ARPANET Status Update

Mark Pullen (
Fri 22 Jul 88 10:41:07-EDT

The purpose of this message is to provide members of the Arpanet and
Internet user communities with a progress report on current changes
being made to the Arpanet, as well as some information about their
potential impact on network users. As an earlier message to tcp-ip
explained, DARPA plans to gradually phase out the Arpanet and replace it
with a higher-speed, research-oriented internet (the Defense Research
Internet, or DRI). While work on the DRI is progressing, the first
phase of Arpanet restructuring has been implemented and is nearly
complete. Plans for a second phase are presently being finalized. The
goal of these initial phases is a near-term reduction of Arpanet
operational costs through the elimination of selected Arpanet PSNs
(packet switching nodes) and leased interswitch trunks. What follows is
a summary description of the principal actions taken under Phase I

The most significant aspect of Phase I restructuring is the temporary
use of channel streams derived from the DARPA Wideband Satellite Network
to maintain adequate cross-country connectivity in the Arpanet while
PSNs and leased terrestrial lines comprising existing paths are removed
from service (during Phase II restructuring, cross-country trunks will
be moved off the Wideband Network and onto 56kb/s lines derived from the
terrestrial backbone being implemented for the DRI). Special software
has been written for Butterfly Satellite Imps (BSATs), which enables
them to accept subnetwork packets from an Arpanet PSN trunk port and
encapsulate them in Wideband Network stream messages for transmission to
a distant PSN. Three such trunks, terminated at sites where Arpanet and
Wideband Network nodes are physically collocated, were established
during the first week of May, 1988: BBN to ISI, DCEC to ISI and DCEC to
SRI. The intervening weeks have been spent tuning their performance.

During the same time period, Phase I disconnect orders have been issued
for several of the longest and most expensive leased terrestrial trunks,
along with a small number of PSNs. Once these trunk and PSN deletions
are complete (this should occur within the next few weeks), only one
terrestrial cross-country path will remain in the Arpanet. Trunks
comprising the last remaining terrestrial path are currently scheduled
to be removed by October 1, 1988. At this point, the Arpanet will rely
heavily on the Wideband Network, plus two VSAT satellite trunks,
to carry traffic between the east and west coasts of the United States.
This will make the quality of Arpanet service more dependent on the
Wideband Net.

By placing the Wideband Net in this critical role, we may experience
significant network congestion if there are Wideband Net outages. In the
event such an outage actually occurs, every effort will be made to
restore service to normal as soon as possible. The use of the Wideband
Net in this capacity is a transitional cost saving measure until more
cost effective leased land lines are purchased. They are anticipated
to be installed by Dec 1988. DARPA has plans to bring up early versions
of the Defense Research Internet using some existing Wideband Net
equipment soon afterward. This will produce significant improvement
for users in the high load areas (directly supported by this experiment)
and indirectly by reducing Arpanet load for all of the other Arpanet

Please be patient. Change is often a painful process. There will be
problems in service during transition, but this effort is necessary
to enable future progress.

Mark Pullen, DARPA/ISTO


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