Contents Telektronikk - Telenor

higher for the actual day compared to the
three day mean. These mean values are
calculated for the whole time window
duration. Considering Figure 5.3, it is
visible that there is a 6 hour period during
the night where there is hardly any
traffic at all. Taking the total traffic load
for the day and dividing it by the remaining
18 hours yields a mean for periods of
the day with traffic equal to 443,508
bit/s, which is a more representative
mean.
The busy-hour mean is 3.65 times larger
than the three day mean. The CoV for the
busy-hour is also smaller than for the
other time windows, since the traffic load
is on a more stable level during the busyhour
compared to the rest of the measurement
period.
5.4 LAN interconnection traffic
demands to WAN services
The characteristics of LAN interconnection
traffic comprise three main requirements
for existing and future WAN services:
1) asymmetrical transmission
capacity, 2) efficient traffic mechanisms
for bursts, and 3) flexible allocation of
capacity.
The asymmetrical traffic load is due to
the client-server traffic, where the server
to client traffic can be up to 7 times the
load in the opposite direction. Clearly,
symmetrical WAN links, as today’s leased
lines, must be dimensioned with
respect to the server to client traffic. This
results in idle bandwidth in the less loaded
traffic direction, which represents
extra transmission costs for the customer
and over-booking of network resources
for the network operator.
Customers in the existing data packet
services, like X.25 and Frame Relay, are
charged on the basis of carried traffic
volume, where a different traffic load per
direction is taken into account. Also, the
customer is charged for the symmetrical
subscriber line into the nearest X.25 or
Frame Relay node. The latter is a leased
line with a fixed tariff, regardless of traffic
volume. An early ATM service, with
leased subscriber lines into the nearest
ATM node, is expected to follow a similar
philosophy. When ATM has been
deployed to the customers’ premises, a
tariff totally dependent on asymmetric
traffic loads may be possible.
The bursty nature of the LAN interconnection
traffic represents high demands
in the dynamics of the WAN services.
Present synchronous leased lines services
offer a constant capacity, which means
that the WAN link must be dimensioned
for the peak bursts in order to give all
traffic a good quality of service. As seen
in Table 5.1, the LAN interconnection is
under-dimensioned with respect to the
peak loads in order to save transmission
costs, resulting in severe delays for the
end users during extreme load situations.
The statistical multiplexing in X.25,
Frame Relay and ATM will, to a certain
extent, support transmission of random
peak loads of short duration from one
customer, provided that the link is not
saturated with traffic from other customers.
The ability to handle extreme peaks
is dependent on the buffer sizes in the
nodes. The traffic control mechanisms
will take action if the network becomes
overloaded. In order to prevent network
congestion, the nodes can dispose of low
priority packets/frames/cells or the network
can refuse to accept any more incoming
packets until the overload situation
is relieved.
The flexibility requirement for WAN services
is due to the alternating use of the
LAN interconnection. A branch office
with normal traffic load during the working
hours, may transmit larger quantities
of back-up traffic at off peak times, e.g.
at night. In this case it will be feasible to
change the service capacity in both traffic
directions, either on an on-demand
basis or according to a fixed schedule.
This may be taken care of by future network
or service management facilities,
where the user, on-line or via the network
operator, can change the service
attributes according to instantaneous
LAN interconnection demands.
6 Conclusions
The main conclusions from the LAN
interconnection traffic measurements are:
- Branch offices do generally have larger
incoming than outgoing traffic. This
is due to relatively larger responses
than requests from remote servers,
usually situated in the head office.
- Branch offices without local servers
have significantly larger external traffic
than branch offices with servers on
site. In the latter case, standard office
applications are served locally, while
servers for central applications and
databases are situated in remote head
offices.
- Head offices have larger outgoing than
incoming traffic, which is due to the
central server traffic explained above.
- CAD applications generate considerably
more data traffic per user than standard
office packages.
- IP counts for 60 % of the traffic to and
from the selected LAN sites. The most
used protocols on the application layer
are Novell’s NCP, Telnet over TCP/IP
and IBMs NetBEUI.
- Generally, bulk transfer protocols,
such as FTP and NFS, contains larger
frames than interactive protocols, such
as Telnet and Xwindows.
- The mean external traffic load during
the busiest hour was under 90 % of the
theoretical WAN link capacity for 11
out of 12 LAN sites. One LAN site
generated outgoing traffic equivalent
to 105 % of the WAN link capacity
during the busy hour. The overload has
to be buffered up in the router.
Table 5.2 Traffic load statistics for different time scales, category E
Time Direction Mean Max. Total number 1) 2) Rel. Figure
scale bit/s bit/s of bytes CoV mean ref.
3 days Incoming 164 742 1 947 064 4 914 885 881 1.39 - 5.1
3 days Outgoing 294 571 3 865 168 8 418 091 361 1.74 1.00 5.2
1 day Outgoing 332 631 3 865 168 2 885 985 889 1.71 1.13 5.3
1 hour Outgoing 1 076 560 3 528 670 484 452 053 0.81 3.65 5.4
1) CoV – Coefficient of Variation, the ratio of the standard deviation to the mean. [4]
2) Relative mean – the mean for the time window relative to the 3 day mean.
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