Qos Implementation In Xdsl Gw


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Qos Implementation In Xdsl Gw

  1. 1. QoS Implementation in xDSL GW.
  2. 2. Overview <ul><li>Introduction to QoS </li></ul><ul><li>DSL GW role in relation to QoS. </li></ul><ul><li>DSL GW simplified block diagram. </li></ul><ul><li>Classifications. </li></ul><ul><li>Priority Queues </li></ul><ul><li>Scheduler mixing </li></ul><ul><li>DSL GW (CPE) scheduling example </li></ul><ul><li>Multiple VCC - block diagram </li></ul><ul><li>Multiple VCC – Routing Multi VCC Queue Mechanism & Scheduling </li></ul>
  3. 3. Introduction to QoS <ul><li>QoS is a necessary function in todays 3-play solutions where mission critical applications (VoIP, IPTV, Video on demand, etc) are expected to work in DSL based networks. </li></ul><ul><li>QoS expedites the handling of mission-critical applications, while sharing network resources with non-critical applications. </li></ul><ul><li>QoS gives network managers control over network applications, and enables differentiated services. </li></ul><ul><li>There have been numerous standards proposed to solve QoS issues but it’s a very challenging problem as a end-to-end most be the optimal goal but as a chain it’s only as strong as the weakest link. </li></ul><ul><li>To configure and setup QoS enabled units a well knowlede about the traffic and is need for bandwide is an important information to make sure that the QoS implementation is working as expected. </li></ul>
  4. 4. DSL GW (CPE) role in relation to QoS <ul><li>The DSL GW is a very important piece in the QoS solution as it’s provides a key interface between the high speed (LAN) and the lower speed (WAN). In ADSL the upstream can be more than 100 times less as the LAN which can give congestions from time to time </li></ul><ul><li>The high speed interface on the LAN side typically 100Mbps will have a non- blocking switching fabric. However with the upstream rate of 128-800Kbps is a challenge as data arrives at fast rates the buffer space can be full due to slow uplink. Here a QoS enabled DSL GW most depending on the classification (explain later) secure the packet are send to the right queue. </li></ul><ul><li>For downstream traffic the DSL GW typically don’t need to shape the traffic as the LAN interface is faster than the WAN. </li></ul><ul><li>In a QoS enabled DSL GW, packets received on the LAN side is first classified and then send to the priority Queues for then to be Scheduled and send out on the WAN link. </li></ul>
  5. 5. DSL GW simplified block diagram <ul><li>Non-blocking switching fabric is provided between all seven interfaces </li></ul><ul><li>The router performs the layer 3 function and is responsible for routing traffic from the Home Network to the DSL network, based on the default route in the NTE. </li></ul><ul><li>QOS is divided up see following slides </li></ul>Shaper Switch Fabric Outgoing Packets after QoS DSL GW (CPE) Eth port1 Eth port1 Eth port1 Eth port1 Router / Nat Classifier Scheduler Q1 Q2 Q3 Q4 DSL Link
  6. 6. Classifications. <ul><li>DSL GW’s from Netgear can be customized to use different classifications and based on the classification scheme below packets can be assigned to specific QoS level for then to be forwarded according to their importance. </li></ul><ul><li>Classification Methods: </li></ul>TCP/UDP, protocol, port Application IEEE 802.1D priority field (layer 2) diffServ (layer 3) Information in packet Destination MAC Destination IP address WAN device Source MAC address Source IP address Physical attached port (Multi LAN ports) LAN devices Methods Criteria
  7. 7. Queuing priority <ul><li>When packets have arrived and have been classified, they will be sent into one of four queues, where each queue has it’s importance and behavior according to the scheduler. </li></ul>Classifier Scheduler Q1 Q2 Q3 Q4 Shaper 1 2 3 4 1 2 3 4 Incoming Packets before QoS Outgoing Packets after QoS DSL GW (CPE)
  8. 8. Scheduler mixing <ul><li>DSL GW’s from Netgear can be customized to use 3 different scheduler algorithms where each has some good and bad attributes that vary in behavior and complexity. Each most be selected in relation to the circumstance of the solution and environments where the QoS most work. </li></ul><ul><li>Scheduler methods: </li></ul>This tries to minimize the delay for the high priority traffic without completely starving the traffic Weighted round robin system packet scheduling technique allowing guaranteed bandwidth services Weighted Fair Queuing Queues are served with highest queue taken first until it’s empty then next queue in the priority is taken. Disadvantage with this is that lower priority queues can “starve” if there always is data to be send in higher priority queues. Strict Priority comments Scheduler
  9. 9. DSL GW (CPE) scheduling example <ul><li>4-band priority scheduler </li></ul><ul><ul><li>4 queues </li></ul></ul><ul><ul><ul><li>Two Expedited Forwarding (EF) queues : High Priority queues, with non-preemptable service (strict priority). </li></ul></ul></ul><ul><ul><ul><li>Two Best Effort (BE) queues : Medium and Low Prority queues, with Weighed Round Robin (WRR) service. </li></ul></ul></ul>
  10. 10. DSL GW (CPE) WRR example <ul><li>DSL GW (CPE) WRR example </li></ul>Scheduler Outgoing Packets after QoS DSL GW (CPE) Shaper High 1 High 2 Medium Low Q1 Q2 Q3 Q4
  11. 11. DSL GW (CPE) scheduling example <ul><li>Dequeuing </li></ul><ul><ul><li>The Q1 and Q2 (High priority) queues are serviced to extinction, no preemption. Q3 ( medium priority ) and Q4 ( low priority ) queues are serviced (after high priority queues) based on </li></ul></ul><ul><ul><li>WRR Queue scheduler. </li></ul></ul><ul><ul><ul><li>Weight map is configurable, 1<=L<=M<=N<=10 where N=Sum(L, M); where L and M are weights for Low and Medium Priority queues. The scheduling table (ST) is precomputed based on the weight map in an interleaved fashion. This is an O(1) scheduler </li></ul></ul></ul>
  12. 12. Multiple VCC - block diagram Shaper Switch Fabric DSL GW (CPE) Eth port1 Eth port1 Eth port1 Eth port1 Separate VCCI Router / Nat <ul><li>DSL GW’s from Netgear can be customized to support mulitple VCC’s, The traffic can be either </li></ul><ul><ul><li>Bridge </li></ul></ul><ul><ul><ul><li>This includes Bridge/IP mode </li></ul></ul></ul><ul><ul><li>Routed </li></ul></ul><ul><ul><ul><li>As previously </li></ul></ul></ul>DSL Link Classifier Scheduler Q1 Q2 Q3 Q4
  13. 13. Multiple VCC – Routing <ul><li>DSL GW’s from Netgear can be customized to route the traffic via a particular VCC based upon the following </li></ul>TCP/UDP, protocol, port Application Destination MAC Destination IP address WAN device Source MAC address Source IP address Physical attached port (Multi LAN ports) LAN devices Methods Criteria
  14. 14. Multi VCC Queue Mechanism. <ul><li>DSL GW’s from Netgear using Multiple VCC Queues and allows the support for </li></ul><ul><li>One Queue per ATM VCC. </li></ul><ul><li>It allows the customisation of the VCC QOS type, PCR, SCR, MBS. </li></ul><ul><li>DSL GW’s from Netgear Scheduling nominally uses Weighted fair queuing based upon the ATM Traffic type and parameters. </li></ul><ul><ul><li>CBR </li></ul></ul><ul><ul><li>VBR-rt </li></ul></ul><ul><ul><li>VBR-nrt </li></ul></ul><ul><ul><li>UBR </li></ul></ul><ul><li>and PCR,SCR,MBS </li></ul><ul><li>For the routed traffic IP traffic customized classifications and mapping to the ATM QOS </li></ul>