Connectivity Framework
5: Connectivity Transport Layer
Messaging protocols may be configured and optimized for different network layer configurations. Network layer parameters such as bandwidth, round-trip time and maximum message size should inform the selection of the messaging protocol quality of service.
5.1.2 COMMUNICATION MODES
A connectivity transport may support the following communication modes:
• unicast— suitable for one-to-one communication between two endpoints,
• multicast— suitable for one-to-many communication between endpoints and
• broadcast— suitable for one-to-all communication between endpoints, where“ all” refers to all the endpoints present on the communication transport network at the time of transmission.
5.1.3 ENDPOINT ADDRESSING
Any of the nodes( for example, a device or an application host) in IIoT systems can house one or more components, each with one or more connectivity endpoints. An address identifies a node for network-level communication purposes. This address could be locally unique and possibly globally unique. A node and hence the endpoints residing on it may be reachable over multiple addresses.
The addressing scheme and associated infrastructure should support endpoints on the Internet scale.
5.1.4 CONNECTEDNESS
Network layer protocols( see Figure 2-1) offer either connection-oriented or connectionless services for delivering packets across the network. Connectionless services are more common at the network layer. In many protocol suites, the network-layer protocol is connectionless, and the transport layer provides connection-oriented services. For example, in TCP / IP, the Internet Protocol( IP) and the User Datagram Protocol( UDP) layered on top of it are connectionless, while the Transmission Control Protocol( TCP) is connection-oriented.
A connectionless transport is best for low latency and jitter applications or when a high degree of scalability is required in a local area network. The connectionless UDP transport has proven itself for use real-time applications.
A connection-oriented transport is best suited for high throughput applications in a network with complex topology and high variation of traffic loads, since it provides a“ virtual circuit” that reduces the variation in routing path. The connection-oriented TCP transport is battle tested for transiting through firewalls and network address translation( NAT) routers, and connecting across wide area networks. New applications may call for connection-oriented connectivity transports that do not suffer the drawbacks that we find in TCP today, such as unbounded retransmission delays.
When using a connectionless transport, the connectivity framework design needs to handle failures in the transport caused by loss or out-of-order packets. Consequently, designing a
IIC: PUB: G5: V1.0: PB: 20170228- 39-