Transcript Chapter 6
Integrated Services (RFC 1633) Architecture for providing QoS guarantees to individual application sessions Call setup: a session requiring QoS guarantees must reserve sufficient resources at each router on its path before transmitting data A session must: declare its QoS requirement using R-spec characterize traffic it will send into network using T-spec A signaling protocol is needed to carry R-spec and T-spec to routers Router must determine whether or not it can admit the call Router must maintain per-flow state (allocated resources, QoS requests) RSVP RSVP: a signaling protocol for applications to reserve resources (link bandwidth and buffer space) Make reservations for both unicast and multicast transmissions Receiver-oriented Can reserve resources for heterogeneous receivers Sender sends a PATH message to the receiver specifying R- spec and T-spec Receiver responds with a RESV message to request resources for the flow An intermediate router can reject or accept the request of the RESV message A router may merge the reservation messages arriving from downstream Intserv Service Models Guaranteed service: Provide firm bounds on end-toend datagram queuing delays. Provide bandwidth guarantee Token-bucket-policed source + WFQ arriving traffic Controlled load service: Provide a quality of service closely approximating the QoS that the same flow would receive from an unloaded network element. A very high percentage of transmitted packets will be successfully delivered to the token rate, r destination. A very high percentage of transmitted packets will bucket size, b experience a queuing delay per-flow close to 0. rate, R WFQ Dmax= b/R Differentiated Services (RFC 2475) Concerns with Intserv: Scalability: router need to process resource reservations and maintaining state for each flow. Flexible Service Models: not allow relative service distinctions. Diffserv approach: Goal: provide the ability to handle different classes of traffic in different ways Scalable: simple functions in network core, relatively complex functions at network edge Flexible: don’t define specific service classes, provide functional components to build service classes Diffserv Architecture Edge router: -Packets are marked -The mark of a packet identifies the class of traffic to which the packet belongs Core router: -Packet forwarded to the next hop according to the per-hop behavior (PHB) associated with that packet’s class -PHB determines buffering and scheduling at the routers - Routers needn’t maintain states for individual flows Classification and Marking at Edge-Router Classification: packets classified based on packet header fields (source/destination IP address, source/destination port, protocol ID) Marking: packet marked based on per-flow profile Traffic profile: pre-negotiated rate A, bucket size B Meter used to compare the incoming packet flow with the traffic profile In-profile packet receive priority marking, out-of-profile packets might be marked differently, shaped (i.e. delayed), or dropped Packet Marking Packet is marked in the DS field of the IP packet header (Type of Service (TOS) field in IPv4, and Traffic Class field in IPv6) 6 bits used for Differentiated Service Code Point (DSCP) and determine PHB that the packet will receive 2 bits are currently unused All packets with the same DSCP are referred to as a behavior aggregate Forwarding (PHB) PHB is “a description of externally observable forwarding behavior of a Diffserv node applied to a particular Diffserv behavior aggregate”. A PHB can result in different classes of traffic receiving different performance. A PHB does not specify what mechanisms to use to achieve required behaviors Differences in performance must be observable and hence measurable Examples: Class A gets x% of outgoing link bandwidth over time intervals of a specified length Class A packets leave before class B packets Service Level Agreements A customer must have a Service Level Agreement (SLA) with its ISP. A SLA specifies the service classes supported (traffic profile, performance metrics, actions for non-conformant packets) and the amount of traffic allowed in each class. Static SLA: pre-provisioned Dynamic SLA: signaled on demand Boundary routers mark, drop, shape packets based on SLA When a packet enters one domain from another domain, its DS field may be re-marked, as determined by the SLA between the two domains. Example Diffserv Services Premium Service: low delay and low jitter service Assured Service: better reliability than Best Effort Service Olympic Service: three tiers of services: Gold, Silver and Bronze, with decreasing quality.