What difference between Framed and Unframed E1?

What is E1 ? What’s the difference between framed and unframed E1 ? This article mainly focuses on revealing framed and unframed E1 difference.

Part I.What is E1 and E1 Interface?

What is E1? 

E1 framed and unframed E1

In the field of communications, E1 is the abbreviation of European Group 1, commonly known as 2M.
E1, the European equivalent of T1, is a point-to-point digital line service provided by a common operator.
E1 is used in private data networks as well as cellular, Wi-Fi and fixed network backhaul.

What is E1 interface?

E1 Interface framed and unframed E1

The E1 interface is a digital transmission interface commonly used in telephone networks and data communications.
The E1 interface uses 8-bit data frames with a rate of 2.048Mbps. It is usually used to connect enterprise telephone switches and public switched telephone networks.
The E1 interface can support 30 voice channels or transmit large amounts of data.

Part II.Framed and Unframed E1 – difference and application


1. Time slot

framed and unframed E1 TimeSlot difference

The key difference between framed E1 and unframed E1 is whether time slot 0 is occupied. If it is occupied, it is framed; if it is not occupied, it is unframed.

Framed E1 is divided into two formats: 30 and 31. The 0 time slots of these two formats are all occupied.

The 0 time slot of unframed E1 is not occupied.

2. Speed

framed and unframed E1 Speeds difference

The framed E1 rate is 1984K and the unframed E1 rate is 2048K.

Specifically, since time slot 0 of framed E1 is occupied, time slot 0 of unframed E1 is not occupied, and each time slot supports one 64Kbps channel.

Therefore the rate of framed E1 is 64Kbps lower than the rate of unframed E1.

3. Carrying data

framed and unframed E1 carring data difference

Framed E1 carries data in order, and framing directly encapsulates data into frames for transmission. Instead of carrying data out of order, the unframed E1 directly transmits the digital stream.

Specifically, framed E1 will encapsulate data into small packets.

Such encapsulation forms include frame header, frame trailer and frame format.

Unframed E1 does not encapsulate data into small packets for orderly transmission.

This encapsulation form has no frame header, frame trailer and frame format.


Framed E1 interfaces are usually used to implement E1-to-optical interface conversion and transmit Ethernet data on the E1 channel.

For example, some optical converters use framed E1 interfaces.

framed E1 application framed E1 and unframed E1

Unframed E1 is usually used in remote data transmission scenarios, and it has unique advantages in scenarios that require maximum bandwidth utilization.
It is usually used to transmit various services such as voice, data, image and video.

unframed E1 application framed E1 and unframed E1

Part III.What is framed and Unframed E1? Which One is better?

What is Unframed E1 ?

Unframed E1 does not encapsulate the carried data into small packets for orderly transmission.

Unframed E1 transmits E1 time slots 0 to 31 out of sequence, and these 32 time slots can be used to carry valid service data.


(1)Unframed E1 optical modem equipment usually has an E1 interface and an optical interface, and its data channel rate can reach 2.048Mbps.

(2)Unframed E1 supports adaptive 120 ohm balanced and 75 ohm unbalanced impedances.

This feature allows it to meet ITU-T, G.703 and G.704 standards without additional settings.

What is Framed E1?

Framed E1 is to encapsulate the data carried by E1 into “small packets” one by one for transmission in order.


(1)Framed formats are divided into 30 and 31 formats.

The 30 format refers to E1 time slots 1~15, time slots 17~31 are used to carry valid user data, and time slots 0 and 16 are used for other purposes.

The 31 format means that time slots 1~31 of E1 are used to carry valid user data, and time slot 0 is used for other purposes.

Which one is better? 

Many people will ask which one is better, unframed E1 or framed E1. It depends on your needs.

Post time:2024-04-03


Lomoveishiy – Finland

I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!

Raymond – USA

Great experience – units worked straight out of the box – just needed plug in cables and we were done. I also like the possibility to enable jumbo frames, while we do not have a need for this feature at the current moment it’s great to have this option.

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