° Nine VHF-FM channels (Nos. 24, 25, 26, 27, 28, 84, 85, 86, and
87) have been allocated by the FCC for use as public correspondence
channels for maritime mobile service (see Table 3-1). Each
25-kHz channel could provide full duplex operation between ships
and the shore, although half-duplex operation is commonly used
due to equipment availability and because such equipment is
considerably lower in cost. This is particularly true for the
ship equipment.

Table 2

Public Correspondence VHF Channels
Allocated for Maritime Mobile Service
in the U. S.

Frequency in MHz

Channel Ship Shore
24 157.000 161.800
84 157.225 161.825
25 157.250 161.850
85 157.275 161.875
26 157.300 161.900
86 157.325 161.925
27 157.350 161.950
87 157.375 161.975
28 157.400 162.000

Coast stations use various methods to interface with the public switched
networks. One common method is the phone patch shown in Figure 4. A phone
patch provides an interconnection between the radiotelephone system and an
access line to the telephone network. The phone patch may be used at both
ends of a radio link, i.e., to the on-board telephone system in the ship as
well as for the interconnection to the telephone network at the coast
station. Usually the phone patch is hardwired although sometimes acoustic
coupling may be employed. A hardwired patch is permitted if the equipment
is type approved and registered by the FCC, otherwise a voice connecting
arrangment or protective network is required. Telephone company tariffs

12


There are three basic classes of long-distance calls. The least
expensive is a direct-dial, station-to-station call. Timing starts as soon
as the telephone is answered. Operator involvement for billing purposes in
offices without automatic recorders does not change this class of call.
Station-to-station calls requiring operator assistance to place the call,
e.g., credit-card calls and collect calls, are tariffed at a higher rate.

A person-to-person call is the most expensive, but timing only starts when
the desired person is reached.

The charge rate increases with distance and the duration of a call.
The minimum charge is three minutes for all operator-assisted calls and one
minute for direct-dialed calls. An incremental charge is added for each
additional minute in both cases.

Full rates are charged for interstate calls within the continental
U.S. between 8:00 A.M. and 5:00 P.M. on Monday through Friday. A 35%
discount from the full rate is applied from 5:00 P.M. to 11:00 P.M, Sunday
through Friday. A 60% discount is applied during the remaining hours
(AT&T, 1977).

The telephone industry has both local and centralized systems in many
offices for automatically recording (ticketing) the charging information.
Ticketing data usually includes:

1. Class of service

2. Caller's number (7 digits)

3. Called number (7 or 10 digits)

4. Date and time

5. Call duration

6. Billing number.

Local-Automatic-Message-Accounting (LAMA) systems are located in
class 5 offices. Centralized-Automatic-Message-Accounting (CAMA) systems
are located in class 4 or higher level offices. The calls for several
class 5 offices may be handled by one CAMA-equipped office. (AT&T, 1975)

Bulk billing is used for single and multi-unit short-haul calls. The
customer is charged on the basis of total message units used during a
billing month.

33


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29


7.5. Internetting

The study reported here is primarily concerned with interfacing the
AMMTS with the U. S. public switched telephone network for public correspond-
ence. International record carriers and foreign administrations offer
teletype (TELEX,TWX) and cablegram services to compatible terminals around
the world. There are also a number of specialized common carriers and
value-added networks in the U. S. and overseas. These networks offer
various types of switched services to specialized users including data,
facsimile, and video signal transmissions.

The AMMTS development program should recognize that ultimately it may
be desirable to be able to interconnect with these other networks in addition
to the public switched telephone network. The impact of such internetting
on the AMMTS should be considered as the system evolves.

7.6. Location Registration

The location registration system must be able to accommodate some
special features. For example, some ships, for commercial or other reasons,
may not wish for any land subscriber to be able to determine its location
by merely calling into the system, or to be called by anyone except certain
specific parties. This can, to some extent, be compared to an "unlisted"
number. Another example might be ships that wish to be registered at all
times with their "home" coast station regardless of whether they are actually
in the normal or assigned service area of that coast station. Methods for
incorporating these restrictive features need to be evaluated.

7.7. Cost

A basic issue involving cost is financing the establishment of Regional
and National Maritime Centers and any investments made by the common carriers
to extend specialized service to coast stations. One method of financing
would be a pay-as-you-go basis, i.e., implementation of AMMTS would occur
on a gradual and probably fragmented basis as individual maritime mobile
service providers decided that their traffic load and revenues warranted
automation of their services. Local, regional, and national location
registration would come into being as the need arose and agreement on sharing

38


hierarchy below the class 5 (end office) level could be considered as a
"class 6" level. Examples of this level include Private Automatic Branch
Exchanges (PABX) serving office complexes or a coast station serving the
maritime community.

This outside access to the network requires access lines to an end
office, with the end office usually providing the accounting functions,
line test facilities, and dc dial pulse or dual-tone multifrequency (DTMF)
signaling capabilities normally associated with subscriber line type connec-
tions.

2.1. Numbering Plan

Table 1 indicates some common dialing procedures currently in use in
the United States, Canada, and parts of Mexico. Some variations exist due
to the variety of switching equipment still in use. The North American
continent is divided geographically into Numbering Plan Areas (NPAs) and
each area is assigned a 3-digit code. Subscriber connections within a
given area (i.e., those having the same area code) are considered to be in
a Home Numbering Plan Area (HNPA). Subscribers calling within a HNPA need
not dial the area code but may need to dial a 1 prefix. Direct-dialed
connections to a "Foreign" Numbering Plan Area (FNPA) usually requires the
subscriber to dial a prefix 1, followed by a 3-digit area code. In addition
to this, a 3-digit office code and a 4-digit station code must be dialed.
Together these 10 digits provide a unique address (i.e., national number )
for each telephone.

For operator assisted calls such as person-to-person calls, collect calls,
credit-card calls, and third-number billing calls, the prefix 0 is used.

Toll-switching offices (i.e., those above class 5) generally use step-
by-step, crossbar, or electronic switches with common control. The signaling
equipment from these switches is technically capable of registering 13 to
15 digits although they are usually required to outpulse no more than 10 to
12 digits. The more recently designed electronic switches are arranged to
handle only 10 digits. Digit deletion, substitution or addition is feasible
between certain offices. It is possible to delete an office or area code,
for example, when pulsing into that office or area (AT&T, 1975).


-il-
(Doc. 8/368-E) Netherlands 8/5/2

If an N-subscriber wants to contact a ship of the nationality N, and
assumes that the ship is located within the service area of the MSC)
he dials the ship station number, preceeded by 87S).

The dialled ship station number is accepted by an input register at
the MSC, where it is checked on nationality and of presence in the LR.
If the assumption appears to be correct, the call is routed to the
appropriate BS or CS, and the subscriber is charged in accordance
with the "national tariff".

If, however, the ship cannot be served by any N-station, the call is
diverted either to the manual operated exchange or to an automatic
answering device. In both cases the subscriber is informed that if he
still wants to contact that ship, he then has to dial anew the ship
station number, preceeded by 878,- He will be charged in accordance
with the "international tariff".

So in this system two tariffs are considered. If more numbers of the
range 870-879 are used for this service, the number of tariffs can

pe extended accordingly.

In any case, supplementary taxes like coast- tax, may be included

in ‘the tariffs.

If the N-subscriber dials the ship station number of a non-N-ship
e.g- an X3-ship, using the 87S, access, the MSC, checks whether this
ship is listed in its LR. If so, the same procedure is used as if
an N-ship were dialled.

In case the ship requested is not registered in the LR of MSC, the
call is diverted to either the answering device or to the manual
exchange. In both cases the subscriber is informed of the absence
of the ship in the N-list.

If, nevertheless the subscriber wishes to contact the ship, he has
to dial again via the 878. access. He then will be charged in
accordance with the "international tariff".

The MSC, routes the call to the MSC,

If willbe clear from the procedure description that it is essential
to detect in an easy way the nationality out of the ship station

number.

48


-9-
(Doc. 8/368-E) Netherlands 8/5/2

2. PROPOSED SYSTEM FOR AN AUTOMATED MARITIME MOBILE TELEPHONE SERVICE

2.1 A "Maritime Switching Centre" (MSC) is introduced in each nationa-

lity.
2-14-74

Subscribers of the national telephone network that wish to
contact an MSC, have only access to their national MSC.
This is realized via the international prefix (P,) of that
country (09 in the Netherlands, OO in Belgium, OO in the
Federal Republic of Germany etc.), followed by the "country
code" 87.

The range 870-879 is allocated to the Maritime Mobile Service.
The codes 87845 878, and 878, are used in the Maritime
Mobile Satellite Service; the codes 875, and 878, be
assigned to the Maritime Mobile Service.

Subscribers of the national telex network have access to
the same national MSC in a similar way, using the
"destination codes" 58T,, 581, and 58T, for the Maritime
Mobile Satellite Service and 58, and 58T,, for the Maritime
Mobile Service.

Each MSC has, via the existing international telephone net-
work access to the MSC of any other nationality.

Similarly, for telex the MSC of another nationality can be
reached by the national MSC via the existing international

telex network.

Figure 1 shows a Maritime Switching Centre and its access terminals.

The arrangement of the MSC (located in the country N)

In this document the arrangement of the MSC arid the procedures

will be described for shore to ship telephony only.

2.2.1

The MSC is linked with all the national Coast Stations (GS)
and Base Stations (BS) by means of fixed connections.

(See figure 2.)

This means that MSC), controls all the transmitting and all
the receiving stations employed in the National Maritime
Mobile Service.

Inter-MSC traffic is provided via the international tele-

phone network (para 2.1.3).

46




- 28 -
COM I-No. 99-E
COM II-No, 107-E
GM/SMM-No. 52-E

4, Assignment of nationality identification digits

Each NID represents a discrete capacity assigned according to a plan that
relates assigned capacity to ship population. The plan is to be developed by a
competent World Administrative Radio Conference (WARC) and administered by the
Secretary-General of the ITU.

5. Coast/Shore station identit;

The coast/shore station identities may be derived from the pool of the
ship station identities assigned to each country.

6. Broadcast calls

X, = 0 is assigned to indicate a broadcast call to a group of ships having
a community of interest. Such calls may be barred in the public switched network
and/or at the coast/shore stations. Control of broadcast calls may also be achieved

by the use of special broadcast service access to the coast/shore stations,

T Future expansion of the ship station identification system

X, = 1 as in the format 1 XXXXXXXX has been reserved for future expansion,

8. Evolutionary expansion of ship station identities as applied to
Maritime Mobile (Terrestrial) Services

8.1 The plan permits the identification of ships whose communications
requirements are inter-regional, regional or national. The plan is intended to allow
the automation of Maritime Mobile Services on public switched networks, where feasible,
as the demand for ship station identities increases for the automatic service. This
demand is considered in stages defined by the number of digits in ship station numbers
required to satisfy automatic communication needs. A minimum number of digits is
used for ship station numbers at any given time to permit countries with network
restrictions to provide a maximum of automation. Trailing zeros are added to the
ship station numbers (received from an automatic network) to form 9-digit ship
station identities on the radio path. The X1XpX3 digits are shown as Nationality
Identification Digits in the following illustration.

56
(1446)




to provide automated YHF service over certain portions of the Great Lakes
(Lorain, 1975). Alternatives to the Great Lakes system are also described
along with some of their advantages and limitations.

Since access procedures have considerable impact on the connection
time these procedures should be designed to be simple to use and preferably
the same as the procedures commonly used for normal access to the public
network. The procedures may vary to some extent depending on 1) the orgin-
ation of the call (ship or shore); 2) the equipment used (push button or
rotary dial); 3) the numbering plan employed; 4) the land subscriber's
a priori information concerning the vessel's location, the vessel's access
number, and the telephone number of the accessing coast station, and 5) the
network topology.

The case of a land subscriber calling a ship is the most difficult
problem as the ship's number, in general, may not fit in the national
telephone numbering plan. Paragraphs 5.1 and 5.2 describe two general
concepts to overcome this problem, separated as to whether a one-step or
two-step dialing procedure is required on the part of the calling land
subscriber.

For a fully automated system in which no customer a priori knowledge
of the ship's location is required, some form of ship location registration
is required. This is briefly discussed in paragraph 5.3.

Access to the public switched network by a ship subscriber is relatively
straightforward as the called land subscriber is identified by a number
in the national numbering plan. Thus, the access problem reduces to making
the ship-to-coast station link appear to be an extension of the telephone
plants' local loop. Concepts for accomplishing this are discussed in
paragraphs 5.4, 5.5, and 5.6.

5.1 One-Step Dialing

To fully meet the requirement that the system should perform in a
manner similar, if not identical, to the existing public switched network the
calling subscriber preferably should be allowed to dial, following the

16


Wide Area Telephone Service (WATS) is a special switched service
offered by the Bell system, for a bulk discount. The service is designed
for customers who make or receive large numbers of calls to or from a
geographic area. There are two service offerings -- outward WATS and
inward WATS. Outward WATS allows the user to dial a certain geographic
area within the U.S. at a rate lower than a corresponding DDD call. A
minimum usage charge per month is applied. Inward WATS service is similar
except the caller dials a special area code which connects the caller to
the WATS line in the customer's location. Customer costs are based on the
service area covered and the hours of service, and the caller is not charged.

It is also possible to lease lines. Leased lines are private-line
circuits provided by the major common carriers on a monthly rental basis.
They are commonly known by a series number which indicates the bandwidth
and service grade. Series 2000 circuits, for example, are voice-grade,
voice-only circuits.

6.2. Maritime Mobile Radio Services

Ships may be connected to any telephone in the public network via a
coast station and the appropriate land telephone central office (usually
class 5). The charges for the radio portion of these calls are based on
tariffs filed with the FCC. The maritime mobile tariff is based on air
time used. Thus, the FCC requires a log of shore station operations includ-
ing a record of actual air time used by the customers.

For the radio service, the Great Lakes system (Lorain, 1975) has
considered a flat rate or contract service for large users of that system
to encourage use during slack periods. The contract service offers the
system facilities to users of public channels at a fixed monthly rate
without restricting the number of calls. Some tariffs provide a lower rate
for certain limitations on use, such as night calls only. Other tariff
provisions encourage certain types of calls during hours when channel usage
is low.

Interconnections to the public network are usually made through a
coast station's telephone to a local central office via subscriber lines.

34


TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF ACRONYMS

ABSTRACT

BACKGROUND

CHARACTERISTICS OF THE U.S. SWITCHING ENVIRONMENT
2.1 Numbering Plan

2.2 Performance

CHARACTERISTICS OF MARINE RADIO SERVICE
DESIRABLE FEATURES AND PARAMETERS

INTERFACING CONCEPTS

-1 One-Step Dialing

2 Two-Step Dialing

3 Ship Location Registration

-4 End Office Connection

5 End Office with Regional Control Center

6

aAaaaa»n4»ana

.7 Examples of Detailed Access Arrangement
RATE STRUCTURE
6.1 Common Carrier Services
6.2 Maritime Mobile Radio Services
INTERFACE ISSUES
.1 Channel Allocations
Co-channel Interference and Co-Channel Sharing
Range Extension
Performance
Internetting
Location Registration
Cost
Rates and Rate Structuring

NN NNNNNN
ON AO FWD

End Office with Regional and National Control Center

Page
vii
vii

viit

Onna =

15
16
19
20
21
24
27
31
31
31
34
35
35
36
37
37
38
38
38
39


5.6. End Office With Regional and National Control Center

It is possible to envision a hierarchical control network for coast
stations similar to the one for the public switched network given in
Figure 1. The various levels for a hierarchy of coast station centers are
shown in Figure 8. Note that the national center could be co-located with
a regional center and that regional centers could be co-located with a coast
station.

Ship-to-shore calls could still be accomplished in the same manner as
in the previous cases except that, if the interconnections between coast
stations, regional centers and national center consists of leased lines, it
might be economically advantageous to use these lines as much as practicable
for ship-to-shore connections as well.

However, the cost of leased lines for this hierarchical structure is
probably prohibitive on a national basis (in the U.S.) due to the large
number of public correspondance coast stations, and it would be more practical
to use the public switched network itself for the interconnections on an
"as needed" basis.

Figures 9 and 10 show two of several possible configurations using the
public switched network for all major interconnections. The dotted inter-
connections in Figure 10 between coast stations and regional center are
analogous to the control (order) lines in the Great Lakes system. The
choice of the actual final configuration will depend primarily on economic
and historical growth considerations, and may be subject to change as the
economic factors change. It must also be noted that Figures 9 and 10 are
not mutually exclusive; i.e., a final system could comprise elements of
both.

Internal connections between centers using the public switched network
can always be established using two-step dialing as it would be practical
for any center in the system (i.e., coast stations, regional centers and
national centers) to be equipped for DTMF dialing.

If the land subscriber is to be provided with one-step dialing, access
to the system must always be via the national center, as was discussed in
paragraph 5.1. With two-step dialing for the land subscriber, as described
in paragaraph 5.2, the system could, in principle, be entered at any level,
i.e., national center, regional center, or coast station.

27


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5.2 Two-step Dialing

As an alternative to one-step dialing, two-step dialing can provide
for gradual introduction of the fully automated telephone service since the
incompatibility of an 8- or 9-digit ship identification number with the
national numbering plan can then be circumvented. With two-step dialing,
the calling land subscriber first dials the telephone number of a specific
coast station, regional center, or national maritime switching center, as
appropriate.

When the called station or center is reached, the calling subscriber
hears a second dial tone and then dials the ship identification number,
which may consist of any number of digits, after which the circuit to the
called vessel is set up.

One major advantage of the two-step procedure is that it does allow
implementation on a gradual basis. In the simplest form, individual coast
stations could go automatic. This would, of course, require the land
subscriber to know that the vessel he is calling is accessible through that
coast station.

In the next evolutionary step, a number of coast stations could form a
‘regional or semi-regional service. This process could continue until full
national coverage is attained. The Great Lakes-wide VHF Automated Radiotele-
phone System might be considered an example of a system falling in between
the first and second step. Each of the constituent (unattended) coast
stations provides fully automated service, and a common control center
provides operator assistance and manual call control, as well as system-
wide administrative and operational control.

The major disadvantage of the two-step dialing is that, in general,
the telephone network, after completion of the first step, establishes a
voice-frequency circuit that normally does not pass further dc dial pulses.
There is, of course, no problem if the land subscriber is equipped with
DTMF dialing facilities or special DTMF dialers that can be attached to
rotary dial telephone sets. However, not all end offices, as yet, are
capable of handling DTMF dialing.

19


initially may require an operator's assistance but ultimately it
is desirable that such contacts also can be made by automatic means.

° The system and the public correspondence channel being used
should be capable of operating with either automated or manual
terminals.

Technical

° The AMMTS should be compatible with the existing public switched
network and be adaptable to other networks in the future, including
record carriers and specialized common carriers.

° It is preferred that common channel(s) be provided for digital
signaling during the access phase and separate (working) channnel(s)
be used for the information transfer phase. This may not always
be feasible; e.g., in areas where the channels allocated for
public correspondence are limited and the traffic load is high, or
conversely, in areas where the traffic load is so low that alloca-
tion of separate calling and working channels is not justifiable.

° A standard signaling technique (modulation, format, and coding)
is required for national and international system compatibility.
The digital selective calling system described by CCIR (1978a)
and de Haas (1977), could serve as the common calling channel
signaling.

° A universal numbering plan is necessary for vessel identification,
and a standardized location registration plan will be required
for selective calling.

5. INTERFACING CONCEPTS

In order to discuss interface concepts, it is necessary to describe
the basic access procedures necessary for automated radio-telephone service.
Some of these procedures have already been implemented by a private corporation

15


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o<—— START ACCESS
l.6sec.

9<—— START DIALING

7.0sec.

END DIALING

10.5sec,

RING
46sec.

DISCONNECT 8.5 sec.

O<—— ANSWER

Figure 3. Mean access time on DDD network using pushbutton DTMF dialer.

10


-~ 26 -
COM “I-No. 99-E
COM II-No, 107-E
GM/SMM-No, 52-E

c) that the same unique ship station identity should be used for all
telecommunication services, particularly for radiotelex and radiotelephony;

a) that it is desirable that the ship station mumber and the ship station
identity be the same;

e) that the capacity of the ship station identification system shall be
sufficient to admit all ships wanting, or required, tc participate in the various
Maritime Mobile Services at present and in the foreseeable future;

f) that access to Maritime Mobile Services via the existing international
network in automatic operation should follow the relevant and appropriate CCITT
Recommendations;

g) that the ship identity system shall be a numerical system, and should use
the full range of decimal digits;

h) that two or three of the digits, X)%X> of the ship station identity shall
indicate the ship's nationality;

i) that there are important differences in national networks that promote
different approaches to automation of Maritime Mobile Services;

j) that a numerical assignment Plan should consider current telephone and
telegraph network limitations while it permits change to support future requirements.

2. Ship station identification
: . -, 1) 2) 3)
2.1 Ship station identity

Ship station identity is established as nine digits. It should be assigned
to take into account the implications relating to it in the public switched networks.

Xj KKK KX hey

The initial three digits define the nationality of the ship as indicated in the
following sections.

2.2 Ship station number

The ship station number defines the ship station within the public switched
network and this information is transmitted to a coast or shore station. In the
Maritime Mobile (VHF) Service the ship station number may be different from the
ship station identity to relate to national network needs.

1) Subject to further consideration by CCIR of radio path aspects.

2) A seven digit ship station identity is used in the current generation of
Maritime Satellite System.

3) Some international telex centres are limited to 7 digits and the presently used
Maritime Satellite System employs only 7 digits for ship identification.

54
(1446)


2. CHARACTERISTICS OF THE U.S. SWITCHING ENVIRONMENT

The public switched telephone service and the maritime communication
service in the U.S. have distinct characteristics which differ from many
other countries. It is necessary to interface the two types of service in
order to extend automatic telephone service beyond its present limits. The
establishment of these interface requirements involves our understanding of
the unique character of these services if the needs of the U.S. and the
international maritime community are to be satisfied with the most economical
system.

In most countries outside North America the telecommunications networks
are almost exclusively controlled by government departments or semi-governmental
corporations; for example, Postal, Telegraph and Telephone (PTT) admini-
strations, Post Office corporations, etc. However, in the United States
public voice and record telecommunications services are predominantly
provided by the private sector, i.e., private operating agencies, often
referred to as common carriers.

Distinct characteristics of the public switched network in the U.S.
which should be considered include the following (Polishuk, 1977; AT&T,
1975; CCM, 1975):

° Telecommunication services and equipment manufacture (e.g.,
telephone service, record transmission, satellite transmission
facilities, mobile radio communications) are furnished by
private industries.

° All commerce in communications (interstate and international) by
radio and wire is regulated by the Federal Communications Commission.
This includes approval of rate structures for the various service
offerings, frequency allocations, and station licensing.

0 The largest private industry is the telephone service industry
with over 150 million telephones in service (as of January 1977).
The 23 operating companies of the Bell System supply 80 percent
of the telephones in service. The other 20 percent of the tele-

phones in service are furnished by some 1600 so-called independent
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Figure 1.
Figure 2.
Figure
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Table 1.
Table 2.

LIST OF FIGURES

Switching centers in North American hierarchy.
Basic end office switching system.

Mean access time on DDD network using pushbutton
DIMF dialer.

Typical arrangement for hardwire phone patch
connection to public switched network.

Network access via end office switching centers
Network access via regional centers.

Network topologies for access polling.
Hierarchical coast station network.

Network access arrangement via regional centers and
a national center with regional star configurations.

Network access arrangement with regional and national
centers in a distributed configuration.

Maritime access arrangement.

LIST OF TABLES

Common Dialing Procedures in North America

Public Correspondence VHF Channels Allocated
for Maritime Mobile Service in the U. S.

vii

PAGE

10

13
22
25
26
28

29

30
32

12


REFERENCES
APPENDIX A.

APPENDIX B.

TABLE OF CONTENTS (Cont'd)

AUTOMATED (VHF) MARITIME TELEPHONE SYSTEM,
NETHERLANDS CONTRIBUTION 8/5/2 to CCIR/WP8/5

DRAFT RECOMMENDATION ON COMMON SHIP STATION
NUMBERING SCHEME, CCITT AD HOC JOINT WORKING
PARTY I/II

vi

40

43

51


business needs of the maritime community.

There are approximately 230 VHF-FM public correspondence stations
in the U.S., 40 percent of which are owned by telephone companies.

There are approximately 40,000 km of coastal and inland waterways
carrying marine traffic. The navigable distance on inland rivers
(e.g., Mississippi, Missouri, Ohio, Illinois, Tennessee, etc.) is
over 8,000 km. The combined area of the Great Lakes is about
245,000 square kilometers.

Large numbers of commercial and recreational vessels may be
expected to require access to the public switched network in the
future. Over 270,000 vessels were licensed by the FCC for VHF
equipment by January 1977.

The communication traffic over public correspondence channels
varies both temporally and spatially. Channel overloading
occurs in many areas and at certain times as the result of large
changes in the number of pleasure craft using communications
facilities.

VHF coverage is limited because of the limited number of stations,
the large areas to be covered, and terrain factors which attenuate
the signals (e.g., rough terrain between bends in a river).

VHF channels are susceptable to interference from distant co-
channel stations due to ducting. Ducting may necessitate additional
channel allocations in certain areas irrespective of the traffic
loading requirements.

A network of automated VHF stations currently exists on the Great
Lakes for public correspondence service. Interconnection with the
public switched network is made directly through each Great Lakes
coast station to and from the nearest end office of the telephone

network.
1


INTERFACING THE AUTOMATED MARITIME MOBILE TELEPHONE SYSTEM
WITH THE
U. S$. PUBLIC SWITCHED TELEPHONE NETWORK

R. F. Linfield and T, de Haas*

This report summarizes the characteristics of the U. S.
public switched network and the maritime radio service,
which impact the development of an Automated Maritime Mobile
Telephone System (AMMTS). Features and performance parameters
which appear desirable to an AMMTS user are reviewed and
some basic system concepts capable of satisfying these user's
needs are presented. The interface between the public
switched network and coast stations serving the maritime
community is discussed in detail. Techniques for automatically
placing a call to ships whose location is unknown are described.
The development of an AMMTS involves a number of issues
which may be different in the U. S. than in other countries
of the world. The final section of the report defines some
issues requiring further study.

Key words: Maritime communications, automated telephone systems,
network interfacing

1. BACKGROUND

The International Radio Consultative Committee (CCIR) is studying the
functional requirements, operational characteristics and technical specifi-
cations for Automated VHF/UHF Maritime Mobile Telephone Systems (AMMTS).

This report summarizes some of the concepts, issues, and. alternatives
which should be carefully considered in developing such a system. The emphasis
is on the interface between the U.S. public switched network and the maritime
public correspondence radio telephone. The characteristics of these two
facilities in the U.S. are discussed first since they differ considerably from
most countries of the world. Then, some of the basic requirements for an
automated mobile maritime telephone service are summarized so that some pro-
cedures and techniques for meeting these requirements can be described. Finally,
some issues are raised which require further study so that the most economical
system satisfying the U. S. and the international maritime community can be

developed.

¥The authors are with the Institute for Telecommunication Sciences, National
Telecommunications and Information Administration, U. S. Department of Commerce,
Boulder, Colorado 80303.


appropriate long-distance or international access code, all necessary
digits identifying the called subscriber without interruption. The use of
an 8- or 9-digit ship station identification number* ‘is not compatible with
U.S. national numbering plans which allow at most only 4 digits for station
identification independent of geographical location designation (i.e., area
code plus office code) or service designation (e.g., inwards WATS service).
However, the digital capacity of the local office registers dealing with
international traffic is 12 digits. In addition, the "country code" 87 has
already been reserved for the maritime mobile service (CCITT, 1977a).

Thus, even if a third digit is reserved for service or tariff differentiation
within the maritime mobile service (e.g., terrestrial/satellite, national/
international), up to 9 digits would be available for subscriber selection.
A contribution by the Netherlands to CCIR IWP8/5, reproduced in Appendix A,
Proposes a system based on the use of country code 87. The unique feature
of this system is the assumption of a Maritime Switching Center (MSC) in
each country into which all land subscriber-dialed calls would be directed
for (automatic) routing to the called vessel via the appropriate coast
station. Thus, a land subscriber would dial as follows:

National
Maritime Ships
International Switching Station
Prefix Center Number
o1lt 87X XXXXXXXXX .

9 digits maximum
tin the U.S.

The 87X indicates maritime mobile service where X = 1, 2 or 3 for
maritime mobile satellite service and X = 4 or 5 for maritime mobile
terrestrial service, the 4 or 5 distinguishing the tariff used (e.g.,
national/international) .

*CCIR Interim Working Party IWP 8/6 is studying maritime mobile numbering
plans. Although no decision has been reached on this subject, it has
generally been accepted that unique identification of each vessel will

require at least 8 digits. CCITT Ad Hoc Joint Working Party I/II (common
ship station numbering scheme) has recommended a 9-digit ship station
identification number (CCITT, 1978), see Appendix B.

7


NTIA-REPORT-78-7

Interfacing the Automated

Maritime Mobile Telephone System
with the U.S. Public

Switched Telephone Network

R. F. Linfield
T. de Haas

U.S. DEPARTMENT OF COMMERCE
Juanita M. Kreps, Secretary

Henry Geller, Assistant Secretary
for Communications and Information

August 1978


8. REFERENCES

AT&T (1975), Notes on distance dialing, (American Telephone and Telegraph
Co., New York, NY).

AT&T (1977), Interstate long-distance calling guide, Bell System Publication,
PE 103, Sept.

CCIR (1978a), Digital Selective Calling System for Use in the Maritime
Mobile Service, Recommendation 493-1, CCIR XIVth Plenary Assembly,
Geneva.

CCIR (1978b), Automated VHF/UHF Maritime Mobile Telephone Systems, Report
587-1, CCIR XIVth Plenary Assembly, Geneva.

CCITT (1977a), Numbering Plan and Dialing Procedures in International
Service, Recommendation E,.161, Vol. I1.2, CCITT Sixth Plenary Assembly
(Orange books), Geneva.

CCITT (1977b), Specifications of Signaling Systems Rl and R2, Recommendations
Q.310 to Q.331, Vol. VI.3, CCITT Sixth Plenary Assembly (Orange books),
Geneva.

CCITT (1977c), Specifications of Signaling Systems No. 6, Recommendations
Q.251 to Q.295, Vol. VI. 2, CCITT Sixth Plenary Assembly (Orange
books), Geneva.

CCITT (1977d), Telephone Signaling and Switching, Recommendation Q.11
and Q.23, Vol. VI.1, CCITT Sixth Plenary Assembly (Orange books),
Geneva.

CCITT (1978), Ad Hoc Joint Working Party I/II [Common Ship Station
Numbering Scheme for Radiotelex and Radiotelephony (VHF and Satellite
Services)], Annex to the Report of the meeting held in Geneva, 15-
19 May, 1978; CCITT document COM I - No. 99/COM II No. 107/

GM/SMM No. 52.

CCM (1975), Guide to Communications Services, (Center for Communication
Management, Ramsey, Nd).

de Haas, T. (1977), Digital selective calling and direct printing techniques
in the mobile service, IEEE Trans on Vehicular Tech. VT-26, No. 3,
p. 202.

Duffy, F. P. and R. A. Mercer (1978), A study of network performance and

customer behavior during direct-distance-dialing call attempts in
the U.S.A,, BSTJ 57, No. 1, p. 1.

40


(4) REGIONAL

SECTIONAL

PRIMARY

TOLL

n
HIGH a
Ronee | Ke = AS
\ Uo
a (-
SE SAS
><
pone YG
4) C
TANDEM OFFICE
5

COAST STATION

SUBSCRIBER
TERMINAL

Figure 1.

5 ) END OFFICE

PABX

Switching centers in North American hierarchy.


(i.e., non-Bell System) operating companies. Several independent
operating companies are of a size serving over one million
telephones, such as General Telephone and Equipment (GTE),

United Telephone (UTC), Continental Telephones, and Central
Telephone and Utilities. On the other side of the scale, many
small independent operating companies serve only one community or
rural area with only a few hundred telephones.

Telephone industry standards are largely derived from Bell standards
and are not necessarily compatible with CCIR/CCITT standards.

There is an increased emphasis by the U. S. government to establish
competition in the telecommunications industry.

Telephone equipment, dialing equipment, switching equipment and
signaling equipment may differ throughout the network. For
example, step-by-step, crossbar, and electronic switching centers
may all be interconnected. Decentralized signaling, similar to
CCITT signaling system R1 (CCITT, 1977b), is used in large portions
of the telephone trunking network in the U.S. In this system the
signaling information is progressively carried forward over the
same trunk circuits that will form the end-to-end connection. As
new switching centers are installed Common Channel Inter-office
Signaling (CCIS), similar to CCITT signaling system No. 6 (CCITT,
1977c) is gradually replacing the Rl system for signaling between
switching centers equipped with stored program control. CCIS is
based on central processing of all signaling information in the
switching center and transmission of the signaling information
over separate common signaling channels.

The hierarchical structures and associated class numbers given to

different leyels of switching centers in North America are shown in Figure 1.

Subscriber loops are normally terminated in end offices, which in turn are
interconnected via the hierarchical structures. The basic switching system
for an end office is illustrated in Figure 2. Access to the switching

3


- 25 -
COM I-No. 99-E
COM II-No. 107-E
GM/SMM-No, 52-E

ANNEX
DRAFT RECOMMENDATION

SHIP STATION IDENTIFICATION FOR VHF AND SATELLITE
MARITIME MOBILE SERVICES

1. Introduction
1.1 The purpose of this Recommendation is to specify a method by which an

internationally unique ship station identification may be assigned to all the ships
participating in the Maritime Mobile Services, and to facilitate the introduction of
international automatic VHF and Satellite Maritime Services.

1.2 Terminology

The following terms are used in this Recommendation :

a) Maritime Mobile (Terrestrial) Service : conventional Maritime Mobile Services
such as the HF Maritime Service and the VHF Maritime Service (as defined in the
Radio Regulations).

Maritime Mobile Satellite Service : as defined in the Radio Regulations.

bd) Coast station : radio station on land in the Maritime Mobile (Terrestrial)
Service.

Shore station : earth station on land in the Maritime Mobile Satellite
Service.

ce) Ship station identity : the ship's identification XK yee Ky transmitted on
the radio path. .

Ship station number : the number that identifies a ship for access from a
public network and forms part of the international number to be dialled or keyed by
a public network subscriber.

ad) Coast (shore) station identity : the coast (shore) station
identification XX) +. X transmitted on the radio path.

1.3 Basic considerations

The considerations that form the basis of this ship station identification
system are :

a) that every ship shall have a unique ship station identity;

b) that the same unique ship station identity should be used in both VHF and
Maritime Mobile Satellite Systems;

53
ney


As calling traffic increases, the use of this channel may become impractical.
An additional dedicated channel for calling ships may be required. Separate
calling channels for manual and automated calling may become necessary.

In high traffic areas, it is desirable to assign more than one working
channel to the coast station(s) covering that area. The greater the volume
of traffic, the larger the number of working channels required for a given
grade of service and service delay. When several channels are assigned to
a given coast station, there will be occasions where any given channel is
not being used. If all channels could be made available to all coast
stations, with proper coordination procedures, then a more uniform occupancy
per channel could be obtained.

7.2. Co-channel Interference and Co-channel Sharing

When co-channel transmitters are operating at the same time, interference
may result even though the transmitters are separated by some distance. At
VHF this is caused by propagation conditions known as ducting. Even without
ducting, the allocation of a common channel for contact purposes can cause
interference between adjacent coast stations if they are within reception
range of each other, or if a ship is within the reception range of both.

Various methods for alleviating the problems caused by ducting have
been proposed. One method is to disable the interfering co-channel station
when ducting is detected. The detection process is normally accomplished
at the shore stations because the appropriate equipment is fairly complex
and costly. The method is not an ideal solution because of the loss of
traffic capacity of the disabled station(s).

If sufficient channels are available to handle the traffic it is
possible to alleviate co-channel interference by providing increased separa-
tion between co-channel stations. The Great Lakes prototype system experienced
this type of interference and separations of 360 km were required to provide
acceptable protection. (Herrick, 1977)

Another method involves sharing the co-channel on a time division
basis by assigning time slots for transmission on a coordinated basis.
(Mathews and Fee, 1978). This proposed coordinated assignment scheme
raises several questions concerning its implementation. For example: What

36


5.5. End Office With Regional Control Center

This last limitation can be eliminated to some extent using the network
access configuration depicted in Figure 6. Coast centers providing coverage
in a limited region can still be accessed as before, but, in addition, they
are connected by leased line to a regional coast center (which may itself
be a coast station). This is essentially the configuration used for the
Great Lakes system described by Lorain (1975). Coast stations could be
unattended and controlled from the regional center. The leased lines shown
dotted in Figure 6 are for control and management data only and carry no
voice traffic. The leased-line costs can be reduced using multidrop
lines and conventional polling techniques to each coast station from the
regional center. Various polling networks are illustrated in Figure 7.

Paging, i.e., to locate a particular ship, in the Great Lakes system
is accomplished via the system operator in the central control center
(regional center), who locates the ship by calling via the leased lines
through one or more coast stations as may be necessary. Having located the
ship, the call is established by remotely controlled dialing through the
appropriate coast station and its local telephone network end office back
to the land subscriber's telephone.

An alternative method could be that the regional center accepts the
land subscriber call information, puts the land subscriber on "hold" while
it locates the ship and completes the call via a dial-up line (or via a
permanently leased line) between the appropriate coast station and the
regional center.

The relative advantages of these two methods depend, among other
things, upon the amount of traffic coming into the regional center (rather
than directly to the coast station) and the average time it takes to locate
and establish the radio link with the called ship.

As in the preceding case, a two-step dialing procedure would be used,
as discussed in paragraph 5.2.

24


Herrick, R. H. (1977), The new Great Lakes, lakes-wide, all-VHF, automated
marine telephone system, RTCM Assembly Meeting, Symposium papers 3,
No. V.

Lorain (1975), Great Lakes, lakes-wide all VHF automated radio telephone
system, Final Report by Lorain Electronics Corp. MARAD Contract
3-36280.

Mathews, C., S. and J. J, Fee (1978), Techniques for performing digital
contact data transfer in an automated VHF radio telephone system,
MARAD Development Report No. 3.

McIntyre, R. C. (1977), The FCC-Regulation of the marine radio service,
IEEE Trans. Vehicular Tech. VT-26, No. 3, p. 279.

Panks, J. R. (1976), Radio network for inland waterways, Communications,
p. 10

Polishuk, P. (1977), Special report: United States, Telecommunications,
11, No. 9, p. 84.

Renner, J. J. (1977), VHF maritime mobile communications: A system
approach to serving user requirements, IEEE Trans. on Vehicular
Tech., VI-26, No. 3, p. 213.

Schwartz, M. (1977), Computer communications network design and analysis,

Chap. 13, Random Access Techniques, (Prentice-Hall, Inc., Englewood
Cliffs, NJ),

4]


In the ship-to-shore direction, the ship subscriber selects the calling
channel or a working channel, as appropriate, of the nearest coast station.
If the channel is clear, the transmitter is actuated. This automatically
transmits the ship's registration number to the shore station, which responds
with a dial tone. The ship subscriber then dials any required service
selection code, for example "0" for operator assistance or "1" for a direct-
dialed call. In this latter case, an access line between coast station and
network end office is automatically seized and the ship subscriber then
dials the desired number directly to the end office.

The manual channel selection process can be eliminated if a commonly
assigned (calling) channel is available. With such a method, an off-hook
condition on the ship automatically signals the ship's identification over
the calling channel. A coast station within range responds either on the
calling channel or with a distinctive marker on a "ready" working channel.
After completion of a "hand shake" procedure and seizure of an access line,
the coast station puts a dial tone on the working channel and the ship
subscriber dials directly to the coast station's end office.

Besides availability of a common calling channel, some degree of
automation for working channel selection by the ship's radio equipment is
desirable either by means of channel scanning and automatic seizure or in
response to a coast station command via the calling channel.

A system based on automatic seizure of a working channel has been
developed for the Great Lakes communications system (Herrick, 1977), although
it has not yet been put into use.

The calling channel in this situation could utilize the digital selective
calling system (CCIR, 1978a). Co-channel interference from coast stations
with overlapping coverage areas may be mitigated using Time Division Multiple
Access (TDMA) techniques as proposed by Mathews and Fee (1978).

One difficulty with the configuration in Figure 5 is that switching
and signaling equipment in use at the various end offices around the country
may differ and various dialing procedures may be required. Another limita-
tion is the requirement for a DTMF dialer, as discussed previously.

Finally, the subscriber must know the access number for the coast
station within the ship's contact range and locating the ship must be
accomplished either by the subscriber himself calling the various coast
stations or with operator assistance.

23




LIST OF ACRONYMS
AMMTS Automated Maritime Mobile Telephone System

AT&T American Telephone and Telegraph Co.

CCIR International Radio Consultative Committee
ccIs Common Channel Interoffice Signaling
CCITT International Telephone and Telegraph Consultative Committee
DDD Direct Distance Dialing

DTMF Dual Tone Multifrequency

EO End Office

FCC Federal Communications Commission

FNPA Foreign Numbering Plan Area

FM Frequency Modulation

HNPA Home Numbering Plan Area

Hz Hertz or cycle per second

IWP Interim Working Party (CCIR)

MARAD Maritime Administration (U.S.)

MSC Maritime Switching Center

NC National Center

NPA Numbering Plan Area

PABX Private Automatic Branch Exchange

PTT Postal, Telephone & Telegraph administration
RC Regional Center

TDMA Time Division Multiple Access

UHF Ultra High Frequency (300 MHz to 3 GHz)
U.S. United States

VHF Very High Frequency (30 MHz to 300 MHz)

WATS Wide Area Telephone Service

viii


include phone patches under interconnection arrangements or similar designa-
tions.

The phone-patch system permits the two-way radio operator to connect
an incoming call to the ship by operating a special switch. For ship-to-
shore calls, the operator dials the desired number over the public switched
network and actiivates ‘the patch when the call is completed to connect the
ship's caller to the network.

4. DESIRABLE FEATURES AND PARAMETERS

When the public switched network and the maritime mobile radio services
are interfaced to provide automated telephone service between vessels and
public network subscribers there are certain desirable features and parameters
which should be considered. Generally these features and parameters fall
into one of two categories, operational or technical. They are summarized
below. An extensive list of desirable features and operational requirements
for the AMMTS is given in CCIR Report 587-1 (CCIR, 1978b).

Operational

to) The system should perform in a manner similar, if not identical,
to the existing public switched network. This includes access
phase, information transfer phase, and disengagement phase.

° Dialing procedures for establishing connections from ship-to-
shore and shore-to-ship ideally should be identical and simple to
use.

° Land-side callers should be able to dial directly to contact a
ship without operator assistance via the coast station nearest
that ship. This completely automated procedure requires that the
land-side caller knows the ship's location and registration
number and the number of the coast station nearest the ship.

° Land-side callers should be able to contact ships whose registration
number is known but whose location is unknown. In an AMMTS, this

14


APPENDIX B
DRAFT RECOMMENDATION

SHIP STATION IDENTIFICATION FOR VHF AND SATELLITE
MARITIME MOBLE SERVICES

51


- 30-
COM I-No, 99-E
COM II-No. 107-E
GM/SMM-No, 52-E

9. Ship station identity for Maritime Mobile Satellite Service

The international numbering plans would permit up to 9 digits for ship
station identity and ship station numbering to be used in association with country
codes 87X for telephony and destination codes 58X for telex, where X may indicate
ocean area or system.

lo. Considerations related to ship station identity assignment

An efficient allocation of ship station identity will permit an extension
of the time period in which stage 1 applies. The specific manner in which the
optional techniques indicated in Sections 8.1 and 8.3 are applied depend on the needs
of a given Administration tc achieve an optimum result. Special consideration should
be given to the assignment of ship station identities for ships engaged in regional
and national traffic so that spare capacity remains available for inter-regional
traffic when transition from stage 1 to stage 2 takes place.

Annex

(to the Recommendation)

National network diversity and automation of VHF service

National network numbering and routing requirements provided to satisfy
national subscriber population and service needs result in widely varying abilities to
support automatic VHF service. The following diverse approaches have been recognized
and should be expected.

l The inability of some networks tc carry as few as six digits for ship station
number purposes will tend to defer automation indefinitely in some instances,

2. Some countries will find it practical to provide for automation on the basis
of six digits for ship station numbering in accordance with the proposed plan in this
Recommendation. When seven digits are required (in stage 2) the practice of not
dialling the initial digit of the Nationality Identification Digits may be adopted to
maintain as much automation as feasible. Refer also to Section 8.1.

3. Some countries may find it practical to use national network numbering to
define ship station numbers that are translated to ship station identities at one or
more coast stations and perhaps support this witk locator services.

4. Some countries may find it practical to use two-stage selection, e.g. in the
telephone service a second stage of subscriber dialling with multi-frequency push-button
equipment may be already available or provided specifically for subscribers particularly
interested in maritime services.

5. Some countries may now, or later, provide for centralized maritime centres
that may support automatic location and call routing facilities. The use of such
maritime centres would enable the application of ship station numbers of up to 9 digits
between countries with such centres.

58

(1446)


In either case, the center dialed by the land subscriber would accept
and store the called ship number and then proceed to set up the desired
connection in much the same way as was described in paragraph 5.5.

Finally, as an intermediate step towards a fully automated system, the
national and regional centers could initially be set up as information
centers only. A land subscriber not knowing the location of the ship dials
the national or a regional center, which determines the ship location
registration and informs the land subscriber which coast station to call.

5.7. Example of Detailed Access Arrangement

Figure 11 illustrates in more detail the access arrangement of Figure 9.
In this example it is assumed that the ship's location registration informa-
tion is stored at the appropriate regional center. A land caller, trying
to locate a ship via the national center, sends the ship's identification
number to the national center which in turn sends it to all of the regional
centers. This identification number would then be scanned by the processor
at each regional center and checked against a register file in its memory.
If the ship is registered for that location then the national center is
notified by returning the number of the coast station nearest the ship.
The national center then completes the call via that coast station.

6. RATE STRUCTURES

Because of the complexities of services, features, equipment, and
options offered, the following paragraphs only provide an overview of the
rate structure used in the United States. Details are covered by tariffs
filed by each carrier with the FCC. The domestic long-distance telephone
FCC tariff, for example, is AT&T No. 253 which also covers private land-
mobile radiotelephone service.

6.1. Common Carrier Services

The charging rates for long-distance telephone calls over the public
switched networks in the U.S. are based on: 1) the class of call, 2) the
distance, 3) the call duration, 4) the time of day, and 5) whether the call
is interstate or intrastate.

31


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32


-10-

(Doc. 8/368-E) Netherlands 8/5/2

2.2.2 A computer, as a part of the MSC, has rapid access to a
memory containing the ship station numbers of:
2.2.2.1 all ships of the nationality N,
2.2.2.2 ships of other nationality that have more than
incidentally contact with MSG, (these ships are
served as if they were of the N-nationality-.)
2.2.2.3 ships of other nationality located within the ser-

vice area of the MSC) -

Related to each ship station number stored in this memory,
the location of that ship, or the identity of the BS) in
which service area the ship is located, is also recorded
in this memory. The latter information must be updated
continuously, preferably in an automatic way.

This memory will be referred to as "Location Registration

Register" (LR).

3. PROCEDURES
If a ship, having the nationality N enters the service area of the
MSC of the nationality X1 , she reports to MSC, , via cS, or via
a BSy,:

The MSC, , registers this ship in its LR (para 2.2.2.3).

From that moment on the N-ship is treated as if she were of the nationa-

lity X41.

The MSC, , reports to the MSC, that the N-ship is now registered in

the LR of MSC). This fact is recorded in the LR of MSC), in connec-

tion with that ship station number.

If later on that ship enters the service area of MSC), she reports to

the MSCy,- The latter registers the ship in its LR and is served by

the MSC, as if she were an X2-ship.

2
The MSC. reports to MSC), that the N-ship is registered by MSC).

This information replaces the previous one in the LR of MSC), and,
at the same time MSC, informs the MSC), that the ship concerned can
be dropped out of its LR.

The above procedure ensures that the MSC) has always a record of the

location of the N-ships.

47


Equipping the maritime station (i.e., coast station, regional, or
national center) with a pulse counting device to accommodate land sub-
scribers without DTMF dialing facilities may be feasible but is likely to
be sensitive to pulse type interference, e.g., due to fading and protection
switching in microwave links. Such interference may cause errors in the
signaling information which would result in an uncompleted call or a
connection to a wrong vessel.

In the end, most of the political coordination, the cost and revenue
sharing problems, and some of the technical problems referred to in the
discussion of one-step dialing need to be resolved for a fully automated
two-step dialing system as well. However, gradual implementation of auto-
mation can proceed while those problems are being resolved.

5.3. Ship Location Registration

Ship location registration is defined here as that information which
specifies the coast station that provides the final link (i.e., the radio
circuit) between the land network and a particular ship at a particular
time.
Two distinct aspects to ship location registration can be distinguished:
(1) acquisition of the ship location registration and (2) at what point the
location registration is stored in the system.
Acquisition and updating of the ship location registration can be
achieved in a number of ways, among which
(a) the ship location registration is assumed to be the coast station
that last (within some time limit) provided communication with
the ship, until such time as the ship initiates a call via a
different coast station. Beyond this time limit, and at least
for certain classes of vessels, this could be supplemented by
automatic interrogation from the coast station;
(b) the ship location registration is determined in accordance with
a filed route and time schedule plan for the ship; or

(c) the ship registers (either on a voluntary or mandatory basis)
with a coast station whenever it enters the service area of that
coast station.

20


Pi 87

-13-
(Doc. 8/368-E)

SUBSCRIBER

_

FOREIGN
MSC

f—= NATIONAL TARIFF MSC
pe INTERNAT. TARIFF
st REGISTER
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$5 =
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50



FORM OT-29 U.S. DEPARTMENT OF COMMERCE.
(3-73) OFFICE OF TELECOMMUNICATIONS

BIBLIOGRAPHIC DATA SHEET

1, PUBLICATION OR REPORT NO] 2. Gov't Accession No. | 3. Recipient's Accession Now

NTIA Report 78-7

4. TITLE AND SUBTITLE 5. Publication Date
INTERFACING THE AUTOMATED MARITIME MOBILE TELEPHONE Aug 1978
SYSTEM WITH THE U.S. PUBLIC SWITCHED TELEPHONE NETWORK | & Pestorming Organization Code
NTIA/ITS
7. AUTHOR(S) 9. Project/Task/Work Unit No.

R. F. Linfield and T. de Haas
8. PERFORMING ORGANIZATION NAME AND ADDRESS.
U.S. Department of Commerce

National Telecommunications & Information Administration '® Comtact/Grant No.
Institute for Telecommunication Sciences
325 Broadway. Boulder, Colorado 80303
11, Sponsoring Organization Name and Address 12. Type of Report and Period Covered
U.S. Maritime Administration
Department of Commerce

Washington, DC = 20230 13

14, SUPPLEMENTARY NOTES.

15, ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant
bibliography ot literature survey, mention it here. )

This report summarizes the characteristics of the U.S. public switched network
and the maritime radio service, which impact the development of an Automated
Maritime Mobile Telephone System (AMMTS). Features’ and performance parameters
which appear desirable to an AMMTS user are reviewed and some basic system concepts}
capable of satisfying these user's neéds are presented. The interface between the
public switched network and coast stations serving the maritime community is
discussed in detail. Techniques for automatically placing a call to ships whose
location is unknown are described. The development of an AMMTS involves a number
of issues which may be different in the U.S. than in other countries of the world.
The final section of the report defines some issues requiring further study.

16. Key Words (Alphabetical order, separated by semicolons)
Maritime communications; automated telephone systems; network interfacing

17, AVAILABILITY STATEMENT 18. Security Class (This report) 20, Number of pages

(X) UNLIMITED. Unclassified 66

19. Security Class (This page) 21, Price:

(2) FoR OFFICIAL DISTRIBUTION. Unclassified

‘U.S. GOVERNMENT PRINTING OFFICE: 1978 — 778-935/12 REGION NO. 8 USCOMM-DC 29716-P73




of the costs thereof would be reached. Some of the advantages of this
approach are that it minimizes organizational and other non-economic barriers
to an early start of automated services (e.g., the Great Lakes system), and
that it provides maximum assurance of cost effectiveness. Some of the
disadvantages are that attempts at resolution of problems inherent in the
formation of a truly nationwide public AMMTS are easily put off to "some
future time," and that it could foster the creation of a different and not
necessarily compatible automated system which could add to the problems of
integration in a single AMMTS in the future.

An alternative concept would be to implement the AMMTS in a relatively
much shorter timespan and to recover the costs incurred from future traffic
revenues. To, be viable, this would require a single entity to be responsible
for both the technical and economical soundness of the implementation plan.
Such an entity could, for example, be a consortium of maritime mobile
service providers.

The maritime mobile communications environment is subject to Federal
regulation and is also of considerable interest to, for example, maritime
safety. The role of the Federal Government (if any) in providing regulatory
or economic stimuli, or both, towards the development of a nationwide
public AMMTS should be given serious consideration.

7.8. Rates and Rate Structuring

The existing heterogeneous makeup of the maritime communications
industry has resulted in a wide variety of independently developed methods
of rates and charges. In addition, actual operating costs and the ratio of
required investment (for AMMTS) to the amount of public correspondence
traffic handled may vary widely between different coast stations. At
present, the cost to a subscriber for a call to (or from) a vessel consists
of two independent charges; the telephone network charge for the connection
of land subscriber to coast station plus the charge for the radiotelephone
connection set by the particular coast station. To arrive at a uniform
rate structuring for the AMMTS will require major action by the FCC in
addition to cooperation between maritime mobile and telephone network
service providers. On a secondary level come related problems such as
allocation of charges between various carriers, accounting and billing, and
technical interconnect arrangements associated therewith.

39


slot duration should be used? How can these be synchronized? What timing
accuracy is required?

The regional coast centers with dedicated data lines to each coast
station can be used to provide timing information to stations. In areas
where the traffic is highly variable between coast stations, the center
could also allocate transmission slots of different lengths to each station.

There are several other techniques which should be studied for develop-
ing an optimum maritime system. For example, each coast station could
monitor adjacent station transmissions. Stations having limited need for
calling time would so indicate, and an adjacent station could utilize this
time when it senses no other transmissions were taking place. Several
random-access techniques have been evaluated for various types of networks.
Schwartz (1977) summarizes some of the techniques which have been proposed
for multiple access to a single satellite channel. Although these are
designed for packet-switched data networks, they appear to have application
in any multiple-access, single-channel system.

7.3. Range Extension

The coverage range of VHF-FM stations is relatively short, typically
30 to 80 km from shore. It is feasible that this range could be extended
by relaying signals from ship to ship. This aspect should be considered in
developing the AMMTS. A closely related consideration is automated calling
between ships as well as ships to shore.

7.4. Performance

There are various ways in which a communications system's performance
can be evaluated. The performance objectives and the system which evolves
to meet these objectives depends on conflicting viewpoints. The system
user wants to minimize costs by using the service as little as possible and
at the same time have fast access with service always available. On the
other hand, the system supplier wants to maximize revenue by selling as
much service as possible and by sharing facilities among many users. These
conflicting viewpoints in the U.S., along with those of other nations,
should be considered in the system development so that the needs of the
international maritime community can be satisfied.

37


Table 1

Common Dialing Procedures
used in
North America

Prefix Area Office Terminal
Home No. plan area (HNPA)
o local call -- NNX XXXX
o toll call (DDD) (--/1) NNX XXXX
0 operator assisted call 0 NNX XXXX
"Foreign" no. plan area (FNPA)
o toll call (DDD) (--/1) N(0/1)X NNX XXXX
0 operator assisted call 0. <N(0/1)X NNX XXXX ,
national’ number
International
o direct call 011 (country) (national number)
OQ operated assisted call 01 (country) (national number ) |
~~
maximum 12 digits
Notes

(--/1): no prefix or prefix 1
(0/1): digit is 0 or 1
N : any digit between 2 and 9
X : any digit between 0 and 9
DDD: Direct-Distance-Dialed call


-4e-

(Doc. 8/368-E)

FROM FOREIGN

MSC

INTERNATIONAL

SUBSCRIBER NUMBER

st
/, 82

SATELLITE PROCEDURE

NATIONAL PREFIX a Luss
SUBSCRIBER Pi
34
55 \
TELEPHONY REGISTER TERRESTRIAL
TELEGRAPHY PROCEDURE
(TELEX) TS VS
“FIGS” 14
NATIONAI ”
NATIONAL DESTINATION 58 t=
SUBSCRIBER | CODE
_ T2 SATELLITE PROCEDURE
‘+
Th

FROM FOREIGN

SUBSCRIBER NUMBER

MARITIME SWITCHING CENTRE (MSC)

MSC
FIGURE 1
| COUNTRY "X,” COUNTRY “N” | COUNTRY “x2” |
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Ny lest, | Bs3
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FIXED CONNECTION
CONNECTION VIA THE
PUBLIC NETWORK

FIGURE 2
49



-27-
COM I-No. 99-E
COM II-No. 107-E
GM/SMM-No. 52-E

3. Assignment of ship station identification

3.1 Assignment of blocks of numbers

Blocks of numbers should be assigned to countries so that individual
Administrations may systematically assign ship station identities within those blocks.

3.2 Identification of ship's geographical region

The first digit of each ship station identity is intended to identify the
geographical region to which the nationality (registry) of the ship relates. Only
the digits 2 through 7 are used for this purpose to identify easily the world's
regions as follows :

- Europe

- North America

- Asia (except South-East Asia)
Oceania and South-East Asia

- Africa

ANU fF ww
'

South America,

Arrangements may therefore be made to systematically assign a ship station
identity to each ship as soon as national blocks are allocated. The digits zero (0),
one (1), eight (8) and nine (9) are allocated for other purposes as indicated in the
following sections.

3.3 Identification of ship's nationalit:

Since blocks of the ship station identities would be systematically assigned
by country, a ship's nationality can be determined by analyzing the first three
digits of its ship station identity.

The digits to be analyzed are called "Nationality Identification Digits" (NID).
Examples of the Nationality Identification Digits for sh’ps are given below.

Country Nationality Identification Ship Station
Digits (NID) Identities
P 231 from 2 310 00000
to 2 319 99999
Q 233, 234 2 330 00000
2 349 99999
R 236, 237 2 360 00000
238 2 389 99999
s 2ko - ako 2 400 00000
2 499 99999

55

(746)


The mean access time for direct-distance-dialed (DDD) attempts is
indicated in Figure 3 for a user with a Dual Tone Multifrequency (DTMF)
dialer. The DTMF dialer uses 10 push buttons to send the 10 decimal digits,
0 through 9, using a code consisting of two in-band frequencies emitted
simultaneously when a button is depressed. The two frequencies are taken
from two mutually exclusive groups of four frequencies each (CCITT, 1977d).

The time needed for the dialing operation increases by about a factor
of two when a rotary dial telephone is used. The rotary dialer emits a
controlled sequence of dc pulses on the subscriber line by breaking the
circuit. The number of pulses between breaks corresponds to the decimal
digit except 10 pulses are used to indicate 0. The connect time from end
of dialing to ring return is approximately 11 seconds. When all switching
centers are controlled by Common Channel Interoffice Signaling (CCIS), this
connect time is expected to be reduced to 2 or 3 seconds. The tabulation
below summarizes the total mean access times

Dialer Signaling Access Time

Rotary Conventional 35s
DTMF Conventional 28s
DTMF ccis 20s

The disconnect time is typically 4 to 5 seconds.

3. CHARACTERISTICS OF MARINE RADIO SERVICES IN THE U.S.

Radio telephone and telegraph service for the maritime community
in the U.S. also differs in many respects from that found in other countries
where these services are usually provided by the governmental or semi-
governmental telecommunications administration. Some factors which may
influence the development of an economical AMMTS in the U.S. include the
following: (Renner, 1977; McIntyre, 1977; Panks, 1976):

° There are two types of U.S. coast stations operating for the
marine services. They are public coast stations and limited
coast stations. These stations operate in the MF, HF, and VHF
bands depending on the service and coverage desired. Approximately
250 coast stations serve the public correspondence needs, and
over 3700 limited coast stations serve the operational and

9


PREFACE

The study reported here is part of a continuing
program being conducted by the National Telecommunications
and Information Administration for the U.S. Maritime Admini-
stration of the Department of Commerce. The program manager
for the Maritime Administration is Mr. C. S. Mathews.

The views and opinions expressed in this report are
those of the authors and should not be construed as an
official position or policy of the U. S. Maritime Admini-
stration.

The comments and suggestions from members of the
Radio Technical Commission for Marine Services, Special
Committee 71 (RTCM SC-71), in particular from Mr. Ross
H. Herrick, Consultant to Loraine Electronics Corporation
and from Mr. W. H. Keller of the American Telephone and
Telegraph Company (A.T. & T), are gratefully acknowledged.

Vii


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A system based on the above concept would fulfill the requirements of
the Automated VHF/UHF Maritime Mobile Telephone Service. A disadvantage of
the concept is that it would be comparatively more difficult to introduce
such a system on a gradual basis. This, in turn, would mean that the
system might not be cost effective for a period of several years. In the
U.S., where such a system would involve several separate interests, signifi-
cant problems of technical and political cooperation, as well as cost and
revenue sharing, would additionally have to be surmounted.

The concept described above implies the simultaneous introduction of
ship location registration, as the information that the land subscriber can
enter into the system does not include a priori ship location information.
It also means that a land subscriber in San Diego, for example, calling a
ship known to be in the San Diego area, still enters the system through the
MSC which may be located elsewhere, say in New Orleans. However, as trans-
mission costs tend to become less significant in relation to the total call
costs, this disadvantage may be outweighed by the somewhat simpler one-step
dialing procedure.

For a practical implementation, the MSC could be supported on a co-
operative basis by the maritime industry and could, of course, be co-located
with a particular coast station. Alternatively, the MSC could be co-located
with any class of telephone network switching center. This latter alternative
does not imply that the MSC would be owned, or the operating costs would
be borne, by the telephone companies.

For the U.S. telephone network, the concept of an MSC means that all
local offices must be equipped to recognize the "country code" 87X, and
that routing procedures must be established to the MSC "gateway".

The CCITT Ad Hoc Joint Working Party I/II Draft Recommendation, repro-
duced in Appendix B, allows for some schemes by which a limited number of
ships might be accessed using one-step dialing without exceeding the capacity
of the national network and without resorting to an MSC. The applicability
of such techniques to the U.S, network requires further study, in particular
as no spare area codes are available in the North American numbering plan
for assignment to public coast stations, and assignment of office codes to
such stations involves questions of availability of codes, tariffs, and
charging principles.

18






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26


The station's telephone must be answered prior to placing the call to a
ship. A long-distance caller who dials the station directly is therefore
charged for the call to the coast station even though the desired ship may
not be reached.

Leased services may be offered by coast stations by special contract
to provide equipment and operating functions for a particular use. These
leased services must use radio channels allocated for such special use by
the FCC. Services provided include facsimile, printer, and data transmission
as well as voice.

7. INTERFACE ISSUES

A public correspondence radiotelephone system provides interconnection
with the land-telephone network. We have attempted to define the unique
characteristics of the public switched network and the VHF maritime mobile
radiotelephone system in the U.S, Possible interfacing concepts have been
described which would provide a fully automated public correspondence
system capable of meeting certain operational and technical requirements.

There are several issues which still must be resolved in order to
implement fully an automated public correspondence radio system for the
international maritime community. The more pertinent issues are summarized
below.

Some of the issues raised can only be resolved by the regulatory
process (e.g., channel allocations), others require extensive field trials
with operating systems (e.g., contention). They all can benefit from
further study, but to varying degrees depending on the complexity of the
issue.

7.1. Channel Allocations

Preferred methods proposed for AMMTS require a common calling channel
for universal contact and separate working channels for public correspondence.
However, in some areas the number of channels presently available for
public correspondence already is insufficient to handle the working channels
traffic load. In such areas assignment of additional channels may be a
prerequisite for separate common calling channel methods. In the VHF
band, channel 16 is presently allocated for distress, safety, and calling.

35


A mixture of the above and possibly some other methods will probably be
used initially and for some time to come.

From a technical point of view there does not appear to be a clear
advantage as to where the ship location registration should be stored,
assuming that high efficiency data-transmission techniques are used either
to update centralized storage center(s) (i.e., the MSC or the regional
centers) or to poll decentralized storage centers (i.e., coast stations or
regional centers). Some advantage might be given to the centralized storage
center, since polling of decentralized centers would have to be done in
real time in order to keep the call connect time to a minimum. Updating
would allow some margin of departure from real time.

From an operational point of view, safeguards against multiple registra-
tion of a single ship would also favor the centralized approach.

5.4. End Office Connection

It is necessary to consider various cases, including direct-dialed
calls, operator assisted calls, and paging calls. Figure 5 illustrates a
simple situation where all public correspondence traffic enters and leaves
the public switched network via access lines between each coast station and
its nearest end office.

The simplest case to consider is when the access number of the coast
station covering the ship's location is known. A land subscriber contacts
the coast station by dialing (7 or 10 digits) via the national network.
When the station goes off-hook answer supervision is returned and a second
dial tone is provided. The subscriber then dials the ship's access number
with his DTMF dialer (either his push-button telephone set or a DIMP attach-
ment). These DIMF tones are transmitted via the network and the coast
station's common calling channel or working channel directly to the ship
where they are detected and decoded by logic circuits in the receiver.

When the ship's access number is detected, an alerting signal is actuated.
The coast station, if necessary, assigns a working channel and completes
the connection through its control equipment. Alternatively, the ship's
access number can be translated at the coast station in another appropriate
format for establishing the radio circuit with the ship; e.g., using the
digital selective calling system (CCIR, 1978a).

21


CONTROL
COMPLEX

SWITCH TERMINAL TRUNKS
NETWORK INTERFACE SUBSCRIBER

Figure 2. Basic end office switching system.


- 29 -
COM I-No. 99-E
COM II-No. 107-E
GM/SMM-No. 52-E

Stage} Ship Station Number} Digits on | Ship Digits on
the ‘auto- station the Radio
matic net-| identity Path
work

1 NID XX5X¢ 6 NID X,X,%, 000 9
2 NID X, xX, *
ID x, Skok 7 *) NID X XXX, 00 9
3 NID XXX X0 Xe 8 NID X,X,X,X/Xq 0 9
8.2 In stage 1, those countries that would identify VHF calls and plan to

automate VHF in a single stage of subscriber selection would have full access to all
ships if they are able to assign 6 digits to ship station numbering in their networks.
The plan contemplates mutual cooperation to extend this stage as long as possible by
judicious ship station identity assignments to satisfy requirements for automatic VHF
in the face of network limitations.

8.3 Additional ship station numbering techniques may be used to expand network
access to more ship stations in stages 1 and 2, These techniques permit an extension
of the time periods during which stages 1 and 2 apply.

Ship Station Number Ship Station Identity
8Y XXoXeXy NyTDy Ky XoXeX, 00
9 Ky XXX Xp NTP XyXsXeXXq 0

In this arrangement, the digits 8Y may be 80 to 89 to define as many as ten
foreign NIDs (shown as N ID) to permit automatic calling of ships of particular
nationalities. The coast station would be required to translate a given 8Y to a
particular foreign NID. The digit 9 may be used to indicate the Nationality
Identification Digits for ships of the same nationality as the network and the coast
station, The coast station would be required to translate 9 to’one particular
national NID (shown as NID), National application of these techniques could be
adopted to provide an efPidi8nt use of ship station numbers.

*) Due to network limitations, some countries may choose to withhold the first digit
of the NID and insert it automatically at the coast station to retain automatic
access to all ships whose NIDs have identical first digits (ships of the same
geographical area). However, the application of this technique should be
avoided if possible to minimize ambiguity.

(ake) 57


APPENDIX A

AUTOMATIC (VHF) MARITIME MOBILE TELEPHONE SYSTEM,
CONTRIBUTION TO IWP 8/5, NETHERLANDS 8/5/2; NOV. 1977

43


-86-
(Doc. 8/ 368-E) Contribution to
IWP 8/5
Netherlands 8/5,’2

N 4
eX Ir ovember 1977

NETHERLANDS

Original: English

AUTOMATED (VHF) MARITIME MOBILE TELEPHONE SYSTEMS
Question 23 - 1/8

4. INTRODUCTION
One of the prime requirements, when introducing an automated Maritime
Mobile Telephone system, is a unique identification of the ship
stations.
It is the feeling of the Netherlands Administration that an identifica-
tion for a ship station should be constituted of eight figures
(digits) in order to allow all ships to participate. This feeling has
been supported by opinions of the CCIR Interim Working Parties 8/3
(on digital selective calling) and 8/6 (on ship station numbering).
It is also the opinion of the Netherlands Administration that a ship
station identity” should not be adapted or artificially curtailed
in order to fit into an existing transmission system.
This implies that, given eight-digit ship station numbers@), a system
should be developed in which these numbers can be dialled or keyed

by the public network subscribers.

In this paper a system is proposed that enables telephone (and telex)
subscribers to dial (or key) the full eight (even nine) digits of

a ship station number.

7) ship station identity: The ship's identification N,....N,, transmitted
on the radio path.

2) ship station number : the number that identifies a ship for access
from the public network and which forms part
of the international number to be dialled or
keyed by the public network subscriber.

45


In order to conserve office codes, paging service is sometimes provided
on an end-to-end signaling basis, rather than assigning a unique address
to each receiver. A subscriber to this service must first dial the paging
control terminal. He then dials the multidigit number of the desired
receiver using a push-button station equipment which transmits unique dual
frequency tones for each digit. This two-step procedure has potential
application in the maritime-mobile service, as discussed in section 5.

International direct-distance-dialing requires the use of the
international access code 011 or 01 for operator assistance. The second
digit (1) must follow the first digit (0) by less than 3 seconds in order
to distinguish this prefix from the operator assistance prefix 0. The
number of subscriber-dialed digits, excluding the international prefix,
should not be more than 12 (CCITT, 1977d). A total of 12 digits actually
exceeds the capacity of the toll network and is accommodated by two-step
outpulsing by the switching office.

2.2. Performance

In order to make it simpler for the user, a desirable objective of
the AMMTS would be to provide a service similar in all respects to the
service provided by the public switched networks on land. This includes
the dialing procedure, access time, voice quality, disconnect time, grade
of service, and other performance aspects viewed from a user's standpoint.

Therefore, it is useful to consider the present performance of the
public switched network in this subsection.

It is difficult, if not impossible, to predict with certainty the
quality of service any particular user might encounter on the public
switched network. This is due to the complexity and variety of systems in
use. However, some average values of pertinent parameters have been mea-
sured or at least indicated as design objectives, and these can be summarized.

Grade of Service is one design goal which may vary considerably over
different portions of the network. However, a blocking probability of
less than p = 0.01 is normally maintained on the telephone network.

Recently a survey was conducted thoughout the Bell System by Duffy and
Mercer (1978) to gather information on network Performance. Results derived
from that survey are of interest here.