This labs uses traffic traces from Lab 1 and traffic generator and sink components from Lab 2.

Transcription

1 Lab 3 Packet Scheduling Purpse f this lab: Packet scheduling algrithms determine the rder f packet transmissin at the utput link f a packet switch. This lab includes experiments that exhibit prperties f well-knwn scheduling algrithms, such as is FIFO (First-in-First-ut), SP (Static Pririty), and WRR (Weighted Rund Rbin). Sftware Tls: This labs uses traffic traces frm Lab 1 and traffic generatr and sink cmpnents frm Lab 2. The surce cde f a reference implementatin fr a packet scheduler is prvided. What t turn in: Turn in a reprt with yur answers t the questins in this lab, including the plts, and yur Java cde. Versin 2 (February 25, 2008) Versin 3 (March 9, 2011) Jörg Liebeherr, All rights reserved. Permissin t use all r prtins f this material fr educatinal purpses is granted, as lng as use f this material is acknwledged in all derivative wrks.

2 Table f Cntent Table f Cntent 2 Preparing fr Lab 3 2 Cmments 2 The Packet Scheduler class 3 Part 1. FIFO Scheduling 7 Part 2. Pririty Scheduling 10 Part 3. Weighted Rund Rbin (WRR) Scheduler 15 Feedback Frm fr Lab 3 20 Preparing fr Lab 3 This lab requires the prgrams frm Labs 1 and 2. Cmments Quality f plts in lab reprt: This lab asks yu t prduce plts fr a lab reprt. It is imprtant that the graphs are f high quality. All plts must be prperly labelled. This includes that the units n the axes f all graphs are included, and that each plt has a header line that describes the cntent f the graph. Extra credit: Each part f this lab has an extra credit cmpnent (5% each). ECE 466 LAB 3 - PAGE 2 J. Liebeherr

3 The Packet Scheduler class In this lab, yu will implement three different packet scheduling algrithms. All packet schedulers can be implemented by extending the prvided PacketScheduler class. There are many similarities between the PacketScheduler class and the LeakyBucket class frm Lab 2. In essence, a PacketScheduler bject receives packets frm ne r mre traffic generatrs (TG), and frwards packet t a single traffic sink (TS). A PacketScheduler bject has three cmpnents: a scheduler receiver (SR), a scheduler Sender (SS), and ne re mre FIFO Buffers. The Scheduler Receiver SR prcesses incming packets sent by the traffic generatr(s), and adds the packet t ne f the FIFO buffers. The scheduler inspects the first byte f each arriving packet t perfrm a traffic classificatin, which determines the FIFO buffer t which the packet must be added. Imprtant: Traffic classificatin assumes that the traffic generatr sets the first byte f the packet t the crrect value. We refer t this prcess as traffic tagging. Therefre, previusly used traffic generatrs must be mdified s that they include traffic tagging. Fr example, fr a pririty scheduler, the traffic generatrs must tag each packet as either High r Lw pririty. When SR reads the tag, it can classify each packet as High r Lw pririty, and add the packet t the apprpriate FIFO buffer. The fllwing cde segment shws an example f setting and reading the first byte f data frm a packet. // set first byte t 1 and create packet ECE 466 LAB 3 - PAGE 3 J. Liebeherr

4 byte[] buf = new byte[length]; buf[0] = (byte)1; DatagramPacket packet = new DatagramPacket(buf, buf.length, destaddr, destprt); // read first byte frm packet byte value = packet.getdata()[0]; The cmpnent SS transmits packets that are backlgged in ne f the buffers. The key task f SS is the scheduling decisin, which determines the FIFO buffer frm which the next packet is transmitted. Once the decisin is made, the first packet frm the selected FIFO buffer is remved and transmitted n the link, at the specified transmissin rate. The reference implementatin f the Packet Scheduler implements the abve functins, hwever, sme cmpnents are incmplete: In the reference implementatin, SR des nt perfrm traffic classificatin. Instead, it adds packets t the first f the available FIFO buffers (the buffer with the smallest index). The scheduling decisin is simplified, in that the reference implementatin always picks a packet frm the first FIFO buffer. The recrding f arrival times in a file des nt include infrmatin frm the traffic classificatin (that is, it wuld nt cntain pririty infrmatin fr a pririty scheduler). The implementatin is prvided by the package PacketScheduler, which cnsists f fur Java classes: Class PacketScheduler Creates the cmpnents f the packet scheduler, and starts threads that run in SR and SS. An instant f PacketScheduler is created with the fllwing parameters: inprt UDP Prt number, where SR expects arriving packets. utaddress IP address t which SS sends packets. utprt UDP prt number t which SS sends packets. linkcapacity transmissin rate f the scheduler (in bits per secnd). numbuffer number f FIFO buffers. maxpacketsize Maximum size f packet that can be prcessed. (in bytes) buffercapacities[] Array cntaining the capacities f the FIFO buffers (in bytes). filename Name f file, where arrival times are recrded. Buffer This is the same FIFO Buffer that was used fr LeakyBucket. PacketScheduler creates an array f buffers, dented by Buffer[]. The implementatin f the FIFO buffers is thread safe. The buffers stre packets, which must nt exceed maxpacketsize. The ttal number f bytes that can be stred in the buffer is limited by Integer.MAX_VALUE x ECE 466 LAB 3 - PAGE 4 J. Liebeherr

5 maxpacketsize. The capacity f Buffer[i] is given by buffercapacity[i], specified in bytes. Each buffer has methds fr adding packets t the tail f the buffer and remving packets frm the head f the buffer, peeking at the first packet (withut remving it), and querying the currently ccupied buffer size (in terms f packets r bytes). When adding a newly arriving packet wuld exceed buffercapacity[i], the packet is drpped. SchedulerReceiver (SR) Waits n a specified UDP prt fr incming packets. When a packet arrives, the packet is first classified by inspecting the first byte f the packet. The cntent f the byte is mapped t an index f the FIFO buffer. The mapping depends n the type f scheduler used. Once classified, SR recrds the arrival time, size, buffer backlg f the queue, t a file. Then the packet is added t Buffer[index]: Traffic classificatin: class = {cntent f first byte}; {Map class t index f the buffer array}; add packet t Buffer[index]; If a packet cannt be added t the buffer, e.g., because the buffer is full, the packet is drpped and an errr message displayed. SchedulerSender (SS) SchedulerSender (SS) is respnsible fr selecting the buffer frm which the next packet transmissin ccurs. This is referred t as the scheduling decisin. The scheduling decisin is dependent n the type f scheduling algrithm. The scheduler remves the first packet frm the selected buffer and transmits the packet t the specified address (IP address and UDP prt). The time t transmit a packet with size L bits is cmputed t be L/linkCapacity. If the actual transmissin time is shrter than the cmputed transmissin time, SS will sleep fr the remaining time. The prcedure fr transmissin is as fllws: If (at_least_ne_buffer_is_nt_empty) determine buffer frm which packet is transmitted; remve first packet frm selected buffer; determine cmputed transmissin time f packet; transmit packet; sleep until the end f cmputed transmissin time; else wait fr packet t arrive t any buffer; // buffers wakes up SS when a packet arrives Nte: In the reference implementatin, the scheduling decisin f SS nly inspects the first buffer (Buffer[0]). The fllwing cde segment shws hw yu start PacketScheduler f the reference implementatin in a prcess. The implementatin assumes that the class PacketScheduler is in a subdirectry with name PacketScheduler : ECE 466 LAB 3 - PAGE 5 J. Liebeherr

6 imprt PacketScheduler.PacketScheduler; public class Main { public static vid main(string[] args) { /* * Create a new packet scheduler. * Scheduler listens n UDP prt 4444 fr incming *packets * and sends utging packets t lcalhst:4445. * Transmissin rate f scheduler is 2Mbps. The scheduler * has 2 queues, and accepts packets f maximum size 1024 * bytes. * Capacity f first queue is 100*1024 bytes and capacity * if secnd queue is 200*1024 bytes. * Arrivals f packets are recrded t file ps.txt. */ PacketScheduler ps = new PacketScheduler(4444, "lcalhst", 4445, , 2, 1024, new lng [] {100*1024, 200*1024}, "ps.txt"); // start packet scheduler new Thread(ps).start(); } } ECE 466 LAB 3 - PAGE 6 J. Liebeherr

7 Part 1. FIFO Scheduling The first bjective f this lab is t explre the backlg and delay at a link with a FIFO (First-In- First-Out) buffer, when the traffic lad arriving t the link is increased. The FIFO buffer perates at link capacity C=10 Mbps. The situatin is illustrated in the figure, where packets are represented as rectangular bxes. With FIFO, als referred t as FCFS (First-Cme-First-Served), packets are transmitted in the rder f their arrival. The bjective is t bserve and measure the backlg and delay at a FIFO buffer when the lad is varied. Fr traffic arrivals yu will use the cmpund Pissn prcess. Exercise 1.1 Traffic generatr fr cmpund Pissn traffic Wrk with the traffic generatr frm Exercise 2.1 in Lab 2, which is based n the cmpund Pissn arrival prcess frm Lab 1, where packet arrival events fllw a Pissn prcess with rate λ = 1250 packets/sec, and the packet size has an expnential distributin with average size 1/µ = 100 Bytes. The average rate f this flw is 1 Mbps. Dwnlad a trace with the Pissn data frm: Cnsider the traffic generatr that was built in Exercise 2.1 f Lab 2. At a link with 1 Mbps, the abve Pissn surce will generate an average lad f 10% f the link capacity. The lad f a link, als referred t as utilizatin and dented by ρ, indicates the percentage f time that a wrk-cnserving link will be busy (busy = transmitting a packet). The utilizatin is cmputed as fllws: ρ = (Average packet arrival rate) x (average transmissin time f packet) = λ x 1/(µC) Add a feature t the cde f yur traffic generatr that can re-scale the time between packet transmissins t generate an average traffic rate f N Mbps, where N = 1 (lw lad), N=5 (medium lad), N=9 (high lad). Fr example, duble the average rate f generate traffic, the distance between subsequent packets shuld be half f the distance given in the file. Test the crrectness f the traffic generatr, using the traffic sink frm Exercise 2.2 in Lab 2. ECE 466 LAB 3 - PAGE 7 J. Liebeherr

8 Exercise 1.2 Implement a FIFO Scheduler Use the reference implementatin f PacketScheduler t build a FIFO scheduler. The FIFO scheduler transmits packets in the rder f their arrivals. Nte: Set the maximum size f the buffer in the FIFO scheduler t 100 kb. If the available buffer size is t small fr an arriving packet, the packet is discarded (and a message is displayed.) Set the capacity f the link t 10 Mbps. With FIFO the scheduler nly needs a single FIFO buffer. There is n need fr traffic tagging (by the traffic generatr) r traffic classificatin (by PacketReceiver). Exercise 1.3 Observing a FIFO Scheduler at different lads Use the traffic generatr t evaluate the FIFO scheduler with cmpund Pissn traffic at different lads. Use the added feature in the traffic generatr frm Exercise 1.1 and run the re-scaled Pissn trace file with an average rate f N Mbps, where N = 1 (lw lad), N=5 (medium lad), N=9 (high lad). Fr each value f N: Cmpute the backlg and waiting time fr each packet prcessed by the packet scheduler. Nte: The backlg can be determined when a packet arrives. Determining the waiting time requires that yu knw the arrival time and the departure time f a packet. Keep track f arriving packets that are discarded. Present plts that shw the backlg, waiting time, and number f discarded packets, as a functin f time. Designate ranges f N, where the FIFO scheduler is in a regime f lw lad and high lad. Justify yur chice. Exercise 1.4 (Optinal, 5% extra credit) Unfairness in FIFO A limitatin f FIFO is that it cannt distinguish different traffic surces. Suppse that there are many lw-bandwidth surces and a single traffic surce that sends data at a very high rate. If the high-bandwidth surce causes an verlad at the link, then all traffic surces will experience packet lsses due t buffer verflws. Frm the perspective f a lw-bandwidth ECE 466 LAB 3 - PAGE 8 J. Liebeherr

9 surce, this seems unfair. (The lw-bandwidth surce wuld like t see that packet lsses experienced at the buffer are prprtinal t the traffic rate f a surce). The fllwing experiment tries t exhibit the unfairness issues f FIFO fr tw traffic surces. There are tw traffic surces, which are each re-scaled cmpund Pissn surces as in Exercise 1.1: Surce 1 sends at an average rate f N 1 Mbps. Surce 2 sends at an average rate f N 2 Mbps. Bth surces send traffic int a FIFO scheduler (with rate C=1 Mbps) and 100 kb f buffer. Run a series f experiments where the lad f the tw surces is set t (N 1, N 2 ) with N 1 = 5 and N 2 = 1, 5, 10. Recrd the average thrughput (utput rate) f each traffic surce (Nte: Yu must be able t keep track whether a packet transmissin is due t Surce 1 r Surce 2). Prepare a table that shws the average thrughput values and interpret the result. Is it pssible t write a frmula that predicts the thrughput as a functin f the arrival rate? Lab Reprt: Prvide the plts and a discussin f the plts. Als include answers t the questins. ECE 466 LAB 3 - PAGE 9 J. Liebeherr

10 Part 2. Pririty Scheduling FIFO scheduling gives all traffic the same type f service. If the netwrk carries traffic types with different characteristics and service requirements, a FIFO scheduling algrithm is nt sufficient. T differentiate traffic types and give each type a different grade f service, mre sphisticated scheduling algrithms are needed. One f these algrithms is the pririty scheduling algrithm. Fr example, cnsider a mix f file sharing traffic and vice (e.g., vice-ver-ip) traffic: File sharing traffic is high-vlume and transmitted in large packets, whereas vice-ver-ip traffic has a relatively lw data rate and is transmitted in shrt packets. If the traffic is handled by a FIFO scheduler, as shwn belw, then vice packets may experience a pr grade f service dependent n the n the arrivals f file sharing packets. FIFO scheduler A pririty scheduler can imprve the service given t vice packets by giving vice packets higher pririty. A pririty scheduler always selects the packet with the highest pririty level fr transmissin. scheduler Pririty A pririty scheduler assumes that incming traffic can be mapped t a pririty level. A traffic classificatin cmpnent f the scheduler uses an identifier in incming packets t perfrm this mapping. The identifier can be based n surce and destinatin addresses, applicatin type applicatin type (e.g., via the prt number), r ther infrmatin in packet headers. Pririty schedulers are als referred t as static pririty (SP) r Head-f-Line (HOL) schedulers. In this part f the lab, yu will design and implement a pririty scheduler with tw pririty levels, as shwn in the Figure belw. Traffic is transmitted t the scheduler frm tw surces: a cmpund Pissn surce and a vide surce. The surces mark packets with a tag: 1 fr packets frm the Pissn surce and 2 fr packets frm the vide surce. A traffic classifier at the pririty scheduler reads the identifier. Packets with tag 1 are handled as lw pririty, and packets with tag 2 are handled as high pririty packets. ECE 466 LAB 3 - PAGE 10 J. Liebeherr

11 Exercise 2.1 Transmissin f tagged packets Build a traffic generatr as shwn n the left hand side f the figure abve. The requirements fr the transmissin f packets are as fllws: Build a traffic generatr fr a vide tracefile and fr a Pissn tracefile. The transmissins f the vide surce and the Pissn surce are perfrmed by tw distinct prgrams. The Pissn tracefile is the tracefile frm Part 1. The transmissin f the vide surce is frm the vide tracefile, used in previus labs: Nte: The average rate f traffic frm the vide surce is apprx. 15 Mbps. A traffic generatr fr the vide surce can be build by re-using the cde frm Exercise 1.2 and Exercise 2.1 frm Lab 2. As in Lab 2, the maximum amunt f data that can be put int a single packet is 1480 bytes. Frames exceeding this length are divided and transmitted in multiple packets. The transmissin f the Pissn surce is determined by the Pissn traffic generatr built in Exercise 1.1 f this lab (Lab 3). The traffic generatr must be able t run the rescaled Pissn trace file with an average rate f N Mbps, where N = 1 (lw lad), N=5 (medium lad), N=9 (high lad). ECE 466 LAB 3 - PAGE 11 J. Liebeherr

12 Befre a packet is transmitted it must be tagged with an identifier, which is lcated in the first byte f the paylad. The identifier is the number 0x01 fr packets frm the Pissn surce and 0x02 fr the vide surce. Packets are transmitted t a remte UDP prt. Bth surces transmit UDP datagrams t the same destinatin prt n the same hst (e.g., prt 4444). Yu may use a traffic sink as build fr Exercise 2.2 f Lab 2 fr testing the implementatin. Exercise 2.2 Packet classificatin and pririty scheduling Build a traffic classificatin and scheduling cmpnent as shwn n the right hand side f the abve figure. The pririty scheduler cnsists f tw FIFO queues: ne FIFO queue fr high pririty traffic and ne FIFO queue fr lw pririty traffic. Set the maximum buffer size f each FIFO queue t 100 kb. The pririty scheduler always transmits a high-pririty packet, if the high pririty FIFO queue cntains a packet. Lw pririty packets are selected fr transmissin nly when there are n high pririty packets. The transmissin rate f the link is C=20 Mbps. The traffic classificatin cmpnent reads the first byte f the paylad f an arriving packet and identifies the pririty label. Once classified, packets are assigned t the pririty queues. Vide traffic (with label 2 ) is assigned t the high pririty queue and Pissn traffic (with label 1 ) is assigned t the lw pririty queue. If a new packet arrives when the link is idle (i.e., n packet is in transmissin and n packet is waiting in the FIFO queues) the arriving packet is immediately transmitted. Otherwise, the packet is enqueued in the crrespnding FIFO queue. The pririty scheduler is wrk-cnserving: As lng as there is a packet waiting, the scheduler must transmit a packet. Packet transmissins is nn-preemptive: Once the transmissin f a packet has started, the transmissin cannt be interrupted. In particular, when a lw pririty packet is in transmissin, an arriving high-pririty packet must wait until the transmissin is cmpleted. Test the implementatin with the traffic generatr frm Exercise 2.1. Exercise 2.3 Evaluatin f the pririty scheduler Evaluate the pririty scheduler with the traffic generatr Exercise 2.1 using the fllwing transmissin scenaris: The vide surce transmits accrding t the data in the tracefile (see Exercise 2.1). ECE 466 LAB 3 - PAGE 12 J. Liebeherr

13 As in Exercise 1.1, the Pissn surce shuld be scaled s that it transmits with an average rate f N Mbps, where N = 1 (lw lad), N=5 (medium lad), N=9 (high lad). Fr each value f N, determine the fllwing values fr bth high pririty (vide) and lw pririty (Pissn) traffic: Cmpute the backlg and waiting time fr each packet prcessed by the packet scheduler. Nte: The backlg can be determined when a packet arrives. Determining the waiting time requires that yu knw the arrival time and the departure time f a packet. Keep track f arriving packets that are discarded. Present plts that shw the backlg, waiting time, and number f discarded packets, as a functin f time. Cmpare the utcme t Exercise 1.3. Exercise 2.4 (Optinal, 5% extra credit) Starvatin in pririty schedulers A limitatin f SP scheduling is that it always gives preference t high-pririty scheduling. If the lad frm high-pririty traffic is very high, it may cmpletely pre-empt lw-pririty traffic frm the link. This is referred t as starvatin. The fllwing experiment tries t exhibit the starvatin f lw pririty traffic. The experiment is similar t the last exercise f Part 1. The link capacity shuld be set t C=10 Mbps. Cnsider the previusly build pririty scheduler with tw pririty classes. There are tw traffic surces, which are each re-scaled cmpund Pissn surces as in Exercise 1.1: Surce 1 transmits at an average rate f N 1 Mbps. Surce 2 transmits at an average rate f N 2 Mbps. Traffic frm Surce 1 is labelled with identifier 1 (lw pririty) and Surce 2 is labelled with 2 (high pririty). Bth surces send traffic t the pririty scheduler (with rate C=10 Mbps) and 100 kb f buffer fr each queue. Run a series f experiments where the lad f the tw surces is set t (N 1, N 2 ) with N 1 = 5 and N 2 = 1, 5, and 9. Recrd the average thrughput (utput rate) f each traffic surce. ECE 466 LAB 3 - PAGE 13 J. Liebeherr

14 Prepare a table that shws the average thrughput f high and lw pririty traffic and interpret the result. Cmpare the utcme t Exercise 1.4. Lab Reprt: Prvide the plts and a discussin f the plts. Als include answers t the questins. ECE 466 LAB 3 - PAGE 14 J. Liebeherr

15 Part 3. Weighted Rund Rbin (WRR) Scheduler Many scheduling algrithms attempt t achieve a ntin f fairness by regulating the fractin f link bandwidth allcated t each traffic surce. The bjectives f a fair scheduler are as fllws: If the link is nt verladed, a traffic surce shuld be able t transmit all f its traffic. If the link is verladed, each traffic surce btains the same rate guarantee, called the fair share, with the fllwing rules: If the traffic frm a surce is less than the fair share, it can transmit all its traffic; If the traffic frm a surce exceeds the fair share, it can transmit at a rate equal t the fair share. The fair share depends n the number f active surces and their traffic rate. Suppse we have set f surces where the arrival rate f Surce i is r i, and a link with capacity C (bps). If the arrival rate exceeds the capacity, i.e., that satisfies the equatin:, then the fair share is the number f As an example, suppse we have a link with capacity 10 Mbps, and the arrival rates f flws are r 1 =8 Mbps, r 2 = 6 Mbps, and r 3 = 2 Mbps, then the fair share is f = 4 Mbps, resulting in an allcated rate is 4 Mbps fr Surce 1, 4 Mbps fr Surce 2, and 2 Mbps fr Surce 3. Since different surces have different resurce requirements, it is ften desirable t assciate a weight (w i ) with each surce, and allcate bandwidth prprtinally t the weights. In ther wrds, a surce that has a weight twice as large f secnd surce shuld be able t btain twice the bandwidth f the secnd surce. With these weights, the fair share f at an verladed link, i.e., is btained by slving. Fr example, using the previus example, and assigning weights w 1 =3, w 2 =w 3 =1, the allcated rates are 6, 2, and 2 Mbps fr the three surces. A scheduling algrithm that realizes this scheme withut weights is called Prcessr Sharing (PS) and with weights Generalized Prcessr Sharing (GPS). Bth PS and GPS are idealized algrithms, since they treat traffic as a fluid. Realizing fairness in a packet netwrk turns ut t be quite hard, since packet sizes have different sizes ( bytes) and packet transmissins cannt be interrupted. Many cmmercial IP ruters and Ethernet ECE 466 LAB 3 - PAGE 15 J. Liebeherr

16 switches (nt the cheap nes!) implement scheduling algrithms that apprximate the GPS scheduling algrithm. A widely used (and easy t implement) scheduling algrithm that apprximates GPA is the Weighted Rund Rbin (WRR) scheduler. The bjective f this part f the lab is implementing and evaluating a WRR scheduling algrithm. A WRR scheduler, illustrated in the figure abve, perates as fllws: The scheduler has multiple FIFO queues. A traffic classificatin unit assigns an incming packet t ne f the FIFO queues. The WRR scheduler perates in runds. In each rund the scheduler visits each queue in a rund-rbin (sic!) fashin, starting with Queue 1. During each visit f a queue ne r mre packets may be serviced. The WRR assumes that ne can estimate (r knw) the average packet size f the arrivals t Queue i, dented by L i. The WRR calculates the number f packets t be served in each rund: Fr each Queue i: x i = w i / L i x = min i { x i } Fr each Queue i: packets_per_rund i = x i / x Once all packets f a rund are transmitted r if n mre packets are left, the scheduler visits the next queue. ECE 466 LAB 3 - PAGE 16 J. Liebeherr

17 Exercise 3.1 Build a WRR scheduler Build a WRR scheduler as described abve, that supprts at least three queues. The WRR will serve Pissn traffic surces as used in Parts 1 and 2 f this lab. A WRR scheduler requires ne FIFO buffer (queue) fr each flw. There are three traffic generatrs that each transmit re-scaled Pissn traffic as dne in Exercise 1.1. Each Pissn surce is re-scaled s that it transmits with an average rate f N Mbps, where N = 1 (lw lad), N=5 (medium lad), N=9 (high lad). Each transmitted packet is labelled with 1, 2 r 3 as dne in Part 2 f this lab. The label is ne byte lng. The traffic classificatin cmpnent reads the first byte f the paylad f an arriving packet, and adds the packet t the queue (Packets with label 1 are assciated with Queue 1, etc.). If n packet is in transmissin r in the queue, and arriving packet is transmitted immediately. The transmissin rate f the link is C=10 Mbps. The maximum buffer size f each queue is 100 kb. An arrival that cannt be stred in the queue is discarded. Once the implementatin is cmpleted and tested, mve n t the evaluatin. Exercise 3.2 Evaluatin f a WRR scheduler: Equal weights Evaluate the WRR scheduler with three Pissn surces. The weight N f the traffic generatrs are set t N=8 in fr the first surce, N=6 fr the secnd surce and N=2 fr the third surce, resulting in traffic arrival rates f 8 Mbps, 6 Mbps, and 2 Mbps. Set the weights f the queues t w 1 =w 2 =w 3 =1. Nte: Cmpare this scenari t the first figure f Part 3. The average lad n the link is 1.5 Mbps, i.e., the link is verladed. We expect that the bandwidth at the link is shared amng the surces at a rati f 4:4:2. Prepare plts that shw the number f packet transmissins and the number f transmitted bytes frm a particular surce (y-axis) as a functin f time (x-axis). Prvide ne plt fr each surce. ECE 466 LAB 3 - PAGE 17 J. Liebeherr

18 Select a reasnable time scale fr the x-axis, e.g., a time scale f 10 ms per data pint. Cmpare the plts with the theretically expected values f a PS scheduler. Exercise 3.3 Evaluatin f a WRR scheduler: Different weights This exercise re-creates a transmissin scenari as in the secnd figure f Part 3. Evaluate the WRR scheduler with three Pissn surces. As befre, the weight N f the traffic generatrs is set t N=8 in fr the first surce, N=6 fr the secnd surce and N=2 fr the third surce. Set the weights f the queues t w 1 =3 and w 2 =w 3 =1. Nte: Cmpare this scenari t the secnd figure f Part 3. We expect that the bandwidth at the link is shared amng the surces at a rati f 6:2:2. Prepare plts that shw the number f packet transmissins and the number f transmitted bytes frm a particular surce (y-axis) as a functin f time (x-axis). Prvide ne plt fr each surce. Cmpare the plts with the theretically expected values f a GPS scheduler. Exercise 3.4 (Optinal, 5% extra credit) N Unfairness and n Starvatin in WRR A limitatin f SP scheduling is that it always gives preference t high-pririty scheduling. If the lad frm high-pririty traffic is very high, it may cmpletely pre-empt lw-pririty traffic frm the link. This is referred t as starvatin. The fllwing experiment tries t shw that WRR des nt suffer frm the prblems f FIFO (unfair) and SP (starvatin). The experiment retraces the steps f Exercises 1.4 and 2.4. Cnsider the WRR scheduler frm abve with rate C=10 Mbps and 100 kb f buffer fr each queue. There are tw traffic surces, which are each re-scaled cmpund Pissn surces as in Exercise 1.1: Surce 1 transmits at an average rate f N 1 Mbps. Surce 2 transmits at an average rate f N 2 Mbps. Traffic frm Surce 1 is labelled with identifier 1 (lw pririty) and Surce 2 is labelled with 2 (high pririty). Bth surces are assigned the same weight at the WRR scheduler (w 1 =w 2 =1). Run a series f experiments where the lad f the tw surces is set t (N 1, N 2 ) with N 1 = 5 and N 2 = 5, 9, 15. ECE 466 LAB 3 - PAGE 18 J. Liebeherr

19 Recrd the average thrughput (utput rate) f each traffic surce. Prepare a table that shws the average thrughput f the tw surces and interpret the result. Lab Reprt: Cmpare the utcme t Exercises 1.4 and 2.4. Prvide the plts and a discussin f the plts. Als include answers t the questins. ECE 466 LAB 3 - PAGE 19 J. Liebeherr

20 Feedback Frm fr Lab 3 Cmplete this feedback frm at the cmpletin f the lab exercises and submit the frm when submitting yur lab reprt. The feedback is annymus. D nt put yur name n this frm and keep it separate frm yur lab reprt. Fr each exercise, please recrd the fllwing: Part 1. FIFO Scheduling Difficulty (-2,-1,0,1,2) -2 = t easy 0 = just fine 2 = t hard Interest Level (-2,-1,0,1,2) -2 = lw interest 0 = just fine 2 = high interest Time t cmplete (minutes) Part 2. Pririty Scheduling Part 3. Weighted Rund Rbin (WRR) Scheduler Please answer the fllwing questins: What did yu like abut this lab? What did yu dislike abut this lab? Make a suggestin t imprve the lab. ECE 466 LAB 3 - PAGE 20 J. Liebeherr