Interoperability Profile for Relay User Equipment (RUE)
draft-vrs-rue-dispatch-00

Abstract

This document defines and specifies a protocol profile defining an interface between a relay service endpoint used by a deaf or hard-of-hearing user and a relay service.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

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."

This Internet-Draft will expire on January 21, 2017.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 2. Scope
• 3. Terminology
• 4. Normative Language
• 5. General Requirements
• 6. Initial Selection, Configuration and Registration
• 6.1. RUE Provider Selection
• 6.2. RUE Configuration Service
• 6.3. JSON Schemas
• 7. RUE SIP Registration
• 8. NAT Traversal
• 9. RUE CardDAV Login and Synchronization
• 10. Contacts Export Service
• 11. SIP Session Establishment
• 11.1. RUE Normal Call Origination
• 11.2. Dial-Around
• 11.3. RUE Normal Call Termination
• 11.4. Emergency Calls
• 12. RUE Videomail
• 12.1. Mail Waiting Indicator (MWI)
• 12.2. Videomail Retrieval
• 13. URI Representation of Phone Numbers
• 14. Media
• 14.1. Text-Based Communication
• 14.2. Video Codecs
• 14.3. Audio Codecs
• 14.4. DTMF Digits
• 15. RTP & RTCP
• 15.1. Bandwidth Negotiation Flow Control and Media Performance
• 15.2. RTP / AVPF Profile for RTCP Feedback
• 15.3. Negative Acknowledgement, Packet Loss Indicator, Full Intraframe Request
• 16. IANA Considerations
• 17. Security Considerations
• 18. Contributors
• 19. vCard Example
• 20. Normative References
• Authors' Addresses

1. Introduction

Video Relay Service (VRS) is a form of Telecommunications Relay Service (TRS) that enables persons with hearing disabilities who use sign language, such as American Sign Language (ASL), to communicate with voice telephone users through video equipment. These services also enable communication between such individuals directly in suitable modalities, including any combination of sign language via video, real-time text (RTT) and speech.

This Relay User Equipment (RUE) profile is a profile of the Session Initiation Protocol (SIP) and related media protocols which enables end-user equipment registration and calling for video relay service (VRS) calls. It specifies the minimal set of call flows, IETF and ITU-T standards that must be supported, provides guidance where the standards leave multiple implementation options, and specifies minimal and extended capabilities for RUE calls.

This RUE profile supports the requirements of relay services in the United States, as described in 47 CFR 64.601 et seq., but may be applicable to similar uses elsewhere.

2. Scope

This document defines a standard interface between a RUE and the services offered by relay service (RS) providers. This document does not enumerate the features that the RUE or relay service provider must support to meet, for example, national regulatory requirements.

3. Terminology

Communication Assistant (CA):

The American Sign Language (ASL) interpreter stationed in a TRS registered call center working for a VRS provider, acting as part of the wire of a call to provide functionally equivalent phone service.

Communication modality (modality):

A particular form of communication that may be employed by two users, e.g., English voice, Spanish voice, American Sign Language, English lip reading, French real-time-text, or English MSRP instant messaging. Here, one communication modality is assumed to encompass both the language and the manner in which that language is exchanged. For example, English voice and French voice are two different communication modalities.

Default video relay service:

The video relay service operated by a subscriber's default video relay service provider.

Default video relay service provider (default provider):

The video relay service provider that registers, and assigns a telephone number to, a specific subscriber. A subscriber's default provider provides the video relay service that handles incoming relay calls to the user. It also handles outgoing relay calls by default.

Dial-around call:

A relay call where the subscriber specifies the use of a video relay service provider other than one of the providers the subscriber is registered with. This can be accomplished by the user dialing a "front-door" number for a VRS provider and signing or texting a phone number to call ("two-stage") or by the user's RUE software instructing the server of its default VRS provider to automatically route the call through the alternate provider to the desired PSTN directory number ("one-stage").

Full Intra Request (FIR):

A request to a media sender, requiring that media sender to send a Decoder Refresh Point at the earliest opportunity. FIR is sometimes known as "instantaneous decoder refresh request"; "video fast update request"; or "fast update request".

NANP:

North America Numbering Plan (see: http://nationalnanpa.org)

Point-to-Point Call (P2P Call):

A call between two RUEs, without including a CA.

PSTN UE:

User equipment (UE) that interfaces with a human being via the PSTN, and mediates communication via voice. A telephone.

PSTN user:

An individual using PSTN UE.

Relay call:

A call that allows persons with hearing or speech disabilities to use a RUE to talk to users of traditional voice services with the aid of a communication assistant (CA) to relay the communication. See [FCC-VRS-GUIDE].

Relay number database (RND):

The iTRS Relay Number Database (RND) functions as a 10-digit NANP phone number lookup for SIP and H.323 URLs for TRS subscribers.

Relay-to-relay call:

A call between two subscribers each using different forms of relay (video relay, IP relay, TTY), each with a separate communication assistant to assist in relaying the conversation.

Relay service (RS):

A service that allow a registered subscriber to use a RUE to make and receive relay calls, point-to-point, and relay-to-relay calls. The functions provided by the relay service include the provision of media links supporting the communication modalities used by the caller and callee, user registration and validation, authentication, authorization, automatic call distributor (ACD) platform functions, routing (including emergency call routing), call setup, mapping, call features (such as call forwarding and video mail), and assignment of CAs to relay calls.

Relay service provider:

An organization that operates a relay service. A subscriber selects a relay service provider to assign and register a telephone number for their use, to register with for receipt of incoming calls, and as the default service for outgoing calls.

Relay user:

See subscriber.

Relay user E.164 Number (user E.164):

The telephone number assigned to the RUE, in ITU-T E.164 format.

Relay user equipment (RUE):

A SIP user agent (UA) enhanced with extra features to support a subscriber in requesting and using relay calls. A RUE may take many forms, including a stand-alone device, an application running on a general-purpose computing device such as a laptop, tablet or smart phone, or proprietary equipment connected to a server that provides the RUE interface.

Sign language:

A language which uses hand gestures and body language to convey meaning, including but not limited to American Sign Language (ASL).

Subscriber:

An individual that has registered with a relay service provider, and who obtains service by using relay user equipment. This is the traditional telecom term for an end-user customer, in our case, a relay user.

Telecommunications relay services (TRS):

(from the FCC): "Telephone transmission services that provide the ability for an individual who has a hearing or speech disability to engage in communication by wire or radio with a hearing individual in a manner that is functionally equivalent to the ability of an individual who does not have a hearing or speech disability to communicate using voice communication services by wire or radio. Such term includes services that enable two-way communication between an individual who uses a text telephone or other nonvoice terminal device and an individual who does not use such a device, speech-to-speech services, video relay services and non-English relay services."

Video relay service (VRS):

A relay service for people with hearing or speech disabilities who use sign language to communicate using video equipment (video RUE) with other people in real time. The video link allows the CA to view and interpret the subscriber's signed conversation and relay the conversation back and forth with the other party.

4. Normative Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119].

In many portions of this document, the document specifies a required implementation for an optional feature; i.e., that a provider's systems MAY implement a specific feature, and if they do, they MUST implement it in a specific way, in order to implement the functionality provided through this document.

5. General Requirements

All HTTP/HTTPS connections specified throughout this document MUST use HTTPS, and MUST use TLS 1.2 [RFC5246] or later, using a server-side certificate.

During the establishment of a TLS connection with a provider the RUE MAY be asked by the server for a client certificate. In that case it SHOULD provide a client certificate. Providers MAY reject requests that fail to provide a recognized certificate.

RUEs MUST include a "User-Agent" header field uniquely identifying the RUE application, platform and version in all SIP requests, and MUST include a "Server" header field with the same content in SIP responses.

All text data payloads not otherwise constrained by a specification in another standards document MUST be encoded as Unicode UTF/8.

6. Initial Selection, Configuration and Registration

6.1. RUE Provider Selection

In order to allow the user to select a relay service, the RUE SHALL obtain, on startup, a list of providers from a publicly accessible URL, e.g., hosted by the national regulatory agency. This provider will be used for outbound calls; the provider chosen for inbound calls is determined by the user's' E.164 number.

The provider list, formatted as JSON, contains:

version:

Specifies the version number of the provider list format. A new version number SHOULD only be used if the new version is not backwards-compatible with the older version. A new version number is not needed if new elements are optional and can be ignored by older implementations.

providers:

An array where each entry describes one provider. Each entry consists of the following items:

name:

This parameter contains the text label identifying the provider and is meant to be displayed to the human VRS user.

domain:

The domain parameter is used for configuration purposes by the RUE (as discussed in Section 6.2) and also as the domain to use when targetting one-stage dial-around calls to this provider (as discussed in Section 11.2).

operator:

(Optional) The operator parameter is a SIP URL that identifies the operator "front-door" that VRS users may contact for manual (two-stage) dial-around calls.

The VRS user interacts with the RUE to select from the provider list one or more providers with which the user has already established an account.

{
  "version": 1,
  "providers": [
    {
      "name": "Red",
      "domain": "red.example.net",
      "operator": "sip:operator@red.example.net"
    },
    {
      "name": "Green",
      "domain": "green.example.net",
      "operator": "sip:+18885550123@green.example.net;user=phone"
    },
    {
      "name": "Blue",
      "domain": "blue.example.net"
    }
  ]
}

  

{
      "version": 1,
      "lifetime": 86400,
      "display-name" : "Bob Smith",
      "phone-number": "+18135551212",
      "provider-domain": "red.example.net",
      "outbound-proxies": [
         "sip:p1.red.example.net",
         "sip:p2.red.example.net"
      ],
      "mwi": "sip:+18135551212@red.example.net",
      "videomail": "sip:+18135551212@vm.red.example.net",
      "contacts": "https://red.example.net:443/contacts"
                  "/export/xcard" ,
      "carddav": "bob@red.example.com" ,
      "ice-servers": [
        "uri": "stun:stun.l.google.com:19302",
        "uri": "turn:turn.red.example.net:3478"
      ],
      "credentials": [
        {
          "realm": "red.example.net",
          "username": "bob",
          "password": "reg-pw"
        },
        {
          "realm": "proxies.red.example.net",
          "username": "bob",
          "password": "proxy-pw"
        },
        {
          "realm": "cd.red.example.net",
          "username": "bob",
          "password": "cd-pw"
        },
        {
          "realm": "vm.red.example.net",
          "username": "bob",
          "password": "vm-pw"
        },
        {
          "realm": "stun-turn.red.example.net",
          "username": "bob",
          "password": "stun-turn-pw"
        }
      ]
}

      

{
  "version": 1,
  "providers": [
    1*
    {
      "name": string,
      "domain": fqdn,
      ?"operator":           ; "front-door" access to provider
          uri,               ; (sip uri)
      * /^.*$/ : any         ; (allow future extensions)
    }
  ] ,
  * /^.*$/ : any             ; (allow future extensions)
}

      

{
      "version": 1,            ; Interface version
      "lifetime": integer,     ; Deadline (in seconds) for 
                               ; refreshing this config without 
                               ; user input.
      "phone-number": /^\+[0-9]+$/ , ; E.164 phone number
                               ; for this user
      ?"display-name" : string,; display name for From: header
      "provider-domain": fqdn, ; SHOULD match that in Provider List
      ?"outbound-proxies": [ 1* : uri ], ; sip URIs
      ?"mwi": uri ,            ; sip URI for MWI subscriptions
      ?"videomail": uri ,      ; sip URI for videomail retrieval
      "contacts": uri ,        ; https URI for contact list retrieval
      ?"carddav": /^[^@]+@[^@]+$/ , ; for contact list synch
      ?"ice-servers":          ; (Required for ICE use)
         [ 1* : uri ],         ; (stun[s] & turn[s] URIs 
      ?"credentials":          ; for digest authentication
      [ 1* {
          "realm": string,
          "username": string,
          "password": string
      } ],
      * /^.*$/ : any           ; (allow future extensions)
}

      

     ,-.
     `-'
     /|\     ,---.  ,---.  ,------------. ,----------------.  ,---.
      |      |RUE|  |DNS|  |HTTPS Server| |   Provider     |  |CRM| 
     / \     |   |  |   |  |            | |Global Settings |  |   |
  RUE User   `-+-'  `-+-'  `-----+------' `--------+-------'  `-+-'
     |         |      |          |                 |            |
[1] Select a VRS Provider name   |                 |            |
     | ------->|      |          |                 |            |
     |         |      |          |                 |            |
[2] NAPTR "SFUA.CFG" red.example.net               |            |
     |         |----->|          |                 |            |
     |         |      |          |                 |            |
[3] NAPTR "!.*!https://server.red.example.net/!"   |            |
     |         |<-----|          |                 |            |
     |         |      |          |                 |            |
[4] If NAPTR found, query DNS server.red.example.net            |
     |         |----->|          |                 |            |
     |         |      |          |                 |            |
[5] If NXDOMAIN, query DNS config.red.example.net  |            |
     |         | - - >|          |                 |            |
     |         |      |          |                 |            |
[6] IP Address of Config Server  |                 |            |
     |         |<-----|          |                 |            |
     |         |      |          |                 |            |
[7] Establish TLS connection     |                 |            |
     |         |<--------------->|                 |            |
     |         |      |          |                 |            |
[8] HTTP: https://config.red.example.net/v1        |            |
     |         |---------------->|                 |            |
     |         |      |          |                 |            |
[9] HTTP: 401 Unauthorized       |                 |            |
    WWW-Authenticate Digest realm="Y" qop="auth,auth-int" nonce=|
     |         |<----------------|                 |            |
     |         |      |          |                 |            |
[10] Query for userid/pw         |                 |            |
     |<--------|      |          |                 |            |
     |         |      |          |                 |            |
[11] User="bob", pw="bob's global provider pw"     |            |
     |-------->|      |          |                 |            |
     |         |      |          |                 |            |
[12] HTTP: https://config.red.example.net/v1       |            |
     | Authorization Digest username="bob" realm="Y" qop="auth" |
     | nonce=... response="..." ...                |            |
     |         |---------------->|                 |            |
     |         |      |          |                 |            |
     |   [13] Find subscriber information for username="bob"    |
     |         |      |          |----------------------------->|
     |         |      |          |                 |            |
     |   [14] Subscriber specific configuration information     |
     |         |      |          |<-----------------------------|
     |         |      |          |                 |            |
     |   [15] Retrieve provider specific settings               |
     |         |      |          |---------------->|            |
     |         |      |          |                 |            |
     |   [16] Provider configuration information   |            |
     |         |      |          |<----------------|            |
     |         |      |          |                 |            |
[17] 200 OK + JSON merge subscriber + provider configs          |
     |         |<----------------|                 |            |
     |         |      |          |                 |            |
  RUE User   ,---.  ,---.  ,------------. ,----------------.  ,---.
     ,-.     |RUE|  |DNS|  |HTTPS Server| |   Provider     |  |CRM|
     `-'     |   |  |   |  |            | |Global Settings |  |   |
     /|\     `-+-'  `-+-'  `-----+------' `--------+-------'  `-+-'
      |
     / \

   IN NAPTR 50  50 "s" "SIPS+D2T" "" _sips._tcp.p1.red.example.net.
   IN NAPTR 90  50 "s" "SIP+D2T"  "" _sip._tcp.p1.red.example.net
   IN NAPTR 100 50 "s" "SIP+D2U"  "" _sip._udp.p1.red.example.net.

  

    ,-+-.   ,-+-.  ,------+------.
    |RUE|   |DNS|  |SIP Registrar|
    `-+-'   `-+-'  `------+------'
      |       |           |
[1] Look up SRV DNS for _sip._tls.red.example.net
      |------>|           |
      |       |           |
[2] SRV DNS response with red.example.net:5061
      |<------|           |
      |       |           |
[3] Look up DNS A/CNAME for red.example.net
      |------>|           |
      |       |           |
[4] IP Address(es) of SIP REGISTRAR Server(s)
      |<------|           |
      |       |           |
[5] Establish TLS connection to registrar
      |<----------------->|
      |       |           |
[6] SIP: REGISTER sip:red.example.net
    To: sip:+18135551212@red.example.net;...
    From: sip:+18135551212@red.example.net;...
      |------------------>|
      |       |           |
[7] SIP: 401 Unauthorized
    WWW-Authenticate Digest realm="read.example.net" 
      |  qop="auth,auth-int" nonce=...
      |<------------------|
      |       |           |
[8] SIP: REGISTER sip_username@sip_domain
    Authorization Digest username="bob" realm="red.example.net"
      |  qop="auth" nonce=... response="..."
      |------------------>|
      |       |           |
[9] 200 OK    |           |
      |<------------------|
      |       |           |
    ,-+-.   ,-+-.  ,------+------.
    |RUE|   |DNS|  |SIP Registrar|
    `---'   `---'  `-------------'

  

     ,-.
     `-'
     /|\
      |      ,---.   ,---.  ,---------------.  ,---.
     / \     |RUE|   |DNS|  |CardDAV Service|  |CRM|
  RUE User   `-+-'   `-+-'  `-------+-------'  `-+-'
     |         |       |            |            |
[1] Select a VRS Provider name      |            |
     | ------->|       |            |            |
     |         |       |            |            |
[2] Lookup SRV _carddavs._tcp.red.example.net    |
     |         |------>|            |            |
     |         |       |            |            |
[3]  |     SRV carddav.red.example.net:443       |
     |         |<------|            |            |
     |         |       |            |            |
[4] resolve carddav.red.example.net |            |
     |         |------>|            |            |
     |         |       |            |            |
[5]        IP Address of CardDAV Server          |
     |         |<------|            |            |
     |         |       |            |            |
[6] Establish TLS connection to carddav.red.example.net:443
     |         |<------------------>|            |
     |         |       |            |            |
[7] HTTP: (CardDAV request)         |            |
     |         |------------------->|            |                          
     |         |       |            |            |                          
[8] HTTP: 401 Unauthorized          |            |                          
    WWW-Authenticate Digest         |            |
    realm="cd.red.example.net"      |            |
    qop="auth,auth-int" nonce=...   |            |
     |         |<-------------------|            |                          
     |         |       |            |            |                          
[9] HTTP: (CardDAV request)         |            |
    Authorization Digest username="bob"          |
    realm="cd.red.example.net" qop="auth"        |
    nonce=... response="..."        |            |
     |         |------------------->|            |                          
     |         |       |            |            |                          
     |         |  [10] Sync address book         |
     |         |<..................>|<..........>|
     |         |       |            |            |
  RUE User   ,-+-.   ,-+-.  ,-------+-------.  ,-+-.
     ,-.     |RUE|   |DNS|  |CardDAV Service|  |CRM|
     `-'     `---'   `---'  `---------------'  `---'
     /|\
      |
     / \

       

     ,-.
     `-'
     /|\
      |      ,---.   ,---.  ,---------------------------.  ,---.
     / \     |RUE|   |DNS|  |Contacts Export Web Service|  |CRM|
  RUE User   `-+-'   `-+-'  `-------------+-------------'  `-+-'
     |         |       |                  |                  |
[1] Select a VRS Provider name            |                  |
     | ------->|       |                  |                  |
     |         |       |                  |                  |
[2] resolve red.example.net               |                  |
     |         |------>|                  |                  |
     |         |       |                  |                  |
[3] IP Address of Web Server              |                  |
     |         |<------|                  |                  |
     |         |       |                  |                  |
[4] Establish TLS web connection to red.example.net          |
     |         |<------------------------>|                  |
     |         |       |                  |                  |
[5] HTTP: GET /contacts/export/xcard      |                  |
     |         |------------------------->|                  |                          
     |         |       |                  |                  |                          
[6] HTTP: 401 Unauthorized                |                  |                          
    WWW-Authenticate Digest               |                  |
    realm="cd.red.example.net"            |                  |
    qop="auth,auth-int" nonce=...         |                  |
     |         |<-------------------------|                  |                          
     |         |       |                  |                  |                          
[7] HTTP: GET /contacts/export/xcard      |                  |
    Authorization Digest username="bob"   |                  |
    realm="cd.red.example.net" qop="auth" |                  |
    nonce=... response="..."              |                  |
     |         |------------------------->|                  |                          
     |         |       |                  |                  |                          
     |         | [8] Find contacts for username="bob"        |
     |         |       |                  |----------------->|
     |         |       |                  |                  |
     |         | [9] Contacts list in xCard format           |
     |         |      (application/vcard+xml)                |
     |         |       |                  |<-----------------|
     |         |       |                  |                  |
     |         | [10] 200 OK              |                  |
     |         |<-------------------------|                  |
     |         |       |                  |                  |
  RUE User   ,-+-.   ,-+-.  ,-------------+-------------.  ,-+-.
     ,-.     |RUE|   |DNS|  |Contacts Export Web Service|  |CRM|
     `-'     `---'   `---'  `---------------------------'  `---'
     /|\
      |
     / \

    

    ,-+-.        ,----+----.    ,-----+-----.
    |RUE|        |Default  |    |Dial-Around|
    |   |        |Provider |    | Provider  |
    `-+-'        `----+----'    `-----+-----'
      |               |               |
      | [1] INVITE    |               |
      |-------------->| [2] INVITE    |
      |               |-------------->|

Message Details:

[1] INVITE Rue -> Default Provider

INVITE sip:+15551234567@green.example.net;user=phone SIP/2.0
To: <sip:+15551234567@green.example.net;user=phone>
From: "Bob Smith" <sip:+18135551212@red.example.net;user=phone>
Route: sip:green.example.net


[2] INVITE Default Provider -> Dial-Around Provider

INVITE sip:+15551234567@green.example.net;user=phone SIP/2.0
To: <sip:+15551234567@green.example.net;user=phone>
From: "Bob Smith" <sip:+18135551212@red.example.net;user=phone>


      

    ,-+-.        ,----+----.
    |RUE|        |Default  |
    |   |        |Provider |
    `-+-'        `----+----'
      |               |
      | [1] INVITE    |
      |-------------->|
      |               |

Message Details:

[1] INVITE Rue -> Default Provider

INVITE urn:service:sos SIP/2.0
Via: ...
Max-Forwards: ...
To: <urn:service:sos>
From: "Bob Smith" <sip:+18135551212@red.example.net;user=phone>
Call-ID: ...
Geolocation: <geo:40.6777,-111.915;u=0>
Geolocation-Routing: yes
Accept: application/sdp, application/pidf+xml
CSeq: ...
Contact: ...
Content-Type: application/sdp
Content-Length: ...

...Session Description Protocol (SDP) goes here


      

<vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
<vcard>
  <fn><text>Billy Boberson</text></fn>
  <n>
    <surname>Boberson</surname>
    <given>Billy</given>
    <additional/>
    <prefix/>
    <suffix>ing. jr</suffix>
    <suffix>M.Sc.</suffix>
  </n>
  <lang>
    <parameters><pref><integer>1</integer></pref></parameters>
    <language-tag>en</language-tag>
  </lang>
  <tel>
    <parameters>
      <type>
        <text>work</text>
        <text>voice</text>
      </type>
    </parameters>
    <uri>tel:+1-206-656-9254;ext=102</uri>
  </tel>
  <tel>
    <parameters>
      <type>
        <text>work</text>
        <text>voice</text>
        <text>cell</text>
        <text>video</text>
      </type>
    </parameters>
    <uri>tel:+1-253-262-6501</uri>
  </tel>
</vcard>
</vcards>