Transcript Packets
Achieving Multimedia QOS over Hybrid IP/PSTN Infrastructures: IP Traffic and Congestion Control April 26, 2001 Susumu Yoneda Japan Telecom Information & Communication Labs Japan Telecom Information & Communication Labs Outline IP Transfer Capabilities Service models Traffic descriptors Conformance definitions QoS commitments Generic Traffic & Congestion Controls Specific Mechanisms e.g., Diffserv, MPLS Conclusion 2 IP Transfer Capabilities: ITU-T SG13 Draft Rec. Y.iptc Dedicated Bandwidth (DBW) IP Transfer Capability Statistical Bandwidth (SBW) IP Transfer Capability Best-Effort (BE) IP Transfer Capability IP Transfer Capability: a set of network capabilities provided by IP based network to transfer a set of IP packets under a given classification. 3 Service Models & Traffic Descriptors DBW SBW BE Service Model Conforming Packets Assure the negotiated QoS Non-conforming Packets Discarded Conforming Packets Delivered corresponding to the associated QoS Non-conforming Packets Delivered within the limits of available resources All Packets Forwarded by use of available resources Traffic Descriptors Peak Rate, Peak Bucket Size, The maximum allowed packet size DBW’s descriptors + Sustainable Rate, Sustainable Token Bucket Size The maximum allowed packet size 4 Conformance Definitions & QoS Commitments DBW SBW BE Conformance Definition Packet Arrival Conforming to the GBRA(Rp,Bp) Packet Length Not exceed the maximum allowed packet size Packet Arrival Conforming to the peak GBRA(Rp,Bp) and the sustainable GBRA(Rs,Bs) Packet Length Not exceed the maximum allowed packet size Packet Length Not exceed the maximum allowed packet size QoS Commitments Specified Loss and Delay commitments Include IP QoS Class 0 and 1 Specified Loss commitment Include IP QoS Class 2 No absolute commitment 5 Generic Traffic & Congestion Controls Traffic Control Functions Network Resource Management Admission Control Parameter Control Packet Marking Traffic Shaping Packet Scheduling Congestion Control Functions Packet Discard Control Routing (Proposed) 6 Differentiated Services [DiffServ] Two standard per hop behaviors (PHBs) defined that effectively represent two service levels Expedited Forwarding (EF): A single codepoint (DiffServ value). EF minimizes delay and jitter and provides the highest level of aggregate quality of service. Any traffic that exceeds the traffic profile (which is defined by local policy) is discarded. Assured Forwarding (AF): Four classes and three drop-precedences within each class (so a total of twelve codepoints). Excess AF traffic is not delivered with as high probability as the traffic “within profile,” which means it may be demoted but not necessarily dropped. 7 Diffserv Functions (1) •Classifier •Behavior Aggregate (BA): Uses only the Diffserv Code Point (DSCP) value •Multi-Field (MF): Uses other header info (like protocol, or port numbers, etc.) •Marker •Adds DSCP when none exists •Adds DSCP as mapped from RSVP reservation •Changes to Map from DSCP to IP TOS, or back •Changes DSCP as local policy dictates 8 Diffserv Functions (2) • Meter • Accumulates statistics, and provides the inputs to conditioning • Conditioner • Provides queue selection and treatment, policing (shaping traffic) by adding delay or dropping packets in order to conform to the traffic profile described in the SLA with destination or source (depending whether this is an egress or ingress point). • Authenticates the traffic for admission control. 9 MPLS Mechanisms At the first hop router in the MPLS network, the router makes a forwarding decision based on the destination address (or any other information in the header, as determined by local policy) then determines the appropriate label value -- which identifies the Forwarding Equivalence Class (FEC) -- attaches the label to the packet and forwards it to the next hop. At the next hop, the router uses the label value as an index into a table that specifies the next hop and a new label. The LSR attaches the new label, then forwards the packet to the next hop. 10 MPLS Routing protocols Start with existing IGP’s OSPF IS-IS BGP-4 Distribute topology information only Enhance to carry constraint data OSPF-TE IS-IS –TE Constraint data Link capacity,Link utilization Resource class Priority Pre-emption etc Constraint based routing is the key to Traffic Engineering 11 Label Distribution Protocols LDP CR-LDP RSVP-TE Hop by Hop routing Ensures routers agree on bindings between FEC’s and the labels. Label paths follow same route as conventional routed path Explicit constraint based routing Route determined by ingress LSR based on overall view of topology, and constraints Traffic engineering CoS and (QoS) fast (50ms) rerouting 12 MPLS Shim Header Structure MPLS "shim" headers ... Layer 2 Header Label Exp. S 4 Octets Label Switching Look up inbound label + port (+Exp) to determine outbound label + port + treatment TTL IP Packet Label: Exp.: S: TTL: 20-bit value, (0-16 reserved) 3-bits Experimental ( ToS) 1-bit Bottom of stack 8-bits Time To Live Header operations Swap (label) Push (a new header) Pop (a header from stack) MPLS encapsulations are also defined for ATM and Frame relay. 13 Hierarchy via Label stack = Network scalability Layer 2 Header Within each domain the IGP simply needs to allow the Boarder (ingress) routers to determine the appropriate egress boarder router Reducing drastically size of routing table in transit routers Label 3 Label 2 Label 1 IP Packet MPLS Domain 1 MPLS Domain 2 MPLS Domain 3 14 Dynamic-Bandwidth Setting traffic time Link traffic monitor and dynamic-bandwidth setting. 15 Conclusion Provide a summary of Y.iptc: IP Transfer Capabilities, Service models, Traffic descriptors, Conformance definitions, QoS commitments How does it work with many other existing traffic engineering mechanisms? Traffic engineering as well as congestion controls would work well when traffics are effectively monitored and conformance is checked. Utilize Y.iptc for the conformance monitoring purposes. 16