Program Emulation Role in Satellite Delay Compensation.The use of alternative communications techniques has significantly increased over the past two years. There are several reasons: the breakup breakup
The division of a company into separate parts. The most famous breakup to date was the 1984 division of AT&T (formerly, American Telephone & Telegraph Company). This breakup was intended to increase competition in the communications industry. of Ma Bell; the fear of dramatic increases in leased-line charges resulting from current investigations by the FCC (1) (Federal Communications Commission, Washington, DC, www.fcc.gov) The U.S. government agency that regulates interstate and international communications including wire, cable, radio, TV and satellite. The FCC was created under the U.S. and Bellcore; the fact that troubleshooting is much more difficult because of all the operating companies and vendors the user must go to; and the new regulatory and technology factors that are appearing with increasing frequency.
Today's business Today's Business is a show on CNBC that aired in the early morning, 5 to 7AM ET timeslot, hosted by Liz Claman and Bob Sellers, and it was replaced by Wake Up Call on Feb 4, 2002. world relies on data communications data communications, application of telecommunications technology to the problem of transmitting data, especially to, from, or between computers. In popular usage, it is said that data communications make it possible for one computer to "talk" with another. . Businesses such as banks, insurance companies and human services--including police departments, travel agencies and commercial airlines--are especially dependent on data communications.
New operating concepts such as distributed data processing See distributed processing. , local area networks, X.25 public data networks and satellite transmission have promoted the use of data communications and increased the demand for less-expensive and more-reliable facilities and equipment.
Satellite transmission is being used or contemplated by many companies as a method to reduce transmission costs, as a backup and as disaster recovery for prolonged terrestrial communications line outages. In some areas of the country, satellites are the only viable alternative to terrestrial communications lines.
If a corporation is going to use satellite communications it must first choose to contract with a common carrier and obtain site-to-site service, or contract with a satellite or transponder A receiver/transmitter on a communications satellite. It receives a microwave signal from earth (uplink), amplifies it and retransmits it back to earth at a different frequency (downlink). A satellite has several transponders. owner for a space segment and build and own the corporate ground segment. Transponders are divided into C-band and Ku-band. C-band is 4/6 Ghz and Ku-band is 12/14 GHz.
Data transmission by satellite, while fine for some companies, has been a disappointment for others--especially for those using delay-sensitive protocols such as IBM's 3270 Bisync protocol. This is due to the unavoidable effect of satellite propagation delay The time it takes to transmit a signal from one place to another. Propagation delay is dependent solely on distance and two thirds the speed of light. Signals going through a wire or fiber generally travel at two thirds the speed of light. Contrast with nodal processing delay. , the result of satellites orbiting 23,000 miles above the earth.
Some protocols can work with extensive delays. But in the case of IBM's 3270 Bisync, a positive-acknowledgement protocol, these delays can be overwhelming to the point of rendering multidrop lines useless.
Overcoming The Delays
The challenge to today's data communications managers and applications engineers is to understand the applications and effects of satellite transmission delays and the possible corrections.
To overcome inherent delay problems, some users may be able to migrate their network to a protocol that is more immune to the effects of satellite delays than 3270 Bisync.
X.25 and SNA/SDLC are well-suited for satellite transmission because they can support multiple outstanding messages.
These protocols use an acknowledgement sequence number, Nr and Ns, that starts at zero and can increment To add a number to another number. Incrementing a counter means adding 1 to its current value. to seven before cycling to zero again. This is called "modulo-8." It can be expanded to "modulo-128," where 127 messages can be outstanding before cycling to zero. However, most of today's equipment can not handle modulo-128, and it is rarely used.
The fact is, most users already have a large installed base of equipment that cannot be converted. They may want to consider another alternative due to the expense of new equipment and the even greater expense and time delay of retraining re·train
tr. & intr.v. re·trained, re·train·ing, re·trains
To train or undergo training again.
Delay-compensation devices are the logical and most cost-effective way to overcome propagation delay problems. One form of satellite delay compensation is program emulation, which provides local acknowledgement and response to the front-end processor front-end processor - (FEP) 1. A small computer necessary to enable an IBM mainframe using SNA to communicate beyond the limits of the dinosaur pen.
2. A small computer controlling the screen and keyboard of a Symbolics 3600 LISP Machine. and control units. This eliminates time-outs and efficiency loss due to satellite propagation delay.
Program emulation can be handled on a line-by-line basis using external individual "black boxes." But a much more organized and cost-effective way is through program emulation in networked statistical multiplexing See statistical multiplexor. , which provides for multiple lines and greater network efficiency.
Some statistical multiplexing devices also provide statistics, redundancy and other capabilities not available in the "black-box" solutions. For example, Infotron provides program emulation through what it calls "Bisync Emulation," and incorporates it into its 790 Network Concentrator and 990 Network Processor multiplexing multiplexing, in communication, technique whereby two or more independent messages, or information-bearing signals, are carried by a single common medium, or channel. products to compensate for satellite delays and to increase communications link efficiency. Total throughput can be increased by as much as 40 percent with the Bisync emulation feature due to bandwidth savings.
Bisync emulation removes non-productive polling traffic from the communications lines and handles all poll/select requests and acknowledgements locally. This can provide support for additional users without adding equipment, reduce the number of network facilities typically required to expand a system, compensate for satellite-caused delay time-outs and even decrease response time from the user's point of view.
to a user, response time is the amount of time the keyboard is locked. With local acknowledgement, the user's terminal is unlocked very quickly.
The Bisync emulation feature contines to provide all the error-control correction and diagnostics available on all standard IBM (International Business Machines Corporation, Armonk, NY, www.ibm.com) The world's largest computer company. IBM's product lines include the S/390 mainframes (zSeries), AS/400 midrange business systems (iSeries), RS/6000 workstations and servers (pSeries), Intel-based servers (xSeries) 3270 Bisync systems. Data compression data compression
Process of reducing the amount of data needed for storage or transmission of a given piece of information (text, graphics, video, sound, etc.), typically by use of encoding techniques. is incorporated into the Bisync emulation feature to further reduce bandwidth usage and improve communications link efficiency.
Normal IBM 3270 Bisynchronous network operation controls the flow of data transmission by using polling schemes. Polling increases the amount of data traffic over a network because the control characters are transmitted in addition to the normal data-consuming bandwidth on the transmission facility. The Bisync emulation feature controls the flow in a Bisync environment and cuts down on the overhead.
All IBM 3270 and 790NC/990NP control and diagnostics remain intact, giving the user full data integrity.
A unique feature of the 790NC and 990NP is that they allow a user to combine async, Bisync, SDLC (Synchronous Data Link Control) The primary data link protocol used in IBM's SNA networks. It is a bit-oriented synchronous protocol that is a subset of the HDLC protocol. See SNA, DLC and Microsoft DLC.
1. and other multiple-protocols in the same unit.
With the addition of the ANM ANM Azienda Napoletana Mobilità (Italian)
ANM Advancing Native Missions
ANM Answer Message (telecommunications)
ANM Auxiliary Nurse Midwife
ANM Arab Nationalist Movement
ANM Advanced Network Management 800 network monitor, a user can accumulate statistics on the amount of compression in the network, peak and average characters per second, NAKs and other systemwide, technical-control network-management information.