - DTAP messages are exchanged between the RNC and the MSC via the connection oriented Signaling Connection and Control Part (SCCP) protocol
3GPP Release 4: Enhancements for the Circuit‐Switched Core Network
- The most important enhancement of Release 4 was a new concept called the Bearer‐Independent Core Network (BICN). - Instead of using circuit‐switched 64 kbit/s timeslots, traffic is now carried inside Internet Protocol (IP) packets. - For this purpose, the MSC has been split into an MSC‐Server (MSC‐S), which is responsible for Call Control (CC) and Mobility Management (MM), and a Media Gateway (MGW), which is responsible for handling the actual bearer (user traffic)
3GPP Release 5: High‐Speed Downlink Packet Access
- The most important new functionality introduced with 3GPP Release 5 was a new data transmission scheme called High‐Speed Downlink Packet Access (HSDPA) to increase data transmission speeds from the network to the user. - While 384 kbit/s was the maximum speed in Release 99, HSDPA increased speeds per user, under ordinary conditions, to several megabits per second
Explain Soft Handover
- The soft handover procedure has a number of advantages over the hard handover described before. - As no interruption of the user data traffic occurs during the soft handover procedure the overall connection quality increases. - As the soft handover procedure can be initiated while the signal quality of the current cell is still acceptable the possibility of a sudden loss of the connection is reduced.
While a connection is established between the network and a mobile device, several channels are used simultaneously.
- This is because it is not only user data which is being sent but also control information to keep the link established, to control transmit power and so on. - Currently, the Uplink Dedicated Control Channel (UL DPCCH) is transmitted continuously, even during times of inactivity, to remain synchronized. - This way, the mobile device can resume uplink transmissions without delay whenever required.
The core network is not aware of UTRAN registration areas
- This is in contrast to a GSM/ GPRS network, where the MSC and SGSN are aware of the location area and even the cell ID in which the mobile device is located during an active connection. - In UMTS, the location area does not contain single cells but one or more service areas.
A UMTS network has to authenticate itself ____
- To the user to protect against air interface eavesdropping with a false base station. - Once the authentication procedure has been performed, the MSC activates ciphering of the radio channel by issuing a Security Mode command - After successful authentication and activation of the encrypted radio channel, the mobile device then proceeds to inform the MSC of the exact reason for the connection request
To reduce the complexity of the overall solution, the E‐DCH concept introduces ___
- Two new layers called the MAC‐e and MAC‐es. - Both layers are below the existing MAC‐d layer.
As both UMTS and CDMA2000 need to be backward compatible with their respec- tive evolution paths, there are also many differences between them, which include the following:
- UMTS uses a WCDMA carrier with a bandwidth of 5 MHz while CDMA2000 uses a multicarrier approach with bandwidths of multiples of 1.25MHz. This was done to enable use of CDMA2000 in the already available spectrum for IS‐95, while UMTS had no such restriction due to the completely new implementation of the air interface and availability of a dedicated frequency band for the new technology. - UMTS uses unsynchronized base stations, while in CDMA2000 all base stations are synchronized using the Global Positioning System (GPS) clock. - While UMTS has a minimal frame length of 10 milliseconds, CDMA2000 uses 20‐millisecond frames for user data and signaling and 5‐millisecond frames if only signaling has to be sent
What is the The Cell‐DCH RRC state?
- Used similarly to the GSM dedicated mode for circuit‐ switched voice calls. - While in this state, a physical connection is established between the mobile device and the network
Purpose of Scrambling?
- Using OVSF codes, the datarate can be adapted for each user individually while still allowing differentiation of the data streams with different speeds. Some of the OVSF codes are quite uniform - This creates a problem further down the processing chain, as the result of the modulation of long sequences that never change their value would be a very uneven spectral distribution - The use of a unique scrambling code per base station is also necessary to allow a base station to use the complete code tree instead of sharing it with the neighboring cells. - This means that in the downlink direction, capacity is mainly limited by the number of available codes from the code tree as well as the interference of other base stations as experienced by the mobile device.
Is the GSM still relevant?
- While the UMTS radio access network (UTRAN) was a completely new development, many components of the GSM core network were reused, with only a few changes, for the first step of UMTS. - New core and radio network enhancements were then specified in subsequent steps. - Today, this process continues with the LTE and 5G radio access and core network architectures
HSDPA has been designed for ____
- both stationary and mobile users.
Therefore, being in Cell‐DCH state ____
- continuously would drain the battery in a few hours. - the mobile device is in Cell‐FACH state and power consumption is reduced to about 0.8W
The following properties are specified for a RAB:
- service class (conversational, streaming, interactive or background); - maximum speed; - guaranteed speed; - delay; - error probability.
3 different kinds of channels exist
1. Dedicated channels: These channels transfer data for a single user. A dedicated channel is used, for example, for a voice connection, for IP packets between the user and the network or a Location Update message. 2. Common channels: The counterpart to a dedicated channel is a common channel. Data transferred in common channels is destined for all users of a cell. In such a case, each device filters out its packets from the stream broadcast over the common channel and only forwards these to higher layers of the protocol stack. 3. Shared channels: Very similar to common channels are shared channels. These channels are not monitored by all devices but only by those that have been instructed by the network to do so. An example of such a channel is the High‐Speed Downlink Shared Channel (HS‐DSCH)
Depending on the relationship between the old and the new cell, there are several different kinds of cell changes:
1. Intra Node‐B cell change: Old and new cell are controlled by the same Node‐B. This is the simplest version of the operation as data that is still available in the buffer of the Node‐B can simply be sent over the new cell. 2. Inter Node‐B cell change: Old and new cells belong to different Node‐Bs. In this scenario, the RNC has to instruct the new Node‐B to allocate resources for the HSDPA connection. This is done in a similar way to establishing a new connection. User data that is still buffered in the old Node‐B is lost and has to be retransmitted by the RLC layer, which is controlled in the RNC 3. Cell change with Iur interface: If the old and new cells are under the control of different RNCs, the HSDPA connection has to be established over the Iur interface 4. Cell change without Iur interface: If the old and new cells are under the control of different RNCs which are not connected via the Iur interface, an SRNS relocation has to be performed, which also involves core network components (SGSN and possibly also the MSC). 5. Old and new cells use different frequencies (interfrequency cell change): In this scenario additional steps are required in the mobile device to find cells on different frequencies and to synchronize them before data transmission can resume. 6. Inter‐RAT cell change: If the subscriber leaves the UMTS coverage area completely, a cell change procedure from UMTS/HSDPA to GSM has also been specified. Similar to the interfrequency cell change described above, HSDPA connections can use a compressed mode similar to that of dedicated channels to allow the mobile device to search for cells on other frequencies.
The MSC knows the following MM (Mobility Management) states:
1. MM detached: The mobile device is switched off and the current location of the subscriber is unknown. Incoming calls for the subscriber cannot be forwarded to the subscriber and are either rejected or forwarded to another destination if the Call Forward Unreachable (CFU) supplementary service is activated 2. MM idle: The mobile device is powered on and has successfully attached to the MSC. The subscriber can at any time start an outgoing call. For incoming calls, the mobile device is paged in its current location area. 3. MM connected: The mobile device and MSC have an active signaling and communication connection. Furthermore, the connection is used for a voice or a video call. From the point of view of the RNC, the subscriber is in the Cell‐DCH RRC state as this is the only bearer that supports circuit‐switched connections.
The SGSN(Serving GPRS support nod) implements the following PMM states:
1. PMM detached: The mobile device is switched off and the location of the subscriber is unknown to the SGSN. Furthermore, the mobile device cannot have an active PDP context, that is, no IP address is currently assigned to the subscriber. 2. PMM connected: The mobile device and the SGSN have an active signaling and communication connection. The PMM connected state is only maintained while the subscriber has an active PDP context, which effectively means that the GGSN has assigned an IP address for the connection. In this state, the SGSN simply forwards all incoming data packets to the S‐RNC. In contrast to GSM/GPRS, the UMTS SGSN is aware only of the S‐RNC of the subscriber and not of the current cell 3. PMM idle: In this state, the mobile device is attached to the network but no logical signaling connection is established with the SGSN. This can be the case, for example, if no PDP context is active for the subscriber. If a PDP context is established, the RNC has the possibility to modify the RRC state of a connection at any time. This means that the RNC can decide
CPC is a package of features to improve the handling of mobile subscribers while they have a packet connection established, that is, while they have an IP address assigned. Taken together, the features have the following benefits:
1. Reduction of power consumption 2. Reduction of the number of state changes 3. Minimization of delays between state changes 4. Reduction of signaling overhead 5. An increase in the number of mobile devices per cell that can be served simultaneously
Logical Channels:
1. The Broadcast Control Channel (BCCH): This channel is monitored by all mobile devices in idle state to receive general system information from the network 2. The Paging Control Channel (PCCH): This channel is used to inform users of incoming calls or SMS messages. Paging messages are also used for packet‐switched calls if new data arrives from the network once all physical resources (channels) for a subscriber have been released owing to a long period of inactivity. 3. The Common Control Channel (CCCH): This channel is used for all messages from and to individual mobile devices (bidirectional) that want to establish a new connection with the network. This is necessary, for example, if a user wants to make a phone call, send an SMS or establish a channel for packet‐switched data transmission. 4. The Dedicated Control Channel (DCCH). While the three channels described above are common channels observed by many mobile devices in the cell, a DCCH only transports data for a single subscriber. 5. The Dedicated Traffic Channel (DTCH). This channel is used for user data transfer between the network and a single user. User data can, for example, be a digitized voice signal or IP packets of a packet‐switched connection. 6. The Common Traffic Channel (CTCH): This channel is used for cell broadcast information that can be shown on the display of mobile devices.
GSM Security weakness
1. The GSM circuit‐switched part does not protect the link between the base station and the BSC. In many cases microwave links are used, which are vulnerable to third party monitoring 2. GSM allows man‐in‐the‐middle attacks with equipment that masquerades as a GSM base station. 3. The CK length used in GSM is 64 bits. Although secure when GSM was first developed in the early 1990s, the length is considered insufficient today.
Top speeds are highly dependent on a number of conditions:
1. The maximum throughput capability of the mobile device. 2. The sophistication of the receiver and antenna of the mobile device. 3. The capability of the network. 4. The radio conditions at the place of use. This includes the signal level received from a base station and the interference of neighbor cell transmissions on the same frequency. 5. The bandwidth of the back haul link between the base station and the rest of the network. 6. The number of other users in the cell actively exchanging data at the same time.
The control channel carries four parameters:
1. Transmit power control (TPC). 2. Pilot (used for channel estimation of the receiver). 3. TFCI 4. Feedback indicator (FBI).
In practice, many factors influence how fast data can be sent to a mobile device. The following list summarizes, once again, the main factors:
1. signal quality 2. number of active HSDPA users in a cell 3. number of established channels for voice and video telephony in the cell 4. number of users that use a dedicated channel for data transmission in a cell 5. mobile device category 6. antenna and transceiver design in the mobile device 7. sophistication of interference cancellation algorithms in the mobile device 8. bandwidth of the connection of the Node‐B to the RNC 9. interference generated by neighboring cells 10. achievable throughput in other parts of the network, as high datarates cannot be sustained by all web servers or other end points.
Typical mobile device batteries have a capacity of around ___
10 watt hours
3GPP was heavily influenced at the start by existing ....
2G TDMA-based GSM standards.
UMTS uplink speeds were not enhanced until ____
3GPP Release 6.
Transmission speeds that can be reached with HSDPA also have an impact on other parts of the mobile device.
Apart from the increased processing power required in the mobile device, the interface to an external device, such as a notebook, needs to be capable of handling data at these speeds
While UMTS is the dominant 3G technology in Europe, it shares the market with a similar system called ____
CDMA2000
The UTRAN is then responsible for ...
Establishing a RAB that fits the description.
HSUPA introduces a new transport channel called the ___
E‐DCH
HSUPA has a number of benefits as well
For HSDPA, an uplink DCH is required for all mobile devices that receive data via the HS‐DSCHs for TCP acknowledgements and other user data
It is necessary to maintain the connection while the user is moving from cell to cell
For this reason, the mobile device keeps a so‐called Active Set for the DCH of the HSDPA connection, which is required for the soft handover mechanism
What is HSUP
HSUPA increases theoretical uplink user datarates to up to 5.76 Mbit/s in 3GPP Release 6 and 11.5 Mbit/s in 3GPP Release 7.
What happens during an Idle State?
In this state, a mobile device is attached to the network but does not have a physical or logical connection with the radio network. This means that the user is involved neither in a voice call nor in a data transfer
If the network detects that the mobile device is HSDPA‐capable during the establishment of an RRC connection ____
It automatically allocates the necessary resources during the setup of the connection The S‐RNC informs the Node‐B that a new connection is required and the Node‐B will configure the HS‐PDSCH accordingly.
Explain The Universal Mobile Telecommunications System (UMTS)
It's a third‐generation wireless telecommunication system and followed in the footsteps of the Global System for Mobile Communications (GSM) and General Packet Radio Service (GPR
The RNC is connected to the core network via the _______
Iu interface
While network vendors can choose which of the options described below they want to implement, support for all options is required in the mobile device:
Reduction of the spreading factor: For this option, the spreading factor is reduced for some frames. Thus, more data can be transmitted during these periods, which increases the speed of the connection. This allows the insertion of short transmission gaps for interfrequency measurement purposes without reducing the overall speed of the connection. Puncturing: After the channel coder has added error correction and error detection bits to the original data stream, some of them are removed again to allow time for interfrequency measurements. To keep the error rate of the radio bearer within acceptable limits, the transmission power has to be increased. Reduction of the number of user data bits per frame: As fewer bits are sent per frame, the transmission power does not have to be increased. The disadvantage is the reduced user datarate while operating in compressed mode.
A handover is controlled by _______
The RNC and triggered based on measurement values of the quality of the uplink signal measured by the base station and measurement reports on downlink quality sent by the mobile device
Protocols: Circuit‐switched data (e.g. voice calls)
The Transcoding and Rate Adaptation Unit (TRAU) converts the pulse code modulated (PCM)‐coded voice data, which it receives from the MSC, via optimized codecs like enhanced full‐rate (EFR), half‐rate (HR) or Adaptive Multirate (AMR)
From the user's point of view ______
The activation of a PDP context means getting an IP address to be able to communicate with the Internet or another IP network
UMTS has evolved to higher datarates with HSDPA
The corresponding upgrade path of CDMA2000 is referred to as 1xEV‐DO (Evolution‐Data Only) Revision 0 and uses one or more 1.25MHz carriers exclusively for high‐speed packet data transmission.
Intersystem Handover.
The first intersystem handover method is the blind intersystem handover. - In this scenario, the RNC is aware of GSM neighboring cells for certain UMTS cells. In the event of severe signal quality degradation, the RNC reports to the MSC or SGSN that a handover into a 2G cell is necessary. - The procedure is called a 'blind handover' because no measurement reports of the GSM cell are available for the handover decision.
For the E‐DCH concept a number of additional channels were introduced in both uplink and downlink directions
These are used in addition to existing channels
Protocols: Signaling data (circuit‐switched signaling as well as some GPRS channel request messaging and paging)
This data is transferred via the Link Access Protocol (LAPD) protocol, which is already known from the Integrated Services Digital Network (ISDN) world and which has been extended for GSM.
Size and capacity of a Node‐B are variable
True
Explain the 3rd Generation Partnership Project 2 (3GPP2)
U.S.A which intended to develop global specifications for 3G systems based on the evolution of the 2G IS-95 CDMA standards.
How was UMTS an improvement from earlier systems?
UMTS combines the properties of the circuit‐switched voice network with the properties of the packet‐ switched data network, and offers a multitude of new possibilities compared to the earlier systems.
User data is exchanged between ________
User data is exchanged between the RNC and Node‐Bs via the Frame Protocol (FP), which has been standardized for dedicated channels in 3GPP
Benefits of Wideband Code Division Multiple Access (WCDMA)
Users are no longer separated from each other by timeslots and frequencies but are assigned a unique code.
3GPP Releases 10 and Beyond
While 3GPP Release 10 and beyond have continued to bring in new features for UMTS, the vast majority of network operators stopped evolving their UMTS networks after implementing dual‐cell downlink in one frequency band as per 3GPP Release 8.
Protocols: Packet‐switched user and signaling data for GPRS
While user and signaling data are separated in GSM, GPRS combines the two data streams into a single lower‐layer protocol called Release Complete RLC/MAC.
UMTS networks today no longer use DCHs for high‐speed packet transfer
With 3GPP Release 5, HSDPA was introduced to allow more flexibility for bursty data transmissions and to deliver much higher datarates per cell and per user than before
Starting with 3GPP Release 7
a number of enhancements were specified in that direction - CPC and One Tunnel.
The base station, called Node‐B in the 3GPP standards, is responsible for ______
all functions required for sending and receiving data over the air interface. Also responsible for the power control of all connections
To establish an HSDPA connection ____
an additional DCH is required to be able to send data in the uplink direction as well
E‐DCH concept is ___
an evolution of existing standards, it has triggered the creation of a number of new documents as well as the update of a number of existing specifications.
When the Internet first became popular..
circuit‐switched modems were used to establish a dial‐up connection to the network.
Automated Emergency Calls (eCall) from Vehicles
eCall is a functionality required by the European Union to be built into new cars from April 2018
The establishment of a packet‐switched connection is referred to
in the standards as PDP context activation.
The activity of a subscriber determines ________
in which way data is transferred over the air interface between the mobile device and the network
Another application of AMR is to ______
increase the number of simultaneous calls in a cell during cell congestion
One of the reasons for enhancing the dedicated connection principle to _____
increase uplink speeds instead of using a shared‐channel approach is that it enables the soft handover principle to be used in the uplink direction
The advantage of using Wi‐Fi for connectivity ___
is that no special configuration beyond the Wi‐Fi password is required in client devices.
As the mobile device is at a different distance from each base station ____
it communicates with simultaneously, it is not possible to synchronize the mobile device to all base stations because of the different signal propagation delays
While the mobile device is in HSDPA reception mode
it has to constantly monitor all assigned HS‐SCCH channels and also maintain the necessary DCHs. This of course results in higher power consumption
When the Node‐B receives data for a user ___
it is then the task of the HSDPA scheduler in the Node‐B to allocate resources on the air interface and to inform the user's mobile device via the shared control channels whenever it sends data on one or more HS‐PDSCHs
If the spreading factor of the connection is not changed _______
more bits of the bearer can then be used to add additional redundancy
If a subscriber did not send or receive data for some time ___
only control information was sent over the established channel.
The Cell‐DCH state is also used for ______
packet‐switched connections
uplink bandwidth is continually increasing for ___
peer‐to‐peer applications like multimedia calls, video conferencing and social networking applications, e‐mail with large file attachments or large MMS messages
What is EDGE?
provides execution resources (compute and storage) for applications with networking close to the end users, typically within or at the boundary of operator networks.
The MAC‐es layer in the RNC on the other hand is responsible for ____
recombining frames received from different Node‐Bs in case an E‐DCH connection is in soft handover state. Furthermore, the RNC is also responsible for setting up the E‐DCH connection with the mobile device at the beginning
The solution towards satisfying the increasing demand in the uplink direction is
referred to as Enhanced Uplink (EUL) in 3GPP and is also known as HSUP
To reach the highest possible datarate during favorable transmission conditions ___
several new modulation schemes have been introduced with HSDPA over several 3GPP releases
For the exchange of control and configuration messages on the Iub interface ___
the Node‐B Application Part (NBAP) is used between the RNC and the Node‐B. Following tasks: - cell configuration - common channel management; - dedicated channel management such as the establishment of a new connection to a subscriber - forwarding of signal and interference measurement values of common and dedicated channels to the RNC;
To be able to respond to incoming voice calls, short messages _____
the PCH is monitored
Purpose of UTRAN
the UTRAN allows connectivity between the UE (user equipment) and the core network.
While it might be strange from today's point of view to send data inside a speech channel ______
the advantage is that no additional equipment is required in the circuit‐switched mobile and fixed networks between the car and the emergency response center.
If no scrambling code was used?
the chips of the different senders would be out of phase with each other and the result of the equation would change
With AMR _________
the codec is no longer negotiated only at the establishment of a voice call; the system can change the codec every 20 milliseconds - This functionality is quite useful in adapting to a number of changes that can occur during the lifetime of a call
Once the call is established _____
the data is sent inside the speech channel (in‐band).
In addition to setting up a speech call between the inside of the vehicle and a person at an emergency response center, referred to in the specification as the Public Safety Answering Point (PSAP)
the eCall device can also send up to 140 bytes of information such as location, travel direction, vehicle identification, etc. to the emergency center
What is the Iu interface
the interface which links the RNC (Radio Network Controller) with either a 3G MSC (3G Mobile Switching Centre) or a 3G SGSN (3G Serving GPRS Support Node).
While in the Cell‐DCH state ______
the mobile continuously measures the reception quality of the current and neighboring cells and reports the results to the network
Once the signaling connection has been established successfully ____
the mobile device continues the process by sending an Activate PDP Context request message via the RNC to the SGSN
While in idle state _____
the mobile device is passive, that is, no data is sent or received.
In contrast to a pure dedicated connection ___
the mobile device only receives its data over one of the Node‐Bs of the Active Set
If the reception quality deteriorates during a call _____
the network can decide to use a voice codec with a lower bit rate
In a further evolution of the standards, referred to as Revision A __
uplink performance is improved to a level similar to UMTS HSUPA.
For UMTS, it was decided to use the Adaptive Multirate (AMR) codec for ___
voice encoding, which was previously introduced in GSM.
To further increase the single‐user peak datarate, dual‐carrier HSDPA (also referred to as dual‐cell HSDPA) ____
was specified to bundle two adjacent 5MHz carriers.
To set up the emergency call between the car ____
which the specification refers to as the In‐Vehicle System (IVS), and the PSAP, the standard GSM/UMTS emergency voice call setup procedure is used To set up the emergency call between the car,
