Request for Comments: 2458 Editor
Category: Informational M. Krishnaswamy
Lucent Technologies
L. Conroy
Roke Manor Research
S. Bellovin
F. Burg
A. DeSimone
K. Tewani
AT&T Labs
P. Davidson
Nortel
H. Schulzrinne
Columbia University
K. Vishwanathan
Isochrome
November 1998
Toward the PSTN/Internet Inter-Networking
--Pre-PINT Implementations
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 (1998). All Rights Reserved.
Abstract
This document contains the information relevant to the development of
the inter-networking interfaces underway in the Public Switched
Telephone Network (PSTN)/Internet Inter-Networking (PINT) Working
Group. It addresses technologies, architectures, and several (but by
no means all) existing pre-PINT implementations of the arrangements
through which Internet applications can request and enrich PSTN
telecommunications services. The common denominator of the enriched
services (a.k.a. PINT services) is that they combine the Internet and
PSTN services in such a way that the Internet is used for non-voice
interactions, while the voice (and fax) are carried entirely over the
PSTN. One key observation is that the pre-PINT implementations, being
developed independently, do not inter-operate. It is a task of the
PINT Working Group to define the inter-networking interfaces that
will support inter-operation of the future implementations of PINT
services.
Table of Contents
1. Introduction ....................................... 3
2. Terminology ....................................... 3
3. PINT Services ....................................... 4
4. Architectural Overview ............................... 5
4.1 Public Switched Telephone Network ............... 5
4.2 Pre-PINT Systems ............................... 9
5. IN-Based Solutions ............................... 20
5.1 The Lucent System ............................... 20
5.1.1 Roles of the Web Server, Service Node, and SMS ....... 20
5.1.2 A Click-to-Dial-Back Service Scenario ............... 21
5.1.3 Web Server-Service Node Interface ............... 22
5.1.4 Web Server-SMS Interface and SNMP MIB ............... 24
5.1.5 Security Considerations ........................... 26
5.2 Siemens Web Call Center ........................... 27
5.2.1 Service Description ............................... 27
5.2.2 Implementation ................................... 29
5.2.3 Derived Requirements/Lessons ..................... 35
6. Alternative Solutions ............................... 37
6.1 The AT&T System ..................................... 37
6.1.1 High Level Architecture ............................ 38
6.1.2 IP Client to CallBroker Interface .................. 39
6.1.3 Protocol ........................................... 40
6.1.4 APIs Exposed to the IP Client ..................... 41
6.1.5 Voice-Bridge Control API ........................ 41
6.2 Simple Computer Telephony Protocol ............... 41
6.2.1 Overview ........................................... 41
6.2.2 How SCTP Fits in with the Reference PINT Services .. 42
7. Session Initiation Protocol--An Emerging Standard .. 43
7.1 Overview ....................................... 43
7.2 SIP Protocol ....................................... 44
7.3 SIP Entities ....................................... 45
7.4 Providing Call Control Functionality ............... 46
8. Overall Security Considerations ..................... 47
9. Conclusion ....................................... 48
10. Acknowledgments ................................... 48
11. Appendix ....................................... 49
11.1 PSTN/IN 101 ....................................... 49
11.1.1 Public Switched Telephone Network ............... 49
11.1.2 Intelligent Network ............................... 51
11.2 Call Center Features ............................. 54
12. References ....................................... 56
Authors' Addresses ......................................... 57
Full Copyright Statement .................................. 60
1. Introduction
This document contains the information relevant to the development of
the inter-networking interfaces underway in the Public Switched
Telephone Network (PSTN)/Internet Inter-Networking (PINT) Working
Group. It addresses technologies, architectures, and several (but by
no means all) existing pre-PINT implementations of the arrangements
through which Internet applications can request and enrich PSTN
telecommunications services. The common denominator of the enriched
services (a.k.a. PINT services) is that they combine the Internet and
PSTN services in such a way that the Internet is used for non-voice
interactions, while the voice (and fax) are carried entirely over the
PSTN.
The organization of the document is as follows. First, the basic
terminology and a short "intuitive" description of the PINT services
are provided. The rest of the information deals, in one way or the
other, with the pre-PINT support of these services where they are
used as a benchmark. Thus, an architectural overview common to all
present solutions is presented. The flow of the document then
divides into two streams: one is dedicated to the Intelligent Network
(IN)-based solutions; the other explores alternative means (i.e.,
CallBroker and Computer-Telephony Integration (CTI) approach). At
this point, the emerging standards are explored, in particular, the
Session Initiation Protocol (SIP), which promises an elegant solution
to the PINT problem. Each of the above developments is addressed in a
respective section. The final sections of the document contain the
overall security considerations, conclusion, acknowledgments,
appendix, and a set of references. The security section summarizes
the PINT security requirements derived from the pre-PINT experiences
and the appendix presents a tutorial on the PSTN, IN, and Call Center
functions.
2. Terminology
This document uses the following terminology:
Authentication -- verification of the identity of a party.
Authorization -- determination of whether or not a party has the
right to perform certain activities.
PINT Gateway -- the PSTN node that interacts with the Internet.
User or Customer -- the person who asks for a service request to be
issued. In the context of PINT Services, this person will use an
Internet host to make his or her request. The term "user" is also
used to describe a host originating the PINT service request on
behalf of this person.
3. PINT Services
This document addresses four services initially identified by the
PINT Working Group and presently supported by pre-PINT
implementations. These services are: click-to-dial-back, click-to-
fax, click-to-fax-back and voice-access-to-content.
Note that the word "click" should not be taken literally. It is
rather used to point out that initiation of the related services
takes place on the Internet, where point and click are the most
prevalent user actions. In other words, a service request could
originate from any type of IP-based platforms. There is no
implication that these services must be implemented by a device
within the PSTN or the Internet running a Web server.
The common denominator of the PINT services is that they combine the
Internet and PSTN services in such a way that the Internet is used
for non-voice interactions, while the voice (and fax) are carried
entirely over the PSTN. (An example of such a service is combination
of a Web-based Yellow Pages service with the ability to initiate PSTN
calls between customers and suppliers in a manner described in what
follows.)
Some of the benefits of using the PSTN are high quality of the voice,
an ability to route the call to different locations depending on
pre-set criteria (for example, time of the day, day of the week, and
geographic location), outstanding security and reliability, and
access to flexible, low cost, and secure billing and charging
systems. The benefits of using the Internet are the uniform, well-
defined, and widely-used interfaces available anywhere, anytime.
Click-to-Dial-Back
With this service, a user requests (through an IP host) that the PSTN
call be established between another party and himself or herself. An
important pre-requisite for using this service is that the user has
simultaneous access to both the PSTN and Internet.
One example of an application of this service is on-line shopping: a
user browsing through an on-line catalogue, clicks a button thus
inviting a call from a sales representative. Note that (as is the
case with the all-PSTN Free-Phone, or "800", service) flexible
billing arrangements can be implemented here on behalf of the service
provider. In addition (and also similarly to the Free-Phone/800), the
PSTN could route the call depending on the time of day, day of week,
availability of agents in different locations, and so on.
Click-to-Fax
With this service, a user at an IP host requests that a fax be sent
to a particular fax number. In particular this service is especially
meaningful when the fax is to be sent to someone who has only a fax
machine (but no access to the Internet). Consider, as an example, a
service scenario in which a Web user makes a reservation for a hotel
room in Beijing from a travel service page containing hotel
information of major cities around the world. Suppose a specific
Beijing hotel chosen by the user does not have Internet connection
but has a fax machine. The user fills out the hotel reservation form
and then clicks a button sending out the form to the travel service
provider, which in turn generates a fax request and sends it together
with the hotel reservation form to the PSTN. Upon receiving the
request and the associated data, the PSTN translates the data into
the proper facsimile format and delivers it to the Beijing hotel as
specified in the fax request.
Click-to-Fax-Back
With this service, a user at an IP host can request that a fax be
sent to him or her. (Consider the user of the previous example, who
now requests the confirmation from the Beijing Hotel. Another useful
application of the service is when size of the information that a
user intends to get is so large that downloading it to the user's PC
over the Internet will require a long time and a lot of disk space.)
Voice-Access-to-Content
With this service, a user at an IP host requests that certain
information on the Internet be accessed (and delivered) in an audio
form over the PSTN, using the telephone as an informational
appliance. One application of this service is to provide Web access
to the blind. (This may require special resources--available in the
PSTN--to convert the Web data into speech.)
4. Architectural Overview
4.1 Public Switched Telephone Network
From an application perspective, Internet nodes are interconnected
directly, as shown in Figure 1. When two machines are to communicate,
they will have the address of the destination end system, and will
send network level datagrams, assuming that the underlying
infrastructure will deliver them as required.
_____
__ _____/ \_____
[__] / \
[----]-.-.-.-. Internet .-.
\_____ _______/ |
__ \__./ __ .
[__] / [__] |
[----]-. [----]-.
Key: .-.-. Internet Access Link
Figure 1
Where all nodes are on the same (broadcast) network, there is no need
for intervening routers; they can send and deliver packets to one
another directly. The Internet nodes are responsible for their own
communications requests, and act as peers in the communication
sessions that result.
This contrasts with the situation in the PSTN. There, the end systems
are configured as shown in Figure 2. The end systems tend to be
specific to a particular type of traffic, so that, for example, the
majority of terminals are dedicated to carrying speech traffic
(telephones) or to carrying facsimile data (fax machines). The
terminals all connect to Central Offices (COs) via access lines, and
these COs are interconnected into a network.
/--\
()/\()__
/__\ \ .................................
\ ! ! ! /--\
__ \ [-!-] [-!-] ! ()/\()
\ \ \__[CO ]=========[CO ]==\\ ! ___/__\
[Fax]________[---] [---] \\ [-!-] / __
\\=======[CO ]____/ \ \
[---]________[Fax]
Key: ___ Access Lines
=== Trunk Links (inter-CO user data links)
... Inter-CO signaling network links
CO Central Office (Telephone Exchange)
Figure 2
Communications between the terminals are all "circuit switched", so a
dedicated synchronous data path (or circuit) needs to be placed
between the end terminals for carrying all communications. Arranging
for such a circuit to be made or removed (cleared) is the
responsibility of the Central Offices in the network. A user makes a
request via his or her terminal, and this request is passed on to the
"local" Central Office. The relationship between the terminals and
the local Central Offices to which they are connected is strictly
Client/Server.
The COs are interconnected using two different types of connections.
One of these is called a trunk connection (shown as a double line in
the above figure) and is used to carry the data traffic generated by
the terminals. The other connection acts as part of a separate
network (and is shown as a dotted line in the above figure). This is
the signaling network, and is used by the Central Offices to request
a connection to be made between themselves and the destination of the
required circuit. This will be carried across the trunk link to the
"next" Central Office in the path. The path, once in place through
the PSTN, always takes the same route. This contrasts with the
Internet, where the underlying datagram nature of the infrastructure
means that data packets are carried over different routes, depending
on the combined traffic flows through the network at the time.
The call set up process can be viewed as having two parts: one in
which a request for connection is made, and the other in which the
circuit is made across the PSTN and call data flows between the
communicating parties. This is shown in the next pair of figures (3a
and 3b).
/--\
() ()
--____
/++\ \
/----\ \
A \ [-!-]
\->[CO ]
[---]
Time = 13:55
Figure 3a
Key: ___ Access Lines
=== Trunk Links (inter-CO user data links)
... Inter-CO signaling network links
CO Central Office (Telephone Exchange)
/--\
() ()
-- .................................
/ \<--- ^ ! ! /--\
/----\ \ ! v ! () ()
A' \ [-!-] [-!-] ! --
\__[CO ]=========[CO ]==\\ v ->-/ \
[---] [---] \\ [-!-] / /----\
\\=======[CO ]____/ B'
Time = 14:00 [---]
Figure 3b
Figure 3 shows a particular kind of service that can be provided;
call booking. With this service, a request is sent for a connection
to be made between the A and B telephones at a specified time. The
telephone is then replaced (the request phase is terminated). At the
specified time, the CO will make a connection across the network in
the normal way, but will, first, ring the "local" or A' telephone to
inform the user that his or her call is now about to be made.
For more complex services, the requesting telephone is often
connected via its "local" CO to a Service Node (SN), where the user
can be played prompts and can specify the parameters of his or her
request in a more flexible manner. This is shown below, in Figures
4a and 4b. For more details of the operation of the Service Node (and
other Intelligent Network units), see the Appendix.
When the SN is involved in the request and in the call setup process,
it appears, to the CO, to be another PSTN terminal. As such, the
initial request is routed to the Service Node, which, as an end
system, then makes two independent calls "out" to A' and B'.
/--\ [---]
() () [SN ]
--___ [|--]
/++\ \ |
/----\ \ |
\ |
A \ [|-!]
\->[CO ]
[---]
Time = 13:55
Figure 4a
Key: ___ Access Lines
=== Trunk Links (inter-CO user data links)
... Inter-CO signaling network links
CO Central Office (Telephone Exchange)
SN Service Node
/--\ [---]
() () [SN ]
-- [|--] /--\
/ \<-- | ............................... () ()
/----\ \ | ^ ! ! --
\ | / v v / \
A' \ [|-!] [-!-] [-!-] ->-/----\
\--[CO ] [CO ] [CO ] /
[---] [---] [---]___/ B'
Time = 14:00
Figure 4b
Note that in both cases as shown in Figures 3 and 4 a similar service
can be provided in which the B' telephone is replaced by an
Intelligent Peripheral (or an Special Resource Functional entity
within a Service Node), playing an announcement. This allows a "wake
up" call to be requested, with the Intelligent Peripheral or Service
Node Special Resource playing a suitable message to telephone A' at
the specified time. Again, for more details of the operation of the
Special Resources (and other Intelligent Network units), see the
Appendix.
4.2 Pre-PINT Systems
Although the pre-PINT systems reported here (i.e., those developed by
AT&T, Lucent, Siemens and Nortel) vary in the details of their
operation, they exhibit similarities in the architecture. This
section highlights the common features. Specific descriptions of
these systems will follow.
All of the systems can be seen as being quite similar to that shown
in the following diagram. In each case, the service is separated into
two parts; one for the request and another for execution of the
service. Figure 5 summarizes the process.
_____
__ _____/ \_____
[__] / \
[-++-]-.-.>.-. Internet .-.-
\_____ _______/ .
\___/ v
[----] .
[PINT]-.-
[----]
%
v
[---]
[SN ]
[|--]
Figure 5a
Key: CO Central Office (Telephone Exchange)
SN Service Node
PINT PSTN/Internet Gateway
.-.-. Internet Access Link
%%% Gateway/Service Node Link
___ PSTN Access Lines
=== PSTN Trunk Links (inter-CO user data links)
... Inter-CO signaling network links
_____
__ _____/ \_____
[__] / \
[----]-.-.-.-. Internet .-.-
\_____ _______/ .
\___/ |
[----] .
[PINT]-.-
[-%--]
%
%
/--\ [-%-]
() () [SN ]
-- [|--] /--\
/ \<-- | .................... () ()
/----\ \ | ^ ! ! --
\ | / v v / \
A' \ [|-!] [-!-] [-!-] ->-/----\
\--[CO ]=======[CO ]======[CO ] /
[---] [---] [---]__/ B'
Figure 5b
Comparing Figure 4a with Figure 5a, the differences lie in the way
that the information specifying the request is delivered to the
Service Node. In the PSTN/IN method shown in the earlier diagram, the
user connects to the SN from the telephone labeled A, with the
connection being routed via the CO. In the latter case, the request
is delivered from an Internet node, via the PINT gateway, and thence
to the Service Node over a "private" link. The effect is identical,
in that the request for service is specified (although the actual
parameters used to specify the service required may differ somewhat).
The figures depicting the respective service execution phases
(Figures 4b and 5b) show that the operation, from the IN/PSTN
perspective, is again identical. The Service Node appears to initiate
two independent calls "out" to telephones A' and B'.
The alternative systems developed by AT&T and by Nortel allow another
option to be used in which the PINT Gateway does not have to connect
to the PSTN via a Service Node (or other Intelligent Network
component), but can instead connect directly to Central Offices that
support the actions requested by the gateway. In these alternatives,
the commands are couched at a "lower level", specifying the call
states required for the intended service connection rather than the
service identifier and the addresses involved (leaving the
Intelligent Network components to coordinate the details of the
service call on the gateway's behalf). In this way the vocabulary of
the commands is closer to that used to control Central Offices. The
difference really lies in the language used for the services
specification, and all systems can use the overall architecture
depicted in Figure 5; the only question remains whether the
Intelligent Network components are actually needed in these other
approaches.
The following diagram (Figure 6) shows the interface architecture
involved in providing the kind of service mentioned above.
Internet __ __
Server [__] _______ [__]
[W3S-]-. ___/ .-.-.-[W3C-] Internet
_________________|/.-.-.-.-. \ Terminal
/ .. . \
| Internet / . \ |
\___________ . . . /
\/___|____\_________/
. . .
/ | \
(A) (B) (E)
. . .
_|_ _|_ _|_
[SN ]<-(D)--[SMS]--(H)->[SCP]
[|-|] --- [-!-]
/ \ !
(C) (I) ...........(F)...!.(G).
/ \ ! !
[--|] [|-!] [-!-]
[CO ] [MSC] [SSP]
[---] [---] \|/ [---]
/--\ | |____| | /--\
()/\() | | ()/\()
/--\___| 1 |___/--\
Fixed PSTN Terminal [] Fixed PSTN Terminal
Mobile Terminal
Key: W3S HTTP (Web) Server
W3C HTTP (Web) Client/Browser
CO Central Office (Telephone Exchange)
MSC Mobile Switching Center (Mobile Network Telephone
Exchange)
SN Service Node
SSP Service Switching Point
SCP Service Control Point
SMS Service Management System
.-.-. Internet relationship
___ PSTN Access relationship
... PSTN "core" signaling relationship
Figure 6
The interfaces are:
A The interface over which Internet requests for service are
delivered to the Service Node
B The interface over which Service Management requests are sent
from the Internet to the Service Management System
C The interface over which the Service Node sends call control
requests to a connected Central Office
D The interface over which the Service Management System manages
the Service Node
E The interface over which Internet requests for service are
delivered to the Service Control Point
F The interface over which the Service Control Point sends service
call control requests to the Mobile Switching Center
G The interface over which the Service Control Point sends service
control requests to the Service Switching Point
H The interface over which the Service Management System manages
the Service Control Point
I The interface over which the Service Node sends service call
control requests to the Mobile Switching Center
In practice, a number of the interfaces have very similar purposes to
one another. The means by which these purposes are achieved differ,
in that some of the interfaces (C and I) reflect access arrangements,
whilst others (F and G) imply a "core" signaling relationship.
However, it is possible to categorize them in terms of the "intent"
of messages sent across the interfaces.
For example, Interfaces A and E are similar; one of the main aims of
PINT work is to ensure that they are the same. Similarly, Interfaces
D and H imply similar actions and are likely to carry similar
messages. Interfaces C, F, G, and I are all used to request that a
call be initiated, albeit via access or core signaling relationships.
The interfaces can also be viewed in terms of the kind of components
that are involved and the bodies by which they are codified.
Interfaces A, B, and E are all going to be realized as Internet
Protocols. All of the others use existing protocols in the PSTN/IN.
Traditionally, these have been codified by different groups, and this
is likely to be the case in the PINT work.
The general arrangements for the different systems are shown below
(Figures 7, 8, 9, and 10). They differ in the details of their
configurations, but the main tasks they perform are very similar, and
so the overall operation is similar to the generic architecture shown
in Figures 5 and 6.
Key for following diagrams:
Components:
W3C World Wide Web Client
W3S World Wide Web Server
WSA Web Server "Back End Program" Interface (CGI or Servlet
interface)
Srvlt Servlet "back end" program/objects
FS Finger Server
SCTPC Simple Computer Telephony Protocol Client
SCTPS Simple Computer Telephony Protocol Server
CBC CallBroker Client
CBS CallBroker Server
SSTPC Service Support Transport Protocol Client
SSF Service Switching Function
SCF Service Control Function
SRF Special Resource Function
CO Central Office/ Public Telephone Exchange
SSP Service Switching Point
SCP Service Control Point
SR/I.IP Special Resource/ "Internet" Intelligent Peripheral
SMS Service Management System
INAPAd Intelligent Network Application Part Adaptor
PktFlt Packet Filter (Firewall)
SNMPAg Simple Network Management Protocol Agent
Protocols:
P0 HyperText Transfer Protocol
P1 HTTP Server <-> "Back End Program" internal protocol
P2 CallBroker Client <-> CallBroker Server protocol (AT&T system),
or SCTP Client <-> Server protocol (Nortel system)
P3 PINT User Agent <-> PINT Gateway protocol
P4 Intra-Intelligent Network protocol (e.g., INAP)
P5 Proprietary (INAP-based) Gateway-> I.IP protocol
P6 Finger protocol
P7 Digital Subscriber Signaling 1 protocol
P8 Simple Network Management Protocol
P9 SMS <-> Service Control Point/Service Node protocol
_____ _______ _____
|[W3C]|----(p0)-->| [W3S] |<--(p0)----|[W3C]|
|[---]| | [WSA] | |[FS.]|
|-----| | ! | |[-!-]|
| (p1) | |--\--|
| ! | ^
| ! | (p6)
| ! | \
| (p1) | \
| ! | \
|[Srvlt]| \
|___!___| \
! \
(p3) \
Internet ! !
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.!.+.+.+.+.+.
PSTN/IN _______________!_________________ ____!_____ __________
|I [PktFlt] I| |[PktFlt]| |[PktFlt]|
|N Gateway N| | ! | | ! |
|A ___________________________ A| | ! | | ! |
|P | | P| | ! | |[SNMPAg]|
-(p4)-- |A | <-(p4)-> [SCP] <-(p4)-> | A|-(p5)->|[SR/IIP]| | [SMS] |
\ |d | [-^-] | d| |[------]| | [-^-] |
\ |__| ! |__| |________| |___!____|
\ ! !
[-v-] !-----------------(p9)-----------------!
[SSP]
[---]
___| |______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Figure 7: The Siemens Web Call Center
_____ _______
|[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] |
|-----| | ! |
| (p1) |
| ! |
| ! |
| ! |
| (p1) |
| ! |
|[SSTPC]|-<----------------------------------
|___!___| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[-v-] (p7) !-----------------(p9)-----------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Figure 8: The Lucent System
_____ ________
|[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] |
|-----| | ! |
| (p1) |
| ! |
|[WS/CBS]|
|[Adaptr]|
|___!____|
^
(p2)
_____ ___v____
|[CBC]| | [CBS] |
|[---]|<---(p2)-->| [---] |-<---------------------------------
|-----| |___!____| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[---] (p7) !-----------------(p9)-----------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Figure 9: The AT&T System
_____ ________
|[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] |
|-----| | ! |
| (p1) |
| ! |
|[WS/ ]|
|[ SCTPS]|
|[Adaptr]|
|___!____|
^
(p2)
_______ ___v___
|[SCTPC]| |[SCTPS]|
|[-----]| <-(p2)--> |[-----]|-<----------------------------------
|-------| |___!___| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+.
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[---] (p7) !-----------------(p9)-----------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Figure 10: The Nortel System
As these are independent systems developed by different groups, the
names of the components, unsurprisingly, don't match. Some features
are offered by one of the systems, while they aren't by others.
However, there are a number of common features. All of the systems
provide a Web-based interface (at least as an option), using "back
end" programs to construct protocols to pass onwards to the
Intelligent Network system.
Several Intelligent Network Functional Entities are combined into a
Service Node in the Lucent, AT&T , and Nortel systems, while in the
Siemens scheme they are separate units. However, this is not
particularly important for the provision of the services they offer.
The main difference lies in whether or not the SCF is "aware" of the
Internet interface and has been modified to be "complicit" in
supporting these Internet requests. The Siemens approach was to re-
use an existing SCP, providing a gateway function to translate as
needed. The Lucent system used a "lighter weight" SCF adapter to
terminate the Internet protocols, as the SCF was modified to support
the Internet interface directly.
The AT&T CallBroker and Nortel SCTP Servers introduce an intermediate
protocol (labeled p2) that allows an alternative to the Web based
interface supported by the others. This protocol matches the
"CallBroker Client API", or the "SCTP Client API". These options
provide for a bi-directional protocol, with indications sent from the
Call Broker or SCTP Server to the Client as needed. This is not
easily possible using an HTTP-based scheme (and in the Siemens case,
a dedicated Finger client/server pair was used to emulate such an
interface)
The protocol between the Internet server and the Intelligent Network
(labeled p3 in the above diagrams) differs in each of the systems.
One of the main aims of future work will be to develop a common
protocol that will support the services offered, so that the p3
interface will allow different implementations to inter-operate. In
the Lucent, Siemens, and Nortel systems, this was an "internal"
protocol, as it was carried between entities within the Service Node
or Gateway.
Other contrasts between the systems lie in the support for Internet
access to Service Management, and access to the Internet by Special
Resources. Internet Management access was most developed in the
Lucent system, in which a Simple Network Management Protocol (SNMP)
agent was provided to allow inter-operation with the SMS controlling
the Service Node. In the Siemens scheme, the SMS had no direct
Internet access; any management actions were carried out within the
normal PSTN management activities. As for Internet access to special
resources, this was only required by the Siemens system as part of
its support for Call Center agent notification. Equivalent
functionality would be provided in the AT&T and Nortel systems as
mentioned above, and this would in turn be associated with event
notifications being sent as part of their (p3) Internet/IN protocol.
These differences reflect the different emphases in the products as
they were developed; again, future work will have to ensure that
common protocols can be used to support the chosen services fully.
5. IN-Based Solutions
5.1 The Lucent System
Figure 11 depicts the overall interconnection architecture of the
Lucent prototype in support of the four PINT services. The IN-based
architecture utilizes the Service Node and Service Management System
in addition to the Web server, which enables Web-based access to the
PINT services. This section summarizes the roles of these elements
(complemented by a click-to-dial-back service scenario), outlines the
interfaces of Web Server-Service Node and Web Server-Service
Management System (i.e., the interfaces A & B), and addresses the
common security concerns.
5.1.1 Roles of the Web Server, Service Node, and Service Management
System
Web Server
The Web Server stores the profiles of content providers as well as
pre-registered users. The content provider profile contains
information such as content provider ID, telephone number, and fax
number. In addition, the profile may also include service logic that
specifies, for example, the telephone (or fax) number to be reached
based on time of the day, day of the week, or geographical location
of the user, and the conditions to accept the charge of the calls.
Similar to the content provider profile, the pre-registered user
profile contains information such as user name, password, telephone
number, and fax number. The last two pieces of information can also
be linked to time of the day and day of the week so the user can be
reached at the appropriate telephone (or fax) number accordingly.
Service Node
Situated in the PSTN, the SN, like the SCP, performs the service
control function [1, 2, 3]. It executes service logic and instructs
switches on how to complete a call. The SN also performs certain
switching functions (like bridging of calls) as well as a set of
specialized functions (like playing announcements, voice recognition
and text-to-speech conversion).
Service Management System
The SMS performs administration and management of service logic and
customer-related data on the SN. It is responsible for the
replication of content provider profiles and provision of these data
on the SN. These functions are non-real time.
Web Users
____________
O -------------------------- | Internet |-------------------
------------ |
|
|
---------------- -------------- ------------
| Service Node | D | Service | B |Web Server|
| (SN) |------------| Management |---------------| |
| | |System (SMS)| | |
| | A -------------- | |
| |-----------------------------------------| |
---------------- ------------
| |
| I | C
| |
----------- ---------
|Mobile | |Central|
|Switching| |Office |
| Center | ---------
----------- |
| |
| |
O O
Mobile Wireline PSTN
Users Users
Figure 11: Overall Interconnection Architecture of the Lucent System
5.1.2 A Click-to-Dial-Back Service Scenario
A Web user, who has simultaneous access to the Web and telephone
services (this can be achieved, for example, by having an ISDN
connection), is browsing through a sales catalogue and deciding to
speak to a sales representative.
When the Web user clicks a button inviting a telephone call from the
sales office, the Web Server sends a message to the SN over the A
interface, thus crossing the Internet-to-PSTN boundary. By matching
the information received from the Web Server with the content
provider profile that had been previously loaded and activated by the
SMS over the D interface, the SN recognizes the signal.
At this point, the SN calls the Web user. The user answers the call,
hears an announcement, e.g., "Please wait, while we are connecting
you to the sale agent", and is waiting to be connected to the sale
agent. Then the SN invokes service logic as indicated in the profile.
The execution of this logic selects an appropriate sales agent to
call based on the time of the day. It is 8 P.M. in New York where
the Web user is located, and the New York sales office has closed.
The San Francisco office, however, is still open, and so the SN makes
a call to an agent in that office. Finally, the SN bridges the two
calls and establishes a two-party call between the sales agent and
the Web user.
5.1.3 Web Server-Service Node Interface
Lucent developed the Service Support Transfer Protocol (SSTP) for
communications between the SN and Web Server. SSTP is of a
request/response type running on top of a reliable transport layer,
such as TCP. The Web Server sends a request to the SN to invoke a
service and the SN responds with a message indicating either success
or failure. Note that SSTP engages only the service control function
[1, 2, 3] of the SN.
5.1.3.1 Web Server to Service Node
In this direction, three kinds of messages may be sent: the
Transaction Initiator message, the Data Message, and the End of Data
message.
The latter two messages are needed if the service to be invoked
involves data (such as the case in click-to-fax, click-to-fax-back
and voice-access-to-content). This was so designed to handle the
varying size of data and to ensure that the size of each stream is
within the allowable size of the underlying transport packet data
unit (imposed by some implementations of TCP/IP).
a. Transaction Initiator
This message provides all the necessary information but data for
invoking a service. It includes the following information elements:
+ Transaction ID, which uniquely specifies a service request. The
same transaction ID should be used for all the accompanying data-
related messages, if the service request involves data. One way for
generating unique transaction IDs is to concatenate the information:
date, time, Web Server ID (uniquely assigned for each one connected
to the SN), and transaction sequence number (a cyclic counter
incremented for each service request).
+ Service ID, which specifies the service to be invoked. The service
may be click-to-dial-back, click-to-fax, click-to-fax-back or voice-
access-to-content.
+ Content Provider ID, which uniquely represents the content
provider. This information is the key to accessing the content
provider's service logic and data on the SN.
+ Content Provider Directory Number, which is the telephone or fax
number of the content provider to be called through the PSTN.
+ User Directory Number, which is the telephone or fax number of the
user requesting the service.
+ Billed Party, which specifies the party (either the user or content
provider), to be billed.
In addition, optional parameters may be sent from the Web Server to
the SN. For example, a retry parameter may be sent to specify the
number of times the SN will attempt to complete a service request
upon failure before the transport connection times out.
b. Data Message
This message provides the (encapsulated) user data part of a service
request. For example, in the case of click-to-fax-back such data are
the content to be faxed to the user. Each message is composed of the
transaction ID and a data segment. The transaction ID must be the
same as that of the transaction initiator part first invoking the
service.
c. End of Data Message
This message contains the transaction ID and the end of data
delimiter. The transaction ID is the same as that of the relevant
transaction initiator message.
5.1.3.2 Service Node to Web Server
The SN must respond to a service request from the Web Server. The
response message consists of the information elements:
transaction ID, service type, result, time, and error code.
+ Transaction ID, which is the same as that of the original service
request.
+ Service Type, which is the same as that of the original service
request.
+ Result, which is either success or failure.
+ Time, which indicates the time of the day completing the request.
+ Error Code, which gives the reason for failure. Possible reasons
for failure are content provider telephone (or fax) busy, content
provider telephone (or fax) no answer, user telephone busy, user
refusal to complete, user no answer, nuisance control limit reached,
and content provider telephone (or fax) not in the SN database.
5.1.3.3 Usage Scenarios: Click-to-Fax and Click-to-Fax-Back
For the click-to-fax and click-to-fax-back services, the Lucent
system implemented only the case where the data to be sent as
facsimile reside in the Web server. There are at least three messages
that need to be sent from the Web server to the Service Node for
these services.
The first message is the Transaction Initiator that identifies the
service type as well as a unique Transaction ID. It also includes the
sender/receiver fax number.
The next is one or more messages of the data to be faxed. Each
message carries the same unique Transaction ID as the above.
Last comes the end of message. It consists of the Transaction ID
(again, the same as that of the messages preceding it) and the end of
data delimiter.
Upon receiving these messages, the Service Node, equipped with the
special resource of a fax card, converts the data into the G3 format,
calls the receiver fax, and sends back the result to the Web server
immediately. Note that the receiver fax busy or no answer is
interpreted as failure. Further, while the receiver fax answering the
call is interpreted as success, it does not necessarily mean that the
fax would go through successfully.
5.1.4 Web Server-SMS Interface and SNMP MIB
This interface is responsible for uploading the content provider
profile from the Web Server to the SMS and for managing the
information against any possible corruption. The SN verifies the
Content Provider ID and the Content Provider Directory Number sent by
the Web Server with the content provider profile pre-loaded from the
SMS.
The content provider profile was based on ASN.1 [4] structure and
SNMP [5] was used to set/get the object identifiers in the SMS
database.
Following is an example of the simple MIB available on the SMS.
inwebContProviderTable OBJECT-TYPE
SYNTAX SEQUENCE OF InwebContProviderEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
" A table containing Content Provider profiles "
:= { inweb 1}
inwebContProviderEntry OBJECT-TYPE
SYNTAX InwebContProviderEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
" A conceptual row of the inweb. Each row
contains profile of one Content Provider"
INDEX { inwebSmsNumber }
:= { inwebContProviderTable 1 }
InwebContProviderEntry := SEQUENCE {
inwebSmsNumber Integer32,
inwebContentProviderId Integer32,
inwebContentProviderPhoneNumber Integer32,
inwebContentProviderFaxNumber Integer32
}
inwebSmsNumber OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
" Serial number of the SMS - used for SNMP indexing "
:= { inwebContProviderEntry 1 }
inwebContentProviderId OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-create
STATUS current
DESCRIPTION
" A number that uniquely identifies each Content
Provider "
:= { inwebContProviderEntry 2 }
inwebContentProviderPhoneNumber OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-create
STATUS current
DESCRIPTION
" Content Provider's Phone Number "
:= { inwebContProviderEntry 3 }
inwebContentProviderFaxNumber OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-create
STATUS current
DESCRIPTION
" Content Provider's Fax Number "
:= { inwebContProviderEntry 4 }
5.1.5 Security Considerations
The Lucent prototype addressed the security issues concerning the
interface between the Web Server and the SN. Those concerning the
interface between the Web Server and SMS, which was based in SNMP,
were handled by the built-in security features of SNMP.
+ Secure Communication Links
If the Network Operator (PSTN provider) is also the Web Service
provider, the Web Server and SN/SMS will communicate over a corporate
intranet. This network is almost always protected by the
corporation's firewall and so can be deemed secure. This was the case
handled by the Lucent prototype.
Nevertheless, if different corporations serve as the Network Operator
and the Web Service Provider, then it is likely that there may not
exist a dedicated secure communication link between the Web Server
and SN/SMS. This raises serious security considerations. One possible
solution is to use Virtual Private Networks (VPN). VPN features
support authentication of the calling and called parties and
encryption of the messages sent over insecure links (such as those on
the Internet).
+ Non-Repudiation
All transactions were logged on both the Web Server and the Service
Node to account for all operations in case of doubt or dispute. The
log information on the SN may also be used to generate bills.
+ Malicious Requests of Users
A user may make repeated requests to a content provider directory
number maliciously. This scenario was handled by setting a Nuisance
Control Limit (NCL) on either the SN or the Web Server or both. The
NCL has two parameters: one defining the number of requests from a
user and the other the period over which these requests takes place.
A user may also attempt to request a call from a directory number
other than that of a content provider. This scenario was handled by
verifying the directory number (and the content provider ID) against
the database on the SN containing all the content provider
information. If the directory number (or the content provider ID) was
not in the database, the request would be rejected.
5.2 Siemens Web Call Center
5.2.1 Service Description
The Web Call Center is an Intelligent Network System that accepts
requests from Internet nodes for services to be provided on the PSTN.
As the name suggests, it was designed to support a cluster of
services that, taken together, provide a subset of the features of a
Call Center, with almost all user interactions provided via World
Wide Web requests and responses. See the appendix for a background
description of Call Center Features.
From an Intelligent Network perspective, there are a number of
services that, when combined, provide the Call Center features. The
Call Center features as implemented supported the scenario in which a
customer makes a request to be called back by an agent at a time of
the customer's choosing to discuss an item of interest to him or her.
The agent will be selected based on his or her availability and
expertise in this topic; the agent will be told whom he or she is
calling and the topic of interest, and then the agent will be
connected to the customer.
In addition, the individual services that were deployed to support
this scenario provided support for management of the list of
available agents as well. This involved allowing the agent to "log
into" and "out of" the system and to indicate whether the agent was
then ready to handle calls to the customer. The list of services, as
seen from a user perspective, follows.
The services support:
i) Customer Request service - the customer explores a corporate Web
site, selects a link that offers to request an agent to call the
customer back and then is redirected to the Web Call Center server.
This presents customer with a form asking for name, the telephone
number at which he or she wishes to be called, and the time at which
the call is to be made. Note will also be made of the page to which
the customer was referred to when he or she was redirected. Once the
form has been returned, the customer receives an acknowledgment page