[BXXPwg] new BEEP tcpmapping draft (in HTML)

Marshall T. Rose mrose+mtr.netnews@dbc.mtview.ca.us
Thu, 4 Jan 2001 21:08:39 -0800


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<html><head><title>Mapping the BEEP Core onto TCP</title>
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height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<table width=3D"66%" border=3D"0" cellpadding=3D"0" =
cellspacing=3D"0"><tr><td><table width=3D"100%" border=3D"0" =
cellpadding=3D"2" cellspacing=3D"1">
<tr valign=3D"top"><td width=3D"33%" bgcolor=3D"#666666" =
class=3D"header">Network Working Group</td><td width=3D"33%" =
bgcolor=3D"#666666" class=3D"header">M.T. Rose</td></tr>
<tr valign=3D"top"><td width=3D"33%" bgcolor=3D"#666666" =
class=3D"header">Internet-Draft</td><td width=3D"33%" =
bgcolor=3D"#666666" class=3D"header">Invisible Worlds, Inc.</td></tr>
<tr valign=3D"top"><td width=3D"33%" bgcolor=3D"#666666" =
class=3D"header">Expires: July 5, 2001</td><td width=3D"33%" =
bgcolor=3D"#666666" class=3D"header">January 4, 2001</td></tr>
</table></td></tr></table>
<div align=3D"right"><font face=3D"monaco, MS Sans Serif" =
color=3D"#990000" size=3D"+3"><b><br><span class=3D"title">Mapping the =
BEEP Core onto TCP</span></b></font></div>
<div align=3D"right"><font face=3D"monaco, MS Sans Serif" =
color=3D"#666666" size=3D"+2"><b><span =
class=3D"filename">draft-ietf-beep-tcpmapping-06</span></b></font></div>
<font face=3D"verdana, helvetica, arial, sans-serif" size=3D"2">

<h3>Status of this Memo</h3>
<p>
This document is an Internet-Draft and is in full conformance with all =
provisions of Section 10 of RFC2026.</p>
<p>
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups.
Note that other groups may also distribute working documents as
Internet-Drafts.</p>
<p>
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any =
time.
It is inappropriate to use Internet-Drafts as reference material or to =
cite
them other than as "work in progress."</p>
<p>
The list of current Internet-Drafts can be accessed at
<a =
href=3D'http://www.ietf.org/ietf/1id-abstracts.txt'>http://www.ietf.org/i=
etf/1id-abstracts.txt</a>.</p>
<p>
The list of Internet-Draft Shadow Directories can be accessed at
<a =
href=3D'http://www.ietf.org/shadow.html'>http://www.ietf.org/shadow.html<=
/a>.</p>
<p>
This Internet-Draft will expire on July 5, 2001.</p>

<h3>Copyright Notice</h3>
<p>
Copyright (C) The Internet Society (2001). All Rights Reserved.</p>

<h3>Abstract</h3>

<p>
This memo describes how a BEEP session is mapped onto
a single TCP connection.
</p>
<a name=3D"toc"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>Table of Contents</h3>
<ul compact class=3D"toc">
<b><a href=3D"#anchor1">1.</a>&nbsp;
Introduction<br></b>
<b><a href=3D"#anchor2">2.</a>&nbsp;
Session Management<br></b>
<b><a href=3D"#anchor3">3.</a>&nbsp;
Message Exchange<br></b>
<b><a href=3D"#anchor4">3.1</a>&nbsp;
Flow Control<br></b>
<b><a href=3D"#anchor5">3.1.1</a>&nbsp;
Channel Creation<br></b>
<b><a href=3D"#anchor6">3.1.2</a>&nbsp;
Sending Messages<br></b>
<b><a href=3D"#flow.seq">3.1.3</a>&nbsp;
Processing SEQ Frames<br></b>
<b><a href=3D"#flow.use">3.1.4</a>&nbsp;
Use of Flow Control<br></b>
<b><a href=3D"#anchor7">4.</a>&nbsp;
Security Considerations<br></b>
<b><a href=3D"#rfc.references">&#167;</a>&nbsp;
References<br></b>
<b><a href=3D"#rfc.authors">&#167;</a>&nbsp;
Author's Address<br></b>
<b><a href=3D"#anchor8">A.</a>&nbsp;
Acknowledgements<br></b>
<b><a href=3D"#rfc.copyright">&#167;</a>&nbsp;
Full Copyright Statement<br></b>
</ul>
<br clear=3D"all">

<a name=3D"anchor1"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>1.&nbsp;Introduction</h3>

<p>
This memo describes how a <a href=3D"#BEEP-CORE">BEEP</a>[1] session
is mapped onto a single <a href=3D"#RFC0793">TCP</a>[2] connection.
Refer to Section 2.5 of <a href=3D"#BEEP-CORE">[1]</a> for an =
explanation of
the mapping requirements.
</p>

<a name=3D"anchor2"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>2.&nbsp;Session Management</h3>

<p>
The mapping of BEEP session management onto the TCP service is
straight-forward.
</p>

<p>
A BEEP session is established when a TCP connection is established
between two BEEP peers:

<ul class=3D"text">

<li>
the BEEP peer that issues a passive TCP OPEN call is termed the
listener; and,
</li>

<li>
the BEEP peer that issues an active TCP OPEN call is termed the
initiator.
</li>

</ul>

</p>

<p>
If both peers agree to release a BEEP session
(c.f., <a href=3D"#BEEP-CORE">[1]</a>'s Section 2.4),
the peer sending the "ok" reply, immediately issues the TCP CLOSE call.
Upon receiving the reply,
the other peer immediately issues the TCP CLOSE call.
</p>

<p>
A BEEP session is terminated when either peer issues the TCP ABORT call,
and the TCP connection is subsequently aborted.
</p>

<a name=3D"anchor3"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>3.&nbsp;Message Exchange</h3>

<p>
The mapping of BEEP exchanges onto the TCP service is less
straight-forward.
</p>

<p>
Messages are reliably sent and received using TCP's SEND and RECEIVE
calls.
(This also provides ordered delivery of messages on the same channel.)
</p>

<p>
Although TCP imposes flow control on a per-connection basis,
if multiple channels are simultaneously in use on a BEEP session,
BEEP must provide a mechanism to avoid starvation and deadlock.
To achieve this,
BEEP re-introduces a mechanism used by the TCP:
window-based flow control &#151;
each channel has a sliding window that indicates the number of payload
octets that a peer may transmit before receiving further permission.
</p>

<p>

</p>

<h4><a name=3D"anchor4">3.1</a>&nbsp;Flow Control</h4>

<p>
Recall from Section 2.2.1.2 of <a href=3D"#BEEP-CORE">[1]</a> that
every payload octet sent in each direction on a channel has an
associated sequence number.
Numbering of payload octets within a data frame is such that the first
payload octet is the lowest numbered,
and the following payload octets are numbered consecutively.
</p>

<p>
The actual sequence number space is finite,
though very large,
ranging from 0..4294967295 (2**32 - 1).
Since the space is finite,
all arithmetic dealing with sequence numbers is performed modulo 2**32.
This unsigned arithmetic preserves the relationship of sequence
numbers as they cycle from 2**32 - 1 to 0 again.
Consult Sections 2 through 5 of <a href=3D"#RFC1982">[3]</a> for a
discussion of the arithmetic properties of sequence numbers.
</p>

<h4><a name=3D"anchor5">3.1.1</a>&nbsp;Channel Creation</h4>

<p>
When a channel is created,
the sequence number associated with the first payload octet of the
first data frame is 0,
and the initial window size for that channel is 4096 octets.
After channel creation,
a BEEP peer may update the window size by
<a href=3D"#flow.seq">sending a SEQ frame</a>.
</p>

<p>
If a BEEP peer is asked to create a channel and it is unable to
allocate at least 4096 octets for that channel,
it must decline creation of the channel,
as specified in Section 2.3.1.2 of <a href=3D"#BEEP-CORE">[1]</a>.
Similarly,
during establishment of the BEEP session,
if the BEEP peer acting in the listening role is unable to allocate at
least 4096 octets for channel 0,
then it must return a negative reply,
as specified in Section 2.4 of <a href=3D"#BEEP-CORE">[1]</a>,
instead of a greeting.
</p>

<p>

</p>

<h4><a name=3D"anchor6">3.1.2</a>&nbsp;Sending Messages</h4>

<p>
Before a message is sent,
the sending BEEP peer must ensure that the size of the payload is within
the window advertised by the receiving BEEP peer.
If not,
it has three choices:

<ul class=3D"text">

<li>
if the window would allow for at least one payload octet to be
sent,
the BEEP peer may segment the message and start by sending a smaller
data frame
(up to the size of the remaining window);
</li>

<li>
the BEEP peer may delay sending the message until the
window becomes larger; or,
</li>

<li>
the BEEP peer may signal to its application that it is unable to
send the message,
allowing the application to try again at a later time
(or perhaps signaling its application when a larger window is =
available).
</li>

</ul>

The choice is implementation-dependent,
although it is recommended that the application using BEEP be
given a mechanism for influencing the decision.
</p>

<p>

</p>

<h4><a name=3D"flow.seq">3.1.3</a>&nbsp;Processing SEQ Frames</h4>

<p>
As an application accepts responsibility for incoming data frames,
its BEEP peer should send SEQ frames to advertise a new window.
</p>

<p>
The <a href=3D"#RFC2234">ABNF</a>[4] for a SEQ frame is:
</p>
</font><pre>
    seq        =3D "SEQ" SP channel SP ackno SP window CR LF

    ackno      =3D seqno

    window     =3D size

    ; channel, seqno, and size are defined in Section 2.2.1 of [1].
</pre><font face=3D"verdana, helvetica, arial, sans-serif" size=3D"2">

<p>
The SEQ frame has three parameters:

<ul class=3D"text">

<li>
a channel number;
</li>

<li>
an acknowledgement number,
that indicates the value of the next sequence number that the sender
is expecting to receive on this channel; and,
</li>

<li>
a window size,
that indicates the number of payload octets beginning with the one
indicated by the acknowledgement number that the sender is expecting to
receive on this channel.
</li>

</ul>

A single space character (decimal code 32, " ") separates each
component.
The SEQ frame is terminated with a CRLF pair.
</p>

<p>
When a SEQ frame is received,
if any of the channel number, acknowledgement number, or window size
cannot be determined or is invalid,
then the BEEP session is terminated without generating a response,
and it is recommended that a diagnostic entry be logged.
</p>

<p>

</p>

<h4><a name=3D"flow.use">3.1.4</a>&nbsp;Use of Flow Control</h4>

<p>
The key to successful use of flow control within BEEP is to balance
performance and fairness:

<ul class=3D"text">

<li>
large messages should be segmented into frames no larger than two-thirds
of TCP's negotiated maximum segment size;
</li>

<li>
frames for different channels with traffic ready to send should be
sent in a round-robin fashion;
</li>

<li>
each time a frame is received,
a SEQ frame should be sent whenever the window size that will be sent is
at least one half of the buffer space available to this channel; and,
</li>

<li>
if the transport service presents multiple frames to a BEEP peer
simultaneously,
then a single consolidating SEQ frame may be sent.
</li>

</ul>

In order to avoid pathological interactions with the transport
service,
it is important that a BEEP peer advertise windows based on available
buffer space,
to allow data to be read from the transport service as soon as
available.
Further,
SEQ frames for a channel must have higher priority than messages
for that channel.
</p>

<p>
Implementations may wish to provide queue management facilities to the
application using BEEP,
e.g., channel priorities, (relative) buffer allocations, and so on.
In particular,
implementations should not allow a given channel to monopolize the
underlying transport window
(e.g., slow readers should get small windows).
</p>

<p>
In addition,
where possible,
implementations should support transport layer APIs that convey
congestion information.
These APIs allow an implementation to determine its share of the
available bandwidth,
and also be notified of changes in the estimated path bandwidth.
Note that when a BEEP session has multiple channels that are
simultaneously exchanging large messages,
implementations without access to this information may have uncertain
fairness and progress properties during times of network congestion.
</p>

<p>
Finally,
implementors should follow the guidelines given in the relevant portions
of <a href=3D"#RFC1122">RFC1122</a>[5] that deal with flow control=20
(and bear in mind that issues such as retransmission,
while they interact with flow control in TCP,
are not applicable to this memo).
For example,
Section 4.2.2.16 of <a href=3D"#RFC1122">RFC1122</a>[5] indicates
that a "receiver SHOULD NOT shrink the window, i.e., move the right
window edge to the left" and then discusses the impact of this rule on
unacknowledged data.
In the context of mapping BEEP onto a single TCP connection,
only the portions concerning flow control should be implemented.
</p>

<a name=3D"anchor7"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>4.&nbsp;Security Considerations</h3>

<p>
Consult Section <a href=3D"#BEEP-CORE">[1]</a>'s Section 9 for a
discussion of security issues.
</p>
<a name=3D"rfc.references"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>
References</h3>
<table width=3D"99%" border=3D"0">
<tr><td class=3D"author-text" valign=3D"top"><b><a =
name=3D"BEEP-CORE">[1]</a></b></td>
<td class=3D"author-text"><a href=3D"mailto:mrose@invisible.net">Rose, =
M.T.</a>, "<a =
href=3D"http://www.ietf.org/internet-drafts/draft-ietf-beep-framework-10.=
txt">The Blocks Extensible Exchange Protocol Core</a>", =
draft-ietf-beep-framework-10 (work in progress), January 2001.</td></tr>
<tr><td class=3D"author-text" valign=3D"top"><b><a =
name=3D"RFC0793">[2]</a></b></td>
<td class=3D"author-text">Postel, J., "<a =
href=3D"ftp://ftp.isi.edu/in-notes/rfc793.txt">Transmission Control =
Protocol</a>", RFC 793, STD 7, Sep 1981.</td></tr>
<tr><td class=3D"author-text" valign=3D"top"><b><a =
name=3D"RFC1982">[3]</a></b></td>
<td class=3D"author-text"><a href=3D"mailto:kre@munnari.OZ.AU">Elz, =
R.</a> and <a href=3D"mailto:randy@psg.com">R. Bush</a>, "<a =
href=3D"ftp://ftp.isi.edu/in-notes/rfc1982.txt">Serial Number =
Arithmetic</a>", RFC 1982, August 1996.</td></tr>
<tr><td class=3D"author-text" valign=3D"top"><b><a =
name=3D"RFC2234">[4]</a></b></td>
<td class=3D"author-text"><a href=3D"mailto:dcrocker@imc.org">Crocker, =
D. H.</a> and <a href=3D"mailto:paulo@turnpike.com">P. Overell</a>, "<a =
href=3D"ftp://ftp.isi.edu/in-notes/rfc2234.txt">Augmented BNF for Syntax =
Specifications: ABNF</a>", RFC 2234, November 1997.</td></tr>
<tr><td class=3D"author-text" valign=3D"top"><b><a =
name=3D"RFC1122">[5]</a></b></td>
<td class=3D"author-text"><a href=3D"mailto:Braden@ISI.EDU">Braden, =
R.</a>, "<a href=3D"ftp://ftp.isi.edu/in-notes/rfc1122.txt">Requirements =
for Internet Hosts -- Communication Layers</a>", RFC 1122, October =
1989.</td></tr>
</table>

<a name=3D"rfc.authors"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>Author's Address</h3>
<table width=3D"99%" border=3D"0" cellpadding=3D"0" cellspacing=3D"0">
<tr><td class=3D"author-text">&nbsp;</td>
<td class=3D"author-text">Marshall T. Rose</td></tr>
<tr><td class=3D"author-text">&nbsp;</td>
<td class=3D"author-text">Invisible Worlds, Inc.</td></tr>
<tr><td class=3D"author-text">&nbsp;</td>
<td class=3D"author-text">1179 North McDowell Boulevard</td></tr>
<tr><td class=3D"author-text">&nbsp;</td>
<td class=3D"author-text">Petaluma, CA  94954-6559</td></tr>
<tr><td class=3D"author-text">&nbsp;</td>
<td class=3D"author-text">US</td></tr>
<tr><td class=3D"author" align=3D"right">Phone:&nbsp;</td>
<td class=3D"author-text">+1 707 789 3700</td></tr>
<tr><td class=3D"author" align=3D"right">EMail:&nbsp;</td>
<td class=3D"author-text"><a =
href=3D"mailto:mrose@invisible.net">mrose@invisible.net</a></td></tr>
<tr><td class=3D"author" align=3D"right">URI:&nbsp;</td>
<td class=3D"author-text"><a =
href=3D"http://invisible.net/">http://invisible.net/</a></td></tr>
</table>

<a name=3D"anchor8"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>Appendix A.&nbsp;Acknowledgements</h3>

<p>
The author gratefully acknowledges the contributions of:
Dave Crocker,
Steve Harris,
Eliot Lear,
Keith McCloghrie,
Craig Partridge,
Vernon Schryver,
and,
Joe Touch.
In particular,
Dave Crocker provided helpful suggestions on the nature of=20
flow control in the mapping.
</p>
<a name=3D"rfc.copyright"><br><hr size=3D"1" shade=3D"0"></a>
<table border=3D"0" cellpadding=3D"0" cellspacing=3D"2" width=3D"30" =
height=3D"15" align=3D"right"><tr><td bgcolor=3D"#990000" =
align=3D"center" width=3D"30" height=3D"15"><a href=3D"#toc" =
CLASS=3D"link2"><font face=3D"monaco, MS Sans Serif" color=3D"#ffffff" =
size=3D"1"><b>&nbsp;TOC&nbsp;</b></font></a><br></td></tr></table>
<h3>Full Copyright Statement</h3>
<p class=3D'copyright'>
Copyright (C) The Internet Society (2001). All Rights Reserved.</p>
<p class=3D'copyright'>
This document and translations of it may be copied and furnished to
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<p class=3D'copyright'>
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.</p>
<p class=3D'copyright'>
This document and the information contained herein is provided on an
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<h3>Acknowledgement</h3>
<p class=3D'copyright'>
Funding for the RFC editor function is currently provided by the
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