Internet Quality of Service the big picture

1
Internet Quality of Service the big picture

• What is quality of service?
• What does it take for the Internet to support
  QoS?
• Existing Internet QoS architectures
• Integrated services, differentiated services, and
  MPLS overview.

2
What is QoS

• User point of view
• Assurance of end-to-end service.
• E.g. Guaranteed delay (VoIP), Guaranteed
  bandwidth (VPN)
• Relaxed definition
• Service differentiation different packets is
  treated differently.
• end-to-end service guarantees may be achieved by
  provisioning.
• e.g. only a small portion of high priority
  packets.
• Existing IP networks only support best effort
  service. Adding service differentiation is
  non-trivial.

3

• Applications that need QoS
• VoIP bounded delay
• VPN bounded bandwidth
• Video conferencing bounded delay and bounded
  loss rate
• Common QoS parameters
• delay/delay varation (jitter)
• Bandwidth
• error rate

4

• Per flow QoS guarantees and aggregate QoS
  guarantees
• Statistical QoS guarantees .vs. deterministic QoS
  guarantees

5

• What is needed to support QoS
• Between the network and its clients Traffic
  contract. Traffic specification/desired
  QoS/supported QoS
• At network edge
• Signaling and admission control if everything is
  allowed, QoS cannot be guaranteed. Signaling is
  usually needed to setup the network so that QoS
  can be guaranteed.
• Packet classification/marking What kind of
  service do you want to apply to the packet?
• Traffic shaping traffic with a certain shape is
  easier to guarantee service
• Packet classification/marking and traffic shaping
  is also called traffic conditioning.
• Traffic policing packets out of the service
  agreement should be stopped at the edge.

6

• What is needed to support QoS
• At routers
• classification and scheduling FCFS won't work,
  need more advanced packet scheduling scheme (Fair
  Queuing)
• Routing algorithm need to improve find a path
  that satisfies QoS constraints
  (QoS/policy/constraint based routing).
• Buffer management.
• Traffic monitoring find problems as early as
  possible
• Traffic reshaping (at merge and fork points)

7

• QoS in the Internet Do we really need it?
• Alternative buy excessive bandwidth
• Everything is simple in the Internet without QoS,
  everything seems to be much harder in the
  Internet with QoS support.
• What is the main problem?
• Complexity and scalability of QoS mechanisms
• Which is cheaper higher network speed or network
  with QoS support.
• Where is the balance?
• A guess Some form of QoS support will be there,
  per flow QoS guarantee may or may not ever be
  deployed.

8

• Intergrated Services (IntServ)
• trying to match the user demand by providing per
  flow QoS guarantees.
• Two service models
• controlled-load service performance is as good
  as unloaded network
• guaranteed service firm bound of throughput and
  delay
• Signaling protocol RSVP
• IntServ is a reservation based approach
• Main problem
• router complexity (scalability)

9

• Differentiated Services (Diffserv)
• Matching to the user demand has been proven to be
  too much.
• Define per-hop behavior instead of end-to-end
  service model
• no signaling is needed.
• Support a small number of forwarding classes at
  each router.
• Service models to be accomplished through
  provisioning
• Edge routers map packets into forwarding classes
  based on service level agreement (SLA).
• Forwarding class is encoded in the packet header.
• Six bits in the TOS file in the IP packet is used
  in DiffServ
• Examples of forwarding classes
• 101 110 - expedited forwarding
• 010 010 - assured forwarding
• Problems with DiffServ
• end-to-end service guaranteed is hard to maintain.

10

• Multi-Protocol Label Switching (MPLS)
• originally designed for IP over ATM
• A short (fixed length) label is encoded for the
  packet header for packet forwarding
• Allow Label switched path (LSP) to be setup
  (explicit routing).
• allow datagram and virtual circuit to be
  coexisted in an IP network.
• MPLS can be combined with IntServ and DiffServ to
  support QoS.