ISO/IEC TR 21890:2001

Information technology — Telecommunications and information exchange between systems — Interoperation of PISNs with IP networks

The purpose of this Technical Report is to investigate the interoperability of Private Integrated Services Networks (PISNs) and Internet Protocol (IP) networks, with a view to identifying possible scenarios for interoperation, problems that will have to be solved if particular scenarios are to be pursued further, and possible future standardization activities in this area. In particular, the following aspects of interoperability are investigated: 􀂃 the interworking of PISNs and IP networks via a gateway; 􀂃 the connection of PISN components via IP networks. For each of the above, aspects considered include architecture, addressing (including use of IP addressing), services, protocols, security, quality of service and mobility. This is conducted within the context of leading standards for voice and multimedia communication over IP networks, including ITU-T recommendation H.323, IETF Session Initiation Protocol (SIP) and ITU-T recommendation H.248. Possible future standardization activities resulting from this Technical Report can include work items relating to IP networks and work items relating to PISNs, as well as work items concerned specifically with interoperability. The dominant traffic in PISNs is voice, and therefore this Technical Report focuses on interoperability considerations for voice traffic. However, many of the standards that support voice in an IP network are also applicable to multi-media traffic (e.g., voice, video and data). Although in many respects similar to voice, fax traffic has slightly different requirements and is not explicitly considered in this Technical Report. It could be the subject of further study.

Technologies de l'information — Télécommunications et échange d'information entre systèmes — Interopération de PISN avec des réseaux IP

General Information

• Status: Published
• Publication Date: 26-Sep-2001
• ICS: 33.040.35 - Telephone networks
• Technical Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Drafting Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Current Stage: 9060 - Close of review
• Start Date: 18-Dec-2012
• Completion Date: 19-Dec-2012

Standards Content (Sample)

TECHNICAL ISO/IEC
REPORT TR
21890
First edition
2001-10-01

Information technology —
Telecommunications and information
exchange between systems —
Interoperation of PISNs with IP networks
Technologies de l'information — Télécommunications et échange
d'information entre systèmes — Interopération de PISN avec des
réseaux IP




Reference number
ISO/IEC TR 21890:2001(E)
©
ISO/IEC 2001

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ISO/IEC TR 21890:2001(E)
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ISO/IEC TR 21890:2001(E)
Contents

Foreword vi
Introduction vii
1 Scope 1
2 Normative references 1
3 Definitions 3
3.1 Corporate telecommunication Network (CN) 3
3.2 Internet 3
3.3 Intranet 3
3.4 Internet Protocol (IP) 3
3.5 IP network 3
3.6 Private Integrated Services Network (PISN) 3
3.7 Private Integrated services Network eXchange (PINX) 3
3.8 Switched Circuit Network (SCN) 3
3.9 Tunnelling 3
4 Acronyms 3
5 Introduction 5
5.1 Background 5
5.2 Types of network 6
5.3 Arrangements for interworking of SCNs and IP networks 7
5.4 Arrangements for interconnection of SCN components over IP networks 8
6 General principles of multimedia communication over an IP network 8
6.1 Architecture 9
6.1.1 Media processing and packetization (MPP) functional entity 9
6.1.2 Resource control (RC) functional entity 9
6.1.3 Session control (SC) functional entity 10
6.1.4 SC-redirect (SC-R), SC-proxy (SC-P) and RC-proxy (RC-P) functional entities 10
6.1.5 Admission control (AC) functional entities 11
6.1.6 Identity resolution (IR) functional entity 11
6.1.7 Registrar (RGR) and registrant (RGT) functional entities 11
6.1.8 Generic functional architecture (non-interworking) 11
6.1.9 Physical realizations of generic functional architecture for multimedia communication over an IP network
(non-interworking) 12
6.1.10 Generic functional architecture for interworking with an SCN 13
6.1.11 Physical realizations of generic functional architecture for interworking with an SCN 13
6.1.12 Simple terminals 15
6.2 Naming and addressing 16
6.3 Security 16
6.4 Quality of service (QoS) 17
6.5 Mobility 18
7 Standards for multimedia communication over an IP network 18
7.1 Overview 18
7.2 The ITU-T H.323 family of recommendations 19
7.2.1 Functional architecture 19
7.2.2 Naming and addressing 20
7.2.3 Supplementary services 20
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ISO/IEC TR 21890:2001(E)
7.2.4 Security 21
7.2.5 Quality of service 22
7.2.6 Mobility 22
7.3 Other ITU-T standards 22
7.3.1 H.248 22
7.3.2 BICC 23
7.4 IETF specifications for IP telephony 23
7.4.1 Functional architecture 23
7.4.2 Main protocols 24
7.4.3 Naming and addressing 24
7.4.4 Supplementary services 25
7.4.5 Security 25
7.4.6 Quality of service 26
7.4.7 Mobility 26
7.5 ETSI TIPHON specifications 26
7.6 Terminal specifications from TIA TR-41.3.4 26
8 Interworking of PISNs and IP networks via a gateway 26
8.1 Architecture 27
8.2 Signalling 28
8.3 Naming and addressing 28
8.3.1 Naming and addressing in PISNs 28
8.3.2 Naming and addressing in IP networks 28
8.3.3 Naming and addressing interworking when H.323 used in the IP network 28
8.3.4 Naming and addressing interworking when SIP used in the IP network 29
8.4 Supplementary services 29
8.4.1 H.323 supplementary services 29
8.4.2 SIP supplementary services 29
8.5 Security 29
8.6 Quality of service 29
8.7 Mobility 29
8.8 Network management 29
8.9 Aspects requiring further study or standardization work 30
9 Interconnection of remote PISNs via an IP network 30
9.1 Classification of scenarios for the interconnection of PISNs 30
9.2 Solutions for the interconnection of remote PISNs via an IP network 31
9.3 Solution 1 – QSIG tunnelling over IP network transport layer protocol 32
9.3.1 Architecture 32
9.3.2 Aspects requiring further study or standardization work 33
9.4 Solution 2 – QSIG tunnelling over IP network session control protocol 33
9.4.1 Architecture 33
9.4.2 Aspects requiring further study or standardization work 34
9.5 Solution 3 – enhanced QSIG in the IP network 34
9.5.1 Architecture 34
9.5.2 Aspects requiring further study or standardization work 34
10 Connection of telephones to a PINX via an IP network 35
10.1 Architecture 35
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ISO/IEC TR 21890:2001(E)
10.2 Aspect requiring standardization work 37
11 Summary 37
Annexes
A - Overview and status of H.323 39
B - Overview and status of SIP 42
C - Overview of H.248 / MEGACO protocol 45
D - Architecture for Signalling Transport over IP-networks (SIGTRAN) 46

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ISO/IEC TR 21890:2001(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the
specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the
development of International Standards through technical committees established by the respective organization to deal with
particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work.
In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
The main task of technical committees is to prepare International Standards, but in exceptional circumstances a technical
committee may propose the publication of a Technical Report of one of the following types:
— type 1, when the required support cannot be obtained for the publication of an International Standard, despite repeated
efforts;
— type 2, when the subject is still under technical development or where for any other reason there is the future but not
immediate possibility of an agreement on an International Standard;
— type 3, when a technical committee has collected data of a different kind from that which is normally published as an
International Standard (“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they can be
transformed into International Standards. Technical Reports of type 3 do not necessarily have to be reviewed until the data they
provide are considered to be no longer valid or useful.
Technical Reports are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Attention is drawn to the possibility that some of the elements of this Technical Report may be the subject of patent rights. ISO
and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC TR 21890, which is Technical Report of type 3, was prepared by ECMA (as Technical Report ECMA TR/81) and
was adopted, under a special “fast-track procedure”, by Joint Technical Committee ISO/IEC JTC 1, Information technology, in
parallel with its approval by national bodies of ISO and IEC.
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ISO/IEC TR 21890:2001(E)

Introduction
This Technical Report investigates the interoperability of Private Integrated Services Networks (PISNs) and Internet Protocol
(IP) networks within the context of Corporate Telecommunication Networks. The purpose is to identify possible scenarios for
interoperation, problems that will have to be solved if particular scenarios are to be pursued further, and possible future
standardization activities in this area. It forms the foundation for further work in ECMA on this subject, including the
production of Standards where found to be required.
This Technical Report is based upon the practical experience of ECMA member companies and the results of their active and
continuous participation in the work of ISO/IEC JTC1, ITU-T, ETSI, IETF and other international and national standardization
bodies. It represents a pragmatic and widely based consensus.


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TECHNICAL REPORT ISO/IEC TR 21890:2001(E)


Information technology - Telecommunications and information exchange between
systems - Interoperation of PISNs with IP Networks


1 Scope
The purpose of this Technical Report is to investigate the interoperability of Private Integrated Services Networks (PISNs) and
Internet Protocol (IP) networks, with a view to identifying possible scenarios for interoperation, problems that will have to be
solved if particular scenarios are to be pursued further, and possible future standardization activities in this area. In particular,
the following aspects of interoperability are investigated:
� the interworking of PISNs and IP networks via a gateway;
� the connection of PISN components via IP networks.
For each of the above, aspects considered include architecture, addressing (including use of IP addressing), services, protocols,
security, quality of service and mobility. This is conducted within the context of leading standards for voice and multimedia
communication over IP networks, including ITU-T recommendation H.323, IETF Session Initiation Protocol (SIP) and ITU-T
recommendation H.248.
Possible future standardization activities resulting from this Technical Report can include work items relating to IP networks
and work items relating to PISNs, as well as work items concerned specifically with interoperability.
The dominant traffic in PISNs is voice, and therefore this Technical Report focuses on interoperability considerations for voice
traffic. However, many of the standards that support voice in an IP network are also applicable to multi-media traffic (e.g.,
voice, video and data). Although in many respects similar to voice, fax traffic has slightly different requirements and is not
explicitly considered in this Technical Report. It could be the subject of further study.
2 References
ISO/IEC 11571, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Networks - Addressing
ISO/IEC 11572, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Circuit mode bearer services - Inter-exchange signalling procedures and protocol
ISO/IEC 11579-1, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Part 1: Reference configuration for PISN exchanges (PINX)
ISO/IEC 11582, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Generic functional protocol for the support of supplementary services - Inter-exchange signalling
procedures and protocol
ISO/IEC 13864, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Specification, functional model and information flows - Name identification supplementary services
ISO/IEC 13868, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Inter-exchange signalling protocol - Name identification supplementary services
ISO/IEC 13869, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Inter-exchange signalling protocol - Call transfer supplementary service
ISO/IEC 13870, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Inter-exchange signalling protocol - Call completion supplementary services
ISO/IEC 13873, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Inter-exchange signalling protocol - Call diversion supplementary services
ISO/IEC TR 14475, Information technology - Telecommunications and information exchange between systems - Private
Integrated Services Network - Architecture and scenarios for Private Integrated Services Networking
ISO/IEC 15506, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network (PISN) - Inter-Exchange Signalling Protocol - Message Waiting Indication Supplementary Service
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ISO/IEC TR 21890:2001(E)
ISO/IEC 19460, Information technology - Telecommunications and information exchange between systems - Private Integrated
Services Network - Inter-exchange signalling protocol - Single Step Call Transfer Supplementary Service
ECMA TR/57, Private Integrated Services Networks
ETSI TS 101 313, Telecommunications and Internet Protocol Harmonization over Networks (TIPHON); Network architecture
and reference configurations; Phase II: Scenario 1 + Scenario 2
ITU-T Rec. G.107, The E-Model, a computational model for use in transmission planning
ITU-T Rec. G.711, Pulse Code Modulation (PCM) of voice frequencies
ITU-T Rec. G.723.1, Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s
ITU-T Rec. H.225.0, Call signalling protocols and media stream packetization for packet-based multimedia communication
systems
ITU-T Rec. H.235, Security and encryption for H-Series (H.323 and other H.245-based) multimedia terminals
ITU-T Rec. H.245, Control protocol for multimedia communication
ITU-T Rec. H.248, Gateway control protocol
ITU-T Rec. H.261, Video codec for audiovisual services at p ¥ 64 kbits
ITU-T Rec. H.320, Narrow-band visual telephone systems and terminal equipment
ITU-T Rec. H.323, Packet-based multimedia communications systems
ITU-T Rec. H.450.1, Generic functional protocol for the support of supplementary services in H.323
ITU-T Rec. H.450.2, Call transfer supplementary service for H.323
ITU-T Rec. H.450.3, Call diversion supplementary service for H.323
ITU-T Rec. H.450.4, Call hold supplementary service for H.323
ITU-T Rec. H.450.5, Call park and call pickup supplementary services for H.323
ITU-T Rec. H.450.6, Call waiting supplementary service for H.323
ITU-T Rec. H.450.7, Message waiting indication supplementary service for H.323
ITU-T Rec. H.450.8, Name identification supplementary service for H.323
ITU-T Rec. H.450.9, (draft) Call completion supplementary services for H.323
ITU-T Rec. Q.921, ISDN user-network interface - Data link layer specification
ITU-T Rec. Q.931, ISDN user-network interface layer 3 specification for basic call control
IETF RFC 791, Internet Protocol (IP), version 4
IETF RFC 1034, Domain names - Concepts and facilities
IETF RFC 1035, Domain names - Implementation and specification
IETF RFC 1889, RTP: a transport protocol for real-time applications
IETF RFC 2205, Resource ReSerVation Protocol (RSVP) - Version 1 functional specification
IETF RFC 2246, The TLS Protocol Version 1.0
IETF RFC 2251, Lightweight Directory Access Protocol (version 3)
IETF RFC 2326, Real-time streaming protocol (RTSP)
IETF RFC 2327, SDP: Session Description Protocol
IETF RFC 2401, Security Architecture for the Internet Protocol
IETF RFC 2402, IP Authentication Header
IETF RFC 2406, IP Encapsulating Security Payload (ESP)
IETF RFC 2407, The Internet IP Security Domain of Interpretation for ISAKMP
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ISO/IEC TR 21890:2001(E)
IETF RFC 2408, Internet Security Association and Key Management Protocol (ISAKMP)
IETF RFC 2460, Internet Protocol, Version 6 (IPv6) Specification
IETF RFC 2475, An architecture for differentiated services
IETF RFC 2543, SIP: Session Initiation Protocol
IETF RFC 2719, Framework architecture for signaling transport
TIA/EIA/IS-811, Telephone Terminal Equipment - Performance and Interoperability Requirements for Voice-over-IP (VoIP)
Feature Telephones
TIA/EIA/TSB-116, Voice Quality Recommendations for IP Telephony
3 Terms and definitions
For the purposes of this Technical Report the following definitions apply.
3.1 Corporate telecommunication Network (CN) : Sets of equipment (Customer Premises Equipment and/or Customer
Premises Networks) that are located at geographically dispersed locations and are interconnected to provide telecommunication
services to a defined group of users.
NOTE - A CN can comprise a PISN, a private IP network (intranet), or a combination of the two.
3.2 Internet : A public IP network.
3.3 Intranet : A private IP network.
3.4 Internet Protocol (IP) : The protocol specified in RFC 791 (IP version 4) or in RFC 2460 (IP version 6).
3.5 IP network : A public or private network offering connectionless packet-mode services based on the Internet Protocol (IP)
as the network layer protocol.
NOTE - The Internet is the prime example of a public IP network.
3.6 Private Integrated Services Network (PISN) : A private SCN.
3.7 Private Integrated services Network eXchange (PINX) : See ISO/IEC 11579-1.
3.8 Switched Circuit Network (SCN) : A public or private network offering connection-oriented circuit-mode
telecommunication services.
3.9 Tunnelling : A means of transporting protocol information between two entities that are interconnected by a network,
without the need for that interconnecting network to comprehend the transported protocol information.
4 Acronyms
AC Admission Control (functional entity)
AH Authentication Header
BICC Bearer-Independent Call Control
CC Call Control (functional grouping)
CLIP Calling Line Identification Presentation
CLIR Calling/connected Line Identification Restriction
CN Corporate telecommunication Network
COLP Connected Line identification Presentation
DHCP Dynamic Host Configuration Protocol
DNS Domain Name System
ESP Encapsulating Security Payload
GK Gatekeeper
GW Gateway
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ISO/IEC TR 21890:2001(E)
HLS Higher Layer Signalling (functional entity)
HTTP Hyper-Text Transfer Protocol
ICC Inter-PINX Connection Control (functional grouping)
ICN InterConnecting Network
IP Internet Protocol
IPC Inter-PINX Connection
IPL Inter-PINX Link
IR Identity resolution (functional entity)
ISAKMP Internet Security Association and Key Management Protocol
ISDN Integrated Services Digital Network
ISUP ISDN User Part (of SS7)
IVN InterVening Network
IW InterWorking (functional entity)
LAN Local Area Network
LDAP Lightweight Directory Access Protocol
LLS Lower Layer Signalling (functional entity)
MG Media Gateway
MGC Media Gateway Controller
MP Mapping (functional grouping)
MPP Media processing and packetization (functional entity)
MTP Message Transfer Part (of SS7)
PINX Private Integrated services Network eXchange
PISN Private Integrated Services Network
PNP Private Numbering Plan
QoS Quality of Service
RAS Registration, Admission and Status
RC Resource Control (functional entity)
RC-P RC-Proxy (functional entity)
RFC Request For Comment
RGR Registrar (functional entity)
RGT Registrant (functional entity)
RTCP Real-time Transport Control Protocol
RTP Real-time Transport Protocol
SC Session Control (functional entity)
SCN Switched Circuit Network
SC-P SC-Proxy (functional entity)
SC-R SC-Redirect (functional entity)
SCTP Stream Control Transmission Protocol
SG Signalling Gateway
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ISO/IEC TR 21890:2001(E)
SIP Session Initiation Protocol
SSL Session Security Layer
SM Scenario Management (functional grouping)
SS7 Signalling System number 7
SW Switching (functional grouping)
TCP Transmission Control Protocol
TDM Time Division Multiplexing
TIA Telecommunications Industry Association
TLS Transport Layer Security
TRIP Telephony Routing Information Protocol
UDP User Datagram Protocol
URL Universal Resource Locator
VoIP Voice over IP
VPN Virtual Private Network
5 Introduction
5.1 Background
Private Integrated Services Networks (PISNs), based on 64kbit/s-based Time Division Multiplexing (TDM) techniques, have
for many years been the basis of corporate voice communications, and additionally have supported other services such as
facsimile, video and data (circuit-switched and packet-switched). The technology is similar to that of public Integrated Services
Digital Networks (ISDNs). More recently, the connection of virtually every desktop to a Local Area Network (LAN), the
growth of the Internet and the building of “intranets” and “extranets” have led to the desire to use these data networks also for
voice communications. There are a number of motives behind this, including cost savings (by the use of common wiring and
equipment) and the potential for applications that exploit the integration of voice, data and other media to the benefit of the
business.
The network layer protocol is of great importance in data networks, since it has to support a wide range of applications and the
higher layer protocols that they employ, whilst at the same time being able to operate over a wide variety of infrastructures.
Because of the growth of the Internet, the Internet Protocol (IP) has become the dominant network layer protocol. Although at
present version 4 of IP (IPv4, RFC 791) is almost universal, lack of address space and other considerations are creating a lot of
interest in version 6 (IPv6, RFC 2460). Except where otherwise stated, the term IP in this Technical Report refers to either
IPv4 or IPv6.
To carry voice over data networks, it has to be carried over IP, and hence the term “Voice over IP” (VoIP) has come into
being. Voice over IP can be used in a number of ways, including:
� end-to-end between terminal equipments attached to IP networks;
� between a terminal equipment attached to an IP network and a point of interworking with a PISN or other network;
� between two networks, in particular between two PISNs or between a PISN and another network;
� between two parts of the same network, in particular between two Private Integrated Service Network eXchanges (PINXs)
belonging to the same PISN; or
� between a terminal equipment and its point of attachment to its serving network, in particular between a terminal
equipment and its serving PINX.
From this list it can be seen that PISNs can interoperate with IP networks in a number of different ways, and this is the subject
of this Technical Report. The Technical Report focuses chiefly on voice, this being the service most often provided by a PISN.
In particular, this means that packet mode aspects of PISNs are not considered.
Figure 1 shows an example illustrating these different means of voice communication through an IP network. The IP terminal
equipments have direct access to the IP network, telephones 1 and 2 have access to the IP network through a gateway (labelled
as gateway type 1) and PINXs A and B have access to the IP network through a gateway (labelled as gateway type 2). All these
entities can communicate with each other through the IP network using the respective gateways.
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ISO/IEC TR 21890:2001(E)
In addition, PINX A and PINX B may be able to communicate with each other via the IP network using gateways that provide
special support for inter-PINX communication. For this purpose PINX A and PINX B are shown as being attached to the IP
network also through gateways labelled as gateway type 3.
Finally, telephones 3 and 4 are shown as being served by PINX B, access being achieved via the IP network using gateways
(labelled as gateway type 4 on the telephone side of the IP network and gateway type 5 on the PINX side of the IP network).
These telephones cannot make and receive calls directly through the IP network to other destinations (e.g., IP terminal
equipments) but make and receive all calls via PINX B.
NOTE - Although these different gateway types have functional differences, there may also be substantial similarities in practice between
some of these types. Also a physical realisation of a gateway might incorporate more than one of these gateway types.
IP terminal IP terminal
equipment equipment
Telephones 1 and 2
Gateway
type 1
Gateway
type 2
PINX A
IP network
Telephones 3 and 4
Gateway
type 3
Gateway
type 4
Gateway Gateway Gateway
type 5 type 2 type 3
PINX B

Figure 1 – Example of voice communication through an IP network
Gateway type 2 can be used for interworking between PISNs and IP networks, which is considered in clause 8. Gateway type 3
can be used for interconnecting PISNs or PISN components via IP networks, which is considered in clause 9. Gateway types 1,
2, 4 and 5 can be used for connection of (remote) telephones to a PINX via an IP network, which is considered in clause 10.
5.2 Types of network
An IP network operates in packet mode, since information is sent in packets, when information is available, rather than as a
continuous stream. Each packet is routed individually, rather than being switched in accordance with a pre-established
connection. This makes an IP network a connectionless packet network.
This contrasts with a PISN, where information is transmitted along the path of a pre-established connection (connection-
oriented). A PISN can operate in circuit mode, where information is transmitted as a continuous stream of bits, or in packet
mode, where information is sent in packets. In the case of voice, circuit mode is used, and therefore this Technical Report
regards a PISN as a private connection-oriented circuit mode network.
Similar considerations apply to public ISDNs, which can be regarded as public connection-oriented circuit mode networks.
Although the focus of this Technical Report is on PISNs interoperating with IP networks, public ISDNs have to be considered
in the overall picture.
An IP network can provide services to a limited set of users (in a corporation), and therefore can be considered to be a private
IP network (or intranet). Alternatively an IP network can provide services to the general public (as is the case with the existing
Internet), in which case it can be considered to be a public IP network (or Internet). The term “extranet” is often used to
describe an intranet that is spread over multiple administrative domains. “Extranets” are not considered further in this
Technical Report.
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ISO/IEC TR 21890:2001(E)
A Corporate telecommunication Network (CN) can comprise a PISN, an intranet, or a combination of the two.
Based on these considerations, this Technical Report uses the following terminology:
� switched circuit network (SCN): a PISN or public ISDN offering connection-oriented circuit-mode services;
� IP network: a public or private network offering connectionless packet-mode services based on IP as the network layer
protocol.
Therefore in examining the interoperability of PISNs and IP networks, this Technical Report focuses on the interoperation of
SCNs and IP networks, with particular emphasis on Corporate telecommunication Networks.
5.3 Arrangements for interworking of SCNs and IP networks
Figure 2 illustrates possible interworking between the following types of network:
• private switched circuit network (PISN);
• public switched circuit network (public ISDN);
• private IP network (intranet);
• public IP network (Internet).
Circuit network IP network
(connection-oriented, (connectionless,
circuit-mode) packet mode)
public ISDN Internet
Public
network
I
II III
VI
V
PISN intranet
CN
IV

Figure 2 – Interworking arrangements
Arrangements I to VI are listed in table 1, along with their coverage in standards bodies and their security implications.
Table 1 – Interworking arrangements
No. Description Coverage in standards bodies Security implications
I public ISDN / Internet No CN impact, outside the scope of No CN impact, outside the scope of
this Technical Report and covered this Technic
...