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Create the GIG from smaller component building blocks
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Design with interoperability, evolvability, and simplicity in mind
The Transport layer (OSI Layer 4)
The OSI reference model transport layer (layer 4) defines the rules for information exchange and manages end-to-end delivery of information within and between networks, including making provision for error recovery and flow control. It also repackages long messages when necessary into smaller packets for transmission and, at the receiving end, rebuilds packets into the original message. Depending upon which
APPENDIX E – INTEROPERABILITY STANDARDS
Page E-2
layer 4 protocol is in use, the receiving terminal’s transport layer may send acknowledgments of receipt of packets. Two layer 4 protocols are recommended and both should be present on both the transmitting and receiving platforms. The receiver should be able to determine which protocol the transmitting system utilized by the information in the packet header.
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User datagram protocol (UDP), IETF Standard 6, IETF RFC 768. This is a mandated standard identified in the DISR. UDP is used when transport layer delivery assurance of packets sent over the data link is not required (e.g., in the transmission of video frames, a condition where tolerance of errors and/or missing frames is high and low latency is important).
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Transport control protocol (TCP), IETF Standard 7, IETF RFC 793. This is a mandated standard identified in the DISR. The TCP [RFC 761] provides a connection oriented reliable byte stream service. TCP is a bi-directional protocol, which has no concept of messages. Any framing has to be added at the application level. TCP contains an acknowledgement scheme which makes it reliable (bytes are delivered correctly and in order) and which implements flow control.
The Network Layer (OSI Layer 3)
In the OSI reference model, the network layer (layer 3) provides a means for addressing messages and translating logical addresses and names into physical addresses. It also provides a means for determining the route from the source to the destination computer and manages traffic problems, such as switching, routing, and controlling the congestion of data packets. The ubiquitous standard for layer 3 networking is the Internet Protocol (IP). IP version 4 (IPv4) is currently in widespread usage. IP version 6 (IPv6) is an emerging standard that is in development, and mandated for DoD usage with a transition completion goal of 2008, per DoD-CIO memoranda dated 9 June 2003.
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