FAQ Protocol Support
Sixnet Commercial Wireless products use these protocols to provide communications with existing devices and networks.
Click on Protocol to view details.
Async
Tandem
Bisync
TCP/IP
Frame Relay
UDP
Poll/Select
Uniscope
SNA/SDLC
X.25
For information on the optional software available with the Gateways, please click here.
The async support available for our products falls into two categories: polled and character mode. The Polled support is a full implementation of the vendor's Legacy protocol. The character mode is designed for connection of non-polled async devices.
Polled Protocols
The supported polled async protocols are:
- NCR Poll/Select
- Tandem AM6520
- Unisys Poll/Select
- Visa
- 8A1
The async interface is designed to receive non-blocked, character mode transmissions from the attached device. We can expand this interface to support many different types device requirements, including Block Checks, enhanced flow control and retry capabilities.
- Data Format - ASCII data format is supported with 7 or 8 bit words
- Flow Control - RS-232C hardware, XON/XOFF, ENQ/ACK and specialized device support.
The Gateways support many different types of async terminals used in various industries. These Gateways implement the terminal protocol in two ways:
- Host Emulation. With this mode, the Gateway will emulate an async host and acquire the data for conversion and transfer to another system.
- Intelligent Pass-through. With this mode, the Gateway establishes a connection with a remote async connection and converts the data from TCP/IP to async. The data can be sent from a Telnet or TCP/IP application. The Gateway can accept a connection from the local async device or a remote TCP/IP Client. This mode can be used for transfer of software updates to the terminal or for real-time control.
- XModem. With this mode, the Gateway emulates a host for connection by a remote async system using XModem protocol. XModem is used for simple file transfers between the two systems.
To view the available options that can be specified for this protocol, please click here.
Async Card Comparisons
The Edge Gateways support async through a dedicated microprocessor on each port. The Gateway 1000 (G1000) offers both intelligent and non-intelligent cards for async interface. The data from the non-intelligent cards is processed by the main G1000 processor instead of a dedicated microprocessor at the port. The cards and protocols are:
| Card | Ports | Type | BUS |
| G1000-4PC | 4 | Non-intelligent | ISA |
| G1000-4PC/P | 4 | Non-intelligent | PCI |
| G1000-8PC | 8 | Non-intelligent | ISA |
| G1000-8PC/P | 8 | Non-intelligent | PCI |
| G1000-Mod | 16 - 48 | Non-intelligent | n/a |
| G1000-MPC | 16 | Non-intelligent | ISA |
| G1000-MPC/P | 16 | Non-intelligent | PCI |
| G1000-PQuad | 4 | Intelligent | PCI |
| G1000-Quad | 4 | Intelligent | ISA |
| G1000-RAS-1 | 24 | Non-intelligent | PCI |
| G1000-RAS-2 | 48 | Non-intelligent | PCI |
| G1000-SPC | 1 | Intelligent | ISA |
The Intelligent cards support all of the async protocols available from Sixnet Electronics. The Non-intelligent cards only the following protocols:
- Character Mode
- NCR Poll/Select
- Visa
Binary-Synchronous (bisync) is IBM's version of polled sync protocol. All of our products completely emulate the capabilities of bisync devices. Furthermore, we support most of the features available with the different bisync hosts and terminal.
Bisync Overview
IBM terminals are designed on a controller principle. The controller performs all network interaction and passes the data to the terminal. The terminal performs all device formatting and operator interaction. Depending on the terminal, the controller is placed in a separate unit and cable attached to the terminals. In other units, the controller is incorporated into the terminal. In either case, the controller is assigned a unique network address. Some bisync emulations also assign an address to the attached terminals (for example: 3270).
The terminal only answers polls with the correct controller address. If several terminals are attached to a controller, the controller will determine the status of each terminal before responding to the poll. The host can also directly poll a specific terminal.
Bisync Addressing
There are two methods of device addressing supported by bisync devices. Both methods support switched (dial) and non-switched (leased) connections. The two methods are:
- Contention - This method is designed for switched lines and only allows one device on the communications line. Addresses are not used. Once the connection is established with the other device, the two devices bid for control of the line. This is the normal mode used by RJE terminals.
Multipoint - This method uses addresses to identify the specific terminal. The host controls all message flow on the communications line through poll and select line-bid sequences. The individual terminals respond only when their address is selected by the host. This is the normal mode used by 3270 terminals.
Bisync Terminal SupportBisync TransparencyData Formats
There are many different terminal implementations of bisync protocol. Each terminal supports different hardware and can perform different functions. The terminal designer tailored the bisync support to optimize the terminal's price and performance.
Bisync terminals are grouped into two major categories: Remote Job Entry (RJE) and interactive (3270). The RJE terminals are characterized by large amounts of data sent in long bursts. An interactive terminal is characterized by an exchange of small messages with the network.
RJE and interactive terminals normally do not share the same communications line because the RJE terminals monopolize the line during transmission.
Further information on the RJE terminals is available here. Information on the 3270 terminals is available here.
Some bisync terminals support bisync transparency which allows Data Link Characters to be sent as text. Both devices must support transparency. The Data Link Characters are (SOH, ACK, STX, DLE, ETX, NAK, EOT, SYN, ENQ and ETB)
Bisync devices can support either ASCII or EBCDIC data formats.
Error Reporting
Bisync terminals use error reporting to indicate that a problem has occurred at the terminal (for example: printer out of paper). The error condition is reported to the application program. 3270 terminals use Status and Sense bytes to report error conditions. Most RJE terminals reject inbound Selects when an error condition occurs.
To view the available options that can be specified for this protocol, please review the worksheets. If you need further information on bisync protocol or our implementation and support for this protocol, please e-mail us.
Frame Relay is a simplified form of Packet Switching similar in principle to X.25 in which synchronous frames of data are routed to different destinations depending on header information.
The biggest difference between Frame Relay and X.25 is that X.25 guarantees data integrity and network managed flow control at the cost of some network delays. Frame Relay switches packets end to end much faster, but there is no guarantee of data integrity at all.
Frame Relay is cost effective, partly due to the fact that the network buffering requirements are carefully optimized. Compared to X.25, with its store and forward mechanism and full error correction, network buffering is minimal. Frame Relay is also much faster than X.25: the frames are switched to their destination with only a few byte times delay, as opposed to several hundred milliseconds delay on X.25.
Frame Relay uses the synchronous HDLC frame format up to 4kbytes in length. Each frame starts and ends with a Flag character (7E Hex). The first 2 bytes of each frame following the flag contain the information required for multiplexing across the link. The last 2 bytes of the frame are always generated by a Cyclic Redundancy Check (CRC) of the rest of the bytes between the flags. The rest of the frame contains the user data.
Virtual Circuits
Packets are routed through one or more Virtual Circuits known as Data Link Connection Identifiers (DLCIs). Each DLCI has a permanently configured switching path to a certain destination. Thus, by having a system with several DLCIs configured, you can communicate simultaneously with several different sites. Currently, only permanent virtual circuit connections are supported. This means that all DLCI connections are set up by the network provider at subscription time.
Data Integrity
There is none. The network delivers frames, whether the CRC check matches or not. It does not even necessarily deliver all frames, discarding frames whenever there is network congestion. Thus it is imperative to run an upper layer protocol above Frame Relay that is capable of recovering from errors, such as HDLC, IPX or TCP/IP.
In practice, however, the network delivers data quite reliably. Unlike the analog communication lines that were originally used for X.25, modern digital lines have very low error rates. Very few frames are discarded by the network, particularly at this time when the networks are operating at well below design capacity.
Flow Control and Information Rates
There is no flow control on Frame Relay. The network simply discards frames it cannot deliver.
When you subscribe, you will specify the line speed (e.g. 56kbps or T1) and also, typically, you will be asked to specify a Committed Information Rate (CIR) for each DLCI. This value specifies the maximum average data rate that the network undertakes to deliver under "normal conditions". If you send faster than the CIR on a given DLCI, the network will flag some frames with a Discard Eligibility (DE) bit. The network will do its best to deliver all packets but will discard any DE packets first if there is congestion. Many inexpensive Frame Relay services are based on a CIR of zero. This means that every frame is a DE frame, and the network will throw any frame away when it needs to.
Frame Relay provides indications that the network is becoming congested by means of the Forward Explicit Congestion Notification (FECN) and Backward Explicit Congestion Notification (BECN) bits in data frames. These are used to tell the application to slow down, hopefully before packets start to be discarded.
Our advice is to always accept the highest CIR that your provider will give you for free, but never to pay for a higher CIR until you are absolutely sure that your data is being discarded. There is evidence that some public networks cannot even measure your Information Rate, although that does not stop them for charging for a CIR.
Our products always include a mechanism for accessing detailed statistics on the network performance and operation. These can give you an indication of whether to pay for a higher CIR or not.
Status Polling
The Frame Relay Customer Premises Equipment (CPE) polls the switch at set intervals to find out the status of the network and DLCI connections. A Link Integrity Verification (LIV) packet exchange takes place about every 10 seconds, which verifies that the connection is still good. It also provides information to the network that the CPE is active, and this status is reported at the other end. About every minute, a Full Status (FS) exchange occurs, which passes information on which DLCIs are configured and active. Until the first FS exchange has occurred, the CPE does not know which DLCIs are active, and so no data transfer can take place.
There exist various standards for the Status Polling function. The oldest, the Link Management Interface (LMI), was a temporary standard adopted by manufacturers prior to the international standards bodies getting their standards out. It is supposed to have disappeared when the official ANSI T1.617 Annex D (known as ANSI or Annex D) standard came out, but it has acquired a life of it's own. A newer standard, Q.933 has also been approved, largely to accommodate Switched Virtual Circuits, when these become available.
Our products, support all three standards of Status Polling.
Usage
Frame Relay is used mostly to route Local Area Network protocols such as IPX or TCP/IP. It can also be used to carry asynchronous traffic, SNA or even voice data. Its primary competitive feature is its low cost. In North America it is fast taking on the role that X.25 has had in Europe: the most cost effective way to hook up multiple stations with high speed digital links.
Frame Relay networks do not yet have the reliability of X.25 networks. Expect problems with new installations. You cannot take any features for granted. At the time of writing, some public networks do not even support Status Polling properly. This makes it difficult to find out whether remote links are up or not.
In general, the newer the network, the better the implementation. For instance, one of the best Frame Relay networks around is in Poland, while some of the pioneer US networks are still struggling with older equipment.
Sixnet Electronics Frame Relay Support
Frame Relay networks do not yet have the reliability of X.25 networks. Expect problems with new installations. You cannot take any features for granted. At the time of writing, some public networks do not even support Status Polling properly. This makes it difficult to find out whether remote links are up or not.
In general, the newer the network, the better the implementation. For instance, one of the best Frame Relay networks around is in Poland, while some of the pioneer US networks are still struggling with older equipment.
Our units offer the following Frame Relay support:
- ISO and ITU compliant, network certified.
- Supports up to 100 Logical Channels (DLCIs).
- Both CPE and Access Node configurations.
- ANSI T1.617 Annex D, Q.933 or LMI Local Signaling.
- Frame Size to 4096 Bytes.
- On board flow control using individual Committed Information Rate (CIR) for each DLCI.
- Higher Level APIs:
- TCP/IP and IPX interfaces
- STREAMS interfaces
Information in this document is provided by Sangoma Technologies.
Poll/Select is a proprietary polled protocol developed by Unisys (Burroughs) or NCR that uses half-duplex async or sync transmissions and multipoint addressing. Poll/Select uses three types of polling:
| Specific Poll | Each terminal has a unique, two-level address. With a Specific Poll, the terminal only answers polls with the correct address. |
| Contention Poll | This method allows the host to minimize polling overhead. The terminal can send without receiving a poll. This method is used on point-to- point lines (for example: dial connections). |
| Group Poll/ Group Select |
Poll/Select protocol supports Group Polls and Group Selects when terminals are daisy-chained. Each terminal in the daisy-chain is assigned a Group Poll and Select Address. The host uses the addresses to access a specific terminal in the daisy-chain or all of the terminals. |
When a Group function (poll or select) is used, all other terminals with the same Group Address will see the data. When a poll is issued, only the terminal with data to send to the host will respond. The primary terminal (the one next to the modem) determines which terminal can send data. When a select is issued, all other terminals with the same Group Address will receive the data
Poll/Select terminals use transmission numbers to detect duplicate transmissions. Messages with the same transmission numbers are assumed to be duplicates and are discarded.
Poll/Select TerminalsThere are several models of Poll/Select terminals. There are also programs for the PC and Macintosh that can emulate any of the Poll/Select terminals.
| Terminal | Pages | Rows | Columns | Type | Printer Port |
| TD 830 MT 983 ET 1100 T 27 TT |
One One 25 75 One |
24 24 24 30 4 |
80 80 80 80/132 4 |
CRT CRT CRT CRT Teller |
Shared Shared Addressable Addressable Shared |
All terminals use the same formatting codes. The main difference between the terminals is the number of pages of memory. Normally, applications such as LINC use the first page for data and the second page for error messages (ET 1100 and T 27 only). The TT(Teller Terminal) is a special terminal used for financial applications and does not support screen formatting.
Multi-Environment CapabilityThe T 27 allows up to three separate windows to be displayed on the same screen. Each window has a different network address.
Multi-Page SupportThe ET 1100 and T 27 provide multiple pages. With these terminals, the screen buffer is divided into several pages. The operator can scroll one line at a time through the screen buffer or can move to the next (24 line) segment. The size of each page is determined during setup. The ET 1100 supports up to twelve 24 x 80 pages. The T 27 supports up to seventy-five 24 x 80 pages. The maximum T 27 screen size is 255 rows x 132 columns
The T 27 supports ANSI space compression for the printer data streams.
Screen ModesThe Poll/Select terminals support two types of screen modes. Each of these modes has several sub-modes which are defined by the application program.
| Text Mode | This mode supports the entry of video presentation commands and screen formatting commands. Only the video presentation commands are interpreted by the terminal. This mode can be used to design a Forms Modescreen. Any text entered during this mode is sent to the host when the Transmit key is pressed. |
| Forms Mode | This mode interprets both the video presentation and screen formatting commands to display a form as defined by commands in text mode. The transmitted data is dependent on the field types. |
Poll/Select data streams consist of control codes used to define the Poll/Select protocol. Data formatting codes are used to format the screen display. All of the formatting commands can define the following terminal characteristics:
| Screen Formatting | Right Justified Protected Transmittable Protected Untransmittable Unprotected |
| Video Presentation | Reverse Video High Intensity Secure (non display) UnderscoreBlink |
The T 27 provides a "virtual" 132 column support. The operator can shift the screen to display columns 1 - 80 or columns 52 - 132. Some terminals can display the entire 132 columns on one screen.
Transmission MethodsThe Poll/Select terminal supports two transmission types:
| Line-at-a-time or blocks |
|
| Variable Start and Stop positions (indicated by Start and End markers |
Status Line
The TD 830 and MT 983 terminals use a front-panel LED to indicate a Busy State (Wait Condition). The ET 1100 and T 27 terminals use a Status Line to inform the operator of the terminal's status, network activity, and error conditions. The T 27also provides an Application Status Line which displays messages from host applications
Print OptionsThe Poll/Select terminals support three different types of printing:
| Shared Buffer | The terminal and the printer share a single buffer. The host formats the prints in the buffer while the keyboard is locked, and then sends the buffer to the printer. The TD 830 and MT 983 terminals use this method. The ET 1100 and T 27 can support this method but normally use the next method. |
| Addressable Printer | The terminal has a printer port with its own network address. The host sends the data directly to the printer without disrupting the screen. The ET 1100 and T 27 terminals use this method. |
| Operator Initiated | The terminal operator can send the screen buffer to the printer through a keyboard entry. All of the terminals support this method. |
Tab Ruler
The T 27 provides user definable Tab Stops. A Tab Ruler can be displayed on the Status Line to indicate the Tab Stops.
To view the available options that can be specified for this protocol, please review the worksheets. If you need further information on Poll/Select protocol or our implementation and support for this protocol, please e-mail us: wireless.support@sixnet.com