Chapter 6- Semester4Chapter 6- Semester4

Carl MarandolaCarl Marandola

CCRI

What is Frame Relay? What is Frame Relay?

Frame Relay is an industry-Frame Relay is an industry-standard, switched data standard, switched data link-layer protocol that link-layer protocol that handles multiple virtual handles multiple virtual circuits using High-Level circuits using High-Level Data Link Control (HDLC) Data Link Control (HDLC) encapsulation between encapsulation between connected devices. connected devices. Frame Relay uses virtual Frame Relay uses virtual circuits to make circuits to make connections through a connections through a connection-oriented connection-oriented service. service.

Frame Relay FeaturesFrame Relay Features CCITT and ANSI standard that defines a process for sending CCITT and ANSI standard that defines a process for sending data over a public data network (PDN). data over a public data network (PDN).

high performance, efficient data technology used in networks high performance, efficient data technology used in networks throughout the world. throughout the world.

Sends information over a WAN by dividing data into packets. Sends information over a WAN by dividing data into packets.

Operates at the physical and data link layers of the OSI Operates at the physical and data link layers of the OSI reference model.reference model.

Relies on upper-layer protocols such as TCP for error Relies on upper-layer protocols such as TCP for error correction. correction.

Frame Relay interface can be either a carrier-provided public Frame Relay interface can be either a carrier-provided public network or a network of privately owned equipment, serving a network or a network of privately owned equipment, serving a single enterprise. single enterprise.

Terms used in Frame RelayTerms used in Frame RelayAccess rate -- The clock Access rate -- The clock speed (port speed) of the speed (port speed) of the connection (local loop) to the connection (local loop) to the Frame Relay cloud. It is the Frame Relay cloud. It is the rate at which data travels rate at which data travels into or out of the network. into or out of the network. Data-link connection Data-link connection identifier (DLCI) – A DLCI is identifier (DLCI) – A DLCI is a number that identifies the a number that identifies the end point in a Frame Relay end point in a Frame Relay network. This number has network. This number has significance only to the local significance only to the local network. The Frame Relay network. The Frame Relay switch maps the DLCIs switch maps the DLCIs between a pair of routers to between a pair of routers to create a permanent virtual create a permanent virtual circuit. circuit.

Terms used in Frame Relay- ContinueTerms used in Frame Relay- ContinueLocal management interface (LMI) -- A signaling standard between Local management interface (LMI) -- A signaling standard between the customer premises equipment (CPE) device and the Frame the customer premises equipment (CPE) device and the Frame Relay switch that is responsible for managing the connection and Relay switch that is responsible for managing the connection and maintaining status between the devices.maintaining status between the devices.

LMIs can include support for LMIs can include support for 1.1. a keepalive mechanism, which verifies that data is flowing.a keepalive mechanism, which verifies that data is flowing.2.2. a multicast mechanism, which can provide the network server with its a multicast mechanism, which can provide the network server with its

local DLCI. local DLCI. 3.3. multicast addressing, providing a few DLCIs to be used as multicast multicast addressing, providing a few DLCIs to be used as multicast

addresses and the ability to give DLCIs global (whole Frame Relay addresses and the ability to give DLCIs global (whole Frame Relay network) significance, rather than just local significance (DLCIs used network) significance, rather than just local significance (DLCIs used only to the local switch); only to the local switch);

4.4. a status mechanism, which provides an ongoing status on the DLCIs a status mechanism, which provides an ongoing status on the DLCIs known to the switch. known to the switch.

There are several LMI types, and routers need to be told which LMI type There are several LMI types, and routers need to be told which LMI type is being used. Three types of LMIs are supported: cisco, ansi, and is being used. Three types of LMIs are supported: cisco, ansi, and q933a. q933a.

Terms used in Frame Relay- ContinueTerms used in Frame Relay- ContinueCommitted information rate (CIR) -- The CIR is the guaranteed Committed information rate (CIR) -- The CIR is the guaranteed rate, in bits per second, that the service provider commits to rate, in bits per second, that the service provider commits to providing. providing. Committed burst -- The maximum number of bits that the Committed burst -- The maximum number of bits that the switch agrees to transfer during a time interval. (It is noted Bc) switch agrees to transfer during a time interval. (It is noted Bc) Excess burst -- The maximum number of uncommitted bits that Excess burst -- The maximum number of uncommitted bits that the Frame Relay switch attempts to transfer beyond the CIR. the Frame Relay switch attempts to transfer beyond the CIR. Excess burst is dependent on the service offerings available by Excess burst is dependent on the service offerings available by the vendor, but is typically limited to the port speed of the local the vendor, but is typically limited to the port speed of the local access loop. access loop. Forward explicit congestion notification (FECN) -- A bit set in a Forward explicit congestion notification (FECN) -- A bit set in a frame that notifies a DTE that congestion avoidance frame that notifies a DTE that congestion avoidance procedures should be initiated by the receiving device. When a procedures should be initiated by the receiving device. When a Frame Relay switch recognizes congestion in the network, it Frame Relay switch recognizes congestion in the network, it sends a FECN packet to the destination device, indicating that sends a FECN packet to the destination device, indicating that congestion has occurred. congestion has occurred.

Terms used in Frame Relay- ContinueTerms used in Frame Relay- Continue

Backward explicit congestion notification (BECN) -- A bit Backward explicit congestion notification (BECN) -- A bit set in a frame that notifies a DTE that congestion set in a frame that notifies a DTE that congestion avoidance procedures should be initiated by the receiving avoidance procedures should be initiated by the receiving device. As shown in Figure when a Frame Relay switch device. As shown in Figure when a Frame Relay switch recognizes congestion in the network, it sends a BECN recognizes congestion in the network, it sends a BECN packet to the source router, instructing the router to reduce packet to the source router, instructing the router to reduce the rate at which it is sending packets. If the router receives the rate at which it is sending packets. If the router receives any BECNs during the current time interval, it decreases any BECNs during the current time interval, it decreases the transmit rate by 25%. the transmit rate by 25%.

Terms used in Frame Relay- ContinueTerms used in Frame Relay- ContinueForward explicit congestion notification Forward explicit congestion notification

(FECN) -- A bit set in a frame that notifies a (FECN) -- A bit set in a frame that notifies a DTE that congestion avoidance procedures DTE that congestion avoidance procedures should be initiated by the receiving device. should be initiated by the receiving device. When a Frame Relay switch recognizes When a Frame Relay switch recognizes congestion in the network, it sends a FECN congestion in the network, it sends a FECN packet to the destination device, indicating packet to the destination device, indicating that congestion has occurred. that congestion has occurred.

Backward explicit congestion notification Backward explicit congestion notification (BECN) -- A bit set in a frame that notifies a (BECN) -- A bit set in a frame that notifies a DTE that congestion avoidance procedures DTE that congestion avoidance procedures should be initiated by the receiving device. should be initiated by the receiving device. when a Frame Relay switch recognizes when a Frame Relay switch recognizes congestion in the network, it sends a BECN congestion in the network, it sends a BECN packet to the source router, instructing the packet to the source router, instructing the router to reduce the rate at which it is router to reduce the rate at which it is sending packets. If the router receives any sending packets. If the router receives any BECNs during the current time interval, it BECNs during the current time interval, it decreases the transmit rate by 25%. decreases the transmit rate by 25%.

Terms used in Frame Relay- ContinueTerms used in Frame Relay- Continue

Discard eligibility (DE) indicator -- A set bit that indicates Discard eligibility (DE) indicator -- A set bit that indicates the frame may be discarded in preference to other the frame may be discarded in preference to other frames if congestion occurs. When the router detects frames if congestion occurs. When the router detects network congestion, the Frame Relay switch will drop network congestion, the Frame Relay switch will drop packets with the DE bit set first. The DE bit is set on the packets with the DE bit set first. The DE bit is set on the oversubscribed traffic (that is, the traffic that was oversubscribed traffic (that is, the traffic that was received after the CIR was met). received after the CIR was met).

Frame Relay operation Frame Relay operation

You deploy a public Frame Relay service by putting You deploy a public Frame Relay service by putting Frame Relay switching equipment in the central office of Frame Relay switching equipment in the central office of a telecommunications carrier. In this case, users get a telecommunications carrier. In this case, users get economic benefits from traffic-sensitive charging rates, economic benefits from traffic-sensitive charging rates, and don't have to spend the time and effort to administer and don't have to spend the time and effort to administer and maintain the network equipment and service. and maintain the network equipment and service.

The lines that connect user devices to the network The lines that connect user devices to the network equipment can operate at a speed selected from a broad equipment can operate at a speed selected from a broad range of data rates. Speeds between 56 kbps and 2 range of data rates. Speeds between 56 kbps and 2 Mbps are typical, although Frame Relay can support Mbps are typical, although Frame Relay can support lower and higher speeds lower and higher speeds

Frame Relay DLCIFrame Relay DLCI

Frame Relay provides a Frame Relay provides a means for multiplexing means for multiplexing many logical data many logical data conversations, referred to conversations, referred to as virtual circuits, through a as virtual circuits, through a shared physical medium by shared physical medium by assigning DLCIs to each assigning DLCIs to each DTE/DCE pair of devices.DTE/DCE pair of devices.

Frame Relay's multiplexing Frame Relay's multiplexing provides more flexible and provides more flexible and efficient use of available efficient use of available bandwidth. Therefore, bandwidth. Therefore, Frame Relay allows users Frame Relay allows users to share bandwidth at a to share bandwidth at a reduced cost. reduced cost.

Frame Relay DLCIFrame Relay DLCIFrame Relay standards Frame Relay standards address permanent virtual address permanent virtual circuits (PVCs) that are circuits (PVCs) that are administratively configured and administratively configured and managed in a Frame Relay managed in a Frame Relay network. Frame Relay PVCs network. Frame Relay PVCs are identified by DLCIs are identified by DLCIs The service provider's The service provider's switching equipment constructs switching equipment constructs a table mapping DLCI values to a table mapping DLCI values to outbound ports. When a frame outbound ports. When a frame is received, the switching is received, the switching device analyzes the connection device analyzes the connection identifier and delivers the frame identifier and delivers the frame to the associated outbound to the associated outbound port. The complete path to the port. The complete path to the destination is established destination is established before the first frame is sent. before the first frame is sent.

Frame Relay Frame FormatFrame Relay Frame Format

The Frame Relay frame format The Frame Relay frame format is shown in the Figure. The is shown in the Figure. The flag fields indicate the flag fields indicate the beginning and end of the beginning and end of the frame. Following the leading frame. Following the leading flag field are 2 bytes of flag field are 2 bytes of address information. 10 bits of address information. 10 bits of these 2 bytes make up the these 2 bytes make up the actual circuit ID (that is, the actual circuit ID (that is, the DLCI).DLCI).Congestion Control -- The last Congestion Control -- The last 3 bits in the address field, 3 bits in the address field, which control the Frame Relay which control the Frame Relay congestion notification congestion notification mechanisms. These are the mechanisms. These are the FECN, BECN, and discard FECN, BECN, and discard eligible (DE) bits. eligible (DE) bits.

Frame Relay addressing Frame Relay addressing

DLCI address space is limited to 10 bits. This creates a DLCI address space is limited to 10 bits. This creates a possible 1024 DLCI addresses. The usable portion of possible 1024 DLCI addresses. The usable portion of these addresses are determined by the LMI type used. these addresses are determined by the LMI type used. The remaining DLCI addresses are reserved for vendor The remaining DLCI addresses are reserved for vendor implementation. This includes LMI messages and implementation. This includes LMI messages and multicast addresses. multicast addresses.

Examples:Examples:The Cisco LMI type supports a range of DLCI addresses The Cisco LMI type supports a range of DLCI addresses from DLCI 16-1007 for carrying user-data. from DLCI 16-1007 for carrying user-data. The ANSI/ITU LMI type supports the range of addresses The ANSI/ITU LMI type supports the range of addresses from DLCI 16-992 for carrying user-data. from DLCI 16-992 for carrying user-data.

LMI operation & extensions LMI operation & extensions In addition to the basic Frame Relay In addition to the basic Frame Relay

protocol functions for transferring protocol functions for transferring data, the Frame Relay specification data, the Frame Relay specification includes LMI extensions that make includes LMI extensions that make supporting large, complex supporting large, complex internetworks easier. internetworks easier.

A summary of the LMI extensions A summary of the LMI extensions follows: follows: Virtual circuit status messages Virtual circuit status messages (common) -- Provide (common) -- Provide communication and synchronization communication and synchronization between the network and the user between the network and the user device, periodically reporting the device, periodically reporting the existence of new PVCs and the existence of new PVCs and the deletion of already existing PVCs, deletion of already existing PVCs, and providing general information and providing general information about PVC integrity. about PVC integrity.

Multicasting (optional) -- Allows a sender to transmit a single Multicasting (optional) -- Allows a sender to transmit a single frame but have it delivered by the network to multiple frame but have it delivered by the network to multiple recipients. recipients.

Global addressing (optional) -- Gives connection identifiers Global addressing (optional) -- Gives connection identifiers global rather than local significance, allowing them to be global rather than local significance, allowing them to be used to identify a specific interface to the Frame Relay used to identify a specific interface to the Frame Relay network. Global addressing makes the Frame Relay network network. Global addressing makes the Frame Relay network resemble a local-area network (LAN) in terms of addressing; resemble a local-area network (LAN) in terms of addressing;

Simple flow control (optional) -- Provides for an XON/XOFF Simple flow control (optional) -- Provides for an XON/XOFF flow control mechanism that applies to the entire Frame flow control mechanism that applies to the entire Frame Relay interface. It is intended for devices whose higher Relay interface. It is intended for devices whose higher layers cannot use the congestion notification bits and that layers cannot use the congestion notification bits and that need some level of flow controlneed some level of flow control

LMI extensions -Continue LMI extensions -Continue

LMI frame FormatLMI frame Format

The Frame Relay The Frame Relay specification specification includes the LMI includes the LMI procedures. LMI procedures. LMI messages are messages are sent in frames sent in frames distinguished by distinguished by an LMI-specific an LMI-specific DLCI (defined in DLCI (defined in the consortium the consortium specification as specification as DLCI = 1023). DLCI = 1023).

LMI Feature- Global addressingLMI Feature- Global addressing

In normal Frame Relay there are no addresses that identify In normal Frame Relay there are no addresses that identify network interfaces, or nodes attached to these network interfaces, or nodes attached to these interfaces. Because these addresses do not exist, they interfaces. Because these addresses do not exist, they cannot be discovered by traditional address resolution cannot be discovered by traditional address resolution and discovery techniques. and discovery techniques.

So, static maps must be created to tell routers which DLCIs So, static maps must be created to tell routers which DLCIs to use to find a remote device and its associated to use to find a remote device and its associated internetwork address. internetwork address.

Global addressing provides significant benefits in a large, Global addressing provides significant benefits in a large, complex network. The Frame Relay network now complex network. The Frame Relay network now appears to the routers on its periphery like any LAN. appears to the routers on its periphery like any LAN.

LMI Features- Multicasting LMI Features- Multicasting

Multicast groups are designated by a series of four Multicast groups are designated by a series of four reserved DLCI values (1019 to 1022). Frames reserved DLCI values (1019 to 1022). Frames sent by a device using one of these reserved sent by a device using one of these reserved DLCIs are replicated by the network and sent to DLCIs are replicated by the network and sent to all exit points in the designated set. The all exit points in the designated set. The multicasting extension also defines LMI multicasting extension also defines LMI messages that notify user devices of the messages that notify user devices of the addition, deletion, and presence of multicast addition, deletion, and presence of multicast groups. groups.

LMI Features- Inverse ARP LMI Features- Inverse ARP

The Inverse ARP mechanism The Inverse ARP mechanism allows the router to allows the router to automatically build the Frame automatically build the Frame Relay map, as shown in the Relay map, as shown in the Figure. The router learns the Figure. The router learns the DLCIs that are in use from the DLCIs that are in use from the switch during the initial LMI switch during the initial LMI exchange. The router then exchange. The router then sends an Inverse ARP request sends an Inverse ARP request to each DLCI for each protocol to each DLCI for each protocol configured on the interface if configured on the interface if the protocol is supported. The the protocol is supported. The return information from the return information from the Inverse ARP is then used to Inverse ARP is then used to build the Frame Relay map.build the Frame Relay map.

LMI Features- Frame Relay mappingLMI Features- Frame Relay mapping

The router next-hop address The router next-hop address determined from the routing determined from the routing table must be resolved to a table must be resolved to a Frame Relay DLCI, as shown Frame Relay DLCI, as shown in the Figure. The resolution is in the Figure. The resolution is done through a data structure done through a data structure called a Frame Relay map. called a Frame Relay map. The routing table is then used The routing table is then used to supply the next-hop protocol to supply the next-hop protocol address or the DLCI for address or the DLCI for outgoing traffic. This data outgoing traffic. This data structure can be statically structure can be statically configured in the router, or the configured in the router, or the Inverse ARP feature can be Inverse ARP feature can be used for automatic setup of the used for automatic setup of the map.map.

LMI Features- Frame Relay switching tableLMI Features- Frame Relay switching table

The router next-hop address The router next-hop address determined from the routing determined from the routing table must be resolved to a table must be resolved to a Frame Relay DLCI, as shown Frame Relay DLCI, as shown in the Figure. The resolution is in the Figure. The resolution is done through a data structure done through a data structure called a Frame Relay map. called a Frame Relay map. The routing table is then used The routing table is then used to supply the next-hop protocol to supply the next-hop protocol address or the DLCI for address or the DLCI for outgoing traffic. This data outgoing traffic. This data structure can be statically structure can be statically configured in the router, or the configured in the router, or the Inverse ARP feature can be Inverse ARP feature can be used for automatic setup of the used for automatic setup of the map.map.

LMI Features- Frame Relay SwitchingLMI Features- Frame Relay Switching

The Frame Relay switching The Frame Relay switching table consists of four entries: table consists of four entries: two for incoming port and two for incoming port and DLCI, and two for outgoing DLCI, and two for outgoing port and DLCI, as shown in the port and DLCI, as shown in the Figure. The DLCI could, Figure. The DLCI could, therefore, be remapped as it therefore, be remapped as it passes through each switch; passes through each switch; the fact that the port reference the fact that the port reference can be changed is why the can be changed is why the DLCI does not change even DLCI does not change even though the port reference though the port reference might change.might change.

Frame Relay SubinterfacesFrame Relay Subinterfaces

Subinterfaces are logical Subinterfaces are logical subdivisions of a physical subdivisions of a physical interface. interface.

By logically dividing a By logically dividing a single physical WAN single physical WAN serial interface into serial interface into multiple virtual multiple virtual subinterfaces, the overall subinterfaces, the overall cost of implementing a cost of implementing a Frame Relay network can Frame Relay network can be reduced. be reduced.

Spilt Horizon Use in Frame RelaySpilt Horizon Use in Frame Relay

if a remote router if a remote router sends an update to sends an update to the headquarters the headquarters router that is router that is connecting multiple connecting multiple PVCs over a single PVCs over a single physical interface, physical interface, the headquarters the headquarters router cannot router cannot advertise that route advertise that route through the same through the same physical interface to physical interface to other remote other remote routers routers

SubinterfacesSubinterfaces

You can configure subinterfaces to support the You can configure subinterfaces to support the following connection types: following connection types:

Point-to-point -- A single subinterface is used to Point-to-point -- A single subinterface is used to establish one PVC connection to another establish one PVC connection to another physical interface or subinterface on a remote physical interface or subinterface on a remote router. router.

Multipoint -- A single subinterface is used to Multipoint -- A single subinterface is used to establish multiple PVC connections to multiple establish multiple PVC connections to multiple physical interfaces or subinterfaces on remote physical interfaces or subinterfaces on remote routers. routers.

Writing the IOS command sequence to Writing the IOS command sequence to completely configure Frame Relaycompletely configure Frame Relay

Select the interface and go into interface configuration mode Select the interface and go into interface configuration mode Router(config) # interface serial 0Router(config) # interface serial 0

Configure a network-layer address, for examlple, an IP addressConfigure a network-layer address, for examlple, an IP addressRouter(config-if) # ip address 212.14.249.197 255.255.255.0Router(config-if) # ip address 212.14.249.197 255.255.255.0

Select the encapsulation type used for data traffic end-to-endSelect the encapsulation type used for data traffic end-to-endRouter(config-if) # encapsulation frame-relay [cisco|ietf]Router(config-if) # encapsulation frame-relay [cisco|ietf]

For Cisco IOS 11.1 or earlier specify the LMI type used in the Frame For Cisco IOS 11.1 or earlier specify the LMI type used in the Frame Relay Switch, Relay Switch, Router(config-if) # frame-relay lmi-type {ansi|cisco|q933i} Router(config-if) # frame-relay lmi-type {ansi|cisco|q933i}

for later versions of the Cisco IOS LMI type is autosensedfor later versions of the Cisco IOS LMI type is autosensed

Configure the bandwidth of the linkConfigure the bandwidth of the linkRouter(config-if) # bandwidth Router(config-if) # bandwidth kilobitskilobits

If the inverse ARP was disabled on the router, re-enable itIf the inverse ARP was disabled on the router, re-enable itRouter(config-if) # frame-relay inverse-arp [protocol] [dlci]Router(config-if) # frame-relay inverse-arp [protocol] [dlci]

Configuring subinterfacesConfiguring subinterfaces

Select the interfaceSelect the interfaceRemove any network layer address assigned to the physical Remove any network layer address assigned to the physical interfaceinterfaceConfigure Frame Relay encapsulation as stated perviuslyConfigure Frame Relay encapsulation as stated perviuslySelect the subinterface you want to configureSelect the subinterface you want to configure

Router(config-if)# interface serial number.subinterface-number {multipoint|point-to-point}Router(config-if)# interface serial number.subinterface-number {multipoint|point-to-point} Interface number 1-4294967293Interface number 1-4294967293 Multipoint is used when you want the router to forward broadcasts and routing Multipoint is used when you want the router to forward broadcasts and routing

updates it receivesupdates it receives Point-to-point is used when you do not want the router to forward broadcasts and Point-to-point is used when you do not want the router to forward broadcasts and

routing updates it receives.routing updates it receives.

Configure the network layer address on the subinterfaceConfigure the network layer address on the subinterfaceIf you configured the subinterface as multipoint or point-to-point you If you configured the subinterface as multipoint or point-to-point you must configure a local DLCImust configure a local DLCI

Router(config-if)# frame-relay interface-dlci Router(config-if)# frame-relay interface-dlci dlci-numberdlci-number

Router(config-if)# Router(config-if)# frame-relay mapframe-relay map protocol protocol protocol protocol address dlci address dlci [[broadcastbroadcast] [] [ietf|cisco|payload-compress ietf|cisco|payload-compress packet-by-packetpacket-by-packet]]

GOOD LUCK Carl MGOOD LUCK Carl M