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Protocol converters: the answer to compatibility problems?
Protocol converters: the answer to compatibility problems? System upgrading is often complicated by the need for compatibility. Peter Robinson describes a range of add-on devices that allow: the linking of systems from different vendors
One
of the major data communications problems over the past few years been how to make different vendors" hardware and communicate. Standards proposed by various standardization bodies have been set up to solve problems, rather than prevent them. The paper discusses the use of protocol converters to provide compatibility between devices. The implementation of protocol converters within systems is described, along with suitable applications and environments. A cost comparison of configurations with and without protocol converters is provided.
With the proliferation of suppliers in the computer industry, one ofthe major data communications problems over the last few years has been how to make different vendor's hardware and software communicate. Standards bodies, in particular the International Standards Organisation (ISO), are addressing these problems. However, as with all similar standards within rapidly developing industries, they are set up to solve problems, rather than to stop problems occuring.
because of its size and the obvious potential revenue to be gained, but also because IBM users have, in many instances, already implemented networks obtained from a supplier other than IBM. As a consequence, they are aware of the many benefits of certain nonlBM products, and have already moved into a multivendor environment. A protocol converter will, therefore, generally provide BSC and/or SNA protocols to cover IBM's 2780, 3780, HASP, 3270 and 3770 (see Figure 1).
I Mini I
has
software
Host
I plotter Pen J
J
Console
Keywords: data communications, computercomputer communications, compatibility, tocols, protocol converters
Figure 7. Typical configuration, showing protocol converter (PC) with HASP emulator
GCS,Orion Park,226-236NorthfieldAvenue, LondonW13 9QU,UK
One of the most recent innovations designed to aid product compatibility is the protocol converter. This device converts transmission signals from many different peripherals into the protocol used by a host computer. (A protocol is a communications code unique to a given operating system.) The majority of these protocol converters have been developed for the IBM marketplace, not only
pro-
148
There are three main reasons why a mainframe computer user should look for products outside his existing suppliers.
• Cost: plug-compatible products show greater cost benefits than those offered by the main supplier. The protocol converter has now considerably widened the range of products that can be evaluated.
computer communications
• Upgradeability: supplier policies often dictate that protocol or software changes necessitate a compulsory change of hardware. Upgrades with a protocol converter can avoid this, and can lengthen the life of an installed product. • Technology: certain products, particularly in the CAD/CAM area, are technically more advanced than those offered by the main supplier. The use of a protocol converter can allow the connection of these devices using a standard interface to the host mainframe.
remote cluster controller, allowing a number of these ASCII devices to communicate in a single line to the communications processor on the host mainframe (see Figure 2).
I mplementation A mandatory requirement of a protocol converter is that its implementation within an existing network must be by simple connection, without any change to the hardware or software principles of the controlling host computer. The
BSC 3270
Figure 2. Basic IBM interactive network; protocol converter used as local and remote cluster controller One of the most commonly used range of terminals is the IBM 3270 series, including those equivalents offered by plug-compatible vendors such as Telex, 13-1-and Harris. These relatively expensive IBM synchronous terminals can be supplemented or replaced by a protocol converter and a wide variety of
converter would be handled by a hunting unit. Even if these devices need to be connected on a more general basis, asynchronous modems offer significant savings over bisynchronous modems.
technical capability of a protocol converter supplier should therefore be assessed prior to ordering this type of equipment, particularly its ability to modify firmware within the protocol converter itself. It is also essential to ensure that the right range of products can be seen to be working.
Applications In addition to standard ASCII terminals, other types, particularly graphic terminals, can enjoy the benefits of clustered bisynchronous communications, in terms of both speed and accuracy. For instance, using a protocol converter such as that marketed by GCS, several Tektronix 4000 series devices can be connected as 3270 screens directly into a bisynchronous port on an IBM 3705. A typical IBM cluster will include printer support. A protocol converter should, therefore, allow connection of a number of different asynchronous devices to be intermixed on a unit along with a printer to emulate a 3284 or 3286-type IBM printer. The use of protocol converters has allowed the inclusion of such devices as word processors, micros, minis and datapads into networks, even though their individual protocols are almost certainly either incompatible or uneconomic, in terms of those offered by the main supplier. In addition, they are now being considered for use as gateways into local networks, particularly those offered within the micro market.
Example
"=,"°° Figure 3. Centralized use of a protocol converter with dial-up facilities through a hunting unit dumb or intelligent ASCII terminals. The protocol converter will provide these terminals with most or all of the functional characteristics required of a 3270 terminal. At the same time, it will act as a local or
vol 5 no 3 june 1982
Where a user wants to link ASCII devices directly to an existing network, a protocol converter with dial-up facilities from multiple locations could be used (see Figure 3). Allocation of ports on the
Consider a typical protocol converter, such as the GCS Series II. This will comprise a power supply, status display, a bisynchronous port and typically up to eight asynchronous ports. While this may be installed at board level within another product, it will normally be available boxed, with interfacing achieved by the connection of 25-way Delta plugs. The synchronous-port modem attachment
follows standard EA RS232C interfacing procedures, while for local connection, a switchable modem simulator condition will allow direct connection to the host mainframe. Speeds between 150 bit/s and 19.2 kbit/s can be selected by useroperated switches. Other features include EBCDIC (TN subset), datatransparency protocol (receive only), full BSC 'handshaking', recognizing and/or utilizing NAK, ACK-O, STX, ETB, ETX, WACK, TTD, IUS, ENQ, EOT etc., CRC-16 dataerror detection and recovery, dynamic and switch-selectable control with address and memory selftest on startup.
all terminals on the market, provided that they have addressable cursor positionin& cursor-home and clear-screen capabilities. Control-character sequences are used to support the AID functions (ENTER, CLEAR, PA-1,2, 8 and FP1PF24) as well as character and field manipulation.
Up to eightdevices
On the asynchronous ports, the protocol converter communicates with CRTs in serial asynchronous ASCII format, again using the standard EA RS232C interface procedure. Datarate is switch selectable to 150, 300, 600, 1 200, 2 400, 4 800, 9 600 and 19 200 bit/s. Each port can be tailored to user requirements, with respect to speed parity (even, odd or none) stop bits (I or 2), data bits (7 or 8) and data set/data terminal. The unit maintains a separate
The ultimate determinant when considering the use of a protocol converter must be price, and many low-cost terminals are already available. Table 1 shows a typical cost comparison for an IBM system with and without a converter.
Asynchronous modems
D
Asynchronous ports
Cost
Up to eight devices
Up to eightdevices
Synchronousmodems
Figure 4.
One multipoint line with several protocol converters
The protocol converter with attached printer will emulate an IBM 3287 buffered printer. The printer line width is set at a 132 column maximum for unformatted print buffers, and fixed at 40, 64 or 80 columns for formatted print buffers. It communicates with printers in byte-parallel or serial ASCll (EIA RS232C), or both. In the asynchronous mode, DIP, is used to determine printer online/offline.
The use of one parallel multipoint line reduces both the cost of communications lines and the cost of additional ports on the front-end device (see Figure 4). Each protocol converter has a unique address, and this configuration offers distinct advantages over traditional networks, particularly with the possibility of further economies in the use of additional asynchronous links.
Table I. Cost of adding a protocol converter to an IBM system Configuration
Cost, £
IBM system 5 X 3278 terminals 2 X 3287 printers 1 X controller (including screen) Total
7 250 8 400 4 500 20 150
With protocol converter
Typical protocol converter
150
6 X asynchronous screens 2 X 120 character/s printers 1 X 8 port protocol converter
3 645
Total
8 345
3 000 1 700
computer communications
One
of the major data communications problems over the past few years been how to make different vendors" hardware and communicate. Standards proposed by various standardization bodies have been set up to solve problems, rather than prevent them. The paper discusses the use of protocol converters to provide compatibility between devices. The implementation of protocol converters within systems is described, along with suitable applications and environments. A cost comparison of configurations with and without protocol converters is provided.
With the proliferation of suppliers in the computer industry, one ofthe major data communications problems over the last few years has been how to make different vendor's hardware and software communicate. Standards bodies, in particular the International Standards Organisation (ISO), are addressing these problems. However, as with all similar standards within rapidly developing industries, they are set up to solve problems, rather than to stop problems occuring.
because of its size and the obvious potential revenue to be gained, but also because IBM users have, in many instances, already implemented networks obtained from a supplier other than IBM. As a consequence, they are aware of the many benefits of certain nonlBM products, and have already moved into a multivendor environment. A protocol converter will, therefore, generally provide BSC and/or SNA protocols to cover IBM's 2780, 3780, HASP, 3270 and 3770 (see Figure 1).
I Mini I
has
software
Host
I plotter Pen J
J
Console
Keywords: data communications, computercomputer communications, compatibility, tocols, protocol converters
Figure 7. Typical configuration, showing protocol converter (PC) with HASP emulator
GCS,Orion Park,226-236NorthfieldAvenue, LondonW13 9QU,UK
One of the most recent innovations designed to aid product compatibility is the protocol converter. This device converts transmission signals from many different peripherals into the protocol used by a host computer. (A protocol is a communications code unique to a given operating system.) The majority of these protocol converters have been developed for the IBM marketplace, not only
pro-
148
There are three main reasons why a mainframe computer user should look for products outside his existing suppliers.
• Cost: plug-compatible products show greater cost benefits than those offered by the main supplier. The protocol converter has now considerably widened the range of products that can be evaluated.
computer communications
• Upgradeability: supplier policies often dictate that protocol or software changes necessitate a compulsory change of hardware. Upgrades with a protocol converter can avoid this, and can lengthen the life of an installed product. • Technology: certain products, particularly in the CAD/CAM area, are technically more advanced than those offered by the main supplier. The use of a protocol converter can allow the connection of these devices using a standard interface to the host mainframe.
remote cluster controller, allowing a number of these ASCII devices to communicate in a single line to the communications processor on the host mainframe (see Figure 2).
I mplementation A mandatory requirement of a protocol converter is that its implementation within an existing network must be by simple connection, without any change to the hardware or software principles of the controlling host computer. The
BSC 3270
Figure 2. Basic IBM interactive network; protocol converter used as local and remote cluster controller One of the most commonly used range of terminals is the IBM 3270 series, including those equivalents offered by plug-compatible vendors such as Telex, 13-1-and Harris. These relatively expensive IBM synchronous terminals can be supplemented or replaced by a protocol converter and a wide variety of
converter would be handled by a hunting unit. Even if these devices need to be connected on a more general basis, asynchronous modems offer significant savings over bisynchronous modems.
technical capability of a protocol converter supplier should therefore be assessed prior to ordering this type of equipment, particularly its ability to modify firmware within the protocol converter itself. It is also essential to ensure that the right range of products can be seen to be working.
Applications In addition to standard ASCII terminals, other types, particularly graphic terminals, can enjoy the benefits of clustered bisynchronous communications, in terms of both speed and accuracy. For instance, using a protocol converter such as that marketed by GCS, several Tektronix 4000 series devices can be connected as 3270 screens directly into a bisynchronous port on an IBM 3705. A typical IBM cluster will include printer support. A protocol converter should, therefore, allow connection of a number of different asynchronous devices to be intermixed on a unit along with a printer to emulate a 3284 or 3286-type IBM printer. The use of protocol converters has allowed the inclusion of such devices as word processors, micros, minis and datapads into networks, even though their individual protocols are almost certainly either incompatible or uneconomic, in terms of those offered by the main supplier. In addition, they are now being considered for use as gateways into local networks, particularly those offered within the micro market.
Example
"=,"°° Figure 3. Centralized use of a protocol converter with dial-up facilities through a hunting unit dumb or intelligent ASCII terminals. The protocol converter will provide these terminals with most or all of the functional characteristics required of a 3270 terminal. At the same time, it will act as a local or
vol 5 no 3 june 1982
Where a user wants to link ASCII devices directly to an existing network, a protocol converter with dial-up facilities from multiple locations could be used (see Figure 3). Allocation of ports on the
Consider a typical protocol converter, such as the GCS Series II. This will comprise a power supply, status display, a bisynchronous port and typically up to eight asynchronous ports. While this may be installed at board level within another product, it will normally be available boxed, with interfacing achieved by the connection of 25-way Delta plugs. The synchronous-port modem attachment
follows standard EA RS232C interfacing procedures, while for local connection, a switchable modem simulator condition will allow direct connection to the host mainframe. Speeds between 150 bit/s and 19.2 kbit/s can be selected by useroperated switches. Other features include EBCDIC (TN subset), datatransparency protocol (receive only), full BSC 'handshaking', recognizing and/or utilizing NAK, ACK-O, STX, ETB, ETX, WACK, TTD, IUS, ENQ, EOT etc., CRC-16 dataerror detection and recovery, dynamic and switch-selectable control with address and memory selftest on startup.
all terminals on the market, provided that they have addressable cursor positionin& cursor-home and clear-screen capabilities. Control-character sequences are used to support the AID functions (ENTER, CLEAR, PA-1,2, 8 and FP1PF24) as well as character and field manipulation.
Up to eightdevices
On the asynchronous ports, the protocol converter communicates with CRTs in serial asynchronous ASCII format, again using the standard EA RS232C interface procedure. Datarate is switch selectable to 150, 300, 600, 1 200, 2 400, 4 800, 9 600 and 19 200 bit/s. Each port can be tailored to user requirements, with respect to speed parity (even, odd or none) stop bits (I or 2), data bits (7 or 8) and data set/data terminal. The unit maintains a separate
The ultimate determinant when considering the use of a protocol converter must be price, and many low-cost terminals are already available. Table 1 shows a typical cost comparison for an IBM system with and without a converter.
Asynchronous modems
D
Asynchronous ports
Cost
Up to eight devices
Up to eightdevices
Synchronousmodems
Figure 4.
One multipoint line with several protocol converters
The protocol converter with attached printer will emulate an IBM 3287 buffered printer. The printer line width is set at a 132 column maximum for unformatted print buffers, and fixed at 40, 64 or 80 columns for formatted print buffers. It communicates with printers in byte-parallel or serial ASCll (EIA RS232C), or both. In the asynchronous mode, DIP, is used to determine printer online/offline.
The use of one parallel multipoint line reduces both the cost of communications lines and the cost of additional ports on the front-end device (see Figure 4). Each protocol converter has a unique address, and this configuration offers distinct advantages over traditional networks, particularly with the possibility of further economies in the use of additional asynchronous links.
Table I. Cost of adding a protocol converter to an IBM system Configuration
Cost, £
IBM system 5 X 3278 terminals 2 X 3287 printers 1 X controller (including screen) Total
7 250 8 400 4 500 20 150
With protocol converter
Typical protocol converter
150
6 X asynchronous screens 2 X 120 character/s printers 1 X 8 port protocol converter
3 645
Total
8 345
3 000 1 700
computer communications