This GENI Spiral 1 project (which is a collaboration between WINLAB and NEC Labs, Princeton) aims to leverage a state-of-the-art IEEE 802.16e WiMAX base station product from NEC to prototype an open, programmable and virtualizable cellular base station node for GENI. This open GENI base station node (“GBSN”) device is intended to support flexible experimentation in wide-area mobile network service scenarios similar to today’s cellular systems.
The open/programmable base station node to be developed in this project is a key enabling technology for GENI and the future Internet. In view of the rapid growth in cellular/mobile services worldwide architectures for cellular-Internet convergence are of particular importance in the future Internet research agenda. While the need for cellular is not in dispute, academic networking research has to date relied almost entirely on short-range WiFi devices because of their low cost and availability of open-source Linux software support. The availability of an open wide-area wireless access network in GENI will encourage new categories of experiments directly addressing cellular-Internet convergence, while also making it easer to grow coverage and attract real-world end users.
The figure below shows a schematic of the WiMAX base station router and its connection to the rest of the GENI network. As shown, the WiMAX base station is typically connected to a GENI access network with layer 2 switched connectivity using Ethernet or optical fiber technology. The figure also indicates three distinct interfaces associated with the GENI WiMAX base station. The first is the GENI control interface for experimenter access to virtual networks (slices) supported by the external base station controller. This is the primary interface relevant to a GENI experimenter, and is currently based on the ORBIT Management Framework (OMF). The second interface is the so-called R6+ interface by which the base station controller communicates with the base station hardware (which includes its own internal controller running a proprietary NEC operating system and control/management software). The R6+ interface exposes the hardware features such as assignment of MAC/PHY resources (i.e. OFDMA time-frequency slots, power levels, service classification, etc.) to each flow, as well as management interfaces for initial configuration, scheduler policy selection and queue management.
High level diagram of WiMAX base station and its interfaces to the GENI network
The NEC Release 1 WiMAX base-station hardware (see photo below) is a 5U rack based system which consists of multiple Channel Cards (CHC) and a Network Interface Card. The shelf can be populated with up to three channel cards, each supporting one sector for a maximum of three sectors. The BS operates in the 2.5 Ghz or the 3.5 Ghz bands and can be tuned to use either 5, 7 or 10 Mhz channels. At the MAC frame level, 5 msec frames are supported as per the 802.16e standard. The TDD standard for multiplexing is supported where the sub-channels for the Downlink (DL) and Uplink (UL) can be partitioned in multiple time-frequency configurations. The base-station supports standard adaptive modulation schemes based on QPSK, 16QAM and 64QAM. The interface card provides one Ethernet Interface (10/100/1000) which will be used to connect to the high performance PC used to control the device. The base station has been tested for radio coverage and performance in realistic urban environments and is being used in early WiMAX deployments – typical coverage radius is ~3-5Km, and peak service bit-rates achievable range from 15-30 Mbps depending on operating mode and terrain.
NEC's Release 1 802.16eBS
The WiMAX base station has an external PC controller that runs Linux. In the initial prototype, we use the ORBIT Management Framework (OMF) software to interface the base station to other parts of the GENI network. The Linux controller is implemented using UML virtualization, although we will later consider upgrades to other VM platforms. The OMF software is implemented via “Orbit grid services” on the control slice shown in the Figure below. For more information on OMF, please refer to documentation at http://www.orbit-lab.org/wiki/Documentation .
External Base Station Controller Architecture
The controller provides support for multiple slices assigned to the GENI WiMAX node. Each slice runs within its own virtual machine (using software such as UML – User Mode Linux) as shown. Each VM is capable of providing multiple virtual interfaces, so that programs loaded on a slice that runs within a virtual machine can emulate its own router and perform IP routing. Virtual interfaces are mapped to physical interfaces based on the next hop for a virtual interface. The controller will receive IP packets from the base-station on the R6+ interface mentioned earlier. When a packet is received, it will be forwarded to the appropriate slice for further processing. The outgoing IP packets from a slice will be placed on queues specific to a virtual interface. Outgoing packets on virtual interfaces mapped to the layer 2 interface of the WiMAX base station will be tagged so that they can be assigned traffic class and bandwidth parameters (BE, ertPS, rtPS etc.) as determined by the flow CID (connection ID).
Experimenters will be able to access the WiMAX network through the ORBIT portal, which provides scripting, experiment control, management and measurement tools necessary to run an experiment. OMF facilities will be extended to provide software downloads for Linux-based end-user devices. For more details on running an ORBIT experiment, refer to
Results to Date and Future Work Plan:
The GENI WiMAX project was started under the Spiral 1 GENI program in 4Q08. A Release 1 WiMAX base station from NEC Corp has been installed at WINLAB and has been integrated with the ORBIT management framework for experimenter access and control. A demo of the WiMAX/ORBIT capability was given at the GENI Engineering Conference 4 held in Miami on March 30-April 2.
Work on implementing details of the open WiMAX API and virtualization methods is currently in progress.