Integrated Service in the Internet Architecture

1
Integrated Service in the Internet Architecture

• RFC 1633

2
Introduction

• The Internet only offers simple QoS (quality of
  service)best effort
• Real-time applications do not work well across
  the Internet because of
• Variable queueing delays
• Congestion losses
• The Internet infrastructure must be modified to
  support real-time QoS

3
Introduction

• Real-time QoS is the issue for a next generation
  of traffic management in the Internet
• The term integrated services(IS) for an Internet
  service model includes
• Best-effort service
• Real-time service
• Controlled link sharing

4
Elements of the Architecture

• The fundamental service model of the
  Internetbest effort has been unchanged for 20
  years
• Change the service model of the Internet is a
  major undertaking
• New components will supplement but not replace
  the basic IP service
• Only to extend the original architecture

5
Integrated Service Model

• Two sorts of service targeted towards real-time
  traffic
• Guaranteed service
• Predictive service
• It integrate with controlled link-sharing
• The resources (e.g., bandwidth) must be
  explicitly managed

6
The arguments against resource guarantees

• Bandwidth will be infinite
• In the future, the bandwidth will be so abundant,
  ubiquitous, and cheap?
• Simple priority is sufficient
• Simply giving higher priority to real-time
  traffic is enough?
• Applications can adapt

7
Integrated Service Model

• There is an inescapable requirement for routers
  to be able to reserve resources
• Provide special QoS for specific user packet
  streams, or flows
• Use the existing internet-layer protocol (e.g.,
  IP or CLNP) for real-time data

8
Reference Implementation Framework

• Propose a reference implementation framework to
  realize the IS model
• The framework includes 4 components
• Packet scheduler
• Admission control
• Classifier
• Reservation setup protocol

9
Traffic control

• For integrated services, a router must implement
  an appropriate QoS for each flow
• The router function that creates different
  qualities of service is called traffic control
• Implemented by the packet scheduler, the
  classifier and admission control

10
Traffic control

• Packet Scheduler
• An experimental schedulerCSZ scheduler
• Classifier
• Packets are mapped into some classes
• Packets in same class get the same treatment form
  packet scheduler
• Admission Control
• The decision algorithm used by router

11
The 4th componentreservation setup protocol

• Create and maintain flow-specific state in the
  endpoint hosts and in routers along the path of a
  flow
• RSVP (ReSerVation Protocol) is used to reserve
  the resource

12
Implementation Reference Model for Routers
Reservation Setup Agent
Management Agent
Routing Agent
Admission Control
Routing
Traffic Control Database
Database

Classifier
Packet Scheduler
Input Driver
Internet Forwarder
Output Driver
13
Implementation Reference Model for Routers

• The forwarding path is divided into 3 sections
• Input driver,internet forwarder,output driver
• Internet forwarder interprets the internetworking
  protocol header (e.g., IP header for TCP/IP)
• The output driver implements the packet scheduler

14
Implementation Reference Model for Routers

• In routers, integrated service will require
  changes to both the forwarding path and the
  background functions
• The forwarding path may depend upon hardware
  acceleration for performancedifficult and costly
  to change

15
Quality of Service Requirements

• Per-packet delay is the central quantity about
  which the network makes QoS commitments
• Real-time applications
• Need the data in each packet by a certain time,
  or the data will be worthless
• Elastic applications
• Always wait for data to arrive

16
Real-time applications

• Playback applications
• The source takes some signal, packetizes it, and
  then transmits over the network
• Receiver has to buffer the incoming data and then
  replay the signal at some fixed offset delay form
  the original departure time
• The performance is measured by
• Latency and fidelity

17
Real-time applications

• Delay can affect the performance of playback
  applications in two ways
• The value of the offset delay
• The delays of individual packets can decrease the
  fidelity of the playback by exceeding the offset
  delay

18
Real-time applications

• Intolerant applications
• Must use a fixed offset delay
• Set the upper bound on max delay
• Be called as guaranteed service
• Tolerant applications
• Can tolerate some late packets
• Vary offset delays according to the experience in
  the recent past
• Be called as predictive service

19
Elastic applications

• Always wait for data to arrive
• Example applications
• Interactive burst Telnet
• Interactive bulk burst FTP
• Asynchronous bulk transfer E-mail
• An appropriate service model for these
  applications is to provide as-soon-as-possible
  service (i.e., best-effort service)

20
Resource-sharing requirements

• Multi-entity link-sharing
• When the link is underloaded, any one of the
  entities could utilize all idle bandwidth
• Multi-protocol link-sharing
• Prevent one protocol family from overloading the
  link
• Multi-service sharing
• Limit the amount real-time traffic to avoid
  preempting elastic traffic

21
Other remarks

• Packet dropping
• Some of the packet within a flow could be marked
  as preemptable
• Router use this mark to drop packets
• Usage feedback
• Prevent abuse of network resources
• Reservation model
• Describe how an application negotiates for a QoS
  level

22
Traffic Control Mechanisms

• Basic functions
• Packet scheduling
• Packet dropping
• Packet classification
• Admission control
• An example The CSZ scheme

23
Packet scheduling

• Reorder the output queue
• One approach is a priority scheme
• Packets are ordered by priority
• Highest priority packets leave first
• An alternative scheme is round-robin
• Gives different classes of packets access to a
  share of the link

24
Packet dropping

• A router must drop packets when its buffers are
  all full
• Dropping the arriving packet is simple but may
  cause undesired behavior
• In real-time service, dropping one packet will
  reduce the delay of all the packet behind it
• Dropping and scheduling must be coordinated

25
Packet classification

• The classifier implementation issues are
  complexity and processing overhead
• One approach is to provide a flow-id field in the
  Internet-layer packet header
• Reduce the overhead of classification
• Engineering is required to choose the best design
  of this concept

26
Admission control

• Admission controlthe design about resource
  availability
• The router has to understand the demands that are
  currently being made on its assets
• A recent proposal is to program the router to
  measure the actual usage by existing packet
  flows, then use this information for the
  admitting of new flow

27
The CSZ scheme

• At the top level, CSZ node use WFQ to separate
  guaranteed flows for each other
• Predictive and best-effort service are separated
  by priority
• Inside each predictive sub-class, FIFO queueing
  is used to mix the traffic

28
The CSZ scheme

• Within the best-effort class, WFQ is used to
  provide link sharing
• Within each link share of the best-effort class,
  priority is used to permit more time-sensitive
  elastic traffic
• The CSZ node uses both WFQ and priority in an
  alternating manner to build the mechanism

29
Reservation Setup Protocol

• Requirements for the design of a reservation
  setup protocol
• designed for a multicast environment
• accommodate heterogeneous service needs
• can add/delete one sender/receiver to an existing
  set
• robust and scale well to large multicast groups
• advanced reservation of resources, and for the
  preemption

30
RSVP

• Flowspecs and Filter Specs
• RSVP reservation request specifies the amount of
  resources to be reserved
• The resource quantity is specified by a flowspec
• The packet subset to receive those resources is
  specified by a filter spec
• The service model presented to an app. must
  specify how to encode flowspecs and filter specs

31
RSVPreservation styles

• Offers several different reservation styles
• Wildcard
• All packet destined for the session may use a
  common pool of reserved resource
• Fixed-filter
• Can not be changed during its life time without
  re-invoking admission control
• Dynamic-filter
• Receiver can modify its choice of resource
  without additional admission control

32
RSVPreservation styles

• Wildcard uses a filter spec that is not
  source-specific
• The other two use filter specs that select
  particular sources
• The wildcard reservation is useful in support of
  an audio conference

33
RSVPinitiation

• Sender knows the qualities of the traffic stream
  it can send
• Receiver knows what it wants to (or can) receive
• Sender initiation scales poorly for large,
  dynamic multicast delivery trees and for
  heterogeneous receivers
• Thus, RSVP uses Receiver-Initiation

34
RSVPinitiation

• Receiver Initiation
• Natural choice for multicast sessions
• But may appear weaker for unicast sessions
• Except real-time app. will have its higher-level
  signalling and protocol
• Then this protocol can be used to signal the
  receiver to initiate a reservation

35
RSVPstates

• Hard state approach
• Connection-oriented
• Soft state approach
• Connectionless
• RSVP takes the Soft State approach
• Regards the reservation as cached information
  that is installed and periodically refreshed by
  the end hosts

36
RSVProuting issues

• Find a route that support resource reservation
• Find a route that has sufficient unreserved
  capacity for new flow
• Adapt to a route failure
• Adapt to a route change (without failure)
• The last issue is provide by mobile hosts

37
Conclusion

• The Integrated services framework has four main
  components
• Packet scheduler
• Admission control
• Classifier
• Reservation setup protocol
• RSVP is used to reserve the resource for the
  session belongs to high class level