Iocast is a wireless wide-area network (LPWAN) based on narrowband radio channels. An iocast network enables application servers to exchange datagrams with mobile, low-energy nodes. A real-time control stack, along with base transceivers, form the core of the network.
From an OSI standpoint, an iocast network comprises layers 1-4, while node firmware and application server software complete layers 5-7 as appropriate for the application. Nodes connect to the network using node transceivers, while application servers connect using the API. Nodes may be low-energy objects that require years of battery life or high-performance devices requiring sub-second response times. They may be fixed or mobile, and they may roam between systems. Strong encryption authenticates nodes and protects all node data.
The control stack serves as the "brain" of an iocast network. It includes two software services, conceptually arranged into a two-component stack. The top component, called the home controller, manages high-level network functions such as message queues and API connections. The bottom service, called the sector controller, manages low-level details concerning base transceivers and the air protocol.
The home controller is roughly analogous to a cellular network's Home Location Register (HLR), including a database of node rows, datagram queues, and the API servers. The sector controller is roughly analogous to a Mobile Switching Center (MSC), including a visitor location register, air queues, and real-time logic to control the air protocol for one or more sectors.
The inputs of a home controller are its API connections from application servers, and its outputs are Sector Client Interface (SCI) connections to sector controllers. SCI passes connection requests and reverse datagrams from the sector controller to the home controller. Likewise, SCI passes forward datagrams and supervisory requests from the home controller to the sector controller.
The inputs of a sector controllers are its SCI connections from home controllers, and it's outputs are Base Transceiver Interface (BXI) connections to BXs. BXI sends forward frames and reverse channel scheduling information from the sector controllers to BXs. Likewise, BXI sends reverse packets from BXs to the sector controller. BXI also allows the sector controller to account for variable latency when using satellite connections, and it supports flexible reverse channel diversity and reverse channel reuse algorithms.
For small to medium-sized networks, the control stack may exist as one home controller and one sector controller operating on one physical server computer. However, larger networks may include multiple sector controllers and multiple home controllers. Furthermore, home controller may make SCI connections to sector controllers of other networks in order to facilitate inter-system node roaming.
Iocast operates using narrowband (12.5KHz) radio channels. Base transceivers transmit data to node transceivers using forward channels, while node transceivers transmit data to base transceivers using reverse channels. Node and base transceivers use modulation compatible with 47 CFR Parts 22, 24(D), 90, and 101 (emissions designator 7K60FXD), and transmit a raw rate of 9600 bits per second.
Reverse channels are time-shared between node transceivers while forward channels are always on under control of a base transceiver or set of base transceivers. Forward and reverse channels are universally synchronized together, with the control stack providing coordination, timing, and access arbitration.
Channels are organized into sectors, which include at least one forward channel and one reverse channel, but which may include up to four forward and four reverse channels. All forward channels in a sector are effectively simulcast together, transmitting data and providing synchronization and coordination. Return channels are shared between nodes using slotted ALOHA and deterministic scheduling from the control stack.
Transmission symbols and frames align precisely with GPS time, with forward channels providing synchronization for reverse channels. The data link layer includes both controller-driven scheduling and slotted ALOHA media access. The network and transport layers divide datagrams into packets and transmit them using forward error correction along with selective-repeat ARQ and HARQ.
Iocast organizes channels into sectors. A sector may be as small as a building or campus, or as large as a country, and may include multiple channels and base transceivers. Nodes must connect to a sector before transmitting or receiving datagrams. The connection process mutually authenticates the node and control stack to each other. Sectors are identified by their 16-bit sector identification value secid and operate under control of one control stack. Sectors may be globally referenced in dot decimal form as sysid.secid.
In the above illustration, a control stack, sysid 23, operates 3 sectors and six base transceivers. The sectors include secid 23 (23.1), with simulcasted BXs 23.1.1, 23.1.2, and 23.1.3; secid 2 (23.2) with simulcasted BXs 23.2.1 and 23.2.2; and secid 3 (23.3) with BX 23.3.1. The nodes, shown as white circles, are able to move freely between the three sectors, connecting to each as necessary as they pass through.
Each sector can include up to four forward channels and four reverse channels; however, they do not require strict 1:1 forward/reverse channel pairings. For example, a sector designed for a metering application may include one forward channel coupled with three reverse channels. Alternatively, a large-scale alerting or dispatch application may require two forward channels coupled with one reverse channel.
A node's node availability setting (na) determines how often a node wakes up to receive forward datagrams. This value affects both the node's average power consumption and the length of time required to deliver forward datagrams. Nodes that require low latency (e.g., station alerting units) may be configured to receive datagrams quickly, at the cost of increased power consumption. Nodes that require long battery life (e.g., perimeter sensors), may be configured to receive datagrams infrequently.
Simularly, a group's group availability setting (ga) determines how often a node must wake up to receive a multicast message. For nodes that are members of a group, this value affects their average power consumption and the length of time required to deliver multicast datagrams to the group.
Node availability and group availability do not impact a node's reverse datagram performance. A node may transmit a reverse datagram asynchronously, at any time, regardless of its availability settings.
Node transceivers scan a list of frequencies as they operate, detecting available sectors and connecting to those with the best available signal strength. Because of the synchronous nature of iocast, this process is particularly efficient in terms of both airtime and battery use, and it does not impact datagram performance.
Each time a node connects to a new sector, it re-authenticates to maintain a secure link to its control stack intact. Sector-to-sector mobility is handled by the node transceiver and control stack, largely transparently to nodes and application servers.
With proper authorizations, nodes are able to move between sectors of different systems, thus enabling inter-system roaming.
Each time a node connects to a new system, it re-authenticates to maintain the secure link to its own control stack. Inter-system mobility is handled by the node transceiver and control stacks of the its roaming and hme system, largely transparently to nodes and application servers.
The Node Transceiver Interface (NXI) provides a dedicated hardware/software connection between a node controller and node transceiver.
The controller communicates with the transceiver through a 7-wire interface, which includes handshake lines to establish a session, and an I²C-based link for reading and writing multi-byte registers to perform various real-time functions. NXI is designed to allow both the node controller and node transceiver to enter static low-power states asynchronously, according to their own requirements. This enables the node to operate while consuming the lowest possible average power.
An application server is a software or service platform that connects to an iocast network by way of a the API. An application server communicates with its nodes to create a complete wireless application (e.g. a SCADA system or a clinical alarm manager). An application server is identified by its application identification number (appid), which is unique per system.
A base transceiver is a powerful, fixed digital radio that transmits data to node transceivers on forward channels and receives data from nodes transceivers on reverse channels. Base transceivers connect to their control stacks using the Base Transceiver Interface (BXI), and they are identified within a sector by their base transceiver identification number (bxid).
A channel is a narrowband RF channel used to transmit control and data information between node transceivers and base transeivers. Channels include forward channels and reverse channels. Node transceivers transmit to base transceivers using reverse channels, while base transceivers transmit to node transceivers using forward channels.
A control stack is the "brain" of a system, the real-time software and database required to control sectors and support application server clients. The stack includes two software components, the home controller and the sector controller. The home controller is roughly analogous to a cellular network’s Home Location Register (HLR), while the sector controller is roughly analogous to a Mobile Switching Center (MSC).
A control stack may operate as a single instance on a single server or container, or as a distributed system on a server cluster or cloud platform. Furthermore, home controllers may have many-to-many relationships with sector controllers, supporting node mobility between sectors as well as intersystem roaming.
Nodes and application servers communicate by exchanging datagrams. Application servers send forward datagrams to single nodes (unicast) or to groups (multicast). Nodes send reverse datagrams to application servers. Nodes and application servers know when their unicast datagrams are successfully delivered, and application servers know which recipients successfully receive their multicast datagrams.
Requests and Responses
Optionally, datagrams are divided into request datagrams and response datagrams. Response datagrams allow airtime- and energy-efficient support of low-level request/response protocols.
Datagrams may be natively encrypted, using a shared a private key to provide bidirectional authentication and privacy between a node or group and its control stack. Applications may use their own encryption schemes instead of or in addition to native iocast encryption.
Normal datagrams range in size from 1 byte to 8,128 bytes; however, iocast also includes short datagrams, which are optimized to carry small payloads of 12- to 48-bits. Short datagrams do not support native encryption but in other respects behave identically to normal datagrams at the API and NXI level.
A group is a sets of nodes sharing a common multicast address. A group is identified by its address, and it is conceptually owned by one control stack with which it shares a private encryption key. A group is controlled by an application server, which may transmit datagrams to the group and add/remove nodes to/from the group. Group member nodes receive, and may reply to, datagrams sent to the group’s multicast address. Each group has a group availability value (ga), which describes how often nodes in the group must listen for forward datagrams. Group addresses may be global, wherein multicast datagrams follow nodes as they roam onto other systems, or they may be local and only meaningful on one system.
A node is a wireless object that connects to an iocast system. Nodes conceptually belong to one system and one application server. While they may roam onto other systems, they may ultimately only exchange datagrams with their home system.
A node connects to its network using a node transceivers (NX), a digital radio network adapter. Node transceivers are globally, uniquely identified by their 64-bit node transceiver identification number (nxuid). They operate with a node availability value (na), which describes how often they listen for forward datagrams. This value ranges from 0 to 15, with lower values supporting faster datagram delivery and higher values supporting longer battery life. Node transceivers may be implemented as a physical module, or they may be tightly integrated into a node at a hardware and software level. Node transceivers are configured over-the-air, securely, by their home system.
A sector is a geographical area of coverage, including one or more base transceivers and two or more channels, under common control of one control stack. A node must connect to a sector before sending and receiving datagrams. Sectors are identified by their sector identification number (secid), which is unique per system.
An iocast system includes a real-time control stack plus one or more base transceivers. Systems may range in size from one building to a nation-wide network, and may connect to each other to facilitate inter-system roaming. An system is uniquely identified by its system identification number (sysid).