Description of the E1 interface of an AR router

1. E1/T1: E1/T1 is a technology of using the synchronous time division multiplexing technology to combine multiple audio channels into a 2 Mbit/s or 1.5 Mbit/s high-speed channel.
- Maximum rate of E1 cards: 32 (timeslots) x 64 (kbit/s per timeslot) = 2048 kbit/s
- Maximum rate of T1 cards: 24 (timeslots) x 64 (kbit/s per timeslot) = 1536 kbit/s
- CE1/CT1 cards can determine multiple groups of timeslots and have the Controller view. However, E1 cards can determine only one group of timeslots in the framed mode (other timeslots cannot be used).

2. E1 interfaces are configured on E1/T1 cards and can be seen as serial interfaces (currently supported by AR1200(S)/AR2200(S)/AR3200(S)/AR3600).
- 1E1T1-M/2E1T1-M support the E1/CE1/CT1/PRI(E1&T1) interface.
- 4E1T1-M/8E1T1-M support the E1/CE1/PRI(E1) interface.
- 1E1T1-F/2E1T1-F support the framed/unframed E1/T1 interface.
- 4E1T1-F/8E1T1-F support the framed/unframed E1 interface.
- The character M in a model name indicates Multiflex Trunk, that is, the model can be fully channelized. The character F in a model name indicates Fractional, that is, the model can be partially channelized.

3. The CE1/PRI interface is the physical interface of the E1 system. It can work in E1 mode (unchannelized mode) or CE1/PRI mode (channelized mode).
- In E1 mode, the CE1/PRI interface works as an interface not divided by timeslots, whose bandwidth is 2.048 Mbit/s.
- In CE1/PRI mode, the 2M line is divided into 32 timeslots of 64 KB, which are numbered from 0 to 31. Timeslot 0 is used to transfer frame alignment information.
a. CE1 interface: All timeslots except timeslot 0 are randomly divided into multiple groups (channel sets). Each group is corresponding to a separated channel.
b. PRI interface: Bundle timeslot 16 (D channel) and any one of timeslots 1 to 15 or 17 to 31 (B channel) into a group (PRI set).
c. CE1 interfaces can be divided into multiple groups. However, only one group can be bundled for PRI interfaces.

4. The CT1/PRI interface is the physical interface of the T1 system.
- CT1 interface: All timeslots (timeslot 1 to 24) can be randomly divided into multiple groups. Timeslots in each group are bundled into a channel set.
- PRI interface: Randomly bundle timeslot 24 (D channel) and any one of timeslots 1 to 23 (B channel) into a group (PRI set).
- CT1 interfaces can be divided into multiple groups. However, only one group can be bundled for PRI interfaces.

5. E1 interfaces, channel sets, and PRI sets can all be seen as serial interfaces, which have the same logical characteristics as synchronous serial interfaces and support IP network protocols and protocols in the data link layer, such as PPP and HDLC frame relay X.25 protocol (PRI sets do not support the HDLC frame relay X.25 protocol and channel sets of CT1 interfaces do not support the X.25 protocol).

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