Frame Relay

Frame Relay is a high performance WAN protocol that operates at the Physical and Data Link layers of the OSI model.  Frame Relay originally was designed for use across ISDN interfaces.  Today, it is used over a variety of other network interfaces as well.

Frame Relay is an example of a packet-switched technology.  Packet-switched networks enable end stations to dynamically share the network medium and the available bandwidth.  Variable-length packets are used for more efficient and flexible transfers.  These packets then are switched between the various network segments until the destination is reached.  Statistical multiplexing techniques control network access in a packet-switched network.  The advantage of this technique is that it accommodates more flexibility and more efficient use of bandwidth.

Frame Relay often is described as a streamlined version of X.25, offering fewer of the robust capabilities, such as windowing and retransmission of lost data, that are offered in X.25.  This is because Frame Relay typically operates over WAN facilities that offer more reliable connection services and a higher degree of reliability than the facilities available during the late 1970s and early 1980s that served as the common platforms for X.25 WANs.  Frame Relay is strictly a Layer 2 protocol suite, whereas X.25 provides services at Layer 3 as well.  This enables Frame Relay to offer a higher performance and greater transmission efficiency that X.25 and makes Frame Relay suitable for current WAN applications such as LAN interconnection.

A major development in Frame Relay's history occurred in 1990 when Cisco Systems, StrataCom, Northern Telecom, and DEC formed a consortium to focus on Frame Relay technology development.  This consortium developed a specification that conformed to the basic Frame Relay protocol that was being discussed in CCITT (now called ITU-T) but extended the protocol with features that provide additional capabilities for complex internetworking environments.  These Frame Relay extensions are referred to collectively as the Local Management Interface(LMI).  ANSI and ITU-T have standardized their own variations of the original LMI specification, and these standardized specifications now are more commonly used than the original version.

• Frame Relay is both a Data Link layer encapsulation type implemented on the router and a Physical service provided by a telecommunications company.
• Frame Relay is a packet switching and encapsulation technology that functions at the Data Link and Physical layers of the OSI model and runs on nearly any type of serial interface.
• Access to Frame Relay networks is made through private leased lines at speeds ranging from 56 Kbps to 45 Mbps.
• Frame Relay is a connection oriented packet-switching mechanism that establishes VCs between endpoints.
• The ITU-T and ANSI define Frame Relay as a connection between the DTE (Data Terminating Equipment) and the DCE (Data Communications Equipment).
  • DCE is switching equipment, supplied by a telecommunications provider, that serves as a connection to the public data network (PDN).
  • DTE is also know as customer premise equipment (CPE), because it is the equipment that belongs to, and is maintained by the PDN customer.
  • If you connect your Cisco router to a Frame Relay switch (provided by phone company), the Cisco router is the CPE (DTE) and the Frame Relay switch is the DCE.

The physical equipment can vary between organizations.  Some networks may use routers with separate CSU/DSUs (Channel Service Unit/ Data Service Unit) and some may use routers with built in CSU/DSUs.  The CSU/DSU is located at the customer location of the digital connection, and is used for encoding, filtering, and translating communications to and from the digital line.  In Frame Relay connections, the network device that connects to the Frame Relay switch is known as a Frame Relay access device (FRAD) also called a Frame Relay assembler/ disassembler.  The Frame Relay switch is also called the Frame Relay network device (FRND pronounced "friend").  The network administrator typically handles the local connection up to the point that it enters the PDN.  Items that are part of the PDN, including the Frame Relay switch, fall under control of and responsibility of the telecommunications provider.  Frame Relay is used over a variety of network interfaces.

• IP
• DECnet
• AppleTalk
• Xerox Network Services (XNS)
• Novell IPX
• Connectionless Network Services (CLNS)
• International Organization for Standards (ISO)
• Banyan Vines
• Transparent bridging

Virtual Circuits

Frame Relay can be used with nearly any serial interface.  Communications in a Frame Relay network are connection oriented and a defined communications path must exist between each pair of DTE devices.  Virtual circuits provide a bi-directional communications path from one DTE device to another and are uniquely identified by a Data Link Connection Identifier(DLCI).  The technology used in Frame Relay allows it to multiplex several data flows over the same physical media.

Frame Relay separates each data stream into logical (software maintained) connections called virtual circuits which carry the data transferred on the connection between two DTE devices.  Two types of virtual circuits, SVCs (Switched Virtual Circuit) and PVCs (Permanent Virtual Circuit) connect Frame Relay ports.  Switched Virtual Circuits (SVCs) allow access through a Frame Relay network by setting up a path to the destination endpoints only when the need arises and tearing down the path when it is no longer needed.  Permanent Virtual Circuits (PVCs) are permanently established connections that are used for frequent and consistent data transfers between DTE devices across the Frame Relay network.  SVCs and PVCs can coexist on the same sites and routers.  For example, routers at remote branch offices might set up PVCs to the central headquarters for frequent communications, but set up SVCs with each other as needed for intermittent communication.

DLCI (Data Link Connection Identifier)

Frame Relay virtual circuits are identified by Data Link Connection Identifiers (DLCIs).  A DLCI serves as the addressing scheme within a Frame Relay network.  DLCI values typically are assigned by the Frame Relay provider (e.g. telephone company).  Frame Relay DLCIs have local significance, which means that the values themselves are not unique in the Frame Relay WAN.  For example two DTE devices connected by a virtual circuit may use a different DLCI value to refer to the same connection.  The service provider assigns a DLCI for each VC, which are used by Frame Relay to distinguish between different virtual circuits on the network.  Since many virtual circuits can be terminated on one multipoint Frame Relay interface, many DLCIs are often affiliated with it.

For the IP devices on each end of a virtual circuit to communicate, their IP addresses need to be mapped to DLCIs.  This mapping can function as a multipoint device --one that can identify to the Frame Relay network the appropriate destination virtual circuit for each packet that is sent over the single physical interface.  The mappings can be done dynamically with IARP or manually with the Frame Relay map command.

Every DLCI can have local or global meaning everywhere within the Frame Relay network.  DLCIs are usually assigned by the provider and start with 16.  The following commands apply a DLCI number to an interface

   Router3(config-if)#frame-relay interface-dlci ?
     <16-1007>  Define a DLCI as part of the current subinterface
   
   Router3(config-if)#frame-relay interface-dlci 16
   %FR-5-DLCICHANGE: Interface Serial0 - DLCI 16 state changed to ACTIVE
   Router3(config-fr-dlci)#

Local Management Interface

The Local Management Interface (LMI) is a set of enhancements to the Frame Relay protocol specifications.  The LMI was developed in 1990 by four companies known as the "Gang of Four" (Cisco Systems, StrataCom, Northern Telecom, and DEC).  It offers a number of features (called extensions) for managing complex internetworks.  Key Frame Relay LMI extensions include global addressing, virtual-circuit status messages, and multicasting.  LMI was designed to exchange information about PVC status and to ensure that the link between two points was operating correctly.  LMI is a standard signaling mechanism between CPE (usually a router) and the Frame Relay connection.

The LMI global addressing extensions gives Frame Relay DLCI values global rather than local significance.  DLCI values become DTE addresses that are unique in the Frame Relay WAN.  Providing DLCI numbers that are globally rather than just locally significant makes automatic configuration of the Frame Relay map possible.  With LMI, DLCI values are unique within a Frame Relay network, and standard address resolution protocols such as ARP and reverse ARP and discovery protocols can be used to identify nodes within the network.

The LMI multicasting extension allows multicast groups to be assigned.  Multicasting saves bandwidth by allowing routing updates and address-resolution messages to be sent only to specific groups of routers.  The extension also transmits reports on the status of multicast groups in the update messages.

LMI uses keepalive packets (sent every 10 seconds by default) to verify the Frame Relay link and to ensure the flow of data.  The Frame Relay switch in turn provides to the Frame Relay connectivity device the status of all virtual circuits that the device can utilize.  Each virtual circuit, represented by its DLCI number, can have one of three connection states:

• Active --- The connection is working and routers can use it to exchange data.
• Inactive --- The connection from the local router to the switch is working, but the connection to the remote router is not available.
• Deleted --- No LMI information is being received from the Frame Relay switch; this can indicate that the connection between the CPE and DCE is not functional.

The Frame Relay switch reports this status information to the Frame Relay map on the local router.  The status information is used by the Frame Relay connectivity device to determine whether data can be transmitted over the configured virtual circuit.  The LMI messages can provide information about the following:

• Keepalives -- Verifies that data is flowing.
• Multicasting -- Provides the network server with its local DLCI and the Multicast DLCI.
• Global Addressing -- Gives DLCIs global rather than local significance in Frame Relay networks.
• Status of Virtual Circuits -- Provides an ongoing status report on the DLCIs known to the switch.

Beginning with Cisco IOS Release 11.2, the software supports Local Management Interface (LMI) autosense, which enables the interface to determine the LMI type supported by the switch.  Support for LMI autosense means that you are no longer required to configure the Local Management Interface (LMI) explicitly.  If the Frame Relay responds with more than one type, the Cisco router will automatically configure itself to use the last LMI type received.  You can turn off LMI autosense by explicitly configuring an LMI type.  The LMI type must be written into NVRAM so that the next time the router powers up, LMI autosense will be inactive.  At the end of autoinstall, a frame-relay lmi-type xxx statement is included within the interface configuration.  This configuration is not automatically written to NVRAM; you must explicitly write the configuration to NVRAM by using the copy system:running-config or copy nvram:startup-config commands.

The default type is cisco, but you can manually change it to ANSI or Q.933A.  If you configure the LMI type manually, you will deactivate LMI autosense.  If the router is attached to a public data network (PDN), the LMI type must match the type used on the public network.  Otherwise, the LMI type can be set to suit the needs of your private Frame Relay network.  The following command changes the LMI type to ANSI and explicitly sets the keepalive time interval:

   Router3(config)#int s1
   Router3(config-if)#ip address 192.168.1.55.2 255.255.255.0
   Router3(config-if)#encapsulation frame-relay
   Router3(config-if)#bandwidth 64
   Router3(config-if)#frame-relay lmi-type ?
      cisco
      ansi
      q933a
      
   Router3(config-if)#frame-relay lmi-type ansi
   Router3(config-if)#keepalive 8   
   Router3(config-if)#exit

A keepalive interval must be set to configure the LMI. By default, this interval is 10 seconds (can be from 0 to 32,768 seconds) and, per the LMI protocol, must be less than the corresponding interval on the switch.  To disable keepalives on networks that do not utilize LMI, use the no keepalive interface configuration command.

• Cisco -- LMI defined by the Gang of Four (default). It allows for 992 virtual circuits addresses and uses DLCI 1023 as a management circuit, which transfers link and DLCI status messages
• ANSI -- ANSI standard T1.617 Annex D provides for 976 virtual circuit addresses and uses DLCI 0 as the management circuit.
• q933a -- ITU-T Q.933 Annex A, similar to ANSI T1.617 Annex D, uses DLCI 0 as a management circuit.

Frame Relay frames that conform to the LMI specifications have one of the following message types:

• Status Inquiry Message: Allows a user device to inquire about the status of the network.
• Status Message: Responds to status-inquiry messages.  Status messages include keepalives and PVC status messages.

The LMI virtual circuit status messages provide communication and synchronization between Frame Relay DTE and DCE devices.  These messages are used to periodically report on the status of PVCs, which prevents data from being sent over PVCs that no longer exist.  Information in status messages include all or some of the following:

• New -- Used if a new DLCI connection has been configured
• Active -- Used to indicate whether the virtual circuit is available for data transfer.
• Receiver not ready -- Used for flow control to indicate that the virtual circuit is congested. This option is not available for the q933a LMI type.
• Minimum Bandwidth -- Indicates the minimum available bandwidth.
• Global Addressing -- Used to give DLCI global significance.
• Multicasting -- Used to configure a group of destination addresses rather than a single address.  The IEEE has reserved DLCI numbers 1019 through 1022 for this purpose.  Frame Relay devices use multicasting to make DLCI numbers globally significant by advertising them across the Frame Relay network.
• Provider-Initiated Status Update -- Normally, the Frame Relay switch obtains PVC status information only when the CPE sends a full status message and requests status information for the other DLCI connections.  This option allows the provider to initiate a status inquiry.

Not all Frame Relay providers support every piece of link status information.  All current implementations provide the New and Active information, but support for other information varies by provider.  Note that Frame Relay doesn't provide error checking, as do other network protocols such as Synchronous Data Link (SDLC).  This makes Frame Relay connections more efficient, but it also means Frame Relay must rely on the upper-layer protocols such as TCP, to provide error correction.

Configure Frame Relay Maps

In configurations where Inverse ARP is not used to dynamically discover network protocol addresses on the virtual circuit, the frame-relay map command must be used to map layer 3 protocol addresses to the layer 2 DLCI.

  frame-relay map [protocol] [protocol addresss] [dlci #] [broadcast] [cisco|ietf]

[broadcast] -- Forwards broadcasts to this address.

[cisco|ietf] -- Used to specify Frame Relay encapsulation type.  ietf for connecting to another vendor's equipment across a Frame Relay network.  cisco is the Cisco encapsulation for Frame Relay.

   Router3(config-if)#frame-relay map ip 192.168.1.40 42 b ietf

Frame Relay Inverse ARP is a method of building dynamic address mappings in Frame Relay networks.  Inverse ARP allows the router to discover the protocol address of a device associated with the virtual circuit.  Inverse ARP creates dynamic address mappings, as contrasted with the frame-relay map command.  It is enabled by default, but can be disabled explicitly for a given protocol and DLCI pair.  You do not have to enable or disable Inverse ARP if you have a point-to-point interface, because this is only a single destination and discovery is not required.  In order to maintain the Frame Relay map, routers exchange Inverse ARP messages every 60 seconds by default.  To select Inverse ARP or disable it, use the following commands in interface configuration mode:

frame-relay inverse-arp protocol dlci

no frame-relay inverse-arp protocol dlci

Split Horizons

Split Horizon is a routing technique that reduces the chance of routing loops on a network.  A split horizon implementation prevents routing update information received on one physical interface from being rebroadcast to other devices through that same physical interface.  Although split horizon is good for reducing routing loops, it can cause problems for Frame Relay routing updates.

Consider three routers called A, B, and C, that have one physical connection between them (e.g. A--B--C), routerA can communicate with routerB and routerB can communicate with routerC and routerB can talk to both A and C.  On a LAN, A could talk to C, but not in Frame Relay, unless routerA had a PVC to routerC.  The best solution is to configure subinterfaces for each virtual connection, because the individual virtual circuits can be maintained and split horizon can remain on.  Routing update information that is received through one subinterface can be propagated to other subinterfaces.  Dividing the Serial0 interface on routerB into S0.1 and S0.2 (subinterfaces) allows a different subnet identifier to be assigned to each virtual circuit.  This allows router updates to go from routerC to routerA and vice versa.

• Point-to-Point -- used when a single virtual circuit connects one router to another. Each point-to-point subinterface requires its own subnet.
• Multipoint -- used when the router is the center of a star of virtual circuits. Uses a single subnet for all the routers' serial interfaces connected to the frame switch. Subject to the split horizon rule.

Configuring Subinterfaces on Frame Relay

You first set the encapsulation type on the serial interface, then you can define the subinterfaces.  This example sets three subinterfaces, and the DLCIs associated with the virtual circuits.

Notice how each subinterface is on a different subnet, this is for a point-to-point connection.  The encapsulation frame-relay is using the default of cisco but can be ietf instead.  The b is for enabling broadcast routing updates.

   Router3(config)#interface serial 0 
   Router3(config-if)#no ip address
   Router3(config-if)#encapsulation frame-relay
   Router3(config-if)#exit
   Router3(config)#interface serial 0.1 point-to-point
   Router3(config-subif)#ip address 192.168.10.1 255.255.255.0
   Router3(config-subif)#bandwidth 64
   Router3(config-subif)#frame-relay interface-dlci 200 b
   Router3(config-if)#exit
   Router3(config)#interface serial 0.2 point-to-point
   Router3(config-subif)#ip address 192.168.20.1 255.255.255.0
   Router3(config-subif)#bandwidth 64
   Router3(config-subif)#frame-relay interface-dlci 300 b
   Router3(config-if)#exit
   Router3(config)#interface serial 0.3 point-to-point
   Router3(config-subif)#ip address 192.168.30.1 255.255.255.0
   Router3(config-subif)#bandwidth 64
   Router3(config-subif)#frame-relay interface-dlci 400 b
   Router3(config-if)#exit
   Router3(config)#router igrp 110
   Router3(config-router)#network 192.168.10.0
   Router3(config-router)#network 192.168.20.0
   Router3(config-router)#network 192.168.30.0

For the following commands, notice how each DLCI mapping is on the same subnet, this is for a multipoint connection.  The b is for enabling broadcast updates to the specific virtual circuit.  Instead of using a frame-relay map command for every virtual circuit, you can use the frame-relay inverse-arp function to perform dynamic mapping of the IP address to the DLCI number.  Frame Relay Inverse ARP is on by default, and is only disabled if you explicitly disable it.  When the frame-relay map command is used, Inverse ARP is automatically disabled for the specified protocol on the specified DLCI.

   Router3(config)#interface serial 1 
   Router3(config-if)#no ip address
   Router3(config-if)#encapsulation frame-relay
   Router3(config-if)#exit
   Router3(config)#interface serial 1.2 multipoint
   Router3(config-subif)#ip address 172.16.1.1 255.255.0.0
   Router3(config-subif)#frame-relay interface-dlci 100 b
   Router3(config-subif)#bandwidth 64
   Router3(config-subif)#frame-relay map ip 172.16.1.2 200 b
   Router3(config-subif)#frame-relay map ip 172.16.1.3 300 b
   Router3(config-subif)#frame-relay map ip 172.16.1.4 400 b
   Router3(config-subif)#exit
   Router3(config)#router igrp 222
   Router3(config-router)#network 172.16.1.0

Frame Relay Performance Parameters

Some of the terms used by the telecommunications provider to specify performance parameters are:

• Access Rate -- The speed of the line, which indicates transfer rate.  Common rates are 56K, 64K and 128K with ISDN and 1.544Mbps with T1 connections.  Also known as local access rate.
• Committed Information Rate (CIR) -- The minimum transfer rate that the Frame Relay customer negotiates with the service provider.  The service provider agrees to always allow the customer to transfer information at no less than the rate specified by the CIR.
• Committed Burst Size (CBS) -- The maximum amount of data bits that the service provider agrees to transfer in a set time period under normal conditions.
• Excess Burst Rate (EBS) -- The amount of excess traffic (over the CBS) that the network will attempt to transfer during a set time period.  The network can discard EBS if necessary.
• Oversubscription -- When the sum of the data arriving over all virtual circuits exceeds the access rate, the situation is called oversubscription.  This can occur when the CIR is exceeded by burst traffic from the virtual circuits.  Oversubscription results in dropped packets, which means the packets must be retransmitted.

Frame Relay Congestion Control

This is how Frame Relay handles congestion problems.

• DE (Discard Eligibility) -- If the switch is congested, the Frame Relay switch will discard the frames with the DE bit set first.  You can configure certain types of traffic at the router as discard eligible.  If your bandwidth is configured with a CIR of 0 then the DE bit is always set.
• FECN (Forward-Explicit Congestion Network) -- When the Frame Relay switch recognizes congestion, it will set the FECN bit in the current frame.  This tells the destination DCE that the path just traversed is congested.
• BECN (Backward-Explicit Congestion Network) -- The same switch that sent the FECN sends a BECN to the transmitting source, which should cause the source to slow its transmission rate.

Frame Relay Topologies

Monitoring Frame Relay

You can use the show command to see if the commands you entered produced the desired effect on the router.

   Router3>show frame ?
     ip       show frame relay IP statistics
     lapf     show frame relay lapf status/statistics
     lmi      show frame relay lmi statistics
     map      Frame-Relay map table
     pvc      show frame relay pvc statistics
     route    show frame relay route
     svc      show frame relay SVC stuff
     traffic  Frame-Relay protocol statistics

Enter the EXEC command show frame-relay lmi at the system prompt to display statistics about the Local Management Interface (LMI).  The following is sample output from the show frame-relay lmi command when the interface is a DTE:

Router3#show frame-relay lmi
LMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = ANSI
  Invalid Unnumbered info 0             Invalid Prot Disc 0
  Invalid dummy Call Ref 0              Invalid Msg Type 0
  Invalid Status Message 0              Invalid Lock Shift 0
  Invalid Information ID 0              Invalid Report IE Len 0
  Invalid Report Request 0              Invalid Keep IE Len 0
  Num Status Enq. Sent 9                Num Status msgs Rcvd 0
  Num Update Status Rcvd 0              Num Status Timeouts 9

Use the show frame-relay map EXEC command to display the current Frame Relay map entries and information about these connections.  The following is sample output from the show frame-relay map command:

Router3#show frame-relay map
Serial2 (up): IP 131.108.122.2 dlci 20(0x14,0x0440), dynamic
         CISCO, BW= 56000, status defined, active

Enter the show frame-relay pvc EXEC command at the system prompt to display statistics about permanent virtual circuits (PVCs) for Frame Relay interfaces.  Enter no arguments to obtain statistics about all Frame Relay interfaces.  The following is sample output from the show frame-relay pvc command:

 Router3#show frame-relay pvc
    PVC Statistics for interface Serial1 (Frame Relay DCE)
    DLCI = 100, DLCI USAGE = SWITCHED, PVC STATUS = ACTIVE
      input pkts 0             output pkts 0            in bytes 0
      out bytes 0              dropped pkts 0           in FECN pkts 0
      in BECN pkts 0           out FECN pkts 0          out BECN pkts 0
      in DE pkts 0             out DE pkts 0
      pvc create time 0:03:03 last time pvc status changed 0:03:03
      Num Pkts Switched 0
    DLCI = 101, DLCI USAGE = SWITCHED, PVC STATUS = INACTIVE
      input pkts 0             output pkts 0            in bytes 0
      out bytes 0              dropped pkts 0           in FECN pkts 0
      in BECN pkts 0           out FECN pkts 0          out BECN pkts 0
      in DE pkts 0             out DE pkts 0
      pvc create time 0:02:58 last time pvc status changed 0:02:58
      Num Pkts Switched 0
    DLCI = 102, DLCI USAGE = SWITCHED, PVC STATUS = DELETED
      input pkts 0             output pkts 0            in bytes 0
      out bytes 0              dropped pkts 0           in FECN pkts 0
      in BECN pkts 0           out FECN pkts 0          out BECN pkts 0
      in DE pkts 0             out DE pkts 0
      pvc create time 0:02:58 last time pvc status changed 0:02:58
      Num Pkts Switched 0

Enter the show frame-relay route EXEC command at the system prompt to display all configured Frame Relay routes, along with their status.  The following is sample output from the show frame-relay route command:

 Router3#show frame-relay route
    Input Intf      Input Dlci      Output Intf     Output Dlci  Status
    Serial1         100             Serial2         200          active
    Serial1         101             Serial2         201          active
    Serial1         102             Serial2         202          active
    Serial1         103             Serial3         203          inactive
    Serial2         200             Serial1         100          active
    Serial2         201             Serial1         101          active
    Serial2         202             Serial1         102          active
    Serial3         203             Serial1         103          inactive

Use the show frame-relay traffic EXEC command to display the router's global Frame Relay statistics since the last reload. The following is sample output from the show frame-relay traffic command:

 Router3#show frame-relay traffic
 Frame Relay statistics:
 ARP requests sent 14, ARP replies sent 0
 ARP request recvd 0, ARP replies recvd 10

When using Frame Relay encapsulation, use the show interfaces serial command to display information on the multicast DLCI, the DLCI of the interface, and the LMI DLCI used for the Local Management Interface.  The multicast DLCI and the local DLCI can be set using the frame-relay multicast-dlci and the frame-relay local-dlci commands, or provided through the Local Management Interface.  The status information is taken from the LMI, when active.  The following is sample output from the show interfaces serial command for a serial interface with the CISCO LMI enabled:

 Router3#show interface serial 1
 Serial1 is up, line protocol is down
   Hardware is MCI Serial
   Internet address is 131.108.174.48, subnet mask is 255.255.255.0
   MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 246/255, load 1/255
   Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec)
   LMI enq sent  2, LMI stat recvd 0, LMI upd recvd 0, DTE LMI down
   LMI enq recvd 266, LMI stat sent  264, LMI upd sent  0
   LMI DLCI 1023  LMI type is CISCO  frame relay DTE
   Last input 0:00:04, output 0:00:02, output hang never
   Last clearing of "show interface" counters 0:44:32
   Output queue 0/40, 0 drops; input queue 0/75, 0 drops
   Five minute input rate 0 bits/sec, 0 packets/sec
   Five minute output rate 0 bits/sec, 0 packets/sec
      307 packets input, 6615 bytes, 0 no buffer
      Received 0 broadcasts, 0 runts, 0 giants
      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
      0 input packets with dribble condition detected
      266 packets output, 3810 bytes, 0 underruns
      0 output errors, 0 collisions, 2 interface resets, 0 restarts
      178 carrier transitions

Debugging Frame LMI

To help you verify and troubleshoot the Frame Relay connection by seeing if the routers and switches are exchanging the correct LMI information, use the command debug frame-relay lmi.