Research involving mobile wireless ATM is advancing rapidly. One of the earliest proposals for a wireless ATM architecture is described in . Various alternatives for a wireless Media Access Channel (MAC) are discussed and a MAC frame is proposed. The MAC contains sequence numbers, service type, and a Time of Expiry (TOE) scheduling policy as a means for improving real-time data traffic handling. A related work which considers changes to Q.2931  to support mobility is proposed in . A MAC protocol for wireless ATM is examined in  with a focus on Code Division Multiple Access (CDMA) in which ATM cells are not preserved allowing a more efficient form of packetization over the wireless network links. The ATM cells are reconstructed from the wireless packetization method after being received by the destination. The Rapidly Deployable Radio Network Project (RDRN) architecture described in this paper maintains standard ATM cells through the wireless links. Research work on wireless ATM LANs have been described in  and . The mobile wireless ATM RDRN differs from these LANs because the RDRN uses point-to-point radio communication over much longer distances. The system described in  and  consists of Portable Base Stations (PBS) and mobile users. PBSs are base stations which perform ATM cell switching and are connected via Virtual Path Trees which are preconfigured ATM Virtual Paths (VP). These trees can change based on the topology as described in the Virtual Trees Routing Protocol . However, ATM cells are forwarded rather than switched, which is differs from the ATM standard. An alternative mobile wireless ATM system is presented in this paper which consists of a mobile PNNI architecture based on a general purpose predictive mechanism known as Virtual Network Configuration that allows seamless rapid handoff.
The objective of the Rapidly Deployable Radio Network (RDRN) effort is to create an ATM-based wireless communication system that will be adaptive at both the link and network levels to allow for rapid deployment and response to a changing environment. The objective of the architecture is to use adaptive point-to-point topology to gain the advantages of ATM for wireless networks. A prototype of this system has been implemented and will be demonstrated over a wide area network. The system adapts to its environment and can automatically arrange itself into a high capacity, fault tolerant, and reliable network. The RDRN architecture is composed of two overlaid networks:
The network currently consists of two types of nodes, Edge Nodes (EN) and Remote Nodes (RN) as shown in Figure 1. ENs where designed to reside on the edge of a wired network and provide access to the wireless network; however, EN also has wireless links. The EN components include Edge Switches (ES) and optionally an ATM switch, radio handling the ATM-based communications, packet radio for the low speed orderwire running a protocol based on X.25 (AX.25), GPS receiver, and a processor. Host nodes or remote nodes (RN) consist of the above, but do not contain an ATM switch. The ENs and RNs also include a phased array steerable antenna. The RDRN uses position information from the GPS for steering antenna beams toward nearby nodes and nulls toward interferers, thus establishing the high capacity links as illustrated in Figure 2. Figure 2 highlights an ES (center of figure) with its omni-directional transmit and receive orderwire antenna and an omni-directional receive and directional transmit ATM-based links. Note that two RNs share the same beam from the ES and that four distinct frequencies are in use to avoid interference. The decision involving which beams to establish and which frequencies to use is made by the topology algorithm which is discussed in a later section.
Figure 1: RDRN High-level Architecture.
The ES has the capability of switching ATM cells among connected RNs or passing the cells on to an ATM switch to wire-based nodes. Note that the differences between an ES and RN are that the ES performs switching and has the capability of higher speed radio links with other Edge Switches as well as connections to wired ATM networks.
Figure 2: RDRN Component Overview.
The orderwire network uses a low power, omni-directional channel, operating at 19200 bps, for signaling and communicating node locations to other network elements. The orderwire aids link establishment between the ESs and between the RNs and ESs, tracking remote nodes and determining link quality. The orderwire operates over packet radios and is part of the Network Control Protocol (NCP). An example of the user data and orderwire network topology is shown in Figure 3. In this figure, an ES serves as a link between a wired and wireless network, while the remaining ESs act as wireless switches. The protocol stack for this network is shown in Figure 4.
The focus of this paper is on the NCP and in particular on the orderwire network and protocols. This includes protocol layer configuration, link quality, hand-off, and host/switch assignment along with information provided by the GPS system such as position and time. The details of the user data network will be covered in this paper only in terms of services required from, and interactions with, the NCP.
Section 2 provides a more detailed description of the RDRN system, with a focus on the requirements and interaction of each protocol layer with the NCP. Operation of the NCP is described in Section 3. A new concept known as Virtual Network Configuration (VNC) is explained in Section 4 along with an example application of a Mobile Private Network-Network Interface (PNNI) enhanced with VNC. The development and implementation of the NCP is described along with initial timing results in Section 5. In Section 6, an analysis of NCP indicates the performance of NCP as the system is scaled up. Finally, emulation results are presented in Section 7.
Figure 3: Example Orderwire Topology.
Figure 4: Wireless ATM Protocol Stack.