telecom • networking • design

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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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HTTPS SSL/TLS Session for SPDY Sequence Diagram

This sequence diagram covers the establishment of a SSL/TLS connection for sending Google SPDY data. The protocol flow covers:

  1. SSL/TLS initial cryptographic parameter negotiation.
  2. X.509 Certificate exchange and encryption start with elliptic curve Diffie Hellman key exchange.
  3. Master key generation and encrypted data transfer.
  4. SSL/TLS session release.
    SSL TLS Sequence Diagram for SPDY


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S1AP View of LTE Attach and EPS Bearer Setup

This sequence diagram looks at LTE Attach and EPS Bearer Setup from the S1AP vantage point. The following signaling is covered:

  1. UE Attach, authentication and security signaling
  2. Setup of two EPS Bearers (RAB id 5 and 6)
  3. Release of UE context due to inactivity
  4. Reestablishment of the UE context with a Service Request.

You can click on individual messages in the sequence diagram to see field level details.

Click to see the "S1AP View of LTE Attach & EPS Bearer Setup"  sequence diagram

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