Frame Relay operates at the Layer 2 technology and is an NBMA(Non Broadcast Multiple Access).
DTE and DCE
Router DTE, DCE is the FR-switch at the provider.
Local Management Interface LMI
- runs between DTE and DCE
- Allocation of the DLCI DTE possible
- Keepalives
- LMI types: Cisco, ANSI, Q933a
- Auto Sensing from IOS 11.2
Topologies
- Hub and spoke
- Full mesh [requires n (n-1) / 2 links]
- Partial mesh
In “hub and spoke” and “partial mesh” proposes “to split horizon”. Solution: subinterfaces.
Terms
| CIR | Committed Information Rate |
| MinCIR | minimum transmission rate |
| Tc | CIR-Measurement interval, typically 125 ms |
| Bc | Committed Burts Size, Number of bits in the transmitted normally Tc |
| Be | Excess Burst Size, The amount of data in the time Tc may be transferred to Bc addition, DE is set |
| DE | Discard Eligibility, Marked for loading data can be set for specific individual protocols also |
Basic Configuration
Encapsulation: Cisco or IETF
(Config) # int int
(Config-if) # encapsulation frame-relay
(Config-if) # interface subint point-to-point
(Config-subif) # ip address ip addr mask
(Config-subif) # frame-relay interface-dlci dlci
or
(Config) # int int
(Config-if) # encapsulation frame-relay
(Config-if) # interface subint multipoint
(Config-subif) # ip address ipaddr mask
(Config-subif) # frame-relay map ip ipaddr dlci
The “frame-relay map” of the local and remote IP DLCI is specified.
Router # show frame-relay pvc
PVC status and statistics.
Router # show frame-relay lmi
Router # debug frame-relay lmi
LMI info
Router # show frame-relay map
Traffic Shaping
German: Traffic control
FR-DTE to overload messages from the network to respond to opportunity.
ECN vs. ICN
Frame Relay implements an explicit overload notification (ECN) with the FECN and BECN bits. It will overload the already signaled before frames are dropped.
In implicit message overload (ICN, like TCP), the overload only noticed when frames have been discarded (no ACK).
Configuration
Without a response to BECN (only indication of the CIR)
(Config) # map-class frame-relay name
(Config-map-class) # frame-relay traffic-rate average [peak]
With response to BECN
The router thereby reducing the transmission rate at 25 percent each BECN MinCIR achieved is up.
(Config) # map-class frame-relay name
(Config-map-class) # frame-relay adaptive-shaping BECN
(Config-map-class) # frame-relay cir [in | out] bits
(Config-map-class) # frame-relay bc [in | out] bits
(Config-map-class) # frame-relay be [in | out] bits
(Config-map-class) # frame-relay mincir [in | out] bits
and then on the interface:
(Config) # int int
(Config-if) # encapsulation frame-relay
(Config-if) # frame-relay traffic-shaping
(Config-if) # int subint point-to-point
(Config-subif) # frame-relay interface-dlci dlci
(Config-fr-dlci) # class name
or
(Config) # int int
(Config-if) # encapsulation frame-relay
(Config-if) # frame-relay traffic-shaping
(Config-if) # frame-relay classname
Check again
Router # show frame-relay pvc