RSVP Sessions

• An RSVP session is a flow to a particular end-point.

  • Determined by an (IP address, IP port, IP protocol) triple.

• Multiple flows can be grouped into a session.

• Separate sessions are independent of one-another.

  • “Independent” means no specific coordination over traffic control.

RSVP Operation

• RSVP assumes IP-level services.

• RSVP operation occurs in two phases: set-up and use.

  • Set-up establishes the resource reservations (or not, depending).

  • Use uses the reserved resources (or not, depending).

• Set-up involves (conceptually) the control plane; use involves the bearer plane.

RSVP Set-Up

• The sender-to-receiver request sets up a flow path.

• The receiver-to-sender response reply follows the flow path.

Policy and Admission Control

• Each request is judged twice at each router along the flow path:

  1. Policy: is this request allowed at all?

  2. Admission: are there enough resources at this node to handle the request?

• The receiver may respecify the request and try again.

Adding Flows

• A successful request alters router behavior along the flow path.

  • Admission control recognizes and classifies the packets from flows.

  • Packet scheduling handles packets in a way appropriate to the corresponding flows.

Flow Descriptions

• A flow is described by a flow descriptor.

  • The filterspec modifies admission-control behavior.

  • The flowspec describes packet-scheduling behavior.

• A flow descriptor is a filterspec and a flowspec.

Flowspecs

• A flowspec describes the desired packet-scheduling behavior.

  • The service class.

  • The resource spec (Rspec) gives the desired QoS.

    • Rate, delay slack (jitter).

  • The traffic spec (Tspec) describes the data flow.

    • Peak rate, maximum packet size, and so on.

Reservation Styles

• Service characteristics may influence how reservations are made.

  • How many senders? Statically or dynamically determined?

• Multiple senders can be allocated into sessions.

  • Each session is a separate resource allocation.

  • This is a service-determined feature.

Sender Allocations

• There are three styles of sender allocation supported:

  1. Wildcard: all senders in one session (one fat pipe).

  2. Fixed: each sender has a session.

  3. Shared-explicit: specified senders share a session.

• A concurrency measure;

  • Mostly one active sender can use wildcard or shared-explicit.

  • Mostly several active senders can use fixed.

RSVP Routers

• Routers under RSVP control have to reserve total bandwidth to be used to satisfy RSVP requests.

  • Each router also maintains a per-flow maximum.

• Each router also has to maintain lots of RSVP state.

RSVP Analysis

• RSVP provides per-service resource reservation.

  • With an enormous amount of machinery.

• Shared resources are managed with fair efficiency.

  • At a cost of a lot of state in the network.

• How can integrated-services costs be reduced?

Services Classes

• Provide only a fixed set of QoS levels.

  • Low (best effort), medium, and high quality.

• Services slot themselves into a QoS level, rather than carving out their own custom level.

  • Services can still be adaptive.

Differentiated Services

• Differentiated Services (DiffServ) embodies the idea of a fixed array of QoS levels.

• Routers have an easier time dealing with fixed QoS levels.

Border Control

• DiffServ routers can be further simplified by moving state to the edge of the network.

  • The reservation part is moved out of the network.

• Border nodes are responsible for:

  • Admission: allowing new flows into the network.

  • Classification: marking packets as to QoS required.

  • Shaping: making sure a service instance behaves.

  • Aggregation: combining separate flows at the same QoS level into a single flow.

Classification and Aggregation

• QoS levels are specified by DiffServ (DS) code points.

  • They fit in the IPv4 TOS or IPv6 traffic-class field.

• Flows with the same DS code point are merged to form a DS aggregation.

  • A router handles DS aggregates according to the associated QoS spec.

Agreements

• All border nodes in a network act under the control of a traffic conditioning agreement (TCA)

• The TCA determines the services offered and the amount of traffic for each service accepted.

• Border nodes form service level agreements (SLA) with end-points.

• An SLA determines

  • The QoS end-user expects from the network.

  • The end-user behavior expected by the border node.

DS Domains

• A DS domain is a set of border nodes and routers under a common administration.

  • The policy sets the behavior of routers in the DS domain.

• DS-domain node is a boundary or internal node.

  • A boundary node is either a ingress or egress node.

DS Regions

• Several DS domains can group to form a DS region.

  • The domains share common TCAs and SLAs.

• Example: One DS domain for each school, and all schools in the Monmouth region.

  • The Monmouth and Drew regions.

Ingress Nodes

• Ingress nodes are responsible for controlling access to the network.

• “Controlling” means

  • Classifying: determining DS code points for flows.

  • Metering: determining how DS code points behave.

  • Marking: assigning code points to packets.

  • Shaping: injecting packets into the network to meet QoS requirements.