draft-ietf-ieprep-framework-05.txt   draft-ietf-ieprep-framework-06.txt 
Internet Engineering Task Force Ken Carlberg Internet Engineering Task Force Ken Carlberg
INTERNET DRAFT Ian Brown
June 19, 2003 UCL October 6, 2003 Ian Brown
UCL
Cory Beard Cory Beard
UMKC UMKC
Framework for Supporting ETS in IP Telephony Framework for Supporting ETS in IP Telephony
<draft-ietf-ieprep-framework-05.txt> <draft-ietf-ieprep-framework-06.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1]. all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts. groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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reality in the near future (the mid- to far-term is a subject for reality in the near future (the mid- to far-term is a subject for
others to contemplate). others to contemplate).
In 1998, the IETF produced [8], which presented an architecture for In 1998, the IETF produced [8], which presented an architecture for
Differentiated Services (diff-serv). This effort focused on a more Differentiated Services (diff-serv). This effort focused on a more
aggregated perspective and classification of packets than that of aggregated perspective and classification of packets than that of
[2]. This is accomplished with the recent specification of the [2]. This is accomplished with the recent specification of the
diff-serv field in the IP header (in the case of IPv4, it replaced diff-serv field in the IP header (in the case of IPv4, it replaced
the old ToS field). This new field is used for code points esta- the old ToS field). This new field is used for code points esta-
blished by IANA, or set aside as experimental. It can be expected blished by IANA, or set aside as experimental. It can be expected
^L
that sets of microflows, a granular identification of a set of pack- that sets of microflows, a granular identification of a set of pack-
ets, will correspond to a given code point, thereby achieving an ets, will correspond to a given code point, thereby achieving an
^L
aggregated treatment of data. aggregated treatment of data.
One constant in the introduction of new service models has been the One constant in the introduction of new service models has been the
designation of Best Effort as the default service model. If traffic designation of Best Effort as the default service model. If traffic
is not, or cannot be, associated as diff-serv or int-serv, then it is is not, or cannot be, associated as diff-serv or int-serv, then it is
treated as Best Effort and uses what resources are made available to treated as Best Effort and uses what resources are made available to
it. it.
Beyond the introduction of new services, the continued pace of addi- Beyond the introduction of new services, the continued pace of addi-
tional traffic load experienced by ISPs over the years has continued tional traffic load experienced by ISPs over the years has continued
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centered on the type of application protocols used over a network. centered on the type of application protocols used over a network.
By this we mean that the distinction, and possible bounds on QoS, By this we mean that the distinction, and possible bounds on QoS,
usually centers on the type of application (e.g., audio video tools) usually centers on the type of application (e.g., audio video tools)
that is being referred to. that is being referred to.
While protocols like SMTP [11] and SIP [12] have embedded fields While protocols like SMTP [11] and SIP [12] have embedded fields
denoting "priority", there has not been a previous IETF standards denoting "priority", there has not been a previous IETF standards
based effort to state or define what this distinction means with based effort to state or define what this distinction means with
respect to the underlying network or the end-to-end applications and respect to the underlying network or the end-to-end applications and
how it should be supported at any layer. Given the emergence of IP how it should be supported at any layer. Given the emergence of IP
telephony, a natural inclusion of it as part of a telephony carrier's telephony, a natural inclusion of its service is an ability to sup-
backbone network, or into the Internet as a whole, implies the abil- port existing emergency related services. Typically, one associates
ity to support existing emergency related services. Typically, one emergency calls with "911" telephone service in the U.S., or "999" in
associates emergency calls with "911" telephone service in the U.S., the U.K. -- both of which are attributed to national boundaries and
or "999" in the U.K. -- both of which are attributed to national accessible by the general public. Outside of this exists emergency
boundaries and accessible by the general public. Outside of this telephone services that involved authorized usage, as described in
exists emergency telephone services that involved authorized usage, the following subsection.
as described in the following subsection.
^L
1.1.1. Government Emergency Telecommunications Service (GETS) 1.1.1. Government Emergency Telecommunications Service (GETS)
GETS is an emergency telecommunications service available in the U.S. GETS is an emergency telecommunications service available in the U.S.
and overseen by the National Communications System (NCS) -- an office and overseen by the National Communications System (NCS) -- an office
established by the White House under an executive order [30] and now established by the White House under an executive order [30] and now
^L
a part of the Department of Homeland Security . Unlike "911", it is a part of the Department of Homeland Security . Unlike "911", it is
only accessible by authorized individuals. The majority of these only accessible by authorized individuals. The majority of these
individuals are from various government agencies like the Department individuals are from various government agencies like the Department
of Transportation, NASA, the Department of Defense, and the Federal of Transportation, NASA, the Department of Defense, and the Federal
Emergency Management Agency (to name but a few). In addition, a Emergency Management Agency (to name but a few). In addition, a
select set of individuals from private industry (telecommunications select set of individuals from private industry (telecommunications
companies, utilities, etc.) that are involved in criticial infras- companies, utilities, etc.) that are involved in criticial infras-
tructure recovery operations are also provided access to GETS. tructure recovery operations are also provided access to GETS.
The purpose of GETS is to increase the probability that phone service The purpose of GETS is to achieve a high probability that phone ser-
will be available to selected authorized personnel in times of emer- vice will be available to selected authorized personnel in times of
gencies, such as hurricanes, earthquakes, and other disasters that emergencies, such as hurricanes, earthquakes, and other disasters
may produce a burden in the form of call blocking (i.e., congestion) that may produce a burden in the form of call blocking (i.e., conges-
on the U.S. Public Switched Telephone Network by the general public. tion) on the U.S. Public Switched Telephone Network by the general
public.
GETS is based in part on the ANSI T1.631 standard, specifying a High GETS is based in part on the ANSI T1.631 standard, specifying a High
Probability of Completion (HPC) for SS7 signaling [13]. Probability of Completion (HPC) for SS7 signaling [13].
1.1.2. International Emergency Preparedness Scheme (IEPS) 1.1.2. International Emergency Preparedness Scheme (IEPS)
[18] is a recent ITU standard that describes emergency related com- [18] is a recent ITU standard that describes emergency related com-
munications over international telephone service. While systems like munications over international telephone service. While systems like
GETS are national in scope, IEPS acts as an extension to local or GETS are national in scope, IEPS acts as an extension to local or
national authorized emergency call establishment and provides a national authorized emergency call establishment and provides a
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1.2. Scope of this Document 1.2. Scope of this Document
The scope of this document centers on the near and mid-term support The scope of this document centers on the near and mid-term support
of ETS within the context of IP telephony, though not necessarily of ETS within the context of IP telephony, though not necessarily
Voice over IP. We make a distinction between these two by treating Voice over IP. We make a distinction between these two by treating
IP telephony as a subset of VoIP, where in the former case we assume IP telephony as a subset of VoIP, where in the former case we assume
some form of application layer signaling is used to explicitly estab- some form of application layer signaling is used to explicitly estab-
lish and maintain voice data traffic. This explicit signaling capa- lish and maintain voice data traffic. This explicit signaling capa-
bility provides the hooks from which VoIP traffic can be bridged to bility provides the hooks from which VoIP traffic can be bridged to
^L
the PSTN. the PSTN.
An example of this distinction is when the Robust Audio Tool (RAT) An example of this distinction is when the Robust Audio Tool (RAT)
[14] begins sending VoIP packets to a unicast (or multicast) destina- [14] begins sending VoIP packets to a unicast (or multicast)
tion. RAT does not use explicit signaling like SIP to establish an
end-to-end call between two users. It simply sends data packets to ^L
the target destination. On the other hand, "SIP phones" are host destination. RAT does not use explicit signaling like SIP to estab-
devices that use a signaling protocol to establish a call signal lish an end-to-end call between two users. It simply sends data
packets to the target destination. On the other hand, "SIP phones"
are host devices that use a signaling protocol to establish a call
before sending data towards the destination. before sending data towards the destination.
One other aspect we should probably assume exists with IP Telephony One other aspect we should probably assume exists with IP Telephony
is an association of a target level of QoS per session or flow. [31] is an association of a target level of QoS per session or flow. [31]
makes an argument that there is a maximum packet loss and delay for makes an argument that there is a maximum packet loss and delay for
VoIP traffic, and both are interdependent. For delays of ~200ms, a VoIP traffic, and both are interdependent. For delays of ~200ms, a
corresponding drop rate of 5% is deemed acceptable. When delay is corresponding drop rate of 5% is deemed acceptable. When delay is
lower, a 15-20% drop rate can be experienced and still considered lower, a 15-20% drop rate can be experienced and still considered
acceptable. [32] discusses the same topic and makes an arguement acceptable. [32] discusses the same topic and makes an arguement
that packet size plays a significant role in what users tolerate as that packet size plays a significant role in what users tolerate as
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nothing else, intrinsic differences between the two communications nothing else, intrinsic differences between the two communications
architectures precludes this from happening. Note, this does not architectures precludes this from happening. Note, this does not
prevent us from borrowing design concepts or objectives from existing prevent us from borrowing design concepts or objectives from existing
systems. systems.
Section 2 presents several primary objectives that articulate what is Section 2 presents several primary objectives that articulate what is
considered important in supporting ETS related IP telephony traffic. considered important in supporting ETS related IP telephony traffic.
These objectives represent a generic set of goals and desired capa- These objectives represent a generic set of goals and desired capa-
bilities. Section 3 presents additional value added objectives, bilities. Section 3 presents additional value added objectives,
which are viewed as useful, but not critical. Section 4 presents which are viewed as useful, but not critical. Section 4 presents
^L
protocols and capabilities that relate or can play a role in support protocols and capabilities that relate or can play a role in support
of the objectives articulated in section 2. Finally, Section 5 of the objectives articulated in section 2. Finally, Section 5
presents two scenarios that currently exist or are being deployed in presents two scenarios that currently exist or are being deployed in
the near term over IP networks. These are not all-inclusive the near term over IP networks. These are not all-inclusive
^L
scenarios, nor are they the only ones that can be articulated ([38] scenarios, nor are they the only ones that can be articulated ([38]
provides a more extensive discussion on the topology scenarios provides a more extensive discussion on the topology scenarios
related to IP telephony). However, these scenarios do show cases related to IP telephony). However, these scenarios do show cases
where some of the protocols discussed in section 4 apply, and where where some of the protocols discussed in section 4 apply, and where
some do not. some do not.
Finally, we need to state that this document focuses its attention on Finally, we need to state that this document focuses its attention on
the IP layer and above. Specific operational procedures pertaining the IP layer and above. Specific operational procedures pertaining
to Network Operation Centers (NOC) or Network Information Centers to Network Operation Centers (NOC) or Network Information Centers
(NIC) are outside the scope of this document. This includes the (NIC) are outside the scope of this document. This includes the
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even wide-spread support along the path between the end points. even wide-spread support along the path between the end points.
Potentially, at the network layer there may exist islands of support Potentially, at the network layer there may exist islands of support
realized in the form of overlay networks. There may also be cases realized in the form of overlay networks. There may also be cases
where solutions may be constrained on an end-to-end basis (i.e., at where solutions may be constrained on an end-to-end basis (i.e., at
the transport or application layer). It is this diversity and possi- the transport or application layer). It is this diversity and possi-
bly partial support that need to be taken into account by those bly partial support that need to be taken into account by those
designing and deploying ETS related solutions. designing and deploying ETS related solutions.
Another aspect to consider is that there are existing architectures Another aspect to consider is that there are existing architectures
and protocols from other standards bodies that support emergency and protocols from other standards bodies that support emergency
^L
related communications. The effort in interoperating with these sys- related communications. The effort in interoperating with these sys-
tems, presumably through gateways or similar type nodes with IETF tems, presumably through gateways or similar type nodes with IETF
protocols, would foster a need to distinguish ETS flows from other protocols, would foster a need to distinguish ETS flows from other
flows. One reason would be the scenario of triggering ETS service flows. One reason would be the scenario of triggering ETS service
^L
from an IP network. from an IP network.
Finally, we take into consideration the requirements of [39, 40] in Finally, we take into consideration the requirements of [39, 40] in
discussing the protocols and mechanisms below in Secytion 4. In discussing the protocols and mechanisms below in Secytion 4. In
doing this, we do not make a one-to-one mapping of protocol discus- doing this, we do not make a one-to-one mapping of protocol discus-
sion with requirement. Rather, we make sure the discussion of Sec- sion with requirement. Rather, we make sure the discussion of Sec-
tion 4 does not violet any of the requirements in [39,40]. tion 4 does not violet any of the requirements in [39,40].
4. Protocols and Capabilities 4. Protocols and Capabilities
In this section, we take the objectives presented above and present a In this section, we take the objectives presented above and present a
set of protocols and capabilities that can be used to achieve them. set of protocols and capabilities that can be used to achieve them.
Given that the objectives are predominantly atomic in nature, the Given that the objectives are predominantly atomic in nature, the
measures used to address them are to be viewed separately with no measures used to address them are to be viewed separately with no
specific dependency upon each other as a whole. Various protocols specific dependency upon each other as a whole. Various protocols
and capabilities may be complimentary to each other, but there is no and capabilities may be complimentary to each other, but there is no
need for all to exist given different scenarios of operation, and need for all to exist given different scenarios of operation, and
that ETS support is not viewed as a ubiquitously available service. that ETS support is not expected to be a ubiquitously available ser-
We divide this section into 4 areas: vice. We divide this section into 4 areas:
1) Signaling 1) Signaling
2) Policy 2) Policy
3) Traffic Engineering 3) Traffic Engineering
4) Security 4) Security
5) Routing 5) Routing
4.1. Signaling & State Information 4.1. Signaling & State Information
Signaling is used to convey various information to either intermedi- Signaling is used to convey various information to either intermedi-
ate nodes or end nodes. It can be out-of-band of a data flow, and ate nodes or end nodes. It can be out-of-band of a data flow, and
thus in a separate flow of its own, such as SIP messages. It can be thus in a separate flow of its own, such as SIP messages. It can be
in-band and part of the state information in a datagram containing in-band and part of the state information in a datagram containing
the voice data. This latter example could be realized in the form of the voice data. This latter example could be realized in the form of
diff-serv code points in the IP packet. diff-serv code points in the IP packet.
In the following subsections, we discuss potential augmentations to In the following subsections, we discuss the current state of some
different types of signaling and state information to help support protocols and their use in providing support for ETS. We also dis-
the distinction of emergency related communications in general, and cuss potential augmentations to different types of signaling and
IEPS specifically. state information to help support the distinction of emergency
related communications in general.
^L
4.1.1. SIP 4.1.1. SIP
With respect to application level signaling for IP telephony, we With respect to application level signaling for IP telephony, we
focus our attention to the Session Initiation Protocol (SIP). focus our attention to the Session Initiation Protocol (SIP).
^L
Currently, SIP has an existing "priority" field in the Request- Currently, SIP has an existing "priority" field in the Request-
Header-Field that distinguishes different types of sessions. The Header-Field that distinguishes different types of sessions. The
five currently defined values are: "emergency", "urgent", "normal", five currently defined values are: "emergency", "urgent", "normal",
"non-urgent", "other-priority". These values are meant to convey "non-urgent", "other-priority". These values are meant to convey
importance to the end-user and have no additional sematics associated importance to the end-user and have no additional sematics associated
with them. with them.
[15] is a (soon to be) RFC that defines the requirements for a new [15] is an RFC that defines the requirements for a new header field
header field for SIP in reference to resource priority. This new for SIP in reference to resource priority. The requirements are
header field is meant to provide an additional measure of distinction meant to lead to a means of providing an additional measure of dis-
that can influence the behavior of gateways and SIP proxies. tinction that can influence the behavior of gateways and SIP proxies.
4.1.2. Diff-Serv 4.1.2. Diff-Serv
In accordance with [16], the differentiated services code point In accordance with [16], the differentiated services code point
(DSCP) field is divided into three sets of values. The first set is (DSCP) field is divided into three sets of values. The first set is
assigned by IANA. Within this set, there are currently, three types assigned by IANA. Within this set, there are currently, three types
of Per Hop Behaviors that have been specified: Default (correlating of Per Hop Behaviors that have been specified: Default (correlating
to best effort forwarding), Assured Forwarding, and Expedited For- to best effort forwarding), Assured Forwarding, and Expedited For-
warding. The second set of DSCP values are set aside for local or warding. The second set of DSCP values are set aside for local or
experimental use. The third set of DSCP values are also set aside experimental use. The third set of DSCP values are also set aside
for local or experimental use, but may later be reassigned to IANA in for local or experimental use, but may later be reassigned to IANA in
case the first set has been completely assigned. case the first set has been completely assigned.
One candidate approach to consider involves the specification of a One approach discussed on the IEPREP mailing list is the specifica-
new type of Per-Hop Behavior (PHB). This would provide a specific tion of a new Per-Hop Behaviour (PHB) for emergency related flows.
means of distinguishing emergency related traffic (signaling and user The rationale behind this idea is that it would provide a baseline by
data) from other traffic. The existence of this PHB then provides a which specific code points may be defined for various emergency
baseline by which specific code points may be defined related to related traffic: authorized emergency sessions (e.g., ETS), general
various emergency related traffic: authorized emergency sessions public emergency calls (e.g., "911"), MLPP, etc. However, in order
(e.g., ETS), general public emergency calls (e.g., "911"), MLPP. to define a new set of code points, a forwarding characteristic must
Aggregates would still exist with respect to the bundling of applica- also be defined. In other words, one cannot simply identify a set of
tions per code point. Further, one would associate a forwarding bits without defining their intended meaning (e.g.,the drop pre-
paradigm aimed at a low loss rate reflective of the code point cedence approach of Assured Forwarding). The one caveat to this
selected. The new PHB could be in the form of a one or more code statement are the set of DSCP bits set aside for experimental pur-
points that duplicate EF-type traffic characteristics. Policies poses. But as the name implies, experimental is for internal examina-
would determine if a measure of importance exists per EF-type code- tion and use and not for standardization.
point.
A potential issue that could be addressed by a new PHB involves merge
points of flows within a diff-serv domain. With EF, one can expect
admission control being performed at the edges of the domain.
Presumably, careful traffic engineering would be applied to avoid
^L Comments
congestion of EF queues at internal/core merge points stemming from --------
flows originating from different ingress nodes of the diff-serv
domain. However, traffic engineering may not be able to compensate
for congestion of EF-type traffic at the domain's core routers.
Hence, a new PHB that has more than one code point to identify EF-
type traffic may address congestion by associating a drop precedence
for certain types of EF-type datagrams. Note that local policy and
SLAs would define which EF-type of traffic, if any, would be associ-
ated with a specific drop precedence.
4.1.3. Variations Related to Diff-Serv and Queuing It is important to note that as of the time that this document was
written, the IETF has been taking a conservative approach in specify-
ing new PHBs. This is because the number of code points that can be
defined is relatively small and understandably considered a scarce
resource. Therefore, the possibility of a new PHB being defined for
emergency related traffic is at best a long term project that may or
One variation to consider with respect to existing diff-serv work ^L
would be to define a new or fifth class for the existing AF PHB. may not be accepted by the IETF.
Unlike the other currently defined classes of 3 levels, this new one
would be based on five levels of drop precedence. This increase in
the number of levels would conveniently correlate to the levels of
MLPP, which has five types of priorities. The five levels would also
correlate to a recent effort in the Study Group 11 of the ITU to
define 5 levels for Emergency Telecommunications Service (ETS).
Beyond these other standardization efforts, the 5 levels would pro-
vide a higher level of variance that could be used to supercede the
existing 3 levels used in the other classes. Hence, if other non-
emergency aggregate traffic were assigned to the new class, the
highest drop precedence they are assigned to is (3) -- corresponding
to the other four currently defined classes. Emergency traffic would
be set to (4) or (5), depending on the SLA that has been defined.
Another variation to Another approach would be to make modifications In the near term, we would initially suggest using the Assured For-
or additions to the existing AF PHBs, with their four classes and warding (AF) PHB [20] for distinguishing emergency traffic from other
three drop precedences per class. One could use the existing AF PHBs types of flows. At a minimum, AF could be used for the different SIP
if one assumed that a relatively homogeneous set of packet flows were call signaling messages. If EF was also supported by the domain,
marked with the same AF class markings (i.e., have only TCP flows, or then it would be used for IP telephony data packets. Otherwise,
only UDP-voice flows, but not both, within a class). Then one could another AF class would be used for those data flows.
allocate the lowest drop precedence to the emergency traffic, and the
other two drop precedences to the rest of the traffic.
An original rationale for having three drop precedences was to be 4.1.3. Variations Related to Diff-Serv and Queuing
able to separate TCP flows from UDP flows by different drop pre-
cedences, so UDP packets could be dropped more frequently than TCP
packets. TCP flows would reduce their sending rates while UDP likely
would not, so this could be used to prevent UDP from bullying the TCP
traffic. But if the design does not create a mixing of TCP and UDP,
then three drop precedences are not as necessary and one could be
used for emergency traffic.
To implement preferential dropping between classes of traffic, with Scheduling mechanisms like Weighted Fair Queueing and Class Based
Queueing are used to designate a percentage of the output link
bandwidth that would be used for each class if all queues were back-
logged. Its purpose, therefore, it to manage the rates and delays
experienced by each class. But emergency traffic may not necessarily
require QoS any better or different than non-emergency traffic. It
may just need higher probability of being forwarded to the next hop,
which could be accomplished simply through drop precedences within a
class.
^L To implement preferential dropping between classes of traffic, one of
one being emergency traffic, one would need to use a more advanced which being emergency traffic, one would probably need to use a more
form of Active Queue Management (AQM). AQM would need to protect advanced form of Active Queue Management (AQM). Current implementa-
emergency traffic as much as possible until most, if not all, of the tions use an overall queue fill measurement to make decisions; this
non-emergency traffic had been dropped. This would require creation might cause emergency classified packets to be dropped. One new from
of drop probabilities based on counting the number of packets in the of AQM could be a Multiple Average-Multiple Threshold approach,
queue for each drop precedence individually. Instead, current imple- instead of the Single Average-Multiple Threshold approach used today.
mentations use an overall queue fill measurement to make decisions; This allows creation of drop probabilities based on counting the
this might cause emergency packets to be dropped. This new from of number of packets in the queue for each drop precedence individually.
AQM would be a Multiple Average-Multiple Threshold approach, instead
of the Single Average-Multiple Threshold approach used today.
So, it could be possible to use the current set of AF PHBs if each So, it could be possible to use the current set of AF PHBs if each
class where reasonably homogenous in the traffic mix. But one might class where reasonably homogenous in the traffic mix. But one might
still have a need to be able to differentiate three drop precedences still have a need to be able to differentiate three drop precedences
just within non-emergency traffic. If so, more drop precedences just within non-emergency traffic. If so, more drop precedences
could be implemented. Also, if one wanted discrimination within could be implemented. Also, if one wanted discrimination within
emergency traffic, as with MLPPs five levels of precedence, more drop emergency traffic, as with MLPPs five levels of precedence, more drop
precedences might also be considered. The five levels would also precedences might also be considered. The five levels would also
correlate to a recent effort in the Study Group 11 of the ITU to correlate to a recent effort in the Study Group 11 of the ITU to
define 5 levels for Emergency Telecommunications Service. define 5 levels for Emergency Telecommunications Service.
The other question with AF PHBs would be whether one should create a
new fifth class. This might be a useful approach, but, given the
above discussion, a fifth class would only be needed if emergency
traffic were considered a totally different type of traffic from a
QoS perspective. Scheduling mechanisms like Weighted Fair Queueing
and Class Based Queueing are used to designate a percentage of the
output link bandwidth that would be used for each class if all queues
were backlogged. Its purpose, therefore, it to manage the rates and
delays experienced by each class. But emergency traffic does not
necessarily require QoS any better or different than non-emergency
traffic. It just needs higher probability of completion which could
be accomplished simply through drop precedences within a class.
Emergency requirements are primarily related to preferential packet
dropping probabilities.
Comments
--------
It is important to note that as of the time that this document was
written, the IETF is taking a conservative approach in specifying new
PHBs. This is because the number of code points that can be defined
is relatively small, and understandably considered a scarce resource.
Therefore, the possibility of a new PHB being defined for emergency
related traffic is at best a long term project that may or may not be
accepted by the IETF.
In the near term, we would initially recommend using the Assured
^L
Forwarding (AF) PHB [20] for distinguishing emergency traffic from
other types of flows. At a minimum, AF could be used for the dif-
ferent SIP call signaling messages. If EF was also supported by the
domain, then it would be used for IP telephony data packets. Other-
wise, another AF class would be used for those data flows.
It is also critical to understand that one cannot specify an exact
code point used exclusively for emergency related data flows. This
is because the relevance of a code point is local to the given diff-
serv domain (i.e., code points are not globally unique per micro-flow
or aggregate of flows).
4.1.4. RTP 4.1.4. RTP
The Real-Time Transport Protocol (RTP) provides end-to-end delivery The Real-Time Transport Protocol (RTP) provides end-to-end delivery
services for data with real-time characteristics. The type of data services for data with real-time characteristics. The type of data
is generally in the form of audio or video type applications, and are is generally in the form of audio or video type applications, and are
^L
frequently interactive in nature. RTP is typically run over UDP and frequently interactive in nature. RTP is typically run over UDP and
has been designed with a fixed header that identifies a specific type has been designed with a fixed header that identifies a specific type
of payload representing a specific form of application media. The of payload representing a specific form of application media. The
designers of RTP also assumed an underlying network providing best designers of RTP also assumed an underlying network providing best
effort service. As such, RTP does not provide any mechanism to effort service. As such, RTP does not provide any mechanism to
ensure timely delivery or provide other QoS guarantees. However, the ensure timely delivery or provide other QoS guarantees. However, the
emergence of applications like IP telephony, as well as new service emergence of applications like IP telephony, as well as new service
models, presents new environments where RTP traffic may be forwarded models, presents new environments where RTP traffic may be forwarded
over networks that support better than best effort service. Hence, over networks that support better than best effort service. Hence,
the original scope and target environment for RTP has expanded to the original scope and target environment for RTP has expanded to
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In 4.1.2, we discussed one means of marking a data packet for emer- In 4.1.2, we discussed one means of marking a data packet for emer-
gencies under the context of the diff-serv architecture. However, we gencies under the context of the diff-serv architecture. However, we
also pointed out that diff-serv markings for specific PHBs are not also pointed out that diff-serv markings for specific PHBs are not
globally unique, and may be arbitrarily removed or even changed by globally unique, and may be arbitrarily removed or even changed by
intermediary nodes or domains. Hence, with respect to emergency intermediary nodes or domains. Hence, with respect to emergency
related data packets, we are still missing an in-band marking in a related data packets, we are still missing an in-band marking in a
data packet that stays constant on an end-to-end basis. data packet that stays constant on an end-to-end basis.
There are three choices in defining a persistent marking of data There are three choices in defining a persistent marking of data
packets and thus avoid the transitory marking of diff-serv code packets and thus avoiding the transitory marking of diff-serv code
points. One can propose a new PHB dedicated for emergency type points. One can propose a new PHB dedicated for emergency type
traffic as discussed in 4.1.2. One can propose a specification of a traffic as discussed in 4.1.2. One can propose a specification of a
new shim layer protocol at some location above IP. Or, one can add a new shim layer protocol at some location above IP. Or, one can add a
new specification to an existing application layer protocol. The new specification to an existing application layer protocol. The
first two cases are probably the "cleanest" architecturally, but they first two cases are probably the "cleanest" architecturally, but they
are long term efforts that may not come to pass because of a limited are long term efforts that may not come to pass because of a limited
amount of diff-serv code points and the contention that yet another amount of diff-serv code points and the contention that yet another
shim layer will make the IP stack too large. The third case, placing shim layer will make the IP stack too large. The third case, placing
^L
a marking in an application layer packet, also has drawbacks; the key a marking in an application layer packet, also has drawbacks; the key
weakness being the specification of a marking on a per-application weakness being the specification of a marking on a per-application
basis. basis.
Discussions have been held in the Audio/Visual Transport (AVT) work- Discussions have been held in the Audio/Visual Transport (AVT) work-
ing group of augmenting RTP so that it can carry a marking that dis- ing group of augmenting RTP so that it can carry a marking that dis-
tinguishes emergency-related traffic from that which is not. Specif- tinguishes emergency-related traffic from that which is not. Specif-
ically, these discussions centered on defining a new extention that ically, these discussions centered on defining a new extention that
contains a "classifier" field indicating the condition associated contains a "classifier" field indicating the condition associated
with the packet (e.g., authorized-emergency, emergency, normal) [29]. with the packet (e.g., authorized-emergency, emergency, normal) [29].
The rationale behind this idea was that focusing on RTP would allow The rationale behind this idea was that focusing on RTP would allow
one to rely on a point of aggregation that would apply to all pay- one to rely on a point of aggregation that would apply to all pay-
loads that it encapsulates. However, the AVT group has expressed a loads that it encapsulates. However, the AVT group has expressed a
rough consensus that placing additional classifier state in the RTP rough consensus that placing additional classifier state in the RTP
header to denote the importance of one flow over another is not an header to denote the importance of one flow over another is not an
approach that they wish to advance. Objections ranging from relying approach that they wish to advance. Objections ranging from relying
on SIP to convey importance of a flow, as well as the possibility of on SIP to convey importance of a flow, as well as the possibility of
adversely affecting header compression, were expressed. There was adversely affecting header compression, were expressed. There was
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also the general feeling that the extension header for RTP that acts also the general feeling that the extension header for RTP that acts
as a signal should not be used. as a signal should not be used.
4.1.5. MEGACO/H.248 4.1.5. MEGACO/H.248
The Media Gateway Control protocol (MEGACO) [23] defines the interac- The Media Gateway Control protocol (MEGACO) [23] defines the interac-
tion between a media gateway and a media gateway controller. [23] is tion between a media gateway and a media gateway controller. [23] is
viewed as common text with ITU-T Recommendation H.248 and is a result viewed as common text with ITU-T Recommendation H.248 and is a result
of applying the changes of RFC 2886 (Megaco Errata) to the text of of applying the changes of RFC 2886 (Megaco Errata) to the text of
RFC 2885 (Megaco Protocol version 0.8). RFC 2885 (Megaco Protocol version 0.8).
In [23], the protocol specifies a Priority and Emergency field for a In [23], the protocol specifies a Priority and Emergency field for a
context attribute and descriptor. The Emergency is an optional context attribute and descriptor. The Emergency is an optional
boolean (True or False) condition. The Priority value, which ranges boolean (True or False) condition. The Priority value, which ranges
from 0 through 15, specifies the precedence handling for a context. from 0 through 15, specifies the precedence handling for a context.
The protocol does not specify individual values for priority. We The protocol does not specify individual values for priority. We
also do not recommend the definition of a well known value for the also do not recommend the definition of a well known value for the
MEGAGO priority. Any values set should be a function of any SLAs MEGAGO priority -- that is out of scope of this document. Any values
that have been established regarding the handling of emergency set should be a function of any SLAs that have been established
traffic. In addition, given that priority values denote precedence regarding the handling of emergency traffic.
(according to the Megaco protocol), then by default the ETS telephony
data flows should probably receive the same priority as other non-
emergency calls. This approach follows the objective of not relying
on preemption as the default treatment of emergency-related.
^L
4.2. Policy 4.2. Policy
One of the objectives listed in section 3 above is to treat ETS- sig- One of the objectives listed in section 3 above is to treat ETS- sig-
naling, and related data traffic, as non-preemptive in nature. naling, and related data traffic, as non-preemptive in nature.
Further, that this treatment is to be the default mode of operation Further, that this treatment is to be the default mode of operation
or service. This is in recognition that existing regulations or laws or service. This is in recognition that existing regulations or laws
of certain countries governing the establishment of SLAs may not of certain countries governing the establishment of SLAs may not
allow preemptive actions (e.g., dropping existing telephony flows). allow preemptive actions (e.g., dropping existing telephony flows).
On the other hand, the laws and regulations of other countries On the other hand, the laws and regulations of other countries
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outside the scope of the IETF and its specification of designs and outside the scope of the IETF and its specification of designs and
protocols. However, these constraints can be used as a guide in pro- protocols. However, these constraints can be used as a guide in pro-
ducing a baseline capability to be supported; in our case, a default ducing a baseline capability to be supported; in our case, a default
policy for non-preemptive call establishment of ETS signaling and policy for non-preemptive call establishment of ETS signaling and
data. data.
Policy can be in the form of static information embedded in various Policy can be in the form of static information embedded in various
components (e.g., SIP servers or bandwidth brokers), or it can be components (e.g., SIP servers or bandwidth brokers), or it can be
realized and supported via COPS with respect to allocation of a realized and supported via COPS with respect to allocation of a
domain's resources [17]. There is no requirement as to how policy is domain's resources [17]. There is no requirement as to how policy is
^L
accomplished. Instead, if a domain follows actions outside of the accomplished. Instead, if a domain follows actions outside of the
default non-preemptive action of ETS related communication, then we default non-preemptive action of ETS related communication, then we
stipulate that some type of policy mechanism is in place to satisfy stipulate that some type of policy mechanism is in place to satisfy
the local policies of an SLA established for ETS type traffic. the local policies of an SLA established for ETS type traffic.
4.3. Traffic Engineering 4.3. Traffic Engineering
In those cases where a network operates under the constraints of In those cases where a network operates under the constraints of
SLAs, one or more of which pertains to ETS based traffic, it can be SLAs, one or more of which pertains to ETS based traffic, it can be
expected that some form of traffic engineering is applied to the expected that some form of traffic engineering is applied to the
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and/or data traffic. We recommend a review of [36] by clients and and/or data traffic. We recommend a review of [36] by clients and
prospective providers of ETS service, which gives an overview and a prospective providers of ETS service, which gives an overview and a
set of principles of Internet traffic engineering. set of principles of Internet traffic engineering.
MPLS is generally the first protocol that comes to mind when the sub- MPLS is generally the first protocol that comes to mind when the sub-
ject of traffic engineering is brought up. This notion is heightened ject of traffic engineering is brought up. This notion is heightened
concerning the subject of IP telephony because of MPLS's ability to concerning the subject of IP telephony because of MPLS's ability to
permit a quasi-circuit switching capability to be superimposed on the permit a quasi-circuit switching capability to be superimposed on the
current Internet routing model [33]. current Internet routing model [33].
^L
However, having cited MPLS, we need to stress that it is an intra- However, having cited MPLS, we need to stress that it is an intra-
domain protocol, and so may or may not exist within a given ISP. domain protocol, and so may or may not exist within a given ISP.
Other forms of traffic engineering, such as weighted OSPF, may be the Other forms of traffic engineering, such as weighted OSPF, may be the
mechanism of choice by an ISP. mechanism of choice by an ISP.
As a counter example of using a specific protocol to achieve traffic As a counter example of using a specific protocol to achieve traffic
engineering, [41] presents an example by one ISP relying on a high engineering, [41] presents an example by one ISP relying on a high
amount of overprovisioning within its core to satisfy potentially amount of overprovisioning within its core to satisfy potentially
dramatic spikes or bursts of traffic load. In this approach, any dramatic spikes or bursts of traffic load. In this approach, any
configuring of queues for specific customers (neighbors) to support configuring of queues for specific customers (neighbors) to support
target QoS is done on the egress edge of the transit network. target QoS is done on the egress edge of the transit network.
Note: As a point of reference, existing SLAs established by the NCS Note: As a point of reference, existing SLAs established by the NCS
for GETS service tend to focus on a maximum allocation of (e.g., 1%) for GETS service tend to focus on a loosely defined maximum alloca-
of calls allowed to be established through a given LEC using HPC. tion of (e.g., 1% to 10%) of calls allowed to be established through
Once this limit is reached, all other GETS calls experience the same a given LEC using HPC. It is expected, and encouraged, that ETS
probability of call completion as the general public. It is related SLAs of ISPs will have a limit with respect to the amount of
expected, and encouraged, that ETS related SLAs will have a limit traffic distinguished as being emergency related, and initiated by an
with respect to the amount of traffic distinguished as being emer- authorized user.
gency related, and initiated by an authorized user.
4.4. Security 4.4. Security
If ETS support moves from intra-domain PSTN and IP networks to If ETS support moves from intra-domain PSTN and IP networks to
^L
inter-domain end-to-end IP, authenticated service becomes more com- inter-domain end-to-end IP, authenticated service becomes more com-
plex to provide. Where an ETS call is carried from PSTN to PSTN via plex to provide. Where an ETS call is carried from PSTN to PSTN via
one telephony carrier's backbone IP network, very little IP-specific one telephony carrier's backbone IP network, very little IP-specific
security support is required. The user authenticates themself as security support is required. The user authenticates themself as
usual to the network using a PIN. The gateway from the PSTN connec- usual to the network using a PIN. The gateway from the PSTN connec-
tion into the backbone IP network must be able to signal that the tion into the backbone IP network must be able to signal that the
flow has an ETS label. Conversely, the gateway back into the PSTN flow has an ETS label. Conversely, the gateway back into the PSTN
must similarly signal the call's label. A secure link between the must similarly signal the call's label. A secure link between the
gateways may be set up using IPSec or SIP security functionality. If gateways may be set up using IPSec or SIP security functionality. If
the endpoint is an IP device, the link may be set up securely from the endpoint is an IP device, the link may be set up securely from
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As flows traverse more than one IP network, domains whose peering As flows traverse more than one IP network, domains whose peering
agreements include ETS support must have the means to securely signal agreements include ETS support must have the means to securely signal
a given flow's ETS status. They may choose to use physical link secu- a given flow's ETS status. They may choose to use physical link secu-
rity and/or IPSec authentication, combined with traffic conditioning rity and/or IPSec authentication, combined with traffic conditioning
measures to limit the amount of ETS traffic that may pass between the measures to limit the amount of ETS traffic that may pass between the
two domains. The inter-domain agreement may require the originating two domains. The inter-domain agreement may require the originating
network to take responsibility for ensuring only authorized traffic network to take responsibility for ensuring only authorized traffic
is marked with ETS priority; the downstream domain may still perform is marked with ETS priority; the downstream domain may still perform
redundant conditioning to prevent the propagation of theft and denial redundant conditioning to prevent the propagation of theft and denial
of service attacks. Security may be provided between ingress and of service attacks. Security may be provided between ingress and
egress gateways or IP endpoints using IPSec or SIP security egress gateways or IP endpoints using IPSec or SIP security func-
tions.
^L
functions.
When a call originates from an IP device, the ingress network may When a call originates from an IP device, the ingress network may
authorize IEPS traffic over that link as part of its user authentica- authorize IEPS traffic over that link as part of its user authentica-
tion procedures. These authentication procedures may occur at the tion procedures. These authentication procedures may occur at the
link or network layers, but are entirely at the discretion of the link or network layers, but are entirely at the discretion of the
ingress network. That network must decide how often it should update ingress network. That network must decide how often it should update
its list of authorized ETS users based on the bounds it is prepared its list of authorized ETS users based on the bounds it is prepared
to accept on traffic from recently-revoked users. to accept on traffic from recently-revoked users.
4.5. Alternate Path Routing 4.5. Alternate Path Routing
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path to route IP telephony traffic around congestion points and thus path to route IP telephony traffic around congestion points and thus
avoid them. Ideally, the discovery process would be accomplished in avoid them. Ideally, the discovery process would be accomplished in
an expedient manner (possibly even a priori to the need of its an expedient manner (possibly even a priori to the need of its
existence). At this level, we make no assumptions as to how the existence). At this level, we make no assumptions as to how the
alternate path is accomplished, or even at which layer it is achieved alternate path is accomplished, or even at which layer it is achieved
-- e.g., the network versus the application layer. But this kind of -- e.g., the network versus the application layer. But this kind of
capability, at least in a minimal form, would help contribute to capability, at least in a minimal form, would help contribute to
increasing the probability of ETS call completion by making use of increasing the probability of ETS call completion by making use of
noncongested alternate paths. We use the term "minimal form" to noncongested alternate paths. We use the term "minimal form" to
emphasize the fact that care must be taken in how the system provides emphasize the fact that care must be taken in how the system provides
^L
alternate paths so it does not significantly contribute to the alternate paths so it does not significantly contribute to the
congestion that is to be avoided (e.g., via excess control/discovery congestion that is to be avoided (e.g., via excess control/discovery
messages). messages).
At the time that this document was written, we can identify two areas At the time that this document was written, we can identify two areas
in the IETF that can be helpful in providing alternate paths for call in the IETF that can be helpful in providing alternate paths for call
signaling. The first is [10], which is focused on network layer signaling. The first is [10], which is focused on network layer
routing and describes a framework for enhancements to the LDP specif- routing and describes a framework for enhancements to the LDP specif-
ication of MPLS to help achieve fault tolerance. This in itself does ication of MPLS to help achieve fault tolerance. This in itself does
not provide alternate path routing, but rather helps minimize loss in not provide alternate path routing, but rather helps minimize loss in
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document [19] has been published as an RFC which describes the document [19] has been published as an RFC which describes the
discovery and exchange of IP telephony gateway routing tables between discovery and exchange of IP telephony gateway routing tables between
providers. The TRIP protocol [22] specifies application level providers. The TRIP protocol [22] specifies application level
telephony routing regardless of the signaling protocol being used telephony routing regardless of the signaling protocol being used
(e.g., SIP or H.323). TRIP is modeled after BGP-4 and advertises (e.g., SIP or H.323). TRIP is modeled after BGP-4 and advertises
reachability and attributes of destinations. In its current form, reachability and attributes of destinations. In its current form,
several attributes have already been defined, such as LocalPreference several attributes have already been defined, such as LocalPreference
and MultiExitDisc. Additional attributes can be registered with and MultiExitDisc. Additional attributes can be registered with
IANA. IANA.
^L
Inter-domain routing is not an area that should be considered in Inter-domain routing is not an area that should be considered in
terms of alternate path routing support for ETS. The Border Gateway terms of alternate path routing support for ETS. The Border Gateway
Protocol is currently strained in meetings its existing requirements, Protocol is currently strained in meetings its existing requirements,
and thus adding additional features that would generate an increase and thus adding additional features that would generate an increase
in advertised routes will not be well received by the IETF. Refer to in advertised routes will not be well received by the IETF. Refer to
[42] for a commentary on Inter-Domain routing. [42] for a commentary on Inter-Domain routing.
4.6. End-to-End Fault Tolerance 4.6. End-to-End Fault Tolerance
This topic involves the work that has been done in trying to compen- This topic involves the work that has been done in trying to compen-
skipping to change at page 16, line 29 skipping to change at page 15, line 4
packets. (Note that our aim is fault tolerance, as opposed to an packets. (Note that our aim is fault tolerance, as opposed to an
expectation of always achieving it). expectation of always achieving it).
In the former case, additional FEC data packets are constructed from In the former case, additional FEC data packets are constructed from
a set of original data packets and inserted into the end-to-end a set of original data packets and inserted into the end-to-end
stream. Depending on the algorithm used, these FEC packets can stream. Depending on the algorithm used, these FEC packets can
reconstruct one or more of the original set that were lost by the reconstruct one or more of the original set that were lost by the
network. An example may be in the form of a 10:3 ratio, in which 10 network. An example may be in the form of a 10:3 ratio, in which 10
original packets are used to generate three additional FEC packets. original packets are used to generate three additional FEC packets.
Thus, if the network loses 30% or less number of packets, then the Thus, if the network loses 30% or less number of packets, then the
^L
FEC scheme will be able to compensate for that loss. The drawback to FEC scheme will be able to compensate for that loss. The drawback to
this approach is that to compensate for the loss, a steady state this approach is that to compensate for the loss, a steady state
increase in offered load has been injected into the network. This increase in offered load has been injected into the network. This
makes an arguement that the act of protection against loss has con- makes an arguement that the act of protection against loss has con-
tributed to additional pressures leading to congestion, which in turn tributed to additional pressures leading to congestion, which in turn
helps trigger packet loss. In addition, in using a ratio of 10:3, helps trigger packet loss. In addition, in using a ratio of 10:3,
the source (or some proxy) must "hold" all 10 packets in order to the source (or some proxy) must "hold" all 10 packets in order to
construct the three FEC packets. This contributes to the end-to-end construct the three FEC packets. This contributes to the end-to-end
delay of the packets as well as minor bursts of load in addition to delay of the packets as well as minor bursts of load in addition to
changes in jitter. changes in jitter.
skipping to change at page 17, line 4 skipping to change at page 15, line 30
first glance, this would appear to be even less friendly to the net- first glance, this would appear to be even less friendly to the net-
work than that of adding FEC packets. However, the encodings of the work than that of adding FEC packets. However, the encodings of the
redundant packets can be of a different type (or even transcoded into redundant packets can be of a different type (or even transcoded into
a lower quality) that produce redundant data packets that are signi- a lower quality) that produce redundant data packets that are signi-
ficantly smaller than the original packet. ficantly smaller than the original packet.
Two RFCs [24, 25] have been produced that define RTP payloads for FEC Two RFCs [24, 25] have been produced that define RTP payloads for FEC
and redundant audio data. An implementation example of a redundant and redundant audio data. An implementation example of a redundant
audio application can be found in [14]. We note that both FEC and audio application can be found in [14]. We note that both FEC and
redundant transmissions can be viewed as rather specific and to a redundant transmissions can be viewed as rather specific and to a
^L
degree tangential solutions regarding packet loss and emergency com- degree tangential solutions regarding packet loss and emergency com-
munications. Hence, these topics are placed under the category of munications. Hence, these topics are placed under the category of
value added objectives. value added objectives.
5. Key Scenarios 5. Key Scenarios
There are various scenarios in which IP telephony can be realized, There are various scenarios in which IP telephony can be realized,
each of which can imply a unique set of functional requirements that each of which can imply a unique set of functional requirements that
may include just a subset of those listed above. We acknowledge that may include just a subset of those listed above. We acknowledge that
a scenario may exist whose functional requirements are not listed a scenario may exist whose functional requirements are not listed
skipping to change at page 17, line 30 skipping to change at page 16, line 5
with respect to supporting emergency-related telephony traffic. We with respect to supporting emergency-related telephony traffic. We
stress that this does not preclude an IP-only end-to-end model, but stress that this does not preclude an IP-only end-to-end model, but
rather the inclusion of the PSTN expands the problem space and rather the inclusion of the PSTN expands the problem space and
includes the current dominant form of voice communication. includes the current dominant form of voice communication.
Note: as stated in section 1.2, [36] provides a more extensive set of Note: as stated in section 1.2, [36] provides a more extensive set of
scenarios in which IP telephony can be deployed. Our selected set scenarios in which IP telephony can be deployed. Our selected set
below is only meant to provide an couple of examples of how the pro- below is only meant to provide an couple of examples of how the pro-
tocols and capabilities presented in Section 3 can play a role. tocols and capabilities presented in Section 3 can play a role.
^L
Single IP Administrative Domain Single IP Administrative Domain
------------------------------- -------------------------------
This scenario is a direct reflection of the evolution of the PSTN. This scenario is a direct reflection of the evolution of the PSTN.
Specifically, we refer to the case in which data networks have Specifically, we refer to the case in which data networks have
emerged in various degrees as a backbone infrastructure connecting emerged in various degrees as a backbone infrastructure connecting
PSTN switches at its edges. This represents a single isolated IP PSTN switches at its edges. This scenario represents a single iso-
administrative domain that has no directly adjacent IP domains con- lated IP administrative domain that has no directly adjacent IP
nected to it. We show an example of this scenario below in Figure 1. domains connected to it. We show an example of this scenario below
In this example, we show two types of telephony carriers. One is the in Figure 1. In this example, we show two types of telephony car-
legacy carrier, whose infrastructure retains the classic switching riers. One is the legacy carrier, whose infrastructure retains the
architecture attributed to the PSTN. The other is the next genera- classic switching architecture attributed to the PSTN. The other is
tion carrier, which uses a data network (e.g., IP) as its core the next generation carrier, which uses a data network (e.g., IP) as
infrastructure, and Signaling Gateways at its edges. These gateways its core infrastructure, and Signaling Gateways at its edges. These
"speak" SS7 externally with peering carriers, and another protocol gateways "speak" SS7 externally with peering carriers, and another
(e.g., SIP) internally, which rides on top of the IP infrastructure. protocol (e.g., SIP) internally, which rides on top of the IP infras-
tructure.
^L
Legacy Next Generation Next Generation Legacy Next Generation Next Generation
Carrier Carrier Carrier Carrier Carrier Carrier
******* *************** ************** ******* *************** **************
* * * * ISUP * * * * * * ISUP * *
SW<--->SW <-----> SG <---IP---> SG <--IAM--> SG <---IP---> SG SW<--->SW <-----> SG <---IP---> SG <--IAM--> SG <---IP---> SG
* * (SS7) * (SIP) * (SS7) * (SIP) * * * (SS7) * (SIP) * (SS7) * (SIP) *
******* *************** ************** ******* *************** **************
SW - Telco Switch SW - Telco Switch, SG - Signaling Gateway
SG - Signaling Gateway
Figure 1 Figure 1
The significant aspect of this scenario is that all the resources of The significant aspect of this scenario is that all the resources of
each IP "island" fall within a given administrative authority. each IP "island" fall within a given administrative authority.
Hence, there is not a problem of retaining toll quality Grade of Ser- Hence, there is not a problem of retaining toll quality Grade of Ser-
vice as the voice traffic (data and signaling) exits the IP network vice as the voice traffic (data and signaling) exits the IP network
because of the existing SS7 provisioned service between telephony because of the existing SS7 provisioned service between telephony
carriers. Thus, the need for support of mechanisms like diff-serv, carriers. Thus, the need for support of mechanisms like diff-serv in
and an expansion of the defined set of Per-Hop Behaviors is reduced the presence of overprovisioning, and an expansion of the defined set
(if not eliminated) under this scenario. of Per-Hop Behaviors, is reduced under this scenario.
Another function that has little or no importance within the closed Another function that has little or no importance within the closed
IP environment of Figure 1 is that of IP security. The fact that IP environment of Figure 1 is that of IP security. The fact that
each administrative domain peers with each other as part of the PSTN, each administrative domain peers with each other as part of the PSTN,
means that existing security, in the form of Personal Identification means that existing security, in the form of Personal Identification
Number (PIN) authentication (under the context of telephony infras- Number (PIN) authentication (under the context of telephony infras-
tructure protection), is the default scope of security. We do not tructure protection), is the default scope of security. We do not
claim that the reliance on a PIN based security system is highly claim that the reliance on a PIN based security system is highly
secure or even desirable. But, we use this system as a default secure or even desirable. But, we use this system as a default
^L
mechanism in order to avoid placing additional requirements on exist- mechanism in order to avoid placing additional requirements on exist-
ing authorized emergency telephony systems. ing authorized emergency telephony systems.
Multiple IP Administrative Domains Multiple IP Administrative Domains
---------------------------------- ----------------------------------
We view the scenario of multiple IP administrative domains as a We view the scenario of multiple IP administrative domains as a
superset of the previous scenario. Specifically, we retain the superset of the previous scenario. Specifically, we retain the
notion that the IP telephony system peers with the existing PSTN. In notion that the IP telephony system peers with the existing PSTN. In
addition, segments addition, segments
(i.e., portions of the Internet) may exchange signaling with other IP (i.e., portions of the Internet) may exchange signaling with other IP
administrative domains via non-PSTN signaling protocols like SIP. administrative domains via non-PSTN signaling protocols like SIP.
^L
Legacy Next Generation Next Generation Legacy Next Generation Next Generation
Carrier Carrier Carrier Carrier Carrier Carrier
******* *************** ************** ******* *************** **************
* * * * * * * * * * * *
SW<--->SW <-----> SG <---IP---> SG <--IP--> SG <---IP---> SG SW<--->SW <-----> SG <---IP---> SG <--IP--> SG <---IP---> SG
* * (SS7) * (SIP) * (SIP) * (SIP) * * * (SS7) * (SIP) * (SIP) * (SIP) *
******* *************** ************** ******* *************** **************
SW - Telco Switch SW - Telco Switch
SG - Signaling Gateway SG - Signaling Gateway
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We conclude this section by mentioning a complimentary work in pro- We conclude this section by mentioning a complimentary work in pro-
gress in providing ISUP transparency across SS7-SIP interworking gress in providing ISUP transparency across SS7-SIP interworking
[37]. The objective of this effort is to access services in the SIP [37]. The objective of this effort is to access services in the SIP
network and yet maintain transparency of end-to-end PSTN services. network and yet maintain transparency of end-to-end PSTN services.
Not all services are mapped (as per the design goals of [37], so we Not all services are mapped (as per the design goals of [37], so we
anticipate the need for an additional document to specify the mapping anticipate the need for an additional document to specify the mapping
between new SIP labels and existing PSTN code points like NS/EP and between new SIP labels and existing PSTN code points like NS/EP and
MLPP. MLPP.
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6. Security Considerations 6. Security Considerations
Information on this topic is presented in sections 2 and 4. Information on this topic is presented in sections 2 and 4.
7. References 7. References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996. 9, RFC 2026, October 1996.
2 Braden, R., et. al., "Integrated Services in the Internet 2 Braden, R., et. al., "Integrated Services in the Internet
Architecture: An Overview", Informational, RFC 1633, June 1994. Architecture: An Overview", Informational, RFC 1633, June 1994.
3 Braden, R., et. al., "Resource Reservation Protocol (RSVP) 3 Braden, R., et. al., "Resource Reservation Protocol (RSVP)
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Version 1, Functional Specification", Proposed Standard, RFC Version 1, Functional Specification", Proposed Standard, RFC
2205, Sept. 1997. 2205, Sept. 1997.
4 Shenker, S., et. al., "Specification of Guaranteed Quality of 4 Shenker, S., et. al., "Specification of Guaranteed Quality of
Service", Proposed Standard, RFC 2212, Sept 1997. Service", Proposed Standard, RFC 2212, Sept 1997.
5 Wroclawski, J., "Specification for Controlled-Load Network 5 Wroclawski, J., "Specification for Controlled-Load Network
Service Element", Proposed Standard, RFC 2211, Sept 1997. Service Element", Proposed Standard, RFC 2211, Sept 1997.
6 Baker, F., et. al., "Aggregation of RSVP for IPv4 and IPv6 6 Baker, F., et. al., "Aggregation of RSVP for IPv4 and IPv6
skipping to change at page 20, line 40 skipping to change at page 19, line 4
11 Postel, J., "Simple Mail Transfer Protocol", Standard, RFC 821, 11 Postel, J., "Simple Mail Transfer Protocol", Standard, RFC 821,
August 1982. August 1982.
12 Handley, M., et. al., "SIP: Session Initiation Protocol", 12 Handley, M., et. al., "SIP: Session Initiation Protocol",
Proposed Standard, RFC 2543, March 1999. Proposed Standard, RFC 2543, March 1999.
13 ANSI, "Signaling System No. 7(SS7), High Probability of 13 ANSI, "Signaling System No. 7(SS7), High Probability of
Completion (HPC) Network Capability", ANSI T1.631-1993, (R1999). Completion (HPC) Network Capability", ANSI T1.631-1993, (R1999).
14 Robust Audio Tool (RAT): 14 Robust Audio Tool (RAT):
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http://www-mice.cs.ucl.ac.uk/multimedia/software/rat http://www-mice.cs.ucl.ac.uk/multimedia/software/rat
15 Schulzrinne, H, "Requirements for Resource Priority Mechanisms for 15 Schulzrinne, H, "Requirements for Resource Priority Mechanisms for
the Session Initiation Protocol", Informational, RFC 3487, the Session Initiation Protocol", Informational, RFC 3487,
February 2003 February 2003
16 Nichols, K., et. al.,"Definition of the Differentiated Services 16 Nichols, K., et. al.,"Definition of the Differentiated Services
Field (DS Field) in the Ipv4 and Ipv6 Headers", Proposed Field (DS Field) in the Ipv4 and Ipv6 Headers", Proposed
Standard, RFC 2474, December 1998. Standard, RFC 2474, December 1998.
17 Durham, D., "The COPS (Common Open Policy Service) Protocol", 17 Durham, D., "The COPS (Common Open Policy Service) Protocol",
Proposed Standard, RFC 2748, Jan 2000. Proposed Standard, RFC 2748, Jan 2000.
18 ITU, "International Emergency Preparedness Scheme", ITU 18 ITU, "International Emergency Preparedness Scheme", ITU
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Recommendation, E.106, March 2000. Recommendation, E.106, March 2000.
19 Rosenburg, J., Schulzrinne, H., "A Framework for Telephony Routing 19 Rosenburg, J., Schulzrinne, H., "A Framework for Telephony Routing
Over IP", Informational, RFC 2871, June 2000 Over IP", Informational, RFC 2871, June 2000
20 Heinanen. et. al, "Assured Forwarding PHB Group", Proposed 20 Heinanen. et. al, "Assured Forwarding PHB Group", Proposed
Standard, RFC 2597, June 1999 Standard, RFC 2597, June 1999
21 ITU, "Multi-Level Precedence and Preemption Service, ITU, 21 ITU, "Multi-Level Precedence and Preemption Service, ITU,
Recomendation, I.255.3, July, 1990. Recomendation, I.255.3, July, 1990.
skipping to change at page 21, line 40 skipping to change at page 20, line 4
26 ANSI, "Signaling System No. 7, ISDN User Part", ANSI T1.113-2000, 26 ANSI, "Signaling System No. 7, ISDN User Part", ANSI T1.113-2000,
2000. 2000.
27 Brown, I., "Securing IEPS over IP", White Paper, 27 Brown, I., "Securing IEPS over IP", White Paper,
http://iepscheme.net/docs/secure_IEPS.doc http://iepscheme.net/docs/secure_IEPS.doc
28 "Description of an International Emergency Preference 28 "Description of an International Emergency Preference
Scheme (IEPS)", ITU-T Recommendation E.106 March, 2002 Scheme (IEPS)", ITU-T Recommendation E.106 March, 2002
29 Carlberg, K., "The Classifier Extension Header for RTP", Internet 29 Carlberg, K., "The Classifier Extension Header for RTP", Internet
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Draft, Work In Progress, October 2001. Draft, Work In Progress, October 2001.
30 National Communications System: http://www.ncs.gov 30 National Communications System: http://www.ncs.gov
31 Bansal, R., Ravikanth, R., "Performance Measures for Voice on IP", 31 Bansal, R., Ravikanth, R., "Performance Measures for Voice on IP",
http://www.ietf.org/proceedings/97aug/slides/tsv/ippm-voiceip/, http://www.ietf.org/proceedings/97aug/slides/tsv/ippm-voiceip/,
IETF Presentation: IPPM-Voiceip, Aug, 1997 IETF Presentation: IPPM-Voiceip, Aug, 1997
32 Hardman, V., et al, "Reliable Audio for Use over the Internet", 32 Hardman, V., et al, "Reliable Audio for Use over the Internet",
Proceedings, INET'95, Aug, 1995. Proceedings, INET'95, Aug, 1995.
33 Awduche, D, et al, "Requirements for Traffic Engineering Over 33 Awduche, D, et al, "Requirements for Traffic Engineering Over
MPLS", Informational, RFC 2702, September, 1999. MPLS", Informational, RFC 2702, September, 1999.
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34 Polk, J., "An Architecture for Multi-Level Precedence and 34 Polk, J., "An Architecture for Multi-Level Precedence and
Preemption over IP", Internet Draft, Work In Progress, Preemption over IP", Internet Draft, Work In Progress,
November, 2001. November, 2001.
35 "Service Class Designations for H.323 Calls", ITU 35 "Service Class Designations for H.323 Calls", ITU
Recommendation H.460.4, November, 2002 Recommendation H.460.4, November, 2002
36 Awduche, D., et. al., "Overview and Principles of Internet Traffic 36 Awduche, D., et. al., "Overview and Principles of Internet Traffic
Engineering", Informational, RFC 3272, May 2002. Engineering", Informational, RFC 3272, May 2002.
skipping to change at page 22, line 37 skipping to change at page 21, line 5
Emergency Telecommunications Service", Work In Progress, Internet- Emergency Telecommunications Service", Work In Progress, Internet-
Draft, January, 2003 Draft, January, 2003
41 Meyers, D., "Some Thoughts on CoS and Backbone Networks" 41 Meyers, D., "Some Thoughts on CoS and Backbone Networks"
http://www.ietf.org/proceedings/02nov/slides/ieprep-4.pdf http://www.ietf.org/proceedings/02nov/slides/ieprep-4.pdf
IETF Presentation: IEPREP, Dec, 2002 IETF Presentation: IEPREP, Dec, 2002
42 Huston, G., "Commentary on Inter-Domain Routing In the Internet", 42 Huston, G., "Commentary on Inter-Domain Routing In the Internet",
Informational, RFC 3221, December 2001. Informational, RFC 3221, December 2001.
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8. Appendix A: Government Telephone Preference Scheme (GTPS) 8. Appendix A: Government Telephone Preference Scheme (GTPS)
This framework document uses the T1.631 and ITU IEPS standard as a This framework document uses the T1.631 and ITU IEPS standard as a
target model for defining a framework for supporting authorized emer- target model for defining a framework for supporting authorized emer-
gency related communication within the context of IP telephony. We gency related communication within the context of IP telephony. We
also use GETS as a helpful model to draw experience from. We take also use GETS as a helpful model to draw experience from. We take
this position because of the various areas that must be considered; this position because of the various areas that must be considered;
from the application layer to the (inter)network layer, in addition from the application layer to the (inter)network layer, in addition
to policy, security (authorized access), and traffic engineering. to policy, security (authorized access), and traffic engineering.
The U.K. has a different type of authorized use of telephony services The U.K. has a different type of authorized use of telephony services
referred to as the Government Telephone Preference Scheme (GTPS). At referred to as the Government Telephone Preference Scheme (GTPS). At
present, GTPS only applies to a subset of the local loop lines of present, GTPS only applies to a subset of the local loop lines of
within the UK. The lines are divided into Categories 1, 2, and 3. within the UK. The lines are divided into Categories 1, 2, and 3.
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The first two categories involve authorized personnel involved in The first two categories involve authorized personnel involved in
emergencies such as natural disasters. Category 3 identifies the emergencies such as natural disasters. Category 3 identifies the
general public. Priority marks, via C7/NUP, are used to bypass general public. Priority marks, via C7/NUP, are used to bypass
call-gaping for a given Category. The authority to activate GTPS has call-gaping for a given Category. The authority to activate GTPS has
been extended to either a central or delegated authority. been extended to either a central or delegated authority.
8.1. GTPS and the Framework Document 8.1. GTPS and the Framework Document
The design of the current GTPS, with its designation of preference The design of the current GTPS, with its designation of preference
based on physical static devices, precludes the need for several based on physical static devices, precludes the need for several
skipping to change at page 23, line 37 skipping to change at page 22, line 4
SS7 ISUP Initial Address Message. This single label or value is SS7 ISUP Initial Address Message. This single label or value is
referred to as the National Security and Emergency Preparedness referred to as the National Security and Emergency Preparedness
(NS/EP) indicator and is part of the T1.631 standard. The following (NS/EP) indicator and is part of the T1.631 standard. The following
subsections presents a snap shot of parallel on-going efforts in subsections presents a snap shot of parallel on-going efforts in
various standards groups. various standards groups.
It is important to note that the recent activity in other groups have It is important to note that the recent activity in other groups have
gravitated to defining 5 labels or levels of priority. The impact of gravitated to defining 5 labels or levels of priority. The impact of
this approach is minimal in relation to this ETS framework document this approach is minimal in relation to this ETS framework document
because it simply generates a need to define a set of corresponding because it simply generates a need to define a set of corresponding
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labels for the resource priority header of SIP. labels for the resource priority header of SIP.
9.1. Study Group 16 (ITU) 9.1. Study Group 16 (ITU)
Study Group 16 (SG16) of the ITU is responsible for studies relating Study Group 16 (SG16) of the ITU is responsible for studies relating
to multimedia service definition and multimedia systems, including to multimedia service definition and multimedia systems, including
protocols and signal processing. protocols and signal processing.
A contribution [35] has been accepted by this group that adds a A contribution [35] has been accepted by this group that adds a
Priority Class parameter to the call establishment messages of H.323. Priority Class parameter to the call establishment messages of H.323.
This class is further divided into two parts; one for Priority Value This class is further divided into two parts; one for Priority Value
and the other is a Priority Extension for indicating subclasses. It and the other is a Priority Extension for indicating subclasses. It
is this former part that roughly corresponds to the labels is this former part that roughly corresponds to the labels tran-
sported via the Resource Priority field for SIP [15].
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transported via the Resource Priority field for SIP [15].
The draft recommendation advocates defining PriorityClass information The draft recommendation advocates defining PriorityClass information
that would be carried in the GenericData parameter in the H323-UU-PDU that would be carried in the GenericData parameter in the H323-UU-PDU
or RAS messages. The GenericData parameter contains Priori- or RAS messages. The GenericData parameter contains Priori-
tyClassGenericData. The PriorityClassInfo of the PriorityClassGener- tyClassGenericData. The PriorityClassInfo of the PriorityClassGener-
icData contains the Priority and Priority Extension fields. icData contains the Priority and Priority Extension fields.
At present, 5 levels have been defined for the Priority Value part of At present, 4 levels have been defined for the Priority Value part of
the Priority Class parameter: Low, Normal, High, Emergency-Public, the Priority Class parameter: Normal, High, Emergency-Public,
Emergency-Authorized. An additional 8-bit priority extension has been Emergency-Authorized. An additional 8-bit priority extension has been
defined to provide for subclasses of service at each priority. defined to provide for subclasses of service at each priority.
The suggested ASN.1 definition of the service class is the following: The suggested ASN.1 definition of the service class is the following:
ServiceClassInfo ::= SEQUENCE CALL-PRIORITY {itu-t(0) recommendation(0) h(8) 460 4 version1(0)}
DEFINITIONS AUTOMATIC TAGS::=
BEGIN
IMPORTS
ClearToken,
CryptoToken
FROM H235-SECURITY-MESSAGES;
CallPriorityInfo::= SEQUENCE
{ {
priority CHOICE priorityValue CHOICE
{ {
emergencyAuthorized NULL, emergencyAuthorized NULL,
emergencyPublic NULL, emergencyPublic NULL,
high NULL, high NULL,
normal NULL, normal NULL,
low NULL },
}
priorityExtension INTEGER (0..255) OPTIONAL; ^L
requiredClass NULL OPTIONAL priorityExtension INTEGER (0..255) OPTIONAL,
tokens SEQUENCE OF ClearToken OPTIONAL tokens SEQUENCE OF ClearToken OPTIONAL,
cryptoTokens SEQUENCE OF CryptoH323Token OPTIONAL cryptoTokens SEQUENCE OF CryptoToken OPTIONAL,
rejectReason CHOICE
{
priorityUnavailable NULL,
priorityUnauthorized NULL,
priorityValueUnknown NULL,
} OPTIONAL, -- Only used in CallPriorityConfirm
} }
The advantage in using the GenericData parameter is that an existing The advantage in using the GenericData parameter is that an existing
parameter is used, as opposed to defining a new parameter and causing parameter is used, as opposed to defining a new parameter and causing
subsequent changes in existing H.323/H.225 documents. subsequent changes in existing H.323/H.225 documents.
10. Acknowledgments 10. Acknowledgments
The authors would like to acknowledge the helpful comments, opinions, The authors would like to acknowledge the helpful comments, opinions,
and clarifications of Stu Goldman, James Polk, Dennis Berg, as well and clarifications of Stu Goldman, James Polk, Dennis Berg, as well
as those comments received from the IEPS and IEPREP mailing lists. as those comments received from the IEPS and IEPREP mailing lists.
Additional thanks to Peter Walker of Oftel for private discussions on Additional thanks to Peter Walker of Oftel for private discussions on
the operation of GTPS, and Gary Thom on clarifications of the SG16 the operation of GTPS, and Gary Thom on clarifications of the SG16
draft contribution. draft contribution.
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11. Author's Addresses 11. Author's Addresses
Ken Carlberg Ian Brown Ken Carlberg Ian Brown
University College London University College London University College London University College London
Department of Computer Science Department of Computer Science Department of Computer Science Department of Computer Science
Gower Street Gower Street Gower Street Gower Street
London, WC1E 6BT London, WC1E 6BT London, WC1E 6BT London, WC1E 6BT
United Kingdom United Kingdom United Kingdom United Kingdom
Cory Beard Cory Beard
skipping to change at page 26, line 10 skipping to change at page 24, line 10
5100 Rockhill Road 5100 Rockhill Road
Kansas City, MO 64110-2499 Kansas City, MO 64110-2499
USA USA
BeardC@umkc.edu BeardC@umkc.edu
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Table of Contents Table of Contents
1. Introduction ................................................... 2 1. Introduction ................................................... 2
1.1 Emergency Related Data ....................................... 3 1.1 Emergency Related Data ....................................... 3
1.1.1 Government Emergency Telecommunications Service (GETS) ..... 4 1.1.1 Government Emergency Telecommunications Service (GETS) ..... 3
1.1.2 International Emergency Preparedness Scheme (IEPS) ......... 4 1.1.2 International Emergency Preparedness Scheme (IEPS) ......... 4
1.2 Scope of this Document ....................................... 4 1.2 Scope of this Document ....................................... 4
2. Objective ..................................................... 6 2. Objective ..................................................... 6
3. Considerations ................................................ 6 3. Considerations ................................................ 6
4. Protocols and Capabilities .................................... 7 4. Protocols and Capabilities .................................... 7
4.1 Signaling & State Information ................................ 7 4.1 Signaling & State Information ................................ 7
4.1.1 SIP ........................................................ 8 4.1.1 SIP ........................................................ 7
4.1.2 Diff-Serv .................................................. 8 4.1.2 Diff-Serv .................................................. 8
4.1.3 Variations Related to Diff-Serv and Queuing ................ 9 4.1.3 Variations Related to Diff-Serv and Queuing ................ 9
4.1.4 RTP ........................................................ 11 4.1.4 RTP ........................................................ 9
4.1.5 MEGACO/H.248 ............................................... 12 4.1.5 MEGACO/H.248 ............................................... 11
4.2 Policy ....................................................... 13 4.2 Policy ....................................................... 11
4.3 Traffic Engineering .......................................... 13 4.3 Traffic Engineering .......................................... 12
4.4 Security ..................................................... 14 4.4 Security ..................................................... 12
4.5 Alternate Path Routing ....................................... 15 4.5 Alternate Path Routing ....................................... 13
4.6 End-to-End Fault Tolerance ................................... 16 4.6 End-to-End Fault Tolerance ................................... 14
5. Key Scenarios ................................................. 17 5. Key Scenarios ................................................. 15
6. Security Considerations ....................................... 19 6. Security Considerations ....................................... 18
7. References .................................................... 19 7. References .................................................... 18
8. Appendix A: Government Telephone Preference Scheme (GTPS) ..... 22 8. Appendix A: Government Telephone Preference Scheme (GTPS) ..... 21
8.1 GTPS and the Framework Document .............................. 23 8.1 GTPS and the Framework Document .............................. 21
9. Appendix B: Related Standards Work ............................ 23 9. Appendix B: Related Standards Work ............................ 21
9.1 Study Group 16 (ITU) ......................................... 23 9.1 Study Group 16 (ITU) ......................................... 22
10. Acknowledgments .............................................. 24 10. Acknowledgments .............................................. 23
11. Author's Addresses ........................................... 25 11. Author's Addresses ........................................... 23
Full Copyright Statement Full Copyright Statement
"Copyright (C) The Internet Society 2003. All Rights Reserved. This "Copyright (C) The Internet Society 2003. All Rights Reserved. This
document and translations of it may be copied and furnished to oth- document and translations of it may be copied and furnished to oth-
ers, and derivative works that comment on or otherwise explain it or ers, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind, distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
 End of changes. 

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