telecom • networking • design

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Tracking Area Updates in an LTE Network

LTE Tracking Area Update signaling flow describes how mobiles keep the network updated about their location.

A Tracking Area Update takes place if:

  • UE detects it has entered a new Tracking Area that is not in the list of TAIs that the UE registered with the network;
  • the periodic Tracking Area update timer has expired;
  • UE was in UTRAN PMM_Connected state (e.g. URA_PCH) when it reselects to E UTRAN;
  • UE was in GPRS READY state when it reselects to E UTRAN;
  • the TIN indicates “P-TMSI” when the UE reselects to E-UTRAN (e.g. due to bearer configuration modifications performed on
    GERAN/UTRAN);
  • the RRC connection was released with release cause “load re-balancing TAU required”;
  • a change of the UE Core Network Capability and/or UE Specific DRX Parameters information of the UE.

Tracking area update in LTE


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Generate sequence diagrams from PCAP files that carry tunneled GTP traffic

VisualEther 6.1.103 now supports generating sequence diagrams from tunneled messages in PCAP files. You can create filters that will ignore the outer GTP message and extract the fields from the inner message.
Capture inner and outer messages is GTP


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SIP call setup with authentication

This call flow shows the SIP call setup between a SIP client (192.168.0.10) and a SIP server (216.234.64.8). The flow also shows the RTP message flow between the SIP client and the Media Gateway (216.234.64.16).
The example covers the following:

  1. SIP invite from the client.
  2. The SIP server challenges the client to authenticate.
  3. The client responds to the authentication challenge.
  4. The call is connected.
  5. The call enters the conversation phase with RTP traffic.
  6. The SIP call is cleared.

SIP call flow with authentication


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More Object Oriented Design Tips

We have already covered object oriented design tips in a previous article. Here we will look at more tips that will help you improve your object oriented design skills:

  1. Class with just get-set methods points to missed delegation
  2. Replace an array of structures with an array of objects
  3. Delegate work to helper class
  4. Multi-dimensional arrays point to incomplete class identification
  5. Multiple nested loops point to incomplete delegation
  6. Class with very large numbers of methods points to incomplete class identification
  7. Don’t go overboard with inheritance
  8. Prefer delegation to inheritance
  9. Don’t scatter the abstraction
  10. Consider group of objects to split work amongst team members
  11. Use nested classes for lightweight helper classes
  12. Use templates to improve type safety and performance
  13. Divide your code into framework and application parts


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Object Oriented Design Tips

Here are a few object oriented design tips to help you with class design:

  1. Stay close to problem domain
  2. Object discovery vs. object invention
  3. Pick nouns or noun phrases as classes
  4. Method names should contain a verb
  5. Prefix adjectives when naming inheriting classes
  6. Do not add suffixes to class names
  7. Avoid one-to-one mapping from structured design
  8. Replace multiple get-set methods with operations
  9. Model classes that handle messages as state machines
  10. Use const whenever possible
  11. Restrict header file level dependency
  12. Don’t reinvent the wheel; use STL

Manager design pattern


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LTE Physical Layer Introductory Videos

Learn about the LTE physical layer from the video series from IEEE and Ericsson. Th video series covers:

  1. LTE protocol structure and architecture
  2. Downlink frame structure, reference signal and MIMO
  3. Downlink control signaling
  4. Uplink SC-FDMA, reference signals and control signaling
  5. TDD and half duplex FDD
  6. Transmission procedures
  7. Cell search, SI and random access procedures

LTE multi antenna transmission


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LTE Random Access Procedure and Contention Resolution

LTE random access procedure is used by the UEs to initiate a data transfer. The UEs also obtain uplink timing information from the initial handshake.

This sequence diagram describes the tale of three UEs (UE-A, UE-B and UE-C) that are powered on at the same time:

  1. UEs synchronize with the downlink channel by decoding the PSS and SSS signal. The UEs are synchronized to the downlink frames after completing this procedure.
  2. The three UEs initiate the random access procedure at exactly the same time. Two of them (UE-A and UE-B) happen to pick the same preamble. This results in a resulting in a collision. UE-C picks a distinct preamble so it succeeds in the random access procedure.
  3. Contention between UE-A and UE-B is resolved in UE-A’S favor. UE-A proceeds with the RRC connection.
  4. UE-C times out and retries the random access procedure.

LTE random access procedure

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