Internet DRAFT - draft-worley-sip-he-connection
draft-worley-sip-he-connection
SIPCORE O. Johansson
Internet-Draft Edvina AB
Intended status: Standards Track G. Salgueiro
Expires: June 15, 2017 Cisco Systems
D. Worley
Ariadne
December 12, 2016
Happy EarBalls: Success with Dual-Stack, Connection-Oriented SIP
draft-worley-sip-he-connection-01
Abstract
The Session Initiation Protocol (SIP) supports multiple transports
running both over IPv4 and IPv6 protocols. In more and more cases, a
SIP user agent (UA) is connected to multiple network interfaces. In
these cases setting up a connection from a dual stack client to a
dual stack server may suffer from the issues described in RFC 6555
[RFC6555] ("Happy Eyeballs") - significant delays in the process of
setting up a working flow to a server. This negatively affects user
experience.
This document builds on RFC 6555 and explains how a [RFC3261]
compliant SIP implementation can minimize delays when contacting a
host name (obtained by using DNS NAPTR and SRV lookups) in a dual
stack network using connection-oriented transport protocols.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on June 15, 2017.
Johansson, et al. Expires June 15, 2017 [Page 1]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Conventions Used in This Document . . . . . . 3
3. DNS Procedures in a Dual-Stack Network . . . . . . . . . . . 4
4. Establishing a Connection . . . . . . . . . . . . . . . . . . 5
4.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. Address Preferences . . . . . . . . . . . . . . . . . 6
4.1.2. Stateful Behavior . . . . . . . . . . . . . . . . . . 6
4.1.3. Reset on Network (Re-)Initialization . . . . . . . . 7
4.1.4. Abandon Non-Winning Connections . . . . . . . . . . . 7
5. Using an Existing Connection . . . . . . . . . . . . . . . . 8
6. Additional Considerations . . . . . . . . . . . . . . . . . . 8
6.1. Preemtive Actions . . . . . . . . . . . . . . . . . . . . 8
6.2. Determining the Type of an Address . . . . . . . . . . . 9
6.3. Debugging and Troubleshooting . . . . . . . . . . . . . . 9
6.4. Three or More Interfaces . . . . . . . . . . . . . . . . 9
6.5. Multiple A and AAAA Resource Records . . . . . . . . . . 9
6.6. Connection Timeout . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. History . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Changes from draft-worley-sip-he-connection-00 to draft-
worley-sip-he-connection-01 . . . . . . . . . . . . . . . 11
9.2. Changes from draft-johansson-sip-he-connection-01 to
draft-worley-sip-he-connection-00 . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
Johansson, et al. Expires June 15, 2017 [Page 2]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] and the documents
that extended it provide support for both IPv4 and IPv6. However,
this support has problems with environments that are characteristic
of the transitional migratory phase from IPv4 to IPv6 networks.
During this phase, many server and client implementations run on
dual-stack hosts. In such environments, a dual-stack host will
likely suffer greater connection delay, and by extension an inferior
user experience, than an IPv4-only host. The need to remedy this
diminished performance of dual-stack hosts led to the development of
the "Happy Eyeballs" [RFC6555] algorithm, which has since been
implemented in many protocols and applications.
This document revises the the [RFC3263] procedures to apply the
"Happy Eyeballs" framework. A dual-stack client using connection-
oriented transport should set up multiple connections in parallel, to
targets based on the result of DNS queries. This document starts at
the point where a SIP implementation has a host name that resolves
using A and AAAA records. Such a host name can either be the host
part of a SIP URI (possibly including a port number) or the result of
a lookup using DNS NAPTR and SRV records as described in RFC 3263 (as
updated by RFC 7984[RFC7984]).
Procedures for connectionless transport protocols for SIP are outside
the scope of this document. Procedures allowing a client to change
the order of contacting targets that were derived from different host
names are outside the scope of this document.
The concepts in this document are elaborated from those developed in
[RFC6555], and so some background information in RFC 6555 is not
repeated here. The reader is encouraged to read the available
documentation regarding implementations of RFC 6555, as well as study
Open Source implementations, in order to learn from the experience
accumulated since the publishing of RFC 6555 in 2012.
2. Terminology and Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
RFC 3261 [RFC3261] defines additional terms used in this document
that are specific to the SIP domain such as "proxy"; "registrar";
"redirect server"; "user agent server" or "UAS"; "user agent client"
or "UAC"; "back-to-back user agent" or "B2BUA"; "dialog";
"transaction"; "server transaction".
Johansson, et al. Expires June 15, 2017 [Page 3]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
This document uses the term "SIP Server" that is defined to include
the following SIP entities: user agent server, registrar, redirect
server, a SIP proxy in the role of user agent server, and a B2BUA in
the role of a user agent server.
This document also uses the following terminology to make clear
distinction between SIP entities supporting only IPv4, only IPv6 or
supporting both IPv4 and IPv6.
IPv4-only UA/UAC/UAS: An IPv4-only UA/UAC/UAS supports SIP signaling
and media only on the IPv4 network. It does not understand IPv6
addresses.
IPv6-only UA/UAC/UAS: An IPv6-only UA/UAC/UAS supports SIP signaling
and media only on the IPv6 network. It does not understand IPv4
addresses.
IPv4/IPv6 UA/UAC/UAS: A UA/UAC/UAS that supports SIP signaling and
media on both IPv4 and IPv6 networks; such a UA/UAC/UAS is known
(and will be referred to in this document) as a "dual-stack"
[RFC4213] UA/UAC/UAS.
Discussion: Do we need special handling of websocket transport?
While this document uses the term "dual-stack" based on RFC 6555 and
earlier terminology, the authors acknowledge that the same solution
can be applied to multi-interface environments as well as future
versions of IP alongside with the current ones.
3. DNS Procedures in a Dual-Stack Network
A SIP client uses DNS to find a server based on a SIP URI. This
process is described in [RFC3263] and updated in [RFC7984]. Using
this process, a list of "targets" is constructed, where each target
consists of an IP address, a port number, and a protocol (e.g., TCP,
UDP, TLS) by which to contact that address/port. The process
proceeds by constructing a sequence of host names, possibly by
looking up NAPTR and/or SRV DNS records, and then for each host name
looking up DNS address records (for all address families supported by
the client) to generate the list of IP addresses for targets that are
derived from that host name. The addresses for each host name are
ordered using the client's destination selection rules[RFC6724]. The
sorted targets for all the host names are then concatenated into the
sequence of targets to which the client will attempt to send the SIP
message.
Previously, the client contacts the targets in order until one is
contacted successfully. In order to contact a target, the client
Johansson, et al. Expires June 15, 2017 [Page 4]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
establishes a transport connection (if necessary), sends the message
using the transport (possibly resending the message several times),
and then (for requests) waits for a response (either provisional or
final). The process ends successfully if the client receives a
response. The process ends unsuccessfully if the client receives a
permanent error from the transport layer or if a SIP timer (Timer B
or Timer F in [RFC3261]) expires. Timeouts generally default to 32
seconds.
If the user has to wait for even one timeout, this will seriously
degrade the user experience. Thus, it is desirable to minimize the
number of times the client has timeouts when sending requests.
If the target list contains both IPv6 addresses and IPv4 addresses,
this procedure can degrade the user's experience in common
situations. Typically, this problem arises when the client has an
IPv6 interface, the server's preferred address is an IPv6 address,
but the transit networks between the client and server do not carry
IPv6. This can cause the client to attempt to send a SIP request for
32 seconds before it times out that target and continues with an IPv4
target. This problem parallels a problem that was widely seen in web
browsers that was cured by specifying that web browsers should use a
"Happy Eyeballs" algorithm[RFC6555] to determine the order in which
to contact target addresses.
This document specifies an amendment to these procedures, by which
the subsequences of targets derived from individual host names may be
contacted in a different order than is specified by the destination
selection rules. As in [RFC6555], the algorithm that the client uses
is not specified by this document, but this document places
requirements on the algorithm that improve the user's experience
without unduly burdening the Internet infrastructure. By analogy
with the name "Happy Eyeballs" for similar algorithms in web
browsers, we label these algorithms "Happy EarBalls"[UD].
This document modifies the transport procedures only in the case when
all targets for a host name have connection-oriented protocols
(currently, TCP, TLS, and SCTP). Other cases are outside the scope
of this document. The case of SIP using WebSocket transport is
outside the scope of this document because there is only one
transport target, the WebSocket transport provided by the context.
4. Establishing a Connection
This section discusses the situation that most closely resembles RFC
6555, which is when the SIP client has no active connection to any of
the targets in a subsequence of targets derived from one host name.
This specification allows the client to attempt to send a request to
Johansson, et al. Expires June 15, 2017 [Page 5]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
targets in the subsequence in a different order than is prescribed by
RFC 3262 and RFC 6724. In addition, this specification allows the
client to attempt to initiate a connection to a target without
subsequently sending a request to the target. However, the algorithm
which the client uses use meet the constraints in this section.
Typically, the SIP client will set up two connections, with some head
start for one address family (which is possibly be configurable) and
then select the first completed connection for use and close the
other one. The SIP message is sent on the selected connection only.
The reason for this approach is to avoid the timeout associated with
sending an unsuccessful SIP request, requiring the client to wait for
a timeout before the request can be sent on a connection to another
target - which in the case of SIP with default timers is 32 seconds.
Waiting for timeout before trying with a secondary address will lead
to a very poor user experience.
4.1. Requirements
The following requirements apply to any implementation that takes
advantage of the relaxed requirements on message transmission
specified by this document.
4.1.1. Address Preferences
An implementation MUST prefer the first IP address family returned by
the host's address preference policy, unless it implements a stateful
algorithm as described in Section 4.1.2. This usually means giving
preference to IPv6 over IPv4, although that preference can be
overridden by user configuration or by network configuration. If the
host's policy is unknown or not attainable, the implementation MUST
prefer IPv6 over IPv4.
4.1.2. Stateful Behavior
The algorithm may be stateful -- that is, the algorithm will remember
that IPv6 always fails, or that IPv6 to certain prefixes always
fails, and so on. This section constrains such algorithms.
Stateless algorithms, which do not remember the success/failure of
previous connections, are not discussed in this section.
After making a connection attempt using the preferred address family
(e.g., IPv6) and failing to establish a connection within a certain
time period (see Section 6.6), a Happy EarBalls implementation will
decide to initiate a second connection attempt using the same address
family or the other address family.
Johansson, et al. Expires June 15, 2017 [Page 6]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
Such an implementation MAY make prioritize making subsequent
connection attempts (to the same host or to other hosts) using the
successful address family (e.g., IPv4). So long as new connections
are being attempted by the host, such an implementation MUST
occasionally make connection attempts using the host's preferred
address family, as that family may have become functional again, and
the client SHOULD do so every 10 minutes. The 10-minute delay before
retrying a failed address family avoids the simple doubling of
connection attempts on both IPv6 and IPv4. This can be achieved by
flushing Happy EarBalls state every 10 minutes, which does not
significantly harm the application's subsequent connection setup
time. If connections using the preferred address family are again
successful, the preferred address family MUST be used for subsequent
connections. A stateful implementation MAY track connection success
and failure based on IPv6 or IPv4 prefix. E.g., connections to
addresses with the same prefix as the interface's address may be
successful whereas connections to addresses with different prefixes
fail.
4.1.3. Reset on Network (Re-)Initialization
Because every network has different characteristics (e.g., working or
broken IPv6 or IPv4 connectivity), a Happy EarBalls algorithm SHOULD
re-initialize when the interface is connected to a new network.
Interfaces can determine network (re-)initialization by a variety of
mechanisms (e.g., Detecting Network Attachment in IPv4 (DNAv4)
[RFC4436], DNAv6 [RFC6059]).
4.1.4. Abandon Non-Winning Connections
Non-winning connections that are not assigned as flows for the
purposes of [RFC5626] SHOULD be abandoned, even though they could --
in some cases -- be put to reasonable use.
Justification: This reduces the load on the server (file descriptors,
TCP control blocks) and stateful middleboxes (NAT and firewalls).
Also, if the abandoned connection is IPv4, this reduces IPv4 address
sharing contention.
(There are some unlikely situations where a non-winning connection
could be useful in the future: If at a later time, the client must
send a request to a different host name, but one which has as a
target the peer of the non-winning connection and does not have as a
target the peer of the winning connection.)
Johansson, et al. Expires June 15, 2017 [Page 7]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
5. Using an Existing Connection
When a client desires to send a message to a target that is within a
subsequence of targets derived from one host name, the client may
already have a connection established to one of the targets through
either SIP Outbound[RFC5626] or the procedures of Section 4. The
client SHOULD attempt to send the message using the existing
connection in preference to using a new connection to one of the
targets.
If, in the client's operational environment, there is a significant
risk that the connection has become unusable without the client
becoming aware of it, the client SHOULD consider testing whether the
connection is usable before sending the message using the connection.
Some possible ways to probe a connection to determine if it is still
usable are:
o Send a keep-alive, as specified by the protocol of the connection.
o Send a CR-LF-CR-LF keep-alive on a SIP Outbound
connection[RFC5626].
o Send an OPTIONS request with "Max-Forwards: 0".
(Note that a probe using an OPTIONS request can be used with any
protocol. If the OPTIONS reaches the target, the target is required
to respond with either a 200 or 483 response[RFC3261] without
forwarding it to another entity. Conveniently, a server can respond
to such a request statelessly, so such requests are low-overhead.
(Although the [RFC5626] keep-alive methods have even lower
overhead.))
6. Additional Considerations
This section discusses additional considerations related to Happy
EarBalls.
6.1. Preemtive Actions
A client may be in a situation where it has advance notice that it is
likely to need to send a message to a particular host name, for
instance, if the user of a UA begins dialing an outgoing call which
will be routed through a particular outgoing proxy. In such a
situation, the client SHOULD consider preemptively establishing a
connection (Section 4) or probing an existing connection (Section 5).
Johansson, et al. Expires June 15, 2017 [Page 8]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
6.2. Determining the Type of an Address
For some transitional technologies, such as a dual-stack host, it is
easy for the application to recognize a native IPv6 address (learned
via a AAAA query) and a native IPv4 address (learned via an A query).
The use of IPv6/IPv4 translation in the local network makes it
difficult or impossible to determine the address family by which the
connection will traverse the global network. However, IPv6/IPv4
translators do not need to be deployed on networks with dual-stack
clients because dual-stack clients can use their native IP address
family. Environments where IPv6/IPv4 translation is active will
degrade the ability of Happy EarBalls algorithms to establish working
connections.
6.3. Debugging and Troubleshooting
Happy EarBalls is aimed at ensuring a reliable user experience
regardless of connectivity problems affecting any single transport.
However, this naturally means that applications employing these
techniques are by default less useful for diagnosing issues with a
particular address family. To assist in that regard, an
implementation MAY provide a mechanism to disable their Happy
EarBalls behavior via a user setting, and to provide data useful for
debugging (e.g., a log or way to review current preferences).
6.4. Three or More Interfaces
A dual-stack host normally has one physical interface, and all
network access is done via IPv4 and IPv6 addresses assigned to that
interface. However, a dual-stack host might have additional physical
interfaces or additional logical interfaces (e.g., because of a VPN).
Additional Happy EarBalls considerations for optimal operation with
additional physical or logical interfaces is for further study and is
outside the scope of this document.
6.5. Multiple A and AAAA Resource Records
It is possible that a DNS query for an A or AAAA resource record will
return more than one A or AAAA address. When this occurs, it is
RECOMMENDED that a Happy EarBalls implementation order the responses
following the host's address preference policy and then try the first
target. If that fails after a certain time (see Section 6.6), the
next target SHOULD be chosen from the other address family.
If the second attempt fails to connect, a Happy EarBalls
implementation SHOULD try the other targets; the order of these
connection attempts is not important.
Johansson, et al. Expires June 15, 2017 [Page 9]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
Servers sometimes have multiple A records to provide load-balancing
across their servers (although load-balancing is better obtained
using SRV records). This same technique can be used for AAAA
records, as well. However, if multiple AAAA records are returned to
a client that is not using Happy EarBalls and that has broken IPv6
connectivity, the multiple AAAA records will further increase the
delay to fall back to IPv4, as the client will attempt to connect to
all of their addresses first. Thus, SIP server operators with native
IPv6 connectivity SHOULD NOT offer multiple AAAA records. If Happy
EarBalls is widely deployed in the future, this recommendation might
be revisited.
6.6. Connection Timeout
The primary purpose of Happy EarBalls is to reduce the wait time for
a dual-stack connection to complete, especially when the IPv6 path is
broken and IPv6 is preferred. Using a short timeout between
initiating an IPv6 connection and initiating an IPv4 connection (on
the order of tens of milliseconds) achieves this goal, but at the
cost of network traffic. This network traffic may be billable on
certain networks, will create state on some middleboxes (e.g.,
firewalls, intrusion detection systems, NATs), and will consume ports
if IPv4 addresses are shared. For these reasons, it is RECOMMENDED
that connection attempts be paced to give connections a chance to
complete. It is RECOMMENDED that connection attempts be paced
150-250 ms apart to balance human factors against network load. A
stateful algorithm MAY be more aggressive (that is, make connection
attempts closer together), if it maintains estimates of the expected
connection completion times.
7. Security Considerations
This document places additional restrictions on the existing
procedures in the SIP protocol. The specific security
vulnerabilities, attacks and threat models of the various protocols
discussed in this document (SIP, DNS, SRV records, etc.) are well-
documented in their respective specifications.
8. IANA Considerations
This document does not require any actions by IANA.
9. History
Note to RFC Editor: Upon publication, remove this section.
Johansson, et al. Expires June 15, 2017 [Page 10]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
9.1. Changes from draft-worley-sip-he-connection-00 to draft-worley-
sip-he-connection-01
9.2. Changes from draft-johansson-sip-he-connection-01 to draft-worley-
sip-he-connection-00
This version has a different name for technical reasons. It is, in
reality, the successor to draft-johansson-sip-he-connection-01.
Move Acknowledgments after References, as that is the style the
Editor prefers.
Updated Security Considerations: This increment of the H.E. work does
not make normative changes in existing SIP.
Copy a lot of text from RFC 6555, as this I-D is parallel to RFC
6555.
Changed "hostname" to "host name", as the latter form is more common
in RFCs by a moderate margin.
Revised some of the introduction text to parallel the introduction of
RFC 7984.
Changed name of algorithm to "Happy EarBalls", added reference to
Urban Dictionary.
Many expansions of the discussion and revisions of the wording.
10. References
10.1. Normative References
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
2012, <http://www.rfc-editor.org/info/rfc6555>.
10.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
Johansson, et al. Expires June 15, 2017 [Page 11]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
DOI 10.17487/RFC3263, June 2002,
<http://www.rfc-editor.org/info/rfc3263>.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213,
DOI 10.17487/RFC4213, October 2005,
<http://www.rfc-editor.org/info/rfc4213>.
[RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
"Managing Client-Initiated Connections in the Session
Initiation Protocol (SIP)", RFC 5626,
DOI 10.17487/RFC5626, October 2009,
<http://www.rfc-editor.org/info/rfc5626>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
[RFC7984] Johansson, O., Salgueiro, G., Gurbani, V., and D. Worley,
Ed., "Locating Session Initiation Protocol (SIP) Servers
in a Dual-Stack IP Network", RFC 7984,
DOI 10.17487/RFC7984, September 2016,
<http://www.rfc-editor.org/info/rfc7984>.
[UD] The Jews Who Stole Christmas, , "Urban Dictionary, entry
'Earballs'", December 2011,
<http://www.urbandictionary.com/define.php?term=Earballs>.
Acknowledgements
The authors would like to acknowledge the support and contribution of
the SIP Forum IPv6 Working Group. This document is based on a lot of
tests and discussions at SIPit events, organized by the SIP Forum.
Most of the material in Section 4 and Section 6 is taken from
[RFC6555], whose authors are Dan Wing and Andrew Yourtchenko.
Johansson, et al. Expires June 15, 2017 [Page 12]
Internet-Draft Connection-Oriented Happy EarBalls December 2016
Authors' Addresses
Olle E. Johansson
Edvina AB
Runbovaegen 10
Sollentuna SE-192 48
SE
Email: oej@edvina.net
Gonzalo Salgueiro
Cisco Systems
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: gsalguei@cisco.com
Dale R. Worley
Ariadne Internet Services
738 Main St.
Waltham, MA 02451
US
Email: worley@ariadne.com
Johansson, et al. Expires June 15, 2017 [Page 13]
