How a Creator Reached 668 Kbps on Dial-Up with a Dozen Modems

A YouTube creator managed to stream video by linking together 12 separate phone lines, proving just how far outdated technology could be pushed. The setup delivered just under 1 Mbps — painfully slow by 2025 standards, but still an impressive showcase of dial-up’s limits in an era once ruled by the familiar screech of modems.

The channel The Serial Port pulled off what most would consider impossible in the age of high-speed broadband: streaming YouTube through a dial-up connection. Their experiment relied on bonding 12 modems with Multilink PPP, producing a combined download speed of 668 kbps on a Windows XP machine barely enough to stream video without interruptions.

According to the team, this may be the first known attempt to successfully bond more than four modems in a real-world test.

Back in the late 1990s, the fastest dial-up speeds peaked at just 56 kbps. By the year 2000, the FCC defined broadband as anything over 200 kbps, a threshold that dial-up was already struggling to meet. Websites at the time were simple, with mostly text and compressed images. Downloading music or video often tied up a phone line for hours, eventually paving the way for DSL and cable internet to take over as demand for faster connections grew.

Back in 1994, Multilink PPP was introduced as a way to merge multiple phone lines into a single, faster data connection. Some companies even tried to commercialize it — Diamond Multimedia’s “Shotgun” PCI card, for instance, paired two 56K modems together. Still, the requirement for extra phone lines and ISP compatibility meant the technology never gained much traction.

Fast-forward thirty years, and The Serial Port decided to revive the concept. Using VoIP line simulators along with leftover enterprise networking hardware, they set out to see just how far MPPP could really go.

The project required vintage client machines and a fairly heavy-duty backend. Their first test platform, a 2001 IBM NetVista running Windows ME, managed to bond two modems without issue. But scaling beyond that quickly ran into obstacles — limited serial ports and weak driver support kept the system from going further.

The team’s next step was upgrading to a 2004 IBM ThinkCentre running Windows XP, which offered far better hardware and software support. With the addition of an Equinox serial expansion card and a Digi four-port card, the system gained access to 13 COM ports. Windows XP’s built-in tools for simultaneous dialing made it possible to connect a fleet of external US Robotics Courier modems, each configured with matching DIP switch settings to avoid interference.

On the service provider side, Cisco VoIP gear was used to emulate multiple phone lines. These calls were routed into a Total Control dial-up access concentrator, a piece of equipment once standard at small ISPs in the 1990s. While the client setup required plenty of fine-tuning, the ISP hardware had no trouble handling multiple concurrent connections.

By gradually scaling the number of bonded modems — from two, to four, and eventually twelve — the experiment managed to hit an aggregate speed of 668.8 kbps. That not only surpassed the FCC’s original broadband benchmark from 2000, but also delivered stable YouTube playback at 144p and even 240p.

According to The Serial Port team, they found no record — in practice or even in references like the Guinness Book of World Records — of anyone ever bonding more than four modems with MPPP.

Of course, the setup is hardly practical when compared to today’s slowest broadband connections. But as a proof-of-concept, it highlights both the creativity and the constraints that defined the dial-up era of the internet.

“The ISP side just worked flawlessly, with no real ceiling in sight,” the hosts remarked, underscoring how surprisingly capable the infrastructure was despite its age.