draft-ietf-ieprep-framework-03.txt   draft-ietf-ieprep-framework-04.txt 
Internet Engineering Task Force Ken Carlberg Internet Engineering Task Force Ken Carlberg
INTERNET DRAFT Ian Brown INTERNET DRAFT Ian Brown
January 24, 2002 UCL March 2, 2003 UCL
Cory Beard
UMKC
Framework for Supporting ETS in IP Telephony Framework for Supporting ETS in IP Telephony
<draft-ietf-ieprep-framework-03.txt> <draft-ietf-ieprep-framework-04.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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emergency related communication within the context of IP telephony. emergency related communication within the context of IP telephony.
We present a series of objectives that reflect a general view of how We present a series of objectives that reflect a general view of how
authorized emergency service, in line with the Emergency authorized emergency service, in line with the Emergency
Telecommunications Service (ETS), should be realized within today's Telecommunications Service (ETS), should be realized within today's
IP architecture and service models. From these objectives, we IP architecture and service models. From these objectives, we
present a corresponding set of protocols and capabilities, which present a corresponding set of protocols and capabilities, which
provide a more specific set of recommendations regarding existing provide a more specific set of recommendations regarding existing
IETF protocols. Finally, we present two scenarios that act as IETF protocols. Finally, we present two scenarios that act as
guiding models for the objectives and functions listed in this guiding models for the objectives and functions listed in this
document. These, models, coupled with an example of an existing document. These, models, coupled with an example of an existing
service in the PSTN, contribute to a constrained solution space.
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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, infers
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
addition of [4] and [5], specifying control load (bandwidth bounds) addition of [4] and [5], specifying controlled load (bandwidth
and guaranteed service (bandwidth & delay bounds) respectively, a bounds) and guaranteed service (bandwidth & delay bounds) respec-
design existed to achieve specific measures of QoS for an end-to-end tively, a design existed to achieve specific measures of QoS for an
flow of traffic traversing an IP network. In this case, our refer- end-to-end flow of traffic traversing an IP network. In this case,
ence to a flow is one that is granular in definition and applying to our reference to a flow is one that is granular in definition and
specific application sessions. applying to specific application sessions.
From a deployment perspective (as of the date of this document), From a deployment perspective (as of the date of this document),
int-serv has been predominantly constrained to intra-domain paths, at int-serv has been predominantly constrained to intra-domain paths, at
best resembling isolated "island" reservations for specific types of best resembling isolated "island" reservations for specific types of
traffic (e.g., audio and video) by stub domains. [6] and [7] will traffic (e.g., audio and video) by stub domains. [6] and [7] will
probably contribute to additional deployment of int-serv to Internet probably contribute to additional deployment of int-serv to Internet
Service Providers (ISP) and possibly some inter-domain paths, but it Service Providers (ISP) and possibly some inter-domain paths, but it
seems unlikely that the original vision of end-to-end int-serv seems unlikely that the original vision of end-to-end int-serv
between hosts in source and destination stub domains will become a between hosts in source and destination stub domains will become a
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
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nternet Draft IEPS Framework March 2, 2003
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
aggregated treatment of data. aggregated treatment of data.
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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
to place a high importance for intra-domain traffic engineering. The to place a high importance for intra-domain traffic engineering. The
explosion of IETF contributions, in the form of drafts and RFCs pro- explosion of IETF contributions, in the form of drafts and RFCs pro-
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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 telco carrier's telephony, a natural inclusion of it as part of a telephony carrier's
backbone network, or into the Internet as a whole, implies the abil- backbone network, or into the Internet as a whole, implies the abil-
ity to support existing emergency related services. Typically, one ity to support existing emergency related services. Typically, one
associates emergency calls with "911" telephone service in the U.S., associates emergency calls with "911" telephone service in the U.S.,
or "999" in the U.K. -- both of which are attributed to national or "999" in the U.K. -- both of which are attributed to national
boundaries and accessible by the general public. Outside of this boundaries and accessible by the general public. Outside of this
exists emergency telephone services that involved authorized usage, exists emergency telephone services that involved authorized usage,
as described in the following subsection. as described in the following subsection.
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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]. Unlike
"911", it is only accessible by authorized individuals. The majority
^L established by the White House under an executive order [30] and now
of these individuals are from various government agencies like the a part of the Department of Homeland Security . Unlike "911", it is
Department of Transportation, NASA, the Department of Defense, and only accessible by authorized individuals. The majority of these
the Federal Emergency Management Agency (to name but a few). In individuals are from various government agencies like the Department
addition, a select set of individuals from private industry (telecom- of Transportation, NASA, the Department of Defense, and the Federal
munications companies, utilities, etc.) that are involved in criti- Emergency Management Agency (to name but a few). In addition, a
cial infrastructure recovery operations are also provided access to select set of individuals from private industry (telecommunications
GETS. companies, utilities, etc.) that are involved in criticial infras-
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 increase the probability that phone service
will be available to selected authorized personnel in times of emer- will be available to selected authorized personnel in times of emer-
gencies, such as hurricanes, earthquakes, and other disasters that gencies, such as hurricanes, earthquakes, and other disasters that
may produce a burden in the form of call blocking (i.e., congestion) may produce a burden in the form of call blocking (i.e., congestion)
on the U.S. Public Switched Telephone Network by the general public. 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].
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controls in order to increase the probability that international controls in order to increase the probability that international
emergency calls will be established. The specifics of how this is to emergency calls will be established. The specifics of how this is to
be accomplished are to be defined in future ITU document(s). be accomplished are to be defined in future ITU document(s).
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
lish and maintain voice data traffic. This explicit signaling capa-
bility provides the hooks from which VoIP traffic can be bridged to ^L
the PSTN. establish and maintain voice data traffic. This explicit signaling
capability provides the hooks from which VoIP traffic can be bridged
to 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) destina-
tion. RAT does not use explicit signaling like SIP to establish an tion. RAT does not use explicit signaling like SIP to establish an
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end-to-end call between two users. It simply sends data packets to end-to-end call between two users. It simply sends data packets to
the target destination. On the other hand, "SIP phones" are host the target destination. On the other hand, "SIP phones" are host
devices that use a signaling protocol to establish a call signal devices that use a signaling protocol to establish a call signal
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 arguement 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.
Regardless of a definitive drop rate, it would seem that interactive Regardless of a definitive drop rate, it would seem that interactive
voice has a lower threshold of loss than other elastic applications. voice has a lower threshold of loss than elastic applications such as
This places a higher burden on the problem space of supporting VoIP email or web browsers. This places a higher burden on the problem
over the Internet. This problem is further compounded when toll- space of supporting VoIP over the Internet. This problem is further
quality service is expected because it assumes a default service compounded when toll-quality service is expected because it assumes a
model that is better than best effort. This in turn can increase the default service model that is better than best effort. This in turn
probability that a form of call-blocking can occur with VoIP or IP can increase the probability that a form of call-blocking can occur
telephony traffic. 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 carriers so that they have an under- provide a framework for ISPs and telephony carriers so that they have
standing of objectives used to support ETS related IP telephony an understanding of objectives used to support ETS related IP
traffic. In addition, we also wish to provide a reference point for telephony traffic. In addition, we also wish to provide a reference
potential customers in order to constrain their expectations. In point for potential customers in order to constrain their expecta-
particular, we wish to avoid any temptation of trying to replicate tions. In particular, we wish to avoid any temptation of trying to
the exact capabilities of existing emergency voice service currently replicate the exact capabilities of existing emergency voice service
available in the PSTN to that of IP and the Internet. If nothing currently available in the PSTN to that of IP and the Internet. If
else, intrinsic differences between the two communications architec- nothing else, intrinsic differences between the two communications
tures precludes this from happening. Note, this does not prevent us architectures precludes this from happening. Note, this does not
from borrowing design concepts or objectives from existing systems. prevent us from borrowing design concepts or objectives from existing
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
bilities. Section 3 presents additional value added objectives,
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capabilities. 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
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
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
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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 of discussed in section 4 apply, and where some of the protocols discussed in section 4 apply, and where
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
"bits" below IP, other specific technologies, and service level "bits" below IP, other specific technologies, and service level
agreements between ISPs and carriers with regard to dedicated links. agreements between ISPs and telephony carriers with regard to dedi-
cated links.
2. Objective 2. Objective
The support of ETS within IP telephony can be realized in the form of The support of ETS within IP telephony can be realized in the form of
several primary objectives. From this set, we present protocols and several primary objectives. From this set, we present protocols and
capabilities (presented below in section 3) to be considered by capabilities (presented below in section 3) to be considered by
clients and providers of ETS type services. This document uses the clients and providers of ETS type services. This document uses the
IEPREP requirements of [39, 40] as a guide in specifying the objec- IEPREP requirements of [39, 40] as a guide in specifying the objec-
tives listed in this section. tives listed in this section.
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operational issues. Examples of this would be the establishment of operational issues. Examples of this would be the establishment of
Service Level Agreements (SLA) with ISPs, and/or the provisioning of Service Level Agreements (SLA) with ISPs, and/or the provisioning of
traffic engineered paths for ETS-related telephony traffic. traffic engineered paths for ETS-related telephony traffic.
A second underlying goal in selecting the following objectives is to A second underlying goal in selecting the following objectives is to
take into account experiences from an existing emergency-type commun- take into account experiences from an existing emergency-type commun-
ication system (as described in section 1.1) as well as the existing ication system (as described in section 1.1) as well as the existing
restrictions and constraints placed by some countries. In the former restrictions and constraints placed by some countries. In the former
case, we do not attempt to mimic the system, but rather extract case, we do not attempt to mimic the system, but rather extract
information as a reference model. With respect to constraints based information as a reference model. With respect to constraints based
on laws or agency regulations, this would normally be considered out- on laws or agency regulations, this would normally be considered
side of the scope of any IETF document. However, these constraints
act as a means of determining the lowest common denominator in speci- ^L
fying technical functional requirements. If such constraints do not outside of the scope of any IETF document. However, these con-
exist, then additional capabilities can be added to the baseline set. straints act as a means of determining the lowest common denominator
This last item will be expanded upon in the description of Objective in specifying technical functional requirements. If such constraints
#3 below. do not exist, then additional capabilities can be added to the base-
line set. This last item will be expanded upon in the description of
Objective #3 below.
The primary Objectives in support of authorized emergency calls: The primary Objectives in support of authorized emergency calls:
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1) High Probability of Call Completion 1) High Probability of Call Completion
2) No loss of information when interacting with 2) No loss of information when interacting with PSTN signaling
PSTN signaling
3) Distinction of ETS data traffic 3) Distinction of ETS data traffic
4) Non-preemptive action 4) Non-preemptive action
5) Non-ubiquitous support 5) Non-ubiquitous support
6) Authenticated service 6) Authenticated service
The first objective is the crux of our work because it defines our The first objective is the crux of our work because it defines our
expectations for both data and call signaling for IP telephony. As expectations for both data and call signaling for IP telephony. As
stated, our objective is achieving a high probability that emergency stated, our objective is achieving a high probability that emergency
related calls (both data and signaling) will be forwarded through an related calls (both data and signaling packets) will be forwarded
IP network. Specifically, we envision the relevance of this objec- through an IP network. Specifically, we envision the relevance of
tive during times of congestion, the context of which we describe this objective during times of congestion, the context of which we
further below in this section. The critical word in this objective describe further below in this section. The critical word in this
is "probability", as opposed to assurance or guarantee -- the latter objective is "probability", as opposed to assurance or guarantee --
two placing a higher burden on the network. It stands to reason, the latter two placing a higher burden on the network. Objectives 4
though, that the word "probability" is a less tangible description and 5 listed above help us to qualify the term probability in the
that cannot be easily quantified. It is relative in relation to context of other objectives.
other traffic transiting the same network. Objectives 4 and 5 listed
above help us to qualify the term probability in the context of other
objectives.
The second objective involves the interaction of IP telephony signal- The second objective involves the interaction of IP telephony signal-
ing with existing PSTN support for emergency related voice communica- ing with existing PSTN support for emergency related voice communica-
tions. As mentioned above in Section 1.2, standard T1.631 [26] speci- tions. As mentioned above in Section 1.2, standard T1.631 [26] speci-
fies emergency code points for SS7. Specifically, the National Secu- fies emergency code points for SS7. Specifically, the National Secu-
rity and Emergency Preparedness (NS/EP) Calling Party Category code rity and Emergency Preparedness (NS/EP) Calling Party Category code
point is defined for ISUP IAM messages used by SS7 [26]. =A0Hence, point is defined for ISUP IAM messages used by SS7 [26]. Hence, when
when IP providers choose to interconnect with the PSTN, it is our IP providers choose to interconnect with the PSTN, it is our objec-
objective that this interaction between the PSTN and IP telephony tive that this interaction between the PSTN and IP telephony with
with respect to ETS (and national indicators) is a semantically respect to ETS (and national indicators) is a semantically straight-
straightforward, reversible mapping of comparable code points. forward, reversible mapping of comparable code points.
The third objective focuses on the ability to distinguish ETS data The third objective focuses on the ability to distinguish ETS data
packets from other types of VoIP packets. With such an ability, packets from other types of VoIP packets. With such an ability,
transit providers can more easily ensure that pre-existing service transit providers can more easily ensure that pre-existing service
level agreements relating to ETS are adhered to. Note that we do not level agreements relating to ETS are adhered to. Note that we do not
assume that the actions taken to distinguish ETS type packets are assume that the actions taken to distinguish ETS type packets are
easy. Nor, in this section, do we state the form of this distinc- easy. Nor, in this section, do we state the form of this distinc-
tion. We simply present the objective of identifying flows that tion. We simply present the objective of identifying flows that
relate to ETS versus others that traverse a transit network. relate to IEPS versus others that traverse a transit network.
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At an abstract level, the fourth objective pertains to the actions At an abstract level, the fourth objective pertains to the actions
taken when an IP telephony call, via a signaling protocol such as taken when an IP telephony call, via a signaling protocol such as
SIP, cannot be forwarded because the network is experiencing a form SIP, cannot be forwarded because the network is experiencing a form
of congestion. We state this in general terms because of two of congestion. We state this in general terms because of two rea-
sons: a) there may exist applications other than SIP, like H.248,
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reasons: a) there may exist applications other than SIP, like H.248,
used for call establishment, and b) congestion may come in several used for call establishment, and b) congestion may come in several
forms. For example, congestion may exist at the IP packet layer with forms. For example, congestion may exist at the IP packet layer with
respect to queues being filled to their configured limit. Congestion respect to queues being filled to their configured limit. Congestion
may also arise from resource allocation (i.e., QoS) attributed per may also arise from resource allocation (i.e., QoS) attributed per
call or aggregated sets of calls. In this latter case, while there call or aggregated sets of calls. In this latter case, while there
may exist resources to forward the packets, a stateful signaling may exist resources to forward the packets, a stateful signaling
server may have reached its configured limit as to how many telephony server may have reached its configured limit as to how many telephony
calls it will support while retaining toll-quality service per call. calls it will support while retaining toll-quality service per call.
Typically, one terms this form of congestion as call blocking. Note Typically, one terms this form of congestion as call blocking. Note
that we do not address the case when congestion occurs at the bit that we do not address the case when congestion occurs at the bit
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expectation for ubiquitous support of ETS across all administrative expectation for ubiquitous support of ETS across all administrative
domains of the Internet. While it would be desirable to have ubiqui- domains of the Internet. While it would be desirable to have ubiqui-
tous support, we feel the reliance of such a requirement would doom tous support, we feel the reliance of such a requirement would doom
even the contemplation of supporting ETS by the IETF and the expected even the contemplation of supporting ETS by the IETF and the expected
entities (e.g., ISPs and vendors) involved in its deployment. entities (e.g., ISPs and vendors) involved in its deployment.
We use the existing GETS service in the U.S. as an existing example We use the existing GETS service in the U.S. as an existing example
in which emergency related communications does not need to be ubiqui- in which emergency related communications does not need to be ubiqui-
tous. As mentioned previously, the measure and amount of support tous. As mentioned previously, the measure and amount of support
provided by the U.S. PSTN for GETS does not exist for all U.S. IXCs provided by the U.S. PSTN for GETS does not exist for all U.S. IXCs
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nor LECs. Given the fact that GETS still works within this context, nor LECs. Given the fact that GETS still works within this context,
it is our objective to follow this deployment model such that we can it is our objective to follow this deployment model such that we can
accomplish the first objective listed above -- a higher probability accomplish the first objective listed above -- a higher probability
of call completion than that of normal IP telephony call traffic. of call completion than that of normal IP telephony call traffic.
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Our final objective is that only authorized users may use the ser- Our final objective is that only authorized users may use the ser-
vices outlined in this framework. GETS users are authenticated using vices outlined in this framework. GETS users are authenticated using
a PIN provided to the telecommunications carrier, which signals a PIN provided to the telephony carrier, which signals authentication
authentication to subsequent networks via the HPC class mark. In an to subsequent networks via the HPC class mark. In an IP network, the
IP network, the authentication center will need to securely signal authentication center will need to securely signal back to the IP
back to the IP ingress point that a given user is authorized to send ingress point that a given user is authorized to send ETS related
ETS related flows. Similarly, transit networks that chose to support flows. Similarly, transit networks that chose to support ETS SLAs
ETS SLAs must securely interchange authorized ETS traffic. In both must securely interchange authorized ETS traffic. In both cases,
cases, IPSec authentication transforms may be used to protect this IPSec authentication transforms may be used to protect this traffic.
traffic. This is entirely separate from end-to-end IPSec protection This is entirely separate from end-to-end IPSec protection of user
of user traffic, which will be configured by users. IP-PSTN gateways traffic, which will be configured by users. IP-PSTN gateways must
must also be able to securely signal ETS authorization for a given also be able to securely signal ETS authorization for a given flow.
flow. As these gateways are likely to act as SIP servers, we further As these gateways are likely to act as SIP servers, we further con-
consider the use of SIP's security functions to aid this objective. sider the use of SIP's security functions to aid this objective.
3. Value Added Objective 3. Value Added Objective
This objective is viewed as being helpful in achieving a high proba- This objective is viewed as being helpful in achieving a high proba-
bility of call completion. Its realization within an IP network bility of call completion. Its realization within an IP network
would be in the form of new protocols or enhancements to existing would be in the form of new protocols or enhancements to existing
ones. Thus, objectives listed in this section are treated as value ones. Thus, objectives listed in this section are treated as value
added -- an expectation that their existence would be beneficial, and added -- an expectation that their existence would be beneficial, and
yet not viewed as critical to support ETS related IP telephony yet not viewed as critical to support ETS related IP telephony
traffic. traffic.
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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 call completion of IEPS traffic by mak- increasing the probability of call completion of IEPS traffic by mak-
ing use of noncongested alternate paths. We use the term "minimal ing use of noncongested alternate paths. We use the term "minimal
form" to emphasize the fact that care must be taken in how the system form" to emphasize the fact that care must be taken in how the system
provides alternate paths so it does not significantly contribute to provides alternate paths so it does not significantly contribute to
the congestion that is to be avoided (e.g., via excess the congestion that is to be avoided (e.g., via excess
control/discovery messages). control/discovery messages).
^L
At the time that this document was written, we can identify two At the time that this document was written, we can identify two
work-in-progress areas in the IETF that can be helpful in providing work-in-progress areas in the IETF that can be helpful in providing
alternate paths for call signaling. The first is [10], which is alternate paths for call signaling. The first is [10], which is
focused on network layer routing and describes a framework for focused on network layer routing and describes a framework for
^L
enhancements to the LDP specification of MPLS to help achieve fault enhancements to the LDP specification of MPLS to help achieve fault
tolerance. This in itself does not provide alternate path routing, tolerance. This in itself does not provide alternate path routing,
but rather helps minimize loss in intradomain connectivity when MPLS but rather helps minimize loss in intradomain connectivity when MPLS
is used within a domain. is used within a domain.
The second effort comes from the IP Telephony working group and The second effort comes from the IP Telephony working group and
involves Telephony Routing over IP (TRIP). To date, a framework involves Telephony Routing over IP (TRIP). To date, a framework
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
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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
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
^L
changes in jitter. changes in jitter.
The other form of fault tolerance we discuss involves the use of The other form of fault tolerance we discuss involves the use of
redundant transmissions. By this we mean the case in which an redundant transmissions. By this we mean the case in which an origi-
nal data packet is followed by one or more redundant packets. At
^L first glance, this would appear to be even less friendly to the net-
original data packet is followed by one or more redundant packets. work than that of adding FEC packets. However, the encodings of the
At first glance, this would appear to be even less friendly to the redundant packets can be of a different type (or even transcoded into
network than that of adding FEC packets. However, the encodings of a lower quality) that produce redundant data packets that are signi-
the redundant packets can be of a different type (or even transcoded ficantly smaller than the original packet.
into a lower quality) that produce redundant data packets that are
significantly 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
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.
4. Protocols and Capabilities 4. Protocols and Capabilities
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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 viewed as a ubiquitously available service.
We divide this section into 4 areas: 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
4.1. Signaling 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.
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In the following subsections, we discuss potential augmentations to In the following subsections, we discuss potential augmentations to
different types of signaling and state information to help support different types of signaling and state information to help support
the distinction of emergency related communications in general, and the distinction of emergency related communications in general, and
IEPS specifically. IEPS specifically.
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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).
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.
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data) from other traffic. The existence of this PHB then provides a data) from other traffic. The existence of this PHB then provides a
baseline by which specific code points may be defined related to baseline by which specific code points may be defined related to
various emergency related traffic: authorized emergency sessions various emergency related traffic: authorized emergency sessions
(e.g., ETS), general public emergency calls (e.g., "911"), MLPP. (e.g., ETS), general public emergency calls (e.g., "911"), MLPP.
Aggregates would still exist with respect to the bundling of applica- Aggregates would still exist with respect to the bundling of applica-
tions per code point. Further, one would associate a forwarding tions per code point. Further, one would associate a forwarding
paradigm aimed at a low loss rate reflective of the code point paradigm aimed at a low loss rate reflective of the code point
selected. The new PHB could be in the form of a one or more code selected. The new PHB could be in the form of a one or more code
points that duplicate EF-type traffic characteristics. Policies points that duplicate EF-type traffic characteristics. Policies
would determine IF a measure of importance exists per EF-type code- would determine IF a measure of importance exists per EF-type code-
^L
point. point.
A potential issue that could be addressed by a new PHB involves merge 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 points of flows within a diff-serv domain. With EF, one can expect
admission control being performed at the edges of the domain. admission control being performed at the edges of the domain.
Presumably, careful traffic engineering would be applied to avoid Presumably, careful traffic engineering would be applied to avoid
^L
congestion of EF queues at internal/core merge points stemming from congestion of EF queues at internal/core merge points stemming from
flows originating from different ingress nodes of the diff-serv flows originating from different ingress nodes of the diff-serv
domain. However, traffic engineering may not be able to compensate domain. However, traffic engineering may not be able to compensate
for congestion of EF-type traffic at the domain's core routers. 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- Hence, a new PHB that has more than one code point to identify EF-
type traffic may address congestion by associating a drop precedence type traffic may address congestion by associating a drop precedence
for certain types of EF-type datagrams. Note that local policy and 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- SLAs would define which EF-type of traffic, if any, would be associ-
ated with a specific drop precedence. ated with a specific drop precedence.
Another approach to consider would be to define a new or fifth class 4.1.3. Variations Related to Diff-Serv and Queuing
for the existing AF PHB. Unlike the other currently defined classes,
this new one would be based on five levels of drop precedence. This One variation to consider with respect to existing diff-serv work
increase in the number of levels would conveniently correlate to the would be to define a new or fifth class for the existing AF PHB.
levels of MLPP, which has five types of priorities. The five levels Unlike the other currently defined classes, this new one would be
would also correlate to a recent effort in the Study Group 11 of the based on five levels of drop precedence. This increase in the number
ITU to define 5 levels for Emergency Telecommunications Service of levels would conveniently correlate to the levels of MLPP, which
(ETS). Beyond these other standardization efforts, the 5 levels has five types of priorities. The five levels would also correlate
would provide a higher level of variance that could be used to super- to a recent effort in the Study Group 11 of the ITU to define 5 lev-
cede the existing 3 levels used in the other classes. Hence, if els for Emergency Telecommunications Service (ETS). Beyond these
other non-emergency aggregate traffic were assigned to the new class, other standardization efforts, the 5 levels would provide a higher
the highest drop precedence they are assigned to is (3) -- level of variance that could be used to supercede the existing 3 lev-
corresponding to the other four currently defined classes. Emergency els used in the other classes. Hence, if other non-emergency aggre-
traffic would be set to (4) or (5), depending on the SLA that has gate traffic were assigned to the new class, the highest drop pre-
been defined. cedence 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
or additions to the existing AF PHB's, with their four classes and
three drop precedences per class. One could use the existing AF
PHB's if one assumed that a relatively homogeneous set of packet
flows were marked with the same AF class markings (i.e., have only
TCP flows, or only UDP-voice flows, but not both, within a class).
Then one could allocate the lowest drop precedence to the emergency
traffic, and the other two drop precedences to the rest of the
traffic.
One original rationale for having three drop precedences was to be
able to separate TCP flows from UDP flows by different drop pre-
cedences, so UDP packets could be dropped more frequently than TCP
^L
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
one being emergency traffic, one would need to use a more advanced
form of Active Queue Management (AQM). AQM would need to protect
emergency traffic as much as possible until most, if not all, of the
non-emergency traffic had been dropped. This would require creation
of drop probabilities based on counting the number of packets in the
queue for each drop precedence individually. Instead, current imple-
mentations use an overall queue fill measurement to make decisions;
this might cause emergency packets to be dropped. This new from of
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 PHB's if each
class where reasonably homogenous in the traffic mix. But one might
still have a need to be able to differentiate three drop precedences
just within non-emergency traffic. If so, more drop precedences
could be implemented. Also, if one wanted discrimination within
emergency traffic, as with MLPP's five levels of precedence, more
drop precedences might also be considered. 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.
The other question with AF PHB's 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.
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 is taking a conservative approach in specifying new written, the IETF is taking a conservative approach in specifying new
PHBs. This is because the number of code points that can be defined PHBs. This is because the number of code points that can be defined
is relatively small, and understandably considered a scarce resource. is relatively small, and understandably considered a scarce resource.
^L
Therefore, the possibility of a new PHB being defined for emergency 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 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 accepted by the IETF. In the near term, we would initially recommend
using the Assured Forwarding (AF) PHB [20] for distinguishing emer- using the Assured Forwarding (AF) PHB [20] for distinguishing emer-
gency traffic from other types of flows. At a minimum, AF could be gency traffic from other types of flows. At a minimum, AF could be
used for the different SIP call signaling messages. If EF was also used for the different SIP call signaling messages. If EF was also
supported by the domain, then it would be used for IP telephony data supported by the domain, then it would be used for IP telephony data
packets. Otherwise, another AF class would be used for those data packets. Otherwise, another AF class would be used for those data
flows. flows.
It is critical to note that one cannot specify an exact code point It is critical to understand that one cannot specify an exact code
used for emergency related data flows because the relevance of a code point used for emergency related data flows because the relevance of
point is local to the given diff-serv domain (i.e., they are not glo- a code point is local to the given diff-serv domain (i.e., they are
bally unique per micro-flow or aggregate of flows). In addition, we not globally unique per micro-flow or aggregate of flows). In addi-
can expect that the existence of a codepoint for emergency related tion, we can expect that the existence of a codepoint for emergency
flows is based on the service level agreements established with a related flows is based on the service level agreements established
given diff-serv domain. with a given diff-serv domain.
^L
4.1.3. 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
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
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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 avoid 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
^L
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
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
^L
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
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.
4.1.4. 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. Any values set should be a function of any SLAs
^L
that have been established regarding the handling of emergency that have been established regarding the handling of emergency
traffic. In addition, given that priority values denote precedence traffic. In addition, given that priority values denote precedence
(according to the Megaco protocol), then by default the ETS telephony (according to the Megaco protocol), then by default the ETS telephony
data flows should probably receive the same priority as other non- data flows should probably receive the same priority as other non-
emergency calls. This approach follows the objective of not relying emergency calls. This approach follows the objective of not relying
on preemption as the default treatment of emergency-related. on preemption as the default treatment of emergency-related.
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-
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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
influencing the specification of SLA(s) may allow preemption, or even influencing the specification of SLA(s) may allow preemption, or even
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
^L
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
accomplished. Instead, if a domain follows actions outside of the accomplished. Instead, if a domain follows actions outside of the
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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
operation of the network. We make no recommendations as to which operation of the network. We make no recommendations as to which
type of traffic engineering mechanism is used, but that such a system type of traffic engineering mechanism is used, but that such a system
exists in some form and can distinguish and support ETS signaling exists in some form and can distinguish and support ETS signaling
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
^L
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].
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.
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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 maximum allocation of (e.g., 1%)
of calls allowed to be established through a given LEC using HPC. of calls allowed to be established through a given LEC using HPC.
Once this limit is reached, all other GETS calls experience the same Once this limit is reached, all other GETS calls experience the same
probability of call completion as the general public. It is probability of call completion as the general public. It is
expected, and encouraged, that ETS related SLAs will have a limit expected, and encouraged, that ETS related SLAs will have a limit
with respect to the amount of traffic distinguished as being emer- with respect to the amount of traffic distinguished as being emer-
gency related, and initiated by an authorized user. gency related, and initiated by an authorized user.
^L
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
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 carrier's backbone IP network, very little IP-specific security one telephony carrier's backbone IP network, very little IP-specific
support is required. The user authenticates themself as usual to the security support is required. The user authenticates themself as
network using a PIN. The gateway from the PSTN connection into the usual to the network using a PIN. The gateway from the PSTN connec-
backbone IP network must be able to signal that the flow has an ETS tion into the backbone IP network must be able to signal that the
label. Conversely, the gateway back into the PSTN must similarly flow has an ETS label. Conversely, the gateway back into the PSTN
signal the call's label. A secure link between the gateways may be must similarly signal the call's label. A secure link between the
set up using IPSec or SIP security functionality. If the endpoint is gateways may be set up using IPSec or SIP security functionality. If
an IP device on the carrier's network, the link may be set up the endpoint is an IP device, the link may be set up securely from
securely from the ingress gateway to the end device. the ingress gateway 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
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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 IEPS traffic over that link as part of its user authentica-
tion procedures without necessarily communicating with a central ETS tion procedures. These authentication procedures may occur at the
authentication center as happens with POTS-originated calls. These link or network layers, but are entirely at the discretion of the
authentication procedures may occur at the link or network layers, ingress network. That network must decide how often it should update
but are entirely at the discretion of the ingress network. That net- its list of authorized ETS users based on the bounds it is prepared
work must decide how often it should update its list of authorized to accept on traffic from recently-revoked users.
ETS users based on the bounds it is prepared to accept on traffic
from recently-revoked users.
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 infer 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
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
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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
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.
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 represents a single isolated IP
administrative domain that has no directly adjacent IP domains con- administrative domain that has no directly adjacent IP domains con-
nected to it. We show an example of this scenario below in Figure 1. nected to it. We show an example of this scenario below in Figure 1.
In this example, we show two types of carriers. One is the legacy In this example, we show two types of telephony carriers. One is the
carrier, whose infrastructure retains the classic switching architec- legacy carrier, whose infrastructure retains the classic switching
ture attributed to the PSTN. The other is the next generation car- architecture attributed to the PSTN. The other is the next genera-
rier, which uses a data network (e.g., IP) as its core infrastruc- tion carrier, which uses a data network (e.g., IP) as its core
ture, and Signaling Gateways at its edges. These gateways "speak" infrastructure, and Signaling Gateways at its edges. These gateways
SS7 externally with peering carriers, and another protocol (e.g., "speak" SS7 externally with peering carriers, and another protocol
SIP) internally, which rides on top of the IP infrastructure.
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(e.g., SIP) internally, which rides on top of the IP infrastructure.
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
^L carriers. Thus, the need for support of mechanisms like diff-serv,
because of the existing SS7 provisioned service between carriers. and an expansion of the defined set of Per-Hop Behaviors is reduced
Thus, the need for support of mechanisms like diff-serv, and an (if not eliminated) under this scenario.
expansion of the defined set of Per-Hop Behaviors is reduced (if not
eliminated) 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
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 (i.e., portions of the Internet) may exchange sig- addition, segments
naling with other IP administrative domains via non-PSTN signaling
protocols like SIP. (i.e., portions of the Internet) may exchange signaling with other IP
administrative domains via non-PSTN signaling protocols like SIP.
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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
Figure 2 Figure 2
Given multiple IP domains, and the presumption that SLAs relating to Given multiple IP domains, and the presumption that SLAs relating to
ETS traffic may exist between them, the need for something like ETS traffic may exist between them, the need for something like
diff-serv grows with respect to being able to distinguish the emer- diff-serv grows with respect to being able to distinguish the emer-
gency related traffic from other types of traffic. In addition, IP gency related traffic from other types of traffic. In addition, IP
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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
anticipate the need for an additional document to specify the mapping anticipate the need for an additional document to specify the mapping
skipping to change at page 20, line 32 skipping to change at page 22, line 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
Reservations", Proposed Standard, RFC 3175, September 2001. Reservations", Proposed Standard, RFC 3175, September 2001.
7 Berger, L, et. al., "RSVP Refresh Overhead Reduction Extensions", 7 Berger, L, et. al., "RSVP Refresh Overhead Reduction Extensions",
Proposed Standard, RFC 2961, April, 2001. Proposed Standard, RFC 2961, April, 2001.
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",
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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”,
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
skipping to change at page 21, line 33 skipping to change at page 23, line 5
gress, gress,
December, 2001. December, 2001.
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.
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18 ITU, "International Emergency Preparedness Scheme", ITU 18 ITU, "International Emergency Preparedness Scheme", ITU
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.
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, "Megaco Protocol Version 1.0", Standards
Track, RFC 3015, November 2000 Track, RFC 3015, November 2000
24 Perkins, C., et al., "RTP Payload for Redundant Audio Data", 24 Perkins, C., et al., "RTP Payload for Redundant Audio Data",
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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,
2000. 2000.
27 Brown, I., "Securing IEPS over IP", White Paper, 27 Brown, I., "Securing IEPS over IP", White Paper,
skipping to change at page 22, line 36 skipping to change at page 24, line 5
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.
37 Vemuri, A., Peterson, J., "SIP for Telephones (SIP-T): Context and 37 Vemuri, A., Peterson, J., "SIP for Telephones (SIP-T): Context and
Architectures", work in progress, Internet-Draft, June, 2002. Architectures", work in progress, Internet-Draft, June, 2002.
38 Polk, J., "IEPREP Topology Scenarios", Work in Progress, Internet- 38 Polk, J., “IEPREP Topology Scenarios”, Work in Progress, Internet-
Draft, December, 2002 Draft, December, 2002
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,
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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
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
skipping to change at page 23, line 32 skipping to change at page 25, line 5
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.
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.
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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
aspects presented in this document. However, one component that can aspects presented in this document. However, one component that can
have a direct correlation is the labeling capability of the proposed have a direct correlation is the labeling capability of the proposed
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
labels for the resource priority header of SIP. labels for the resource priority header of SIP.
skipping to change at page 24, line 36 skipping to change at page 26, line 5
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 tran- is this former part that roughly corresponds to the labels tran-
sported via the Resource Priority field for SIP [15]. sported 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.
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At present, 5 levels have been defined for the Priority Value part of At present, 5 levels have been defined for the Priority Value part of
the Priority Class parameter: Low, Normal, High, Emergency-Public, the Priority Class parameter: Low, 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 ServiceClassInfo ::= SEQUENCE
{ {
priority CHOICE priority CHOICE
{ {
emergencyAuthorized NULL, emergencyAuthorized NULL,
emergencyPublic NULL, emergencyPublic NULL,
high NULL, high NULL,
normal NULL, normal NULL,
low NULL low NULL
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} }
priorityExtension INTEGER (0..255) OPTIONAL; priorityExtension INTEGER (0..255) OPTIONAL;
requiredClass NULL OPTIONAL requiredClass NULL OPTIONAL
tokens SEQUENCE OF ClearToken OPTIONAL tokens SEQUENCE OF ClearToken OPTIONAL
cryptoTokens SEQUENCE OF CryptoH323Token OPTIONAL cryptoTokens SEQUENCE OF CryptoH323Token OPTIONAL
} }
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.
skipping to change at page 26, line 4 skipping to change at page 27, line 4
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 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
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Cory Beard
University of Missouri-Kansas City
Division of Computer Science
Electrical Engineering
5100 Rockhill Road
Kansas City, MO 64110-2499
USA
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) ..... 3 1.1.1 Government Emergency Telecommunications Service (GETS) ..... 4
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. Value Added Objective ......................................... 9 3. Value Added Objective ......................................... 9
3.1 Alternate Path Routing ....................................... 9 3.1 Alternate Path Routing ....................................... 9
3.2 End-to-End Fault Tolerance ................................... 10 3.2 End-to-End Fault Tolerance ................................... 10
4. Protocols and Capabilities .................................... 11 4. Protocols and Capabilities .................................... 11
4.1 Signaling & State Information ................................ 11 4.1 Signaling & State Information ................................ 11
4.1.1 SIP ........................................................ 12 4.1.1 SIP ........................................................ 12
4.1.2 Diff-Serv .................................................. 12 4.1.2 Diff-Serv .................................................. 12
4.1.3 RTP ........................................................ 14 4.1.3 Variations Related to Diff-Serv and Queuing ................ 13
4.1.4 MEGACO/H.248 ............................................... 15 4.1.4 RTP ........................................................ 15
4.2 Policy ....................................................... 15 4.1.5 MEGACO/H.248 ............................................... 16
4.3 Traffic Engineering .......................................... 16 4.2 Policy ....................................................... 17
4.4 Security ..................................................... 17 4.3 Traffic Engineering .......................................... 17
5. Key Scenarios ................................................. 17 4.4 Security ..................................................... 18
6. Security Considerations ....................................... 20 5. Key Scenarios ................................................. 19
7. References .................................................... 20 6. Security Considerations ....................................... 21
8. Appendix A: Government Telephone Preference Scheme (GTPS) ..... 23 7. References .................................................... 21
8.1 GTPS and the Framework Document .............................. 23 8. Appendix A: Government Telephone Preference Scheme (GTPS) ..... 24
9. Appendix B: Related Standards Work ............................ 23 8.1 GTPS and the Framework Document .............................. 25
9.1 Study Group 16 (ITU) ......................................... 24 9. Appendix B: Related Standards Work ............................ 25
10. Acknowledgments .............................................. 25 9.1 Study Group 16 (ITU) ......................................... 25
11. Author's Addresses ........................................... 25 10. Acknowledgments .............................................. 26
11. Author's Addresses ........................................... 26
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