Frame Relay & ATM 1 Lecture 7 Paul Flynn

2 Virtual Circuit Switching Virtual Circuit Switching Digital Line Connection Identifier (DLCI) Three Phases Data Transfer Phase Setup Phase Teardown Phase

3 Virtual circuit wide area network Frame Relay does not provide flow or error control; they must be provided by the upper-layer protocols. Frame Relay operates only at the physical and data link layers.

4 A 'local identifier' between the DTE and the DCE, it identifies the logical connection that is multiplexed into the physical channel. Value that specifies a PVC in a Frame Relay network. In the basic Frame Relay specification, DLCIs are 'locally significant'. In the LMI extended specification, DLCIs are 'globally significant' (DLCIs specify individual end devices). The FR Switch maps the DLCIs between each pair of routers to create a PVC. DLCI values are typically assigned by the Frame Relay service provider DLCI (Data-link Connection Identifier)

5 Frame Relay Interface types UNI: User-|Network Interface NNI: Network-Network Interface Frame Relay network Frame Relay network Frame Relay network user UNI NNI PVC segment Multi-network PVC

666 Frame Relay Functions

7 VCI

8 VCI phases

9 Switch and table

10 Frame Relay Local addressing DLCI (Data Link Connection Identifier) - identification of a virtual circuit DLCI - of local (for a given port) meaning there can be max. 976 VCs on an interface user-network DLCI values: 0 - LMI channel, reserved, available for VCs, layer 2 management of FR service, reserved, in channel layer management A B C To A: DLCI 121 To B: DLCI 243 To A: DLCI 182 To C: DLCI 121

11 Local Significance of DLCIs The data-link connection identifier (DLCI) is stored in the Address field of every frame transmitted.

12 Frame Relay Architecture Frame Relay Layers FRAD VOFR LMI

13 Frame Relay network VCIs in Frame Relay are called DLCIs.

14 Frame Relay layers

15 Frame Relay frame

16 Frame Relay Global addressing Extension proposed by “Group of Four” Each end user access device FRAD is assigned a unique DLCI number - a global address Transmission to a given user goes over VC identified by a unique DLCI Current DLCI format limits number of devices to less than 1000 Another addition to the standard - extended DLCI addresses

17 Three address formats

18 LAPF Frame – Address Field 6-bits 4-bits

19 FRAD

20 Frame Relay Flow and congestion control There is no explicit flow control in FR; the network informs a user about congestion Congestion: FR frames are discarded from overflowed buffers of switching devices Congestion information: –FECN - Forward Explicit Congestion Notification –BECN - Backward Explicit Congestion Notification There are recommendations for access devices what to do with FECN and BECN (usually not implemented) Transmission direction BECN FECN FRAD

21 Frame Relay Concepts Queue

22 Frame Relay Concepts

23 Frame Relay Concepts

DLCI-identifies logical connections on the Frame Relay switch to which the customer is attached BECN-tells sending DTE device to reduce the rate of sending data. FECN-tells receiving DTE device to implement congestion avoidance procedures FRAMES BECN FECN

25 Frame Relay Parameters of a UNI interface Physical speed - just clock rate Guaranteed bandwidth parameters –CIR: Committed Information Rate –B C : Committed Burst Size Extended bandwidth parameters –EIR: Extended Information Rate –B E : Extended Burst Size T C : Measurement Interval User traffic 192kbps 64kbps EIR CIR 256kbps time

26 Frame Relay CIR and EIR - how does it work B C = T C * CIR B E = T C * EIR Frame 1 Frame 2Frame 3Frame 4Frame 5 Within CIR Marked DE Discarded Bits B C +B E BCBC T0T0 T 0 +T C Time CIR CIR + EIR Clock rate

27 CIR (Committed Information Rate - The rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated tariff metrics. Local access rate - The clock speed (port speed) of the connection (local loop) to the Frame Relay cloud. It is the rate at which data travels into or out of the network. Committed Burst (Bc) - The maximum number of bits that the switch agrees to transfer during any Committed Rate Measurement Interval (Tc). Excess Burst - The maximum number of uncommitted bits that the Frame Relay switch will attempt to transfer beyond the CIR. Excess Burst is dependent on the service offerings available by your vendor, but is typically limited to the port speed of the local access loop. Glossary

28 ECN (Forward explicit congestion notification) - When a Frame Relay switch recognizes congestion in the network, it sends an FECN packet to the destination device indicating that congestion has occurred. BECN (Backward explicit congestion notification) - When a Frame Relay switch recognizes congestion in the network, it sends a BECN packet to the source router instructing the router to reduce the rate at which it is sending packets. DE (Discard Eligibility indicator) - When the router detects network congestion, the FR switch will drop packets with the DE bit set first. The DE bit is set on the oversubscribed traffic; that is, the traffic that was received after the CIR was met. More Terms

29 Data Link Control Identifier The 10-bit DLCI associates the frame with its virtual circuit It is of local significance only - a frame will not generally be delivered with the same DLCI with which it started Some DLCI’s are reserved

30 Frame Relay Local Management Interface - LMI LMI - a signaling protocol used on an interface: end user - network (UNI) Implementation optional (everybody implements it...) Usage: –notification about: creation, deletion, existence of PVCs on a given port –notification about status and availability of PVCs –periodic checks of integrity of physical connection Planned extensions: –dynamic (SVC) channel creation and deletion –congestion notification Also planned: LMI for network-network interface (NNI)

31 A signalling standard between the CPE device and the FR Switch that is responsible for managing the connection and maintaining " status " between the devices. Set of enhancements to the basic Frame Relay specification. LMI includes support for: 'keepalive mechanism', which verifies that data is flowing; 'multicast mechanism', which provides the network server with its local DLCI and the multicast DLCI; ‘ global addressing', which gives DLCIs global rather than local significance in Frame Relay networks; 'status mechanism', which provides an on-going status report on the DLCIs known to the FR Switch. LMI (Local Management Interface)

32 The main purpose for the LMI process is: ( management of the connection ) –PVC status - What is the operational status of the various PVCs that the router knows about? –Transmission of 'keepalive' packets - Insure that the PVC stays up and does not shut down due to inactivity. Three types of LMIs are supported: 1.cisco - LMI type defined jointly by Cisco, StrataCom, Northern Telecom, and DEC (frame relay forum) 2.ansi - Annex D defined by ANSI standard T q933a - ITU-T Q.933 Annex A LMI encapsulation types: 1.IETF Encapsulation Type 2.Cisco Encapsulation Type LMI

33 Local Management Interface (LMI) Three types of LMIs are supported by Cisco routers: Cisco — The original LMI extensions Ansi — Corresponding to the ANSI standard T1.617 Annex D q933a — Corresponding to the ITU standard Q933 Annex A

Frame Relay Map The term map means to “map” or bind a Layer 2 address to a Layer 3 address. An ARP table maps MACs to IPs in a LAN In ISDN, we use the dailer-map command to map SPIDs to IP addresses In Frame Relay, we need to map the data link layer’s DLCI to the IP address We use the frame-relay map command

Frame Relay Map The Frame Relay switch builds a table of incoming/outgoing ports and DLCIs. The router builds a Frame Relay Map through Inverse ARP requests of the switch during the LMI exchange process. The Frame Relay Map is used by the router for next- hop address resolution.

36 Frame Relay IARP FRADs know DLCIs of available PVCs (through LMI), but don’t know IP addresses of other ends IP addresses for given DLCIs are obtained automatically; mapping IP-DLCI is generated - dynamic mapping IARP can be switched of; static maps have to be generated by FRAD user

37 Configuring Basic Frame Relay

38 Configuring a Static Frame Relay Map

39 Reachability Issues with Routing Updates in NBMA

40 Reachability Issues with Routing Updates in NBMA By default, a Frame Relay network provides nonbroadcast multiaccess (NBMA) connectivity between remote sites. An NBMA environment is treated like other multiaccess media environments, where all the routers are on the same subnet.

41 Frame Relay Subinterfaces

42 Configuring Point-to-Point Subinterfaces

43 Verifying Frame Relay The show interfaces command displays information regarding the encapsulation and Layer 1 and Layer 2 status. It also displays information about the following: The LMI type The LMI DLCI The Frame Relay data terminal equipment/data circuit-terminating equipment (DTE/DCE) type

44 The show interface Command LMI Type LMI DLCI LMI Status

45 The show frame-relay lmi Command

46 The show frame-relay pvc Command

47 The show frame-relay map Command

48 Troubleshooting Frame Relay The debug frame-relay lmi Command PVC Status 0x2 – Active 0x0 – Inactive 0x4 – Deleted

49 ATM Design Goals Problems Architecture Switching Layers

50 Multiplexing using different frame sizes A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-sized block of information.

51 Multiplexing using cells

52 ATM multiplexing

53 Architecture of an ATM network

54 TP, VPs, and VCs

55 Example of VPs and VCs Note that a virtual connection is defined by a pair of numbers: the VPI and the VCI.

56 Connection identifiers

57 Virtual connection identifiers in UNIs and NNIs

58 An ATM cell

59 Routing with a switch

60 ATM layers

61 ATM layers in endpoint devices and switches

62 ATM layer

63 ATM headers

64 AAL1

65 AAL2

66 AAL3/4

67 AAL5