Качество обслуживания QoS

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    03-Oct-2015

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QoS

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<ul><li><p>*QoS (Quality of Service)</p></li><li><p> QoS?: QoS IP/Ethernet - : - . , QoS:Video-on-Demand (VOD), VOIP, : , , . , , .</p><p>*: QoS.</p></li><li><p> IEEE 802.1p*</p></li><li><p> 802.1p ( , CoS)*CFIVID3 bits1 bit12 bits 802.1Q TCI, 3- CoS CoS - 0 ( ) 7 ( ). CoS</p><p> TPID : Tag Protocol Identifier, 802.1Q TPID = 0x8100 CFI : Canonical Format Indicator, 0 Ethernet VID : VLAN ID, 4096 VLAN 802.1Q VLAN </p></li><li><p>*QoS MAN MAN :VoIP- QoS 5IPTV- QoS 4DataManagement Internet Intranet (Local) - QoS 7- QoS 3- QoS 0: QoS- , . </p></li><li><p>* oS MAN </p><p>CoS PriorityTypical Application111 (7) ( )110 (6) ( )101 (5) 100 (4)011 (3) (SIP)010 (2) 001 (1) 000 (0) </p></li><li><p>IEEE 802.1p , 802.1p/1q . 0.</p><p>DES-3200-26:4# show 802.1p default_priorityCommand: show 802.1p default_priorityPort Priority------ ------------- 1 02 03 0</p><p>config 802.1p default_priority *</p></li><li><p>CoS MappingCoS Mapping QoS (IEEE 802.1p) CoS ( )*</p></li><li><p>* 802.1p . , , 1p. DGS-3627G:4# show 802.1p user_priorityCOS Class of TrafficPriority-0 -&gt; Priority-1 -&gt; Priority-2 -&gt; Priority-3 -&gt; Priority-4 -&gt; Priority-5 -&gt; Priority-6 -&gt; Priority-7 -&gt; config 802.1p user_priority DES-3200-26:4# show 802.1p user_priorityCOS Class of TrafficPriority-0 -&gt; Priority-1 -&gt; Priority-2 -&gt; Priority-3 -&gt; Priority-4 -&gt; Priority-5 -&gt; Priority-6 -&gt; Priority-7 -&gt; CoS Mapping</p></li><li><p>* , , :- FIFO- Priority queuing ( )- Weighted round robin (WRR) ( )- Custom queuing (, )- Shared Round Robin (SSR) ( </p></li><li><p> FIFO*FIFO , </p><p> , B 1FIFOHW FIFO , . .</p><p> .</p><p> , </p></li><li><p> , . </p><p> , . , , . , . . (Strict Priority)*</p></li><li><p>* (Realtime service)456142563</p></li><li><p>* , (WRR) , , .., , .</p><p> . , . , , . (Class of Service (CoS)) 8- .</p><p> config scheduling (WRR), 8 . , max_packets 0. max_packet , (). CoS, . 0 15 .</p><p>config scheduling {max_packet } (Weighted Round-Robin)</p></li><li><p>* (WRR)WRR </p><p> BTail-DropWREDWRR Weight Round RobinHW WRR System 1 (40%) 3 (20%) 2 (30%) 8 (10%)....Tail-DropWREDTail-DropWREDTail-DropWRED....Class 1Class 2Class 3Class 8</p></li><li><p>*138111214161513 (WRR)</p></li><li><p>: B D VoIP, (QoS) .TTUUUUB VoIPD VoIPACDES3526_ADES3526_B* Port-Based QoS</p></li><li><p> DES-3526_A1. , Des-3526_1 2 untagged tagged , 1p . config vlan default delete 1config vlan default add tagged 1</p><p>2. 23, VoIP, 0 7. config 802.1p default_priority ports 23 7 </p><p>3. .</p><p> DES-3526_B1. , Des-3526_1 2 untagged tagged , 1p . config vlan default delete 1config vlan default add tagged 1</p><p>2. 24, VoIP, 0 7.config 802.1p default_priority ports 24 7 </p><p>3. .* Port-Based QoS</p></li><li><p>* QoS - - .- FIFO .</p><p> - QoS - - IntServ Resource Reservation Protocol (RSVP) , .</p><p> - QoS - - type of Service (ToS) IP - L2 CoS (Class of service) L3 DSCP (Differentiated service code points) QoS 7 L2 64 L3 </p></li><li><p>* 3: IP ToSversion0 3 8 15 19 31version IHLType of Service Total lengthIdentificationFlagsFragment OffsetTime to LiveProtocol Header ChecksumSource AddressDestination AddressOptions + PaddingData .</p></li><li><p>Layer 3: IP ToS *Version LengthLenProtoToS ByteIDOffsetTTLFCSIP SAIP DAData76543210IP Precedence DiffServ (DSCP)Flow Ctrl IPV4DiffServ IP Precedence</p><p> IP Precedence 3 0 7. . .</p><p>DiffServ (DSCP) </p><p> DSCP IETF DiffServ. 6 ToS 64 ( 0 63). DSCP 3- IP Precedence IP-.</p></li><li><p>802.1p ( , CoS)*L2 802.1QVersion LengthLenProtoToS ByteIDOffsetTTLFCSIP SAIP DADataL3 IPv4 L2 3 , QoSIP Precedence DSCP (1 )IP Precedence: 3 Most Significant Bits (MSBs) ToSDSCP: 6 MSBs ToS </p></li><li><p>*Type of Service (ToS) MBZPrecedenceTOSMBZ: </p><p>IP Precedence IP Precedence TOS: </p><p>111 (7)Network control1000 110 (6)Internetwork control0100 101 (5)Critical0010 100 (4)Flash Override0001 011 (3)Flash0000 010 (2)Immediate001 (1)Priority000 (0)Routine</p></li><li><p>*ToS type 2 DiffServ Code Point (DSCP)unusedClassDrop PrecedenceEF/AF0 1 2 3 4 5 6 7DSCPCUEx: 001010 001 01 0 0</p><p>Class 1Class 2Class 3Class 4 001010 (DSCP 10) AF 110100010(DSCP 18)AF 21011010(DSCP 26)AF 31100010(DSCP 34)AF 41 001100(DSCP 34)AF 12010100(DSCP 34)AF 22011100(DSCP 34)AF 32100100(DSCP 34)AF 42 001110(DSCP 34)AF 13010110(DSCP 34)AF 23011110(DSCP 34)AF 33100110(DSCP 34)AF 43</p></li><li><p> QoS, 802.1, IP- DSCP ToS.. </p><p>*: DSCP 46, , DSCP 46DSCP: 0 / CoS:0DSCP: 16 / CoS:2DSCP: 36 / CoS:4DSCP: 48 / CoS:6</p></li><li><p> QoS (DSCP, CoS, IP Precedence) . . :</p><p>: 40 DSCP, .*MarkingL2 : CoS L3 : DSCP , Port 1Port 10L2 CoS , R1 CoS Precedence DSCP .L3 DSCP/IP Precedence .R1R3R2</p></li><li><p>IP Precedence and DSCP Values* CoS DSCP IP Precedence DSCP</p><p>CoS01234567DSCP08162432404856</p><p>IP Precedence01234567DSCP08162432404856</p></li><li><p>!</p><p>***Why we need QoS? The most important reason is that some important packets (delay sensitive) should arrive at the destination without packet loss cause by heavy network traffic. For traditional packet forwarding, Switches or Routers use best-effort this mechanism to transfer the data. It means the switches try itself the best to forward the packet without the assurance and send the packets according to their capability. Nowadays, end users use lots of application on the network, for instance, BT, VOIP, IPTV, Mail, etc. Some of applications need more reliability, robustness, efficient for their packet transferring. That is why we need QoS to assist accomplishing packet forwarding with assurance. The network design influence network performance as well. In some situations, it generates congestion issue. Following situations shown in above figures.</p><p>Scenario example:3 Gigabyte connections (input) connect to a router respectively but only 1 path (1 G bandwidth) out of it. </p><p>Issue:Delay sensitive applications is influenced. For instance, the congestion will cause voice packet loses and interrupt voice communication. **Implementing QoS in layer 2 environment should bring QoS sign into tag field of Layer 2 frame.Tag is 4 bytes tag information including 2 segments (One for TPID and another 2 Bytes for TCI).TCI field is divided into 3 sub-fields. QoS use first 3 bits to indicate priority. </p><p>**802.1p Priority - this ranges from binary 000 (0) for low priority to binary 111 (7) for high priority. This maps to the Quality of Service (QoS) values used in the TOS field IP precedence values.*****Strict Priority Queue is strict and all traffic transmission will follow the queue priority to forward out. In above example, the traffic stay in higher priority queue will be send out of switch firstly. If high priority queue is empty, the switch starts to check next queue with second priority ( Medium Priority Queue in above example ) and send the packets stored in it. It means that the packets stored in the low priority queue should wait all other queues having higher priority are clear and those packets can get chance to forward out of the switch. Sometimes, it generates starving" issue that the packets in the low priority queue have no chance to be send out.**WRR is another Queuing mechanism. The packets stored in different queue should take turn to forward out according to weight value set manually. **In the example, the switch take 40% packets from high priority queue and then take 30% packets from medium priority queue and so on. After finished sending out 10% packets in the low priority queue, the process will back to check high priority queue and repeat it again.****There are three kinds of model to implement QoS in the network:Best effort device uses best-effort mechanism to transfer the data base on its capacity. Integrated Services It is so called Hard QoS. It is flow base and use RSVP protocol which should be enable at both the endpoints between the network devices. Differentiated Service Per-class polices. It reassigns bits in the ToS filed of packet.</p><p>**For layer 3 QoS, the switch or router checks and reassign value in ToS field to accomplish.</p><p>*There are two ways to implement L3 QoS by add parameters into ToS byte. IP Precedence Total 3 bits to indicate 7 level priorities. DSCP Adopt 6 bits to indicate 64 level priorities.**For L2 frame, the QoS value is added into a tag field. (The frame should have tag information).For L3 packet, QoS value change and reassign ToS bytes, there have two ways for implementation. IP Precedence (3 bit for QoS level). DSCP (6 bit for QoS level) .**These parameters are to be used to guide the selection of the actual service parameters when transmitting a datagram through a particular network. Several networks offer service precedence, which somehow treats high precedence traffic as more important than other traffic (generally by accepting only traffic above a certain precedence at time of high load). The major choice is a three way tradeoff between low-delay, high-reliability, and high-throughput. Bits 0-2: Precedence. Bit 3: 0 = Normal Delay, 1 = Low Delay. Bits 4: 0 = Normal Throughput, 1 = High Throughput. Bits 5: 0 = Normal Relibility, 1 = High Relibility. Bit 6-7: Reserved for Future Use.</p><p> 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ | | | | | | | | PRECEDENCE | D | T | R | 0 | 0 | | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+</p><p> Precedence</p><p> 111 - Network Control 110 - Internetwork Control 101 - CRITIC/ECP 100 - Flash Override 011 - Flash 010 - Immediate 001 - Priority 000 - Routine</p><p>******The switch support trusting via DSCP, IP Precedence, or CoS values on ingress frames.When trusting CoS or IP Precedence, switches map an ingress packets mapping table for CoS-to-DSCP and IP Precedence to an internal DSCP value.</p><p>*</p></li></ul>