Internet%20resource%20allocation%20and%20QoS

1
Lecture 15

• Internet resource allocation and QoS
• Resource Reservation Protocol
• Integrated Services
• Differentiated Services

2
QoS in a datagram network?

• Packet Classification.
• Buffer acceptance algorithms.
• Explicit Congestion Notification.
• Flow measurements

3
A QoS Capable Router
4
Packet classification

• Identify the flow the packet belongs to.
• The edge routers may be able to do that.
• MPLS multi protocol label switch. Add an extra
  header in front of the IP header. Now a router
  decides the output link based upon the input link
  and the MPLS header.

5
Buffer acceptance algorithms

• Tail Drop.
• RED Random Early Detection
• RIO Random Early Detection with In and Out
  packet dropping strategies.

6
(No Transcript)
7
Explicit Congestion Notification (ECN)

• Routers could prevent congestion by informing the
  source of the packets when they become lightly
  congested, but before they start dropping
  packets.
• This strategy is called source quench.

8
Source quench

• A router sets a congestion notification flag in
  the IP header to inform the destination that
  signs of congestion are visible.
• The destination informs the source by setting a
  flag in the TCP header of segments carrying
  acknowledgments.

9
Problems with ECN

• (1) TCP must be modified to support the new flag.
• (2) Routers must be modified to distinguish
  between ECN-capable flows and those who do not
  support ECN.
• (3) IP must be modified to support the congestion
  notification flag.
• (4) TCP should allow the sender to confirm the
  congestion notification to the receiver, because
  acknowledgments could be lost.

10
Flow measurements

• How to choose the measurement interval to
  accommodate bursty traffic?
• Token bucket

11
The token bucket filter

• Characterized by (1) A token rate R, and (2)
  The depth of the bucket, B
• Basic idea the sender is allocated tokens at a
  given rate and can accumulate tokens in the
  bucket until the bucket is filled. To send a byte
  the sender must have a token. The maximum burst
  can be of size B because at most B token can be
  accumulated.

12
Example

• Flow A generates data at a constant rate of 1
  Mbps. Its filter will support a rate of 1 Mbps
  and a bucket depth of 1 byte,
• Flow B alternates between 0.5 and 2.0 Mbps. Its
  filter will support a rate of 1 Mbps and a bucket
  depth of 1 Mbps
• Note a single flow can be described by many
  token buckets.

13
Example
14
(No Transcript)
15
Token bucket

• L packet length
• C of tokens in the bucket
• --------------------------------------------------
  -
• if ( L lt C )
• accept the packet
• C C - L
• else
• drop the packet

16
A shaping buffer delays packets that do not
confirm to the traffic shape

• if ( L lt C )
• accept the packet
• C C - L
• else / the packet arrived early, delay it /
• while ( C lt L )
• wait
• transmit the packet
• C C - L

17
Packet Scheduling

• PS and GPS Processor Sharing Generalized
  Processor Sharing
• Round Robin, Weighted Round Robin
• Priority Scheduling
• Weighted Fair Queuing practical version of GPS.
  Transmits packets in the order of their finishing
  time.

18
Weighted queuing
19
RSVP- Resource Reservation Protocol

• Used to establish a path for a flow and reserve
  resources along the path.
• Requirements
• Accommodate faults soft state.
• Support unicast as well as multicast.
• PATH messages ? issued by sender includes TSpec
• RESV messages ? issued by the receiver includes
  RSpec

20
RSVP
21
RSVP message
22
RSVP multicast
23
Integrated Services

• Support fine-grain QoS for individual flows.
• Mechanisms
• Specification of flow requirements - Flowspecs
• Admission decisions
• Resource reservation and policing
• Policy enforcement

24
Flowspecs

• TSpec specify the traffic characteristics
• Rspec describe services required from network.

25
Admission decisions

• Two classes
• Guaranteed Services based upon token buckets
• Controlled Load approximates a best effort
  model in a lightly loaded network.

26
Integrated Service Router
27
Differentiated Services

• Two classes of traffic
• Regular
• Premium
• Edge routers mark the packets.
• Premium packets enjoy
• EF Expedited Forwarding
• AF Assured Forwarding