The Feasibility of ATM operations over high frequency radio and the viability of the ATM/HF architecture

High Frequency (HF) radio is still a vital part of communications networks because its low cost and long distance capabilities, and still plays important roles as primary, supplemental, or redundant backup systems. Asynchronous Transfer Mode (ATM) is increasingly becoming an important part of communications, especially with LAN Emulation (LANE) specifications. Add to this the importance and increasing interest and dependency upon wireless networking, and it becomes inevitable that research into mobile ATM networking over HF radio would be considered. To test the feasibility of ATM networking over HF radio it was decided that a simulation would be developed to collect some basic information on call blocking and throughput. In order to build the simulation it was necessary to have an architectural framework of a mobile ATM network operating over HF radio. ATM/HF (ATM over HF) is the proposed architecture. ATM/HF is a proposed architecture that provides for networking mobile ATM nodes such as ships, planes, and trucks, over HF radio. It is based upon a recommended 64 kHz bandwidth which allows for a 128 kbps data rate. The ATM/HF architecture utilizes three different Media Access Control (MAC) protocols for network startup and access from the various network states, and incorporates several recently proposed dynamic capabilities for control of bandwidth and the integration of voice, data, and video. The proposal provides frame and wireless ATM (WATM) packet structures and a reference model for flow of the cells from the ATM Adaptation Layer (AAL) through the radio. An important feature is the use of channels, called channelization, to increase both network capacity and distance. The simulation was built to represent an active network state with active nodes connecting and disconnecting calls in a dynamic way with explicit connection messages. The purpose of starting from this network state was to measure the call blocking and throughput of a single channel. Two user types were developed, one to represent telephone voice and the other to represent computer data traffic. By varying the number of users per node and by type, the level of call blocking and throughput could be changed. Graphing the levels it could be determined the maximum capacity a single channel could support and thus determine if ATM over HF radio is feasible. In addition, the same information was used to determine the viability of the ATM/HF architecture. Although the simulation did not incorporate all the dynamic features of the recommended protocols, it does dynamically assign slots, rearrange slots to utilize non-contiguous available slots, and adjust the data rate of computer connections to accommodate voice call requests. This was done to reduce the level of voice call blocking which became the determining factor in deciding feasibility. It was determined that mobile ATM networking over HF radio is possible since the voice call blocking of a single channel was at the 10% level, overall call blocking was at the 6% level, and throughput was at the 53% level. It was determined that a single channel could support six voice and a minimum of ten data users. Although throughput, which is defined as the number of available slot used, was lower than expected, the possibility exists for utilizing the unused slots by incorporating additional dynamic capabilities that would increase the number of users supportable by a single channel. Throughput can be also be increased by incorporating Available Bit Rate (ABR) and Unspecified Bit Rate (UBR) traffic. The call blocking and throughput levels prove that ATM/HF is a viable method for supporting ATM operations. Although the call blocking level achieved the voice call blocking level and exceeding the overall call blocking level, the throughput level shows that there is a lot of wasted bandwidth. Further study of the design is required to improve the throughput level. Further development of the simulation is required in order to test the MAC protocols and to test the effects of the Bit Error Rate and fading effects of HF radio. The final conclusion, however, is that ATM over HF radio is feasible, that ATM/HF is a viable architecture, and that further research should be conducted into both