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 -