Qos routing and forwarding
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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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QoS Routing and Forwarding

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Qos routing and forwarding

QoS Routing and Forwarding

2006


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


Qos routing and forwarding

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


Qos routing and forwarding

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


Qos routing and forwarding

1

A

2

C

1

E

2

3

B

3

D

2

OSPF Overview (cont)

“Link State Update Flooding”


Qos routing and forwarding

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)


Qos routing and forwarding

0

1

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30

50 Km

15 Mbit/sec


Qos routing and forwarding

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


Qos routing and forwarding

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)


Qos routing and forwarding

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


Qos routing and forwarding

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


Qos routing and forwarding

0

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50 Km

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15 Mbit/sec

25

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34

30

MINHOP ROUTING


Qos routing and forwarding

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


Qos routing and forwarding

0

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50 Km

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15 Mbit/sec

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QoS ROUTING


Qos routing and forwarding

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50 Km

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15 Mbit/sec

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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


Qos routing and forwarding

  • OSPF packet size was 350 bytes

  • OSPF (LSA) updates were generated every 2 seconds

  • Measurements were performed on a “perfect square grid” topology


Qos routing and forwarding

75ms voice call generation rate


Qos routing and forwarding

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)


Qos routing and forwarding

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)


Qos routing and forwarding

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11


Qos routing and forwarding

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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