Prognosemetoder – en oversikt - Telenor

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less than 2 Mbit/s, Frame Relay will be an economical solution.
And if a customer wants more random open communication
with many other customers, it will be an economical solution to
lease a logical channel via a router service. This will provide an
open connectionless service for the customer. In fact, this may
be a suitable solution for electronic mail services.
In figure 9 is depicted a network structure that we believe to be
a cost effective solution for the short and medium term for the
type of business infrastructure that we have in Norway. And, as
we will see, it has a structure that easily evolves into an ATM
network.
The traffic in the network will continue to grow as a result of a
general increase in data applications but also from the increasing
use of graphics and visualization in applications. This will
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FR - Frame Relay node
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Routers
Frame Relay
Transmission network
Telephony
Figure 9 Frame Relay overlay: a first step towards a broadband network
ATM
ATM
FDDI
Router
Bridge
Figure 10 Step 2: Coexistence between Frame Relay and ATM
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gradually move the customer towards higher bandwidths and
drive the networks towards their limiting capacity.
In the core network there will be a continuous upgrading with
SDH based optical systems and cross connects for a flexible
handling of the various services. SDH based solutions will probably
grow further out in the regional networks and also in the
local loop for medium and large business users.
Step 2
FR DTE
Bridge
There will be an overlay of ATM nodes (cross connects and
switches) in the core network. This is partly due to a demand for
interconnecting FDDIs and local ATM-LANs, and partly a need
for interconnecting Frame Relay networks in a flexible way.
Figure 10 visualizes the next step in the evolution. In this scenario
the ATM network is transparent for the Frame Relay services.
This means that the various functions for the service have
to be performed in the Frame Relay nodes (FR), and ATM is
solely responsible for transmission between the FRs. Conflicting
situations between the overload controls in the two networks
might, however, arise in this scheme.
Step 3
The next step would be to introduce InterWorking Units
(IWU) between the Frame Relay and ATM networks. This
can be done by associating each DLCI with a virtual channel
(VCC) in ATM. Then each Frame Relay connection
can also be identified in the ATM network, the individual
users can be given the same QoS and overload control can
be harmonized.
Step 4
At this stage the Frame Relay nodes are replaced by ATM
nodes. This situation will arise when the customers start to
use new multimedia applications that need larger functionality
from the LANs. ATM based local area network will
frequently be the interface to the public network.
Users that want to stick to Frame Relay
will be provided with ATM adapters. Since
both services are connection oriented and
operate in a packet mode, such adapters are
assumed to be relatively cheap.
The connectionless router based service can
stay in the network until the traffic takes off.
It might then be changed into an open CBDS
server. This service will have the same type
of functionality as the router service, but
offer higher throughput. The combination of
a permanent virtual link service for the main
traffic, and an open connectionless service
for the more random switched traffic gives a
flexible structure for the early broadband networks.