Overview of T1-F Interfaces
If T1 access does not require multiple channel sets or ISDN PRI, using a CT1/PRI interface is a waste of resources. In this scenario, you can use a T1-F interface to provide the T1 access service. Compared with a CT1/PRI interface, a T1-F interface provides T1 access at a low cost.
A T1-F interface works only in framed mode. In this mode, a T1-F interface is divided into 24 timeslots, which are numbered 1 to 24. All the 24 timeslots can be bundled into a channel set. The rate of a T1-F interface is n x 64 kbit/s or n x 56 kbit/s, in which n is the number of timeslots bundled into a channel set. A T1-F interface is similar to a synchronous serial interface and supports link layer protocols such as the Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), and Frame Relay (FR) and network protocols such as IP.
A T1-F interface differs from a CT1/PRI interface in the following aspects:
- When working in framed mode, a T1-F interface allows timeslots to be bundled into only one channel set, whereas a CT1/PRI interface allows timeslots to be randomly bundled into multiple channel sets.
- A T1-F interface does not support the PRI mode.
Clock Mode
To exchange data correctly, communicating parties must have their clocks synchronized.
- Master clock mode (local clock mode): In this clock mode, a T1-F interface uses the local clock generated by the chip as the reference clock.
- Slave clock mode (line clock mode): In this clock mode, a T1-F interface uses the line clock as the reference clock.
Generally, the interface at one end of a link works in master clock mode, and the interface at the other end works in slave clock mode.
Frame Format
- Super frame (SF): consists of 12 frames that share the same frame alignment information and signaling information. Frame 6 and frame 12 are signaling frames.
- Extended super frame (ESF): consists of 24 frames that share the same frame alignment information and signaling information. Frames 6, 12, 18, and 24 are signaling frames.
Line Idle Code
The line idle code is the code sent over a timeslot that is not bundled to form a channel.
The router supports two line idle codes: 0x7e and 0xff.
Interframe Filling Tag
The interframe filling tag is the code sent when the timeslot bundled to form a logical channel does not send any service data.
The router supports two interframe filling tags: 0x7e and 0xff. On the router, you can set the minimum number of interframe filling tags.
RAI Detection
A remote alarm indication (RAI) alarm is sent to an upstream device after the router detects loss of frame (LoF) caused by clock asynchronization or loss of signal (LOS).