FUTURE COMMUNICATIONS SYSTEMS The planning and implementation of

The Special Requirements of Data Communications Traffic

FUTURE COMMUNICATIONS SYSTEMS The planning and implementation of

communi-cations systems in the future are going to be both easier and harder than today. It will be easier for those who want to implement rather conventional communications systems because they will be able to simply connect to one of the several digital value-added or common carrier digital systems now being developed. A variety of services will be available, including dial up, circuit switching, and packet switching with a high degree of data integrity, on the order of losing one bit per year on the average.

Communications systems planning and implementa-tion will be more difficult for those who need a dedicated system to meet improved cost, per-formance, or reliability goals beyond those provided by the value-added or common carrier networks. The proliferation of network architectures, protocol standards, carrier services, hardware products in the form of.front end ..£!..oce~, concentrators, network.

Qrocessors, and communicatiollssoftware will m

t h e · . . a custo m

communications system a formidable task.

No matter which approach is taken, value-added network, common carrier network, or custom design (the large organization may use all three), the technology options available will be the same, with the following exception. Since computers are used for both communications functions and data processing functions, it is often desirable to combine both functions on the same computer. Government regulations prevent common carriers from combining functions; however, private network systems using only transmission facilities from common carriers can combine functions and thus gain an added measure of efficiency. The following describes the system functions and components that will be used by any communications network in the next several years.

The greatest difference between communications systems in the past and in the 1980's is that at that time the communications system will have an existence of its own rather than being dependent on a host; so that the communicating system will continue

to function even if one or more hosts fail. The host

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will be treated as an optional peripheral attached to the communications system. The network processor will perform the communications functions now performed by several, more specialized products, including:

• Front-end processor

• Remote /line concentrator

• Host (interface functions)

• Store-and-forward message switching

• Communications node

A front-end processor now interfaces the host processor to the communications system, often to a number of low speed dedicated lines to terminals. The front-end processor function is to perform highly repetitive functions of terminal polling, message assembly / disassembly, error detection/ correction, and network support if the host fails. The network processor performs this same function independent of the nature of the communications load, be it many low speed lines, a few high speed lines, or a packet switching system. Where formerly it was necessary to multiplex many low speed lines into one high speed line, a concentrator was used; the network processor will also perform this function.

In order to interface terminals to a current communications system, a host must be present. With network systems, the network processor will interface terminals to the communications system with no host present. And network processors, as nodes in a communications system, will provide store-and-forward functions whether the information is text or data, message switched, or packet switched.

The configurations supported will be quite varied, to conform to the specific needs of individual users. The most common configuration will be hierarchical (which includes the star configuration) because of the match to people organizations, which are usually hierarchical. Also, star configurations as drops along a backbone communications link will also be common in larger organizations with decentralized operations. The more general network configurations will also be supported, using rather arbitrary interconnect of nodes with combinations of high speed, low speed, and redundant lines. The supported configurations will also allow interfacing among value added, common carrier, and private networks.

Many systems will also allow interfacing of equipments (especially hosts) from various manu-facturers, because most medium to large users have hosts from various manufacturers which must be

JUNE 1979

The Special Requirements of Data Communications Traffic integrated. This will be accomplished by using either

network standard protocols or by using software adapt modules at appropriate places. An example of a complex network system is shown in Figure 3.

FRONT·ENO PROCESSOR

TS;TERMINATION SYSTEM TNC;TRANSPORT NETWORK CONTROL

Figure 3. Complex network

FRONT·ENO PROCESSOR

The communications system will provide a very high degree of both data integrity and reliability in a manner transparent to the user. End-to-end (i.e., user to user) data integrity will be provided by a combination of:

• Cyclic redundancy checks (error detection codes for bursts)

• Checksums

• Holding packets/messages at transmission end until acknowledgement of correct reception

• Acknowledgement of correct reception

• Packet/ message sequence numbers

• Error logging/ reporting

Undetected error rates should be less than one bit per year. Reliability will be provided by redundancy at several levels. Red undant network processor configurations, often as multiprocessors, will be provided to enable failsoft operation. Multiple lines and mUltiple trunks will be used to avoid impact of

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processor in case of an outage. The availability of such a system will depend strongly on the degree of redundancy used; therefore, availability will be a strong function of cost of the system.

The various modes of communications now used will be supported, including packet switching, message

switching, dial up, and dedicated. It will be possible to mix these in various parts of the system, depending on specific local needs.

A number of services will be provided to the user by the manufacturer-supplied system software, thus relieving him of the very large software development to accomplish these, including:

• Session establishment

• T mnk selection

• Circuit load balancing

• Congestion control

• Directory service

• Circuit selection

• Flow control

• Encryption/ decryption

There is also experimental work in progress to provide automatic host load-leveling. In this approach, individual hosts are allowed to "bid" on incoming tasks, depending on the backlog each has at the time and the efficiency of performing that kind of task. Although the feasibility of this approach remains to be validated, it appears to be attractive in a packet switching environment where transmission cost is relatively independent of distance.

Although the communications system software relieves the user of considerable software develop-ment, he still must provide the information necessary to configure the software. Because of the large number of options and the considerable complexity of communications systems, this will be a rather complex task, even after the desired system design has been developed. Also, installation, checkout, and acceptance testing of a large communications system will continue to be rather complex, although the total effort will be reduced by an order of magnitude relative to a custom system because of manufacturer supplied software.

The availability of LSI is already having a significant impact on the communications capabilities of new

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intelligence available will permit incorporation of sophisticated protocols such as X.25 in the terminal so that it can be interfaced directly to a communi-cations system rather than being attached to a host or a network processor. The terminal will be able to provide functions such as encryption and error detection/ correction. Also, terminals in the next few

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Basic Concepts

The Special Requirements of Data Communications Traffic years are likely to have built-in modems as a low cost

option.

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^REGIONAL

COMMUNICATION CENTERS

~ MAJOR FACILITY COMMUNICATION CENTERS

• MINOR FACILITY COMMUNICATION CENTERS

A typical total corporate communications system of the mid 1980's is shown in Figure 4. Each location will use a variety of communications services, all digital, including voice, messages, facsimile, and computer data. The sources of the data will be telephone, electronic office work stations, and computer hosts or terminals. The various office locations are linked together by land lines (probably fiber optics) to a regional satellite ground station. A common carrier satellite is used to link together the

regional centers, both domestic and overseas. 0 ^Figure4. Tlpical corporate communications netH'ork

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Im Dokument COMMUNICATIONS SOLUTIONS (Seite 53-56)