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⟦ef6351859⟧ Wang Wps File
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Derivation
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WangText
CHAPTER
3
Page
#
DOCUMENT
III TECHNICAL
PROPOSAL Oct.
8,1981
Rev.:
Febr.1,1982
3. P̲R̲O̲P̲O̲S̲E̲D̲ ̲S̲O̲L̲U̲T̲I̲O̲N̲
o The Air Canada Data Network proposed is based on
state of the art software and hardware technology.
The layered software structure reflects the current
trends in standardization as presented by the Open
Systems Interconnection. The proposed backbone
network provides packet switch based service between
multiple processors and devices as well as additional
services in form of protected message service and
collection of billing information.
The network supports interfacing host and terminal
equipment which complies to international, mainframe
vendor or Air Canada provided standards. Furthermore,
it implements interoperability between multivendor
equipment. Thus, it allows equipment from different
vendors to be interconnected and thereby to provide
equipment transparency to the user.
The proposed network architecture is well suited
to the large transaction volumes characteristic
to the airlines industri. Due consideration has
been given in the proposed solution to allow Air
Canada achieve an efficient utilization of the
communication media, which provide the physical
interface between the ACNET and the user equipment.
Furthermore, this has been achieved by balancing
the overall response time without sacrificing reliable
transmission
The fault-tolerant multiprocessor hardware architecture
of the CR80 provides a modular framework well suited
for the graceful evolution required for a network
like Air Canada's; an evolution progressing in
small steps based on a continuous adaptation by
means of standard CR80 expansion elements and modules.
The CR80 architecture can provide processing power
and connectivity several times beyond the projected
needs for 1991.
The software reflects an architecture based on
the concepts of the Open Systems Interconnection.
This reflects the intent to provide an environment
well suited to adaptations required as future new
hosts, terminals, or other devices emerge. It
reflects a philosophy of implementation of international
and mainframe vendor standards as applicable.
3.1 I̲n̲t̲r̲o̲d̲u̲c̲t̲i̲o̲n̲
The purpose of this chapter is to present a basis for
understanding the functions supported by the proposed
Air Canada Data Net (ACNET). This chapter also serves
to provide a high level breakdown of the proposed network
including the associated rationale. The breakdown is
covered in terms of hardware and software architectures.
The software is presented in terms of the 7-layer
OSI architecture. Additionally, this chapter presents
the predicted performance and response times.
Section 3.2 defines and presents the external 'environments'
to which the proposed ACNET provides service. Furthermore,
it covers the internal environments by presenting the
mapping of the internal environments onto the proposed
hardware and software.
Section 3.3 provides the high-level break-down of the
hardware.
The software functional basis and structure is presented
in section 3.4. This section covers interfaces to
the backbone network from users, i.e. host computers,
other networks, via the Gateway to the existing network,
and the terminal access equipment.
Results of the performance analysis, i.e. response
times and capacities, are presented in section 3.5.
Finally, section 3.6 discusses the future growth capabilities
of the network with respect to capacity and functionality.
Figure 3.1-1
3.2 P̲r̲o̲p̲o̲s̲e̲d̲ ̲T̲e̲c̲h̲n̲i̲c̲a̲l̲ ̲S̲o̲l̲u̲t̲i̲o̲n̲
The solution to the Air Canada Data Network (ACNET)
proposed herein, is based on a network architecture
developed during the last more than five years and
used in national as well as international private networks,
where high performance, reliability, security and flexibility
were essential.
The computing facilities of Air Canada as they exist
today, are presented in a generalized and simplified
view in Figure 3.1-1 "Present Air Canada Data Networks".
Each of the networks provides specific sets of services
to the user.
The proposed network provides the means for integrating
present as future computer facilities assigned to the
following environments :
- User Environment
- Host Environment
- External Network Environment
- Internal Network Environment
- Terminal Environment
The users, host applications and terminal operators,
uses a combination of the facilities implemented in
the Host, Network, and Terminal Environments supported
by the ACNET, which interconnects these environments
and provides a level of integration which makes the
actual network topology transparent to the user. This
is illustrated on Figure 3.2-2 "Air Canada Data Network".
Each of these environments is described more detailed
later in this section.
Furthermore, in addition to the packet switch based
services which implements the interconnection between
users, the network itself provides the following services:
- Network control
- Network Management
- Protected Message Service
The network control services is provided to designated
personel, network supervisors and field technicians.
These services provide a centrally controlled environment
which can protect the entegrity of the network and
ensure consistent service to all users.
Figure 3.2-1
The network management services covers collection of
statistical information for billing purposes, the provision
of facilities for planning and development.
The protected message service provides acknowledged
message transportation between users.
Flexibility in several dimensions
- projected network expansion,
- local area network capability, and
- new equipment types
is supported by the proposed network.
The projected network expansion is seen as an evolution
progressing in small steps based on a continuous adaptation
to the connecting environments by means of standard
expansion elements and modules.
Support of local area includes a capability to include
the Christian Rovsing X-net local area network at the
agent's facilities. This net provides a means for adding
circuit switching to the packet switching facilities
implemented by the proposed network.
Addition of new equipment types is facilitated by the
modular structure of the CR80 hardware and proposed
software. Thus, addition of new equipment, whether
hosts or terminals, can take place with a minimum of
customization and without interrupting the live network
activities.
The proposed backbone network is well suited to the
dynamic environment in which Air Canada operates. An
architecture is proposed which essentially provides
Air Canada with open ended growth capability, an architecture
which allows optimal allocation of services and terminations
and which meet current as projected requirements to
connectivity and transaction volumes, an architecture
which enables Air Canada to make use of mainframe equipment
best suited for a given purpose.
3.2.1 E̲x̲t̲e̲r̲n̲a̲l̲ ̲E̲n̲v̲i̲r̲o̲n̲m̲e̲n̲t̲s̲
A user of the backbone network is either a host application
or a subscriber using a (terminal) device. An important
function of the proposed network is to establish and
maintain the connection between subscriber and application
on behalf of and transparent to the user. The network
presents a stable environment to the user which ensures
data integrity and provides highly resilient services
for data exchange between users.
The term user as used in this proposal covers both
the requester of services and the provider of services.
A requester may be a subscriber from his terminal while
a provider may be an internal network service in form
of PMS or external in form of a host application, e.g.
ticket reservation. A requester may also be a host
application, etc. The term session describes the logical
connection and associated transactions between two
users of the ACNET.
Privacy is important in a multiservice environment
like the one proposed for Air Canada. The proposed
network implements a high level protection against
unauthorized disclosure of data and information, based
as it is on a hardware and operating system architecture
derived from well recognized security principles and
implementations. Higher levels of software reflects
the same discretionary access control and capability
check-out philisophy as implemented by the proposed
operating system.
The Terminal Environment consists of a multitude of
multivendor terminal equipment which provide the immediate
environment used by the subscribers of the Air Canada
data services. The proposed network fully supports
the following variety of terminal types :
- CRTs -types 405, 406, 407, 408
- Flight Information Displays (FIDs)
- Printers- attached to CRT's
- teletype model 40
- ticket printers - DI - AN
- Extel
- Other devices
- ASTAC (self ticketing machines)
- MAC (microcomputer based travel agent
administrative system)
- IBM 3270 compatible terminals
The backbone network provides connectivity but also
host transparency to the users of the terminal environment.
The proposed network supports multiple applications
running concurrent between a given user and the relevant
hosts. The network established and maintains the connection(s)
between user and application(s) on behalf of the user.
The communication management functions are kept transparent
to the subscriber where possible.
The Host environment consists of multiple multivendor
processors which provide the majority of the Air Canada
computer provided services. A major objective in the
proposed network was to achieve an architecture well
suited for allowance of existing and new hosts to be
integrated into the Host Environment of the network
without constraints with respect to selection of processor
equipment from one vendor. The proposed Host Environment
consists of seven hosts implementing the following
applications:
- Passenger Management (PMH
- Reservation, VIA (VIA)
- Support(Corp Services (CORP)
- Maintenance/P & S (MTCE)
- Operations (OPNS)
- Cargo (CRGO)
- Corporate Services (CSIH)
The backbone network establishes and maintains connections
between host applications and other users. It allows
relieving the hosts for complex access software occupying
host resources but also the task of network monitoring
and control.
The network includes additional buffering capacity
provided to a avoid heavy retransmission activities
resulting from host recovery lasting a short period
of time. This added resilience implies protection
of the service level of other network users against
short-term variations of host application service;
this results in a lowering of the transmission utilization
of transmission media as retransmission resulting from
short outages may be avoided for a majority of transactions.
The ACNET interconnects the External Networks Environment
which consists of a number of national and international
network. This environment establishes paths between
Air Canada resources of the Host and Terminal environment
and external users and information providing sources,
i.e. resources which are not controlled by Air Canada.
The External Networks Environment consists of the
following data networks:
- SITA
- ARINC
- CNT
The Internal Network Environment includes the present
network excluding those hosts and terminals which are
moved to the proposed network, i.e.
- RES Host
- ACNC and connected concentrators and terminals.
This environment plays a major role in the proposed
migration from the existing network to the new network
as presented in this proposal. It provides the means
for enabling the migration to take place without interrupting
the services provided to users.
