What is TFO Tandem Free Operation

TFO: Unveiling the Secrets of Tandem Free Operation

In the world of mobile telephony, particularly within the realm of GSM (Global System for Mobile Communications) and related technologies, TFO stands for Tandem Free Operation. It's a mechanism that aims to improve voice call quality by reducing the number of times speech is encoded and decoded during a mobile-to-mobile call.

Understanding the Problem:

• Traditional mobile network architectures involve several stages for connecting two mobile users for a voice call. The call typically traverses:
  • The mobile station (MS) of the calling user.
  • The Base Transceiver Station (BTS) serving the calling user.
  • The Mobile Switching Center (MSC), which acts as the core network element for call routing.
  • The BTS serving the called user.
  • The mobile station (MS) of the called user.

The Issue of Double Encoding/Decoding:

• Within these stages, the speech signal undergoes multiple encoding and decoding processes.
  • At the MS, the analog voice signal is converted into a digital format using a specific codec (coder-decoder) like AMR (Adaptive Multi-Rate) in GSM.
  • Each network element (BTS and MSC) might further transcode the speech signal to a different format for efficient transmission on its internal links.
• This repeated encoding and decoding can introduce some degradation in voice quality, affecting factors like clarity and naturalness of the conversation.

TFO: Optimizing for Better Voice Quality:

• TFO aims to bypass this issue by enabling direct transmission of the encoded speech signal between the two mobile stations involved in the call. This eliminates the need for transcoding within the network core (MSC).

How Does TFO Work?

• To achieve TFO, several conditions need to be met:
  • Compatible Codecs: Both mobile stations involved in the call must support the same speech codec (e.g., both using AMR in GSM).
  • Network Support: The network infrastructure (BTS and MSC) must be equipped to handle TFO and facilitate the direct connection between the mobile stations.
• When these conditions are met, the network establishes a dedicated path for the encoded speech signal to travel directly between the two mobile stations, bypassing the core network transcoding stage.

Benefits of TFO:

• Improved Voice Quality: By eliminating unnecessary encoding and decoding steps, TFO can lead to a noticeable improvement in voice call quality. This translates to clearer and more natural-sounding conversations for mobile users.
• Reduced Network Load: Bypassing transcoding in the core network can reduce processing overhead and improve network efficiency.

Limitations of TFO:

• TFO is not always feasible. As mentioned earlier, it requires compatible codecs and network support.
• Additionally, security considerations might limit TFO usage in certain scenarios.

Conclusion:

TFO is a valuable technique for enhancing voice call quality in mobile networks. By enabling direct transmission of encoded speech between mobile stations, it helps to minimize the impact of multiple encoding and decoding stages. Understanding TFO is crucial for appreciating the efforts taken by cellular network providers to improve call quality and user experience.