Hybrid Fiber/Copper Access Networks
Hybrid fiber/copper access networks consist of both fiber and copper segments to reach network subscribers. These hybrid access networks utilize passive optical network (PON) technology on the fiber segment and either digital subscriber line (DSL) or cable modem technology on the copper segment. A PON is an economically sensitive candidate technology for bringing fiber optic transmission to individual subscribers (businesses or individuals) through the access network.
Communication networks can be partitioned into two broad categories: 1) public and 2) private. Public networks are those that are established by service provider companies (e.g., AT&T, and Qwest) for public use. Private networks are those that are established by private entities (e.g., UTEP) for use by the entity. Individuals or institutions pay one or more service providers for a connection to one or more public networks that typically offer global connectivity (i.e., the Internet).
The access network interconnects the public and private networks. The access network is actually a portion of the public network that reaches out to the individual subscriber (i.e., private) networks. At present, the access network consists primarily of copper transmission media (e.g., twisted pair [digital subscriber lines], and coaxial [cable tv]). PONs are an attractive option for converting the access network to a fiber optic transmission media because of their low cost.
We have leveraged our deep expertise of dynamic bandwidth allocation (DBA) for Ethernet Passive Optical Networks (read information on that project below) to study access networks consisting of both fiber and copper segments. In many access network deployment scenarios it is still not economically attractive for service provider companies to deploy fiber all the way to subscriber locations despite the low cost of PON deployments. In these scenarios, service provider companies will deploy a PON within 100 meters or so of subscribers and utilize existing twisted pair copper or coaxial copper to reach subscribers. The point at which the fiber segment is terminated is referred to as a "drop point". For that reason the equipment that bridges the fiber and copper segments of the network at the "drop point" is simply called a "drop point" device. The fundamental goal of our research is to study mechanisms to reduce energy consumption at the "drop-point" device.
We have pursued two strategies to reduce energy consumption at the "drop point" device. The first strategy moves some of the copper technology logic blocks (e.g., DSL logic blocks) from the drop point to the service provider companies central office (CO) where power is abundant. Less logic at the drop point translates to fewer transistors that consume power. Moving logic blocks to the CO location has performance repercussions. Our study uncovered these repercussions and mechanisms to alleviate or reduce their impact. The second strategy reduces the buffering that occurs at the drop point device. Reduced buffering means smaller memory devices with fewer transistors that consume power. Our research uncovered a few mechanisms for reducing buffering in both the downstream and upstream directions. Please read our published articles for further detail.
Ethernet Passive Optical Networks (EPONs)
Ethernet PONs (EPONs) are PONs that utilize the ubiquitous Ethernet protocol.
The fundamental goal of this research on EPONs has been to increase channel utilization. Increasing channel utilization increases the useable bandwidth on each individual PON. Increased useable bandwidth reduces the cost per unit of bandwidth. Stated more directly, the goal has been to lower the cost per unit of bandwidth on EPONs to help promote their rapid deployment.
Through analytical and behavioral modeling of EPONs, we came to understand what contributes to wasted bandwidth and have used the scheduling component of dynamic bandwidth allocation to minimize this wasted bandwidth. This research has resulted in the discovery of two transmission scheduling (i.e., grant scheduling) techniques that can significantly improve channel utilization: 1) online just-in-time scheduling, and 2) shortest propagation delay first scheduling. Dynamic Bandwidth Allocation (DBA) is the act of managing the bandwidth or information capacity of transmission channels. For EPONs, DBA can be broken into two components: 1) grant sizing, and 2) grant scheduling. Please read our published articles for further detail.
Video Bandwidth Forecasting
According to a report from Cisco Systems, video will make up 90% of consumer network traffic by 2012. Optimizing communication networks for the delivery of video information is obviously critical for these networks to meet the information transfer requirements of the future.
Digital video is compressed to reduce its bandwidth requirements so that transport over communication networks is feasible. The compression of video results in time variance of the bandwidth requirements of the video. This time variance makes allocating bandwidth in communication networks challenging. The easiest approach is to allocate for the maximum bandwidth of the video but that approach will result in significant wasted bandwidth in the network. The more efficient approach is to allocate for the mean bandwidth and use statistical multiplexing to share transmission channels among many videos. A bandwidth forecast can be used to improve the efficiency of statistical multiplexing.
The fundamental goal of our research on video bandwidth forecasting is to discover a forecast method that is accurate and simple to implement.
It turns out that most video communication involves pre-recorded video. With pre-recorded video, true bandwidth forecasts are not required since the size of all of the video frames is known prior to their delivery over a communication network. The problem therefore reduces to simply getting future video frame size information into the network. Rami Haddad and I came up with a technique we call Feed-Forward Bandwidth Indication (FFBI) that places "future" video frame size information in "past" video frame headers where network equipment can access them. This technique can also be used with live (i.e., real-time) video if we introduce a little delay at the source. Please read our published articles for further detail.