Frame Relay Interview Questions & Answers

Question 1. Protocol Of Frame Relay Rely On For Error Checking?

Answer :

Frame Relay does not rely on any certain protocol for error checking. Instead, it relies on upper-layer protocols to provide error checking. For example, Frame Relay relies on TCP to provide error checking in an IP network.

Question 2. Difference Between Switched Virtual Circuits (svcs) And Permanent Virtual Circuits (pvcs)?

Answer :

Switched Virtual Circuits: Switched virtual circuits are dynamically established when data needs to be transferred and that are terminated when data transmission is complete.

SVCs consist of four states: call setup, data transfer, idle, and call termination.

Permanent Virtual Circuit: Permanent Virtual Circuits are permanently established virtual circuits that operate in one of two states: idle or data transfer. When the PVC is idle, the connection between the DTE devices is still active.

Question 3. At What Layers Of The Osi Model Does Frame Relay Operate?

Answer :

Frame Relay operates at the two lower layers of the OSI model (data link and physical).

Question 4. What Is A Data Link Connection Identifier (dlci)?

Answer :

A DLCI is a number that identifies the logical circuit between the router and the Frame Relay switch. It is the Frame Relay Layer 2 address. The Frame Relay switch maps DLCIs between each pair of routers to create a PVC. For IP devices at the end of each virtual circuit to communicate, their IP addresses need to be mapped to DLCIs. If you are running Cisco IOS 11.2 or later, mapping is done automatically using Inverse ARP. DLCIs have local significance. Think of DLCIs as the MAC address of the Frame Relay network.

Question 5. What Are The Bandwidth Specifications Of Frame Relay?

Answer :

• Access Rate
• Committed Information Rate

Question 6. Explain The Encapsulation Types Of Frame Relay?

Answer :

Cisco and IETF (Internet Engineering Task Force)

Question 7. What Is The Committed Information Rate (cir)?

Answer :

The CIR is the committed information rate, by the service provider, in bits per second, at which data will be transferred. The service provider sends any data in excess of this rate if its network has capacity at that time.

Question 8. How Does Frame Relay Use Inverse Arp?

Answer :

Frame Relay uses Inverse ARP as a way to dynamically map a network layer address to a DLCI. With Inverse ARP, the router can discover the network address of a device associated with a VC.

Question 9. What Is The Local Management Interface (lmi)?

Answer :

Local Management Interface (LMI)is a signaling standard used between your router and the first Frame Relay switch it's connected to. It allows for passing information about the operation and status of the virtual circuit between the provider's network and the DTE (your router).

Question 10. What Is Backward Explicit Congestion Notification (becn) ?

Answer :

When the switch detects congestion in the Frame Relay network, it'll set the Backward Explicit Congestion Notification (BECN)bit in a Frame Relay frame that's destined for the source router. This notifies the router that congestion is ahead.

Question 11. What Is Forward Explicit Congestion Notification (fecn)?

Answer :

The FECN is the bit in the Frame Relay header that signals to anyone receiving the frame (switches and DTEs) that congestion is occurring in the same direction as the frame. Switches and DTEs can react by slowing the rate at which data is sent in that direction.

Question 12. In The Frame Relay Header, What Is The Discard Eligibility (de) Bit?

Answer :

If congestion is detected on the Frame Relay network, the DE bit is turned on in the Frame Relay header. The DE bit is turned on for frames that are in excess of the CIR. The DE bit tells a switch which frames to discard if they must be discarded.

Question 13. What Is The Default Lmi Type For Cisco Routers That Are Configured For Frame Relay?

Answer :

Three types of LMIs supported by Cisco routers are: Cisco, ANSI, Q933a.

Question 14. When A Router Receives Lmi Information, It Updates Its Vc Status To One Of Three States. What Are These Three States?

Answer :

Routers receive LMI information from the service provider's Frame Relay switch on a frameencapsulated interface and update the virtual circuit status to one of three different states:

• Active state : Everything is up, and routers can exchange information.
• Inactive state: The router's interface is up and working with a connection to the switching office, but the remote router isn't up.
• Deleted state : No LMI information is being received on the interface from the switch, which could be due to a mapping problem or a line failure.

Question 15. How Do You Enable Frame Relay On A Cisco Router?

Answer :

To enable Frame Relay on a Cisco router, you must first enable the serial interface for Frame Relay encapsulation with the encapsulation frame-relay interface command:

RouterB(config)#int s 0 

RouterB(config-if)#ip address 192.168.1.1 255.255.255.0 

RouterB(config-if)#encapsulation frame-relay