Monthly Archives: November 2010

3GPP Message Decoder

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3GPP message decoder is a very simple but powerful tool to decode GSM, UMTS, LTE, IP messages. This is developed by protocolanalyze. 3GPP decoder is a simple application using Wireshark to decode messages.

3GPP Message Decoder has a very simple interface.

Message Decoder extended

The user interface has the following sections:

  • Enter the HEX message to decode in the top text area.
  • You can choose between GSM, WCDMA, LTE or IP Protocol.
  • Use the dropdown to select between different message types to select.
  • The decode button.
  • Decoded message window

Mesage Type to Select

Message Type Supported

3GPP Message Decoder supports the following message types.

GSM

  • GAN TCP
  • GAN UDP
  • GSM CCCH
  • GSM SACCH
  • LLC
  • NAS
  • SNDCP
  • SNDCPXID

UMTS

  • NAS
  • RRC BCCH.BCH
  • RRC BCCH.FACH
  • RRC DL.CCCH
  • RRC DL.DCCH
  • RRC DL.SHCCH
  • RRC MCCH
  • RRC MSCH
  • RRC PCCH
  • RRC UL.CCCH
  • RRC UL.DCCH
  • RRC UL.SHCCH
  • RRC SIs (SIBs and MIB)

LTE

  • RRC BCCH.BCH
  • RRC BCCH.DL.SCH
  • RRC DL.CCCH
  • RRC DL.DCCH
  • RRC PCCH
  • RRC UL.CCCH
  • RRC UL.DCCH
  • NAS EPS

IP Protocols

  • ICMP
  • IP
  • RTSP
  • RTP
  • UDP

Decoding Message

After entering a correct hex string and choosing the appropriate option press the decode button to decode the message. You can copy (Ctrl A and Ctrl C) and paste (Ctrl V) the output result from the output window to a notepad or word processor.
decoded

Download 3GPP Message Decoder

Download 3GPP Message Decoder from the following link:

Download 3GPP Decoder

Basics of data transmission in a UMTS system

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In a UMTS system, the maximum supported downlink data rate is 2.048 Mbps. With other technologies such as HSPA, LTE, higher data rates are possible, but we look at data rates for UMTS only systems.

Each application has a certain Quality of service (QOS) requirement. A user who wishes to run a application that demands high data rate informs the network of his throughput requirement in Quality Of Service (QOS) attributes during PDP context activation. It is from this message that the network becomes aware of the user’s data rate requirement.

Apart from data rate, other parameters like application’s error resilience, time sensitivity etc is negotiated.

If the network could fulfill the requirement, it informs the user by accepting and activating the PDP context and sets up a Radio Access Bearer (RAB). Network provides channel details that UE has to use in order to send and receive data in a RAB setup Message.

RAB message also provides parameters like transport block (TB) size and number of Transport blocks per Transmission Time Interval (TTI). Figure A shows the message exchange between Mobile and Network.

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Fig A. Message exchange between Network and Mobile during and after PDP context activation

The payload is segmented into several TB’s and are sent over the air interface.

As an example, let’s look at the configuration for a user downloading a file at the rate of 2.048 Mbps.

  • TB size = 1720 bits
  • Number of TBs per TTI = 12
  • TTI = 10 ms
  • RLC header (Doesn’t contain user data) = 16 bits
  • Payload size = 1704
  • 12 TBs of size 1704 bits are transmitted every 10 milliseconds.

So, the data rate is 1704 * 12 * 100 = 2048 kbps.

Fig. B shows how user data is contained in 10 ms TTI and transmitted.

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Fig B data blocks contained in 10ms TTI

However, Apart from user data, network is also required to send signaling data. Each TB also carries CRC bits and RLC header (discussed above) which add up further to the total data transmitted.