Debunking the Myths of Shared Networks: The Point-to-Multipoint Effect
“I don’t want to have to share a pipe. The problem with ‘cable’ is shared pipes. If my neighbor is doing a bunch of stuff over the network, I get impacted too. With fiber I get speed and no shared pipes.”
--- Entrepreneur in a focus group
The notion that subscribers connected to residential fiber networks do not “share pipes” is often misunderstood. For residential fiber networks, sharing pipes is one of the main reasons fiber to the home (FTTH) is even remotely cost-effective for service providers to deploy. But what is most surprising is the following: deploying shared network solutions has led to a more rapid increase in residential broadband speeds than otherwise would have been the case with non-shared access network solutions. I like to call this the Point-to-Multipoint Effect. In the process, sharing pipes has allowed broadband speed growth to surpass the predicted 50% compounded annual growth rate commonly known as Nielsen’s Law of Internet Bandwidth. Read on to learn more…
First, a couple of definitions:
- A (non-shared) point-to-point (P2P) network topology is one in which there is a single dedicated connection between two endpoints. In the case of access networks, one endpoint is typically located at the hub or central office, or could be located at a remote distribution point. The other endpoint is a digital subscriber line (DSL) modem, for example, or a simple Ethernet switch, located on the customer premise. In P2P networks, the peak capacity of a link is used exclusively by only the two endpoints.
- A (shared) point-to-multipoint (P2MP) network topology is one in which there is a single downstream transmitter and multiple access termination devices that all selectively listen to the same downstream data stream. A key characteristic with P2MP networks is the peak capacity of the network is shared between all connected endpoints. Two examples of P2MP networks are HFC and passive optical networking (PON), shown in the figure below (showing downstream transmission).
Two examples of (shared) point-to-multipoint networks: HFC and PON
The PON solution represents the most prevalent residential fiber solution in the world, primarily due to lower costs compared to P2P fiber solutions. To illustrate the sharing, referring to the diagram above, if 10G-EPON is the technology choice, each optical network unit (ONU) connected to the network transmits upstream at ~10 Gbps, but they don’t transmit simultaneously. Instead, an ONU must be scheduled by the OLT for upstream transmission to avoid collisions with other ONUs. In essence, the scheduling of ONUs results in the sharing of the 10 Gbps peak capacity. Consequently, there is a whole lotta pipe sharing going on in PON solutions.
Do shared networks necessarily perform better or worse than non-shared networks? It depends on how performance is measured, but in one key area, residential broadband speeds, shared networks have significantly outperformed non-shared networks by a substantial amount.
A recent blog discussed Nielsen’s Law of Internet Bandwidth and how the cable industry was preparing to meet future broadband speeds with 100G-EPON. When Mr. Nielsen made his initial prediction in 1998, residential broadband access was dominated by dialup and ISDN connections, which are both P2P solutions. Indeed, for approximately the first 14 years since that initial 300 bits per second dialup connection in 1982/1983, the progression of available peak service tier bit rates followed the 50% annual growth rate prediction.
**various sources compiled by CableLabs
The release of the first DOCSIS® specifications by CableLabs in 1996 essentially represented the dawn of P2MP solutions, i.e. shared, for residential Internet connectivity. According to the data in the chart above, the tremendous rate of technology advancements resulting from the shared DOCSIS/HFC network solution, and later with the development of shared PON technologies, coupled with the relative cost-effectiveness of these solutions, has far exceeded other P2P technologies for residential broadband. While the initial growth prediction in 1998 was a 50% annual growth rate, the Point-to-Multipoint Effect increased the growth rate closer to 70% for residential Internet connectivity. The Point-to-Multipoint Effect indicates that sharing pipes for residential connectivity has provided a solution that has actually allowed residential high speed data rates to increase at a faster pace! This “sharing” trend is expected to continue with the development of Full Duplex DOCSIS and 100G-EPON, making the introduction of new services possible. Thus, just like our parents always told us, it is good to share.
In his role as Vice President Wired Technologies at CableLabs, Curtis Knittle leads the activities which focus on cable operator integration of optical technologies in access networks. Curtis is also Chair of the 100G-EPON (IEEE 802.3ca) Task Force.
Technology Implications of 2Gbps Symmetric Services
Service providers and municipalities alike continue their push toward offering gigabit services over fiber networks. In fact, fiberville is a web site dedicated to listing which service providers and municipalities provide fiber solutions. Recently, Comcast significantly upped the ante by announcing a 2 Gbps symmetric service that will become available in certain locations. The services announced will be 2 Gbps downstream and 2 Gbps upstream. This is a substantial announcement due to the 2 Gbps speeds and symmetrical services which facilitate faster file uploads which is of interest to individuals who work from home, small businesses and gamers.
With all that speedy yumminess, let’s examine some of the technologies required for delivering multi-gigabit symmetrical services to homes and businesses.
Setting the Stage
When a provider deploys broadband services there is typically a peak rate, above the advertised speeds, that provides the headroom necessary for them to support the speeds and service level agreements (SLAs) associated with the service.
When the total available bandwidth is shared among multiple users, like it is in PON solutions, an unscientific but common practice is for the network to support at least twice the highest advertised rate. Specifically, to support an advertised service of N Gbps, the peak rate must provide for at least 2xN Gbps. Thus, for a 2 Gbps service the peak rate must be at least 4 Gbps to safely support the SLA using common practices. This premise allows the operator to investigate and determine the technology to use in order to support the advertised speeds. Once the technology is chosen, then the engineering work required to build out the solution may begin.
Let’s look at the two fiber to the home solutions that will support a 2 Gbps symmetric service today: Point-to-Point Fiber and 10 Gbps Ethernet Passive Optical Network (10G-EPON).
Point to Point Fiber: Best Performance
Point-to-point topology is a “home-run” active Ethernet fiber implementation that provides dedicated fiber from the home all the way through the access network to the headend. It is analogous to building your own personal highway from home to your office so you can get to work faster. While this solution provides the ultimate future-proof network, in terms of bandwidth, flexibility and network reach, it requires a significant amount of fiber and associated optical transceivers. Running a dedicated fiber to a residential customer premise is both complex and resource intensive due to additional fiber management and ongoing maintenance. However, it delivers the best performance to meet customer needs.
10G-EPON: An Efficient 2-Gig Symmetrical Solution
While there are many flavors of Passive Optical Networks (PON), (see: OnePON), 10G-EPON with its symmetric 10 Gbps links, is the only standardized, and commercially available PON technology able to provide at least 4 Gbps peak rate to support a 2 Gbps symmetrical service level agreement. Because of its point-to-multipoint topology and passive implementation, 10G-EPON is a cost effective solution in terms of operations, fiber consolidation, and headend real estate required.
CableLabs has championed PON initiatives through contributions to international standards, hardware and software certification, and interoperability events. CableLabs is facilitating a common approach to provide fiber solutions that will allow for quicker and higher-scale PON deployments.
Both 10G-EPON and point-to-point fiber solutions can provide 2 Gbps symmetrical services, opening up a world of possibilities for cable operators and customers alike. From the realization of all-IP delivered services, more efficient network implementations, improved cloud services, and overall future proofing the network, 2 Gbps symmetrical fiber deployments are a reality today.
Jon Schnoor is a Senior Engineer at CableLabs.