Frame - Relay

1. Frame - Relay Semester 4 – chapter 6

3. Frame Relay Technology

4. What is a Frame – Relay ? Introduction: • Circuit – switched services (T1): • Physical circuit must be established in advance between nodes (resources must be reserved). • Resources are dedicated for each connection (bandwidth is not shared).

5. In case of using leased lines (T1), a physical router interface is required for each destination node. • Frame-Relay (Packet – switched service): • Uses Virtual Circuits (VC) for data transmission (connection-oriented). • Bandwidth can be shared by different sources. • Path is predetermined and well known for each destination.

6. Only one physical interface is required on each router. • Frame-relay operates at the data-link and physical layers of OSI model. • Frame –Relay • doesn't support • error correction.

7. Frame-Relay Terminology: -Access rate-- It is the rate at which data travels into or out of the network. • Data-link connection identifier (DLCI)- • DLCIis a number that identifies the VC between the end device and the switch. DLCI has local significance.

9. LMI: • Is a signaling standard between the frame relay switch and CPE. • Responsible for keepalive messages between the switch and CPE. • Ability to give DLCI global significance. • Keeps track of DLCIs status.

10. Three types of LMIs are supported: • cisco • ansi • q933a • and routers need to be told which LMI type is being used (In IOS 11.2 LMI is auto sensed).

11. Committed information rate (CIR): The CIR is the guaranteed rate, in bits per second, that the service provider commits to providing. • Committed Burst The maximum number of bits that the switch agrees to transfer during a time interval.

12. Excess Burst: The maximum number of uncommitted bits that the Frame Relay switch attempts to transfer beyond the CIR. • Forward Explicit Congestion Notification (FECN): FECN is sent to the destination device, indicating that congestion has occurred.

13. Backward Explicit Congestion Notification (BECN): A bit set in a frame that notifies a source router that a congestion has occurred.

14. Discard Eligibility Indicator (DE): • A set bit that indicates the frame may be discarded in preference to other frames if congestion occurs. (DE: Set with Excess Burst traffic).

15. Frame-Relay DLCIs: • Frame – Relay uses PVCs (logical circuits) to identify connections with destination nodes. • Each VC is identified by a DLCI number. • A table mapping is constructed by administrator within each switch to identify the incoming / outgoing ports and associated DLCIs numbers.

16. X DLCI 200 Y DLCI 100 P4 P1 DLCI 110 DLCI 500 DLCI 300 B P2 DLCI 600 P0 DLCI 700 A Switch A Z P4 Switch B DLCI 400 In-DLCI Out-DLCI In-port out-port In-DLCI Out-DLCI In-port out-port P0 100 P2 110 P4 110 P1 200 P0 300 P4 400 P1 500 P4 600 P2 600 P4 700

17. DLCI address space is 10 digits • Possible DLCI addresses is 1024. • Usable portion of these addresses depends on the LMI type: • Cisco LMI type uses DLCI addresses from16to1007for user data • ANSI LMI type supports the range of address from16 – 992to carry user data.

18. Frame-Relay frame format: • Flag: the start and end of the frame. • Address field: 2 bytes, • Data field: variable • DLCI: 10 digits • FECN: 1 bit • BECN: 1 bit. • DE: 1 bit.

19. LMI operation

21. LMI functions: • To determine the operational status of the PVCs that the router knows about. • To transmit keepalive messages to ensure that the PVCs stays up and doesn’t shut down. • To tell the router about the active PVCs. • LMI types: • cisco • ansi • Q 933a

22. Global addressing: • One of the most important features of LMI options is global addressing. • It uses different DLCI values on each end of the connection.

23. DLCIs are locally significant, needs to be unique only on the same interface. • Global addressing makes DLCIs resemble the MAC address. • DLCI is assigned to the DTE not to the access link and must be unique. • Global address for one DTE means that all DTEs with VC to this one DTE use its global address on their access links.

24. With normal addressing, a static maps of destination IP address to corresponding DLCI, must be created.

25. 40 42 40 42 50 22 50 22

26. 200 42 50 200 200

27. Multicasting and Inverse ARP: • The IARP allows the router to automatically build the frame relay map. • The router learns the active DLCIs from the switch during the initial LMI exchange.

28. The router sends an status inquiry message to the switch, which replies with active DLCIs. • The router then sends an IARP to each DLCI for each protocol configured on the interface. • The returned information is used to build the frame relay map.

30. Frame – Relay mapping: • The router from the routing table determines the next hop address. • The next hop address then resolved to DLCI from map table.

31. Frame – Relay switching tables

32. Frame – Relay subinterfaces

33. What are frame-rlay subinterfaces: • Subinterfaces are logical subdivisions of a physical interface. • Early implementation of Frame Relay required that a router has a WAN serial interface for every PVC. • A single router interface can service many remote locations through individual unique subinterfaces

34. Configuration of subinterfaces: • Point – to – point , and • Multipoint configuration.

35. Point–to–point configuration: • Most widely used with spoke and partially meshed frame – relay topologies. • A single subinterface is used to establish one PVC to another physical interface or subinterface on a remote router. • Each point-point connection has its own subnet. • Each interface/subinterface would have a single DLCI. • Routing updates are not subject to split horizon.

36. A S0 S1 S0 C B S0.2 192.20.30.1 DLCI 40 DLCI 50 S0.1 192.20.20.1 DLCI 41 192.20.30.2 192.20.20.2 DLCI 51

37. A S1 S0 C B (config-if)# encaps frame-relay (Config)# interface s0.1 point-to-point (Config-if)# ip address 192.20.20.1 255.255.255.0 (Config-if)# frame-relay interface-dlci 40 (Config)# interface s0.2point-to-point (Config-if)# ip address 192.20.30.1 255.255.255.0 S0.1 DLCI 40 S0.2 192.20.20.1 DLCI 50 (Config-if)# frame-relay interface-dlci 50 -IARP is not required -LMI – is auto sensed in IOS 11.2 & later.

38. Multipoint configuration • May be used with fully meshed frame-relay topology. • A single subinterface has multiple PVC to multiple physical interfaces/ subinterfaces . • All subinterfaces/ interfaces would be in the same subnet. • Routing updates are subject to split horizon.

39. A S0.1 C B S1.1 S0.2

40. A S0.1 C B S1.1 S0

41. A S0.1 C B S1.1 S1 (config_# Int s0 (config-if)# no ip address (config-if)# encaps frame 193.40.40.1 (config)# int s0.1 multipoint DLCI 100 (config-if)# DLCI 200 ip address 193.40.40.1 Frame-relay interface-dlci 100 Frame-relay interface-dlci 200 193.40.40.2 193.40.40.3 Frame-relay map ip 193.40.40.2 100 (If IARP not supported)

42. A S0.1 C B S1.1 S1 Router C (config_# Int s1 193.40.40.1 (config-if)# encaps frame DLCI 100 (config-if)# DLCI 200 ip address 193.40.40.3 Frame-relay map ip 193.40.40.1 300 (If IARP not supported) DLCI 300 193.40.40.2 193.40.40.3

43. Good Luck !