E.1 GENERAL. 497E.1.1 Scope. 497E.1.2 Applicability. 497E.2 APPLICABLE DOCUMENTS. 497E.2.1 General. 497E.2.2 Government documents. 497E.2.2.1 Specifications, standards, and handbooks. 497E.2.2.2 Other Government documents, drawings, and publications. 498E.2.3 Non-Government publications. 498E.2.4 Order of precedence. 498E.3 DEFINITIONS. 498E.3.1 Standard definitions and acronyms. 498E.3.2 Abbreviations and acronyms. 498E.4 GENERAL REQUIREMENTS 499E.4.1 Introduction. 499E.4.1.1 Required HF subnetwork protocols. 500E.4.1.2 Support for Internet applications. 500E.4.1.3 Security. 501E.4.2 Electronic mail transfer. 502E.4.2.1 Mail transfer within HF networks. 502E.4.2.2 Mail retrieval by call-in users. 502E.4.3 Digital imagery transfer. (not yet standardized) 502E.4.4 Digital voice operation. (not yet standardized) 502E.4.5 Other applications. 502E.5 DETAILED REQUIREMENTS. 502E.5.1 Introduction. 502E.5.2 Electronic mail protocols. 503E.5.2.1 HF mail transfer protocol. 503E. HMTP command grouping. 503E. HMTP over TCP. 503E. HMTP without TCP. 503E.5.2.2 HF mail retrieval protocols. 503E.5.3 Digital imagery protocol. 503E.5.4 Digital voice protocol. 504E.5.5 Radio facsimile protocol. 504E.6 NOTES. 504


FIGURE E-1. HF application interoperation. 499FIGURE E-2. Application interoperation via internet gateway. 500FIGURE E-3. Application-layer mail gateway. 501



E.1.1 Scope.

This appendix contains the requirements for the prescribed protocols and directions for the implementation and use of various communications applications in HF radio networks.

E.1.2 Applicability.

Applications provide advanced technical capabilities of automated HF radio. None of the features and functions described in this appendix are mandatory requirements for the user in the acquisition of an HF radio system. However, if the user requires the features and functions described herein, they shall be provided in accordance with the technical parameters specified in this appendix.


E.2.1 General.

The documents listed in this section are specified in sections E.3, E.4, and E.5 of this standard. This section does not include documents cited in other sections of this standard or recommended for additional information or as examples. While every effort has been made to ensure the completeness of this list, document users are cautioned that they must meet all specified requirements documents cited in sections E.3, E.4, and E.5 of this standard, whether or not they are listed.

E.2.2 Government documents.

E.2.2.1 Specifications, standards, and handbooks.

The following specifications, standards, and handbooks form a part of this document to the extent specified herein. Unless otherwise specified, the issues of these documents are those listed in the issue of the Department of Defense Index of Specifications and Standards (DoDISS) and supplement thereto, cited in the solicitation.
FED-STD-1037 Telecommunications: Glossary of Telecommunication Terms

Unless otherwise indicated, copies of federal and military specifications, standards, and handbooks are available from the Naval Publications and Forms Center, ATTN: NPODS, 5801 Tabor Avenue, Philadelphia, PA 19120-5099.

E.2.2.2 Other Government documents, drawings, and publications.

The following other Government documents, drawings, and publications form a part of this document to the extent specified herein. Unless otherwise specified, the issues are those cited in the solicitation.


E.2.3 Non-Government publications.

The following documents form a part of this document to the extent specified herein. Unless otherwise specified, the issues of the documents which are DoD adopted are those listed in the issues of the DODISS cited in the solicitation. Unless otherwise specified, the issues of the documents not listed in the DODISS are the issues of the documents cited in the solicitation (see 6.3).
RFC-854Telnet Protocol specification
RFC-821Simple Mail Transfer Protocol
RFC-959File Transfer Protocol
RFC-1651SMTP Service Extensions
RFC-1730Internet Message Access Protocol - Version 4
RFC-1854SMTP Service Extensions for Command Pipelining
RFC-1939Post Office Protocol - Version 3
RFC-2068Hypertext Transfer Protocol - HTTP/1.1

(Internet documents may be obtained by anonymous file transfer protocol (ftp) from or

E.2.4 Order of precedence.

In the event of a conflict between the text of this document and the references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.


E.3.1 Standard definitions and acronyms.


E.3.2 Abbreviations and acronyms.

The abbreviations and acronyms used in this document are defined below. Those listed in the current edition of FED-STD-1037 have been included for the convenience of the reader.
ALEautomatic link establishment
ALMautomatic link maintenance
ARQautomatic repeat request
COMSECCommunications Security
e-mailelectronic mail
FTPfile transfer protocol
HFhigh frequency
HMTPHF mail transport protocol
HTTPhypertext transfer protocol
IMAP4Internet Mail Access Protocol - version 4
IPInternet Protocol
NSAPnetwork service access point
PDUprotocol data unit
POP3Post Office Protocol - version 3
SMTPsimple mail transfer protocol
TCPtransmission control protocol
UDPuser datagram protocol


E.4.1 Introduction.

Figure E-1 illustrates the relationship of application-layer protocols to the protocols defined elsewhere in this standard. Interoperation among applications in use at different stations requires that the applications and all supporting protocols at the stations interoperate. Performance will then be determined by how well the protocol stacks work with each other and with the HF medium.

FIGURE E-1. HF application interoperation.

E.4.1.1 Required HF subnetwork protocols.

To simplify the task of ensuring interoperability among applications using the HF medium, a small number of protocols is approved for use with the application protocols specified in this appendix. Systems that implement any application from this appendix shall use the following protocols to convey the corresponding application protocol data units (PDUs) over the HF medium:

E.4.1.2 Support for Internet applications.

When an HF subnetwork is connected to other subnetworks using the Internet Protocol (IP) suite, Internet applications can use the resulting Internet as illustrated in figure E-2. For Internet applications, the third-generation link-layer suite (shown in figure E-2) will generally provide higher performance than the second-generation suite.

FIGURE E-2. Application interoperation via internet gateway.

When a host computer is connected to the Internet via an HF network (e.g., HF Host in
figure E-2), most Internet applications will call upon the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP) for end-to-end transport service to the distant Internet Host. These two protocols, in turn, require the services of IP for routing packets through the Internet. HF network designers should be aware of several potential performance problems that arise when TCP and IP are used in an HF network:

a. The two protocols together add 40 bytes of overhead to each application PDU sent.

b. TCP connection setup requires an additional three-way handshake after the link establishment handshake and data link protocol startup. Each link turnaround consumes at least three interleaver times; when the MIL-STD-188-110 serial-tone modem is using its 4.8 s interleaver, this three-way handshake will add at least 43 s to the time to establish a link (at least 58 s if the data rate is 75 bps).

c. The TCP congestion avoidance mechanisms can significantly reduce throughput each time the HF data link throughput changes abruptly.

For electronic mail (e-mail) transport through HF networks, an application-layer mail gateway can be employed at the boundary of the HF network that will eliminate the need for TCP within the HF network (see figure E-3). However, interactive applications (e.g., remote terminals, file

transfer, and web browsing) will generally require the use of TCP.

FIGURE E-3. Application-layer mail gateway.

E.4.1.3 Security.

Figures E-1, E-2, and E-3 show optional encryption of application data. If Communications Security (COMSEC) is implemented in this way, the control information conveyed to lower layers shall bypass encryption using an approved method. Link layer encryption may also be used. Further COMSEC considerations are beyond the scope of this appendix.

E.4.2 Electronic mail transfer.

An HF e-mail system will be found to comply with this appendix if it conveys e-mail through HF networks using the required HF subnetwork protocols (see Required HF subnetwork protocols above) and the HF Mail Transfer Protocol (HMTP) described in E.5.2.1 (HF Mail Transfer Protocol).

E.4.2.1 Mail transfer within HF networks.

Mail shall be transferred within HF networks using HMTP, except as provided in the next paragraph. Wherever possible, application-layer mail gateways (see figure E-3) shall be employed to translate between SMTP and HMTP at the boundaries of the HF subnetwork, so that TCP is not used to convey mail over HF links.

E.4.2.2 Mail retrieval by call-in users.

When connectivity to a user is too infrequent to use HMTP to push messages to that user's host computer, a mail drop should be created at a host that can usually be reached by that user over a single HF link. One of the mail retrieval protocols from E.5.2.2 (HF mail retrieval protocols) shall be used to pull mail from the mail drop host to the user's host.

E.4.3 Digital imagery transfer. (not yet standardized)

E.4.4 Digital voice operation. (not yet standardized)

E.4.5 Other applications.

Interactive applications such as file transfer and hypertext transfer (in support of the worldwide web) shall employ the usual Internet application protocols for those applications:
ApplicationProtocol Reference
Remote terminaltelnet RFC-854
File transferFile Transfer Protocol (FTP) RFC-959
Hypertext transferHypertext Transfer Protocol (HTTP) RFC-2068

TCP shall be implemented at the client and server hosts that support these applications. IP and related protocols shall be implemented at client and server hosts and at subnetwork gateways (often termed "routers") that interconnect HF subnetworks with other subnetworks (see
figure E-2). Neither TCP nor IP is needed at other HF nodes.


E.5.1 Introduction.

The functions supported by the protocols specified in this section are optional. However, when the functionality provided by one of these protocols is required, that protocol shall be implemented as specified to provide that functionality.

E.5.2 Electronic mail protocols.

The HMTP shall be used to "push" e­mail messages through HF networks from one mail server to the next. The Post Office Protocol version 3 (POP3) or the Internet Mail Access Protocol version 4 (IMAP4) shall be used within HF networks to retrieve ("pull") e­mail messages from servers.

E.5.2.1 HF mail transfer protocol.

The HF Mail Transfer Protocol (HMTP) is an extended version of the Simple Mail Transfer Protocol (SMTP). HMTP clients and servers shall implement SMTP in accordance with RFC 821, the SMTP service extension ("EHLO") protocol in accordance with RFC 1651, and command pipelining in accordance with RFC 1854.

E. HMTP command grouping.

When connected to a server that supports command pipelining, HMTP clients shall group commands to the maximum extent permitted in RFC 1854:

a. All setup commands, including RSET (if required), MAIL, RCPT, and DATA, for each message shall be sent as a single group.

b. Multiple messages sent to a single server shall be chained by appending the setup commands for each subsequent message to the message body of the preceding message.

When connected to a server that does not support command pipelining, HMTP clients shall execute SMTP in its basic interlocked mode in accordance with RFC 821.

E. HMTP over TCP.

When HMTP uses TCP transport services, it shall listen on TCP port 25 (the well-known SMTP port), and, in general, use TCP in the same manner as does SMTP.

E. HMTP without TCP.

When TCP is not used to transport HMTP data, the HMTP server shall listen for calls on network service access point (NSAP) 8 of the HF subnetwork service.

E.5.2.2 HF mail retrieval protocols.

When a user is usually not reachable (i.e., the user connects sporadically to pick up e­mail), HMTP will not be appropriate for delivery of mail to that user. In such cases, POP3 in accordance with RFC 1939 or IMAP4 in accordance with RFC 1730 shall be used to retrieve mail from a mail drop server (see E.4.2.2). Messages sent by such users shall be conveyed to the server using HMTP.

E.5.3 Digital imagery protocol.

(not yet standardized)

E.5.4 Digital voice protocol.

(not yet standardized)

E.5.5 Radio facsimile protocol.

(not yet standardized)