Presentation on theme: "Frame Relay Performance"— Presentation transcript:
1 Frame Relay Performance Peter HicksActing Rapporteur Q2/17 “ Data Network Performance”Tel:Fax:
2 Why worry about Network Performance Importance:Network Management & PlanningBoth customers & network operators have an interest (contractual arrangements / SLAs)Benefits of understanding performanceAble to provide Performance Guarantees for customersAccurate and cost effective dimensioning and network provisioningCustomer reportingCompliance with International Standards / National Regs.
3 ITU-T Performance Objectives Framework End to end performance3 x 3 matrixNetwork(X.25, FR, ATM, IP)TERM.TERM.DependabilityAccuracySpeedCriteriaSpeedAccuracyDependabilityFunctionAccessAccess/call setupCall setup delayCall setup error probabilityCall setup failure probabilityOnly the Info transfer stage is applicable to IP networksInformationTransferResidual error rateUser information misdelivery prob.Info TransferPacket, Frame, cell transfer delayThroughputUser information loss probability - eg Frame Loss RatioDisengagementcall clearingSee RLR 8399 , ATM Standards Update from d.giddyDisengage-mentCall Clearing (Delay)Premature disconnect probabilityCall clear failure probabilityAvailability (function of the primary parametersAvailability
4 Packet Network Performance ATM, Frame Relay, X.25 all examples of Packet Switching technologiesConnection oriented; simultaneous circuits (virtual circuits) able to be supported on a single access lineFor FR and ATM, no acknowledgment of frames / cells sent into the network (requires transport layer protocol to ensure end to end data integrity)Can essentially use the same techniques for measuring and quantifying performancePerformance (Loss & delay) is very dependent on the network architecture, the capacity provided within the network (buffering and transmission trunk speed) and traffic loading.
5 What are the important parameters that can be readily measured? X.25:throughput and packet transfer delay, Call setup delayFrame Relay: for CIR or EIR trafficFrame transfer delay , Frame delay jitter & Frame loss ratioATMCell transfer delay, Cell delay variation, Cell loss ratioIP (best effort / connectionless)packet transfer delay, traffic flowspacket loss ratiopacket delay jitter
6 Frame Relay Performance Parameters User information transfer performance parameters for the FR PVC services defined in X.144Key Primary Performance Parameters:User information Frame Transfer DelayFrame Delay JitterFrame Loss RatioResidual Frame Error RatioExtra Frame Rate
7 Frame Relay Performance Parameters Connection set-up performance parameters for the FR SVC services defined in X.145Key Performance ParametersConnection Set-up DelayDisconnect DelayRelease DelayConnection set-up error probabilityConnection set-up failure probability
8 Frame Relay Performance Parameters Frame Transfer Delaytime taken for a frame to traverse the network. Time taken commences when the first bit of frame is transmitted and ends when the last bit of the frame is receivedFrame Loss Ratio (FLRc or FLRe)The ratio of lost frames to total number sent for either the committed or excess traffic streamsFrame Delay Jitter = FTDMax – FTDMinResidual Frame Error RateThe rate of errored frames arriving at the destinationExtra Frame RateThe rate at which extra frames which were not part of the source traffic are detected in the destination traffic stream
9 Frame Relay Performance Parameters Frame Based Conformant Traffic Distortion:distortion from the traffic contract, measure of clumping or spacing of traffic burstsConnection Set-up DelayTime interval between the occurrence of a Set-up message and the occurrence of the corresponding return Connect messageDis-connect Delayone way delay based on the transport of the a disconnect message from the clearing to the cleared end terminal.
10 FR Performance Objectives Objective values for frame transfer delay, frame loss ratio & frame delay jitter specified in ITU-T Recommendation X.146End to end objectives (not including contributions of the access line) apply to an international frame relay data connection.National Network (portion) allocated 34.5% of the end to end objective for FTD & FLRInternational Network (portion) allocated 31% of the end to end objective for FTD & FLR4 Quality of Service classes specified
11 X.146: FLR, FTD FDJ Objectives Service ClassFLRFTD: byte FramesFDJNo upper boundNot applic.1< 1 X 10-395 %< 400 ms< 52 ms2< 3 X 10-5< 17 ms3< 150 ms
12 FR Performance Objectives - Notes All values are provisional and they need not be met by networks until they are revised (up or down) based on real operational experience. The FTD objectives apply edge-to-edge.For FTD performance, all objectives apply to frames of size 256 (i.e. to frames with user information fields of 256 octets). If frames of size 128 are used to estimate compliance with these objectives, then the following tighter 95th percentile objectives of for FTD should be used; 380 ms for classes 1 & 2, and 130 ms for class 3.Frame Relay Forum have specified 128 octet frame sizeNetworks with high speed backbone should meet objective when using 512 frame sizeIn the case of service class 3, if the international portion route length exceeds 9300 km, an allowance of 6.25 ms per 1000 km of route length is allocated to the international portion.
13 Frame Transfer DelayHighly sensitive to network topology/architecture, internode trunk transmission speeds & traffic levelsCan predict delay by simple modelCan measure using echo / loop back techniquesavoids use of synchronised real-time clocks at remote sitessimple to setup, approach favoured / adopted by ITUextensive testing of X.25 (and Frame relay & ATM)Can also use OAM techniques specified in X.148 and FRF.19 (Requires OAM to be implemented)
14 Impact of performance objectives on network design The transfer delay performance objectives and geographic span impose a maximum transit node limit .Network Architecture and Infrastructure impactFor example the mean frame transfer delay (Class 3) objective across a national FR network (excluding the customers access lines) is specified in Recommendation X.146 as 34.5% of 150ms, and can be used to calculate the maximum number of nodes that a frame can transit.
15 Simple model to calculate transit delay Notes1. Model can be applied to X.25, Frame Relay, ATM or IP networks2. Propagation delay may or may not be a dominant component of the overalldelay. This depends on distance, trunk transmission speeds and pkt size.
16 Transit Delay ModelThe model consists of a concatenation of nodes and internode transmission links.Each FR switch can be characterised by a mean (or worst case) processing delay of N ms.The transmission time across the internode trunks is dependent or the size of the data frame and the transmission speed and can also be expressed as a fixed delay of L ms.The propagation delay is distance dependent (5ms/1000 km) but can be readily calculated for each internode transmission section as tpi. Propagation delay may or may not be a significant component of the overall delay.Hence overall delay depends on distance (propagation delay), trunk transmission speeds & frame size.
17 Transfer Delay Model (cont) Using this model an active connection can be shown as:a series of (k-1) transmission links (l1 to lk-1) through k switching nodes (n1 to nk)..each link li has a clocking delay of L mseach link has a propagation delay of tpi &each switch ni has a processing & queuing delay of N ms.
18 Expression for mean transit delay The mean or alternatively the upper-bound - worst case packet transfer delay across the network is readily calculated asmean delay approx = (k-1)L + Propagation Delay + kNmeanworst case delay < (k-1)L + Propagation Delay + kNworst-caseWith a high speed backbone (34 Mbits/s) the transmission (clocking) delay for a 1024 byte data Frame is 240 ms. This delay reduces to 53ms if the transmission backbone is 155 Mbits/s.For a 48 byte Frame the clocking delay is approximately 3ms. The switching and queuing delay (the variable parameter) through a high speed ATM/FR switch is of the order of 1ms.Over long distances the dominant factor will be the propagation delay (Melbourne to Perth 17 ms, Melbourne to Sydney 5ms, Perth to Brisbane 28 ms).For “old style” X.25 networks with low speed (64kbit/s) transmission trunks, switching/clocking delay may dominate_
19 Expression to calculate maximum number of switching nodes From the above expressions we can also derive an expression for the maximum number of switching (or routing) stages within a network( Delay Objective + L – Prop-delay )Max number of hops k =(L+ N)For example for a National FR network, delay objective = 52msAssume Geographic span 4000 km -> Prop Delay = 20msFrame size 256 Bytes, Trunk transmission 34 Mb/s -> L = 61sFor N = 2 ms: k=15.6 maximum node of switches = 15
20 Clocking delay for various transmission rates and frame sizes
21 Effect of transmission delay and frame size on FTD Consider a national network which has a geographic span of 4000 km, consisting of 8 switching stages and inter-trunk transmission speeds of 2Mbit/s. Each switch contributes 1ms of queuing delay. Propagation delay 5ms / 1000km.For a 256 octet test frame, each trunk will contribute a clocking delay of 1 ms. (see Table 1). The total FTD is calculated as 8 x 1 ms km x x 1 ms = 35 ms. This network meets the national portion FTD objective allocation of ms for Class 3 FR Services.For a 512 octet test frame, each trunk will contribute a clocking delay of 2 ms. (see Table 1). The total FTD is calculated as 8 x 1 ms km x x 2 ms = 42 ms. This network meets the national portion FTD objective allocation of ms for Class 3 FR Services.
22 Effect of transmission delay & frame size on network architecture Question: Can a network with 10 switching stages and a trunk speed of Mbit/s meet the national portion FTD objective allocation for class 3 if a frame size of 512 octets is used?what is the maximum frame size allowed in order to meet the objectiveQuestion: Show that that only in the case where the number of switching stages exceeds eight (8), and the inter-node trunk transmission speed is than Mbit/s or less will the national portion FTD objective be exceeded when the test frame size is 512 octets
23 Practical Measurement of transit delay Accurate measurement of transit delay requires synchronised real time clocks located at appropriate locations. Very expensivealternative technique / practical low cost method required.measure the round trip delay time of a 256 byte test frame sent to an echo facility or loop backecho facility receives a frame and retransmits the frame on the same virtual connectionecho technique standardised in Rec X.139 & ( X.148)Use OAM (FRF.19 frames) techniques as per X.148
24 Measurement of Network Transit Delay using echo technique X.36FR networkX.36EchodeviceTest DTEAccess lines can be at different speedsIdeally echo device retransmits after set period of time.Use 256 octet test frame.
25 Measurement of round trip delay time Define:Tr = round trip delay time to the echo facilityTd = access line transmission delay (1ms for 256 byte frame transmitted at kbit/s)Tnw = Network transit delayTech = Echo facility delayAssuming the echo facility is connected to destination pkt exchange by kbit/s lineTnw ~ Tr/2 - 2Td - Tech/2
26 Application of echo technique to measure national & international transit delay National network delay can be made by locating echo device at the international gateway exchangeestablish logical channels to national gateway exchange and to a destination international gateway.Definet1 = round trip delay time to national gatewayt2 = round trip delay time to destination international gatewaytint = (t2 - t1)/2 - tgwwhere tgw = transit delay of the destination gateway
27 Arrangements for Performance testing for ATM & FR 155 Mbit/s Trunk between core switchesBrisbane34 Mbit/s Trunk from core to access switchCoreSwitchAccessSwitchloopback(128 kbit/s)loopback(128 kbit/s)Legend for transmission links:d = distance [km]tp = propagation delay [ms]d = 1000 kmtp = 5 msAccessSwitchPerthd = 500 kmtp = 3 msSydneyCoreSwitchCanberraCoreSwitchCoreSwitchAccessSwitchBloopback(128 kbit/s)Ad = 500 kmtp = 3 msd = 1000 kmtp = 5 msAccessSwitchAccessSwitchd = 3500 kmtp = 17 msloopback(128 kbit/s)CoreSwitchAccessSwitchMelbourneBloopback(128 kbit/s)loopback(128 kbit/s)AAccessSwitchArrangements for Performancetesting for ATM & FRCentral MeasurementTest Equipment256 kbit/s access
28 Some Frame Relay Transfer Delay Results FR traffic test source located at Melbourne,used 512 octet test frameone way delay to other capital citiesSydney (1000 km) 11 msBrisbane (2000 km) 18 msCanberra (500km) 11 msPerth (3500 km) 24 mseach switch contributes in the order of msend to end delay dominated by propagation delay, but switching & clocking delay of the edge / access switches make noticeable contributions
29 Frame Loss Ratio Performance Rec X.146 specifies 1 X 10-3 for Class 1 networkMeasurement of Frame loss ratio for CIR trafficmean monthly figure < 1 X 10-5worst case 4 X 10-5Have we over dimensioned the network? Is our Class 0 network providing Class 3 service?Loss ratio very dependent on network dimensioning and traffic levelsAlso noting the large number of small frames (voice and TCP acknowledgment) causing some functional processors to be very heavily loaded. If the switch becomes overloaded it discards frame
30 What’s new from Q2/17 New Recs covering: FR Network Availability Metrics for FR/ATM Service Inter-workingPerformance of IP over FRFR OAM
31 FR Network Availability Availability is the percentage of time that the network can successfully transfer frames. Availability is a Key parameter often specified in SLAsTraditional ITU approach is to choose a significant primary performance parameter (eg FLR) and assess the performance of a connection against a defined threshold for that parameter.For example: If the FLR > 10% over a period of time the connection is declared to be unavailable.New Rec X.147 provides a number of options for assessing availability – based on use of OAM Frames or Status messages
32 Availability vs Connectivity Availability (ITU)represents the point at which the IP service is so bad as to be unusable: eg. extremely high packet loss will impact on the achieved transfer rate (FTP or HTTP) but the transport layer protocols will still work.(a digit bearer is consider unavailable if BER>10-3 for 10 consecutive seconds : Rec G.826)Connectivity (IETF IPPM)defines the period when there is no working route between source and destination - nothing gets through.Perhaps we need both
33 Performance of IP over FR What is the performance of an IP network when the backbone infrastructure (connectivity) is provided by FR connectionsCan the IP service classes defined by Y.1541 be supported?Propagation delay dominant for long distances. Difficult to achieve a user-to-user IPTD of 100ms on long IP Paths.New Rec X.FRIP provides guidelines for use of frame relay as the lower layer transport.
34 Metrics to characterise FR/ATM Service Interworking Performance DTEFRDTEATMFRIWFThe ATM DTE has noknowledge that it istalking to a FR DTE.The FR DTE has noknowledge that it istalking to an ATM DTE.FR / ATM Service Interworking
35 FR/ATM Service Interworking Metrics End-to-end performance or the performance of the IWF can be characterized by the following user layer parameters:Data Block Delivery RatioData Block Transfer DelayData Block Delay JitterParameters are independent of the FR or ATM Traffic Contracts
36 FR OAM SG13 developed I.620 (1998) covering FR OAM Only basic functionality defined - detection of fault conditions using loop-back framesSG13 have agreed to withdraw I.620 in favour of FRF.19Frame Relay Forum have developed FR.19Extensive capabilities to monitor primary performance parameters FTD, FLR (Data Delivery Ratio) and fault detectionFor completeness of the FR Recommendations propose new Rec X.FROAM (text to be technically aligned with FRF.19)