> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/telecom-references/protocols/mtp2-architecture.md).

# MTP2 Architecture

[MTP Level 2](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/mtp2/README.md) defines the functions and procedures of the signaling system for providing reliable transfer of signaling messages over a signaling link. The MTP2 layer is a service provider to the MTP3 Link layer. The MTP2 layer is a service user of line interfaces / line services as seen in the shown in the figure below.

![MTP2 architecture](https://docs.telcobridges.com/w/images/9/99/MTP2-architecture.jpg)

MTP2 is used in conjunction with an above local MTP3 layer.

![MTP2 layer hierarchy](https://docs.telcobridges.com/w/images/3/35/MTP2-layer-hierarchy.jpg)

A MTP2 Link must be associated with one line interface/service. It’s a 1-to-1 association. MTP Level 2 defines the functions and procedures of the signaling system for providing reliable transfer of signaling messages over a signaling link.

**IMPORTANT NOTE:** It is important to ensure that the received and transmitted clocks of the line interface/service were synchronized. This can be useful for removing/limiting undesirable FIB and BSN errors. (See section “Clock Configurations” in the TB640 user’s guide.)

### Priorities

No pre-emption of data occurs in the process of being transmitted or requiring retransmission. Only a single congestion priority is supported for ANSI and ITU. For a TTC/NTT link, transmitted data buffers are prioritized based on the priority indicated by [MTP Level 3](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/mtp3/README.md).

### Flow control

The MTP Level 2 software regulates data flow when resource utilization (such as buffer pool size or queue length) reaches specifies thresholds. For each threshold, MTP Level 2 performs one of the following actions:

* Informs the layer manager about flow control.
* Sends a link status signal unit with status "B" (busy).
* Sends a flow control indication to the upper layer.

The MTP Level 2 software prevents deadlocks and overload conditions from occurring.


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