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Defense Information Systems Network (DISN)
DISA ATM network (DATM)
Non-Classified Internet Protocol Router Network (NIPRNET)

In September 1991, OSD directed DISA to implement the Defense Information Systems Network (DISN). In addition to consolidating all service agency transmission multiplexor infrastructures, it called for the consolidation of all service and agency Internet Protocol (IP) router networks. The transmission infrastructures would be consolidated by converting all service and agency multiplexor networks to the same hardware base, the NET IDNX. While the specifics of consolidating the router networks vary between DISA and the various router network managers, DISA is centrally operating at least two worldwide IP router networks, one for the sensitive but unclassified (N) environment, NIPRNET, and one for the secret (S) environment, SIPRNET.

The Non-Classified but Sensitive Internet Protocol Router Network (NIPRNET), Secure Internet Protocol Router Network (SIPRNET), and DISA ATM network (DATM) are DoD internetworks which provide unclassified and classified computer networking service for official DoD business, using ATM.

The NIPRNET is comprised of the former DLA Corporate Network (DCN) in the CONUS, the former DDN Pilot Network, also in the CONUS and extensions into the Pacific and Europe. The former Pilot Network portion of the NIPRNET has been renamed the Joint Interconnection Service (JIS) because it serves as a central network with which routes are available to facilitate reachability with the various router networks to include the Global Internet.

The DISN uses a three layer model to define the different areas of NM responsibility. The top management center is referred to as the Global Control Center (GCC) which is operated by the DISA C4I Network Systems Management Division (D31). The GCC provides management oversight for the deployed networks of the Defense Information Infrastructure (DII) for which DISA has NM responsibility. The second layer is comprised of the Regional Control Centers (RCCs). The RCCs are responsible for the day to day operations of the networks under their immediate control. They are geographically oriented with several centers dispersed across the United States, a center located at the DISA European facilities to cover Europe, and another located at the DISA Pacific facilities to cover the Pacific assets. The RCCs are responsible for the DISA assets within their areas and operate as peers to each other. The RCCs and the GCC are responsible for DISA assets only. The third layer of the hierarchy model is the Local Control Centers (LCCs) which belong to the individual subscriber communities. These management centers control or monitor the assets owned by the individual Service/Agencies connected to the WANs.

The Defense Information System Network provides a wide range of information services to DOD users, including voice telephony, formal messaging, data networking and video. Each of these services today is largely provided by independent and duplicative transmission and switching infrastructures. Enabling technologies such as ATM can overcome the limitations of the existing "stovepipe" systems while improving the overall quality of service.

The DISA ATM network (DATM) is a DoD internetworks which provides unclassified and classified computer networking service for official DoD business. DATM connections are controlled by the Defense Information Systems Agency (DISA) and must be requested from DISA via normal long-haul communications request procedure. Asynchronous Transfer Mode (ATM) is the only protocol specifically designed for multimedia transmissions. It is designed to accommodate data, video, and voice traffic simultaneously and provide the various levels of service required for each type of data. Furthermore, ATM supports data bursting for sudden, unexpected bandwidth requirements.

ATM is standardized for use in the local area network (LAN), metropolitan area network (MAN), and wide area network (WAN). It operates on most transmission media -- copper, fiber, satellite, radio frequency, and laser. DISA's Defense Information Systems Network (DISN) wide area network employs ATM technology for its backbone. DOD has determined that DISA will provide the network, including the entire WAN up to the end device. This serves to centralize network management and support, a cost saving advantage. DISA's costs for ATM network bandwidth are less than bandwidth costs for fixed point-to-point lines. For instance, the cost of a point-to-point T1 line (providing 1.5 Mbps) is about $2,000 per month, which works out to about $1,333 per Mbps per month. The cost of 10 Mbps guaranteed bandwidth for ATM is $2,850 per month, which works out to $285 per Mbps per month.

An encryption device compatible with the transport data rate is employed on numerous DISN transmission links, especially O-CONUS and on satellite/microwave links. There are two types of encryption: (1) Bulk encryption and (2) Cell encryption. Bulk encryption devices, such as the KG-189, KG-95, KG-194, etc., approved by either the National Institute for Standards and Technology (NIST) or the National Security Agency (NSA) are used as point to point bulk encryption devices. The KG-75 (FASTLANE) is used to provide ATM cell encryption. This encryption device is typically installed as part of the CLASSIFIED DISN SDN, on the trunk side of the CLASSIFIED DISN SDN ATM switch.

The existing DISN Transmission Segment is composed of both Government owned and commercially leased connectivity. There is a direct relationship between the performance of the transport systems and the resulting ATM services. A variety of transport systems are used in the DISN transmission subsystem. An issue when using ATM over transmission media such as SATCOM (or similar media such as line of sight radios) is error correction and interoperability. Forward Error Correction (FEC) is necessary to condition these transmission links for ATM service. FEC can be applied at the Physical Layer or at the ATM Layer. A number of current and planned ATM systems offer proprietary FEC at the ATM Layer.

The following performance parameters can be expected from the various DISN transport systems:

Error Free Seconds (EFS) or Error Seconds (ES). Error Free Seconds are defined as the percentage or the probability of one-second error measurements that are error free (EFS) or in error (ES).

Average Bit Error Rate (BER). Average Bit Error Rate is defined as the ratio of errored bits to the total bits transmitted in some time interval.

Degraded Minutes (DM). Degraded Minutes are defined as the percentage of one-minute measurements that have BER> 10-6.

Severely Errored Seconds (SES). Severely Errored Seconds are defined as the percentage of probability of one-second measurements that have BER>10-3.

Residual Bit Error Rate (RBER). Residual Bit Error Rate is defined as the remaining bit error rate which results when SES and Unavailable Seconds are subtracted out from cumulative testing results.

Availability. Availability is defined as 1-U , where U = Unavailability. A period of unavailable time starts when the bit error ratio (BER) in each second is worse than 10-3 for a period of ten consecutive seconds. These ten seconds are considered to be unavailable time. The period of unavailable time terminates when the BER in each second is better than 10-3 for a period of ten consecutive seconds. These ten seconds are considered to be available time.

Loss of Bit Count Integrity (LBCI). Bit Count Integrity is defined as the preservation of the number of bits transmitted in an interval of time. If one or more bits is either added or subtracted in a given interval of time, a loss of bit count integrity occurs which will cause a loss of synchronization in digital transmission equipment.

Delay. Transmission delay of any circuit is the transit time of the transmitted information between the end points of the circuit. Total delay in a circuit is a function of propagation time (path distance and media dependent), buffering, equipment processing delay, and filter delay (for a voice circuit). Propagation delay is independent of data rate, while buffering and processing delay is inversely proportional to the data rate. The specification and threshold for delay is important to voice and interactive data users because of the waiting time effect.

Jitter. Jitter is defined as a short-term variation of the transition instant from its intended position or time. Longer-term variation of the transition is sometimes called wander. Jitter can cause several forms of degradation at bit rates greater than 1.544 Mb/s, from bit errors to loss of synchronization so that it must be carefully controlled in a digital communications system.

Performance Parameters (terrestrial and satellite)

[extracted from DISAC 300-175-9 (draft).]





F/O Copper





Line Rate





1. EFS





2. SES

< .054%




3. DM





4. BER











1/2688 hrs.

1/2688 hrs.

1/78 hrs.

1/2688 hrs.

6. Delay

2 msec

2 msec

300 msec

2 msec

7. Availability



99.4 %



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Page last modified: 28-07-2011 00:48:47 ZULU