Network Working Group H. Lu, Editor
Request for Comments: 2995 I. Faynberg
Category: Informational J. Voelker
M. Weissman
W. Zhang
LUCent Technologies
S. Rhim
J. Hwang
Korea Telecom
S. Ago
S. Moeenuddin
S. Hadvani
NEC
S. Nyckelgard
Telia
J. Yoakum
L. Robart
Nortel Networks
November 2000
Pre-SPIRITS Implementations of PSTN-initiated Services
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document contains information relevant to the work underway in
The Services in the PSTN/IN Requesting InTernet Services (SPIRITS)
Working Group. It describes four existing implementations of
SPIRITS-like services from Korea Telecom, Lucent Technologies, NEC,
and Telia in cooperation with Nortel Networks. SPIRITS-like services
are those originating in the Public Switched Telephone Network (PSTN)
and necessitating the interactions of the Internet and PSTN.
Surveying the implementations, we can make the following
observations:
o The ICW service plays the role of a benchmark service. All
four implementations can support ICW, with three specifically
designed for it.
o Session Initiation Protocol (SIP) is used in most of the
implementations as the base communications protocol between the
PSTN and Internet. (NEC's implementation is the only exception
that uses a proprietary protocol. Nevertheless, NEC has a plan
to support SIP together with the extensions for SPIRITS
services.)
o All implementations use IN-based solutions for the PSTN part.
It is clear that not all pre-SPIRITS implementations inter-operate
with each other. It is also clear that not all SIP-based
implementations inter-operate with each other given that they do not
support the same version of SIP. It is a task of the SPIRITS Working
Group to define the inter-networking interfaces that will support
interoperation of the future implementations of SPIRITS services.
Table of Contents
1. Introduction ................................................ 3
2. Service Description of Internet Call Waiting ................ 4
3. Korea Telecom's ICW Implementation .......................... 5
3.1. Overview .................................................. 5
3.2. Network Architecture ...................................... 6
3.3. Network Entities .......................................... 7
3.3.1. SSP ..................................................... 7
3.3.2. SCP ..................................................... 7
3.3.3. IP ...................................................... 7
3.3.4. ICW Server System ....................................... 7
3.3.5. ICW Client System ....................................... 8
3.3.6. Firewall ................................................ 9
3.4. Network Interfaces ........................................ 9
3.5. Protocols ................................................. 9
3.5.1. Intelligent Network Application Part Protocol (INAP) .... 9
3.5.2. PINT Protocol ........................................... 9
3.6. Example Scenarios ........................................ 11
3.6.1. ICW Service Subscription ................................ 11
3.6.2. ICW Client Installation ................................. 11
3.6.3. ICW Service Activation .................................. 12
3.6.4. Incoming Call Notification .............................. 14
3.6.5. Incoming Call Processing ................................ 15
3.6.5.1. Accept the Call ....................................... 16
3.6.5.2. Forward the Call to Another Number .................... 18
3.6.6. ICW service De-activation ............................... 20
4. The Lucent Technologies Online Communications Center ........ 21
4.1 Overview ................................................... 21
4.2. Architecture .............................................. 22
4.3. Protocol and Operations Considerations .................... 25
5. NEC's Implementation ........................................ 28
5.1. Overview .................................................. 28
5.2. Architecture and Overall Call Flow ........................ 29
5.3. Interfaces and Protocols .................................. 31
5.3.1. SCP (SPIRITS Client)-SPIRITS Server Interface ........... 31
5.3.1.1. Connecting to SPIRITS Services ........................ 31
5.3.1.2. Message Types ......................................... 31
5.3.1.2.1 Connection Management Message Type ................... 31
5.3.1.2.2. Data Message Type ................................... 33
5.3.2. SPIRITS Server-ICW Client Application Interface ......... 34
5.3.3. Secure Reliable Hybrid Datagram Session Protocol
(SRHDSP) for Use .............................................. 35
5.3.3.1. Overview .............................................. 35
5.3.3.2. Session Initiation .................................... 35
5.3.3.3. Secure Reliable Datagram Transport .................... 36
5.3.3.4. Session closure ....................................... 36
6. Telia/Nortel's Implementation ............................... 36
6.1. Overview .................................................. 36
6.2. Architecture and Protocols ................................ 37
6.3. Security .................................................. 39
7. Security Considerations ..................................... 40
8. Conclusion .................................................. 40
9. References .................................................. 41
10. Authors' Addresses ......................................... 41
11. Full Copyright Statement ................................... 44
1. Introduction
This document contains information relevant to the work underway in
The Services in the PSTN/IN Requesting InTernet Services (SPIRITS)
Working Group. It describes four existing implementations of
SPIRITS-like services from Korea Telecom, Lucent Technologies, NEC,
and Telia in cooperation with Nortel Networks. SPIRITS-like services
are those originating in the Public Switched Telephone Network (PSTN)
and necessitating the interactions of the Internet and PSTN.
Invariably supported by the implementations examined in this document
is the Internet Call Waiting (ICW) service. With ICW, service
subscribers, while using their telephone lines for Internet Access,
can be notified of incoming voice calls and specify how to handle the
calls over the same telephone lines.
The document first gives a detailed description of the ICW service.
Then it proceeds to discuss each of the four implementations. The
final sections of the document contains security considerations, the
conclusion and references.
It is important to note that even though the term "SPIRITS server" is
used throughout the document, it has no universal meaning. Its
connotation depends on the context and varies from implementation to
implementation.
2. Service Description of Internet Call Waiting
Internet call waiting is the single service that is specifically
supported by all the implementations in question. In a nutshell, the
service enables a subscriber engaged in an Internet dial-up session
to
o be notified of an incoming call to the very same telephone line
that is being used for the Internet connection;
o specify the desirable treatment of the call; and
o have the call handled as specified.
The details of the ICW service lie in the ways that a waiting call
can be treated, which vary from implementation to implementation. In
this section, we describe the features that are supported by at least
one of the implementations. They are as follows:
o Incoming Call Notification - The subscriber is notified of an
incoming call over the Internet, without having any effect on the
telephone line that is being used by the modem. When a call comes
in, the subscriber is presented with a pop-up dialog box on the
PC. The dialog box may display any combination of the calling
party number, calling party name, and calling time. Note that the
display of the calling party name (or number) requires the
availability of the caller name (or number) delivery feature.
o Online Incoming Call Disposition - Once informed of the incoming
call, the subscriber has various options (indicated in the pop-up
window) for handling the call. Possible options are:
+ Accepting the call over the PSTN line, thus terminating the
Internet (modem) connection
+ Accepting the call over the Internet using Voice over IP (VoIP)
+ Rejecting the call
+ Playing a pre-recorded message to the calling party and
disconnecting the call
+ Forwarding the call to voice mail
+ Forwarding the call to another number
+ Rejecting (or Forwarding) on no Response - If the subscriber fails
to respond within a certain period time after the dialog box has
been displayed, the incoming call can be either rejected or
handled based on the treatment pre-defined by the subscriber.
o Automatic Incoming Call Disposition - Incoming calls are
automatically handled based on dispositions pre-defined by the
subscriber without his or her real-time intervention. The
subscriber can pre-define the default disposition (e.g., re-
directed to voice mail) for general calls as well as customized
dispositions for calls from specific numbers. In the latter case,
the subscriber selects a particular disposition for each
originating number and stores this information in a profile. When
a call comes in, the subscriber won't be presented the call but
can examine the treatment and outcome of the call from the caller
log (as described in the call logging bullet). Naturally, this
feature also allows the subscriber to specify the desired
treatment for calls originating from private or unpublished
numbers.
o Multiple Call Handling - Multiple calls can arrive during call
disposition processing. With multiple call handling, the
subscriber is notified of the multiple calls one by one.
o Call Logging - A detailed log of the incoming calls processed
during the ICW service is kept. Typical information recorded in
the log include the incoming call date and time, calling party
number, calling party name, and call disposition.
3. Korea Telecom's ICW Implementation
3.1. Overview
Korea Telecom's ICW implementation supports most of the features
described in Section 2. (The major exception is the feature of
receiving the incoming call over the Internet using voice over IP.)
In addition, the Korea Telecom implementation supports flexible
activation and de-activation of the ICW service:
o Automatic Activation/De-activation - When Internet dial-up
connection is set up, the ICW service is activated or de-activated
automatically.
o Manual Activation/De-activation - The subscriber can de-activate
the ICW service manually when call notification is not desired
during the Internet dial-up session and activate it when needed.
3.2. Network Architecture
Figure 1 depicts the network architecture of the Korea Telecom ICW
service. The Service Switching Point (SSP), Service Control Point
(SCP), and Intelligent Peripheral (IP) are legacy PSTN IN elements
based on IN CS-1. In contrast, both the ICW Server System and the
ICW Client System are new network elements that are installed in the
Internet domain to support of the ICW service.
+---------------------------+ +--------------+
+--------+propr-+---------+ PINT (Proxy Server) PINT
(ICW SL)ietary(UAC/UAS)--- ------ ICW ----+
SCF/SDF ------ SCGF firewall Server System
+--------+ i/f +---------+ +------------- +
SCP
+------+--------------+-----+
INAP INAP firewall=====
+---+---+ +---+---+
IP SSP
+-------+ +---+---+ +-------------+
+---+ (UAC/UAS)
+---+---+ ICW
--------- LEX -------------- + + Client System
+---+ +-------+ +++++----+-------------+
(callee)
+ + ICW Subscriber's Phone and PC
+++++
(caller)
INAP : Intelligent Network Application Protocol
PINT : PSTN/Internet Interworking Protocol
SL : Service Logic
UAS : User Agent Server
UAC : User Agent Client
Figure 1: Network Architecture of the Korea Telecom ICW Service
3.3. Network Entities
3.3.1. SSP
The SSP performs the Service Switching Function (SSF) and Call
Control Function (CCF). When detecting that the called party is busy
(T_Busy), the SSP sends a query to the SCP and processes the call
under the control of the SCP.
3.3.2. SCP
The SCP performs the Service Control Function (SCF) and Service Data
Function (SDF). It, when queried, instructs the SSP to process the
call based on the service logic. In the case of the ICW service, the
service logic ultimately governs the notification of a waiting call
to an online ICW subscriber and the disposition of the call. In
addition, the SCP performs the Service Control Gateway Function
(SCGF) for protocol inter-working between the PSTN/IN and Internet.
It translates the SIP message from the ICW Server to the service
control interface message and vise versa. The SCGF is an IP end
point and behaves as a UAS (User Agent server) or UAC (User Agent
client).
3.3.3. IP
The IP contains Service Resource Function (SRF). It, when necessary,
plays announcements to the calling party during the ICW service
before/after receiving the response from the ICW subscriber and
records the calling party number or voice message from the calling
party when the call is forwarded to the Voice Mail System (VMS).
3.3.4. ICW Server System
The ICW Server system serves as a SIP proxy or a redirect server for
message routing between the ICW Client and SCGF. The ICW Server is
also responsible for managing the ICW Clients that are connected to
it. When an ICW Client (subscriber) sends a registration request for
the ICW service, the ICW Server relays that request to the SCP, waits
for the result of authorization from the SCP, and registers the
authorized subscriber in its data base. In addition, the ICW Server
monitors the connection status of the registered ICW Clients. As
soon as a client deactivates the ICW service or terminates the
Internet connection, the ICW Server detects the status change and
deactivates the ICW service for the client. Finally, the ICW Server
manages profiles for each ICW subscribers as well as logs all the
call processing results.
3.3.5. ICW Client System
The ICW Client System is an application program running on the
subscriber's PC. Launched as soon as the subscriber powers on the
PC, it monitors the Internet connection status of the PC (or
subscriber). Upon the subscriber's connection to the Internet, the
ICW Client sends a REGISTRATION request to the SCGF via the ICW
Server and then eventually to the SCP. In this capacity, the ICW
Client acts as a UAC to the SCGF, which acts as a UAS. Thereafter it
notifies the ICW Server periodically of the connection status of the
subscriber.
The ICW Client is also responsible for popping up a dialog box on the
subscriber's PC to announce an incoming call. The dialog box
displays the number and name of calling party, calling time, and the
call processing options (including Accept, Reject, Forward to another
number or VMS). After the subscriber selects the option, the ICW
Client sends it to the SCP. In this capacity, the ICW Client acts as
a UAS.
Depending on the pre-defined ICW Service Profile, the ICW Client may
screen the incoming call before notifying the subscriber.
The ICW Client manages the ICW Service Profile, which contains the
following fields:
o Subscriber Information (including, Name, Directory Number,
PassWord)
o Service Status (Activation/De-activation)
o Automatic Call Processing Method
+ Call Processing Method on No Answer (Reject/Forward/VMS) - The
call is automatically handled by the method if the subscriber
doesn't respond after a pre-defined period of time.
+ Do Not Disturb Mode (On/Off) - When this is set on, the subscriber
won't be notified of the incoming calls.
+ Call Processing Method on Do Not Disturb (Reject/Forward/VMS)
+ Call Processing List by Calling Party Numbers
(Accept/Reject/Forward/VMS) - Calls originated from a number on
the list are handled by the associated call processing method.
o The ICW Client records the call processing method and the result
for each incoming call in a log file on the subscriber's PC. The
call record in the call log contains the following information:
- Calling Time
- Calling Party Number
- Calling Party Name (optional)
- Call Processing Method (Accept/Reject/Forward/Forward to VMS)
- Result (Success/Fail)
3.3.6. Firewall
Packet Filtering Firewall Systems are between the ICW server and
clients as well as between the SCGF and ICW server for accessing the
Korea Telecom IN Nodes.
3.4. Network Interfaces
o The SCF-SDF, SCF-SSF, and SCF-SRF interfaces are the same as
existing PSTN IN Interfaces based on the KT INAP CS-1.
o The SCGF-SCF interface relays requests either from the IN or the
Internet and is implemented based on the internal API of the SCP.
o The SCGF-ICW Server and ICW Server-ICW Client interfaces are
implemented based on the PINT Service Protocol V.1. We adopted
UAS-Proxy-UAC relationships as shown in Figure 2.
+---------+ +-------------+ +---------+
(UAC/UAS)PINT 1.0 (Proxy) PINT 1.0(UAC/UAS)
-------- ICW -------- ICW
SCGF Server Client
+---------+ +-------------+ +---------+
Figure 2: PINT Protocol Architecture
3.5. Protocols
3.5.1. Intelligent Network Application Part Protocol (INAP)
The SCP, SSP, and IP support the KT INAP V1.0, which is based on
ITU-T INAP CS-1 with the incorporation of two INAP CS-2 messages [PRM
(PromptAndReceiveMessage) and EM (EraseMessage)] for recording the
voice message.
3.5.2. PINT Protocol
The ICW service uses the PINT Service Protocol 1.0 [1] for
communications between the SCP and the ICW Server System, and between
the ICW Server System and the ICW Client System. Developed in the
IETF PINT Working Group for invoking telephone services from an IP
network, the PINT Service Protocol 1.0 specifies a set of
enhancements to SIP 2.0 and SDP.
Summarized below are the elements of the PINT Service Protocol 1.0
relevant to the Korea Telecom ICW implementation:
o REGISTER
The REGISTER method is used to inform the SCP of the connection
status of an ICW subscriber. With this method, the ICW Client
sends to the ICW Server the IP address (of the PC) and phone
number of the subscriber when the subscriber is first connected to
the Internet. The ICW server relays the information to the SCP,
which updates the data base (if the subscriber is authorized), and
in the end sends a registration acknowledgment to the ICW Server
and then the Client. After the subscriber is connected to the
Internet, the ICW Client sends a REGISTER request to the ICW
Server periodically at a pre-defined interval (e.g., 20 seconds)
to indicate its connection status. The request is not relayed to
the SCP. The ICW Server only checks if it is from the authorized
subscriber. Finally, when the subscriber terminates the Internet
connection, the Client sends the last REGISTER request to the SCP
via the ICW Server. If the REGISTER request does not arrive
during the pre-defined interval, the ICW Server can also detect
the change of the connection status of the ICW Client.
o INVITE
The SCP uses the INVITE method to notify the ICW Client, via the
ICW Server, of an incoming call.
o ACK
Both the SCP and the ICW Server use the ACK method to confirm the
receipt of the final responses to their requests.
o BYE
The BYE method terminates a service session. In addition to this
original usage, we use the value (success or failure) of the
Subject header to indicate the result of the desired disposition
of an incoming call in the PSTN.
o CANCEL
When the calling party releases the call before the called party
responds, the SCP sends a CANCEL request to the ICW Client to
cancel the INVITE request that it sent previously.
o OPTION
This method is not used in the KT implementation.
o Responses
The SCP responds to a REGISTER request with one of the status
codes and associated comments below:
. 100 Trying: Trying
. 200 OK: Registered
The ICW Client responds to an INVITE request with one of the
status codes and associated comments below:
. 100 Trying: Trying
. 200 OK: Accept the Call
. 303 see other: Forward the Call to Another Number
. 380 alternative service: Forward the Call to the VMS
. 603 decline: Reject the Call
3.6. Example Scenarios
3.6.1. ICW Service Subscription
Access to the Korea Telecom ICW service is by subscription. Here
Korea Telecom serves as both the PSTN operator and IN-based ICW
service provider. Note that the subscription data need to be loaded
onto the relevant SSPs, including the local ones that may not be
operated by Korea Telecom.
3.6.2. ICW Client Installation
An ICW subscriber should install the ICW Client program in his or her
PC. The ICW Client is automatically activated to run as a daemon
process when the subscriber's PC is turned on. The Client monitors
the Internet connection status of the subscriber.
3.6.3. ICW Service Activation
When the subscriber initiates the Internet connection or activates
the ICW service manually, the ICW service is activated. That is done
by sending a REGISTER request with the directory number and IP
address from the ICW Client to the SCP through the ICW Server.
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
0A
0BREG(DN1,IP1)
1 ----------->REG(DN1,IP1)
2 ----------->
2A
reg(DN1,IP1)
3 -.-.-.-.-.->
3A
reg ok 3B
4 <-.-.-.-.-.-
200 OK 4A
5 <-----------
200 OK 5A
6 <-----------
6A
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 3: ICW Service Activation
As depicted in Figure 3, the relevant information flows are as
follows:
(0A) The ICW subscriber dials the ISP access number and establishes a
PPP connection.
(0B) The ICW Client detects the PPP connection.
1. The ICW Client sends a registration request to the ICW Server in
order to register the IP address-DN relationship for the dial-up
connection.
2. The ICW Server relays registration request to the SCGF.
2A. The SCGF translates the user registration information from the
SIP message to the SCP internal API message.
3. The SCGF relays the user registration message to the SCF/SDF.
3A. The SCF/SDF authorizes the subscriber with the directory number
based on the user registration information.
3B. The SCF/SDF stores the IP address of the ICW Client and sets the
status to "Internet on-line."
4. The SCF/SDF sends the result of registration to the SCF/SCGF.
4A. The SCGF translates the user registration response of the SCP
internal API message to the PINT message.
5. The SCGF relays the user registration response to the ICW Server.
5A. The ICW Server records the user registration information and the
Internet on-line status for the subscriber in the data base.
6. The ICW Server sends the user registration response to the ICW
Client.
6A. The ICW Client notifies the subscriber that the registration is
completed successfully and the ICW service is in the active state.
3.5.4. Incoming Call Notification
When a calling party makes a call to the ICW subscriber, the SCP
notifies the ICW Client of the incoming call and waits for the
subscriber's response.
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
setup(DN1,DN2)
1 <+++++++++++
1A
IDP(T-busy,DN1)
2 <--.--.--.--
2A
2B
2C
noti(DN1,IP1,DN2)
3 <-.-.-.-.-.-
3A
INV(DN1,IP1,DN2)
4 <-----------
4A
100 Trying
5 ----------->
INV(DN1,IP1,DN2)
6 <-----------
6A
100 Trying
7 ----------->
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 4: Incoming Call Notification
As depicted in Figure 4, the relevant information flows are as
follows:
1. The calling party at DN2 (a telephone user) makes a call to the
ICW subscriber (PC user) at DN1. The connection is set up using the
existing ISDN signaling.
1A. The SSF/CCF detects that the callee (the ICW subscriber) is busy.
2. The SSF/CCF sends InitialDP (T_Busy) to the SCF/SDF.
2A. The SCF/SDF determines whether the user at DN1 is PSTN on-line or
Internet on-line. (The SCF/SDF executes the KT Telephone Mail
Service logic in the PSTN on-line case and the ICW service Logic in
the Internet on-line case.)
2B. The SCF/SDF retrieves the IP address corresponding to DN1.
2C. The SCF/SDF may play an announcement to the calling party, while
waiting for the response of the called party.
3. The SCF sends an incoming call notification to the SCGF.
3A. The SCGF translates the incoming call notification from the SCP
internal format to the PINT format.
4. The SCGF relays the notification to the ICW Server.
4A. The ICW Server double-checks the subscriber's status using the
ICW subscribers profile in its own data base.
5. The ICW Server sends trying message to the SCGF.
6. The ICW Server relays the notification to the ICW Client.
6A. The ICW Client consults the ICW service profile to see if there
is a pre-defined call disposition for the incoming call. If so, then
the procedure for automatic call processing is performed.
6B. If there is no pre-defined call disposition for the incoming
call, the subscriber is notified of the call via a pop-up dialog box.
7. The ICW Client sends trying message to the ICW Server.
3.6.5. Incoming Call Processing
The incoming call can be accepted, rejected, forwarded to another
number, or forwarded to the VMS depending on the on-the-fly or pre-
defined choice of the subscriber. This section describes the
information flows for the cases of "Accept the call" and "Forward the
call to another number."
3.5.5.1. Accept the Call
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
0A 200 OK
1 ----------->
1A
1B 200 OK
2 ----------->
ACK 2A
3 <-----------
Accept(DN1,IP1,DN2)
4 -.-.-.-.-.->
Connect(DN1,DN2)
5 --.--.--.-->
Setup(DN1,DN2)
6 <++++++++++++++++++++++++++++++++++++++++++++++++++
<==============================6A==============================>
ERB
7 <--.--.--.--
ok
8 <-.-.-.-.-.-
8A
BYE
9 <-----------
9A
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 5: Incoming Call Processing - Accept the Call
As depicted in Figure 5, the relevant information flows are as
follows:
0A. The ICW subscriber chooses to "Accept" the incoming call.
1. The ICW Client sends the "Accept" indication to the ICW Server.
1A. The ICW Client records the subscriber's selection for the
incoming call in the call log.
1B. The ICW Client terminates the subscriber's Internet connection.
2. The ICW Server sends an "Accept" message to the SCGF.
2A. The SCGF translates the "Accept" message to an SCP internal API
message.
3. The SCGF sends an "ACK" message to the ICW Server.
4. The SCGF sends the "Accept" message to the SCF.
5. The SCF instructs the SSF/CCF to route the call to DN1.
6. The SSF/CCF initiates the connection setup to DN1.
6A. The bearer connection between the calling party (DN2) and the ICW
subscriber(DN1) is set up.
7. The connection result is returned to the SCF through ERB.
8. The SCF sends a call completion message to the SCGF.
8A. The SCGF translates the call completion message to a PINT
message.
9. The SCGF sends a "BYE" message to the ICW Server.
9A. The ICW Server records the call completion result in the log
file.
3.5.5.2. Forward the Call to Another Number
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling Another
ICW Client party Phone
(DN1/IP1) (IP2) (IP3) (DN2) (DN3)
0A
303 SeeOther
1 --------->
1A ACK
2 <---------303 SeeOther
3 --------->
ACK 3A
4 <---------Connect(DN2,DN3)
5 -.-.-.-.->
Connect(DN2,DN3)
6 .--.--.-->
Setup(DN2,DN3)
7 ++++++++++++++++++++>
8 ERB <===5A==>
<--.--.--.
ok
9 <-.-.-.-.-
BYE 9A
10 <---------
BYE 10A
11 <---------
11A
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 6: Incoming Call Processing - Forward the Call to Another
As depicted in Figure 6, the relevant information flows are as
follows:
0A. The ICW subscriber chooses to "Forward to another number (DN3)"
for the incoming call.
1. The ICW Client sends the "Forward to another number" indication to
the ICW Server.
1A. The ICW Client records the subscriber's selection for the
incoming call in the call log.
2. The ICW Server sends an "ACK" message to the ICW Client.
3. The ICW Server relays the "Forward to another number" message to
the SCGF.
3A. The SCGF translates the "Forward to another number" message to an
SCP internal API message.
4. The SCGF sends an "ACK" message to the ICW Server.
5. The SCGF sends the "Forward to another number" message to the SCF.
6. The SCF instructs the SSF/CCF to route the call to DN3.
7. The SSF/CCF initiates the connection setup to DN3.
7A. The bearer connection between the calling party (DN2) and the new
termination number (DN3) is set up.
8. The connection result is returned to the SCF through ERB.
9. The SCF sends a call completion message to the SCGF.
9A. The SCGF translates the call completion message to a PINT
message.
10. The SCGF sends the call completion message to the ICW Server.
10A. The ICW Server records the call completion result in the log
file.
11. The ICW Server sends the success of "Forwarding to another
number" to the ICW Client.
11A. The ICW Client records the call completion result in the log
file.
3.6.6. ICW service De-activation
The SCP de-activates the ICW service for a subscriber either upon the
termination of the subscriber's Internet connection or upon the
subscriber's manual request. In this section, we illustrate the
former scenario.
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
0A
0B
Unreg(DN1,IP1)
1 ----------->
1A
Unreg(DN1,IP1)
2 -.-.-.-.-.->
2A
ok 2B
3 <-.-.-.-.-.-
3A
200 OK
4 <-----------
4A
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 7: ICW Service De-activation
As depicted in Figure 7, the relevant information flows are as
follows:
0A. The ICW subscriber terminates the Internet connection.
0B. The ICW Server determines that the Internet connection has been
terminated when it does not receive the periodic on-line notification
from the ICW Client.
1. The ICW Server sends an un-register message to the SCGF.
1A. The SCGF translates the un-register message to an SCP internal
API message.
2. The SCGF sends the un-register message to the SCF.
2A. The SCF/SDF authorizes the subscriber with the directory number
based on the un-registration information.
2B. The SCF/SDF records the Internet off-line status for that ICW
Client.
3. The SCF/SDF sends a user un-registration response to the SCF/SCGF.
3B. The SCGF translates the user un-registration response to a PINT
message.
4. The SCGF relays the user un-registration response to the ICW
Server.
4A. The ICW Server records the Internet off-line status for the ICW
Client (subscriber) in the data base.
4. The Lucent Technologies Online Communications Center
4.1 Overview
The Lucent Technologies Online Communications Center (OCC) is an
Intelligent Network (IN)-based platform that supports the Internet
call waiting service. Its basic components are the OCC Server and
OCC Client, which are described in detail in the Architecture
section. The OCC Server interacts with the PSTN entities over the
secure intranet via plain-text Session Initiation Protocol (SIP)
messages [2]. With the PC Client, the OCC Server interacts via
encrypted SIP messages.
The OCC Server run-time environment effectively consists of two
multi-threaded processes responsible for Call Registration and Call
Notification services, respectively.
OCC call registration services are initiated from an end-user's PC
(or Internet appliance). With those, a subscriber registers his or
her end-points and activates the notification services. (The
registration services are not, strictly speaking, SPIRITS services
but rather have a flavor of PINT services.)
All OCC call notification services are PSTN-initiated. One common
feature of these services is that of informing the user of the
incoming telephone call via the Internet, without having any effect
on the line already used by the modem. (A typical call waiting tone
would interrupt the Internet connection, and it is a standard
practice to disable the "old" PSTN call waiting service for the
duration of the call in support of the Internet connection between
the end-user and the ISP.)
When a call comes in, the user is presented with a pop-up dialog box,
which displays the caller's number (if available), name (again, if
available), as well as the time of the call. If the called party
does not initiate an action within a specified period of time the
call is rejected.
As far as the disposition of the call is concerned, OCC supports all
the features described in Section 2.
4.2. Architecture
+------------+
Compact +-------------+
Service Service
+----- Node (CSN) Management
OCC Server System (SMS)
OCC CSN SPA +-------------+
+-------:---+
+-------------[ IP INTRANET ]---------+
===== firewall :
+-------+ +-------+
Central-..-..-..-..-..-..-..-..-..-..-Service
+-%-Office -..-..-: Control
+------+ Point
% : (SCP)
+-----+ +-------+ +----------+ OCC SCP
% PC VoIP VoIP SPA
OCC Cl Gateway Gatekeeper +-------+
% +------+ +------+ +---------+
===== firewall =====
%
+------------------+
+-%- ----------+
+---------- I N T E R N E T
+-------------------+
Figure 8: The Lucent OCC Physical Architecture
Figure 8 depicts the joint PSTN/Internet physical architecture
relevant to the OCC operation. The Compact Service Node (CSN) and
SCP are Lucent's implementations of the ITU-T IN Recommendations (in
particular, the Recommendation Q.1205 where these entities are
defined) augmented by the requirements of Bellcore's Advanced
Intelligent Network (AIN) Release 1.0) and equipped with other
features. The Central Office (CO) may be any switch supporting the
Integrated Services Digital Network (ISDN) Primary Rate Interface
(PRI) and the call forwarding feature that would allow it to
interwork with the CSN. Alternatively, in order to interwork with
the SCP, it needs to be an IN Service Switching Point (SSP). In the
latter case, the central office is connected to the SCP via the
signaling system No. 7 (SS7) and INAP at the application layer.
The Service Management System (SMS) is responsible for provisioning
of the SCPs, CSNs, and central offices. In particular, for IN
support of the Internet Call Waiting, it must provision the Central
Office to direct a terminating attempt query to the subsystem number
corresponding to the OCC SCP SPA based on the Termination Attempt
Trigger (TAT). In addition, the Subscriber Directory Number (DN),
Personal Identification Number (PIN) and Language ID are provisioned
for each subscriber into the OCC Subscriber entry of the SCP Real
Time Data Base (RTDB). Figure 9 shows the structure of an RTDB
entry.
+-------------------------------------------------------+
DN PIN IP Address Session Key CNF Language ID
+-------------------------------------------------------+
Field Descriptions:
(DN) Directory Number - the subscriber's telephone number
(PIN) Personal Identification Number - the subscriber's password
IP Address - Internet Protocol Address of the subscriber
(CNF) Call Notification In Progress Flag (boolean) - the flag
indicating if an attempt to notify the subscriber of a call is
currently in progress
Session Key - unique identifier for the current registration session
of the subscriber
Language ID - language identifier for the subscriber
Figure 9: Structure of the RTDB Subscriber Record
The Central Office, SMS, CSN, and SCP are the only PSTN elements of
the architecture. The other elements are VoIP Gateway and Gatekeeper
defined in the ITU-T Recommendation H.323, whose roles are to
establish and provide the part of the voice path over IP. The
Central Office is eXPlicitly connected to the VoIP Gateway via the
ISDN PRI connection. In this architecture, CSN, VoIP Gateway, and
VoIP Gatekeeper are the only entities connected to the Internet, with
each respective connection protected by a firewall. The CSN and SCP
are interconnected via a secure IP Intranet. There may be more than
one CSN or SCP (or both) (and the SCPs come in mated pairs
interconnected by X.25, anyway) in a network, but these details are
not essential to the level of description chosen for this document.
However, we note that load balancing and adaptation to failures by
the use of alternative nodes is incorporated into the architecture.
When someone attempts to call the subscriber, the central office
serving that subscriber interrupts normal termination processing and
notifies the SCP which, in turn, can check whether that subscriber
has registered that he (or she) is logged onto the Internet.
Exploiting the standardized layering of service logic that
characterizes the intelligent network, the central office will do
this without requiring the installation or development of any central
office software specific to OCC. The central office is simply
provisioned to query the SCP when there is a termination attempt
(i.e., TAT) directed to the subscriber's directory number. (Note
that the Central Office has no bearer circuit connection to the SCP,
only a signaling one over SS7).
TCP/IP communication between the SCP and CSN utilizes a secure
intranet. The subscriber, of course, is assumed to have access only
to the Internet.
The intelligent network entities, the SCP and CSN, do have OCC
related software. The OCC server is implemented on the CSN. In
addition, one service package application (SPA) is installed on the
SCP. Another SPA is located in the CSN and is needed only when the
subscriber elects to accept an incoming call using voice over IP.
The OCC Server is a collection of Java servers on the CSN whose
responsibilities include:
o Listening for incoming Call Notification (TCP/IP) messages from
the SCP SPA.
o De-multiplexing/multiplexing incoming Call Notification messages
sent from the SCP SPA.
o Relaying messages between the OCC Client and the SCP SPA.
o Listening for and authentication of OCC Client requests for
service registration.
o Handling encryption/decryption of messages exchanged with the OCC
Client, and generating session-specific encryption/decryption
keys.
The OCC Client is a collection of software components that run on the
Subscriber's PC. Its components include the SIP User Agent Server
(which handles the exchange of SIP messages with the OCC Server and
invokes the Call Notification pop-up window) and a daemon process
that monitors the Point-to-Point Protocol (PPP) actions and is
responsible for starting and stopping the SIP User Agent Server.
4.3. Protocol and Operations Considerations
The OCC Server uses distinct TCP/IP ports configured on the CSN to
o Listen for incoming SIP REGISTER messages (in support of
registration service) sent from the OCC Client.
o Listen for incoming SIP INVITE messages (in support of call
notification service) sent from the SCP.
During call notification, the SCP SPA is the client and thus is
started after the OCC Server has been started. The SCP SPA and OCC
Server exchange SIP messages over TCP/IP (via the Secure Intranet)
using a "nailed-up" connection which is initiated by the SCP SPA.
This connection is initiated at the time the SCP SPA receives the
very first SIP REGISTER request from the OCC Server, and must prevail
for as long as the SPA is in the in-service state. The SCP SPA also
supports restarting the connection after any failure condition.
The OCC Server supports multithreading. For each Call
Notification/Call Disposition event, a separate thread is used to
handle the call. This model supports multi-threading on a "per
message" basis where every start message (SIP INVITE) received from
the SCP SPA uses a separate thread of control to handle the call.
Subsequent messages containing the same session Call-ID (which
includes the SPA's instance known as "call_index" and the SCP
hostname) as the original start message is routed to the same thread
that previously handled the respective initiating message.
The OCC Server dynamically opens a new TCP/IP socket with the OCC
Client for each Call Notification/Call Disposition session. This
socket connection uses the IP address and a pre-configured port on
the PC running the OCC Client software.
For session registration, the OCC Server dynamically opens TCP/IP
sessions with the SCP SPA. The SCP SPA listens at a pre-configured
port to incoming SIP REGISTER messages sent by OCC Clients via the
OCC Server. To exchange SIP messages with the OCC Server, the OCC
Client dynamically opens a TCP/IP socket connection with the OCC
Server using a pre-configured port number on the CSN and the CSN's IP
address.
For the VoIP Scenario, the CSN SPA, acting as a client, dynamically
opens TCP/IP sessions with the SCP that handled the initial TAT
query. As soon as the CSN SPA has successfully made the correlation
and connected the two incoming call legs pertaining to a VoIP call
back, the SIP 180 RINGING message will be sent back to the SCP SPA
running on the actual SCP that instructed the SSP to forward the
Caller to the CSN. This SIP message, which contains the VoIP Call
Back DN dialed by one of the bridged call legs, is an indication to
the SCP SPA that the VoIP Call Back DN is freed up.
A typical subscription scenario works like as follows:
1. Each VoIP Gateway is provisioned with a list of authorized VoIP
Call Back DNs, each terminating on a particular CSN. These
special DNs are used when an on-line subscriber elects to receive
an incoming call via VoIP. In particular, they assist in routing
an outgoing call from the subscriber's NetMeeting to the
particular CSN to which the SCP is (roughly concurrently)
forwarding the incoming call. (These two calls are joined in the
CSN to connect the incoming call to the subscriber's Netmeeting
client.) Furthermore, these special DNs permits that CSN to
associate, and hence bridge, the correct pair of call legs to join
the party calling the subscriber to the call from the subscriber's
NetMeeting client.
2. The subscriber calls a PSTN service provider and signs up for the
service.
3. An active Terminating Attempt Trigger (TAT) is assigned to the
subscriber's DN at the subscriber's central office.
4. The PSTN service provider uses the SMS to create a record for the
subscriber and provision the Subscriber DN and PIN in the OCC RTDB
table in the SCP.
5. The subscriber is provided with the OCC Client software, a PIN and
a file containing the OCC Server IP Addresses.
Finally, we describe the particular scenario of the OCC Call
Disposition that involves voice over IP, which proceeds as follows:
1. The OCC subscriber clicks on "Accept VoIP".
2. The OCC Client sends a "SIP 380 Alternative Service" message to
the OCC Server. This message includes a reference to the Call
Back DN which will ultimately be used by the CSN to associate the
call leg (soon to be initiated by the subscriber's NetMeeting)
connecting to the subscriber (via the VoIP gateway) with the PSTN
call leg connecting to the calling party.
3. The OCC Server closes the TCP/IP session with the OCC Client and
sends to the SCP SPA the "SIP 380 Alternative Service" message
which includes the Call Back DN.
4. The SCP SPA instructs the Central Office to forward the call
incoming to the subscriber to the CSN. This instruction includes
the Call Back DN.
5. The SSP forwards the Caller to the CSN referencing the Call Back
DN. Note that the Call Back DN, originally assigned to the OCC
client by the SCP when the subscriber was alerted to the presence
of an incoming call attempt, flowed next to the OCC server when
the client elected to receive the call via VoIP, then to the SCP,
then to the central office in association with a SCP command to
forward the incoming call to the CSN, then to the OCC server on
the CSN in association with that forwarded call.
6. Meanwhile, the OCC Client extracts 1) the VoIP Call Back DN from
the SIP INVITE message received during Call Notification and 2)
the H323UID and H323PIN values from its properties file and
updates the 'netmtg.cnf' file.
7. The NetMeeting application is launched and sets up a connection
with the VoIP Gateway.
8. Once a connection is established between NetMeeting and the VoIP
Gateway, NetMeeting initiates a phone call - passing to the VoIP
Gateway the Call Back DN as the destination DN.
9. The VoIP Gateway consults the VoIP Gatekeeper and authenticates
the NetMeeting call by verifying the H323UID and H323PIN values,
and by ensuring the called DN (i.e., Call Back DN) is authorized
for use.
10. After passing the authentication step, the VoIP Gateway dials
(via PSTN) the Call Back DN and gets connected to the CSN. The
CSN notes that it was reached by the particular Call Back DN.
11. The CSN bridges the Calling and Called parties together by
matching on the basis of the Call Back DN.
12. The CSN notifies the SCP (SIP 180 Ringing) of status and
references the Call Back DN so that the SCP can reuse it for
other calls.
13. If the central office supports that two B-channel transfer
(Lucent, Nortel, and perhaps other central office vender's do),
an optimization is possible. The CSN can have the central office
rearrange the topology of the newly connected call in such a way
that it flows only through the central office and no longer
through the CSN.
5. NEC's Implementation
5.1. Overview
The NEC implementation of the ICW service is based on IN. Via a
SPIRITS server and an ICW client, incoming calls will be presented to
the user via a pop-up screen dialogue box. This dialogue box informs
the user of the call arrival time and the calling party's number and
name (if available). The arrival of the call is also indicated with
an accompanied audible indication.
The pop-up dialogue box offers the user various call management
options. Selecting a call management option allows the user to
answer the call, forward it to another destination or to voice mail,
or ignore it.
The user will be able to customize their service through various
service set-up options. All calls presented to the user during an
Internet session will be recorded in a call log.
Other features include Multiple call arrival management with which
each new call arrival will generate its own pop-up dialogue box and
audible indication.
5.2. Architecture and Overall Call Flow
Figure 10 depicts the NEC ICW system.
====================================
I n t e r n e t
====================================
/ : (p1) : : (p2)
/ +-------+ +------------+ +-----+
SPIRITS ISP W3S
Server ISP W3S
+-------+ +------------+ +-----+
: :
Internet :
PSTN/IN (p0) :
: :
============:======
+------+ (p3) +-----+ :
SCP -..-..-..- SSP :
+------+ +-----+ :
(p4) :
+-------+ : :
ICW (p1)+-----+ :
Client ..... M/D ............+------+
+-------+ (p2)+-----+ CO
-------------------- -------
/ +------+ /--\ / P S T N \ /-- ()/\() / =================== \ ()/\()
_/__\___/ \______/__\_
ICW Subscriber Calling Party
Legend:
ISP : Internet Service Provider
W3S : WWW Server
SCP : Service Control Point(acts as SPIRITS Client)
SSP : Service Switching Point
CO : Central Office
M/D : Modem
Traffic:
--- : PSTN Voice Traffic
... : PPP(IP traffic)
-..-: Signaling Traffic
Interfaces:
p0 : SPIRITS Server-SCP(SPIRITS Client) interface
p1 : SPIRITS Server-ICW Client interface
p2 : ICW Client-W3S interface
(Web access through HTTP)
p3 : SCP-SSP interface(INAP)
p4 : SSP-CO interface(ISUP)
Figure 10: the NEC ICW system
The description below provides the necessary steps to initiate the
ICW service on a CO line, and how the ICW service is applied to an
incoming call based on the above architecture:
1. The CO line is primed for the ICW service when the customer
connects to their ISP by inserting a special activation code
(e.g., *54) prefix in front of the ISP Directory Number.
2. The ICW service is activated when the user opens a secured
session from an ICW client to the SPIRITS server. Once a session
is open, the SPIRITS server will know the relationship between the
line and the PC (i.e., it will know the Directory Number of the
user's Internet line and the user's IP Address).
3. When a call arrives at a busy Internet line, the SSP will trigger
the ICW service. The SCP which acts as the SPIRITS client will
inform the SPIRITS server that a call is terminating to a busy
Internet line. The message will include the Caller ID and Calling
Line Identify Restriction (CLIR) Status of the calling party, and
DN of the busy line.
4. The SPIRITS server will verify that if an ICW session has been
established for the busy line. If so, the SPIRITS server will
communicate with the user's ICW client application. The user will
receive a real-time pop-up dialogue box including the Calling Name
and Number of the Calling Party if available. The user will then
select one of the following call management options:
- Answer the call (the Internet connection will be automatically
dropped and the phone will ring)
- Send the call to Voice Mail
- Forward the call to another destination
- Ignore the call
5. When the Internet user has made a selection, the ICW client
application will transmit this to the SPIRITS server. The SPIRITS
server will instruct the PSTN via the SCP how to handle the call.
5.3. Interfaces and Protocols
5.3.1. SCP (SPIRITS Client)-SPIRITS Server Interface
5.3.1.1. Connecting to SPIRITS Services
The physical connection between the SCP and the SPIRITS server will
be via a LAN/WAN. The logical connection will use the UDP/IP
communications as defined in RFC768 and RFC1122.
If a socket connection is not currently established, the SCP will
periodically try to open a connection. The SCP routing tables will
be configured so that all available connections to a SPIRITS server
are used.
5.3.1.2. Message Types
Two different types of message are used between the SCP and the
SPIRITS server: "Connection Management Message Type" and the "Data
Message Type". These messages will carry the remote operation
messages which are based on ITU-T Q.1228 SCF-SCF interface with some
NEC proprietary extensions.
NEC also has a plan to support SIP/SDP-based protocols for the SPIR-
ITS client-server interface in the near future.
5.3.1.2.1 Connection Management Message Type
Connection management messages are to support functions related to
the opening and closing of connections and monitoring connections to
ensure reliable communications are maintained between the SCP and a
SPIRITS server. The SCP is responsible for establishing a connection
to a SPIRITS server. A connection can be closed by either the SCP or
the SPIRITS server.
The "Connection Management Message Type" includes the following
operations:
- scfBind - scfUnbind - activitytest
Opening a Connection
If a connection is not open to an SPIRITS server, the SCP will
periodically try to open a connection until it is opened. If after a
pre-determined number of attempts the connection is not opened, the
socket connection will be released and then re-established and then
the attempt to open the connection will be repeated.
The sequence for opening a connection is:
1. SCP will transmit a scfBind invokation message to the SPIRITS
server. This message also carries the version information and
activity test interval.
2. The SPIRITS server, upon receiving an invokation of the scfBind
from a particular SCP, will reset all the data concerning the
connection and then responds with either a return result containing
the Web Server Identification number or a return error with a reason.
3. When the SCP receives a return result, if the ID number does not
match the number configured in the SCP, then a scfUnbind will be sent
indicating the wrong ID number. If the SCP receives nothing or a
return error is received, then the scfBind will be retried after a
pre-determined period of time.
4. Once the SCP has received a return result, the SCP will send
Handling Information Request or Activity Test.
Upon receiving an invokation of activityTest, the SPIRITS server
should reply with a return result of activityTest. If the SPIRITS
server does not receive any invokation messages of Handling
Information Request or Activity Test from the SCP for four times the
Activity Test Interval value in milliseconds, the SPIRITS server
should then close the connection.
To close a connection an invokation of the scfUnbind is sent by
either the SCP or SPIRITS server to the remote end. When an
invokation message of the scfUnbind is received, the receiving end
should terminate the connection.
scfBind
The scfBind operation is used to open the connection between the SCP
and the SPIRITS server. The SCP will send the SPIRITS server an
invokation of the scfBind to establish an association. If the
SPIRITS server is ready to handle the request then it should respond
with a return result.
The return result of scfBind contains the identifier of the SPIRITS
server. If the SCP receives the return result where the
identification of the SPIRITS server does not match that registered
against the SPIRITS server, then the SCP will send an invokation of
the scfUnbind indicating an incorrect identifier was received.
If the SPIRITS server is not ready to handle the request or cannot
handle the version, then it should respond with a return error.
scfUnbind
The scfUnbind operation is used to close the connection between the
SCP and the SPIRITS server. Either the SCP or the SPIRITS server can
invoke this operation.
Upon receiving an invokation message the receiving end should
terminate the connection.
activityTest
If the SCP has not sent a Data Message for the time period specified
by the "Activity Test Interval", it will send an invokation message
of activityTest. When the SPIRITS server receives such an
invokation, it will reply with a return result message of
activityTest.
Its contents should be retained by the SPIRITS server. They are to
be echoed back in the return result so that the message reply time
can be calculated.
5.3.1.2.2. Data Message Type
SCPs use the following operations, which are sent to the SPIRITS
server via a Data-Message-Type message, to request execution of some
service procedure or notification of an event that takes place at the
SCPs:
o handlingInformationRequest
The handlingInformationRequest message will request a SPIRITS
server the execution of some service procedure.
o handlingInformationResult
The handlingInformationResult message will show the SCP the result
of the execution, which was carried out by the SPIRITS server.
o confirmedNotificationProvided
The confirmedNotificationProvided message will indicate to the
SPIRITS server of an event, which takes place at the SCP. If the
confirmedNotificationProvided indicating 'caller abandon' is
received, the SPIRITS server will inform the client of the caller
abandon and send the SCP a return result for the
confirmedNotificationProvided.
The invoked operation has always a response which is either a
return result of the operation or an invokation of another
operation.
If a Data Message is not replied to within a pre-determined time
out period then the message will be resent a number of specified
times. Once the number of times has been exceeded, if another node
exists, the message will be sent to another node if it is
available. If all available SPIRITS servers have been queried then
Message Time out will be returned to the calling process.
If an invokation of the handlingInformationResult is received with
the cause=63 (Service not available), the
handlingInformationRequest will be sent to another node if it is
available. If all available SPIRITS severs have been queried then
cause=63 will be returned to the calling process.
5.3.2. SPIRITS Server-ICW Client Application Interface
The following is a list of the application messages that are sent via
the secure protocol (refer to section 5.3.3):
o VersionInfo (ICW client -> SPIRITS server)
Indicate the current version of ICW client software. The SPIRITS
server uses this information to determine if the client software is
out of date.
o VersionInfoAck (SPIRITS server -> ICW client)
If the VersionInfo message from an ICW client indicates to a
SPIRITS server that it is an out of date version, the URL
information is returned within the VersionInfoAck message for use
in downloading the newer version. If the client software is up to
date, the message simply indicates so and does not include any URL
information.
o CallArrival (SPIRITS server -> ICW client)
Sent by the server to tell the client someone has called the DN.
o CallID
An identifier for this call. Unique in the domain of this
client/server session.
o CallingNumber
o CallingName
The name of the calling party is sent to the Client Application
from the SPIRITS server. When available, the name is sent as a
15-character string. If the name is unavailable it is sent as
"Name Unavailable". If the calling party has CLIR set, it is sent
as empty (" ").
o CallConnect (ICW client -> SPIRITS server)
If a corresponding CallConnect is not received within a certain
period after sending a CallArrival, the SPIRITS server will behave
as though a CallConnect, Handling=Ignore had been received.
o CallLost (SPIRITS server -> ICW client)
Sent by server to cancel a CallArrival before a CallConnect is
received by the server.
5.3.3. Secure Reliable Hybrid Datagram Session Protocol (SRHDSP) for Use
Between ICW Client Application and SPIRITS Server
5.3.3.1. Overview
In principle the solution involves session initiation over SSL
(meeting requirements for standards based security) after which the
SSL session is closed, thereby reducing the number of simultaneous
TCP/IP sessions. The rest of the session is communicated over
UDP/IP, secured using keys and other parameters exchanged securely
during the SSL session.
5.3.3.2. Session Initiation
The ICW client initiates an SRHDSP session, by reserving a UDP/IP
port, and opening an SSL session with the service (e.g., ICW) on the
service's well known SSL/TCP port. After establishing the SSL
Session, the ICW client sends the server its IP address, the reserved
UDP port number, and the set of supported symmetric key algorithms.
The server responds with a symmetric key algorithm chosen from the
set, the server's UDP port for further communication, heartbeat
period, and the value to use for the sequencing window.
The client then generates a symmetric key using the selected
algorithm and transmits this to the server. The SSL session is then
closed and the SRHDSP session is considered open.
5.3.3.3. Secure Reliable Datagram Transport
Application, and subsequent session management messages use symmetric
signaling. That is, the signaling is the same whether the client is
sending a message or the server is sending a message.
The message packets are transmitted securely. The protocol corrects
for lost, duplicated and out of sequence packets.
5.3.3.4. Session closure
The client or server may close the session.
A session is closed using a Close message including the next sequence
number, and encrypted with the agreed key.
The receiver, on processing (as opposed to receiving) a Close
message, should set a timer, when the timer expires all details of
the session should be forgotten. The timer is to allow for
retransmission of the close if the Ack gets lost, we still need to be
able to decrypt the subsequent retransmission and re-acknowledgment.
If any message other than a close is received after a close is
processed, it is ignored.
6. Telia/Nortel's Implementation
6.1. Overview
The system implemented by Telia in cooperation with Nortel Networks
is designed to support services that execute before the end-to-end
media sessions are established. These services include, for example:
- call transfer and number portability for redirecting calls
- call waiting and call offering for announcing a pending call
- call screening and don't disturb for filtering incoming calls
- automatic call distribution and 800-services for selecting
termination point
The Telia/Nortel system aims to allow service providers to develop
the services mentioned above. Presently, prototypes for online
incoming call disposition and automatic incoming call disposition
(described in Section 2) have been developed to prove the concept.
In the Telia/Nortel architecture, services run on top of SIP Redirect
Servers. The distributed nature of SIP enables these servers to be
hosted, for example, by an enterprise server, a Service Provider's
server cluster, a user's desktop PC, or even by a hand-held cordless
device.
The SIP Redirect Server receives a SIP INVITE message for each call
regardless of which network the call is being set up in. The server
MAY apply any kind of service logic in order to decide on how to
respond to the invitation. Service logic may interact with the user
to allow the user to specify how to handle a call such as described
in Section 2. This, however, is not the focus of the Telia/Nortel
system.
6.2. Architecture and Protocols
The general idea behind the architecture is to create services as if
all communication was based on IP and all clients and servers were
SIP enabled. This of cause is not true in existing
telecommunications networks. Hence, a new type of network element,
the Service Control Gateways (SCG) hides the true situation from the
services.
SCGs convert network-specific call control signaling to SIP messages
and vice versa. A SCG behaves as a regular SIP User Agent (UA)
towards the services and as a network-specific service control node
in the network where the call is being set up. For example, when
connecting to a GSM network, the SCG can play the role of an SCP or a
MAP or an ISUP proxy. The specific role depends on what service
triggers are being used in the GSM network.
SCGs handle protocol conversions but not address translation, such as
telephone number to SIP URL, which is handled by a regular SIP Server
to keep the SCG as simple as possible.
Consider a service example of number portability. A conventional
number portability implementation in a mobile Circuit Switched
Network (CSN) uses INAP messages to carry number queries to a
network-internal data base application. Here, a SCG and a high-
performance SIP Redirect Server, referred to as the Number Server
(NS), have replaced the data base typically located in an SCP. (See
Figure 11.)
+-----------+ INAP +-----+ SIP +--------------------------+
CSN node -------- SCG ------- NS (SIP Redirect Server)
+-----------+ +-----+ +--------------------------+
Figure 11: An Architecture for Number Portability
The INAP IDP message that carries the number query is converted to a
SIP INVITE message by the SCG and is then forwarded to the NS (SIP
Redirect Server).
If the called number is not registered, then the NS will return "404
Not Found". The SCG interprets this as "non ported number" and
returns a CON message to the CSN network, making it connect the call
to the called number.
If the number is ported and hence registered, then the NS will return
"301 Moved Permanently" with a TEL URL (routing number) in the
contact field. The SCG then returns a CON message to the CSN
network, making it connect the call to the number that was conveyed
in the contact field.
The solution above enables the same Number Server to provide Number
Portability to multiple networks by means of using multiple SCGs.
If we make the SIP server in the number portability example operate
in proxy mode for selected numbers, then it will become a kind of
service router, able to relay number queries to any SIP-Redirect-
Server-based service anywhere, provided there is an IP connection to
the host in concern. Figure 12 shows the arrangement.
+------+ INAP +-----+ SIP +----------------+ SIP +----------+
CSN ------ SCG ----- NS ----- Service
node (redirect/proxy) (redirect)
+------+ +-----+ +----------------+ +----------+
Figure 12: SIP-Based Service Router
Suppose that we connect a value-added service, such as a Personal
Call Filtering service hosted by a user's desktop PC, to a certain
telephone number. The INAP IDP message is converted to a SIP INVITE
message by the SCG and is then forwarded to the NS, just as in the
previous example. However, in this case, the number is registered
with a reference to a SIP URL. This makes the Number Server proxy
the SIP INVITE message to the registered URL, which is the address of
the service.
The service responds as a SIP Redirect Server and the Personal Call
Filtering service logic determines the response. The NS sends the
response back to the SCG which converts the response to an
appropriate INAP message. The response from the service is typically
"302 Moved Temporarily" with a telephone number in the Contact field.
If the response is 301 or 302, as the examples above suggest, then a
telephone number is carried in the contact field. If the user can be
reached via several different addresses, then all of them SHOULD be
added to the response by means of multiple contact fields. The SCG
then selects an address that is valid for the node or application
that issued the number query.
As illustrated by the service examples, the Telia/Nortel system aims
to allow the introduction of multi-network services without requiring
multi-protocol support. The services hence operate in the same way
regardless of in which network the call is made and common IP
services can be shared across heterogeneous networks.
+-----------+ +-------+ SIP +----+ ...... SIP +-----------+
Network 1 --- SCG 1 ----- ---: :----- Service A
+-----------+ +-------+ : : +-----------+
: :
+-----------+ +-------+ SIP : : SIP +-----------+
Network 2 --- SCG 2 ----- NS ---: :----- Service B
+-----------+ +-------+ : Any : +-----------+
: IP :
+-----------+ +-------+ SIP : net- : SIP +-----------+
Network n --- SCG n ----- ---: work :----- Service C
+-----------+ +-------+ +----+ : : +-----------+
: :
+--------+ SIP : : SIP +-----------+
SIP UA -----------------------------: :----- Service x
+--------+ '......' +-----------+
Figure 13: Interconnecting Heterogeneous Networks via SIP
6.3. Security
The Telia/Nortel architecture uses security mechanisms available to
ordinary SIP services, implemented as they would be in a pure SIP
network. The architecture described here does not impose any
additional security considerations.
General security issues that must be considered include
interconnection of two different networks. SCGs must therefore
include mechanisms that prevent destructive service control signaling
from one network to the other. For example, a firewall-type
mechanism that can block a denial-of- service attack from an Internet
user toward the PSTN.
7. Security Considerations
Overall, the SPIRITS security requirements are essentially the same
as those for PINT [3, 4], which include, for example:
+ Protection of the PSTN from attacks from the Internet.
+ Peer entity authentication to allow a communicating entity to
prove its identity to another in the network.
+ Authorization and access control to verify if a network entity
is allowed to use a network resource.
+ Confidentiality to avoid disclosure of information (e.g., the
end user profile information and data) without the permission of
its owner.
+ Non-repudiation to account for all operations in case of douBT
or dispute.
As seen in the previous sections, most implementations examined in
this document have employed means (e.g., firewalls and encryption) to
meet these requirements. The means are, however, different from
implementation to implementation.
8. Conclusion
This document has provided information relevant to the development of
inter-networking interfaces between the PSTN and Internet for
supporting SPIRITS services. Specifically, it described four
existing implementations of SPIRITS-like services. Surveying these
implementations, we can make the following observations:
o The ICW service plays the role of a benchmark service. All four
implementations can support ICW, with three specifically designed
for it.
o SIP is used in most of the implementations as the based
communications protocol between the PSTN and Internet. (NEC's
implementation is the only exception that uses a proprietary
protocol. Nevertheless, NEC has a plan to support SIP together
with the extensions for SPIRITS services.)
o All implementations use IN-based solutions for the PSTN part.
It is clear that not all pre-SPIRITS implementations inter-operate
with each other. It is also clear that not all SIP-based
implementations inter-operate with each other given that they do not
support the same version of SIP. It is a task of the SPIRITS Working
Group to define the inter-networking interfaces that will support
inter-operation of the future implementations of SPIRITS services.
9. References
[1] Petrack, S. and L. Conroy, "The PINT Service Protocol: Extensions
to SIP and SDP for IP Access to Telephone Call Services", RFC
2848, June 2000.
[2] Handley, H., Schulzrinne, H., Schooler, E. and J. Rosenberg,
"SIP: Session Initiation Protocol", RFC2543, March 1999.
[3] Lu, H. (Ed.), Krishnaswamy, M., Conroy, L., Bellovin, S., Burg,
F., DeSimone, A., Tewani, F., Davidson, D., Schulzrinne, H. and
K. Vishwanathan, "Toward the PSTN/Internet Inter-Networking--
Pre-PINT Implementations", RFC2458, November 1998.
10. Authors' Addresses
Igor Faynberg
Lucent Technologies
Room 4L-334
101 Crawfords Corner Road
Holmdel, NJ, USA 07733-3030
Phone: +1 732 949 0137
EMail: faynberg@lucent.com
Hui-Lan Lu
Lucent Technologies
Room 4L-317
101 Crawfords Corner Road
Holmdel, NJ, USA 07733-3030
Phone: +1 732 949 0321
EMail: huilanlu@lucent.com
John Voelker
Lucent Technologies
Room 1A-417
263 Shuman Blvd PO Box 3050
Naperville, IL, USA 60566-7050
Phone: +1 630 713 5538
EMail: jvoelker@lucent.com
Mark Weissman
Lucent Technologies
Room NE406B
200 Lucent Lane
Cary, NC, USA 27511-6035
Phone: +1 919 463 3258
EMail: maw1@lucent.com
Weizhong Zhang
Lucent Technologies
Room 01-A5-17
2000 Regency Parkway
Cary, NC, USA 27511-8506
Phone: +1 919 380-6638
EMail: wzz@lucent.com
Sung-Yurn Rhim
Korea Telecom
17 Woomyun-dong
Seocho-gu, Seoul, Korea
Phone: +82 2 526 6172
EMail: syrhim@kt.co.kr
Jinkyung Hwang
Korea Telecom
17 Woomyun-dong
Seocho-gu, Seoul, Korea
Phone: +82 2 526 6830
EMail: jkhwang@kt.co.kr
Shinji. Ago
NEC Corporation
1131, Hinode, Abiko,
Chiba, 270-1198, Japan
Phone: +81 471 85 7412
EMail: ago@ssf.abk.nec.co.jp
S. Moeenuddin
NEC America, Inc
1525 Walnut Hill Lane,
Irving, TX, USA 75038
Phone: +1 972 518 5102
EMail: moeen@asl.dl.nec.com
S. Hadvani
NEC America, Inc
1525 Walnut Hill Lane,
Irving, TX, USA 75038
Phone: +1 972 518 3628
EMail: hadvani@asl.dl.nec.com
Soren Nyckelgard
Telia Research
Chalmers Teknikpark
41288 Gothenburg
Sweden
EMail: soren.m.nyckelgard@telia.se
John Yoakum
Nortel Networks
507 Airport Blvd, Suite 115,
Morrisville, NC, USA 27560
EMail: yoakum@nortelnetworks.com
Lewis Robart
Nortel Networks
P.O. Box 402
Ogdensburg, NY, USA 13669
EMail: robart@nortelnetworks.com
11. Full Copyright Statement
Copyright (C) The Internet Society (2000). 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. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFCEditor function is currently provided by the
Internet Society.
