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Chapter 8

Asynchronous Transfer Mode Switch

This chapter gives an overview of the asynchronous transfer mode (ATM) switch for high-speed data switching.


  8-1. ATM technology provides a highly efficient communication system for high-speed data switching. This capability transmits voice, video, and data in a single communication link. Figure 8-1 shows the basic ATM switch technology. The system can also transmit still photography, images, and graphics.

Figure 8-1. ATM Switch Technology


8-2. The ATM basic technology concept involves using a virtual path identifier (VPI) and a virtual circuit identifier (VCI). The VPI and VCI are used for ATM address assignment. The VPI directs the data to the correct receiver, and the VCI identifies the different cell streams within a transmission. Virtual circuits are one-way ATM connections from source to destination, which means that two connections are required for full-duplex (two-way) communications.

8-3. ATM technology offers additional advantages that include-

  • More efficient use of radio bandwidth because it dynamically assigns bandwidth as needed.
  • Ability to assign priority and precedence for designated users, allowing data from high priority users to be sent out first.

8-4. ATM switching shows significant potential, especially for large throughput and fast speed of service. The ATM hub switch provides the tactical ATM backbone switching support for all tactical users. The switch terminates wideband fiber optics, synchronous optic network (SONET) radios, and currently employed tactical digital radios and DTG network interfaces. It has an adaptive forward error correction (FEC) capability that improves the quality and reliability of the DTGs.



8-5. The ATM switch package provides a multimedia and a video teleconference (VTC) capability for commanders in the field. ATM technology applies to selected switches in the MSE ACUS. ATM switches support workstations where key commanders participate in VTCs using the MSE network as a transmission medium. ATM cells created at the workstation and those created in the ATM switch are transmitted across MSE links according to designated addresses.

8-6. The ATM switch package is the Integrated Systems Technology (IST) Model LDR-100 ATM switch card, which has two versions. The first is the LDR-100C compact version installed in the SENs. The other is the LDR-100S standard version installed in the AN/TTC-47 NCS. The LDR-100-

  • Uses the Lucent Limitless ATM Network (LANET) ATM protocol that puts ATM cells into frame for synchronization and ease of identification.
  • Provides cell leader error correction that allows address mapping according to possible errors if a header or address contains error data (bits).
  • Supports ATM and non-ATM links that supports VTC, multimedia, MSE voice, and TPN traffic.
  • Contains special buffers to minimize the delay of constant-bit-rate (CBR) traffic and to allow peak data rates for variable-bit-rate traffic.
  • Supports up to 4,095 independent ATM addressees for each port.
  • Uses four serial ports using the Communications-Electronics Command (CECOM) Quad-Serial Card. This card supports programmable data rates of 300 bytes per second (bps) to 1.544 megabytes per second (mbps) using serial protocols (RS-232 or RS-422) and the transmission of cell-bearing and non-cell bearing data. The Quad-Serial Card interfaces the ATM switch with the MSE system.
  • Uses one transparent asynchronous transceiver interface (TAXI) card to support connections for one serial system and one parallel port. It allows programmable data rates for each port and supports the transmission of cell-bearing and non-cell bearing data.
  • Uses a TAXI card to connect the user's VTC workstation to the ATM switch.
  • Uses an interface card that has its own CPU. The CPU stores the configuration and settings for that interface card, and it allows preconfiguration of ATM switches during the predeployment phase.


  8-7. The ATM switch package is embedded in selected NCs, LENs, and SENs of the MSE network. Figure 8-2 shows the NC and LEN switch configuration. Figure 8-3 shows the SEN switch configuration.

Figure 8-2. ATM Switch Configuration for NC/LEN

Figure 8-3. ATM Switch Configuration for SEN

  8-8. ATM-enabled MSE switches are positioned according to the factors of METT-T to best support the commander's concept of the operation. ATM switches usually locate with the DTAC, the brigade TOC, the aviation TOC (AVTOC), and the brigade rear TOC. ATM-enabled MSE switches also locate as needed with the Army Air Missile Defense Command (AAMDC), Air and Missile Defense Planning and Control System (AMDPCS), and Air and Missile Defense Task Force. Figure 8-4 shows an example of a typical deployment of the MSE network with ATM-enabled NCSs and SENSs.


Figure 8-4. Deployment of the MSE Network with ATM-Enabled NCSs and SENSs


  8-9. Sun Net Manager is the operational software used and is contained in a laptop computer. To support the operational requirements for efficient high-speed data switching, the ATM switch applies the advanced ATM technology in its operational software design. Figure 8-5 shows that the data being transferred is broken down into very small pockets (53 bytes) called cells and given specific addresses for their destination. Each cell contains a 5-byte leader for control purposes and 48 bytes for the data payload. The software design supports the transmission of video, audio, and data from their sources to their destinations within the MSE architecture.


Figure 8-5. ATM Source Multiplexing Function


  8-10. Operational planning for the ATM network focuses on ensuring the required communication capabilities are available and tailored to the commander's requirements. ATM facilities and capabilities are tuned to support the operational requirements of the mission. ATM connections and naming requirements are determined well before deployment. Figure 8-6 shows a typical DTG path for ATM-enabled telephone circuits.

Figure 8-6. DTG Path for MSE Telephone Circuits

  8-11. Data rates between an NC and a SEN are increased from 256 kbps to 1024 kbps. This allows 256 kbps for MSE switching and the TPN; and 786 kbps to support user VTC, whiteboarding, and high-data requirements through the ATM switch. Links between two NCs (internodal links) will operate at 1024 kbps. The NCS will configure their databases to operate at 512 kbps. This allows 512 kbps for VTC/whiteboarding workstation connections and MSE switching and TPN data. Figure 8-7 shows the use of two DTGs for the ATM. Network planning factors include workstation needs to operate within hardware and software parameters. For example, ATM network interface cards (NICs) in the workstations listen only for ATM connections addressed with O as the VPI.


Figure 8-7. Using Two DTGs for an ATM Solution



8-12. The current ATM-enabled MSE switch contains limitations that affect employment techniques in the field. ATM technology relies on LOS radios operating at 1024 kbps. Potential frequency allocation problems are due to the number of frequencies available within the battlespace. Current MSE systems were designed for 1024 kbps for internodal links between NCs and 512 kbps for links for LENs and SENs (256 kbps was typically used for links leading from SENs). The requirement for increasing the bandwidth for all links to support ATM switching can lead to frequency allocation problems. Careful planning is required to allow adequate bandwidth and frequency allocation.

8-13. Within the NCs, it is impossible to use the same DTG for interface in and out of the ATM switch. This is because the transmission group modem and orderwire (TGMOW) card in the NCs cannot support multiple data rates. The TGMOW card provides the interface to both the plain text and cipher test sides of the TED. On the plain text side of the TGMOW, the card creates and manages the framing channel to the DTG. On the cipher text side, the TGMOW provides a reclocking buffer to adjust for differences between network and switch timing. Although both sides are running synchronous interfaces (clock and data), the two sides are not independent of each other. The TGMOW card requires a common clock for both sides and must operate at different data rates.

8-14. The necessity to run the TGMOW at two different rates is due to inherent properties of CBR cell encapsulation. The CECOM Quad card provides two modes: a non-cell bearing CBR RS-442 access and cell bearing DTG trunk. The access modes on the CECOM Quad card encapsulate incoming data into ATM cells. This process takes the CBR data, regardless of content, and places it within the payload of an ATM cell.

8-15. The resulting output has an additional 10 percent in ATM header information in addition to the data. This results in a higher data rate on the cell-bearing side of the CECOM Quad card. To resolve the multiple data rate problem, a second DTG is set up to interface to the output of the CECOM Quad card at the cell-bearing rate while the DTG connected to the switch matrix will run at the access data rate. This keeps the TGMOWs in agreement with the input and output rates at the ATM switch. NCs must also modify the database so that the TED corresponding to the actual DTG used is consistent with the setup. This way, the COMSEC controller card knows which TED to control if an AUTO-RESYNC COMMAND occurs.

8-16. An ATM-enabled SEN does not have the same problem as the NCs with the TGMOW card. The ATM-enabled SEN can only connect to an ATM-enabled NC. This reduces the flexibility of reconfiguring the MSE network during movement across the battlefield. The ATM-enabled NCs must have a CECOM Quad card and two DTGs available before it can connect the SEN into the MSE system. Network planners must know the contents and configuration information of the NCs database and the ATM switch configuration to reconfigure the network.


  8-17. A high-speed multiplexer (HSMUX) circuit card that replaces the multiplexer-demultiplexer (MXDMX) card in MSE switch modems provides video and high-speed data access through the MSE network at ECB and the TRI-TAC network at EAC. The HSMUX expands the group rate from 256 to 512 kbps and provides a port for local connections and four high-speed ports that support data rates of 64, 128, and 256 kbps. The HSMUX enables high-speed data access over the existing backbone network. Circuit configuration is via the channel reassignment function (CRF) that allows the switch operator to configure automatic connection for VTC service. An enhancement option will allow automatic circuit configuration through programming software. Appendix D provides a more detailed description of the HSMUX.


  8-18. The enhanced transmission group modem and orderwire (ETGMOW) cards will be an interim solution to increased data capabilities prior to the Warfighter Information Network (WIN). The ETGMOW and HSMUX II cards alleviate customizing the standard database (channel reassignment) at the NC and assigning multiplexers that reduce extension capabilities.


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