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What is Local Management Interface (LMI) In Frame Relay?

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  • Last Updated : 09 Mar, 2022
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Frame Relay sends information in packages called frames via a shared Frame Relay network. Each frame contains all the information needed to move it to the right place. Therefore, each end can connect to multiple locations with a single network access link. Frame Relay is like a direct connection between the last two points online. The storage areas are called DTE (Data Terminal Device) and the device that helps the packet to get to its destination is called DCE (Data Circuit-terminating equipment). It can be a modem too. Therefore, when a dedicated connection is established between two points, the connection carries a unique ID number called a  DLCI (Data-Link Connection Identifier). Because DTE addresses differ from the transmitted frame, they become DLCI. 

However, in order to provide synchronization between DTE and DCE devices, LMI (Local Management Interface)continues to send status messages from time to time about the state of the visible optical rotation. If there are no status messages and the PVC is down, the data is stopped to be sent to the virtual circuit. Multicasting allows multiple broadcast groups to be shared and also maintains bandwidth by allowing route updates and address resolution messages to be sent only to certain groups of hosts.

The main advantages of Frame Relay include:

  1. Provides maximum speed. This is because no error is detected and therefore more is less.
  2. Provides high-resolution X-ray installation.

Local Management Interface (LMI):

Local Management Interface is a Cisco-proprietary technology that assists in managing Permanent Regions while using LMI extensions. Uses address editing, keeplife packs, and similar status messages. Local Management Interface (LMI), a technology developed by Cisco, is a display standard used between routers and frame switches for a variety of purposes such as timekeeping information exchange, global address, multi-broadcast, and current state of the visual circuits. the local area management interface (LMI) follows the global address which is responsible for providing the reference number to the Frame Relay data-link connection identifier (DLCI).

LMI in Frame Relay:

Frame Relay uses the LMI protocol to exchange Keepalive messages between DTE (last point of contact) and DCE (last frame switch directly connected to storage). DTE (Routers) sends LMI status query messages to the connected DCE (Frame Relay switch). Local Management Interface (LMI) is a set of Personal Transfer Protocol extensions designed to provide information about the status of Frame Relay networks and to extend technical skills. LMI is very much focused on diagnostic activities.

LMI Messages:

Local Management Interface (LMI) messages carry a local access link between the route and the Frame Relay switch. DTE Transmission Transmission can send an LMI Status Inquiry message to change; The switch then responds with an LMI Status message to inform the route about the defined DLCI VCs, as well as the status of each VC. By default, LMI messages flow every 10 seconds. Each of the six messages contains a full Status message, which includes full status information about each VC. LMI Status Investigation (Route) and Status (switch) messages act as life-saving. The router considers the interface to fail as the router ceases to receive LMI messages from the switch with the default number (default 3) for the default time (10 seconds). As a result, FR LMI is actually enabled/disabled using the keepalive / no keepalive interface subcommands on the Independent Transfer interface.

Purpose of LMI:

LMI is very much focused on diagnostic activities. For example, LMI is used to send life-saving messages between a router and a Frame Relay switch. These messages confirm the status of the PVCs and help ensure that data can be transferred between Frame Relay DTE and DCE assets. LMI extensions also allow DLCI values ​​to be made world-class and bring more streaming capabilities to independent transmission networks.

LMI Types:

When we first learn about Frame Relay, it is often easy to confuse the LMI and encapsulation used with Frame Relay, but Cisco expects CCNAs to hold the difference well. LMI is a description of the messages used between DTE (for example, route) and DCE (for example, Frame Relay voice used by the service provider). Encapsulation describes topics used by DTE to transfer certain information to DTE on the other side of VC. The switch and its connected channel take care to use the same LMI; the switch does not care about encapsulation. Endpoint Raters (DTEs) deal with encapsulation. The most important LMI message related to topics in tests is the LMI status query message. 

Three LMI protocol options are available for Cisco IOS Software: Cisco, ITU, and ANSI. Each LMI option is slightly different, therefore, not compatible with the other two. 

For example, Cisco and ANSI Q.933-A LMIs call the use of DLCI 1023 in LMI messages; whereas, T1.617-D specifies DLCI 0. Some of the messages have different fields in their headings. DTE just needs to know which three LMIs will be used, and location switching must agree. Setting up the LMI type is easy. Today’s most popular option is to use the default LMI setting, which uses the LMI autosense feature. Because the LMI default setting is supported by Cisco IOS Software Release 11.2 and later, We do not need to enter the LMI type code. The LMI version can be configured, but this disables the autosense feature.

Benefits of LMI:

  1. The global LMI extension gives the Frame Relay DLCI global values ​​rather than local values. DLCI values ​​become DTE addresses that are different from Frame Relay WAN. Global address extension adds functionality and management to the Frame Relay network. Individual network links and attachments can be detected using standard address resolution methods and retrieval methods. Additionally, the entire Frame Relay network appears to be a standard LAN for routers in its area.
  2. Visible LMI circuit breaker messages provide communication and synchronization between Frame Relay DTE equipment and DCE. These messages are used to report periodically the status of PVCs, which prevent data from being sent to dark holes (i.e., over existing PVCs).
  3. Multi-LMI streaming extension allows multiple streaming groups to be shared. Multiple streaming saves bandwidth by allowing route updates and address resolution messages to be sent only to certain groups of users. The extension also sends reports on the status of multiple broadcast groups in review messages.
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