Businesses relied on dedicated phone-company lines to carry calls and data. This was before cable modems and fiber arrived. The T1 line was the workhorse of that era. E1 did the same job in Europe and much of the world. A T1 internet connection once powered offices and banks.
It was also a key element in powering schools and call centers. Both standards still show up in phone systems and ATMs. You will find it in older networks today. They look similar on paper.
However, they differ in speed and channel count. You will also find differences in coding and where in the world they're used. This article will explain each one and lay out the differences side by side.
What Is A T1 Line?
A T1 line is a dedicated digital circuit that carries voice and data over copper or fiber. AT&T's Bell System rolled it out in 1962 to link busy telephone offices. Let’s see the real T1 line speeds. You will also learn how the line packs calls and data into one steady stream.
How Fast Is A T1 Line?
A T1 runs at 1.544 Mbps. That number is the same in both directions. That means uploads move as fast as downloads. The line splits into 24 channels of 64 kbps each. Together they carry 1.536 Mbps. The last 8 kbps goes to framing. The T1 speed feels slow by modern standards.
A 5 MB photo takes about 26 seconds to download. A single 4K Netflix stream needs nearly ten times that bandwidth. Still, the speed is guaranteed by contract. It never dips at rush hour. This is because nobody else shares the line with you.
How Does A T1 Line Work?
A T1 uses time-division multiplexing. Each of the 24 channels gets a tiny time slot in turn. The line sends 8,000 frames every second. Each frame holds 193 bits. There are 8 bits per channel plus one framing bit. Two pairs of copper wire do the work. One pair sends while the other receives.
Repeaters boost the signal about every 6,000 feet. At each end, a box called a CSU/DSU connects the line to your router or phone system through an RJ-48C jack. That steady and precise rhythm keeps the T1 line speed locked at 1.544 Mbps.
What Is E1?
E1 is the European version of T1. The ITU-T defined it in its G.703 and G.704 standards. It became the norm across:
- Europe
- Asia
- Africa
- Latin America
- Australia
An E1 runs at 2.048 Mbps. It splits into 32 time slots of 64 kbps each. Slot 0 handles framing and timing. Slot 16 usually carries call signaling. This includes dial tones and hang-ups. That leaves 30 channels for voice or data. Phone companies bundle 16 E1s into an E3. These can run at 34.368 Mbps.
E1 uses a line code called HDB3, which keeps the signal from going quiet during long strings of zeros. It connects over 120-ohm twisted pair or 75-ohm coaxial cable with BNC connectors. Voice calls use A-law encoding. T1 uses µ-law.
That small detail matters when a call crosses from one system to the other. This is because the gear has to convert between them. Japan went its own way with J1, which runs at the same 1.544 Mbps as T1.
Many carriers outside North America still deliver business phone trunks over E1 today. It remains a trusted choice for voice. This is because every channel gets a fixed and predictable share of the line.
Key Differences Between E1 and T1
T1 and E1 do the same basic job, but the details split them apart. The table below lines up their speeds and other differences. The T1 connection speed of 1.544 Mbps is only the start. Each row adds a plain-language note on what the difference means in real life.
|
Feature |
T1 |
E1 |
What It Means for You |
|
Full name |
Transmission System 1, part of the T-carrier family |
E-carrier level 1, part of the E-carrier family |
Both are digital telephone company circuits from the same time period. They are designed to send numerous phone calls on a single pair of wires. |
|
Developed by |
AT&T Bell Labs in 1962 |
CEPT in Europe, later published by the ITU-T |
T1 was the first to arrive. E1 was developed so that countries other than North America would have a common format. |
|
Governing standards |
· ANSI T1.102 · T1.403 |
· ITU-T G.703 · G.704 · G.706 |
The documents are used to test equipment sold in each region. Always read the spec sheet before purchasing any interface card! |
|
Main regions |
· United States · Canada |
· Europe · Asia · Africa · Latin America · Australia |
Typically, you will be able to choose between the two based on your location. A close cousin is used in Japan: J1. |
|
Line rate |
1.544 Mbps |
2.048 Mbps |
E1 transfers 33% more data per second. Both are far short of today's broadband speeds. |
|
Transmission direction |
Full duplex at 1.544 Mbps each way |
Full duplex at 2.048 Mbps each way |
The rate of upload and download is the same on both lines. Because of that balance, they were used for servers, video calls, and branch office connections. |
|
Wire pairs used |
Two pairs, one to send and one to receive |
Two pairs, or one coax cable for each direction |
They both require their own lane for each direction. If one pair of the circuit is broken, the entire circuit fails. |
|
Total time slots |
24 |
32 |
There are 8 more slots to use with E1. A small lane that transports one voice or data stream is called a slot. |
|
Usable voice channels |
24, or 23 with ISDN PRI |
30 |
E1 can support 6 additional simultaneous phone calls. This makes it more suitable for busy call centers. |
|
Speed per channel |
64 kbps, or 56 kbps with robbed-bit signaling |
64 kbps |
E1 does not lose channel speed as there is a dedicated slot for signaling. T1 occasionally leases bits and sacrifices a bit of capacity. |
|
Framing method |
One framing bit added to each frame |
All of time slot 0 |
Framing is used to indicate the beginning of each frame. E1 uses more bandwidth, but maintains simplicity of design. |
|
Bits per frame |
193 |
256 |
More data is contained in each E1 frame. The number of frames sent per second is the same for both lines. |
|
Frames per second |
8,000 |
8,000 |
Both lines are sampled at the same rate of voice. That rate is sufficient for normal speech in the case of phone calls. |
|
Framing formats |
SF (D4) and ESF |
Basic frame and CRC-4 multiframe |
Both ESF and CRC-4 allow the carriers to check the line quality without interrupting service. ESF or CRC-4 are most commonly used for most modern installs. |
|
Error checking |
CRC-6 inside ESF framing |
CRC-4 inside the multiframe |
Both lines keep a tally of small errors as they occur. These counts are used by carriers to identify a failing line before customers realize there is a problem. |
|
Built-in data link |
A 4 kbps facility data link in ESF |
Spare national bits in time slot 0 |
This hidden side channel is used for sending performance reports by the carriers. It doesn't eat up your calls and data. |
|
Clock accuracy |
Within 32 parts per million |
Within 50 parts per million |
Timing is crucial for both lines. Slips are caused by clocks that drift too far, which result in data errors. |
|
Signaling |
Robbed-bit signaling or an ISDN D channel |
Time slot 16 or an ISDN D channel |
Signaling conveys information about call setup and hangup, including dial tones. It is never borrowed from voice channels by E1. |
|
Line coding |
AMI or B8ZS |
HDB3 |
Line coding helps to maintain the signal stability when there are long runs of zeros. The ends must match; otherwise, it won't come up. |
|
Voice encoding |
µ-law |
A-law |
There are two ways of converting a voice into numbers. There is a need for a fast conversion between the two systems. |
|
Cable impedance |
100 ohms on twisted pair |
120 ohms on twisted pair or 75 ohms on coax |
If the cable is matched to the impedance, there will be no signal error. Drops that are difficult to trace can be caused by the wrong cable. |
|
Common connector |
RJ-48C |
RJ-48C or BNC |
E1 gear can be found with both types of connectors. Baluns are adapters that convert coax to twisted pair and vice versa. |
|
Pulse amplitude |
3.0 volts |
3.0 volts on twisted pair or 2.37 volts on coax |
Test equipment should be configured for the appropriate line type. A line that is in good condition can display incorrect errors if the setting is incorrect. |
|
Line build-out |
Adjustable from 0 to -22.5 dB |
Usually not required |
T1 equipment can attenuate its signal for short runs. This will avoid overloading the equipment at the other end with a strong pulse. |
|
Alarm names |
Red, yellow, and blue alarms |
LOS, LOF, AIS, and RAI |
Both systems alert you to the same issues. They simply use different names for each alarm. |
|
Common test patterns |
QRSS and 3-in-24 |
PRBS 2^15-1 |
These patterns are sent by the technicians to locate the faults in the line. Follow the pattern your carrier is used to. |
|
Customer-side box |
CSU/DSU |
NTU, short for network terminating unit |
Each region will have a different name for the device used to connect the carrier line to the router. It can be used either way. |
|
Typical monthly cost |
A few hundred dollars in most US markets |
Varies widely from country to country |
They are much more expensive than modern fibre, both on a per megabit basis. Many companies store them for voice or backup purposes. |
|
ISDN PRI layout |
23 bearer channels plus 1 D channel |
30 bearer channels plus 1 D channel |
For business phone systems, the version is called PRI. An E1 PRI provides a greater number of calls per circuit. |
|
Next level up |
T3 at 44.736 Mbps, made from 28 T1s |
E3 at 34.368 Mbps, made from 16 E1s |
Every family grows in a different manner. The higher levels are primarily used for carriers and very large sites. |
|
Fiber network mapping |
VT1.5 inside SONET |
VC-12 inside SDH |
Both can be carried in the modern fiber backbones. They can be delivered by carriers via fiber and handed off to you at the building via copper. |
|
Fractional service |
Fractional T1 in 64 kbps steps |
Fractional E1 in 64 kbps steps |
Only the channels that businesses need can be rented. This reduces the monthly cost of small offices. |
|
Internet use |
Carried PPP, HDLC or Frame Relay traffic for early business internet |
Carried the same protocols for business internet outside North America |
Both connected office buildings to the Internet. One line now has to handle even one HD video call. |
|
Bonding options |
Several T1s can be bonded with MLPPP |
Several E1s can be bonded with MLPPP |
Bonding combines lines together to achieve more bandwidth. Still, there are only about 12 Mbps for 8 bonded T1s. |
|
Common uses today |
· PBX trunks · ATMs · Alarm panels · Legacy WAN links |
· PBX trunks · Mobile backhaul · Legacy WAN links |
Both are found primarily in older systems that continue to function well. Fiber or Ethernet is now being marketed to customers by many carriers. |
Upgrade Your Business Connection With Confidence
T1 and E1 carried the world's calls and data for decades. T1 runs at 1.544 Mbps with 24 channels. E1 offers 2.048 Mbps and 30 usable channels. Fiber wins on speed and price in the T1 line vs. fiber debate. Many legacy systems still count on both circuits.
Shop TS Cables for T1/E1 crossover cables and Ethernet patch cords. Find fiber jumpers that keep legacy and modern networks running strong.
FAQs
Are T1 lines still used?
Yes, but far less often. Banks and alarm companies still rely on them. Keep in mind that many carriers are retiring copper networks.
Is a T1 faster than Ethernet?
No. Ethernet is much faster. In a T1 vs Ethernet matchup. Even basic Ethernet over copper hits 10 Mbps. While fiber Ethernet can reach 10 Gbps or more.
Can a T1 and an E1 connect directly?
Not without extra equipment. Their speeds and voice coding differ. That is why you need a converter or a carrier that maps between the two formats.
What cable does a T1 line use?
Most T1 lines use shielded or unshielded twisted pair ending in RJ-48C jacks. Cat5e and Cat6 cables often work well for short runs inside a building.
How much does a T1 line cost?
Prices vary by location and carrier. Most businesses pay a few hundred dollars per month, which is far more per megabit than cable or fiber service.
Further Reading
Plenty of other networking topics are waiting on our blog. Learn about fiber basics and cable buying tips. Explore a few articles and turn tricky tech terms into plain everyday knowledge.
