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Configuring X.25

Introduction to Ascend X.25 implementation

Configuring the logical link to an X.25 network

Configuring X.25 IP connections

Configuring X.25 PAD connections

Setting up X.25 PAD sessions

Customizing script support for X.25 PAD

Setting up ISDN D-channel X.25 support

Always On/Dynamic ISDN (AO/DI)

The X.25 protocol operates at the network layer to provide virtual circuits and deliver such services as multiplexing, in-sequence delivery of packets, transfer of addressing information, segmentation and reassembly, flow control, error control, reset, and restart. Allocation of logical channels can be either static (PVC) or dynamic (SVC).

X.25 is not as fast as newer protocols that operate at the data-link layer, leaving network-layer functions to the processors at each end of the connection. However, X.25 became widely established, especially in Europe, and remains in widespread use in many geographical areas.

The MAX supports a single physical X.25 connection. You must configure a physical link and at least one logical link to an X.25 switch. Once you have configured a logical link in an X.25 profile, you can configure individual IP-routing connections in Connection profiles. (The Ascend implementation of X.25 does not support other routing protocols, nor does it support bridging.)

The MAX enables several terminals to share a single network line by performing the functions of an X.25 Packet Assembler/Disassembler (PAD). The MAX PAD supports a unique command interface, and you can configure an X.3 profile to fine-tune PAD settings.

If you use X.25 on an ISDN connection, you can configure the D channel to transmit data. Always On/Dynamic ISDN (AO/DI) can send low-bandwidth transmissions over the D channel and add switched B channels as bandwidth requirements increase. (For example, the D channel is usually sufficient for email transmissions, but not for WWW pages with graphics.) X.25 Transaction Processing Protocol for Point of Service (T3POS) sends transaction data over the D channel.

Introduction to Ascend X.25 implementation

X.25 is a connection oriented (virtual circuits) protocol, providing services such as multiplexing, in-sequence delivery, transfer of addressing information, segmenting and reassembly, flow control, error control, reset, and restart. Allocation of logical channels can be either static (PVC) or dynamic (SVC).

Configuring the MAX to communicate with an X.25 network involves the following elements:

• A physical interface to the X.25 network. This can be a nailed serial-WAN, one of the D-channels in T1 or E1 PRI, or a BRI D-channel connection. The MAX supports only one physical X.25 connection. (To configure the interface, see Chapter 3, Configuring WAN Access.)

• A logical datalink to the X.25 network. Defined in an X.25 profile, the link should normally be set in DTE. See Configuring the logical link to an X.25 network.

• Dial-in connections (defined in Connection profiles) may use X.25. The application layer of an X.25 connection can be a TCP/IP network connection or terminal emulation using X.25 Packet Assembler/Disassembler (PAD).

• STAC compression

• PAP authentication

• multiprotocol encapsulation including: IP routing, IPX routing, Appletalk routing, and bridging

Configuring the logical link to an X.25 network

Ethernet
      X.25
        any X.25 profile
            Name=
            Active= No
            Call Type=Nailed
            Nailed Grp=1
            Data Svc=56K
            Tei #=N/A
            PRI #=N/A
            Dial #=N/A
            Bill #=N/A
            Call-by-Call=N/A
            Transit #=N/A
            LAPB T1=3
            LAPB T2=0
            LABP N2=20
            LAPB k=7
            X.25 Seq Number Mode=NORMAL
            X.25 Link Setup Mode=ACTIVE
            X.25 Node Type=DTE
            X.25 window size=2
            X.25 pkt size=128
            X.25 Min pkt size=64
            X.25 Max pkt size=1024
            X.25 lowest PVC=0
            X.25 highest PVC=0
            X.25 lowest SVC=1
            X.25 highest SVC=8
            X.25 Clear/Diag=Yes 
            X.25 Reset/Diag=Yes
            X.25 Restart/Diag=Yes
            X.25 options=NPWS
            X.25 Rev Charge Accept=No
            X.25 Network Type=CCITT
            X.25 T20=18
            X.25 R20=1
            X.25 T21=20
            X.25 T22=18
            X.25 T22=1
            X.25 R23=18
            X.25 R23=1
            X.121 src addr=
            VCE Timer Val=300

Profile name and activation

To make the profile available for use, set the Active parameter to Yes.

Type of connection

LAPB and reliable data transfer

• LAPB T1-Maximum number of seconds the transmitter waits for acknowledgment before initiating a recovery procedure (Response timeout). The default is 3 seconds.

• LAPB T2-Maximum number of milliseconds LAPB waits for outgoing data before sending a Restart-Request packet to the network. The default of 0 (zero) specifies immediate acknowledgment.

• LAPB N2-How many times the MAX can resend a frame when the LAPB T1 timer expires. The default is 20. This relatively high value increases the probability of a correct transfer of data.

• LAPB K-Maximum number of sequentially numbered frames that can be unacknowledged at a given time. This value is also called the Level 2 Window Size or the Frame Window Size. The default is 7. Higher values enable faster throughput.

• X.25 Seq Number Mode selects between modulo 8 (Normal) and modulo 128 (Extended) sequence-number mode.

• X.25 Link Setup Mode specifies whether the X.25 link comes up in active- or passive- disconnect mode. In active-disconnect mode (the default), the link layer sends a DISC, and the packet layer sends a Restart-Request packet, upon initialization. In passive-disconnect mode, the link layer sends SABM(E), upon initialization and issues a restart to the network only upon receipt of a Restart-Request packet. It does not issue a Restart-Request packet upon initialization, but responds to Restart packets it receives.

• X.25 Node Type specifies whether the MAX interacts with the remote end of the connection as a DTE (the default) or a DCE (when emulating the X.25 network).

• X.25 Window Size is the default for maximum number of outstanding data packets that can accumulate before the MAX requires an acknowledgment. The default is 2.

• X.25 packet-size parameters as specify the default, maximum, and minimum number of bytes in the data field of a data packet.

The X.25 Lowest SVC and X.25 Highest SVC parameters define a range of SVCs from 1 to 4096. If the lowest SVC number is zero, no SVCs are supported.

X.25 diagnostic fields in packet types

X.25 Reset/Diag specifies whether Reset-Request packets include the diagnostic field. The default is No.

X.25 Restart/Diag specifies whether Restart-Request packets include the diagnostic field. The default is No.

X.25 options

X.25 reverse charge accept

X.25 network type

Timer and limit for Restart-Requests

Timer for Call-Requests

Timer and limit for Reset-Requests

Timer and limit for Clear-Requests

X.121 source address

Virtual Call Establishment (VCE) timer value

Example of an X.25 profile configuration

You must obtain a copy of the telco's subscription form containing the values provisioned in the switch and then configure the MAX X.25 profile to comply with those values.

Table 6-1 shows a sample telco subscription form and the corresponding settings to enter in an X.25 profile:

Table 6-1. Sample telco subscription form

Subscription-item	Value	X.25 profile setting
Maximum seconds the transmitter waits for acknowledgment before starting recovery procedure (T1)	5	LAPB T1=5
Maximum times to resend a frame after the T1 timer expires (N2)	10	LAPB N2=10
Maximum sequentially numbered frames that a given DTE/DCE link can have unacknowledged at any given time (K)	7	LAPB K=7
Is the X.25 node a DTE or DCE?	DTE	X.25 Node Type=DTE
Is the link SVC or PVC?	SVC	X.25 Link Setup Mode=Active X.25 Lowest PVC=1 X.25 Highest PVC=8
Maximum packet size	1024	X.25 Max Pkt Size=1024
Maximum number of data packets that can be outstanding between a DTE and a DCE before acknowledgment is required (W)	2	X.25 Window Size=2
Number of PVCs	0	X.25 Lowest PVC=0
Highest PVC channel number	0	X.25 Highest PVC=0
Default packet size	256	X.25 Pkt Size=256
Minimum packet size	64	X.25 Min Pkt Size=64
Maximum packet size	1024	X.25 Max Pkt Size=1024

To configure the X.25 profile to comply with the subscription form in this example:

1. Open the X.25 profile, assign the profile a name, and activate it:

   Ethernet
         X.25...
             any X.25 profile
                   Name=ATT
                 Active=Yes
   

2. Set Call Type to Nailed and specify the nailed group number:

                   Call Type=Nailed
                   Nailed Grp=7
   

3. Set the LAPB parameters to comply with the settings in the subscription form:

                 LAPB T1=5
                 LAPB T2=0
                 LAPB N2=10
               LAPB k=7
   

4. Set the X.25 Node Type to DTE, as specified in the subscription form:

               X.25 Node Type=DTE
   

5. Configure the profile to support up to 8 switched virtual circuits:

                 X.25 Link Setup Mode=ACTIVE
                 X.25 lowest PVC=0
                 X.25 highest PVC=0
                 X.25 lowest SVC=1
                 X.25 highest SVC=8
   

6. Configure packet sizes and flow control:

               X.25 window size=2 
               X.25 pkt size=128
               X.25 Min pkt size=64
               X.25 Max pkt size=1024
   

7. Specify the X.121 source address to use on this link:

               X.121 src addr=031344159782738
   

8. Close the X.25 profile.

Configuring X.25 IP connections

Ethernet
    Answer
            Encaps...
            X25/IP=Yes

Ethernet
    Connections
        any Connection profile
            Encaps=X25/IP

            Encaps options...
                  X.25 Prof=ATT
                  LCN=0
                  Encaps Type=RFC877
                  Reverse Charge=No
                  RPOA=1234
                  CUG Index=
                  NUI=
                  Max Unsucc. calls=0
                  Inactivity Timer=0
                  MRU=1500
                  Call Mode=Both
                  Answer X.121 Addr=
                  Remote X.121 addr=

            Route IP=Yes

            Ip options...
                  LAN Adrs=10.65.212.226/24

Understanding the X.25 IP connection parameters

X.25 Prof

LCN

Encap Type

Reverse Charge

RPOA

CUG Index

NUI

Max Unsucc. calls

Inactivity Timer

MRU

Call Mode

• Incoming-The MAX does not issue a call request when data shows up for forwarding. If there is no virtual circuit is established, the MAX drops the IP packet. If a host receives an incoming call from a host whose address matches the Answer X.121 address (below), the MAX accepts the call.

• Outgoing-The MAX issues a call request to the Remote X.121 address setting when data shows up for forwarding. If the MAX does not establish a virtual circuit and the MAX receives an incoming call request, the MAX rejects the call.

• Both-The MAX accepts incoming call requests and issues a call request to the Remote X.121 address setting when data shows up for forwarding. The called address must match the Answer X.121 address. If the MAX does not establish a virtual circuit and IP packets arrive, the MAX issues a call request to the Remote X.121 address.

Remote X.121 address

IP configuration parameters

Example of an X.25 IP configuration

Figure 6-1. Example of an X.25 IP connection

To configure this sample connection:

1. Open the Answer profile and enable X.25 IP encapsulation:

   Ethernet
         Answer
               Encaps...
                     X25/IP=Yes
   

2. Open a Connection profile, name it, and activate the profile:

   Ethernet
         Connections
             any Connection profile
               Name=newyork
               Active=Yes
   

3. Enable IP routing and specify the IP address of the answering unit:

               Route IP=Yes
               Ip options...
                     LAN Adrs=10.65.212.226/24
   

4. Enable X.25/IP encapsulation and then open the Encaps Options subprofile.

5. Specify the name of the X.25 profile that carries this connection:

               Encaps=X25/IP
               Encaps options...
                     X.25 Prof=ATT
   

6. Set the inactivity timer. (to 30 seconds, for example):

                     Inactivity Timer=30
   

7. Set the call mode and the local and remote X.121 addresses:

                     Call Mode=Both
                     Answer X.121 Addr=031344159782111
                     Remote X.121 addr=031344159782111
   

8. Close the Connection profile.

Configuring X.25 PAD connections

When a user calls an X.25 PAD through a modem, a digital modem processes and forwards the call to the terminal server. The terminal server authenticates the call, using the password specified in the caller's Connection profile, and establishes the session. If the MAX does not authenticate the session, either because an unauthenticated user enters the PAD command at the terminal-server prompt or because you use the terminal server's immediate X25/PAD services, the MAX uses X.25 parameters specified in the Answer Profile.

When the MAX establishes the session, the caller can see the terminal-server command line or is directed immediately to an X.121 host. If the connection auto-calls an X.121 host, the initial session display is similar to the following:

ATDT 555-1212
CONNECT 9600
ASCEND TERMINAL PAD v0.99:  ASYNC PORT # 1, 9600 BAUD
*

ascend% pad

*

*call 031344159782738

Ethernet
      Answer
            PAD options...
                  X25 Prof=
                  X.3 Param Prof=CRT
                  VC Timer enable=DISABLE
                  Auto-Call X.121 addr=
                  Reverse Charge=No
                  RPOA=
                  CUG Index=
                NUI=

Ethernet
      Connections
        any Connection profile
            Encaps=X25/PAD
            Encaps options...
                  X.25 Prof=
                  Recv PW=localpw
                  X.3 Param Prof=CRT
                  VC Timer enable=DISABLE
                  Auto-Call X.121 addr=
                  Reverse Charge=No
                  RPOA=1234
                  CUG Index=
                  NUI=
                  PAD banner msg=
                  PAD prompt=
                  NUI prompt=
                  NUI PW prompt=
                  PAD Alias #1=
                  PAD Alias #2=
                  PAD Alias #3

Auto-Call X.121 Addr

CUG Index

NUI

NUI prompt

NUI PW prompt

PAD Alias #1
PAD Alias #2
PAD Alias #3

PAD banner msg

PAD prompt

Recv PW

Reverse Charge

RPOA

VC Timer Enable

X.25 Prof

X.3 Param Prof

Example of X.25 PAD

Figure 6-2. Example of an X.25 PAD connection

To configure this sample X.25 PAD connection:

1. Open the Answer profile and enable X.25/PAD encapsulation:

   Ethernet
         Answer
               Encaps...
                     X25/PAD=Yes
   

2. Open a Connection profile, name it, and activate the profile:

   Ethernet
       Connections
           any Connection profile
               Name=rchan
               Active=Yes
   

3. Enable X.25/PAD encapsulation:

               Encaps=X25/PAD
   

4. Open the Encaps Options subprofile and specify the name of the X.25 profile that carries this connection:

               Encaps options...
                     X.25 Prof=ATT
   

5. Specify the password that authenticates the user connection:

                     Recv PW=localpw
   

6. Specify a default X.3 parameter profile for this connection:

                     X.3 Param Prof=CRT
   

7. Specify the X.121 address and password for automatic calling:

                     Auto-Call X.121 Addr=031344159782111 *Dpassword
   

8. Close the Connection profile.

Setting up X.25 PAD sessions

X.3 parameters and profiles

Table 6-2. X.3 parameters

Table 6-3 lists the permanent (noncustom) X.3 profiles, and the settings of their parameters.

Table 6-3. X.3 profiles

X.3 profile	Contents
CRT	1:64, 2:1, 3:2, 4:0, 5:0, 6:5, 7:2, 8:0, 9:0, 10:0, 11:0, 12:1, 13:4, 14:0, 15:1, 16:8, 17:24, 18:18, 19:2, 20:0, 21:3, 22:0
INFONET	1:1, 2:0, 3:2, 4:0, 5:0, 6:0, 7:21, 8:0, 9:2, 10:0, 12:1, 13:0, 14:2, 15:1, 16:8, 17:24, 18:18, 19:0, 20:0, 21:0, 22:0
SCEN	1:64, 2:1, 3:2, 4:0, 5:1, 6:5, 7:21, 8:0, 9:0, 10:0, 12:1, 13:4, 14:0, 15:1, 16:127, 17:24, 18:18, 19:1, 20:0, 21:0, 22:0
CC_SSP	1:1, 2:1, 3:126, 4:0, 5:1, 6:1, 7:2, 8:0, 9:0, 10:0, 12:1, 13:0, 14:0, 15:0, 16:127, 17:24, 18:18, 19:1, 20:0, 21:0, 22:0
CC_TSP	1:0, 2:0, 3:0, 4:20, 5:0, 6:0, 7:2, 8:0, 9:0, 10:0, 12:0, 13:0, 14:0, 15:0, 16:127, 17:24, 18:18, 19:1, 20:0, 21:0, 22:0
HARDCOPY	1:64, 2:1, 3:2, 4:0, 5:2, 6:5, 7:21, 8:0, 9:5, 10:80, 12:1, 13:4, 14:5, 15:1, 16:8, 17:24, 18:18, 19:1, 20:0, 21:3, 22:0
HDX	1:1, 2:1, 3:2, 4:0, 5:2, 6:5, 7:2, 8:0, 9:0, 10:0, 12:1, 13:4, 14:0, 15:1, 16:8, 17:24, 18:18, 19:2, 20:0, 21:3, 22:0
SHARK	1:0, 2:0, 3:2, 4:0, 5:0, 6:0, 7:2, 8:0, 9:0, 10:0, 12:0, 13:0, 14:0, 15:0, 16:0, 17:0, 18:0, 19:0, 20:0, 21:0, 22:0
DEFAULT (MINIMAL)	1:64, 2:1, 3:2, 4:0, 5:2, 6:5, 7:2, 8:0, 9:25, 10:72, 12:1, 13:5, 14:25, 15:1, 16:8, 17:24, 18:18, 19:1, 20:0, 21:0, 22:0
NULL	1:0, 2:0, 3:0, 4:0, 5:0, 6:0, 7:0, 8:0, 9:0, 10:0, 12:0, 13:0, 14:0,15:0, 16:0, 17:0, 18:0, 19:0, 20:0, 21:0, 22:0

X.25 PAD commands

help

• par? [param1[,param2,...]]

  The Par? command displays the current values of the specified X.3 parameters. Or, if you specify no parameters, the command displays all current X.3 settings. For example:

  par 2
  

• prof [profile | ?]

  The Prof command activates the X.3 profile (specified by the name shown in Table 6-3), or if you use this command with the question mark (?) keyword, it displays the currently active profile followed by a list of available profiles. If you do not specify any arguments, the Prof command displays the currently active profile. For example:

  prof infonet
  

• set [param1:value1 [,param2:value2,...]]

  The Set command sets one or more X.3 parameter values. For example:

  set 1:0, 2:1
  

• set? [param1:value1 [,param2:value2,...]]

  The Set command is identical to the Set command, except that it displays all X.3 parameter values after setting those specified on the command line.

• tabs [LCL num1][REM num2][EXP num3]

  The Tabs command sets and reads three nonstandard X.3 parameters that control tab expansion. You cannot access these parameters by the remote host using Q-bit packet PAD commands on the remote host. You must keep the PAD's view of the current screen position accurate by setting EXP to 0 and LCL to the number of columns to which your terminal expands tabs. The settings enable the PAD to perform correct line folding, line deletion, and character deletion. The keywords function as follows:

  • LCL sets the number of columns to which tabs are expanded locally (num1). If the EXP keyword disables local tab expansion, LCL num1 specifies the number of columns to which the asynchronous device expands tabs sent to it. You can specify a number from 0 to 16. Zero specifies that no expansion takes place.

  • REM sets the number of columns to which tabs are expanded remotely (num2), that is, on input from the terminal to the network. You can specify a number from 0 to 16. Zero specifies that no expansion takes place.

  • EXP enables (1) or disables (0) tab expansion locally. If you specify 1 after this keyword, the MAX expands tabs according to the LCL specification.

• rpar? [param1[,param2,...]]

  The Rpar? command displays the current values of the specified X.3 parameters on the remote PAD. Or, if you specify no parameters, the command displays all current X.3 settings. For example:

  rpar 2
  

• rprof [profile | ?]

  The Rprof command activates the X.3 profile for the remote PAD. Or, if you use this command with the question mark (?) keyword, it displays the currently active profile followed by a list of available profiles. If you do not specify any arguments, the Rprof command displays the currently active profile. For example:

  rprof infonet
  

• rset [param1:value1 [,param2:value2,...]]

  The Rset command sets one or more X.3 parameter values for the remote PAD. For example:

  set 1:0, 2:1
  

• rset? [param1:value1 [,param2:value2,...]]

  The Reset? command is identical to the Reset command, except that it displays all X.3 parameter values after setting those specified on the command line.

• call [?] | [[address][*P|*D|*F data]]

  The Call command generates a call by sending a Call-Request packet. If you enter the Call command with only a question mark (?), the MAX displays the address the PAD would use if you entered the Call command with no address.

  The address argument specifies the X.121 address to which the MAX makes the call. The address can contain up to 15 characters. If you do not specify a value for address, the MAX makes the call request for the last address specified.

  The MAX inserts the data following the *P and *D keywords into the last 12 bytes of the user data field. If you specify *P, the screen does not echo the data as you enter it, even if you set X.3 parameter number 2 to Echo. This specification is useful for entering passwords. If you specify *D, the screen echoes the data as you enter it.

  If you specify *F, the MAX inserts all the <data> into the user data portion of the call packet (with a maximum length of 124 bytes), and the MAX flags the packet as a fast select call. For example:

            call 3331055567
  

• clr

  The Clr command clears a virtual circuit by sending a Clear-Request packet (from a DTE) or a Clear-Indication packet (from a DCE).

• facilities [ * | facilities ]

  The Facilities command specifies which facilities to use in subsequent Call commands. If you enter the Facilities command with no arguments, the MAX displays the current facilities.

  • If you specify an asterisk (*), the command clears the current facilities and resets them to their default values. The default facilities are window size 2 and packet size 128 (420202430707).

  • The facilities argument can consist of up to 63 hexadecimal digits. The MAX converts the specified value you specify from hexadecimal format, and it becomes the byte sequence inserted in the Facilities field of outgoing Call-Request packets.

    For example,

    facil *
    

• full

  The Full command selects full-duplex mode.

• half [*] | [[-] <ch1>, <ch2>,...]

  The Half command selects half-duplex mode and specifies the characters echoed. In half-duplex mode, the MAX does not echo most characters. In half-duplex mode with echo enabled, the PAD does most of the work of echoing and then discards the data instead of sending it to the asynchronous device. The PAD can therefore provide line folding, tab expansion, linefeed insertion, carriage return and linefeed padding, and character and line deletion. For more information about these features, see X.3 parameters and profiles.

  If you disable echo, the amount of processing the PAD must perform on every character decreases substantially, and the PAD cannot perform line folding, tab expansion, or other actions described in the previous paragraph. This mode is most efficient for file transfers. The command's arguments function as follows:

  • If you specify an asterisk (*), the MAX does not echo any characters.

  • If you specify only a list of characters (<ch1>, <ch2>, and so on), the MAX echoes only these characters.

  • You must specify each character in decimal format.

  • If you insert a hyphen (-) before the list of characters, only the characters you specify are not echoed.

  • If you enter the Half command with no arguments, the command sets half-duplex mode without altering the characters selected for echo by any previously entered Half command.

• interrupt

  The Interrupt command generates an Interrupt packet. An Interrupt packet can transmit from 1 to 32 bytes of data to the remote DTE without being subject to flow control. The exchange of Interrupt packets does not affect the exchange of data packets or flow-control packets.

• listen [addr=<address> | data=data]

  The Listen command specifies the match pattern for accepting an incoming call. It uses the following syntax:

  • The MAX matches the <address> argument against the subaddress specified by the incoming call. If the subaddresses match, the MAX accepts the incoming call.

  • The MAX matches the <data> against the last 12 bytes of the user data field of incoming calls. If the data matches, the MAX accepts the incoming call.

• reset

  The Reset command resets a virtual circuit by generating a Reset-Request packet with 0 cause (DTE originated) and 0 diagnostic.

• status

  The Status command requests the status of a virtual call placed to a remote DTE.

Table 6-4. PAD service signals

X.25 clear cause codes

Table 6-5. Clear cause codes

X.25 diagnostic field values

Table 6-6. X.25 diagnostic field values

Customizing script support for X.25 PAD

Parameters and commands

• Five parameters appear in the Ethernet > Connections >Encaps Options submenu for an X.25/PAD connection.

  • Banner

  • PAD prompt

  • NUI prompt

  • NUI PW prompt

  • PAD Alias #n (where n=1-3)

• One terminal server command

  • X28

• Two X.25 PAD commands

  • storeprofile

  • call

NUI prompt

NUI PW prompt

PAD Alias #n (n=1-3)

PAD prompt

Terminal server command

To access the PAD, enter the X28 command at the terminal-server prompt:

% X28

To store the current settings of the PAD parameters to the X.3 profile name custom, enter the Storeprof command at the PAD prompt using the following syntax:

storeprof custom

The table listing the 10 named X.3 profile should include the X.3 profile named custom noting that the settings of the X.3 parameters is not preset, but accomplished through X.25 commands.

Call

call 123456789,CallUserData

Assume that the following aliases have been established by the following parameter settings:

PAD Alias #1=call/n

PAD Alias #2=prof CUSTOM/profile 6

PAD Alias #3=storeprof CUSTOM/storeprofile 6

Assume that a calling device, such as a PC with a modem attached, dials into the MAX, successfully matching a Connection profile that uses X25/PAD encapsulation. The user at the calling device can enter a series of commands as illustrated below. (Note that the user at the calling end may be a result of an application running a PAD script.)

The bold face type gives the user or the calling devices input. The normal face type gives the prompts and messages sent to the user from the PAD at the MAX. In this example, the user starts by command his modem to dial to the MAX atd12234567. The MAX connects and starts the X.25 session by returning the message CONNECTED.

% atd1234567

CONNECTED 

THIS IS A BANNER MESSAGE

ENTER NUI:

% 123456

123456

ENTER NUI PASSWORD:

% 654321

******

PROMPT>

PROMPT> profile 6 */User loads the CUSTOM profile. */

PROMPT> set 1:1 /* User sets the Escape char to ctrl-P */

PROMPT> n 031454159782738 /* User places X.25 call. */

PROMPT>

COM /* X.25 call connected. */

PROMPT> <ctrl-P> /* After exchanging some data with the called host, 
the user escapes to command mode. */

PROMPT>

PROMPT> clr /* User clears the X.25 call. */

CLR CONF

PROMPT>

PROMPT> storeprofile 6 /* User saves the changed parameters to the CUSTOM
profile */

PROMPT>

PROMPT>+++ /* User quitting modem call */

OK

% ath

OK

Setting up ISDN D-channel X.25 support

Configuring ISDN D-channel X.25 support

1. Open Ethernet > X25 > any X25 profile.

2. Set TEI to the value specified by your X.25 carrier.

   You can set TEI to any value from 0 to 63. The default is 23. If you set TEI to 0 (zero), the MAX requests a TEI assignment from the network.

3. Set Call Type to D Channel.

4. Exit and save the settings.

T3POS is a character-oriented, frame-formatted protocol designed for point-of-service (POS) transactions through an X.25-based packet switched network. T3POS enables you to send data over the ISDN D channel while continuing to send traffic over both B channels. The T3POS protocol involves three parties: the T3POS DTE (DTE), the T3POS PAD (PAD) and the T3POS Host (host), as shown in Figure 6-3.

Figure 6-3. T3POS set up

A typical use of T3POS is performing credit card authorization over the D channel while using the B channels to transmit inventory control data and other traffic. Figure 6-4 shows an example of a T3POS setup.

Figure 6-4. Example of a T3POS configuration

The Ascend T3POS implementation supports the following T3POS features:

• Local, Transparent, Blind, and Binary-Local mode

• T1-T6 timers

• All the control characters, described in Bellcore GR-2803

• Error recovery procedures, described in Bellcore GR-2803 and EIS 1075-V2.1

• DTE-initiated calls

• Host-initiated calls

The T3POS protocol provides reliable and efficient data interchange (transactions) between a host (usually a transaction server) and a DTE (usually a client). The T3POS DTE is usually a client device communicating through an asynchronous port, while the T3POS host is a mainframe or server communicating through an X.25 packet network. The T3POS PAD (the MAX) converts data arriving from a T3POS DTE to a format that can be transmitted over a packet network. It also ensures reliability and efficiency as described in the protocol specifications.

Note that the T3POS PAD does not alter, check, or convert the parity of characters it receives from or sends to the X.25 network or the T3POS DTE. T3POS essentially uses a data format of 8 bits no parity. The format is actually 7 bits, 1 parity, but the MAX ignores the parity bit.

Depending on the current state of a transaction or call, and the mode of operation selected, T3POS uses different data formats and frame structures. The MAX supports four modes of operation: Local, Binary-Local, Transparent, and Blind.

General frames

STX [data] ETX XRC

where:

• STX is the ascii character \002.

• Data is the user data being sent in this frame.

• ETX the ascii character \003.

• XRC is the checksum. For all modes except Binary-Local, the checksum is a one character Longitudinal Redundancy Check (LRC) checksum. For Binary Local mode, the checksum is a two character Cyclic Redundancy Check (CRC) checksum.

SOH MSS CUD STX [data] ETX XRC

where:

• SOH is the ascii character \001.

• MSS is the Mode Selection Signal which can be (optionally) used to indicate the mode for the call.

• CUD is the Called User Data. It can contain an X.121 address, and user facilities or call user data in an X.28 format.

• Data is optional in the control frame. In Transparent and Blind modes, the T3POS PAD is essentially restricted to passing data frames between the T3POS DTE and the T3POS host.

• ETX is the ascii character \003.

• XRC is the checksum. For all modes except Binary-Local the checksum is a one character Longitudinal Redundancy Check (LRC) checksum. For Binary-Local mode, the checksum is a two character Cyclic Redundancy Check (CRC) checksum.

• T1: Char-to-Char timer

• T2: SYN-to-SYN timer

• T3: ENQ Handling timer

• T4: Response timer

• T5: DLE, EOT timer

• T6: Frame Arrival timer

Host-initiated calls

Flow control

References

• GR-2803-"Generic requirements for a Packet Assembler/Disassembler supporting T3POS," Bellcore GR-2803-CORE Issue 2, Dec. 1995. This is the basic defining document.

• EIS 1075-V2.1-"External Interface Specification for Data-Terminal-Equipment Support of T3POS," Applied Digital Design, version 2.1, March 1994. Specifies error recovery mechanisms between a T3POS DTE and a T3POS PAD on one side and a T3POS PAD and the T3POS host in the other side.

• Create a Connection profile for each authenticated user connecting to the T3POS, or configure the Answer profile for unauthenticated users.

• Create an X.25 profile that defines the X.25 connection the T3POS PAD uses.

To configure a T3POS Connection profile:

1. From the Main Edit Menu select Ethernet > Connections > any Connection profile.

2. Set Active to Yes.

3. Set Encaps to X25/T3POS.

4. Open the Encaps Options submenu.

5. Set X.25 Prof to the name of the X.25 profile that is to be used for this T3POS connection.

   The X.25 profile must exist and be active before you can save this Connection profile.

6. Specify the Recv PW value used to authenticate the caller.

7. Set specify the parameters used for the T3POS connection.

8. Exit and save the Connection profile.

1. From the Main Edit Menu select Ethernet > Answer > Encaps.

2. Set X25/PAD to Yes and X25/T3POS to Yes.

3. Exit the Encaps submenu.

4. Select T3POS Options.

5. Set X.25 Prof to the name of the X.25 profile that is to be used for this T3POS connection.

   The X.25 profile must exist and be active before you can save the Answer profile.

6. Set the parameters used for the T3POS connection.

7. Exit and save the Answer profile.

• Through a modem (for MAX units only).

• Via a TCP/IP client to the default TCP modem port 6150 (or to the TCP modem port configured on the Ascend unit).

• Via a TCP/IP client to port 23 (for Telnet access) or to 513 (for Rlogin access).

In this example:

1. A user dial in through a modem or through Telnet.

2. The user is authenticated against a Connection profile. If no Connection profile exists for the user, the Answer profile is used (if configured).

   Both the Connection and the Answer profile specify that the user is an X.25 user (that is, Encaps is set to X25/T3POS). An X.25 profile specifies the physical interface where the X.25 call is to be established. The X.25 profile determines the settings for the LAPB (or LAPD) and packet level, (for example, timers and window size). For LAPB, the X.25 profile also specifies the nailed group to use for the logical call.

3. The connection is then established on the basis of the settings in both the Connection profile (or Answer profile) and the X.25 profile, and the call is directed to the T3POS.

4. The user then must use the normal X.25/PAD commands.

1. At the terminal-server prompt, the user enters the T3POS command. For example:

   ascend% t3pos

2. The user is directed to the T3POS PAD, and T3POS traffic can be transmitted.

Ascend recommends that, when using immediate service, you set the Banner parameter to suppress the terminal-server banner, and reduce the PPP Delay parameter to its minimum value. Both parameters are in the Ethernet > Mod Config > TServ Options submenu.

Always On/Dynamic ISDN (AO/DI)

Introduction

In a traditional ISDN environment, data moves across B-channels, and signalling information moves across the D-channel. Because signalling information uses a small percentage of available D-channel bandwidth, AO/DI was developed to maximize bandwidth usage while reducing the necessity that all data travel over B-channels. Ascend's implementation of AO/DI enables you to configure a nailed X.25 connection over a BRI D-channel, BRI B-channel, or over a leased-56k line.

Among the functions that can take advantage of AO/DI are the following:

• Transfer of email

• Reception of news broadcasts and other pushed information

• Automated collection of data

How it works

When the MAX adds bandwidth on the basis of DBA, it brings up a B-channel to transport data and stops sending data over the X.25 connection. Because the 9600 bps bandwidth available over the X.25 connection is so small when compared to that available through the B-channel, it is not efficient to continue to transfer data over the X.25 connection simultaneously.

When ALU for the connection drops below the value specified in the Target Util parameter for the amount of seconds specified in the Sub Pers parameter, the MAX disconnects the switched channel and data traffic flows over the X.25 connection.

The MAX can add bandwidth to a connection using multiple B-channels to transfer data for a specific call, but discontinues using the X.25 connection for data transfer if at least one B-channel is active.

Configuring an AO/DI connection

• Create an X.25 profile that defines the X.25 connection.

• Configure the Answer profile to enable BACP and MP support.

• Create a Connection profile for each AO/DI connection.

Configuring the X.25 profile

1. Open Ethernet > X25 > any X25 profile.

2. Set Name to a descriptive name for the X.25 link.

3. Set Active to Yes.

4. Set TEI to the value specified by your X.25 carrier.

   You can set TEI to any value from 0 to 63. The default value is 23. If you set TEI to 0, the Ascend unit requests a TEI assignment from the network.

5. Set Call Type as follows:

   • Call Type = D-Channel if X.25 services are over the D-channel.

   • Call Type = Nailed if X.25 services are over either a B-channel or the leased-56k line.

6. Set Nailed Grp that AO/DI-related Connection profiles reference when using the X.25 connection.

   The value specified for Nailed Grp must match the value specified in the Ethernet > Connections > any Connection profile > Telco options > Group parameter of any AO/DI-related profile that uses the X.25 connection.

7. Set X.25 highest SVC as directed by your carrier.

8. Set X.25 lowest SVC as directed by your carrier.

9. Set X.121 src addr to the called number that the remote side sends when establishing the X.25 connection with the MAX. Contact your carrier for the correct value.

10. Set any remaining X.25 parameters as your carrier specifies.

11. Exit and save the settings.

1. From the main Edit menu, select Ethernet > Answer profile.

2. Open the Encaps submenu.

3. Set MP to Yes.

4. Set PPP to Yes.

5. Close the Encaps submenu.

6. Open the PPP options submenu.

7. Set BACP = Yes.

8. Exit and save the Answer profile.

Understanding the X.25 connection parameters

Configuring a Connection profile

1. From the main Edit menu select Ethernet > Connections > any Connection profile.

2. Set Active to Yes.

3. Set Encaps to MP.

4. Set Dial # to the phone number that the MAX dials when additional bandwidth from a B-channel is needed.

5. Open the Telco options submenu

6. Set Call Type to AO/DI.

7. Set Group to the group number that you specified in the Ethernet > X25 > X25 profile > Nailed Grp parameter.

8. From the Connection profile menu, open the Encaps options submenu.

9. Set BACP to Yes.

10. Set both Base Ch Cnt and Max Ch Cnt parameters to the maximum number of channels allowed for the connection.

11. Set InterfaceType to X.25.

12. From the Connection profile main menu, open the Interface options submenu.

13. Set X.25 Prof to the name of the X.25 profile that the MAX uses for the connection.

14. Specify additional parameters for the X.25 connection as directed by the carrier.

1. From the Connection profile menu, open the Interface options submenu.

2. Set Answer X.121 addr to the value specified in the X.121 src addr parameter of the X.25 profile on the MAX.

   Note: You can substitute the beginning portion of the address with the wildcard * which indicates that the MAX should accept any value, requiring a match only on the trailing digits that you specify after the wildcard character.

1. From the Connection profile menu, open the Interface options submenu.

2. Set Remote X.121 addr to the value specified in the X.121 source address of the remote X.25 host to which the profile connects. You should not leave Remote X.121 addr blank if you set Call Mode to Both or Outgoing. Also, for incoming calls, the MAX attempts to match the called number of the incoming call to Remote X.121 address (if specified) and the calling number of the incoming call to Answer X.121 address (if specified).

   Note: You can substitute the beginning portion of the address with the wildcard * which indicates that the MAX should accept any value, requiring a match only on the trailing digits that you specify after the wildcard character. For outgoing calls, the MAX dials only the trailing digits specified, ignoring the beginning wildcard character.

When the session and profile are active, the Connection profile displays an asterisk to the left of the profile name on the Ethernet > Connections submenu which indicates that a call is up or is available for a call.

Displaying AO/DI operation

Displaying whether or not the MAX supports AO/DI

When the MAX displays the Sys Options window, press the down arrow key until the AO/DI feature appears. For example, the following screen indicates that the MAX supports AO/DI:

|-------------------|

|00-100 Sys Options |

|ISDN Sig Installed  |

|AO/DI Installed        |

|Net Mgmt Installed  |

|-------------------|

Displaying active AO/DI calls

|-------------------|

|DMILLER                       |

|Qual Good 05:07:00 |

|9k            1 channels |

|CLU    12%    ALU    30% |

|-------------------|

|-------------------|

|DMILLER                       |

|Qual Good 05:07:00 |

|56k          2 channels |

|CLU    50%    ALU    34% |

|-------------------|

When the MAX adds a second B-channel on the basis of bandwidth utilization, the following window appears:

|-------------------|

|DMILLER                       |

|Qual Good 05:07:00 |

|112k        3 channels |

|CLU    88%    ALU    64% |

|-------------------|

Displaying packet processing for a specific session

|-------------------|

|DMILLER                       |

|Rx Pkt:              7085 |

|Tx Pkt:                603 |

|      CRC:                    0 |

|-------------------|

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Copyright © 1998, Ascend Communications, Inc. All rights reserved.