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SIP-I vs. SIP-T: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 16, 2024
SIP-I (Session Initiation Protocol with encapsulated ISUP) encapsulates ISUP messages for VoIP. SIP-T (SIP for Telephones) transports PSTN/ISDN information using SIP.

Key Differences

SIP-I, or Session Initiation Protocol with encapsulated ISUP, is a protocol used to integrate traditional telephony signaling with VoIP networks by encapsulating ISUP messages. SIP-T, or SIP for Telephones, similarly bridges traditional telephony and VoIP, but focuses on transporting PSTN and ISDN information using SIP.
SIP-I facilitates seamless communication between VoIP and traditional telephony systems, preserving the ISUP part of the signaling. SIP-T, while also ensuring compatibility between different systems, primarily deals with the transport of PSTN and ISDN signaling over IP networks.
In SIP-I, the ISUP messages are encapsulated within the SIP messages, which allows for a more direct translation of traditional telephony signals. SIP-T extends the SIP capabilities to include telephone-specific functionalities like caller ID, thus offering a broader scope of telephony features over IP.
SIP-I is typically used in scenarios where there is a need for detailed signaling information to be transferred between IP and traditional telephony networks. SIP-T is often preferred in environments where the integration of telephony features with IP technology is a priority.

Comparison Chart

Primary Function

Encapsulates ISUP messages in VoIP
Transports PSTN/ISDN information using SIP

Integration Focus

Between VoIP and traditional telephony signaling
PSTN and ISDN signaling over IP networks

Signal Translation

Direct translation of traditional telephony signals
Extends SIP for telephone-specific functionalities

Usage Scenarios

Detailed signaling transfer between IP and telephony networks
Integration of telephony features with IP technology

Technical Approach

Encapsulation of ISUP within SIP messages
Extension of SIP capabilities to include PSTN/ISDN features

SIP-I and SIP-T Definitions


A method to preserve traditional telephony signals within a VoIP environment.
SIP-I's ability to encapsulate ISUP messages simplified our network upgrade.


A protocol bridging the gap between traditional telephony and VoIP technology.
Implementing SIP-T was a key step in modernizing our telecommunications infrastructure.


Enhances VoIP with detailed telephony signaling via ISUP encapsulation.
Using SIP-I allowed for more detailed call control and management in our network.


Enhances IP communication with broader telephony features from PSTN and ISDN.
SIP-T's integration capabilities allowed for a smoother transition to a fully IP-based communication system.


A protocol integrating VoIP with traditional telephony by encapsulating ISUP messages.
The company implemented SIP-I to improve their VoIP system's compatibility with older telephony infrastructure.


Transports PSTN and ISDN signaling information over IP networks using SIP.
SIP-T enabled us to integrate our existing telephony systems with the new IP-based platform.


Facilitates seamless communication between IP and traditional telephony networks.
SIP-I was crucial in our transition to VoIP without losing legacy system functionalities.


Extends SIP to include telephone-specific functionalities for VoIP systems.
With SIP-T, we could maintain essential telephony features like caller ID on our VoIP network.


What is SIP-T?

A protocol that transports PSTN and ISDN signaling over IP networks using SIP.

What is SIP-I?

A protocol that integrates VoIP and traditional telephony by encapsulating ISUP messages.

How does SIP-I work?

It encapsulates traditional ISUP telephony signals within SIP messages for VoIP networks.

Is SIP-I compatible with older telephony systems?

Yes, it's designed to integrate VoIP with traditional telephony systems.

What are the benefits of using SIP-T?

It allows for the integration of telephony features with IP technology.

Does SIP-T support advanced telephony features?

Yes, it supports a range of PSTN and ISDN features in VoIP.

How does SIP-T enhance VoIP systems?

By extending SIP to include telephone-specific functionalities like caller ID.

Can SIP-I be used with modern VoIP technology?

Yes, it's often used to enhance VoIP systems with legacy telephony features.

What makes SIP-I unique in VoIP integration?

Its ability to encapsulate ISUP messages within SIP.

Can SIP-I improve call management?

Yes, it enhances call control and management in VoIP systems.

Is SIP-I suitable for all VoIP networks?

It's best suited for networks needing detailed signaling information.

How does SIP-T improve communication networks?

By enabling seamless integration of IP and traditional telephony systems.

Can SIP-T be used in any IP network?

Yes, it's versatile but best in networks integrating telephony features.

Does SIP-I affect network speed?

It shouldn't if properly configured in a well-designed network.

Is SIP-I secure?

With proper security measures, it can be secure.

Can SIP-I be combined with other VoIP protocols?

Yes, it's often used in conjunction with other VoIP standards.

Is SIP-T difficult to implement?

It requires technical expertise but is manageable with proper planning.

Can SIP-T handle high call volumes?

Yes, it's capable of managing high call volumes efficiently.

How does SIP-T compare to other VoIP protocols?

It's more focused on integrating traditional telephony features.

Is SIP-T a future-proof solution?

It helps bridge current and future telecommunication technologies.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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