draft-ietf-ieprep-framework-06.txt   draft-ietf-ieprep-framework-07.txt 
Internet Engineering Task Force Ken Carlberg Internet Engineering Task Force Ken Carlberg
October 6, 2003 Ian Brown December 1, 2003 Ian Brown
UCL 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-06.txt> <draft-ietf-ieprep-framework-07.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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service in the PSTN, contribute to a constrained solution space. service in the PSTN, contribute to a constrained solution space.
1. Introduction 1. Introduction
The Internet has become the primary target for worldwide communica- The Internet has become the primary target for worldwide communica-
tions. This is in terms of recreation, business, and various ima- tions. This is in terms of recreation, business, and various ima-
ginative reasons for information distribution. A constant fixture in ginative reasons for information distribution. A constant fixture in
the evolution of the Internet has been the support of Best Effort as the evolution of the Internet has been the support of Best Effort as
the default service model. Best Effort, in general terms, infers the default service model. Best Effort, in general terms, implies
that the network will attempt to forward traffic to the destination that the network will attempt to forward traffic to the destination
as best as it can with no guarantees being made, nor any resources as best as it can with no guarantees being made, nor any resources
reserved, to support specific measures of Quality of Service (QoS). reserved, to support specific measures of Quality of Service (QoS).
An underlying goal is to be "fair" to all the traffic in terms of the An underlying goal is to be "fair" to all the traffic in terms of the
resources used to forward it to the destination. resources used to forward it to the destination.
In an attempt to go beyond best effort service, [2] presented an In an attempt to go beyond best effort service, [2] presented an
overview of Integrated Services (int-serv) and its inclusion into the overview of Integrated Services (int-serv) and its inclusion into the
Internet architecture. This was followed by [3], which specified the Internet architecture. This was followed by [3], which specified the
RSVP signaling protocol used to convey QoS requirements. With the RSVP signaling protocol used to convey QoS requirements. With the
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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
"intelligible" VoIP. The larger the packet, correlating to longer "intelligible" VoIP. The larger the packet, correlating to longer
sampling rate, the lower the acceptable rate of loss. sampling rate, the lower the acceptable rate of loss. Note that
[31,32] provide only two of several perspectives in examining VoIP.
A more indepth discussion on this topic is outside the scope of this
document.
Regardless of a definitive drop rate, it would seem that interactive Regardless of a single and definitive characteristic for stressed
voice has a lower threshold of loss than elastic applications such as conditions, it would seem that interactive voice has a lower thres-
email or web browsers. This places a higher burden on the problem hold of some combinations of loss/delay/jitter than elastic applica-
space of supporting VoIP over the Internet. This problem is further tions such as email or web browsers. This places a higher burden on
compounded when toll-quality service is expected because it assumes a the problem space of supporting VoIP over the Internet. This problem
default service model that is better than best effort. This in turn is further compounded when toll-quality service is expected because
can increase the probability that a form of call-blocking can occur it assumes a default service model that is better than best effort.
with VoIP or IP telephony traffic. This in turn can increase the probability that a form of call-
blocking can occur with VoIP or IP telephony traffic.
Beyond this, part of our motivation in writing this document is to Beyond this, part of our motivation in writing this document is to
provide a framework for ISPs and telephony carriers so that they have provide a framework for ISPs and telephony carriers so that they have
an understanding of objectives used to support ETS related IP an understanding of objectives used to support ETS related IP
telephony traffic. In addition, we also wish to provide a reference telephony traffic. In addition, we also wish to provide a reference
point for potential customers in order to constrain their expecta- point for potential customers in order to constrain their expecta-
tions. In particular, we wish to avoid any temptation of trying to tions. In particular, we wish to avoid any temptation of trying to
replicate the exact capabilities of existing emergency voice service replicate the exact capabilities of existing emergency voice service
currently available in the PSTN to that of IP and the Internet. If currently available in the PSTN to that of IP and the Internet. If
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
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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
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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
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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
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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
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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 the current state of some In the following subsections, we discuss the current state of some
protocols and their use in providing support for ETS. We also dis- protocols and their use in providing support for ETS. We also dis-
cuss potential augmentations to different types of signaling and cuss potential augmentations to different types of signaling and
state information to help support the distinction of emergency state information to help support the distinction of emergency
related communications in general. related communications in general.
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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).
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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 an RFC that defines the requirements for a new header field [15] is an RFC that defines the requirements for a new header field
for SIP in reference to resource priority. The requirements are for SIP in reference to resource priority. The requirements are
meant to lead to a means of providing an additional measure of dis- meant to lead to a means of providing an additional measure of dis-
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bits without defining their intended meaning (e.g.,the drop pre- bits without defining their intended meaning (e.g.,the drop pre-
cedence approach of Assured Forwarding). The one caveat to this cedence approach of Assured Forwarding). The one caveat to this
statement are the set of DSCP bits set aside for experimental pur- statement are the set of DSCP bits set aside for experimental pur-
poses. But as the name implies, experimental is for internal examina- poses. But as the name implies, experimental is for internal examina-
tion and use and not for standardization. tion and use and not for standardization.
Comments Comments
-------- --------
It is important to note that as of the time that this document was 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- written, the IETF has been taking a conservative approach in
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
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may not be accepted by the IETF. 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 suggest using the Assured For- In the near term, we would initially suggest using the Assured For-
warding (AF) PHB [20] for distinguishing emergency traffic from other warding (AF) PHB [20] for distinguishing emergency traffic from other
types of flows. At a minimum, AF could be used for the different SIP types of flows. At a minimum, AF could be used for the different SIP
call signaling messages. If EF was also supported by the domain, call signaling messages. If EF was also supported by the domain,
then it would be used for IP telephony data packets. Otherwise, then it would be used for IP telephony data packets. Otherwise,
another AF class would be used for those data flows. another AF class would be used for those data flows.
4.1.3. Variations Related to Diff-Serv and Queuing 4.1.3. Variations Related to Diff-Serv and Queuing
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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.
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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
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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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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
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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. GCP/H.248
The Media Gateway Control protocol (MEGACO) [23] defines the interac- The Gateway Control Protocol (GCP) [23] defines the interaction
tion between a media gateway and a media gateway controller. [23] is 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 an updated version of common text with ITU-T Recommendation
of applying the changes of RFC 2886 (Megaco Errata) to the text of H.248 and is a result of applying the changes of RFC 2886 (Megaco
RFC 2885 (Megaco Protocol version 0.8). Errata) to the text of 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 -- that is out of scope of this document. Any values GCP priority -- that is out of scope of this document. Any values
set should be a function of any SLAs that have been established set should be a function of any SLAs that have been established
regarding the handling of emergency traffic. regarding the handling of emergency traffic.
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
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require its existence. Given this disparity, we rely on local policy require its existence. Given this disparity, we rely on local policy
to determine the degree by which emergency related traffic affects to determine the degree by which emergency related traffic affects
existing traffic load of a given network or ISP. Important note: we existing traffic load of a given network or ISP. Important note: we
reiterate our earlier comment that laws and regulations are generally reiterate our earlier comment that laws and regulations are generally
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.
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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
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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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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 loosely defined maximum alloca- for GETS service tend to focus on a loosely defined maximum alloca-
tion of (e.g., 1% to 10%) of calls allowed to be established through tion of (e.g., 1% to 10%) of calls allowed to be established through
a given LEC using HPC. It is expected, and encouraged, that ETS a given LEC using HPC. It is expected, and encouraged, that ETS
related SLAs of ISPs will have a limit with respect to the amount of related SLAs of ISPs will have a limit with respect to the amount of
traffic distinguished as being emergency related, and initiated by an traffic distinguished as being emergency related, and initiated by an
authorized user. authorized user.
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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
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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. The gateway from the PSTN connection into the
tion into the backbone IP network must be able to signal that the backbone IP network must be able to signal that the flow has an ETS
flow has an ETS label. Conversely, the gateway back into the PSTN label. Conversely, the gateway back into the PSTN must similarly sig-
must similarly signal the call's label. A secure link between the nal the call's label. A secure link between the gateways may be set
gateways may be set up using IPSec or SIP security functionality. If up using IPSec or SIP security functionality. If the endpoint is an
the endpoint is an IP device, the link may be set up securely from IP device, the link may be set up securely from the ingress gateway
the ingress gateway to the end device. to the end device.
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 func- egress gateways or IP endpoints using IPSec or SIP security func-
tions. tions.
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 ETS 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
This subject involves the ability to discover and use a different This subject involves the ability to discover and use a different
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
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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
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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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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.
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 meeting 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-
sate for lossy networks providing best effort service. In particu- sate for lossy networks providing best effort service. In particu-
lar, we focus on the use of a) Forward Error Correction (FEC), and b) lar, we focus on the use of a) Forward Error Correction (FEC), and b)
redundant transmissions that can be used to compensate for lost data redundant transmissions that can be used to compensate for lost data
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
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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
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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 15, line 50 skipping to change at page 16, line 4
above. Our intention is not to consider every possible scenario by above. Our intention is not to consider every possible scenario by
which support for emergency related IP telephony can be realized. which support for emergency related IP telephony can be realized.
Rather, we narrow our scope using a single guideline; we assume there Rather, we narrow our scope using a single guideline; we assume there
is a signaling & data interaction between the PSTN and the IP network is a signaling & data interaction between the PSTN and the IP network
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
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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.
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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 scenario represents a single iso- PSTN switches at its edges. This scenario represents a single iso-
lated IP administrative domain that has no directly adjacent IP lated IP administrative domain that has no directly adjacent IP
domains connected to it. We show an example of this scenario below domains connected to it. We show an example of this scenario below
in Figure 1. In this example, we show two types of telephony car- in Figure 1. In this example, we show two types of telephony car-
skipping to change at page 16, line 38 skipping to change at page 16, line 42
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, SG - Signaling Gateway SW - Telco Switch, 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 Quality of
vice as the voice traffic (data and signaling) exits the IP network Service as the voice traffic (data and signaling) exits the IP net-
because of the existing SS7 provisioned service between telephony work because of the existing SS7 provisioned service between
carriers. Thus, the need for support of mechanisms like diff-serv in telephony carriers. Thus, the need for support of mechanisms like
the presence of overprovisioning, and an expansion of the defined set diff-serv in the presence of overprovisioning, and an expansion of
of Per-Hop Behaviors, is reduced under this scenario. the defined set 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
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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
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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
skipping to change at page 17, line 46 skipping to change at page 18, line 4
gency related traffic from other types of traffic. In addition, IP gency related traffic from other types of traffic. In addition, IP
security becomes more important between domains in order to ensure security becomes more important between domains in order to ensure
that the act of distinguishing ETS-type traffic is indeed valid for that the act of distinguishing ETS-type traffic is indeed valid for
the given source. the given source.
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
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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
This is an informational document. The following are Informative
References, and there are no Normative 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)
Version 1, Functional Specification", Proposed Standard, RFC Version 1, Functional Specification", Proposed Standard, RFC
2205, Sept. 1997. 2205, Sept. 1997.
skipping to change at page 18, line 45 skipping to change at page 19, line 4
8 Blake, S., et. al., "An Architecture for Differentiated 8 Blake, S., et. al., "An Architecture for Differentiated
Service", Proposed Standard, RFC 2475, Dec. 1998. Service", Proposed Standard, RFC 2475, Dec. 1998.
9 Faucheur, F., et. al., "MPLS Support of Differentiated Services", 9 Faucheur, F., et. al., "MPLS Support of Differentiated Services",
Standards Track, RFC 3270, May 2002. Standards Track, RFC 3270, May 2002.
10 Sharma, V., Hellstrand, F., "Framework for MPLS-Based Recovery", 10 Sharma, V., Hellstrand, F., "Framework for MPLS-Based Recovery",
Informational, RFC 3469, February 2003 Informational, RFC 3469, February 2003
11 Postel, J., "Simple Mail Transfer Protocol", Standard, RFC 821, 11 Postel, J., "Simple Mail Transfer Protocol", Standard, RFC 821,
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August 1982. August 1982.
12 Handley, M., et. al., "SIP: Session Initiation Protocol", 12 Rosenberg, J., et. al., "SIP: Session Initiation Protocol",
Proposed Standard, RFC 2543, March 1999. Proposed Standard, RFC 3261, June 2002.
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.
skipping to change at page 19, line 34 skipping to change at page 19, line 43
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.
22 Rosenburg, J, et. al, "Telephony Routing over IP (TRIP)", 22 Rosenburg, J, et. al, "Telephony Routing over IP (TRIP)",
Standards Track, RFC 3219, January 2002. Standards Track, RFC 3219, January 2002.
23 Cuervo, F., et. al, "Megaco Protocol Version 1.0", Standards 23 Cuervo, F., et. al, "Gateway Control Protocol Version 1",
Track, RFC 3015, November 2000 Standards Track, RFC 3525, June 2003
24 Perkins, C., et al., "RTP Payload for Redundant Audio Data", 24 Perkins, C., et al., "RTP Payload for Redundant Audio Data",
Standards Track, RFC 2198, September, 1997 Standards Track, RFC 2198, September, 1997
25 Rosenburg, J., Schulzrinne, H., "An RTP Payload Format for 25 Rosenburg, J., Schulzrinne, H., "An RTP Payload Format for
Generic Forward Error Correction", Standards Track, RFC 2733, Generic Forward Error Correction", Standards Track, RFC 2733,
December, 1999. December, 1999.
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,
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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.
skipping to change at page 20, line 45 skipping to change at page 21, line 4
39 Carlberg, K., Atkinson, R., "General Requirements for Emergency 39 Carlberg, K., Atkinson, R., "General Requirements for Emergency
Telecommunications Service", Work in Progress, Internet-Draft, Telecommunications Service", Work in Progress, Internet-Draft,
January, 2003 January, 2003
40 Carlberg, K., Atkinson, R., "IP Telephony Requirements for 40 Carlberg, K., Atkinson, R., "IP Telephony Requirements for
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"
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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.
skipping to change at page 21, line 43 skipping to change at page 22, line 4
Resource Priority extension to SIP. A new label mechanism for SIP Resource Priority extension to SIP. A new label mechanism for SIP
could allow a transparent interoperation between IP telephony and the could allow a transparent interoperation between IP telephony and the
U.K. PSTN that supports GTPS. U.K. PSTN that supports GTPS.
9. Appendix B: Related Standards Work 9. Appendix B: Related Standards Work
The process of defining various labels to distinguish calls has been, The process of defining various labels to distinguish calls has been,
and continues to be, pursued in other standards groups. As mentioned and continues to be, pursued in other standards groups. As mentioned
in section 1.1.1, the ANSI T1S1 group has previously defined a label in section 1.1.1, the ANSI T1S1 group has previously defined a label
SS7 ISUP Initial Address Message. This single label or value is SS7 ISUP Initial Address Message. This single label or value is
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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.
skipping to change at page 22, line 43 skipping to change at page 23, line 5
CALL-PRIORITY {itu-t(0) recommendation(0) h(8) 460 4 version1(0)} CALL-PRIORITY {itu-t(0) recommendation(0) h(8) 460 4 version1(0)}
DEFINITIONS AUTOMATIC TAGS::= DEFINITIONS AUTOMATIC TAGS::=
BEGIN BEGIN
IMPORTS IMPORTS
ClearToken, ClearToken,
CryptoToken CryptoToken
FROM H235-SECURITY-MESSAGES; FROM H235-SECURITY-MESSAGES;
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CallPriorityInfo::= SEQUENCE CallPriorityInfo::= SEQUENCE
{ {
priorityValue CHOICE priorityValue CHOICE
{ {
emergencyAuthorized NULL, emergencyAuthorized NULL,
emergencyPublic NULL, emergencyPublic NULL,
high NULL, high NULL,
normal NULL, normal NULL,
}, },
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priorityExtension INTEGER (0..255) OPTIONAL, priorityExtension INTEGER (0..255) OPTIONAL,
tokens SEQUENCE OF ClearToken OPTIONAL, tokens SEQUENCE OF ClearToken OPTIONAL,
cryptoTokens SEQUENCE OF CryptoToken OPTIONAL, cryptoTokens SEQUENCE OF CryptoToken OPTIONAL,
rejectReason CHOICE rejectReason CHOICE
{ {
priorityUnavailable NULL, priorityUnavailable NULL,
priorityUnauthorized NULL, priorityUnauthorized NULL,
priorityValueUnknown NULL, priorityValueUnknown NULL,
} OPTIONAL, -- Only used in CallPriorityConfirm } OPTIONAL, -- Only used in CallPriorityConfirm
} }
skipping to change at page 23, line 33 skipping to change at page 23, line 43
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.
11. Author's Addresses 11. Author's Addresses
Ken Carlberg Ian Brown Ken Carlberg Ian Brown
University College London University College London G11 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
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Cory Beard Cory Beard
University of Missouri-Kansas City University of Missouri-Kansas City
Division of Computer Science Division of Computer Science
Electrical Engineering Electrical Engineering
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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skipping to change at page 24, line 17 skipping to change at page 25, line 17
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) ..... 3 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 ........................................................ 7 4.1.1 SIP ........................................................ 8
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 ........................................................ 9 4.1.4 RTP ........................................................ 10
4.1.5 MEGACO/H.248 ............................................... 11 4.1.5 GCP/H.248 .................................................. 11
4.2 Policy ....................................................... 11 4.2 Policy ....................................................... 11
4.3 Traffic Engineering .......................................... 12 4.3 Traffic Engineering .......................................... 12
4.4 Security ..................................................... 12 4.4 Security ..................................................... 13
4.5 Alternate Path Routing ....................................... 13 4.5 Alternate Path Routing ....................................... 13
4.6 End-to-End Fault Tolerance ................................... 14 4.6 End-to-End Fault Tolerance ................................... 14
5. Key Scenarios ................................................. 15 5. Key Scenarios ................................................. 15
6. Security Considerations ....................................... 18 6. Security Considerations ....................................... 18
7. References .................................................... 18 7. References .................................................... 18
8. Appendix A: Government Telephone Preference Scheme (GTPS) ..... 21 8. Appendix A: Government Telephone Preference Scheme (GTPS) ..... 21
8.1 GTPS and the Framework Document .............................. 21 8.1 GTPS and the Framework Document .............................. 21
9. Appendix B: Related Standards Work ............................ 21 9. Appendix B: Related Standards Work ............................ 21
9.1 Study Group 16 (ITU) ......................................... 22 9.1 Study Group 16 (ITU) ......................................... 22
10. Acknowledgments .............................................. 23 10. Acknowledgments .............................................. 23
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