Describe the architecture of a 3G network. What are the various services associated with a 3G network?
The 3G system consists of two main parts: the User Equipment (UE) and the UMTS
Terrestrial Radio Access Network (UTRAN). The UE is the mobile phone and the UTRAN is
the base station and the network intelligence. Both the UE and the UTRAN are composed of
different layers. The four lowest layers are: the physical layer (PHY), the Medium Access
Layer (MAC), the Radio Link Layer (RLC) and the Radio Resource Layer (RRC).
The RRC layer is the highest layer in the protocol stack and it handles most of the decisions
and supervisory functions. Below follows a sample of the functions:
• Broadcast of information.
• Establishment, maintenance and release of an RRC connection between the UE and
UTRAN.
• Establishment, reconfiguration and release of Radio Bearers.
• Assignment, reconfiguration and release of radio resources for the RRC connection.
• RRC connection mobility functions.
• Control of requested Quality of Service.
• UE measurement reporting and control of the reporting.
• Outer loop power control.
• Control of ciphering.
• Paging
• Initial cell selection and cell re-selection.
• RRC message integrity protection.
The RRC layer dynamically establishes and releases logical communication channels
(Transport Entities), which is used by the various services in the UMTS network. It controls
the parameters available, for example: bit rate, level of retransmission and coding scheme. It
can give commands to each of the other layer through separate communication channels.
The RLC layer is the layer below the RRC in the protocol stack and it is focused on the actual
data transfers. Below follows a sample of the functions:
• Segmentation and reassembly.
• Padding.
• Error correction.
• In-sequence delivery of upper layer Packet Data Units (PDU:s).
• Duplicate detection.
• Flow control.
• Sequence number check.
• Protocol error detection and recovery.
• Ciphering.
The RLC is responsible for retransmission, segmentation and reassembly. This layer contains
the transport entities, which are created and deleted dynamically in pairs as services are
established or released. One transport entity handles the incoming traffic and the other
handles the outgoing traffic.
The MAC layer handles the timing of the packet releases and the adding of transport entity
addresses on the outgoing traffic. The received traffic is sent to the corresponding transport
entity via the MAC layer, which reads the address and removes it.
The physical layer takes care of coding, interleaving and the adding of CRC to the packets.
Some of the features of the physical layers are:
• Error detection on transport channels and indication to higher layers.
• Encoding/decoding of transport channels.
• Modulation and spreading/demodulation and dispreading of physical channels.
• Frequency and time (chip, bit, slot, frame) synchronisation.
• Radio characteristics measurements and indication to higher layers.
• Inner - loop power control.
• Radio frequency processing.
The Physical layer administrates all radio communication. It handles power control,
modulation and measurements.
The UMTS protocol stack is an enormous project with specifications involving thousands of
pages. Therefore the stack used in this project is a much smaller version with a limited
amount of features. However, even it is reduced with the ambition to be true to the original
standard, the system is more likely to give a picture of the principle behind the standard than
an accurate description of it.
3G services:
1)wireless voice telephony
2)mobile Internet access
3)Internet access
4)video calls
5)mobile TV
Write short note on Call setup of GSM network for mobile-to-mobile call.
Difference between Statement coverage and Branch coverage.
Discuss the different stages of ‘Capability Maturity Model’.
