Table Of Contents
X.25 Record Boundary Preservation for
Data Communications NetworksWhen to Use Record Boundary Preservation
How Record Boundary Preservation Works
Supported Standards, MIBs, and RFCs
Configuring a PVC to Use RBP for Incoming X.25 Connections
Configuring SVCs to Use RBP for Incoming X.25 Connections
Configuring a PVC to Use RBP for Incoming TCP Connections
Configuring SVCs to Use RBP for Incoming TCP Connections
Verifying Record Boundary Preservation
Monitoring and Maintaining RBP
PVC Configured to Use RBP for Incoming X.25 Connections Example
SVCs Configured to Use RBP for Incoming X.25 Connections Example
PVC Configured to Use RBP for Incoming TCP Connections Example
SVCs Configured to Use RBP for Incoming TCP Connections Example
X.25 Record Boundary Preservation for
Data Communications Networks
Feature History
This document describes the X.25 Record Boundary Preservation for Data Communications Networks feature in Cisco IOS Release 12.2(8)T. It includes the following sections:
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Supported Standards, MIBs, and RFCs
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Feature Overview
The X.25 Record Boundary Preservation for Data Communications Networks feature enables hosts using TCP/IP-based protocols to exchange data with devices that use the X.25 protocol, retaining the logical record boundaries indicated by use of the X.25 "more data" bit (M-bit).
When to Use Record Boundary Preservation
Before the introduction of the X.25 Record Boundary Preservation for Data Communications Networks feature, Cisco IOS software provided two methods for enabling the exchange of data between X.25 hosts and hosts using TCP/IP-based protocols: protocol translation and X.25 over TCP (XOT). Protocol translation supports a variety of configurations, including translation of a data stream between an X.25 circuit that is using X.29 and a TCP session. The X.29 protocol is an integral part of protocol translation. One aspect of X.29 is that it is asymmetric and allows the packaging of data into X.25 packets to be controlled in one direction only. The TCP protocol is stream-oriented, rather than packet-oriented. TCP does not attach significance to TCP datagram boundaries, and those boundaries can change when a datagram is retransmitted. This inability to preserve boundaries makes protocol translation appropriate only for configurations in which the X.25 packet boundary is not significant.
The XOT feature allows X.25 packets to be forwarded over a TCP session. This allows full control over the X.25 circuit, but the host terminating the TCP session must implement the XOT protocol and the X.25 packet layer protocol.
The Record Boundary Preservation (RBP) feature offers a solution positioned between these two options: it allows logical message boundaries to be indicated without requiring the TCP host to be aware of X.25 protocol details.
How Record Boundary Preservation Works
The TCP protocol does not attach significance to datagram boundaries, so a protocol must be layered over a TCP session to convey record boundary information. The Record Boundary Preservation protocol implements a 6-byte record header that specifies the amount of data following and indicates whether that data should be considered the final part of a logical record. Table 1 describes the format and contents of the record header.
When a router configured with RBP receives an X.25 call that matches a configured X.25 RBP map, the router attempts to open a TCP connection to the specified TCP destination. Each TCP session is mapped to one X.25 virtual circuit. If the TCP session is established, then X.25 data packets received from the caller are combined into logical records as indicated by use of the X.25 M-bit, and the contents of the data packets are forwarded to the TCP destination. The boundaries of these records are preserved by the record header.
The router will not split an X.25 data packet across multiple records unless the data packet exceeds the configured maximum record size; however, TCP will segment the data stream at arbitrary byte boundaries in accordance with TCP specifications.
X.25 data packets with the M-bit set may be combined as long as the resulting record does not exceed the configured maximum record size or, if a maximum record size was not configured, the maximum datagram size for the X.25 interface. The "more data" flag in the record header will reflect the value of the M-bit in the final X.25 data packet. This process of combining packets results in a series of zero or more records whose "more data" flag is set to the value 1 followed by a record whose "more data" flag is set to 0.
Incoming X.25 calls with the "delivery confirmation" bit (D-bit) set will be answered with the D-bit set. However, since the router is the endpoint of the X.25 circuit, X.25 data packets will be acknowledged as soon as their contents have been passed to the TCP connection without waiting for an acknowledgment for the TCP data, regardless of the value of the D-bit. TCP data will be acknowledged as soon as it has been converted to X.25 data packets.
The router will not send Receiver Not Ready (RNR) packets on the X.25 circuit; flow control will be accomplished by withholding acknowledgment.
The following situations will cause the X.25 circuit to be cleared (for an SVC) or reset (for a PVC) and the TCP connection to be closed: receipt of a data packet with the "qualified" bit (Q-bit) set; receipt of any packet type other than data, Receiver Ready (RR), or RNR; or a restart or lower-layer reset on the X.25 interface. When the circuit is cleared or reset, any data not yet passed to the TCP connection will be discarded.
When the router receives the records from the TCP session, it strips the record header and, on the basis of the information in the record header, reassembles the records into X.25 data packets. The data is interpreted as a fixed-length header followed by a variable-length payload whose length is specified in the record header. If the protocol ID or flag field in the header is invalid, the TCP connection will be closed and the X.25 circuit will be cleared or reset. The payload length may be greater than the X.25 packet size and need not be a multiple of the X.25 packet size.
A record that has the "more data" flag set will be logically combined with following records until a record that has the "more data" flag cleared is received. This process results in a sequence of maximum-sized X.25 data packets, each with the M-bit set, followed by an X.25 data packet containing the remaining data that does not have the M-bit set. The router will not wait for an entire record to be received before sending a maximum-size X.25 data packet.
As the records are reassembled into X.25 data packets, the packets are forwarded to the corresponding X.25 circuit.
The router will not set the D-bit or Q-bit on X.25 data packets being sent over circuits that are configured with RBP.
Data received by a router from a TCP session will be buffered while waiting for the other connection to be established. If the connection attempt fails, the data will be discarded. When a TCP connection is closed, the X.25 circuit will be cleared or reset, and any data not yet sent on the X.25 circuit will be discarded.
RBP Header Encoding Examples
The following tables show examples of coding of the RBP header length field for both directions of data transfer (X.25 to RBP and RBP to X.25) for various data sizes. The tables also show the assembly of X.25 complete packet sequences into RBP records and vice versa.
In Table 2, the maximum X.25 packet size is 128 bytes, and the maximum RBP record size is 130 bytes.
In Table 3, the maximum RBP record size is 130 bytes, and the maximum X.25 packet size is 128 bytes.
Benefits
The X.25 Record Boundary Preservation for Data Communications Networks feature enables X.25 and TCP/IP hosts to exchange data while preserving X.25 packet boundaries and without having to carry the full X.25 protocol over the TCP session.
Restrictions
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Related Documents
For more information about configuring X.25 networks, refer to the following documents:
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Supported Platforms
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Determining Platform Support Through Feature Navigator
Cisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Feature Navigator. Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image.
Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Feature Navigator home page at the following URL:
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
RFCs
No new or modified RFCs are supported by this feature.
Prerequisites
Documentation of the configuration tasks in this document assumes that you know how to configure X.25 networks.
Configuration Tasks
See the following sections for configuration tasks for the X.25 Record Boundary Preservation for Data Communications Networks feature. One or more of the following tasks must be completed:
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Configuring a PVC to Use RBP for Incoming X.25 Connections
To configure the router to establish a TCP session in response to data received on an X.25 PVC and to use RBP protocol to transfer data between the X.25 host and the TCP session, use the following command in interface configuration mode:
When the x25 pvc rbp remote command is configured, the router will wait until a data packet is received on the specified X.25 PVC; in the meantime, the router will acknowledge any X.25 reset packets on the circuit. When a data packet is received, the router will attempt to establish a TCP connection to the configured IP address and TCP port, using a dynamically assigned local TCP port number. If the connection attempt fails, the router will reset the permanent virtual circuit and will wait for another data packet before attempting to establish the TCP connection. Since this command is associated with a specific X.25 circuit, at most one connection may be active per command.
Configuring SVCs to Use RBP for Incoming X.25 Connections
To configure the router to establish TCP sessions in response to incoming X.25 calls, and to use RBP to transfer data between the X.25 circuit and the corresponding TCP session, use the following command in interface configuration mode:
When the x25 map rbp remote command is configured, the router will accept an incoming X.25 call if the destination address matches an X.25 address configured on the interface on which the call is received, and if the calling address and call user data matches the configured value. When the call is accepted, the router will attempt to open a TCP connection to the configured IP address and TCP port, using a dynamically assigned local TCP port number. If the TCP connection cannot be opened, the X.25 call will be cleared. The number of X.25 calls that may be accepted is limited only by router resources. No information from the X.25 call packet is provided to the TCP/IP host.
Configuring a PVC to Use RBP for Incoming TCP Connections
To configure the router to accept an incoming TCP connection on a specified TCP port, and to use RBP over that session to transfer data between the TCP host and an X.25 PVC, use the following command in interface configuration mode:
When the x25 pvc rbp local command is configured, the router will listen for a TCP connection request to the configured TCP port. Until the connection request is received, any data packets received on the X.25 PVC will cause the PVC to be reset. When the TCP connection request is received, the connection will be accepted, and the router will send an X.25 reset packet over the configured X.25 destination circuit. If the reset packet is not acknowledged, the TCP connection will be closed. Since this command is associated with a specific X.25 circuit, only one connection may be active per command.
Configuring SVCs to Use RBP for Incoming TCP Connections
To configure the router to establish X.25 circuits in response to incoming TCP connections, and to use RBP to transfer data between the TCP session and the corresponding X.25 circuit, use the following command in interface configuration mode:
When the x25 map rbp local port command is configured, the router will listen for a TCP connection request to the configured TCP port. When the connection is accepted, the router will place an X.25 call using the configured X.25 destination interface, destination address, and call user data. If the call is not successfully completed, the TCP connection will be closed. The number of connections that may be established to the TCP port is limited only by router resources. No information from the TCP connection is included in the X.25 call packet sent to the X.25 host.
Verifying Record Boundary Preservation
To verify that RBP connections are configured and performing correctly, complete the following steps.
Step 1
The following is sample output of the show x25 map command for a router that is configured with RBP using the x25 pvc rbp remote command:
Router# show x25 mapSerial1/0:-> rbp, destination host 10.0.0.33 port 9999PVC, 1 VC:1/PThe following is sample output of the show x25 map command for a router that is configured with RBP using the x25 map rbp remote command:
Router# show x25 mapSerial3/0:12132 -> rbp, destination host 10.0.0.32 port 9999permanent, 1 VC:1024The following is sample output of the show x25 map command for a router that is configured with RBP using the x25 pvc rbp local command:
Router# show x25 mapSerial3/0:<- rbp, listening at port 9999PVC, 1 VC:2/PThe following is sample output of the show x25 map command for a router that is configured with RBP using the x25 map rbp local command:
Router# show x25 mapSerial1/0:12131 <- rbp, listening at port 9999permanent, 1 VC:1For descriptions of the show x25 map display fields, see the show x25 map command page later in this document.
Step 2
The following is sample output of the show x25 vc command for a PVC configured with record boundary preservation:
Router# show x25 vcPVC 2, State:D1, Interface:Serial3/0Started 00:08:08, last input 00:00:01, output 00:00:01recordsize:1500, connectedlocal address 10.0.0.1 port 9999; remote address 10.0.0.5 port 11029deferred ack:1Window size input:2, output:2Packet size input:128, output:128PS:2 PR:2 ACK:1 Remote PR:2 RCNT:1 RNR:noP/D state timeouts:0 timer (secs):0data bytes 8000/8000 packets 80/80 Resets 9/0 RNRs 0/0 REJs 0/0 INTs 0/0For descriptions of the show x25 pvc display fields, see the show x25 vc command page later in this document.
Step 3
The following is sample output of the show tcp command:
Router# show tcpStand-alone TCP connection from host 10.0.0.5Connection state is ESTAB, I/O status:1, unread input bytes:0Local host:10.0.0.1, Local port:9999Foreign host:10.0.0.5, Foreign port:11003Enqueued packets for retransmit:0, input:0 mis-ordered:0 (0 bytes)TCP driver queue size 0, flow controlled FALSEEvent Timers (current time is 0x1D0CF8):Timer Starts Wakeups NextRetrans 11 0 0x0TimeWait 0 0 0x0AckHold 10 0 0x0SendWnd 0 0 0x0KeepAlive 20 0 0x1DF68CGiveUp 0 0 0x0PmtuAger 0 0 0x0DeadWait 0 0 0x0iss:2946187848 snduna:2946188909 sndnxt:2946188909 sndwnd: 7132irs:1353667951 rcvnxt:1353669012 rcvwnd: 7132 delrcvwnd: 1060SRTT:231 ms, RTTO:769 ms, RTV:538 ms, KRTT:0 msminRTT:0 ms, maxRTT:300 ms, ACK hold:200 msFlags:passive open, retransmission timeout, keepalive runninggen tcbsDatagrams (max data segment is 1460 bytes):Rcvd:22 (out of order:0), with data:10, total data bytes:1060Sent:21 (retransmit:0, fastretransmit:0), with data:10, total data bytes:1060
Monitoring and Maintaining RBP
To monitor RBP, use the following command in privileged EXEC mode:
Configuration Examples
This section provides the following configuration examples:
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PVC Configured to Use RBP for Incoming X.25 Connections Example
Interface Serial1/0encapsulation x25x25 pvc 1 rbp remote host 10.0.0.1 port 9999SVCs Configured to Use RBP for Incoming X.25 Connections Example
In the following example, if serial interface 1/0 receives an X.25 call from 12132, the router will map the call and open a TCP connection to port number 9999 at the remote TCP/IP host that has the IP address 10.0.0.1.
interface Serial1/0encapsulation x25 dcex25 address 12030x25 map rbp 12132 remote host 10.0.0.1 port 9999PVC Configured to Use RBP for Incoming TCP Connections Example
Interface serial2/1encapsulation x25x25 pvc 2 rbp local port 9999SVCs Configured to Use RBP for Incoming TCP Connections Example
interface Serial1/0encapsulation x25 dcex25 address 13133x25 map rbp 12131 local port 9999Command Reference
This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.
New Commands
Modified Commands
debug x25
To display information about X.25 traffic, use one of the following debug x25 commands in privileged EXEC mode. The commands allow you to display all information or an increasingly restrictive part of the information.
Caution
—Disable logging of debug output to the console. Refer to the logging console command for more information.
—Configure the router to discard console output when the buffer overflows. Refer to the logging console guaranteed command for more information.
—Use this command only when all of the reportable X.25 traffic is less than five packets per second (pps).
To display information about all X.25 traffic, including traffic for X.25, Connection Mode Network Service (CMNS), and X.25 over TCP (XOT) services, use the debug x25 command (default all). To disable debugging output, use the no form of this command.
debug x25
no debug x25
To display information about all X.25 traffic except data and resource record packets, use the debug x25 events command. To disable debugging output, use the no form of this command.
debug x25 events
no debug x25 events
To display information about a specific X.25 service class, use the following form of the debug x25 command. To disable debugging output, use the no form of this command.
debug x25 [only | cmns | xot] [events | all]
no debug x25 [only | cmns | xot] [events | all]
To display information about a specific X.25 or CMNS context, use the following form of the debug x25 command. To disable debugging output, use the no form of this command.
debug x25 interface {serial-interface | cmns-interface mac mac-address} [events | all]
no debug x25 interface {serial-interface | cmns-interface mac mac-address} [events | all]
To display information about a specific X.25 or CMNS virtual circuit, use the following form of the debug x25 command. To disable debugging output, use the no form of this command.
debug x25 interface {serial-interface | cmns-interface mac mac-address} vc number
[events | all]no debug x25 interface {serial-interface | cmns-interface mac mac-address} vc number
[events | all]To display information about traffic for all virtual circuits that use a given number, use the following form of the debug x25 command. The no form of this command removes the filter for a particular virtual circuit from the debug x25 all or debug x25 events output. To disable debugging output, use the no form of this command.
debug x25 vc number [events | all]
no debug x25 vc number [events | all]
To display information about traffic to or from a specific X.25 over TCP (XOT) host, use the following form of the debug x25 xot command. To disable debugging output, use the no form of this command.
debug x25 xot [remote ip-address [port number]] [local ip-address [port number]]
[events | all]no debug x25 xot [remote ip-address [port number]] [local ip-address [port number]]
[events | all]Use the debug x25 command with the aodi keyword to display information about an interface running PPP over an X.25 session. To disable debugging output, use the no form of this command.
debug x25 aodi
no debug x25 aodi
Syntax Description
Defaults
All traffic is displayed.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
This command is particularly useful for diagnosing problems encountered when placing calls. The debug x25 all output includes data, control messages, and flow control packets for all virtual circuits of the router.
All debug x25 command forms can take either the events or all keyword. The keyword all is the default and causes all packets meeting the other debug criteria to be reported. The keyword events omits reports of any Data or Receiver Ready (RR) flow control packets; the normal flow of data and RR packets is commonly large and less interesting to the user, so event reporting can significantly decrease the processor load induced by debug reporting.
The debug x25 interface command is useful for diagnosing problems encountered with a single X.25 or CMNS host or virtual circuit.
Because no interface is specified by the debug x25 vc command, traffic on any virtual circuit that has the specified number is reported.
Virtual circuit zero (vc 0) cannot be specified. It is used for X.25 service messages, such as RESTART packets, not virtual circuit traffic. Service messages can be monitored only when no virtual circuit filter is used.
The debug x25 xot output allows you to restrict the debug output reporting to XOT traffic for one or both hosts or host/port combinations. Because each XOT virtual circuit uses a unique TCP connection, an XOT debug request that specifies both host addresses and ports will report traffic only for that virtual circuit. Also, you can restrict reporting to sessions initiated by the local or remote router by specifying 1998 for the remote or local port. (XOT connections are received on port 1998.)
Use the debug x25 aodi command to display interface PPP events running over an X.25 session and to debug X.25 connections between a client and server configured for AO/DI.
Examples
The following is sample output from the debug x25 command, displaying output concerning the functions X.25 restart, call setup, data exchange, and clear:
Router# debug x25Serial0: X.25 I R/Inactive Restart (5) 8 lci 0Cause 7, Diag 0 (Network operational/No additional information)Serial0: X.25 O R3 Restart Confirm (3) 8 lci 0Serial0: X.25 I P1 Call (15) 8 lci 1From(6): 170091 To(6): 170090Facilities: (0)Call User Data (4): 0xCC000000 (ip)Serial0: X.25 O P3 Call Confirm (3) 8 lci 1Serial0: X.25 I D1 Data (103) 8 lci 1 PS 0 PR 0Serial0: X.25 O D1 Data (103) 8 lci 1 PS 0 PR 1Serial0: X.25 I P4 Clear (5) 8 lci 1Cause 9, Diag 122 (Out of order/Maintenance action)Serial0: X.25 O P7 Clear Confirm (3) 8 lci 1The following example shows a sequence of increasingly restrictive debug x25 commands:
Router# debug x25X.25 packet debugging is onRouter# debug x25 eventsX.25 special event debugging is onRouter# debug x25 interface serial 0X.25 packet debugging is onX.25 debug output restricted to interface Serial0Router# debug x25 vc 1024X.25 packet debugging is onX.25 debug output restricted to VC number 1024Router# debug x25 interface serial 0 vc 1024X.25 packet debugging is onX.25 debug output restricted to interface Serial0X.25 debug output restricted to VC number 1024Router# debug x25 interface serial 0 vc 1024 eventsX.25 special event debugging is onX.25 debug output restricted to interface serial 0X.25 debug output restricted to VC number 1024The following examples show the normal sequence of events for both the AO/DI client and the server sides:
Client Side
Router# debug x25 aodiPPP-X25: Virtual-Access1: Initiating AODI call requestPPP-X25: Bringing UP X.25 AODI VCPPP-X25: AODI Client Call Confirm Event ReceivedPPP-X25: Cloning interface for AODI is Di1PPP-X25: Queuing AODI Client Map EventPPP-X25: Event:AODI Client MapPPP-X25: Created interface Vi2 for AODI servicePPP-X25: Attaching primary link Vi2 to Di1PPP-X25: Cloning Vi2 for AODI service using Di1PPP-X25: Vi2: Setting the PPP call direction as OUTPPP-X25: Vi2: Setting vectors for RFC1598 operation on BRI3/0:0 VC 0PPP-X25: Vi2: Setting the interface default bandwidth to 10 KbpsPPP-X25: Virtual-Access2: Initiating AODI call requestPPP-X25: Bringing UP X.25 AODI VCPPP-X25: AODI Client Call Confirm Event ReceivedServer Side
Router# debug x25 aodiPPP-X25: AODI Call Request Event ReceivedPPP-X25: Event:AODI Incoming Call RequestPPP-X25: Created interface Vi1 for AODI servicePPP-X25: Attaching primary link Vi1 to Di1PPP-X25: Cloning Vi1 for AODI service using Di1PPP-X25: Vi1: Setting vectors for RFC1598 operation on BRI3/0:0 VC 1PPP-X25: Vi1: Setting the interface default bandwidth to 10 KbpsPPP-X25: Binding X.25 VC 1 on BRI3/0:0 to Vi1debug x25 events for X.25 CUGs
The following example of the debug x25 events command shows output related to the X.25 closed user groups (CUGs) feature. It shows messages concerning a data communications equipment (DCE) device rejecting a call because the selected network CUG had not been subscribed to by the caller.
Router# debug x25 events00:48:33:Serial1:X.25 I R1 Call (14) 8 lci 102400:48:33: From (3):111 To (3):44400:48:33: Facilities:(2)00:48:33: Closed User Group (basic):4000:48:33: Call User Data (4):0x01000000 (pad)00:48:33:X.25 Incoming Call packet, Closed User Group (CUG) protection, selected network CUG not subscribed00:48:33:Serial1:X.25 O R1 Clear (5) 8 lci 102400:48:33: Cause 11, Diag 65 (Access barred/Facility code not allowed)debug x25 events for DNS-Based X.25 Routing
The following example of the debug x25 events command shows output related to the DNS-Based X.25 Routing feature. It shows messages concerning access to the Domain Name System (DNS) server. In the following example, nine alternate addresses for one XOT path are entered in the DNS server database. All nine addresses are returned to the host cache of the router by the DNS server. However, only six addresses will be used during the XOT switch attempt because this is the limit that XOT allows.
Router# debug x25 events00:18:25:Serial1:X.25 I R1 Call (11) 8 lci 102400:18:25: From (0): To (4):44400:18:25: Facilities:(0)00:18:25: Call User Data (4):0x01000000 (pad)00:18:25:X.25 host name sent for DNS lookup is "444"00:18:26:%3-TRUNCATE_ALT_XOT_DNS_DEST:Truncating excess XOT addresses (3)returned by DNS00:18:26:DNS got X.25 host mapping for "444" via network00:18:32:[10.1.1.8 (pending)]:XOT open failed (Connection timed out; remote host not responding)00:18:38:[10.1.1.7 (pending)]:XOT open failed (Connection timed out; remote host not responding)00:18:44:[10.1.1.6 (pending)]:XOT open failed (Connection timed out; remote host not responding)00:18:50:[10.1.1.5 (pending)]:XOT open failed (Connection timed out; remote host not responding)00:18:56:[10.1.1.4 (pending)]:XOT open failed (Connection timed out; remote host not responding)00:20:04:[10.1.1.3,1998/10.1.1.3,11007]:XOT O P2 Call (17) 8 lci 100:20:04: From (0): To (4):44400:20:04: Facilities:(6)00:20:04: Packet sizes:128 12800:20:04: Window sizes:2 200:20:04: Call User Data (4):0x01000000 (pad)00:20:04:[10.1.1.3,1998/10.1.1.3,11007]:XOT I P2 Call Confirm (11) 8 lci 100:20:04: From (0): To (0):00:20:04: Facilities:(6)00:20:04: Packet sizes:128 12800:20:04: Window sizes:2 200:20:04:Serial1:X.25 O R1 Call Confirm (5) 8 lci 102400:20:04: From (0): To (0):00:20:04: Facilities:(0)Record Boundary Preservation Examples
The following examples show output for the x25 debug events command when record boundary preservation (RBP) has been configured using the x25 map rbp local command.
The following display shows establishment of connection:
X25 RBP:Incoming connection for port 9999 from 10.0.155.30 port 11001Serial0/1:X.25 O R1 Call (10) 8 lci 64From (5):13133 To (5):12131Facilities:(0)Serial0/1:X.25 I R1 Call Confirm (3) 8 lci 64The following display shows that the X.25 call was cleared by the X.25 host:
Serial0/1:X.25 I R1 Clear (5) 8 lci 64Cause 0, Diag 122 (DTE originated/Maintenance action)X25 RBP:X.25 circuit clearedSerial0/1:X.25 O R1 Clear Confirm (3) 8 lci 64The following display shows that the TCP session has terminated:
[10.0.155.30,11000/10.0.155.33,9999]:TCP receive error, End of data transferX25 RBP:End of data transferSerial0/1:X.25 O R1 Clear (5) 8 lci 64Cause 9, Diag 122 (Out of order/Maintenance action)Serial0/1:X.25 I R1 Clear Confirm (3) 8 lci 64The following examples show output of the x25 debug events command when RBP has been configured using the x25 pvc rbp local command.
The following display shows data on the PVC before the TCP session has been established:
X25 RBP:Data on unconnected PVCSerial1/0:X.25 O D1 Reset (5) 8 lci 1Cause 0, Diag 113 (DTE originated/Remote network problem)Serial1/0:X.25 I D2 Reset Confirm (3) 8 lci 1The following display shows establishment of connection:
X25 RBP:Incoming connection for port 9998 from 2.30.0.30 port 11002Serial1/0:X.25 O D1 Reset (5) 8 lci 1Cause 0, Diag 0 (DTE originated/No additional information)Serial1/0:X.25 I D2 Reset Confirm (3) 8 lci 1The following display shows termination of connection when the X.25 PVC was reset:
Serial1/0:X.25 I D1 Reset (5) 8 lci 1Cause 15, Diag 122 (Network operational (PVC)/Maintenance action)X25 RBP:Reset packet receivedSerial1/0:X.25 O D3 Reset Confirm (3) 8 lci 1The following display shows that the TCP session has terminated:
[2.30.0.30,11003/2.30.0.33,9998]:TCP receive error, End of data transferX25 RBP:End of data transferSerial1/0:X.25 O D1 Reset (5) 8 lci 1Cause 0, Diag 113 (DTE originated/Remote network problem)Serial1/0:X.25 I D2 Reset Confirm (3) 8 lci 1The following examples show output of the x25 debug events command when RBP has been configured using the x25 map rbp remote command.
The following display shows that the X.25 call was cleared:
Serial0/1:X.25 I R1 Clear (5) 8 lci 1024Cause 0, Diag 122 (DTE originated/Maintenance action)X25 RBP:X.25 circuit clearedSerial0/1:X.25 O R1 Clear Confirm (3) 8 lci 1024The following display shows that the X.25 call was reset:
Serial0/1:X.25 I D1 Reset (5) 8 lci 1024Cause 0, Diag 122 (DTE originated/Maintenance action)X25 RBP:Reset packet receivedSerial0/1:X.25 O R1 Clear (5) 8 lci 1024Cause 9, Diag 122 (Out of order/Maintenance action)Serial0/1:X.25 I R1 Clear Confirm (3) 8 lci 1024The following examples show output of the x25 debug events command when RBP has been configured using the x25 pvc rbp remote command.
The following display shows that the X.25 PVC has been reset:
Serial0/0:X.25 I D1 Reset (5) 8 lci 1Cause 0, Diag 122 (DTE originated/Maintenance action)X25 RBP:Reset packet receivedSerial0/0:X.25 O D2 Reset Confirm (3) 8 lci 1The following display shows that the connection was terminated when the X.25 interface was restarted:
Serial0/0:X.25 I R1 Restart (5) 8 lci 0Cause 0, Diag 122 (DTE originated/Maintenance action)X25 RBP:X.25 PVC inactiveSerial0/0:X.25 O R2 Restart Confirm (3) 8 lci 0Serial0/0:X.25 O D1 Reset (5) 8 lci 1Cause 1, Diag 113 (Out of order (PVC)/Remote network problem)Serial0/0:X.25 I D3 Reset Confirm (3) 8 lci 1Table 4 describes the significant fields shown in the displays.
show x25 map
To display information about configured address maps, use the show x25 map command in EXEC mode.
show x25 map
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
10.0
This command was introduced.
12.2(8)T
This command was modified to display record boundary preservation information for address maps.
Usage Guidelines
The show x25 map command shows information about the following:
•
•
•
Examples
Record Boundary Preservation Examples
The following is sample output of the show x25 map command for a router that is configured with RBP using the x25 pvc rbp remote command:
Router# show x25 mapSerial1/0:-> rbp, destination host 10.0.0.33 port 9999PVC, 1 VC:1/PThe following is sample output of the show x25 map command for a router that is configured with RBP using the x25 map rbp remote command:
Router# show x25 mapSerial3/0:12132 -> rbp, destination host 10.0.0.32 port 9999permanent, 1 VC:1024The following is sample output of the show x25 map command for a router that is configured with RBP using the x25 pvc rbp local command:
Router# show x25 mapSerial3/0:<- rbp, listening at port 9999PVC, 1 VC:2/PThe following is sample output of the show x25 map command for a router that is configured with RBP using the x25 map rbp local command:
Router# show x25 mapSerial1/0:12131 <- rbp, listening at port 9999permanent, 1 VC:1Table 5 describes significant fields shown in the display.
Typical X.25 Maps Example
The following is sample output from the show x25 map for five maps that were configured with the x25 map command:
Router# show x25 mapSerial0: X.121 1311001 <--> ip 172.20.170.1PERMANENT, BROADCAST, 2 VCS: 3 4Serial0: X.121 1311005 <--> appletalk 128.1PERMANENTSerial1: X.121 2194441 cud hello <--> padPERMANENT, windowsize 5 5, accept-reverse, idle 5Serial1: X.121 1311005 <--> bridgePERMANENT, BROADCASTSerial2: X.121 001003 <--> apollo 1.3,appletalk 1.3,ip 172.20.1.3,decnet 1.3,novell 1.0000.0c04.35df,vines 00000001:0003,xns 1.0000.0c04.35df,clnsPERMANENT, NVC 8, 1 VC: 1024The display shows that five maps have been configured for a router: two for serial interface 0, two for serial interface 1, and one for the serial interface 2 (which maps eight protocols to the host).
Table 6 describes significant fields shown in the display.
show x25 vc
To display information about active switched virtual circuits (SVCs) and permanent virtual circuits (PVCs), use the show x25 vc command in EXEC mode.
show x25 vc [lcn]
Syntax Description
Command Modes
EXEC
Command History
8.3
This command was introduced in a release prior to Release 8.3.
12.2(8)T
This command was modified to display information about record boundary preservation.
Usage Guidelines
To examine a particular virtual circuit number, add an LCN argument to the show x25 vc command.
This command displays information about virtual circuits (VCs). VCs may be used for a number of purposes, such as the following:
•
•
•
•
The connectivity information displayed will vary according to the traffic carried by the VC. For multiprotocol circuits, the output varies depending on the number and identity of the protocols mapped to the X.121 address and the encapsulation method selected for the circuit.
Examples
Record Boundary Preservation Example
The following is sample output of the show x25 vc command for a PVC configured with record boundary preservation:
Router# show x25 vcPVC 2, State:D1, Interface:Serial3/0Started 00:08:08, last input 00:00:01, output 00:00:01recordsize:1500, connectedlocal address 10.0.0.1 port 9999; remote address 10.0.0.5 port 11029deferred ack:1Window size input:2, output:2Packet size input:128, output:128PS:2 PR:2 ACK:1 Remote PR:2 RCNT:1 RNR:noP/D state timeouts:0 timer (secs):0data bytes 8000/8000 packets 80/80 Resets 9/0 RNRs 0/0 REJs 0/0 INTs 0/0Table 7 describes the fields shown in the sample output that are typical for virtual circuits.
Table 7 show x25 vc Field Descriptions
SVC n or PVC n
Identifies the type of virtual circuit (switched or permanent) and its LCN (also called its "virtual circuit number").
State
State of the virtual circuit (which is independent of the states of other virtual circuits); D1 is the normal ready state. See the International Telecommunication Union Telecommunication Standardization Sector (ITU-T)1 X.25 Recommendation for a description of virtual circuit states.
Interface
Interface or subinterface on which the virtual circuit is established.
Started
Time elapsed since the virtual circuit was created.
last input
Time of last input.
output
Time of last output.
Connects...<-->..
Traffic-specific connection information. See Table 9, Table 10, Table 11, and Table 12 for more information.
D-bit permitted
Indicates that the X.25 D-bit (Delivery Confirmation) may be used on this circuit (displayed as needed).
Fast select VC
Indicates that the Fast Select facility was present on the incoming call (displayed as needed).
Reverse charged
Indicates reverse charged virtual circuit (displayed as needed).
Window size
Window sizes for the virtual circuit.
Packet size
Maximum packet sizes for the virtual circuit.
PS
Current send sequence number.
PR
Current receive sequence number.
ACK
Last acknowledged incoming packet.
Remote PR
Last receive sequence number received from the other end of the circuit.
RCNT
Count of unacknowledged input packets.
RNR
State of the Receiver Not Ready flag; this field is true if the network sends a Receiver-not-Ready packet.
Window is closed
This line appears if the router cannot transmit any more packets until the X.25 Layer 3 peer has acknowledged some outstanding packets.
P/D state timeouts
Number of times a supervisory packet (Reset or Clear) has been retransmitted.
Timer
A nonzero time value indicates that a control packet has not been acknowledged yet or that the virtual circuit is being timed for inactivity.
Reassembly
Number of bytes received and held for reassembly. Packets with the M-bit set are reassembled into datagrams for encapsulation virtual circuits; switched X.25 traffic is not reassembled (and is displayed only when values are not zero).
Held Fragments/Packets
Number of X.25 data fragments to transmit to complete an outgoing datagram, and the number of datagram packets waiting for transmission (displayed only when values are not zero).
data bytes m/n packets p/q
Total number of data bytes sent (m), data bytes received (n), data packets sent (p), and data packets received (q) since the circuit was established.
Resets t/r
Total number of reset packets transmitted/received since the circuit was established.
RNRs t/r
Total number of Receiver Not Ready packets transmitted/received since the circuit was established.
REJs t/r
Total number of Reject packets transmitted/received since the circuit was established.
INTs t/r
Total number of Interrupt packets transmitted/received since the circuit was established.
1 The ITU-T carries out the functions of the former Consultative Committee for International Telegraph and Telephone (CCITT).
Table 8 describes the fields specific to VCs configured with record boundary preservation.
Encapsulated Traffic Example
The following is sample output of the show x25 vc command used on an encapsulated traffic circuit:
Router# show x25 vc 1024SVC 1024, State: D1, Interface: Serial0Started 0:00:31, last input 0:00:31, output 0:00:31Connects 170090 <-->compressedtcp 172.20.170.90ip 172.20.170.90Call PID multi, Data PID ietfReverse chargedWindow size input: 2, output: 2Packet size input: 128, output: 128PS: 5 PR: 5 ACK: 4 Remote PR: 5 RCNT: 1 RNR: FALSEWindow is closedP/D state timeouts: 0 Timer (secs): 0data bytes 505/505 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0Table 9 describes the connection fields specific to encapsulation traffic.
Locally Switched X.25 Traffic Example
The following is sample output of the show x25 vc command used on a virtual circuit carrying locally switched X.25 traffic:
Router# show x25 vcPVC 1, State: D1, Interface: Serial2Started 0:01:26, last input never, output neverPVC <--> Serial1 PVC 1, connectedWindow size input: 2, output: 2Packet size input: 128, output: 128PS: 0 PR: 0 ACK: 0 Remote PR: 0 RCNT: 0 RNR: FALSEP/D state timeouts: 0 Timer (secs): 0data bytes 0/0 packets 0/0 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0SVC 5, State: D1, Interface: Serial2Started 0:00:16, last input 0:00:15, output 0:00:15Connects 170093 <--> 170090 from Serial1 VC 5Window size input: 2, output: 2Packet size input: 128, output: 128PS: 5 PR: 5 ACK: 4 Remote PR: 5 RCNT: 1 RNR: FALSEP/D state timeouts: 0 Timer (secs): 0data bytes 505/505 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0Table 10 describes the connection fields for virtual circuits carrying locally switched X.25 traffic.
Table 10 show x25 vc Local Traffic Field Descriptions
PVC <-->
Indicates a switched connection between two PVCs.
Serial1 PVC 1
Identifies the other half of a local PVC connection.
connected
Identifies connection status for a switched connection between two PVCs. See Table 13 for PVC status messages.
170093
Identifies the Calling (source) Address of the connection. If a Calling Address Extension was encoded in the call facilities, it is also displayed. If the source host is a CMNS host, its MAC address is also displayed.
170090
Identifies the Called (destination) Address of the connection. If a Called Address Extension was encoded in the call facilities, it is also displayed. If the destination host is a CMNS host, its MAC address is also displayed.
from Serial1
Indicates the direction of the call and the connecting interface.
VC 5
Identifies the circuit type and LCN for the connecting interface. VC indicates an SVC, and PVC indicates a PVC. If the connecting host is a CMNS host, its MAC address is also displayed.
Locally Switched X.25 Traffic Between PVCs and SVCs Example
The following is sample output of the show x25 vc command used on a virtual circuit carrying locally switched PVC to SVC X.25 traffic:
Router# show x25 vcPVC 5, State: D1, Interface: Serial0Started 4d21h, last input 00:00:14, output 00:00:14Connects 101600 <--> 201700 from Serial2 VC 700D-bit permittedWindow size input: 2, output: 2Packet size input: 128, output: 128PS: 5 PR: 5 ACK: 4 Remote PR: 5 RCNT: 1 RNR: noP/D state timeouts: 0 timer (secs): 0data bytes 1000/1000 packets 10/10 Resets 1/0 RNRs 0/0 REJs 0/0 INTs 0/0SVC 700, State: D1, Interface: Serial2Started 00:00:16, last input 00:00:16, output 00:00:16Connects 101600 <--> 201700 from Serial0 PVC 5Window size input: 2, output: 2Packet size input: 128, output: 128PS: 5 PR: 5 ACK: 5 Remote PR: 4 RCNT: 0 RNR: noP/D state timeouts: 0 timer (secs): 103data bytes 500/500 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0Table 11 describes the connection fields for virtual circuits carrying locally switched X.25 traffic between PVCs and SVCs.
Remotely Switched X.25 Traffic Example
The following is sample output from the show x25 vc command used on a virtual circuit carrying remotely switched X.25 traffic:
Router# show x25 vcPVC 2, State: D1, Interface: Serial2Started 0:01:25, last input never, output neverPVC <--> [172.20.165.92] Serial2/0 PVC 1 connectedXOT between 171.20.165.91, 1998 and 172.20.165.92, 27801Window size input: 2, output: 2Packet size input: 128, output: 128PS: 0 PR: 0 ACK: 0 Remote PR: 0 RCNT: 0 RNR: FALSEP/D state timeouts: 0 Timer (secs): 0 Reassembly (bytes): 0Held Fragments/Packets: 0/0data bytes 0/0 packets 0/0 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0SVC 6, State: D1, Interface: Serial2Started 0:00:04, last input 0:00:04, output 0:00:04Connects 170093 <--> 170090 fromXOT between 172.20.165.91, 1998 and 172.20.165.92, 27896Window size input: 2, output: 2Packet size input: 128, output: 128PS: 5 PR: 5 ACK: 4 Remote PR: 5 RCNT: 1 RNR: FALSEP/D state timeouts: 0 Timer (secs): 0 Reassembly (bytes): 0Held Fragments/Packets: 0/0data bytes 505/505 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0Table 12 describes the connection fields for virtual circuits carrying remotely switched X.25 traffic.
Table 12 show x25 vc Remote X.25 Traffic Field Descriptions
PVC
Flags PVC information.
[172.20.165.92]
Indicates the IP address of the router remotely connecting the PVC.
Serial 2/0 PVC 1
Identifies the remote interface and PVC number.
connected
Identifies connection status for a switched connection between two PVCs. See Table 13 for PVC status messages.
170093
Identifies the Calling (source) Address of the connection. If a Calling Address Extension was encoded in the call facilities, it is also displayed.
170090
Identifies the Called (destination) Address of the connection. If a Called Address Extension was encoded in the call facilities, it is also displayed.
from
Indicates the direction of the call.
XOT between...
Identifies the IP addresses and port numbers of the X.25-over-TCP (XOT) connection.
Table 13 lists the PVC states that can be reported. These states are also reported by the debug x25 command in PVC-SETUP packets (for remote PVCs only) and in the PVCBAD system error message. Some states apply only to remotely switched PVCs.
x25 map rbp local
To configure the router to establish X.25 circuits in response to incoming TCP connections on a specified TCP port, and to use record boundary preservation (RBP) to transfer data between the TCP session and the corresponding X.25 circuit, use the x25 map rbp local command in interface configuration mode. To delete the map, use the no form of this command.
x25 map rbp x121-address [cud string] local port port [cug group-number] [packetsize in-size out-size] [recordsize size] [reverse] [roa name] [throughput in out] [transit-delay milliseconds] [windowsize in-size out-size]
no x25 map rbp x121-address [cud string] local port port
Syntax Description
Defaults
No SVC is configured.
Command Modes
Interface configuration
Command History
Usage Guidelines
RBP enables X.25 hosts to exchange data with TCP/IP hosts via TCP sessions while maintaining X.25 packet boundaries.
When the x25 map rbp local command is configured, the router will listen for a request for a TCP connection to the specified TCP port. When the connection request is accepted, the router will then attempt to place an X.25 call on the interface on which the command was configured, using the X.25 address of the interface as the calling address, the X.121 address specified in the command as the destination address, and the call user data specified in the command. If the call is not successfully completed, the TCP connection will be closed.
The number of connections that may be established to the TCP port is limited only by router resources (such as memory, processor utilization, and available X.25 circuits).
When connections that will be established by the TCP/IP host are configured, the local TCP port number must be unique, with the exception that the same TCP port number may be configured once on each of multiple X.25 interfaces that will not be active simultaneously; this includes the case in which one X.25 interface is configured as a backup interface for another X.25 interface.
No information from the TCP connection is included in the X.25 Call packet sent to the X.25 host.
Examples
interface Serial1/0encapsulation x25 dcex25 address 13133x25 map rbp 12131 local port 9999Related Commands
x25 map rbp remote
To configure the router to establish TCP sessions in response to incoming X.25 calls, and to use record boundary preservation (RBP) to transfer data between the X.25 circuit and the corresponding TCP session, use the x25 map rbp remote command in interface configuration mode. To delete the map, use the no form of this command.
x25 map rbp x121-address [cud string] remote host ip-address port port [accept-reverse] [recordsize size] [source-interface interface]
no x25 map rbp x121-address [cud string] remote host port port
Syntax Description
Defaults
No SVC is configured.
Command Modes
Interface configuration
Command History
Usage Guidelines
RBP enables X.25 hosts to exchange data with TCP/IP hosts via TCP sessions while maintaining X.25 packet boundaries.
The router will accept an incoming X.25 call if the source address and call user data in the call request match the values configured in the x25 map rbp remote command. If the cud parameter is specified in the command, the call user data in the incoming call must match the configured value exactly. If the cud parameter is not specified in the command, the call user data must not conflict with any protocol ID recognized by the router, but it is otherwise ignored.
If an incoming call requests reverse charging, and the accept-reverse option is not specified in the matching map, the call will be refused.
If the incoming call is accepted, the router will attempt to open a TCP connection to a configured IP address and TCP port using a dynamically assigned local TCP port number. If the TCP connection cannot be opened, the X.25 call will be cleared.
The number of X.25 calls that may be accepted is limited only by router resources.
No information from the X.25 call packet is provided to the TCP/IP host.
Examples
interface Serial1/0encapsulation x25 dcex25 address 12030x25 map rbp 12132 remote host 10.0.0.1 port 9999Related Commands
x25 pvc rbp local
To configure the router to accept an incoming TCP connection on a specified TCP port, and to use record boundary preservation (RBP) over that session to transfer data between the TCP host and an X.25 permanent virtual circuit (PVC), use the x25 map rbp local command in interface configuration mode. To delete the PVC, use the no form of this command.
x25 pvc circuit rbp local port port [packetsize in-size out-size] [recordsize size] [windowsize in-size out-size]
no x25 pvc circuit
Syntax Description
Defaults
No PVC is configured.
The PVC window and maximum packet sizes default to the interface default values.
Command Modes
Interface configuration
Command History
Usage Guidelines
Record boundary preservation (RBP) enables X.25 hosts to exchange data with TCP/IP hosts via TCP sessions while maintaining X.25 packet boundaries.
When connections that will be established by the TCP/IP host are configured, the local TCP port number must be unique, with the exception that the same TCP port number may be configured once on each of multiple X.25 interfaces that will not be active simultaneously. This includes situations in which one X.25 interface is configured as a backup interface for another X.25 interface.
When the x25 pvc rbp local command is configured, the router will listen for a TCP connection request to the configured TCP port. Until the connection request is received, the router will acknowledge any X.25 reset packets on the circuit. When the TCP connection request is received, the connection will be accepted, and the router will send an X.25 reset packet over the configured X.25 destination circuit. If the reset packet is not acknowledged, the TCP connection will be closed.
Since this command is associated with a specific X.25 circuit, only one connection may be active per command.
When a PVC is configured, the virtual circuit must be unique. Multiple commands referencing the same virtual circuit (matching logical channel identifier and interface) are not permitted.
When connections that will be established by the TCP/IP host are configured, the local TCP port number must be unique, with the exception that the same TCP port number may be configured once on each of multiple X.25 interfaces that will not be active simultaneously. This includes the case in which one X.25 interface is configured as a backup interface for another X.25 interface.
Examples
Interface serial2/1encapsulation x25x25 pvc 2 rbp local port 9999Related Commands
x25 pvc rbp remote
To configure the router to establish a TCP session in response to data received on an X.25 permanent virtual circuit (PVC) and to use record boundary preservation (RBP) to transfer data between the X.25 host and the TCP session, use the x25 pvc rbp remote command in interface configuration mode. To delete the PVC, use the no form of this command.
x25 pvc circuit rbp remote host ip-address port port [packetsize in-size out-size] [source-interface interface] [recordsize size] [windowsize in-size out-size]
no x25 pvc circuit
Syntax Description
Defaults
The PVC window and maximum packet sizes default to the interface default values.
Command Modes
Interface configuration
Command History
Usage Guidelines
RBP enables X.25 hosts to exchange data with TCP/IP hosts via TCP sessions while maintaining X.25 packet boundaries.
When a PVC is configured, the virtual circuit must be unique. Multiple commands referencing the same virtual circuit (matching logical channel identifier and interface) are not permitted.
When the x25 pvc rbp remote command is configured, the router will wait until a data packet is received on a specific X.25 PVC. Until it receives a data packet, the router will acknowledge any X.25 reset packets on the circuit. When a data packet is received, the router will attempt to establish a TCP connection to a configured IP address and TCP port, using a dynamically assigned local TCP port number. If the connection attempt fails, the router will reset the PVC and wait for another data packet before reattempting to establish the TCP connection.
Since the x25 pvc rbp remote command is associated with a specific X.25 circuit, at most one connection may be active per command.
Examples
interface serial1/0encapsulation x25x25 pvc 1 rbp remote host 10.0.0.1 port 9999Related Commands
Glossary
CUD—call user data. Field in an X.25 data packet that contains encapsulated upper-layer information.
CUG—closed user group. A collection of DTE devices for which the network controls access among members and between members and nonmembers. A DTE may subscribe to zero, one, or more CUGs. A DTE that does not subscribe to a CUG is referred to as being in the open part of the network.
D-bit—"delivery confirmation" bit. Data packet flag used to request end-to-end acknowledgment for the packet.
DCE—data communications equipment. Devices and connections of a communications network that make up the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Modems and interface cards are examples of DCE.
DTE—data terminal equipment. Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device (for example, a modem) and typically uses clocking signals generated by the DCE. DTE includes such devices as computers, protocol translators, and multiplexers.
local acknowledgment—Method whereby a switch acknowledges a received data packet before it has received acknowledgment of the data from the next hop.
M-Bit—"more data" bit. Data packet flag that indicates that at least one more data packet is required for completion of a message of contiguous data.
PVC—permanent virtual circuit. Virtual circuit that is permanently established.
Q-bit—"qualified" bit. Data packet flag that signifies that the packet's user data is a control signal for the remote device, not a message for the user.
RBP—record boundary preservation. Protocol that defines a way for hosts using TCP/IP-based protocols to exchange data with devices that use the X.25 protocol, preserving the logical record boundaries conveyed by the X.25 M-bit ("more data" bit).
SVC—switched virtual circuit. Virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used in situations in which data transmission is sporadic.
X.121—ITU-T standard describing an addressing scheme used in X.25 networks. Sometimes called the X.25 address.
X.25— ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in PDNs. X.25 specifies LAPB, a data-link layer protocol, and PLP, a network layer protocol.
XOT—X.25 over TCP.
