1Netcomm 2005

Communication NetworksCommunication Networks

Recitation 10Recitation 10

2Netcomm 2005

Multimedia, QoSMultimedia, QoS& Multicast Routing& Multicast Routing

3Netcomm 2005

Quality of Service: What is it?Quality of Service: What is it?

Multimedia applications: network audio and video

network provides application with level of performance needed for application to function.

QoS

4Netcomm 2005

Multimedia QoS RequirementsMultimedia QoS Requirements

• live sources, stored sourceslive sources, stored sources• requirements:requirements: deliver data in timely manner deliver data in timely manner

– short end-end delay for interactive multimediashort end-end delay for interactive multimedia• e.g., IP telephony, teleconf., virtual worlds, DISe.g., IP telephony, teleconf., virtual worlds, DIS

– in time for “smooth” playoutin time for “smooth” playout

• relaxed reliabilityrelaxed reliability– 100% reliablity not always required100% reliablity not always required

5Netcomm 2005

Why is QoS so hard?Why is QoS so hard?

need session’s input trafficneed session’s input traffic• must know app’s traffic demandmust know app’s traffic demand

To provide performance (delay, loss) guarantees: To provide performance (delay, loss) guarantees:

compute session’s outputcompute session’s output• scheduling disciplinescheduling discipline

6Netcomm 2005

7Netcomm 2005

RTP - Real-time Transport ProtocolRTP - Real-time Transport Protocol

• Ip-based protocol providingIp-based protocol providing– time-reconstructiontime-reconstruction– loss detectionloss detection– securitysecurity– content identificationcontent identification

• Designed primarily for multicast of real-Designed primarily for multicast of real-time datatime data

8Netcomm 2005

General ViewGeneral View

• and the result…and the result…

9Netcomm 2005

RTCP – Real-time Control ProtocolRTCP – Real-time Control Protocol

• Designed to work together with RTPDesigned to work together with RTP• In an RTP session the participants In an RTP session the participants

periodically send RTCP packet to give periodically send RTCP packet to give feedback on the quailty of the datafeedback on the quailty of the data

• Comparable to flow and congestion Comparable to flow and congestion control of other transport protocolscontrol of other transport protocols

• RTP produces sender and receivers RTP produces sender and receivers reports; statistics and packet countsreports; statistics and packet counts

10Netcomm 2005

RTSP – Real-time Streaming ProtocolRTSP – Real-time Streaming Protocol

• Client-server multimedia presentation Client-server multimedia presentation protocol to enable controlled delivery.protocol to enable controlled delivery.

• Provides ”vcr”-style remote controlProvides ”vcr”-style remote control

• RTSP is an application-level protocol RTSP is an application-level protocol designed to work with RTP (and RSVP) to designed to work with RTP (and RSVP) to provide a complete streaming service over provide a complete streaming service over internetinternet

11Netcomm 2005

RTSP Cont.RTSP Cont.

Multimedia DataEthernetheader

UDPheader

IPheader

RTPheader

RTSPheader

12Netcomm 2005

Example: Media on DemandExample: Media on Demand

client

web server

mediaservers

HTTP GET

presentation description (sdp)

SETUP

PLAY

RTP audio/video

RTCP

TEARDOWN

13Netcomm 2005

Intserv: QoS guaranteesIntserv: QoS guarantees• Resource reservationResource reservation

– call setup, signaling (RSVP)call setup, signaling (RSVP)– traffic, QoS declarationtraffic, QoS declaration– admission controladmission control

– QoS-sensitive QoS-sensitive scheduling (e.g., WFQ)scheduling (e.g., WFQ)

request/reply

14Netcomm 2005

RSVP RSVP –– Reservation ProtocolReservation Protocol

• Reservation is done in one directionReservation is done in one direction• Receiver-initiatedReceiver-initiated• The sender sends QoS wanted to the The sender sends QoS wanted to the

receiver which sends an RSVP receiver which sends an RSVP message back to the sendermessage back to the sender

• The sender does not need to know the The sender does not need to know the capabilities along the path or at the capabilities along the path or at the receiverreceiver

15Netcomm 2005

Intserv QoS: Service ModelsIntserv QoS: Service ModelsGuaranteed service:Guaranteed service:• worst case traffic arrival: worst case traffic arrival:

leaky-bucket-policed leaky-bucket-policed source source

• simple simple boundbound on delay on delay

WFQ

token rate, r

bucket size, b

per-flowrate, R

D = b/Rmax

Controlled load service:Controlled load service:• "a quality of service closely "a quality of service closely

approximating the QoS that approximating the QoS that same flow would receive same flow would receive from an unloaded network from an unloaded network element."element."

arrivingtraffic

16Netcomm 2005

Differentiated ServicesDifferentiated Servicesedge routers:edge routers:• profile of allowable user trafficprofile of allowable user traffic• packet marking:packet marking:

• in-profilein-profile• out-of-profileout-of-profile

““stateless” core routers:stateless” core routers:• no notion of sessionsno notion of sessions• forwarding: in-profile have “priority” over forwarding: in-profile have “priority” over

out-of-profileout-of-profile

17Netcomm 2005

Differentiated Services Cont.Differentiated Services Cont.

• Complexity (per-flow state) at network edgeComplexity (per-flow state) at network edge– leaky bucket markingleaky bucket marking

• High-speed, stateless core routersHigh-speed, stateless core routers– 1-bit determines forwarding behavior1-bit determines forwarding behavior

• Over-provisioned bandwidth:Over-provisioned bandwidth: for in-profile for in-profile traffic used for out-profile, best effort traffictraffic used for out-profile, best effort traffic

18Netcomm 2005

QoS RoutingQoS Routing

• QoS Routing = Multiple parameter QoS Routing = Multiple parameter routing subject to constraintsrouting subject to constraints– Link metrics are vectorsLink metrics are vectors– NP-complete (good heuristics needed)NP-complete (good heuristics needed)

A

B C D

EF G

H

IJ

K

delay: 10 msbandwidth :100 Mb/scell loss ratio: 1.0e-6

19Netcomm 2005

The ProblemThe ProblemTraditional unicast model does not scaleTraditional unicast model does not scale

– Millions of clientsMillions of clients– Server and network meltdownServer and network meltdown

20Netcomm 2005

Solution: IP MulticastSolution: IP Multicast• Source sends single streamSource sends single stream• Routers split stream towards all clientsRouters split stream towards all clients• Guarantee only one copy in each linkGuarantee only one copy in each link

21Netcomm 2005

Multicast Routing TreeMulticast Routing Tree

On tree relay router

Router with directly attached group membersIGMP

Multicast Routing Protocol

22Netcomm 2005

Internet Group Management Internet Group Management Protocol (IGMP)Protocol (IGMP)

• Used by routers to learn about Multicast Used by routers to learn about Multicast Group Memberships on their directly Group Memberships on their directly attached subnetsattached subnets

• Implemented over IPImplemented over IP• Designated RouterDesignated Router

– Each network has one QuerierEach network has one Querier– All routers begin as QueriersAll routers begin as Queriers– Mrouter with the lowest IP address chosenMrouter with the lowest IP address chosen

23Netcomm 2005

How IGMP WorksHow IGMP Works

one router is elected the “querier”one router is elected the “querier”querier periodically sends a Membership Query messagequerier periodically sends a Membership Query message

to the all-systems group (224.0.0.1), with TTL = 1to the all-systems group (224.0.0.1), with TTL = 1on receipt, hosts start random timers (between 0 and 10 on receipt, hosts start random timers (between 0 and 10

seconds) for each multicast group to which they belong seconds) for each multicast group to which they belong

Qrouters:

hosts:

24Netcomm 2005

How IGMP Works (cont.)How IGMP Works (cont.)

when a host’s timer for group G expires, it sends a when a host’s timer for group G expires, it sends a Membership Report Membership Report to group Gto group G, with TTL = 1, with TTL = 1

other members of G hear the report and stop their timersother members of G hear the report and stop their timersrouters hear routers hear allall reports, and time out non-responding groups reports, and time out non-responding groups

Q

G G G G

25Netcomm 2005

Type of Service (TOS) RoutingType of Service (TOS) Routing

“low delay”

“high throughput”

Does not support real QoS

26Netcomm 2005

Multicast Tree with QoSMulticast Tree with QoS

• QoS constraintsQoS constraints– Link: minimum bandwidth; available buffer space.Link: minimum bandwidth; available buffer space.– Tree constraints: end-to-end delay; jitter.Tree constraints: end-to-end delay; jitter.

• Optimization objectivesOptimization objectives– Link: maximize bandwidth.Link: maximize bandwidth.– Tree optimization: minimize the cost.Tree optimization: minimize the cost.

27Netcomm 2005

Core-Based Trees (CBT)Core-Based Trees (CBT)

• Core-based multicast routing:Core-based multicast routing:– One router is selected as the core for each One router is selected as the core for each

multicast group.multicast group.– A tree rooted at the core spans all group A tree rooted at the core spans all group

members.members.– Data packets are forwarded on all Data packets are forwarded on all on-treeon-tree

interfaces except the one on which packets interfaces except the one on which packets arrive.arrive.

28Netcomm 2005

CBT Multicast RoutingCBT Multicast Routing

Core

On tree relay router

On tree routerRouter with directlyattached group member

Sender

29Netcomm 2005

Member Join in CBTMember Join in CBT

Core

Requesting routerwith a new member

join-request

join-request

join-ack

join-ack

30Netcomm 2005

QoS-Aware Member JoinQoS-Aware Member Join

Core

On tree relay router

On tree group routerjoin-request

join-request

u

v

Eligibility Test

Only after the join-request passes the eligibilitytests will a join-acknowledgement be returned.

31Netcomm 2005

Shortest Path Tree (SPT)Shortest Path Tree (SPT)

• Source Based Tree:Source Based Tree: Rooted at the source, Rooted at the source, composed of the shortest paths between composed of the shortest paths between the source and each of the receivers in the the source and each of the receivers in the multicast group.multicast group.

• If the routing metric used is the latency If the routing metric used is the latency between neighbors, the resulted tree will between neighbors, the resulted tree will minimize delay over the multicast group.minimize delay over the multicast group.

• Example: DVMRP. Example: DVMRP.

32Netcomm 2005

Distance-Vector Multicast Distance-Vector Multicast Routing Protocol (DMVRP)Routing Protocol (DMVRP)

DVMRP consists of two major components:DVMRP consists of two major components:(1) a conventional distance-vector routing (1) a conventional distance-vector routing

protocol (like RIP)protocol (like RIP)

(2) a protocol for determining how to forward (2) a protocol for determining how to forward multicast packets, based on the routing table multicast packets, based on the routing table and routing messages of (1)and routing messages of (1)

33Netcomm 2005

Example TopologyExample Topologyg g

s

g

34Netcomm 2005

Phase 1: FloodingPhase 1: Floodingg g

s

g

35Netcomm 2005

Phase 2: PruningPhase 2: Pruningg g

s

prune (s,g)

prune (s,g)

g

36Netcomm 2005

Steady StateSteady State

g g

s

g

g

37Netcomm 2005

graft (s,g)

graft (s,g)

Joining on New ReceiversJoining on New Receivers

g g

s

g

g

report (g)

38Netcomm 2005

Steady State after JoiningSteady State after Joining

g g

s

g

g

39Netcomm 2005

Steiner Minimal Tree (SMT)Steiner Minimal Tree (SMT)

• Shared Tree: All sources use the same Shared Tree: All sources use the same shared tree. shared tree.

• SMT is defined to be the minimal cost SMT is defined to be the minimal cost subgraph (tree) spanning a given subgraph (tree) spanning a given subset of nodes in a graphsubset of nodes in a graph

• Approximate SMT: KMBApproximate SMT: KMB

40Netcomm 2005

An example of a Steiner TreeAn example of a Steiner Tree

AB

D G

H

I

C

F

K J

E

4

54

52

2

1

64

15

1

132

3

Mcast group members

Relay Nodes

*

41Netcomm 2005

• Step 1Step 1: Construct a complete directed distance : Construct a complete directed distance graph Ggraph G11=(V=(V11,E,E11,c,c11).).

• Step 2Step 2: Find the min spanning tree T: Find the min spanning tree T11 of G of G11. .

• Step3Step3: Construct a subgraph G: Construct a subgraph GSS of G by replacing of G by replacing

each edge in Teach edge in T11 by its corresponding shortest path in by its corresponding shortest path in

G. G.

• Step 4Step 4: Find the min spanning tree T: Find the min spanning tree TSS of G of GS.S.

• Step 5Step 5: Construct a Steiner tree T: Construct a Steiner tree THH from T from TSS by by

deleting edges in Tdeleting edges in TSS if necessary, so that all the if necessary, so that all the

leaves in Tleaves in TH H are Steiner points. are Steiner points.

KMB AlgorithmKMB Algorithm

42Netcomm 2005

Due to [Kou, Markowsky and Berman 81’]Due to [Kou, Markowsky and Berman 81’]

Worst case Worst case time complexitytime complexity O(|S||V| O(|S||V|22).).

CostCost no more than 2(1 - 1/ no more than 2(1 - 1/ll) *optimal cost ) *optimal cost

where where ll = number of leaves in the steiner tree. = number of leaves in the steiner tree.

KMB Algorithm Cont.KMB Algorithm Cont.

43Netcomm 2005

KMB ExampleKMB Example

A

C

D4

4

444 4

B

A

C

D4

4

4

B

A

B

C D

EF

G

HI

10

1

1

2

9

8

1 1

1/2

2

1/2

1

B

C D

EF

G

HI

1

1

2

1 1

1/2

2

1/2

1

A

Destination Nodes

Intermediate Nodes

44Netcomm 2005

KMB Example Cont.KMB Example Cont.

B

C D

EF

G

HI

1

1

2

1 1

1/2

2

1/2

A

B

C D

EF

I

1

1

2

1 1

2

A

Destination Nodes

Intermediate Nodes