draft-ietf-core-coap-tcp-tls-00.txt   draft-ietf-core-coap-tcp-tls-01.txt 
CORE C. Bormann, Ed. CORE C. Bormann, Ed.
Internet-Draft Universitaet Bremen TZI Internet-Draft Universitaet Bremen TZI
Intended status: Standards Track S. Lemay Intended status: Standards Track S. Lemay
Expires: May 21, 2016 V. Solorzano Barboza Expires: May 22, 2016 V. Solorzano Barboza
Zebra Technologies Zebra Technologies
H. Tschofenig H. Tschofenig
ARM Ltd. ARM Ltd.
November 18, 2015 November 19, 2015
A TCP and TLS Transport for the Constrained Application Protocol (CoAP) A TCP and TLS Transport for the Constrained Application Protocol (CoAP)
draft-ietf-core-coap-tcp-tls-00 draft-ietf-core-coap-tcp-tls-01
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) was designed with TCP as the The Hypertext Transfer Protocol (HTTP) was designed with TCP as the
underlying transport protocol. The Constrained Application Protocol underlying transport protocol. The Constrained Application Protocol
(CoAP), while inspired by HTTP, has been defined to make use of UDP (CoAP), while inspired by HTTP, has been defined to make use of UDP
instead of TCP. Therefore, reliable delivery and a simple congestion instead of TCP. Therefore, reliable delivery and a simple congestion
control and flow control mechanism are provided by the message layer control and flow control mechanism are provided by the message layer
of the CoAP protocol. of the CoAP protocol.
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on May 21, 2016. This Internet-Draft will expire on May 22, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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+----------------------+ +----------------------+
Figure 1: The CoAP over TLS/TCP Protocol Stack Figure 1: The CoAP over TLS/TCP Protocol Stack
Since TCP offers reliable delivery, there is no need to offer a Since TCP offers reliable delivery, there is no need to offer a
redundant acknowledgement at the CoAP messaging layer. redundant acknowledgement at the CoAP messaging layer.
Since there is no need to carry around acknowledgement semantics, Since there is no need to carry around acknowledgement semantics,
messages do not require a message type; no message layer messages do not require a message type; no message layer
acknowledgement is expected or even possible. Because something acknowledgement is expected or even possible. Because something
needs to be put into the two bits indicating the message type (unless needs to be put into the two bits indicating the message type, we put
alternative L3 below is chosen), we put the bits for a Non- the bits for a Non-Confirmable message (NON) into the header. By the
Confirmable message (NON) into the header. By the nature of TCP, nature of TCP, messages are always transmitted reliably over TCP.
messages are always transmitted reliably over TCP. Figure 2 (derived Figure 2 (derived from [RFC7252], Figure 3) shows this message
from [RFC7252], Figure 3) shows this message exchange graphically. A exchange graphically. A UDP-to-TCP gateway will therefore discard
UDP-to-TCP gateway will therefore discard all empty messages, such as all empty messages, such as empty ACKs (after operating on them at
empty ACKs (after operating on them at the message layer), and re- the message layer), and re-pack the contents of all non-empty CON,
pack the contents of all non-empty CON, NON, or ACK messages (i.e., NON, or ACK messages (i.e., those ACK messages that have a piggy-
those ACK messages that have a piggy-backed response) into untyped backed response) into untyped messages (that happen to look like NON
messages (that happen to look like NON messages). messages).
Similarly, there is no need to detect duplicate delivery of a Similarly, there is no need to detect duplicate delivery of a
message. In UDP CoAP, the Message ID is used for relating message. In UDP CoAP, the Message ID is used for relating
acknowledgements to Confirmable messages as well as for duplicate acknowledgements to Confirmable messages as well as for duplicate
detection. Since the Message ID thus is not meaningful over TCP, it detection. Since the Message ID thus is not meaningful over TCP, it
is elided (as indicated by the dashes in Figure 2). is elided (as indicated by the dashes in Figure 2).
Client Server Client Server
| | | |
| (no type) [------] | | (no type) [------] |
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