Network Working Group K. Carlberg I. Brown Internet Draft University College London 11/00 Framework for Supporting IEPS in IP Telephony Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. For potential updates to the above required-text see: http://www.ietf.org/ietf/1id-guidelines.txt Abstract This document presents a framework for supporting authorized emergency-related communication within the context of IP telephony. We present a series of objectives that reflect a general view of how authorized emergency service, in line with International Emergency Preparedness Scheme (IEPS), should be realized within today's IP architecture and service models. From these objectives, we present a corresponding set of functional requirements, which provide a more specific set of recommendations regarding existing IETF protocols. Finally, we present two scenarios that act as guiding models for the objectives and functions listed in this Carlberg & Brown Expires May,2001 1 Framework for Supporting IEPS in IP Telephony Nov,2000 document. These, models, coupled with an example of an existing service in the PSTN, contribute to a constrained solution space. 1. Introduction The Internet has become the primary target for worldwide communications. This is in terms of recreation, business, and various imaginative reasons for information distribution. A constant fixture in the evolution of the Internet has been the support of Best Effort as the default service model. Best Effort, in general terms, infers that the network will attempt to forward traffic to the destination as best as it can with no guarantees being made, nor any resources reserved, to support specific measure of Quality of Service (QoS). An underlying goal is to be 'fair' to all the traffic in terms of the resources used to forward it to the destination. In an attempt to go beyond best effort service, [2] presented an overview of Integrated Services (int-serv) and its inclusion into the Internet architecture. This was followed by [3], which specified the RSVP signaling protocol used to convey QoS requirements. With the addition of [4] and [5], specifying control load (bandwidth bounds) and guaranteed service (bandwidth & delay bounds) respectively, one was now able to achieve specific measures of QoS for an end-to-end flow of traffic traversing an IP network. In this case, our reference to a flow is one that is granular in definition and applying to specific application sessions. From a deployment perspective (as of the date of this document), int-serv has been predominantly constrained to stub intra-domain paths, at best resembling isolated "island" reservations for specific types of traffic (e.g., audio and video) by stub domains. [6] and [7] will probably contribute to additional deployment of int-serv to ISPs and possibly some inter-domain paths, but it seems unlikely that the original vision of end-to-end int-serv 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 others to contemplate). In 1998, the IETF produced [8], which presented an architecture for Differentiated Services (diff-serv). This effort focused on a more aggregated perspective and classification of packets than that of [2]. This is accomplished with the recent specification of the diff-serv field in the IP header (in the case of IPv4, it replaced Carlberg & Brown Expires May,2001 2 Framework for Supporting IEPS in IP Telephony Nov,2000 the old ToS field). This new field is used for code points established by IANA, or set aside as experimental. It can be expected that sets of microflows, a granular identification of a set of packets, will correspond to a given code point, thereby achieving an aggregated treatment of data. One constant in the introduction of new service models has been the 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 treated as Best Effort and uses what resources are made available to it. Beyond the introduction of new services, the continued pace of additional traffic load experienced by ISPs over the years has continued to place a high importance for intra-domain traffic engineering. The explosion of IETF contributions, in the form of drafts and RFCs produced in the area of Multi Protocol Label Switching (MPLS), exemplifies the interest in versatile and manageable mechanisms for intra-domain traffic engineering. One interesting observation is the work involved in supporting QoS sensitive traffic like Voice over IP (VoIP). Specifically, we refer to the discussion of a framework to support VoIP using MPLS [9], and the inclusion of fault tolerance [10]. This latter item can be viewed as being similar to "crank-back", a term used to describe the means by which the Public Switched Telephone Network (PSTN) routes around congested switches. 1.2 Emergency Related Data The evolution of the IP service model architecture has traditionally centered on the type of application protocols used over a network. By this we mean that the distinction, and possible bounds on QoS, usually centers on the type of application (e.g., audio video tools). While protocols like SMTP [11] and SIP [12] have embedded fields denoting "priority", there has not been a previous IETF standards based effort to state or define what this distinction means with respect to the underlying network and how it should be supported. Given the emergence of IP telephony, a natural inclusion of it as part of a telco carriers backbone network, or into the Internet as a whole, implies the ability to support existing emergency related services. Typically, one associates emergency calls with "911" telephone service in the U.S., or "999" in the U.K. -- both of Carlberg & Brown Expires May,2001 3 Framework for Supporting IEPS in IP Telephony Nov,2000 which are attributed to national boundaries and accessible by the general public. Outside of this exists emergency telephone services that involved authorized usage, as described in the following subsection. 1.2.1 Government Emergency Telecommunications Service (GETS) GETS is an emergency telecommunications service available in the U.S. and established by the National Communications System (NCS) -- an office established by the White House under an executive order. Unlike "911", it is only accessible by authorized individuals. The majority of these individuals are from various government agencies like the Department of Transportation, NASA, the Department of Defense, and the Federal Emergency Management Agency (to name but a few). The purpose of GETS is to increase the probability that phone service will be available to selected government agency personnel in times of emergencies, such as hurricanes, earthquakes, and other disasters that 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. The key aspect is that GETS only supports a probabilistic approach to call completion, as opposed to call preemption. This distinction is important because under U.S. law, emergency systems like GETS are not allowed to terminate existing calls in order to allow a GETS call to be established. Thus, the mechanisms and specifications that comprise GETS only focus on increasing the chances that a particular telephone call will be established. The basis for GETS with respect to Signaling System 7 (SS7) support is found in the T1.619 protocol on High Probability of Completion (HPC) network capability [13]. This document describes the specification of a National Security and Emergency Preparedness (NS/EP) code point used for SS7 ISDN User Part (ISUP) Initial Address Message (IAM). Together with this code point, Local Exchange Carriers (LEC) increase the time out period for call establishment in the hopes of increasing the chances that a circuit will be freed and thus be made available for a GETS call. If necessary (and if the ability is supported), the LEC will attempt to forward the call through alternate inter-exchange carriers (IXC) if it cannot complete the call through the default IXC. The procedure for a user (i.e., a person) establishing a GETS call is as follows: Carlberg & Brown Expires May,2001 4 Framework for Supporting IEPS in IP Telephony Nov,2000 1) Dial a non-geographical area code number: 710-XXX-XXXX 2) Dial a PIN used to authenticate the call 3) Dial the actual destination number to be reached In conjunction with the above, the source LEC (where the call originated) attempts to establish the call through an IXC that it has arbitrarily chosen. This is done even if the destination number is within the LEC itself. If the IXC cannot forward the call to the destination LEC, then the source LEC attempts to forward the call through an alternate IXC. If alternate IXCs cannot help establish the call, then a busy signal is finally returned to the user. Otherwise, the call is completed and retains the same quality of service and priority as all other telephone calls. The HPC component of GETS is not ubiquitously supported by the U.S. PSTN. The only expectation is that the 710 area code is recognized by all carriers. Additional support is conditional and dependent upon the equivalent service level agreements established between the U.S. Government and various telco carriers. Thus, the default end-to-end service for establishing a GETS call can be viewed as best effort and associated with the same priority as calls from the general public. The exception to this rule is when the call is forwarded through carriers that have been contracted to support HPC, which results in a higher probability that the GETS call will be established. 1.2.2 International Emergency Preparedness Scheme (IEPS) [18] is a recent ITU standard that describes emergency related communications over international telephone service. While systems like GETS are national in scope, IEPS acts as an extension to local authorized emergency call establishment and provides a building block for a global service. As in the case of GETS, IEPS promotes mechanisms like extended queuing, alternate routing, and exemption from restrictive management controls in order to increase the probability that international emergency calls will be established. The specifics of how this to be accomplished are to be specified in future ITU document(s). Carlberg & Brown Expires May,2001 5 Framework for Supporting IEPS in IP Telephony Nov,2000 1.3 Scope of this Document The scope of this document centers on the support of IEPS within the context of IP telephony, though not necessarily Voice over IP. We make a distinction between these two by treating IP telephony as a subset of VoIP, where in the former we assume some form of application layer signaling is used to explicitly establish and maintain voice data traffic. This explicit signaling capability provides the hooks from which VoIP traffic can be bridged to the PSTN. As an example of the distinction is when the Redundant Audio Tool (RAT) [14] begins sending VoIP packets to a unicast (or multicast) destination. RAT does not use an explicit signaling like SIP to establish an end-to-end call between two users. It simply sends data packets to the target destination. On the other hand, "SIP phones" are host devices that use a signaling protocol to establish a call signal before sending data towards the destination. Beyond this, part of our motivation in writing this document is to provide a reference point for ISPs and carriers so that they have an understanding of objectives and accompanying function requirements used to support IEPS related IP telephony traffic. In addition, we also wish to provide a reference point for potential customers (users of IEPS) in order to constrain their expectations. In particular, we wish to avoid any temptation of trying to replicate the exact capabilities of existing emergency voice service currently available in the PSTN to that of IP and the Internet. If nothing else, intrinsic differences between the two communications architectures precludes this from happening. Note, this does not prevent us from borrowing design concepts or objectives from existing systems. Section 2 presents several primary objectives that articulate what is considered important in supporting IEPS related IP telephony traffic. These objectives represent a generic set of goals and capabilities attributed to supporting IEPS based IP telephony. Section 3 presents additional value added objectives. These are capabilities that are viewed as useful, but not critical in support of IEPS. Section 4 presents a series of functional requirements that stem from the objectives articulated in section 2. Finally, Section 5 presents two scenarios in IEPS can be deployed over IP networks. These are not all-inclusive scenarios, nor are they the only ones that can be articulated. However, they do show cases Carlberg & Brown Expires May,2001 6 Framework for Supporting IEPS in IP Telephony Nov,2000 where some of the functional requirements apply, and where some do not. Finally, we need to state that this document focuses its attention on the IP layer and above. Specific operational procedures pertaining to Network Operation Centers (NOC) or Network Information Centers (NIC) are outside the scope of this document. This includes the "bits" below IP, other specific technologies, and service level agreements between ISPs and carriers with regard to dedicated links. 2. Objective The support of IEPS within IP telephony can be realized in the form of several primary objectives. These objectives define the generic functions or capability associated with IEPS, and the scope of the support needed to achieve these capabilities. From this generic set of objectives, we present specific functional requirements of existing IP protocols (presented below in section 3). There are two underlying goals in the selection of these objectives. One goal is to produce a design that maximizes the use of existing IP protocols and minimizes the set of additional specifications needed to support IP-telephony based IEPS. Thus, with the inclusion of these minimal augmentations, the bulk of the work in achieving IEPS over a proprietary IP network, or the Internet, involves operational issues. Examples of this would be the establishment of Service Level Agreements (SLA) with Internet Service Providers (ISP), and/or the provisioning of traffic engineered paths for IEPS-related telephony traffic. A second underlying goal in selecting the following objectives is to take into account experiences from an existing emergency-type communication system (as described in section 1.2.1) as well as the existing restrictions and constraints placed by some countries. In the former case, we do not attempt to mimic the system, but rather extract information as a reference model. With respect to constraints based on laws or agency regulations, this would normally be considered outside of the scope of any IETF document. However, these constraints act as a means of determining the lowest common denominator in specifying technical functional requirements. If such constraints do not exist, then additional functions can be added to the baseline set of functions. This last item will be expanded upon in the description of Objective #3 below. Carlberg & Brown Expires May,2001 7 Framework for Supporting IEPS in IP Telephony Nov,2000 The following list of objectives are termed primary because they pertain to that which defines the underlying goals of IEPS in relation to IP telephony. However, the primary objectives are not meant to dictate major overhauls of existing IP protocols, nor do they require new protocols to be developed. Primary Objectives in support of authorized emergency calls: 1) High Probability of Call Completion 2) Interaction with PSTN 3) Distinction of IEPS data traffic 4) Non-preemptive action 5) Non-ubiquitous support 6) Authenticated service The first objective is the crux of our work because it defines our expectations for both data and call signaling for IP telephony. As stated, our objective is achieving a high probability that emergency related calls (both data and signaling) will be forwarded through an IP network. Specifically, we envision the relevance of this objective during times of congestion, the context of which we describe further below in this section. The critical word in this objective is "probability", as opposed to assurance or guarantee -- the latter two placing a higher burden on the network. It stands to reason, though, that the word "probability" is a less tangible description that cannot be easily quantified. It is relative in relation to other traffic transiting the same network. Objectives 3 through 5 below help us to qualify the term probability in the context of other objectives. The second objective involves the interaction of IP telephony signaling with existing PSTN support for emergency related voice communications. As mentioned above in Section 1.2, standard T1.613 specifies code points for SS7. Specifically, the National Security and Emergency Preparedness (NS/EP) code point is defined for ISUP IAM messages used by SS7. Hence, our objective in the interaction between the PSTN and IP telephony with respect to IEPS is a direct mapping between directly related code points. The third objective focuses on the ability to distinguish IEPS data packets from other types of VoIP packets. With such an ability, transit providers can more easily ensure that service level agreements relating to IEPS are adhered. Note that we do not assume that the actions taken to distinguish IEPS type packets is Carlberg & Brown Expires May,2001 8 Framework for Supporting IEPS in IP Telephony Nov,2000 easy. Nor, in this section, do we state the form of this distinction. We simply present the objective of identifying flows that relate to IEPS versus others that traverse a transit network. At an abstract level, the forth objective pertains to the actions taken when an IP telephony call, via a signaling protocol such as SIP, cannot be forwarded because the network is experiencing a form of congestion. We state this in general terms because of two reasons: a) there may exist applications other than SIP, like H.248, used for call establishment, and b) congestion may come in several forms. For example, congestion may exist at the IP packet layer with respect to queues being filled to their configured limit. Congestion may also arise from resource allocation attributed per call or aggregated sets of calls. In this latter case, while there may exist resources to forward the packets, a signaling server may have reached its limit as to how many telephony calls it will support while retaining toll-quality service per call. Typically, one terms this form of congestion as call blocking. Note that we do not address the case when congestion occurs at the bit level below that of IP, due to the position that it is outside the scope of IP and the IETF. So, given the existence of congestion in its various forms, our objective is to support IEPS-related IP telephony call signaling and data traffic via non-preemptive actions taken by the network. More specifically, we associate this objective in the context of IP telephony acting as part of the Public Telephone Network (PTN). This, as opposed to the use of IP telephony within a private or stub network. In section 5 below, we expand on this through the description of two distinct scenarios of IP telephony and its operation with IEPS and the PSTN. It is important mention that this is a default objective influenced by existing laws & regulations. those countries not bound by these restrictions can remove this objective and make provisions to enforce preemptive action. In this case, it would probably be advantageous to deploy a signaling system similar to that proposed in [15], wherein multiple levels of priority are defined and preemption via admission control from SIP servers is enforced. The fifth objective stipulates that we do not advocate the need or expectation for ubiquitous support of IEPS across all administrative domains of the Internet. While it would be desirable to have ubiquitous support, we feel the reliance of such a requirement would doom even the contemplation of supporting IEPS Carlberg & Brown Expires May,2001 9 Framework for Supporting IEPS in IP Telephony Nov,2000 by the IETF and the expected entities (e.g., ISPs) involved in its deployment. We use the existing GETS service in the U.S. as an existing example in which emergency related communications does not need to be ubiquitous. As mentioned previously, the measure and amount of support provided by the U.S. PSTN for GETS is not ubiquitous across all U.S. Inter-exchange Carriers (IXC) nor Local Exchange Carriers (LEC). The fact that GETS still works within this context, it is our objective to follow this deployment model such that we can accomplish the first objective listed above -- a higher probability of call completion than that of normal IP telephony call traffic. Our final objective is that only authorized users may use the services outlined in this framework. GETS users are authenticated using a PIN provided to the telecommunications carrier, which signals approval back to the user's local exchange over SS7. In an IP network, the authentication center will need to securely signal back to the IP ingress point that a given user is authorized for the NS/EP diffserv codepoint. Similarly, transit networks with IEPS SLAs must securely interchange authorized IEPS traffic. In both cases, IPSec authentication transforms may be used to protect this traffic. This is entirely separate from end-to-end IPSec protection of user traffic, which will be configured by users. IP-PSTN gateways must also be able to securely signal IEPS authorization for a given flow. As these gateways are likely to act as SIP servers, we further consider the use of SIP's security functions to aid this objective. 3. Value Added Objectives These are objectives that are viewed as being helpful in achieving a high probability of call completion. It is expected that their realization within an IP network would be in the form of new protocols or major enhancements to existing ones. Thus, objectives listed in this section are treated as value added -- an expectation that their existence would be beneficial, and yet not viewed as critical to support IEPS related IP telephony traffic. The value added objectives are: 1) Alternate Path Routing 2) IEPS Domain Discovery Carlberg & Brown Expires May,2001 10 Framework for Supporting IEPS in IP Telephony Nov,2000 The first involves the ability to discover and use a different path to route IP telephony traffic around congestion points and thus avoid them. Ideally, the discovery process would be accomplished in an expedient manner (possibly even a priori to the need of its existence). At this level, we make no assumptions how the alternate path is accomplished, or even at which layer it is achieved -- e.g., the network versus the application layer. But this kind of capability, at least in a minimal form, would help contribute to increasing the probability of call completion of IEPS traffic by making use of noncongested alternate paths. We use the term "minimal form" to concede the fact that care must be taken in how the system provides an alternate paths so it does not significantly contribute to the congestion that is to be avoided (e.g., via excess control/discovery messages). The second item above stems from one of the primary objectives that precludes the need for ubiquitous support for IEPS. Thus, given that we assume only a subset of transit ISPs will be contracted to support IEPS, it stands to reason that it would be beneficial to have networks/domains discover the nearest domain that supports IEPS, and in turn forward IEPS telephony messages in that direction. 4. Functional Requirements In this section, we take the objectives presented above and specify a corresponding set of functional requirements to achieve them. Given that the objectives are predominantly atomic in nature, the corresponding functional requirements are to be viewed as separate with no specific dependency upon each other as a whole. They may be complimentary with each other, but there is no need for all to exist given different scenarios of operation, and that IEPS support is not viewed as a ubiquitously available service. We divide the functional requirements into 4 areas: 1) Signaling 2) Policy 3) Traffic Engineering 4) Security Carlberg & Brown Expires May,2001 11 Framework for Supporting IEPS in IP Telephony Nov,2000 4.1 Signaling SIP Signaling is further divided into two perspectives. The first is application level signaling. We focus our attention on the Session Initiation Protocol (SIP), since it is viewed as being used by applications like IP telephony. Currently, SIP has an existing "priority" field that distinguishes different types of sessions. The five currently defined values are: "emergency", "urgent", "normal", "non-urgent", "other-priority". We propose the addition of a new value for this field titled "authorized-emergency". This new value is used to denote an emergency-related session that has been initiated by an authorized user. In particular, we distinguish this value from the existing "emergency" value, which could be attributed to emergency sessions from the general public (e.g., a "911" call). It is important to note that this is the one functional requirement that is considered mandatory with respect to supporting IEPS within IP telephony. We take this position because regardless of the extent by which the underlying network supports IEPS-based traffic, there is a need to distinguish IEPS sessions from others. The existence of this new value in the SIP priority field allows an IP telephony domain to map the NS/EP code point from an SS7 telephony domain. This will help facilitate a seamless interaction between the PSTN and the an IP network acting as either an internal backbone or as a peering ISP. Author's Note: We do not make reference to the current Polk draft [16] and its advocacy of expanding the SIP priority field to include values attributed to Multi-Level Precedence and Preemption. However, if that document were to be advanced, we could satisfy our requirement of adding an "authorized-emergency" value with minimal changes to the Polk draft. Specifically, by make "preemption" a local and optional administrative issue, and adding to the values specified in [16]. Diff-Serv In accordance to [16] , the differentiated services code point (DSCP) field is divided into 3 sets of values. The first set are assigned by IANA. Within this set, there are currently, three Carlberg & Brown Expires May,2001 12 Framework for Supporting IEPS in IP Telephony Nov,2000 types of Per Hop Behaviors have been specified: Default (correlating to best effort forwarding), Assured Forwarding, and Expedited Forwarding. The second set of DSCP values are set aside for local or experimental use. The third set of DSCP values are also set local or experimental use, but may later be reassigned to IANNA in case the first set has been completely assigned. We recommend the specification of a new type of PHB referred to as Emergency Related Forwarding (ERF). This provides a means of distinguishing emergency related traffic (signaling and user data) from other traffic. The existence of this PHB then provides a baseline by which specific code points may be defined related to various emergency related traffic: authorized emergency sessions (e.g., IEPS), general public emergency calls (e.g., "911"), etc. Authors note: It is probable that this section may be contentious given the advocacy of a new PHB group. Hence, this section may require additional input and refinement. 4.2 Policy One of the objectives listed in section 3 above is to treat IEPS- signaling, and related data traffic, as non-preemptive in nature. Further, that this treatment is to be the default mode of operation or service. This is in recognition that existing regulations or laws of certain countries governing the establishment of SLAs may not allow preemptive actions (e.g., dropping existing telephony flows). On the other hand, the laws and regulations of other countries influencing the specification of SLA(s) may allow preemption, or even require its existence. Given this disparity, we rely on local policy to determine the degree by which emergency related traffic affects existing traffic load of a given network or ISP. Important note: we reiterate our earlier comment that laws and regulations are generally outside the scope of the IETF and its specification of designs and protocols. However, these constraints can be used as a guide in producing a baseline function to be supported; in our case, a default policy for non-preemptive call establishment of IEPS-signaling and data. Policy can be in the form of static information embedded in various components (e.g., SIP servers or bandwidth brokers), or it can be realized and supported via COPS with respect to allocation of a domain's resources [17]. There is no requirement as to how policy Carlberg & Brown Expires May,2001 13 Framework for Supporting IEPS in IP Telephony Nov,2000 is accomplished. Instead, if a domain follows actions outside of the default non-preemptive action of IEPS-related communication, then we stipulate a functional requirement that some type of policy mechanism is in place to satisfy the local policies of an SLA established for IEPS type traffic. 4.3 Traffic Engineering In those cases where a network operates under the constraints of SLAs, one or more of which pertains to IEPS based traffic, it can be expected that some form of traffic engineering is applied to the operation of the network. We make no requirements as to which type of traffic engineering mechanism is used, but that such a system exists and can distinguish and support IEPS signaling and data traffic. A potentially complimentary work in progress can be found in [9], which articulates a framework for Voice over MPLS. We cite the draft only as a point of reference, with the idea that it may be augmented to reflect labeled path(s) dedicated to different values in the SIP priority field -- such as those pertaining to emergencies. But of more significance, [9] presents a specific framework for traffic engineering support of toll quality (i.e., a particular grade of service) IP telephony. Note: As a point of reference, existing SLAs established by the NCS for GETS service tend to focus on a maximum allocation of 1% of calls allowed to be established through a given LEC using HPC. Once this limit is reached, all other GETS calls experience the same probably of cal completion as the general public. It is expected, and encouraged, that IEPS related SLAs will have a limit with respect to the amount of traffic distinguished as being emergency related, and initiated by an authorized user. 4.4 Security As IEPS support moves from intra-domain PSTN and IP networks to diffuse inter-domain pure IP, authenticated service becomes more complex to provide. Where an IEPS call is carried from PSTN to PSTN via one carrier's backbone IP network, very little IP-specific security support is required. The user authenticates herself as usual to the network using a PIN. The gateway from her PSTN connection into the backbone IP network must be able to signal that Carlberg & Brown Expires May,2001 14 Framework for Supporting IEPS in IP Telephony Nov,2000 the flow has IEPS priority. The carrier's traffic engineering measures than attempt to provide a higher probability of call completion to that flow. The gateway back into the PSTN must similarly signal the call's higher priority. A secure link between the gateways may be set up using IPSec or SIP security functionality. If the endpoint is an IP device on the carrier's network, the link may be set up securely from the ingress gateway to the end device. As flows traverse more than one IP network, domains whose peering agreements include IEPS support must have means to securely signal a given flow's IEPS status. They may choose to use physical link security and/or IPSec authentication, combined with traffic conditioning measures to limit the amount of IEPS traffic that may pass between the two domains. The inter-domain agreement may require the originating network to take responsibility for ensuring only authorized traffic is marked with IEPS priority; the downstream domain may still perform redundant conditioning to prevent the propagation of theft and denial of service attacks. Security may be provided between ingress and egress gateways or IP endpoints using IPSec or SIP security functions. When a call originates from an IP device, the ingress network may authorize IEPS traffic over that link as part of its user authentication procedures without necessarily communicating with a central IEPS authentication center as happens with POTS-originated calls. These authentication procedures may occur at the link or network layers, but are entirely at the discretion of the ingress network. That network must decide how often it should update its list of authorized IEPS users based on the bounds it is prepared to accept on traffic from recently-revoked users. 5. Key Scenarios There are various scenarios in which IP telephony can be realized, each of which can infer a unique set of functional requirements that may include just a subset of those listed above. We acknowledge that a scenario may exist whose functional requirements are not listed above. Our intention is not to consider every possible scenario by which support for emergency related IP telephony can be realized. Rather, we narrow our scope using a single guideline; we assume there is a signaling & data interaction between the PSTN and the IP network with respect to supporting emergency-related telephony traffic. We stress that Carlberg & Brown Expires May,2001 15 Framework for Supporting IEPS in IP Telephony Nov,2000 this does not preclude an IP-only end-to-end model, but rather the inclusion of the PSTN expands the problem space and includes the current dominate form of voice communication. There are two scenarios that we use as a model for determining our objectives and subsequent functional requirements. These being: Single IP Administrative Domain ------------------------------- This scenario is a direct reflection of the evolution of the PSTN. Specifically, we refer to the case in which data networks have emerged in various degrees as a backbone infrastructure connecting PSTN switches at its edges. This represents a single isolated IP administrative domain that has no directly adjacent IP domains connected 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 carrier, whose infrastructure retains the classic switching architecture attributed to the PSTN. The other is the next generation carrier, which uses a data network (e.g., IP) as its core infrastructure, and Signaling Gateways at its edges. These gateways "speak" SS7 externally with peering carriers, and another protocol (e.g., SIP) internally, which rides on top of the IP infrastructure. Legacy Next Generation Next Generation Carrier Carrier Carrier ******* *************** ************** * * * * ISUP * * SW<--->SW <-----> SG <---IP---> SG <--IAM--> SG <---IP---> SG * * (SS7) * (SIP) * (SS7) * (SIP) * ******* *************** ************** SW - Telco Switch SG - Signaling Gateway Figure 1 The significant aspect of this scenario is that all the resources of each IP "island" fall within a given administrative authority. Hence, there is no problem of retaining toll quality Grade of Carlberg & Brown Expires May,2001 16 Framework for Supporting IEPS in IP Telephony Nov,2000 Service as the voice traffic (data and signaling) exists the IP network because of the existing SS7 provisioned service between carriers. Thus, the need for support of mechanisms like diff-serv, and an 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 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, means that existing security, in the form of Personal Identification Number (PIN) authentication, is the default scope of security. We do not claim that the reliance of a PIN based security system is highly reliable or even desirable. But, we use this system as a default mechanism in order to avoid placing additional requirements on existing authorized emergency telephony systems. Multiple IP Administrative Domains ---------------------------------- We view the scenario of multiple IP administrative domains as a superset of the previous scenario. Specifically, we retain the notion that the IP telephony system peers with the existing PSTN. In addition, segments (i.e., portions of the Internet) may exchange signaling with other IP administrative domains via non-PSTN signaling protocols like SIP. Legacy Next Generation Next Generation Carrier Carrier Carrier ******* *************** ************** * * * * * * SW<--->SW <-----> SG <---IP---> SG <--IP--> SG <---IP---> SG * * (SS7) * (SIP) * (SIP) * (SIP) * ******* *************** ************** SW - Telco Switch SG - Signaling Gateway Figure 2 Carlberg & Brown Expires May,2001 17 Framework for Supporting IEPS in IP Telephony Nov,2000 Given multiple IP domains, and the presumption that SLAs relating to IEPS traffic may exist between them, the need for something like diff-serv grows with respect to being able to distinguish the emergency related traffic from other types of traffic. In addition, IP security becomes more important between domains in order help ensure that the act of distinguishing IEPS-type traffic is indeed valid for the given source. 8. Security Considerations Information related to this area have been presented in sections 2 and 4. 9. References 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 Braden, R., et. al., "Integrated Services in the Internet Architecture: An Overview", Informational, RFC 1633, June 1994. 3 Braden, R., et. al., "Resource Reservation Protocol (RSVP) _ Version 1, Functional Specification", Proposed Standard, RFC 2205, Sept. 1997. 4 Shenker, S., et. al., "Specification of Guaranteed Quality of Service", Proposed Standard, RFC 2212, Sept 1997. 5 Wroclawski, J., "Specification for Controlled-Load Network Service Element", Proposed Standard, RFC 2211, Sept 1997. 6 Gai, S., et. al., "RSVP Proxy", Internet Draft, Work in Progress, July 2000. 7 Wang, L, et. al., "RSVP Refresh Overhead Reduction by State Compression", Internet Draft, Work In Progress, March 2000. 8 Blake, S., et. al., "An Architecture for Differentiated Service", Proposed Standard, RFC 2475, Dec. 1998. Carlberg & Brown Expires May,2001 18 Framework for Supporting IEPS in IP Telephony Nov,2000 9 Kankkunen, A., et. al., "VoIP over MPLS Framework_, Internet Draft, Work In Progress, July 2000. 10 Sharma, V., et. al., "Framework for MPLS-based Recovery", Internet Draft, Work In Progress, September 2000. 11 Postel, J., "Simple Mail Transfer Protocol", Standard, RFC 821, August 1982. 12 Handley, M., et. al., "SIP: Session Initiation Protocol", Proposed Standard, RFC 2543, March 1999. 13 ANSI, "Signaling System No. 7(SS7) _ High Probability of Completion (HPC) Network Capability_, ANSI T1.631, 1993. 14 Reliable Audio Tool (RAT): http://www-mice.cs.ucl.ac.uk/multimedia/software/rat 15 Polk, J., "SIP Precedence mapping to MLPP Interworking", Internet Draft, Work In Progress, March, 2000. 16 Nichols, K., et. al.,"Definition of the Differentiated Services Field (DS Field) in the Ipv4 and Ipv6 Headers_, Proposed Standard, RFC 2474, December 1998. 17 Durham, D., "The COPS (Common Open Policy Service) Protocol", Proposed Standard, RFC 2748, Jan 2000. 18 ITU, "International Emergency Preparedness Scheme_, ITU Recommendation, E.106, March 2000. Carlberg & Brown Expires May,2001 19 10. Acknowledgments To be done_ 11. Author's Addresses Ken Carlberg University College London Department of Computer Science Gower Street London, WC1E 6BT United Kingdom Ian Brown University College London Department of Computer Science Gower Street London, WC1E 6BT United Kingdom Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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