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QoS Routing and Forwarding. 2006. Benefits of QoS Routing. Without QoS routing: must probe path & backtrack; non optimal path, control traffic and processing OH, latency With QoS routing: optimal route; “focused congestion” avoidance efficient Call Admission Control (at the source)

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benefits of qos routing
Benefits of QoS Routing
  • Without QoS routing:
    • must probe path & backtrack; non optimal path, control traffic and processing OH, latency
  • With QoS routing:
    • optimal route; “focused congestion” avoidance
    • efficient Call Admission Control (at the source)
    • efficient bandwidth allocation (per traffic class)
    • resource renegotiation easier
multiple constraints qos routing
Multiple Constraints QoS Routing

Given:

- a (real time) connection request with specified QoS requirements (e.g., Bdw, Delay, Jitter, packet loss, path reliability, etc)

Find:

- a min cost (typically min hop) path which satisfies such constraints

- if no feasible path found, reject the connection

slide4

D = 25, BW = 55

D = 30, BW = 20

A

B

D = 5, BW = 90

D = 14, BW = 90

D = 5, BW = 90

D = 5, BW = 90

D = 2, BW = 90

D = 1, BW = 90

D = 5, BW = 90

D = 3, BW = 105

Example of QoS Routing2 Hop Path --> Fails (Total delay=55 > 25 and Min BW=20 < 30)3 Hop Path --> Succeeds (Total delay=24 < 25, Min BW=90 > 30)5 Hop Path --> Do not consider, although (Total Delay = 16 < 25, Min BW = 90 > 30)

Constraints: Delay (D) <= 25, Available BW >= 30

We look for feasible path with least number of hops

the components of qos routing
The Components of QoS Routing
  • Q-OSPF: link state based protocol; it disseminates link state updates (including QoS parameters) to all nodes; it creates/maintains global topology map at each node
    • OSPF (Open Shortest Path First): for intra-AS routing
    • is a link-state protocol that uses flooding of link state information and a Dijkstra least cost path algorithm
  • To replace the Dijkstra algorithm using Bellman-Ford constrained path computation algorithm: it computes constrained min hop paths to all destinations at each node based on topology map
  • Call Acceptance Control (CAC)
  • Packet Forwarding: source route or MPLS
slide6

OSPF Overview

5 Message Types

1) “Hello” - lets a node know who the neighbors are

2) Link State Update - describes sender’s cost to its neighbors

3) Link State Ack. - acknowledges Link State Update

4) Database description - lets nodes determine who has the most recent link state information

5) Link State Request - requests link state information

slide7

1

A

2

C

1

E

2

3

B

3

D

2

OSPF Overview (cont)

“Link State Update Flooding”

slide8

OSPF Overview (cont)

 “Hello” message is sent every 10 seconds and only between neighboring routers

 Link State Update is sent every 30 minutes or upon a change in a cost of a path

 Link State Update is the only OSPF message which is acknowledged

 Routers on the same LAN use “Designated Router” scheme

implementation of ospf in qos simulator
Implementation of OSPF in QoS Simulator

Link State Update is sent every 2 seconds

 No ack is generated for Link State Updates

 Link State Update may include (for example):

- Queue size of each outgoing queue (averaged over 10s sliding window)

- Throughput on each outgoing link (averaged over 10s sliding window)

- Total bandwidth (capacity of the link)

 Source router can use above information to calculate

- end-to-end delay, - available buffer size,

- available bandwidth

bellman ford algorithm with delay

1

1

D

D

=1

=00

2

4

10

2

4

2

4

1

1

1

D

=0

one hop

h

1

D

i

1

1

2

4

2

1

1

1

D

D

=3

=00

3

5

3

2

3

3

5

3

5

D

2

2

3

3

D

D

D

D

=1

=11

=1

=7

2

4

2

4

10

2

4

2

4

1

1

2

3

three hops

D

D

=0

=0

two hops

1

1

h*

h

2

1

1

1

1

2

2

3

3

D

D

D

D

=2

=5

=2

=4

3

5

3

5

3

2

2

3

3

5

3

5

Bellman-Ford Algorithm (with delay)

h+1

h

Bellman Equation :

D

=min[

d(i

,j) +

]

D

j

i

b f algorithm properties
B/F Algorithm Properties
  • MC (multiple constraints) Bellman Ford algorithm replaces the Dijkstra algorithm of conventional OSPF implementations
    • B/F slightly less efficient than Dijkstra ( O(NxN) instead of O (NlgN) )
    • However, B/F generates solutions by increasing hop distance; thus, the first found feasible solution is “hop” optimal (ie, min hop)
  • Polynomial performance for most common sets of MC (multiple constraints e.g. bandwidth and delay )
cac and packet forwarding
CAC and Packet Forwarding
  • CAC: if feasible path not found, call is rejected; alternatively, source is notified of constraint violation, and can resubmit with relaxed constraint (call renegotiation)
  • Packet forwarding:

(a) source routing (per flow)

(b) MPLS (per class)

application i ip telephony
Application I: IP Telephony
  • M-CAC at source; no bandwidth reservation along path
  • 36 node, highly connected network
  • Trunk capacity = 15Mbps
  • Non uniform traffic requirement
  • Two routing strategies are compared:
    • Minhop routing (no CAC)
    • QoS routing
  • Simulation platform (UCLA) : PARSEC wired network simulation (QualNet)
slide14

0

1

2

3

4

5

7

8

9

6

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12

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21

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25

24

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27

28

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35

31

32

33

34

30

50 Km

15 Mbit/sec

slide15

TALK

SILENCE

1/ = 352 ms

1/ = 650 ms

QoS Simulator: Voice Source Modeling

  • Voice connection requests arrive according to a Poisson process, or at fixed intervals
  • Once a connection is established, the voice source is modeled as 2 state Markov chain
  • 1 voice packet every 20ms during talk state
slide16

Simulation Parameters

  •  10 Minute Simulation Runs
  •  Each voice connection lasts 3 minutes
  •  OSPF updates are generated every 2 seconds (30 minute OSPF update interval in Minhop scheme)
  •  New voice connections generated with fixed interarrival (150 ms)
  •  Measurements are in Steady-state (after 3 minutes)
  • 100 msec delay threshold
  • 3 Mbit/sec bandwidth margin on each trunk
  • The candidate source destination pairs are : (8,20),(0,34),(3,32), (4,32), (5,32), (10,32), (16, 32)
slide17

Minhop Routing

  • We note that the rate from the 5 sources (3, 4, 5, 10, 16) into destination 32 is 4.76 calls/sec, exceeding the processing capacity of a single path which is 3.2 in Min Hop and 2.6 in MC BF
slide18

Minhop Routing (cont.)

  • The source-destination pairs (0,34) and (8,20) are getting all of their calls through with zero loss and end-to-end delays below 100ms threshold. This is because they enjoy exclusive use of minhop paths (0,1,18,19,25,24,34) and (8,14,20), respectively
  • The remaining source destination pairs (3,32), (4,32), (5,32), (10,32), and (16,32) do not even get a single packet through with delay below 100msec threshold. Moreover, they suffer heavy loss. The reason is very simple: they all share a common subpath (9, 8, 2, 32) and thus compete for the same bottleneck
slide19

0

1

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50 Km

18

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20

15 Mbit/sec

25

24

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35

31

32

33

34

30

MINHOP ROUTING

slide20

QoS Routing

  • MC Bellman-Ford routing algorithm manages to balance the load on alternate paths
  • In fact, two alternate paths are used to route the traffic originating from the 5 sources
slide21

0

1

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12

50 Km

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20

15 Mbit/sec

25

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34

30

QoS ROUTING

slide22

0

1

2

3

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8

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12

50 Km

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20

15 Mbit/sec

25

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34

30

QoS ROUTING

preliminary analysis

QoS Routing

Minhop

Minhop w/ CAC

# voice calls attempted in steady state

2762

2762

2790

# voice calls accepted in steady state

2762

2762

1875

% of packets lost

0.0 %

11.78 %

0.0 %

% of packets above 100 ms

0.0 %

51.34 %

0.0 %

100.0 %

36.88 %

% of packets below 100 ms

100.0 %

Preliminary Analysis
  • The QoS routing accepts all the offered calls by spreading the load on alternate paths
slide24

OSPF packet size was 350 bytes

  • OSPF (LSA) updates were generated every 2 seconds
  • Measurements were performed on a “perfect square grid” topology
slide26

Application II: MPEG Video

  • Res. All. CAC
  • RSVP type signaling required
  • Effective bandwidth & buffer reservations
  • 36 node grid-type topology
  • Trunk capacity = 5.5 Mbps
  • Inputs = Measured MPEG traces
  • QoS guarantees: no-loss; delay < Tmax
  • Simulation platform: PARSEC wired network simulation (QualNet)
slide27

APPLICATION ORDER

SOURCE NODE

DESTINATION NODE

PATH

CAC

Y/N

REJECTION

NODE

1

0

35

1 18 19 20 21 22 28 29 35

Y

2

24

13

25 19 20 14 13

Y

3

19

20

25 31 32 26 20

Y

4

1

18

18

Y

5

34

35

28 29 35

Y

6

18

21

19 20 21

N

19

1 7 8 14 20 21

Y

7

29

35

NO PATH FOUND

8

9

18

8 7 1 18

N

1

8 14 20 19 18

Y

9

27

21

26 20 21

N

20

26 20 14 8 9 15 21

Y

10

22

28

28

Y

11

22

28

21 20 19 25 24 34 28

Y

SIMULATION RESULTS

Bandwidth/link: 5.5 Mbps unidirectional

Tmax: 0.1 s

Effective bandwidth: 2.6 Mbps

Effective buffer: 260 KB (no buffer saturation)

slide28

0

1

2

3

4

5

1

6

9

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9

6

10

11

8

4

13

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8

6

10

2

9

25

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29

5

7

3

35

31

32

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34

30

11

slide29

Video Only Result Comparisons

Class based QoS routing with reservation

vs. Measurement based QoS routing without reservation

Bandwidth/link: 5.5 Mbps unidirectional

Tmax: 0.1 s, Duration 10 min

conclusions
Conclusions
  • QoS routing beneficial for CAC, enhanced routing, resource allocation and resource renegotiation
  • Can efficiently handle flow aggregation (Diffserv)
  • Q-OSPF overhead manageable up to > 100 nodes
  • Can be scaled to thousands of nodes using hierarchical OSPF
  • Major improvements observed in handling of IP telephony and MPEG video
  • MPEG video best served via reservations
  • Future Work:Extension to hierarchical OSPF, to interdomain routing, to multiple classes of traffic and statistical allocation of MPEG sources
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