D-Link QoS Technology Brief

1. D-Link QoS Technology Brief Arthur Chiang Ethernet Switch Product Dept. Jan 2011 HQ

2. Agenda • What is QoS • Policing • Prioritizing • Rate Limiting • Three Color Marker • Queuing • Scheduling • Congestion Control • Shaping

3. QoS is a set of techniques to manage network resources, including delay, delay variation, bandwidth and packet loss. Users or data flows are able to be guaranteed a certain level of performancethrough these functions. Policing Policing QoS QoS Queuing Queuing What is Quality of Service (QoS)Definition

4. Policing A given policy to prioritize or limit the maximum data rate of traffic. Policy can be port-based, flow-based, queue-based. Queuing Manages the data stored in device buffer memory. Decides the sequence of data forwarding. Allocates the buffer resource. What is Quality of Service (QoS)Explanation of Features

5. Agenda What is QoS Policing Prioritizing Rate Limiting Three Color Marker Queuing Scheduling Congestion Control Shaping

6. Two kinds of priority tags IEEE 802.1p tag in L2 Ethernet header Usually inserted by switches as part of 802.1Q VLAN tag according to the policy bound on the ingress port. Might not be carried across L3 networks as it is a L2 tag (Note) DSCP (IP Precedence) tag in L3 IP header. A field of IP header with default value 0. Usually modified by applications such as VoIP, IP-TV, and P2P based on the prioritization needs. Can be carried across L3 networks L3 Header Data ToS L2 Header 802.1Q Delay/Cost/… IP Precedence 802.1p CFI VLAN ID 5bits 3bits 12bits 3bits 1bit DSCP 8bits PrioritizingPriority Tags

7. Priority Queues Switch will store all the packets into port egress buffer before transmitting it. Eachegress buffer is divided into several priority queues and packets stored in higher queues will be served first. Generally speaking, packets with higher priority tag will be mapped to higher queues. However, it can be changed according to the policies of switch itself. PrioritizingSequence of Packet Forwarding Queue Mapping Add Priority Tag Ingress Egress Queue Buffer Highest Priority Higher Priority Lower Priority Lowest Priority

8. Prioritize traffic of endpoints on different ports Insert the priority tag to untagged packets according to the port default priority. Map packets with higher priority tag to higher queue. Policy (Default Port Priority) Action: Add 802.1p tag with low priority Policy (Default Port Priority) Action: Add 802.1p tag with middle priority Prioritizing Applications of Prioritizing High Priority Middle Priority Low Priority No Priority Client-1 IP Phone Client-2

9. Advanced PrioritizingChange Priority Tag and Queue Mapping • Change priority tag • Using ACL to match specific flow (eg. IP, protocol type) and force the change of priority tag of packets. • Change queue mapping • Using either L2 (802.1p) or L3 (DSCP) priority tag to map the system queue. • Force the change of the queue mapping for specific flow by using ACL. Change Priority Tag Change Queue Mapping Add Priority Tag Queue Mapping Change Priority Tag Ingress Egress Queue Buffer Highest Priority Higher Priority Lower Priority Lowest Priority

10. Prioritizes different network services on the same port If two or more applications are in the same port, replace the priority tag of critical applications to make sure it will be served first. Local prioritization For a user or application that need priority in local network only: Changing the priority queue mapping, instead of replacing the priority tag, can limit the impact of the prioritization. Same service level in the internet Policy (ACL Rule) Match: VoIP Protocol Action: Replace priority tag with ‘high’ Policy (ACL Rule) Match: Client-1 MAC Address Action: Force mapping to high queue Advanced Prioritizing Applications of Prioritizing Client-2 ERP Server Client-1 High Priority Middle Priority Low Priority Client-1 IP Phone Client-2

11. Guarantee the service level in the network Set priority policies on access ports of edge switches. Keep the consistent queue mapping policy among the network to save system resource of backbone switches. Policy: Voice changes to high priority Policy: Data changes to low priority Summary Planning Priority Policy for Network High priority maps to high queue High priority maps to high queue High priority maps to high queue High priority maps to high queue Voice Lowpriority maps to low queue Low priority maps to low queue Low priority maps to low queue Low priority maps to low queue Data High Priority Low Priority

12. Rate Limiting A given threshold fordata flow. User can set up QoS actions for traffic exceeding the threshold. Such as:- Drop (Bandwidth Control)- Replacepriority tag- Delay forwarding (Shaping) Rate LimitingDefinition of Rate Limiting bps Action Rate Time Rate Limiting

13. Port-based Rate limiting Hard limits the ingress/egress data rate per physical port, regardless of the content of the data. Manages the data rate at access layer devices, preventing the overloading of backbone networks. Flow-based Rate limiting Controls the data rate of a specific flow by using ACL rules, for example, a specific IP or L4 protocol. Well manages the bandwidth or QoS policies for service running on thephysical ports. Queue-based Rate limiting Hard limits the ingress/egress data rate per egress queue basis, regardless of the content of the data. Prevents the egress bandwidth from being occupied by a specific queue, especially in the applications of Strict Priority scheduling and 3 color marker. Rate LimitingType of Rate Limiting Note: Most of the switch controllers support only drop action on Queue-based Rate Limiting nowadays

14. For some critical applications or customer-signed Service Level Agreement (SLA), administrators define two thresholds for better bandwidth allocation and service quality. Committed Information Rate (CIR): A guaranteed data rate of traffic. The sum of all CIR must be smaller than corresponding physical interface or the bandwidth cannot be guaranteed. Peak Information Rate (PIR): A maximum data rate of traffic. Sometimes called Exceed Information Rate (EIR). Usually, switch will do best-effort delivery for traffic exceeding CIR and drop the traffic exceeding PIR. However, the action can be changed depending on different environment. Rate LimitingAdvanced Rate Limiting bps bps Action Action 2 Rate PIR Action 1 CIR Time Time Single Rate Two Rate

15. Three Color Marker borrows the DSCP value inIP header as the color code. There are three color codes – red, yellow and green, and the ‘DSCP’ to ‘color code’ mapping can be defined by users. Two different Color Marker mechanisms: RFC2697 Single Rate Three Color Marker (srTCM): Adds color tag according to configured buffer size; Focuses more on the size of packets. RFC2698 Two Rate Three Color Marker (trTCM): Adds color tag according to data rates; Focuses more on the data rates. Two different operating modes for 3 color marker Color blind mode:Do not trust the original DSCP value in packet; assume all packets are uncolored. Usually used at access layer network. Color aware mode: Trust the original DSCP value in packet; assumeall packets are colored. Usually used at aggregation/core layer. Rate LimitingAdvanced Rate Limiting – Three Color Marker

16. The srTCM meters a traffic stream and marks its packets according to three traffic parameters: CIR, Committed Buffer Size (CBS) and Excess Buffer Size (EBS). A packet is marked green if it does not exceed the CBS, yellow if it does exceed the CBS, but not the EBS, and red otherwise. Three Color MarkerSingle Rate Three Color Marker Buffer Memory Mark Green Mark Red CIR Mark Yellow CBS EBS

17. The trTCM meters a traffic stream and marks its packets according to twotraffic parameters: CIR and PIR. A packet is marked green if it does not exceed the CIR, yellow if it does exceed the CIR, but not the PIR, and red if it exceed PIR. Three Color MarkerTwo Rate Three Color Marker Buffer Memory Mark Red PIR Mark Yellow CIR Mark Green

18. Three Color MarkerColor Blind/Aware Mode Process • Color Blind Mode • Meters and marks color tag to the packet according to the CIR/PIR or CBS/EBS. • Drop Red packets and remark the DSCP tag to Green or Yellow according to the color tag. • Color Aware Mode • Meters the Green and Yellow traffic and mark to Yellow or Red according to the CIR/PIR or CBS/EBS. • Drop Red packets and remark the DSCP tag of Green packets to Yellow for over-threshold Green traffic. Revise ColorTag Drop Policer 3 Color Marker Queue Mapping R G Y R Y G R Y Ingress Egress Queue Buffer Queue Buffer

19. Set color blind mode and high CIRfor important services at access switches. Set color aware mode to simplify the configuration and unify the QoS policy on aggregation switches. Make sure the green traffic won’t exceed the physical bandwidth. Policy: - Green: Transparent (Do nothing)- Yellow: Set PIR for yellow Action: - Drop Red packet Policy: - VoIP, Admin with high CIR, PIR - Employee with middle CIR, PIR - Guest with low CIR, PIR Action: - RemarkDSCP of Green/Yellow packet - Drop Red packet Physical port bandwidth Traffic Three Color MarkerPlanning a Service Guaranteed Network with Three Color Marker … … Green Traffic

20. Rate LimitingSummary • For single user/service per port, use port-based rate limiting with drop action to control the traffic bandwidth. • For multiple users/services per port, use flow-based rate limiting with drop action to prevent the interference between each service. • To maximize the port bandwidth usage and also guarantee the service level of each service in a multiple users/services per port, use three Color marker function to fine tune the traffic among the port. • Mark Green for minimum bandwidth of each serviceto make sure it will be served first. • Mark Yellow for maximum bandwidth of eachservice, doing best effort forwarding whentraffic conflict. • Mark Red for traffic exceed the maximumbandwidth of each service, drop thesepackets to limit the maximum bandwidthof this port. IPTV VoIP CIR CIR PIR PIR PIR Data CIR Total UNI (User Network Interface) Bandwidth

21. Agenda What is QoS Policing Prioritizing Rate Limiting Three Color Marker Queuing Scheduling Congestion Control Shaping

22. Traditional scheduling mechanism First-In First-Out (FIFO) Queuing, Strict Priority Queuing (SPQ), Round-Robin, Weighted Round-Robin (WRR) Queuing More accurate scheduling is required to make the egress bandwidth usage more properly Fair Queue (FQ), WFQ, Deficit Round Robin (DRR), WDRR: Forwarding/scheduling decision is made by byte count and utilization of queues, the true weight of each queue. Smooth Forwarding: Fairly distributes packets with different priorities in each weighted round, making the weight of queues not impacted by priority. Compound scheduling mechanism is required to well control various IP services nowadays ST + *RR: Mission critical services, such as VoIP & VOD, have to be forwarded without any delay, while other services can share the rest of bandwidth by using any kind of round-robin mechanism. SchedulingScheduled Data Forwarding

23. WRR SchedulingExample of Scheduling High Priority Middle Priority Low Priority • FIFO: Do not change the sequence of traffic. First-in, first-out. • SPQ: Packets with higher priority will always be served first. However, if higher queues are always occupied, traffic in lower queues will never be forwarded. • WRR: Packets will be forwarded depending on the assigned weight (number of packets) of each queue. The forwarding ticket will jump to next queue when “weight” is reached or queue is empty. It solves the problem of SPQ, however, the switch’s real output may not match the weight settings if the packet size of each priority is different. FIFO SPQ

24. DRR/ WFQ Smoothed Round Robin SchedulingExample of Scheduling (continue) High Priority Middle Priority Low Priority • DRR/WFQ: Use byte count instead of packet count as the weight index. The allowed forwarding byte of each queue will increase every round. If the size of next packet is greater than allowed forwarding byte, round-robin mechanism will skip this queue until its allowed forwarding byte is greater than the packet size. It makes the real output more like the weight configuration. • Smooth Forwarding:Makes rapid passes for each queue and use more turns for high queues instead of waiting all packets transmitted in high queues. 3rd 1st round 2nd

25. When ports are overloading, traffic congestion will happen In traditional device, packets will be dropped when corresponding queue is full (Tail-drop). However, Tail-drop causes TCP global synchronization (Note) problem when burst traffic happens. Congestion ControlTraditional Congestion Control Queue 1 Drop Queue 2 Egress Ingress Queue 3 Queue 4

26. To avoid TCP global synchronization, some new drop algorithm were presented: Random Early Detection (RED): Drop packets based on the utilization of queues. By randomly dropping packets prior to congestion, RED informs packet sources decreasing its transmission rate. It prevents the TCP global synchronization (Note) problem and makes queue usage fairer when traffic burst happens. Weighted Random Early Detection (WRED): Associates with the weight of queues, higher drop rate for lower priority queue. Simple Random Early Detection (SRED): Define the drop rates for color tags in specific queue. Assure the QoS not to be impacted especially for Green packets. Congestion ControlRandom Early Detection (RED) Queue 1 Random Drop Queue 2 Egress Ingress Queue 3 Queue 4 Random Drop RED Threshold

27. To lower the packet lose rate, almost all switch controllers have built-in expensive buffer memory to prevent the data re-transmission. Switch stores the traffic in buffer memory and delays the transmission until the egress bandwidth is available. However, the best-effort traffic shaping is no longer enough for the QoS requirement nowadays. ShapingTraditional Devices Buffer Memory bps bps Store to buffer Max. Switching Capacity Time Time Data Data Delay Forwarding Delay Forwarding

28. Due to device buffer memory is limited, reserve the resource for important applications can improve the quality of service. Configurable buffer size: Committed Burst Size (CBS) for Green packets Peak Burst Size (PBS), Excess Burst Size (EBS) for Yellow packets. ShapingFlow-based Traffic Shaping Drop No reservation for Data exceeding CIR PIR CBS for Data Buffer Memory PBS for IPTV bps CIR Drop Drop Max. Switching Capacity Data Store to PBS Store to PBS PIR Time Store to CBS Store to CBS Overall Output CIR Delay Forwarding Delay Forwarding CBS for IPTV IPTV