Frame Relay ATM Lecture 7 Paul Flynn 1

Frame Relay & ATM Lecture 7 Paul Flynn 1

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

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

DLCI(Data-link Connection Identifier) 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 4

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

Frame Relay Functions 6

VCI 7

VCI phases 8

Switch and table 9

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 A C To A: DLCI 121 To B: DLCI 243 B To A: DLCI 182 To C: DLCI 121 • DLCI values: 0 - LMI channel, 1 -15 - reserved, 16 -991 - available for VCs, 992 -1007 - layer 2 management of FR service, 1008 -1022 reserved, 1023 - in channel layer management 10

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

Frame Relay Architecture Frame Relay Layers FRAD VOFR LMI 12

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

Frame Relay layers 14

Frame Relay frame 15

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 16

Three address formats 17

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

FRAD 19

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 Transmission direction FRAD BECN FRAD FECN • There are recommendations for access devices what to do with FECN and BECN (usually not implemented) 20

Frame Relay Concepts Queue 21

Frame Relay Concepts 22

Frame Relay Concepts 23

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

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

Frame Relay CIR and EIR - how does it work • BC = TC * CIR • BE = TC * EIR Bits Clock rate BC+BE CIR + EIR BC CIR T 0 Time Frame 1 Within CIR Frame 2 Within CIR Frame 3 Marked DE Frame 4 Marked DE Frame 5 Discarded T 0+TC 26

Glossary 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. 27

More Terms (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. ECN (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. BECN (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. DE 28

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 29

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) 30

LMI(Local Management Interface) 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. 31

LMI 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, Strata. Com, Northern Telecom, and DEC (frame relay forum) 2. 3. ansi - Annex D defined by ANSI standard T 1. 617 q 933 a - ITU-T Q. 933 Annex A LMI encapsulation types: 1. IETF Encapsulation Type 2. Cisco Encapsulation Type 32

Local Management Interface (LMI) • Three types of LMIs are supported by Cisco routers: Cisco — The original LMI extensions Ansi — Corresponding to the ANSI standard T 1. 617 Annex D q 933 a — Corresponding to the ITU standard Q 933 Annex A 33

Frame Relay Map n The term map means to “map” or bind a Layer 2 address to a Layer 3 address. n n n 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 n We use the frame-relay map command

Frame Relay Map n n n 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 nexthop address resolution.

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 36

Configuring Basic Frame Relay 37

Configuring a Static Frame Relay Map 38

Reachability Issues with Routing Updates in NBMA 39

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. 40

Frame Relay Subinterfaces 41

Configuring Point-to-Point Subinterfaces 42

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 43

The show interface Command LMI Status LMI DLCI LMI Type 44

The show frame-relay lmi Command 45

The show frame-relay pvc Command 46

The show frame-relay map Command 47

Troubleshooting Frame Relay The debug frame-relay lmi Command PVC Status 0 x 2 – Active 0 x 0 – Inactive 0 x 4 – Deleted 48

ATM Design Goals Problems Architecture Switching Layers 49

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. 50

Multiplexing using cells 51

ATM multiplexing 52

Architecture of an ATM network 53

TP, VPs, and VCs 54

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

Connection identifiers 56

Virtual connection identifiers in UNIs and NNIs 57

An ATM cell 58

Routing with a switch 59

ATM layers 60

ATM layers in endpoint devices and switches 61

ATM layer 62

ATM headers 63

AAL 1 64

AAL 2 65

AAL 3/4 66

AAL 5 67