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DiffServ ENTC 345 Dr. Ana Goulart Assistant Professor.

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Presentation on theme: "DiffServ ENTC 345 Dr. Ana Goulart Assistant Professor."— Presentation transcript:

1 DiffServ ENTC 345 Dr. Ana Goulart Assistant Professor

2 Announcement Homework#6 due next Monday

3 Announcements Syllabus Course Topics Network Simulation – Introduction to Opnet Protocol Architecture Wide Area Networks –Frame Relay Local Area Networks Ethernet WLANs Internet and Transport Protocols Quality of Service Architectures Internet Applications – Multimedia and Internet Telephony

4 Announcements Today (Monday) Quality of Service (Ch. 19) WFQ with different weights DS codepoint (TOS byte) Voice-over-IP (Ch. 24) Reminder – Throughput calculation of WLANs

5 Generalized Processor Sharing (GPS) WFQ calculates the finish number for each packet as if it was served by GPS, and then use this finish number to order the service of packets. scheduler N Connections Equal weights Bandwidth 1N1N Bandwidth to each Connection

6 Generalized Processor Sharing (GPS) For different weights: scheduler w1 Bandwidth Scheduler servers an infinitesimal from each connection in turn. w2 wn Queue with weight w1 will have a fraction equal to w1/(Σ i w i ) of the total bandwidth of the outgoing link.

7 Computing finish numbers Packet size/weight + the greater of The finish number of the previous packet in the same queue The current round number F(i, k, t) = P(i, K, t) + max { F(i, k-1, t), R(t) } i = connection identifier k = packet identifier t = time t wi

8 Weighted Fair Queuing Example (1 st part) Assume a WFQ Scheduler with 3 queues (connections) wA = 1, wB=2, wC= 1 Packets of size 1, 2, and 2 units arrive at time 0 on connections A, B, and C. The link rate is 1.0 unit/second Initialize the system with R(t) = 0.

9 WFQ Example – t = 0 A (1)B (2)C(1) TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T=

10 WFQ Example – t = 1 ABC TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T= T=

11 WFQ Example – t = 2 ABC TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T= T= T=

12 WFQ Example – t = 3 ABC TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T= T= T= T=

13 WFQ Example – t = 4 ABC TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T= T= T= T= T=

14 WFQ Example – t = 4 ABC TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T= T=43110*1 21 After 4 units of time, each connection has received 4*0.25 = 1 units of service. That is enough service for the first and second packets to depart, but only half enough for connection C.

15 WFQ Example – t = 5 ABC TimeConnectionsRoundFinish # Rem.Finish #Rem.Finish #Rem. T= T=43110*1 21 T=51210*1 2

16 Actual delivery times Note the finish numbers are not the times when the packets complete service. The first packet to be serviced is packet 1 from A or packet 1 from B. Assume scheduler chooses to deliver packet from B. Service is completed at time 2. The second packet to be serviced is packet from A, which completes at time 3. The third packet to be serviced is packet from C, which completes at time 5. BBACC T=5

17 Differentiated Services

18 Differentiated Services - Overview IP packets are labeled using the DS field (or TOS – Type of Service field) All traffic with the same DS octet is treated the same by the network service

19 VERS HLENTOTAL LENGTH IDENTIFICATION FLAGSFRAGMENT OFFSET TIME TO LIVEPROTOCOLHEADER CHECKSUM SOURCE IP ADDRESS DESTINATION IP ADDRESS PADDING IP OPTIONS (IF ANY) DATA SERVICE TYPE … IP Header - originally

20 IP Header Service type TOS byte – Type of service DTR 3 1 (Unused bit) Precedence higher => better service routers dont look at these bits (DTRM) DS (Differentiated Services) octet M

21 IPv4 Precedence Service IPv4 TOS field included subfields precedence (3 bit) - datagram urgency/priority TOS(4 bit) - guidance on selecting next hop DTR 3 1 (Unused bit) Precedence higher => better service M

22 IPv4 Precedence Service IPv4 TOS field included subfields precedence (3 bit) - datagram urgency/priority TOS(4 bit) - guidance on selecting next hop DTR 3 1 (Unused bit) Precedence higher => better service M Precedence: 111 – Network Control 110 – Internetwork control 101 – Critical 100 – Flash Override … Routine

23 Recommended values for TOS field ApplicationMinimize delay Maximize throughput Maximize reliability Minimize Monetary cost Telnet1000 FTP - data0100 TFTP1000 DNS (UDP)1000 SNMP0010 NNTP0001 However, most routers do not look at those bits.

24 Differentiated Services Routers deal with each packet individually and do not have to save state information on packet flows -> per-hop behavior (phb) Services (specified in TOS bits): Expedited Forwarding PHB Assured Forwarding PHB

25 DS Field (6 bits) Keeps compatibility with original precedence bits

26 Differentiated Services Domains

27 DS Configuration and Operation within domain, interpretation of DS code points is uniform interior nodes implement simple mechanisms per-hop behavior (PHB) on all routers boundary nodes have PHB & more sophisticated mechanisms hence most of complexity

28 DS Traffic Conditioner


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