Chapter 7. Creating Customized Parameter Files

In most cases, the protocol parameter files that SX.25 provides are appropriate for X.25 WANs and LANs, so it is not necessary to create customized parameter files. However, if you determined that the settings in the factory-shipped parameter files do not meet your connection requirements (see “Evaluating SX.25 Parameter Files” in Chapter 2 for details), you need to perform the procedures in this chapter. These procedures explain how to use factory-shipped files as templates to create your own custom parameter files.


Note: Factory-shipped SX.25 parameter files cannot be modified. To create a custom file, you open a factory-shipped file, make your changes, and save them in a new file under a different name.

This chapter contains three procedures for creating configuration files:

Using Parameter Files as Templates

The contents of X.25, LAPB, and LLC2 parameter files are displayed in a series of windows that you use as templates to create custom parameter files. Each template contains a logical grouping of protocol parameters (such as LLC2 timer parameters) and input widgets for specifying custom settings (such as option menus and sliders). In addition, the lower of edge of a template contains tabs and buttons for controlling the file creation process.

Click these topics to view information about parameter window tabs and buttons:

Template Tabs

When you open a protocol parameter file, the General parameters tab is displayed. Use the labeled tabs at the lower edge of the window to display a different group of parameters. If the parameters that you wish to display do not appear on a labeled tab, move the pointer to the unlabeled tab area and use the right mouse button to select a tab from a pull-down list, as shown in Figure 7-1.

Figure 7-1. Unlabeled Tabs on Template Windows


The OK Button

Use the OK button to record changed settings in a previously-created custom parameter file. (You cannot use OK to write to a factory-shipped file; see “The Save As Button.”). Clicking OK confirms your changes and closes the custom file, but it does not save the modified version of the file. The modified parameter file is permanently saved when you save the configuration file (normally, this is done at the end of the port configuration procedure).

The Save As Button

Use the Save As button to record your changes to a factory-shipped file in a custom parameter file. When you click Save As, you are prompted to enter a name for the new custom file. Entering a name for the new custom file does not save it. The file is permanently saved when you save the configuration file (normally, this is done at the end of the port configuration procedure).

The Cancel Button

Use the Cancel button to close the parameter file and discard your entries. When you click Cancel, no changes are made to the parameter file; any information that was in the file from previous sessions remains unchanged.

The Help Button

Use the Help button to get information about using parameter windows.

Creating an X.25 Parameter File

Use the procedure below to create a custom X.25 parameter file for a WAN or LAN port. This procedure assumes that you completed steps 1 through 3 of either “Creating a WAN Port Configuration Record” (for WAN ports) or “LAN Port Configuration Procedure” (for LAN ports) in Chapter 4. It also assumes that you plan to use a factory-shipped file as a template for the custom file, but you can also use a previously-created custom file as a template.

  1. Open a factory-shipped X.25 parameter file.

    To open a factory-shipped file, select a file from the X.25 Parameter Files list, based on the port's function as DTE or DCE equipment and on the X.25 recommendation implemented on the network. Click the Open button (or double-click on the file) to display file contents. Click on the labeled tabs at the bottom of the window to view additional parameter settings. To view an unlabeled tab, move the pointer to the unlabeled area and use the right mouse button to select a tab from a pull down list (see Figure 7-1).

  2. Modify the settings that need changing.

    The contents of X.25 parameter files comprise several windows. Figure 7-2 through Figure 7-13 illustrate X.25 protocol parameters and their factory-shipped settings; see the information that follows each figure for information about the parameters that the figure contains. Use the values specified by your network service provider or your knowledge of the operating characteristics of your network to change X.25 parameter settings. When you finish your changes, return to step 3 of this procedure.

  3. Create a new X.25 parameter file under a different name to save your settings.

    You cannot modify the original X.25 parameter file, but you can create a modified version of the original file and save it under a different name. To save your changes to X.25 parameter settings, click the Save As button; then, enter the name of the new file in the filename dialog box.

    Notice that the new X.25 file appears in the X.25 Parameter Files list and that the new file is selected.

  4. Return to step 5 of “Creating a WAN Port Configuration Record” or “LAN Port Configuration Procedure” in Chapter 4 to continue the configuration process.

X.25 General Operating Parameters

Figure 7-2 illustrates the panel of general operating parameters for X.25. Each parameter is explained in the information that follows the figure.

Figure 7-2. X.25 General Parameters


Network Protocol Mode 


Specifies the characteristics of the network protocol. For example, a value “X25_LLC” specifies either 1984 or 1988 X.25 over LLC2 procedures. Use the option popup menu beside the Network Protocol Mode parameter to make your selection.

X.25 Version 

Specifies the X.25 protocol recommendation used on the network. Use the option popup menu beside the X.25 Version parameter to make your selection.


Note: Selecting X25_LLC as the network protocol mode sets an X.25(80) selection in this field to X.25(84).


Level 3 PLP Mode 


Specifies whether the port will function as a DTE or DCE. Use the option popup menu beside the Level 3 PLP Mode parameter to make your selection.

Sequence Numbering Option 


Sets sequence numbering to Modulo 8 or Modulo 128. Use the option popup menu beside the Sequence Numbering parameter to make your selection.

Logical Channel Parameters

Figure 7-3 illustrates the panel of logical channel parameters for X.25 and their default settings. Channel parameters are explained in the information that follows the figure.

Figure 7-3. Logical Channel Parameters


In a DTE/DTE environment, one DTE sees the range of lowest incoming logical channels as presented in Figure 7-3. The other DTE sees these ranges from the viewpoint of a DCE. For example, it views the range from lowest incoming logical channels to highest incoming logical channels as one-way outgoing.

The numbers of logical channels of each type are calculated from the values of the pairs of parameters:

Number of PVCs = Highest PVC - Lowest PVC + 1


Note: If highest and lowest logical channels are both set to zero, no channels are allocated in that grouping.

These parameters specify logical channel functions:

Low and High PVC Channel Number 


Specifies the range of channels to be allocated to permanent virtual circuits.

Low and High Incoming Channel Number 


Specifies the range of channels to be allocated for receiving inbound calls only.

Low and High Two-way Channel Number 


Specifies the range of channels to be allocated for receiving inbound calls and sending outbound packets.

Low and High Outgoing Channel Number 


Specifies the range of channels to be allocated for sending outbound calls only.

Packet- and Window- Size Parameters

Figure 7-4 illustrates the panel of packet-size and window-size parameters for X.25. Each parameter is explained in the information that follows the figure.

Figure 7-4. Packet- and Window-Size Parameters


Local and Remote Maximum Packet Size 


Specifies the maximum size for outbound packets; remote maximum packet size specifies the maximum size for inbound packets.

Use these parameters to set the maximum size of data packets that are acceptable on the X.25 link. On any incoming call, a value for the packet-size parameter greater than the lowest outgoing logical channel (shown in Figure 7-3) or remote maximum packet size is negotiated down to this value when the call is accepted.


Note: Be sure that lowest outgoing logical channel is greater than the frame size that you set for the underlying protocol: the LAPB I frame on the WAN or the LLC-2 I frame on the LAN. The I frame size is set in the LAPB template (shown in Figure 7-14) or the LLC2 template (shown in Figure 7-17).


Local and Remote Default Packet Size 


Specifies the default size for outbound packets; remote default packet size specifies the default size for inbound packets.

Use this parameter to specify the default packet size for a particular network. The standard value is 7, which sets a default data packet size for each direction of transmission to 128 octets (27, that is, 1 << 7). The value may be nonstandard if it is agreed between all communicating parties on the LAN or between the DTE and DCE.

Local and Remote Maximum Window Size 


Specifies the maximum size of windows for outgoing calls; remote maximum window size specifies the maximum size of windows for incoming calls.

Use this parameter to specify the maximum window size acceptable on the subnetwork. On any incoming call, a window size value greater than lowest outgoing logical channel (shown in Figure 7-3) or remote maximum window size is negotiated down to this value when the call is accepted. For Modulo 8 networks, the range for lowest outgoing logical channel or remote maximum window is 2 through 7, and for Modulo 128 the range is 2 through 127.

Local and Remote Default Window Size 


Specifies the default size of windows for outgoing calls; remote default window size specifies the default size of windows for incoming calls.

Use this parameter to specify the value of the default window size for a particular network. The standard value is 2. The value may be nonstandard provided it is agreed between all communicating parties on the LAN, or between the DTE and DCE.


Note: The sequence numbering scheme, modulo 8 or modulo 128 (shown in Figure 7-2), affects the range of this parameter. For modulo 8 networks, the range for lowest outgoing logical channel (shown in Figure 7-3) or remote default window size is 1 through 7, and for modulo 128 the range is 1 through 127.


Maximum NSDU Length 


Specifies the maximum length of a network service data unit (NSDU). SX.25 tries to concatenate data packets marked with the “More Data” mark (M-bit) into a NSDU. However, you can specify a maximum length to avoid running out of buffers. When this maximum is exceeded, concatenation stops and currently held data is passed to the network service user with the M-bit set. Applications can override this parameter for specific circuits using the nsdulimit field of the Quality Of Service parameter on Connect Requests and Connect Confirmations. The default value for this parameter is 256; the maximum value is 32,000.

Timer Parameters

Figure 7-5 illustrates the tab of timer parameters for X.25. Notice that timer parameter names are descriptive of their function. For parameters known by a mnemonic equivalents, the mnemonic is given in parentheses in the descriptions that follow. All timer values are measured in tenths of a second except where noted.

Figure 7-5. Timer Parameters


Acknowledgement Delay 


Specifies the maximum time during which a pending acknowledgement is withheld. SX.25 attempts to suppress the generation of Level 3 Receive Ready control packets. Acknowledgment carried by data or multiple acknowledgements is preferred to each data packet being explicitly and separately acknowledged. The permitted range is .1 to 3200.

Restart Request Response Timer 


(T20) The default value is 180, the permitted range 0 to 3200.

Call Request Response Timer 


(T21) The default value is 200, the permitted range 0 to 3200.

Reset Request Response Timer 


(T22) The default value is 180, the permitted range 0 to 3200.

Clear Request Response Timer 


(T23) The default value is 180, the permitted range 0 to 3200.

Window Status Transmission Timer 


(similar to T24) Specifies the maximum interval during which data received from the remote transmitter can remain unacknowledged due to a flow control condition. After this timer expires, any outstanding acknowledgements are carried by an X.25 Level 3 Receive-Not-Ready packet. Use this timer to ensure that if the remote transmitter does not receive an acknowledgement, this does not cause resets within the virtual circuit. This timer should be approximately half the value set for the window rotation timer.

The default value is 75, the permitted range 0 to 3200.

Window Rotation Timer 


(T25) This timer should be approximately twice the value set for the window status transmission timer. The default value is 150, the permitted range 0 to 3200.

Interrupt Response Timer 


(T26) The default value is 180, the permitted range 0 to 3200.

LAN Idle Connection Timer 


Specifies the period for maintaining a link-level connection when there is no reciprocating connections. If the link is to a WAN, set the value to zero (that is, infinity). This timer is appropriate only when running X.25 over the LAN.

The default LAN value is 60; the default WAN value is 0. For both, the permitted range is 0 to 3200.

Resolution Timer 


Specifies the interval during which the DTE/DCE resolution should be completed. This prevents two packet-level entities failing to resolve their DTE/DCE nature. When this timer expires, the link connection is disconnected and all pending connections are aborted.

The default value is 200; the permitted range 0 to 3200.

Counter Parameters

Figure 7-6 illustrates the panel of counters parameters for X.25. Each parameter is explained in the information that follows the figure.

Figure 7-6. Counter Parameters


DTE Restart Request Retransmission Count 


(R20) The default value is 1; the permitted range 1 to 255.

DTE Reset Request Retransmission Count 


(R22) The default value is 1; the permitted range 1 to 255.

DTE Clear Request Retransmission Count 


(R23) The default value is 1; the permitted range 1 to 255.

Transit Delay Parameters

Figure 7-7 illustrates the panel of transit delay parameters for X.25. Each parameter is explained in the information that follows the figure.

Figure 7-7. Transit Delay Parameters


Local Delay 

Specifies the transit delay that results from internal processing.

Access Delay 

Specifies the transit delay that results from the line transmission rate. The default for both parameters is .005; the permitted range 0 to 32.

Throughput Class Parameters

Figure 7-8 illustrates the panel of throughput class parameters for X.25. Each parameter is explained in the information that follows the figure.

Figure 7-8. Throughput Class Parameters


Be sure to observe the following points when you set these parameters:

  • The value of local maximum throughput class and remote maximum throughput class should be greater than or equal to that of local default throughput class and remote default throughput class, respectively.

  • The value of local default throughput class and remote default throughput class should be greater than or equal to that of local minimum throughput class and remote minimum throughput class, respectively.

Local and Remote Maximum Throughput Class 


Defines the maximum packets size for each transmission direction: local maximum throughput class specifies the maximum size for outbound packets; remote maximum throughput class specifies the maximum size for inbound packets.

These parameters are the maximum supported value of the throughput class Quality Of Service parameter. ISO 8208 specifies a value for lowest outgoing logical channel (shown in Figure 7-3) or remote maximum throughput class in the range of 3 through 12, corresponding to a range of 75 to 48,000 bps. However, the supported valid range is 0 to 15. This accommodates nonstandard X.25 implementations that use the Throughput Class parameters to map to packet/window sizes (see “Throughput Window and Packet Parameters”).

Local and Remote Default Throughput Class 


Defines the default packet sizes for each transmission direction: local default throughput class specifies the default size for outbound packets; remote default throughput class specifies the default size for inbound packets.

In some networks (TELENET, for example), negotiation of throughput class is towards a configured default throughput class. In such cases, the negotiate throughput class parameter (shown in Figure 7-13) is non-zero and lowest outgoing logical channel (shown in Figure 7-3) or remote default throughput class is the default. In other PSDNs, you should set lowest outgoing logical channel or remote default throughput class to the value of lowest outgoing logical channel or remote default throughput class.

Local and Remote Minimum Throughput Class 


Defines the minimum packet sizes for each transmission direction: local minimum throughput class specifies the minimum size for outbound packets; remote minimum throughput class specifies the minimum size for inbound packets.

According to ISO 8208, the throughput class parameter is defined in the range of 3 through 12. Some PSDNs may provide a different mapping, in which case lowest outgoing logical channel (shown in Figure 7-3) or remote minimum throughput class is the minimum value.

Closed User Group Parameters

Figure 7-9 illustrates the panel of closed user group (CUG) parameters for X.25. To change a CUG parameter, click the check box beside it to turn the parameter on or off. Use the option menu beside the ``CUG Format'' parameter to select either basic or extended CUG format.


Note: Some networks, such as DDN, require you to set the flag to reject incoming calls carrying any closed user group optional facility.

Figure 7-9. Closed User Group Parameters


Subscription Option Parameters

Figure 7-10 illustrates the panel of subscription option parameters for X.25. To change a subscription parameter, click the check box beside it to turn the parameter on or off.


Note: Subscribing to extended call packets enables window- and packet-size negotiation, which permits the exchange of extended call packets. Treating extended incoming call packets as a procedure error prevents the exchange of extended call packets.

Figure 7-10. Subscription Options Parameters


Localization Parameters

Figure 7-11 illustrates the panel of localization parameters for X.25, which are used to tune options for a particular subnetwork. Each parameter is explained in the information that follows the figure.

Figure 7-11. Localization Parameters


International Call Recognition 


Governs whether outgoing international call requests are to be recognized and how. Use the popup option menu beside the International Call Recognition parameter to select one of these settings:

  • Not distinguished: international calls are not distinguished.

  • DNIC mismatch: the data network identification code (DNIC) of the called DTE address is examined and compared with that held in psdn_local members dnic1 and dnic2. A mismatch implies an international call.

  • DTE prefix of 1: International calls are distinguished by a 1111 prefix on the DTE address (DATAPAC, among others, use this feature).

  • DTE prefix of 0: International calls are distinguished by a 0000 prefix on the called DTE address. This feature is generally used in conjunction with the Priority Encode Control parameter.

Priority Encode Control 


Governs how priority requests are to be encoded for this PSDN. Use the popup option menu beside the Priority Encode Control parameter to set the value according to the following:

  • The priority is encoded according to X.25(88).

  • DATAPAC Priority Bit: Encode the priority request using the DATAPAC Priority Bit (1976 version).

  • DATAPAC Traffic Class: Encode the priority request using the DATAPAC Traffic Class (1980 version employing the Calling Network facility marker).

Source Address Control 


Overrides or sets the calling address in outgoing call requests for this PSDN. Use the popup option menu beside the Source Address Control parameter to set the value according to the following:

  • No Action: Calling DTE addresses are encoded as if provided by the network service user.

  • Omit Calling DTE Address: address of the calling DTE is omitted even if the network service user supplied one.

  • Use Local DTE Address: If the network service user does not supply a DTE address, use the configured DTE address for this PSDN (which can be NULL).

  • Calling DTE is Local DTE: Use the local DTE address even if the network service user supplied a calling DTE address.

Priority Packet Forced Value 


Sets the packet size on all priority call requests and incoming calls to the value specified in this parameter.

Data Network Identification Code 


Contains the first four BCD digits of the DNIC and is used only when international call recognition is set.

Prioritize International Calls 


Specifies whether a prioritization method is to be used for international calls (assuming that the PSDN supports such a feature). Use this parameter in conjunction with two other parameters: priority encode control and priority packet forced value.

Subnetwork Modes 


Specify network tuning options for treatment of diagnostic packets and other functions. You can control these functions by setting indicators on or off. Click on the selection box beside an indicator to set it; a check mark indicates that an indicator is on.

D-Bit Control Parameters

The X.25 standard does not give specific recommendations for handling the D-bit. To provide flexibility to accommodate local PSDN requirements, SX.25 lets you specify how the D-bit should be handled. Figure 7-12 illustrates the panel of D-bit control parameters for X.25. Each parameter is explained in the information that follows the figure.

Figure 7-12. D-Bit Control Parameters


Use the popup option menu beside each D-bit control parameter to select a new value for the parameter. Your choices for D-bit parameters are Clear the Call, Zero the D-bit, or No Action.

D-Bit Action on ACCEPT-IN  


Defines what happens during the call setup phase if a Call Accept is received and there is no local D-bit support.

D-Bit Action on ACCEPT-OUT 


Defines what happens during the call setup phase if a Call Accept is sent and there is no request for D-bit from the other end.

D-Bit Action on DATA-IN 


Defines what happens when a data packet is received and there is no request for the D-bit from the local user.

D-Bit Action on DATA-OUT 


Defines what happens when a data packet is sent and there is no indication of D-bit support from the remote party.

Throughput Window and Packet Parameters

Some implementations of X.25 do not use the X.25 packet and window negotiation function. Instead, these implementations use throughput class window and packet mapping to determine window and packet sizes. Figure 7-13 illustrates the panel of X.25 throughput class parameters. Each parameter is explained in the information that follows the figure.

Figure 7-13. Throughput Window and Packet Parameters


Negotiate Throughput Class 


Specifies whether to negotiate throughput class towards the defaults, which are specified by the lowest outgoing logical channel (shown in Figure 7-3) and the remote default throughput class (shown in Figure 7-4).

Click on the check box to set this parameter on for networks like TELENET, which require negotiation of the throughput class towards those defaults. When this parameter is off (the default), throughput class is negotiated according to the X.25 procedures instead.

Throughput Class Type 


When set to a value other than No Action, specifies the way in which window and packet sizes are mapped. The values of lowest outgoing logical channel (shown in Figure 7-3) and remote maximum throughput class (shown in Figure 7-4) may limit the range of the mapped values. The value that you select for this parameter applies to both transmission directions.

Keep these points in mind when setting this parameter:

  • Do not select the Use Low Nibble, Use High Nibble, or Use Both Nibbles value if window and packet size negotiation are necessary: this algorithm is designed for PSDNs that support the mapping procedure only.

  • In call requests, specify equal values for local throughput and remote throughput in the qosformat, to ensure that low nibble and high nibble values behave correctly.

  • Selecting the Use Low Nibble or Use High Nibble value prevents users and applications from negotiating window and packet size.

  • If you select the Use Both Nibbles value, users can negotiate window and packet sizes only through the throughput class parameter.

  • If you subscribe to the extended facility option and you select the Use Both Nibbles value, negotiation using flow negotiation parameters is overridden.

  • Because window and packet size negotiation is suppressed when you use window and packet mapping, it is important that your entries for the window mapping parameter and packet mapping parameter are correct for your PSDN. This ensures that both called and calling parties agree on the values associated with a particular throughput class.

Window Mapping 


Maps the value of the throughput class for each direction of transmission to a window parameter. This value is a number from 0 to 15 (a value of zero for any individual value is interpreted as the default value for the subnetwork). The permitted range is between 1 and the value of either the lowest outgoing logical channel or the remote maximum window size; the maximum possible value is 127. The maximum for the subnetwork is the smaller of two values: lowest outgoing logical channel parameter or remote maximum window size parameter.

Packet Mapping 


Maps the value of the throughput class for each direction of transmission to a packet parameter. This value is a number from 0 to 15. (a value of zero for any individual value is interpreted as the default value for the subnetwork). The permitted range is between 1 and the value of either the lowest outgoing logical channel or the remote maximum window size; the maximum possible value is 127. The maximum for the subnetwork is the smaller of two values: lowest outgoing logical channel parameter or remote maximum window size parameter.

These are the last X.25 parameters. Return to step 3 of “Creating a LAPB Parameter File” to continue the file creation process.

Creating a LAPB Parameter File

Use the procedure in this section to create a custom LAPB parameter file. This procedure assumes that you completed steps 1 through 6 of “Creating a WAN Port Configuration Record” in Chapter 4. It also assumes that you plan to use a factory-shipped file as a template for the custom file, but you can also use a previously-created custom file as a template.

  1. Open the factory-shipped LAPB parameter file.

    To open a factory-shipped file, select the file from the LABP Parameter File list and click the Open button (or double-click on the file) to display its contents. Click on the labeled tabs at the bottom of the window to view additional parameter settings.

  2. Modify the settings that need changing.

    The contents of the LAPB parameter file comprise several windows. Figure 7-14 through Figure 7-16 illustrate LAPB protocol parameters and their factory-shipped settings; see the information that follows each figure for information about the parameters that the figure contains. Use the values specified by your network service provider or your knowledge of the operating characteristics of your network to change LAPB parameter settings. When you finish your changes, return to step 3 of this procedure.

  3. Create a new LAPB parameter file under a different name to save your settings.

    You cannot modify the original LAPB parameter file, but you can create a modified version of the original file and save it under a different name. To save your changes to LAPB parameter settings, click the Save As button; then, enter the name of the new file in the filename dialog box.

    Notice that the new file LAPB appears in the LAPB Parameter Files list and that the new file is selected.

  4. Return to step 8 of “Creating a WAN Port Configuration Record” to continue with the port configuration process.

LAPB General Operating Parameters

Figure 7-14 illustrates the panel of general operating parameters for LAPB. Each parameter is explained in the information that follows the figure.

Figure 7-14. LAPB General Parameters


Maximum Number of Transmissions  


Specifies the maximum number of times that a PDU is sent after the Acknowledgment Timer, the P-bit timer, or the Reject Timer expires. It also limits the number of times Receive Ready with P-bit set is sent when the remote is busy and the Busy Timer expires.

The default value is 65 and the permitted range is 1 to 255.

Maximum Number of Unacknowledged IPDUs 


Specifies the maximum number of unacknowledged IPDUs that can be received before the Reset Request acknowledging them must be sent.

The default value is 12 and the permitted range is 0 to 127.

Transmit Window Size  


The number of unacknowledged IPDUs that LAPB can send.

In normal mode, when Modulo 8 sequence numbering is used, the default value is 7 and the permitted range is 1 to 7.

In extended mode when Modulo 128 sequence numbering is used, the default value is 7 and the permitted range is 1 to 127.

Transmit Probe 


The position before the window is closed at which an IPDU, with the P-bit set, is sent to ask for an acknowledgement from the receiver.

In normal mode when Modulo 8 sequence numbering is used, the default value is 0 and the permitted range is 0 to 7.

In extended mode, when Modulo 128 sequence numbering is used, the default value is 0 and the permitted range is 0 to 127.

Maximum Size of LAPB I frame 


Specifies the maximum size of incoming I frames; I frames above the specified size are rejected by an FRMR. The size is equal to this sum:

maximum X.25 data size + X.25 protocol length + LAPB protocol length

The default value is 261. Permitted values are: 261 to 263, 517 to 519, 1029 to 1031, 2053 to 2055, and 4101 to 4103.

LAPB Timer Parameters

Figure 7-15 illustrates the panel of timer parameters for LAPB. Each parameter is explained in the information that follows the figure. Unless noted otherwise, LAPB timer values are expressed in tenths of a second.

Figure 7-15. LAPB Timer Parameters


Acknowledgement Timer  


Specifies the time during which the LAPB expects to receive an acknowledgement to an outstanding IPDU or an expected response to a sent unnumbered PDU.

The default value is 7.1 and the permitted range is .1 to 300.

P-Bit Timer 


Specifies the time during which the LAPB expects to receive a PDU with the F-bit set to 1 in response to a command with the P-bit set to 1. This value should be less than that specified for the Acknowledgment Timer.

The default value is .7 and the permitted range is .1 to 300.

Reject Timer 


Specifies the time during which the LAPB expects to receive a reply to a sent REJ TPDU.

The default value is 2.5 and the permitted range is .1 to 1000.

Busy-state Timer 


Specifies the time during which the LAPB waits for an indication of the clearance of a busy condition at the other LAPB.

The default value is 10.0 and the permitted range is .1 to 3000.

Link Idle Timer 


Specifies the time during which the LAPB expects to receive a PDU from the other LAPB. If it expires, the P/F cycle is initiated, which may result in link disconnection. A value of zero disables this function.

The default value is 29.9 and the permitted range is 0 to 3200.

Maximum Delay Before Sending RR 


Specifies the maximum delay in tenths of a second before transmitting a delayed RR (Reset Request). This must be considerably less than the Acknowledgment Timer value.

The default value is 2.2 and the permitted range is 0 to 300.

LAPB Link-Level Parameters

Figure 7-16 illustrates the panel of link-level parameters for LAPB.

Figure 7-16. LAPB Link-Level Parameters


Error State and Other Indicators 


These parameters control LAPB conformance tuning by defining its operation in certain states. You can control state operations by setting error state indicators on or off. Click the check box beside an indicator to set it; a check mark indicates that an indicator is on.

These are the last LAPB parameters. Return to step 3 of “Creating a LAPB Parameter File” to complete the file creation process.

Creating an LLC2 Parameter File

Use the procedure below to create a custom LLC2 parameter file. This procedure assumes that you completed steps 1 through 5 of the “LAN Port Configuration Procedure” in Chapter 4. It also assumes that you plan to use a factory-shipped file as a template for the custom file, but you can also use a previously-created custom file as a template.

  1. Open the factory-shipped LLC2 parameter file.

    To open a factory-shipped file, select the file from the LLC2 Parameter File list that is appropriate for the type of media on the LAN where this port will connect. Click the Open button (or double-click on the file) to display file contents. Click on the labeled tabs at the bottom of the window to view additional parameter settings.

  2. Modify the settings that need changing.

    The contents of the LLC2 parameter file comprise several windows. Figure 7-17 through Figure 7-19 illustrate LAPB protocol parameters and their factory-shipped settings; see the information that follows each figure for information about the parameters that the figure contains. Use the values specified by your network service provider or your knowledge of the operating characteristics of your network to change LLC2 parameter settings. When you finish your changes, return to step 3 of this procedure.

  3. Create a new LLC2 parameter file under a different name.

    You cannot modify the original LLC2 parameter file, but you can create a modified version of the original file and save it under a different name. To save your changes to LLC2 parameter settings, click the Save As button; then, enter the name of the new file in the filename dialog box.

    Notice that the new file LLC2 appears in the LLC2 Parameter Files list and that the new file is selected.

  4. Return to step 8 of “LAN Port Configuration Procedure” to complete the port configuration process.

LLC2 General Operating Parameters

Figure 7-17 illustrates the panel of general operating parameters for LLC2, which are the same for all media types. Each parameter is explained in the information that follows the figure.

Figure 7-17. LLC2 General Parameters


Maximum Number of Transmissions  


Specifies the maximum number of times that a PDU is sent after the Acknowledgment Timer, the P-bit timer, or the Reject Timer expires. It also limits the number of times Receive Ready with P-bit set is sent when the remote is busy and the Busy Timer expires.

The default value is 10 and the permitted range is 1 to 255.

Maximum Number of Unacknowledged IPDUs 


Specifies the maximum number of unacknowledged IPDUs that can be received before the Reset Request acknowledging them must be sent.

The default value is 3 and the permitted range is 0 to 127.

Transmit Window Size  


Specifies the maximum number of unacknowledged IPDUs that LLC can send.

The default value is 7 and the permitted range is 1 to 127.

Transmit Probe 


Specifies the position before the window is closed at which an IPDU, with the P-bit set, is sent to ask for an acknowledgement from the receiver.

The default value is 0 and the permitted range is 0 to 127.

Maximum Size of LLC2 I frame 


Specifies the maximum size, which is equal to this sum:

maximum X.25 data size + X.25 protocol length + LLC protocol length

The default value is 263. Permitted values are: 263 to 264, 519 to 520, and 1031 to 1032.

LLC2 Timer Parameters

Figure 7-18 illustrates the panel of timer parameters for LLC2, which are the same for all media types. Each parameter is explained in the information that follows the figure. Timer parameters are expressed in tenths of a second unless otherwise noted.

Figure 7-18. LLC2 Timer Parameters


Acknowledgement Timer 


Specifies the time, in tenths of a second, during which the LLC expects to receive an acknowledgement to an outstanding IPDU or an expected response to a sent unnumbered PDU.

The default value is 1.0 and the permitted range is .1 to 300.

P-Bit Timer 


Specifies the time, in tenths of a second, during which the LLC expects to receive a PDU with the F-bit set to 1 in response to a command with the P-bit set to 1. This value should be less than that specified for the Acknowledgement Timer.

The default value is .7 and the permitted range is .1 to 300.

Reject Timer 


Specifies the time, in tenths of a second, during which the LLC expects to receive a reply to a sent REJ TPDU.

The default value is 2.5 and the permitted range is .1 to 1000.

Busy-state Timer 


Specifies the time, in tenths of a second, during which the LLC waits for the clearance of a busy condition at the other LLC.

The default value is 10.0 and the permitted range is 0 to 3000.

Link Idle Timer 


Specifies the time, in tenths of a second, during which the LLC expects to receive a PDU from the other LLC. If the timer expires, the P/F cycle is initiated, which may result in link disconnection.

The default value is 25.0 and the permitted range is 0 to 3200.

Maximum Delay Before Sending RR 


Specifies the maximum delay in tenths of a second before transmitting a delayed RR (Reset Request). This must be considerably less than the Acknowledgement Timer value.

The default value is .4 and the permitted range is 0 to 300.

LLC2 XID Parameters

Figure 7-19 illustrates the panel of XID parameters for LLC2, which are the same for all media types. Each parameter is explained in the information that follows the figure.

Figure 7-19. LLC2 XID Parameters


XID Window Size 


Specifies the size of the receive window when the remote window size is unknown or zero.

The default value is 7 and the permitted range is 1 to 127.

Duplicate MAC XID Count 


Specifies the number of attempts at finding any stations with duplicate MAC addresses. If you set it to zero, no attempt is made.

The default value is 0and the permitted range is 0 to 255.

Duplicate MAC XID Timer 


Specifies the time in tenths of a second for which incoming XID response frames are checked for a duplicate response to the station LSAP. If a value of zero is specified, the duplicate address check is not performed.

The default value is .5 and the permitted range is 0 to 300.

These are the last LLC2 parameters. Return to step 3 of “Creating an LLC2 Parameter File” to complete the file creation process.