RFC7245: An Architecture for Media Recording Using the Session Initiation Protocol
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(SIP)
Internet Engineering Task Force (IETF) A. Hutton, Ed.
Request for Comments: 7245 Unify
Category: Informational L. Portman, Ed.
ISSN: 2070-1721 NICE Systems
R. Jain
IPC Systems
K. Rehor
Cisco Systems, Inc.
May 2014
An Architecture for Media Recording
Using the Session Initiation Protocol
Abstract
Session recording is a critical requirement in many communications
environments such as call centers and financial trading. In some of
these environments, all calls must be recorded for regulatory,
compliance, and consumer protection reasons. Recording of a session
is typically performed by sending a copy of a media stream to a
recording device. This document describes architectures for
deploying session recording solutions in an environment that is based
on the Session Initiation Protocol (SIP).
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7245.
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Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Session Recording Architecture . . . . . . . . . . . . . . . 5
3.1. Location of the SRC . . . . . . . . . . . . . . . . . . . 5
3.1.1. B2BUA Acts as a SRC . . . . . . . . . . . . . . . . . 5
3.1.2. Endpoint Acts as SRC . . . . . . . . . . . . . . . . 6
3.1.3. A SIP Proxy Cannot Be a SRC . . . . . . . . . . . . . 7
3.1.4. Interaction with MEDIACTRL . . . . . . . . . . . . . 7
3.1.5. Interaction with Conference Focus . . . . . . . . . . 9
3.2. Establishing the Recording Session . . . . . . . . . . . 10
3.2.1. SRC-Initiated Recording . . . . . . . . . . . . . . . 11
3.2.2. SRS-Initiated Recording . . . . . . . . . . . . . . . 11
3.2.3. Pause/Resume Recording Session . . . . . . . . . . . 12
3.2.4. Media Stream Mixing . . . . . . . . . . . . . . . . . 12
3.2.5. Media Transcoding . . . . . . . . . . . . . . . . . . 12
3.2.6. Lossless Recording . . . . . . . . . . . . . . . . . 12
3.3. Recording Metadata . . . . . . . . . . . . . . . . . . . 13
3.3.1. Contents of Recording Metadata . . . . . . . . . . . 13
3.3.2. Mechanisms for Delivery of Metadata to SRS . . . . . 13
3.4. Notifications to the Recorded User Agents . . . . . . . . 13
3.5. Preventing the Recording of a SIP Session . . . . . . . . 13
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
7. Informative References . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
Session recording is a critical requirement in many communications
environments such as call centers and financial trading. In some of
these environments, all calls must be recorded for regulatory,
compliance, and consumer protection reasons. Recording of a session
is typically performed by sending a copy of a media stream to a
recording device. This document describes architectures for
deploying session recording solutions as defined in "Use Cases and
Requirements for SIP-Based Media Recording (SIPREC)" [RFC6341].
This document focuses on how sessions are established between a
Session Recording Client (SRC) and the Session Recording Server (SRS)
for the purpose of conveying the Replicated Media and Recording
Metadata (e.g., identity of the parties involved) relating to the
Communication Session.
Once the Replicated Media and Recording Metadata have been received
by the SRS, they will typically be archived for retrieval at a later
time. The procedures relating to the archiving and retrieval of this
information are outside the scope of this document.
This document only considers active recording, where the SRC
purposefully streams media to a SRS. Passive recording, where a
recording device detects media directly from the network (e.g., using
port-mirroring techniques), is outside the scope of this document.
In addition, lawful intercept is outside the scope of this document,
which takes account of the IETF policy on wiretapping [RFC2804].
The Recording Session that is established between the SRC and the SRS
uses the normal procedures for establishing INVITE-initiated dialogs
as specified in [RFC3261] and uses the Session Description Protocol
(SDP) for describing the media to be used during the session as
specified in [RFC4566]. However, it is intended that some extensions
to SIP (e.g., Headers, Option Tags, etc.) will be defined to support
the requirements for media recording. The Replicated Media is
required to be sent in real-time to the SRS and is not buffered by
the SRC to allow for real-time analysis of the media by the SRS.
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2. Definitions
The first four definitions are quoted from RFC 6341.
Session Recording Server (SRS): A Session Recording Server (SRS) is
a SIP User Agent (UA) that is a specialized media server or
collector that acts as the sink of the recorded media. An SRS is
typically implemented as a multi-port device that is capable of
receiving media from multiple sources simultaneously. An SRS is
the sink of the recorded session metadata.
Session Recording Client (SRC): A Session Recording Client (SRC) is
a SIP User Agent (UA) that acts as the source of the recorded
media, sending it to the SRS. An SRC is a logical function. Its
capabilities may be implemented across one or more physical
devices. In practice, an SRC could be a personal device (such as
a SIP phone), a SIP Media Gateway (MG), a Session Border
Controller (SBC), or a SIP Media Server (MS) integrated with an
Application Server (AS). This specification defines the term
"SRC" such that all such SIP entities can be generically addressed
under one definition. The SRC provides metadata to the SRS.
Communication Session (CS): A session created between two or more
SIP User Agents (UAs) that is the subject of recording.
Recording Session (RS): The SIP session created between an SRC and
SRS for the purpose of recording a CS.
The following terms are defined by this document.
Recording-aware User Agent (UA): A SIP User Agent that is aware of
SIP extensions associated with the CS. Such extensions may be
used to notify the recording-aware UA that a session is being
recorded, or by a recording-aware UA to express preferences as to
whether a recording should be started, paused, resumed, or
stopped.
Recording-unaware User Agent (UA): A SIP User Agent that is unaware
of SIP extensions associated with the CS. Such a recording-
unaware UA will be notified that a session is being recorded or
will express preferences as to whether a recording should be
started, paused, resumed, or stopped via some other means that is
out of scope for the SIP media recording architecture.
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Recording Metadata: The metadata describing the CS that is required
by the SRS. This will include, for example, the identities of
users that participate in the CS and dialog state. Typically,
this metadata is archived with the Replicated Media at the SRS.
The recording metadata is delivered in real-time to the SRS.
Replicated Media: A copy of the media that is associated with the
CS, was created by the SRC, and was sent to the SRS. It may
contain all the media associated with the CS (e.g., audio and
video) or just a subset (e.g., audio). Replicated Media is part
of the Recording Session.
3. Session Recording Architecture
3.1. Location of the SRC
This section contains some example session recording architectures
showing how the SRC is a logical function that can be located in or
split between various physical components.
3.1.1. B2BUA Acts as a SRC
A SIP Back-to-Back User Agent (B2BUA) that has access to the media to
be recorded may act as an SRC. The B2BUA may already be aware that a
session needs to be recorded before the initial establishment of the
CS, or the decision to record the session may occur after the session
has been established.
If the SRC makes the decision to initiate the RS, then it will do so
by sending a SIP INVITE request to the SRS.
If the SRS makes the decision to initiate the Recording Session, then
it will initiate the establishment of a SIP RS by sending an INVITE
to the SRC.
The RS INVITE contains information that identifies the session as
being established for the purposes of recording and prevents the
session from being accidentally rerouted to a UA that is not an SRS
if the RS was initiated by the SRC or vice versa.
The B2BUA/SRC is responsible for notifying the UAs involved in the CS
that the session is being recorded.
The B2BUA/SRC is responsible for complying with requests from
recording aware UAs or through some configured policies indicating
that the CS should not be recorded.
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+-----------+
(Recording Session) | Session |
+------SIP------>| Recording |
| | Server |
| +--RTP/RTCP-->| (SRS) |
| | +-----------+
V V ^
+-------------+ |
| | |
| |-- Metadata -+
| |
| B2BUA |
| |
| Session |
+--------+ | Recording | +---------+
| |<- SIP ->| Client |<- SIP ->| |
| UA-A | | (SRC) | | UA-B |
| |<- RTP/->| |<- RTP/->| |
+--------+ RTCP | | RTCP +---------+
+-------------+
|____________________________________________________|
(Communication Session)
Figure 1: B2BUA Acts as the Session Recording Client
3.1.2. Endpoint Acts as SRC
A SIP endpoint / UA may act as a SRC. In that case, the endpoint
sends the Replicated Media to the SRS.
If the endpoint makes the decision to initiate the Recording Session,
then it will initiate the establishment of a SIP Session by sending
an INVITE to the SRS.
If the SRS makes the decision to initiate the Recording Session, then
it will initiate the establishment of a SIP Session by sending an
INVITE to the endpoint. The actual decision mechanism is out of
scope for the SIP media recording architecture.
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(Recording Session) +-----------+
+----------SIP------>| |
| +----RTP/RTCP---->| Session |
| | | Recording |
| | | Server |
| | +-- Metadata -->| (SRS) |
| | | | |
| | | +-----------+
| | |
| | |
| | |
| | |
V V | (Communication Session)
+--+------+ +---------+
| |<-------SIP--------->| |
| UA-A | | UA-B |
| (SRC) |<-----RTP/RTCP------>| |
+---------+ +---------+
Figure 2: SIP Endpoint Acts as the Session Recording Client
3.1.3. A SIP Proxy Cannot Be a SRC
A SIP Proxy is unable to act as an SRC because it does not have
access to the media and therefore has no way of enabling the delivery
of the Replicated Media to the SRS.
3.1.4. Interaction with MEDIACTRL
The MEDIACTRL architecture [RFC5567] describes an architecture in
which an Application Server (AS) controls a Media Server (MS), which
may be used for purposes such as conferencing and recording media
streams. In the architecture described in [RFC5567], the AS
typically uses SIP Third Party Call Control (3PCC) to instruct the
SIP UAs to direct their media to the Media Server.
The SRC or the SRS described in this document may be architected
according to [RFC5567]; therefore, when further decomposed, they may
be made up of an AS that uses a MEDIACTRL interface to control an MS.
As shown in Figure 3, when the SRS is architected according to
[RFC5567], the MS acts as a sink of the recording media, and the AS
acts as a sink of the metadata and the termination point for RS SIP
signaling. As shown in Figure 4, when the SRC is architected
according to [RFC5567], the MS acts as a source of recording media,
and the AS acts as a source of the metadata and the termination point
for RS SIP signaling.
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Session Recording Server (SRS)
+----------------------------------------+
| |
(Recording Session) | +-----------+ +------------+ |
+------------SIP----|->| | | | |
| | | MEDIACTRL |MEDIACTRL | Media | |
| | |Application|<-------->| Server | |
| +-----Metadata--->| Server | | (Recorder)| |
| | | | | | | |
| | | +-----------+ +------------+ |
| | | ^ |
| | +------------------------------|---------+
| | +--------------- RTP/RTCP -----------------+
| | |
V | V
+---+------+ +---------+
| |<-------SIP-------------->| |
| UA-A | (Communication Session) | UA-B |
| (SRC) |<-------RTP/RTCP--------->| |
+----------+ +---------+
Figure 3: Example of Session Recording Server using MEDIACTRL
+----------+
(Recording Session) | Session |
+-----------SIP------------------------->|Recording |
| +----------Metadata------------------->| Server |
| | | (SRS) |
V | UA-A Session Recording Client (SRC) +----------+
+----------------------------------------+ ^
| | |
| +-----------+ +------------+ | |
| | | Control | |<-RTP/RTCP-+ +---------+
| | UA | Protocol | Media | | | |
| |Application|<-------->| Server | |<----SIP----->| UA-B |
| | Server | | |<-----RTP------>| |
| | | | | | +---------+
| +-----------+ +------------+ |
| |
+----------------------------------------+
Figure 4: Example of Session Recording Client Decomposition
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3.1.5. Interaction with Conference Focus
In the case of a centralized conference, a combination of the
conference focus and mixer [RFC4353] may act as a SRC and therefore
provide the SRS with the Replicated Media and associated recording
metadata. In this arrangement, the SRC is able to provide media and
metadata relating to each of the participants, including, for
example, any side conversations where the media passes through the
mixer.
The conference focus can either provide mixed Replicated Media or
separate streams per conference participant (as depicted in
Figure 5).
The conference focus may also act as a recording-aware UA in the case
when one of the participants acts as a SRC.
In an alternative arrangement, a SIP endpoint that is a conference
participant can act as an SRC. The SRC will in this case have access
to the media and metadata relating to that particular participant and
may be able to obtain additional metadata from the conference focus.
The SRC may, for example, use the conference event package as
described in [RFC4575] to obtain information about other participants
that it provides to the SRS within the recording metadata.
The SRC may be involved in the conference from the very beginning or
may join at some later point of time.
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User 1
+-----------+
| |
| |
|Participant|
| 1 |
| |
+-----------+
^ ^SIP
RTP | |Dialog
| |1
User 2 V V Recording
+-----------+ +-----------+ Session *************
| | | |<------------>* *
| |<-- RTP -->| |<-RTP/RTCP 1->* *
|Participant|<--------->| Focus/SRC |<-RTP/RTCP 2->* SRS *
| 2 | SIP | |<-RTP/RTCP 3->* *
| | Dialog | | * *
+-----------+ 2 +-----------+ *************
^ ^
| |SIP
RTP | |Dialog
| |3
V V
+-----------+
| |
| |
|Participant|
| 3 |
| |
+-----------+
User 3
Figure 5: Conference Focus Acting as an SRC
3.2. Establishing the Recording Session
The SRC or the SRS may initiate the Recording Session.
It should be noted that the Recording Session is independent from the
CS that is being recorded at both the SIP dialog level and at the
session level.
Concerning media negotiation, regular SIP/SDP capabilities should be
used, and existing transcoding capabilities and media encryption
should not be precluded.
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3.2.1. SRC-Initiated Recording
When the SRC initiates the Recording Session for the purpose of
conveying media to the SRS, it performs the following actions:
o Is provisioned with a Unified Resource Identifier (URI) for the
SRS; the URI is resolved through normal [RFC3263] procedures.
o Initiates the dialog by sending an INVITE request to the SRS. The
dialog is established according to the normal procedures for
establishing an INVITE-initiated dialog as specified in [RFC3261].
o Includes in the INVITE an indication that the session is
established for the purpose of recording the associated media.
o Includes an SDP attribute of "a=sendonly" for each media line if
the Replicated Media is to be started immediately, or includes
"a=inactive" if it is not ready to transmit the media.
o Replicates the media streams that are to be recorded and transmits
the media to the SRS.
The Recording Session may replicate all media associated with the CS
or only a subset.
3.2.2. SRS-Initiated Recording
When the SRS initiates the media Recording Session with the SRC, it
performs the following actions:
o Is provisioned with a Unified Resource Identifier (URI) for the
SRC; the URI is resolved through normal [RFC3263] procedures.
o Sends an INVITE request to the SRC.
o Includes in the INVITE an indication that the session is
established for the purpose of recording the associated media.
o Identifies the sessions that are to be recorded. The actual
mechanism of the identification depends on SRC policy.
o Includes an SDP attribute of "a=recvonly" for each media line if
the Recording Session is to be started immediately, or includes
"a=inactive" if it is not ready to receive the media.
If the SRS does not have prior knowledge of what media streams are
available to be recorded, it can make use of an offerless INVITE,
which allows the SRC to make the initial SDP offer.
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3.2.3. Pause/Resume Recording Session
The SRS or the SRC may pause the recording by changing the SDP
direction attribute to "inactive" and resume the recording by
changing the direction back to "recvonly" or "sendonly".
3.2.4. Media Stream Mixing
In a basic session involving only audio, there are typically two
audio/RTP streams between the two UAs involved in transporting media
in each direction. When recording this media, the two streams may be
mixed or not mixed at the SRC before being transmitted to the SRS.
In the case when they are not mixed, two separate streams are sent to
the SRS, and the SDP offer sent to the SRS must describe two separate
media streams. In the mixed case, a single mixed media stream is
sent to the SRS.
3.2.5. Media Transcoding
The CS and the RS are negotiated separately using the standard SDP
offer/answer exchange which may result in the SRC having to perform
media transcoding between the two sessions. If the SRC is not
capable of performing media transcoding it may limit the media
formats in the offer to the SRS depending on what media is negotiated
on the CS or may limit what it includes in the offer on the CS if it
has prior knowledge of the media formats supported by the SRS.
However typically the SRS will be a more capable device which can
provide a wide range of media format options to the SRC and may also
be able to make use of a media transcoder as detailed in [RFC5369].
3.2.6. Lossless Recording
Session recording may be a regulatory requirement in certain
communication environments. Such environments may impose a
requirement generally known as "lossless recording". An overall
solution for lossless recording may involve multiple layers of
solutions. Individual aspects of the solutions may range from
administering networks for appropriate QoS, reliable transmission of
recorded media, and perhaps certain SIPREC protocol-level
capabilities in SRC and SRS.
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3.3. Recording Metadata
3.3.1. Contents of Recording Metadata
The metadata model is defined in [REC-METADATA].
3.3.2. Mechanisms for Delivery of Metadata to SRS
The SRS obtains session recording metadata from the SRC. The
metadata is transported via SIP-based mechanisms as specified in
[REC-PROTOCOL]
It is also possible that metadata is transported via non-SIP-based
mechanisms, but these are considered out of scope.
It is also possible to have an RS session without the metadata; in
that case, the SRS will be receiving the metadata by some other means
or not at all.
3.4. Notifications to the Recorded User Agents
Typically, a user that is involved in a session that is to be
recorded is notified by an announcement at the beginning of the
session or may receive some warning tones within the media. However,
SIPREC enables an indication that the call is being recorded to be
included in the SIP requests and responses associated with that CS.
The SRC provides the notification to all SIP UAs for which it is
replicating received media for the purpose of recording. If the SRC
is acting as a SIP endpoint, as described in Section 3.1.2, then it
also provides a notification to the local user.
3.5. Preventing the Recording of a SIP Session
During the initial session establishment or during an established
session, a recording-aware UA may provide an indication of its
preference with regard to recording the media in the CS. The
mechanisms for this are specified in [REC-PROTOCOL]
4. IANA Considerations
This document has no actions for IANA. This document mentions
SIP/SDP extensions. The associated IANA considerations are addressed
in [REC-PROTOCOL], which defines them.
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5. Security Considerations
The Recording Session is fundamentally a standard SIP dialog and
media session and therefore makes use of existing SIP security
mechanisms for securing the Recording Session and Recording Metadata.
The intended use of this architecture is only for the case where the
users are aware that they are being recorded, and the architecture
provides the means for the SRC to notify users that they are being
recorded.
This architectural solution is not intended to support lawful
intercept, which in contrast requires that users are not informed.
It is the responsibility of the SRS to protect the Replicated Media
and Recording Metadata once it has been received and archived. The
stored content must be protected using a cipher at least as strong
(or stronger) than the original content; however, the mechanism for
protecting the storage and retrieval from the SRS is out of scope of
this work. The keys used to store the data must also be securely
maintained by the SRS and should only be released, securely, to
authorized parties. How to secure these keys, properly authorize a
receiving party, or securely distribute the keying material is also
out of scope of this work.
Protection of the RS should not be weaker than protection of the CS
and may need to be stronger because the media is retransmitted
(allowing more possibility for interception). This applies to both
the signaling and media paths.
It is essential that the SRC will authenticate the SRS because the
client must be certain that it is recording on the right recording
system. It is less important that the SRS authenticate the SRC, but
implementations must have the ability to perform mutual
authentication.
In some environments, it is desirable to not decrypt and re-encrypt
the media. This means the same media encryption key is negotiated
and used within the CS and RS. If for any reason the media are
decrypted on the CS and are re-encrypted on the RS, a new key must be
used.
The retrieval mechanism for media recorded by this protocol is out of
scope. Implementations of retrieval mechanisms should consider the
security implications carefully, as the retriever is not usually a
party to the call that was recorded. Retrievers should be
authenticated carefully. The cryptosuites on the retrieval should be
no less strong than those used on the RS and may need to be stronger.
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6. Acknowledgements
Thanks to John Elwell, Brian Rosen, Alan Johnson, Cullen Jennings,
Hadriel Kaplan, Henry Lum, Paul Kyzivat, Parthasarathi R., Ram Mohan
R., Charles Eckel, Friso Feenstra, and Dave Higton for their
significant contributions and assistance with this document and
working group. Also, thanks to all the members of the SIPREC WG
mailing list for providing valuable input to this work.
7. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263, June
2002.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use
Cases and Requirements for SIP-Based Media Recording
(SIPREC)", RFC 6341, August 2011.
[REC-METADATA]
Ravindranath, R., Ravindran, P., and P. Kyzivat, "Session
Initiation Protocol (SIP) Recording Metadata", Work in
Progress, February 2014.
[REC-PROTOCOL]
Portman, L., Lum, H., Eckel, C., Johnston, A., and A.
Hutton, "Session Recording Protocol", Work in Progress,
February 2014.
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353, February
2006.
[RFC4575] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
Initiation Protocol (SIP) Event Package for Conference
State", RFC 4575, August 2006.
[RFC5567] Melanchuk, T., "An Architectural Framework for Media
Server Control", RFC 5567, June 2009.
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[RFC5369] Camarillo, G., "Framework for Transcoding with the Session
Initiation Protocol (SIP)", RFC 5369, October 2008.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May
2000.
Authors' Addresses
Andrew Hutton (editor)
Unify
Hofmannstrasse 51
81359 Munich
Germany
EMail: andrew.hutton@unify.com
Leon Portman (editor)
NICE Systems
8 Hapnina
Ra'anana 43017
Israel
EMail: leon.portman@gmail.com
Rajnish Jain
IPC Systems
777 Commerce Drive
Fairfield, CT 06825
USA
EMail: rajnish.jain@outlook.com
Ken Rehor
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
USA
EMail: krehor@cisco.com
Hutton, et al. Informational [Page 16]