Download Multimedia, QoS and Multicast

Communication Networks
Recitation 10
Netcomm 2005
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Multimedia, QoS
& Multicast Routing
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Quality of Service: What is it?
Multimedia applications:
network audio and video
QoS
network provides
application with level of
performance needed for
application to function.
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Multimedia QoS Requirements
• live sources, stored sources
• requirements: deliver data in timely manner
– short end-end delay for interactive multimedia
• e.g., IP telephony, teleconf., virtual worlds, DIS
– in time for “smooth” playout
• relaxed reliability
– 100% reliablity not always required
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Why is QoS so hard?
To provide performance (delay, loss) guarantees:
need session’s input traffic
• must know app’s traffic
demand
compute session’s
output
• scheduling discipline
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RTP - Real-time Transport Protocol
• Ip-based protocol providing
– time-reconstruction
– loss detection
– security
– content identification
• Designed primarily for multicast of realtime data
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General View
• and the result…
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RTCP – Real-time Control Protocol
• Designed to work together with RTP
• In an RTP session the participants
periodically send RTCP packet to give
feedback on the quailty of the data
• Comparable to flow and congestion
control of other transport protocols
• RTP produces sender and receivers
reports; statistics and packet counts
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RTSP – Real-time Streaming Protocol
• Client-server multimedia presentation
protocol to enable controlled delivery.
• Provides ”vcr”-style remote control
• RTSP is an application-level protocol
designed to work with RTP (and RSVP) to
provide a complete streaming service over
internet
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RTSP Cont.
Ethernet IP
header header
UDP
header
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RTP
header
RTSP
header
Multimedia Data
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Example: Media on Demand
HTTP GET
presentation description (sdp)
client
web
server
SETUP
PLAY
RTP audio/video
media
servers
RTCP
TEARDOWN
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Intserv: QoS guarantees
• Resource reservation
– call setup, signaling (RSVP)
– traffic, QoS declaration
– admission control
request/
reply
– QoS-sensitive
scheduling
2005
(e.g.,Netcomm
WFQ)
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RSVP – Reservation Protocol
• Reservation is done in one direction
• Receiver-initiated
• The sender sends QoS wanted to the
receiver which sends an RSVP
message back to the sender
• The sender does not need to know the
capabilities along the path or at the
receiver
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Intserv QoS: Service Models
Guaranteed service:
Controlled load service:
• worst case traffic arrival:
leaky-bucket-policed
source
• simple bound on delay
• "a quality of service
closely approximating the
QoS that same flow
would receive from an
unloaded network
element."
arriving
traffic
token rate, r
bucket size, b
WFQ
per-flow
rate, R
D = b/R
max Netcomm 2005
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Differentiated Services
edge routers:
• profile of allowable user traffic
• packet marking:
• in-profile
• out-of-profile
“stateless” core routers:
• no notion of sessions
• forwarding: in-profile have
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“priority” over out-of-profile
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Differentiated Services Cont.
• Complexity (per-flow state) at network edge
– leaky bucket marking
• High-speed, stateless core routers
– 1-bit determines forwarding behavior
• Over-provisioned bandwidth: for in-profile
traffic used for out-profile, best effort traffic
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QoS Routing
C
B
A
H
E
F
D
G
K
J
I
delay: 10 ms
bandwidth :100 Mb/s
cell loss ratio: 1.0e-6
• QoS Routing = Multiple parameter
routing subject to constraints
– Link metrics are vectors
– NP-complete (good heuristics needed)
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The Problem
Traditional unicast model does not scale
– Millions of clients
– Server and network meltdown
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Solution: IP Multicast
• Source sends single stream
• Routers split stream towards all clients
• Guarantee only one copy in each link
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Multicast Routing Tree
Multicast Routing Protocol
On tree relay router
IGMP
Router with directly
attached group members
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Internet Group Management
Protocol (IGMP)
• Used by routers to learn about Multicast
Group Memberships on their directly
attached subnets
• Implemented over IP
• Designated Router
– Each network has one Querier
– All routers begin as Queriers
– Mrouter with the lowest IP address chosen
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How IGMP Works
routers:
Q
hosts:
one router is elected the “querier”
querier periodically sends a Membership Query message
to the all-systems group (224.0.0.1), with TTL = 1
on receipt, hosts start random timers (between 0 and 10
seconds) for each multicast
group to which they belong
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How IGMP Works (cont.)
Q
G
G
G
G
when a host’s timer for group G expires, it sends a
Membership Report to group G, with TTL = 1
other members of G hear the report and stop their timers
routers hear all reports, and time out non-responding
groups
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Type of Service (TOS) Routing
Does not support real QoS
“high throughput”
“low delay”
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Multicast Tree with QoS
• QoS constraints
– Link: minimum bandwidth; available buffer space.
– Tree constraints: end-to-end delay; jitter.
• Optimization objectives
– Link: maximize bandwidth.
– Tree optimization: minimize the cost.
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Core-Based Trees (CBT)
• Core-based multicast routing:
– One router is selected as the core for each
multicast group.
– A tree rooted at the core spans all group
members.
– Data packets are forwarded on all on-tree
interfaces except the one on which packets
arrive.
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CBT Multicast Routing
Core
On tree relay router
Sender
On tree router
Router with directly
attached group member
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Member Join in CBT
Core
join-ack
join-request
join-request
join-ack
Requesting router
with a new member
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QoS-Aware Member Join
Core Eligibility Test
u
On tree relay router
join-request
On tree group router
join-request
v
Only after the join-request passes the eligibility
tests will a join-acknowledgement be returned.
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Shortest Path Tree (SPT)
• Source Based Tree: Rooted at the source,
composed of the shortest paths between
the source and each of the receivers in
the multicast group.
• If the routing metric used is the latency
between neighbors, the resulted tree will
minimize delay over the multicast group.
• Example: DVMRP.
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Distance-Vector Multicast
Routing Protocol (DMVRP)
DVMRP consists of two major components:
(1) a conventional distance-vector routing
protocol (like RIP)
(2) a protocol for determining how to forward
multicast packets, based on the routing table
and routing messages of (1)
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Example Topology
g
g
s
g
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Phase 1: Flooding
g
g
s
g
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Phase 2: Pruning
g
g
prune (s,g)
s
prune (s,g)
g
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Steady State
g
g
g
s
g
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Joining on New Receivers
g
g
g
report (g)
graft (s,g)
s
graft (s,g)
g
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Steady State after Joining
g
g
g
s
g
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Steiner Minimal Tree (SMT)
• Shared Tree: All sources use the same
shared tree.
• SMT is defined to be the minimal cost
subgraph (tree) spanning a given
subset of nodes in a graph
• Approximate SMT: KMB
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An example of a Steiner Tree
5
4
K
F
1
3
Relay Nodes
5
2
3*
1
D
A
E
C
4
I
1
2
5
J
2
B
Mcast group members
4
6
H
1
G
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KMB Algorithm
• Step 1: Construct a complete directed distance
graph G1=(V1,E1,c1).
• Step 2: Find the min spanning tree T1 of G1.
• Step3: Construct a subgraph GS of G by replacing
each edge in T1 by its corresponding shortest path in
G.
• Step 4: Find the min spanning tree TS of GS.
• Step 5: Construct a Steiner tree TH from TS by
deleting edges in TS if necessary, so that all the
leaves in TH are Steiner points.
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KMB Algorithm Cont.
Due to [Kou, Markowsky and Berman 81’]
Worst case time complexity O(|S||V|2).
Cost no more than 2(1 - 1/l) *optimal cost
where l = number of leaves in the steiner tree.
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KMB Example
A
A
4
1
10
H
I
1/2
1/2
G
1
1
1
B
8
1
F
2
C
9
E
2
D
B
D
4
4
4
4
A
1
4
H
C
I
1/2
1/2
1
G
A
4
1
D
B
1
4
B
1
F
2
4
C
E
2
D
C
Destination Nodes
Intermediate
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KMB Example Cont.
A
A
1
1
H
1/2
1/2
G
B
1
1
F
2
C
I
I
1
1
E
B
1
1
F
2
2
C
D
E
2
D
Destination Nodes
Intermediate Nodes
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