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Integrated and Differentiated Services Architecture
for Multimedia Applications over the Internet
• Approaches for providing QoS on the Internet
• Two different service types IntServ and DiffServ : implementation and problems
• Two-bit differentiated services architecture
• Problems with end-end bandwidth allocation based on level of marked traffic
• Discussion
Presentation Plan
Presentation Plan
• Focus on concepts and reasoning• Discuss issues & challenges• Offer personal opinions stimulating
thinking
Two Approaches for Providing QoS on the Internet
1. “Freeway model” – Integrated Services (IntServ)– Build a dedicated highway or “circuit”
between communicating points2. “Doctor’s model” – Differentiated Services
(DiffServ)– Mark a doctor’s vehicle (e.g. ambulance)
or “packet” to get priority on the road and limit the percentage of such high-priority vehicles in the total traffic mix
Integrated Services (IntServ)
• A connection-oriented solution• QoS on a per-flow basis• Depends on resource
reservation (RSVP)
7
Information Network : Scale of Network
LAN
SD2
SD1
RC1
Ingres Egress
BW1 BW2 BW3
S S
RC2
SD = sender, RC = receiver, S = server, LAN = Local Area Network, BW = Bandwidth
Node1
Node2
Node3
ack
Ingress
8
Quality of Service: View at a glance
Multimedia applications: network audio and video
network provides application with level of performance needed for application to function.
QoS
9
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
– in time for “smooth” playout • relaxed reliability
– 100% reliablity not always required
10
Why is QoS so hard?
need session’s input traffic• must know app’s traffic
demand(resources, delivery-time constraint, reliability of information transfer)
To provide performance (delay, jitter, loss) guarantees:
compute session’s output• Priority of scheduling
(scheduling discipline)
11
12
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
13
RSVP : logical frame work
LAN
SD2
SD1
RC1
Ingres Egress
BW1 BW2 BW3
S S
RC2
SD = sender, RC = receiver, S = server, LAN = Local Area Network, BW = Bandwidth
Node1
Node2
Node3
Forward resourceRequest along the Communication path
Backward responseTo resource request
Ingress
14
Intserv: QoS guarantees• Resource reservation
– call setup, signaling (RSVP)– traffic, QoS declaration– admission control
– QoS-sensitive scheduling (e.g., WFQ)
request/reply
15
QoS Routing
• QoS Routing = Multiple parameter routing subject to constraints– Link metrics are vectors– NP-complete (good heuristics needed)
A
B C D
EF G
H J
K
delay: 10 msbandwidth :100 Mb/scell loss ratio: 1.0e-6
I
Difficulties with IntServ & RSVP
• Scalability– Keeping a state (and using it!) for each flow
overloads the router– Periodic messages to refresh the states creates
more traffic
• Router complexity increases (more computing capabilities required)
• How to satisfy heterogeneous QoS requirements for different receivers
• Ambitious signaling is not practical
Differentiated Services (DiffServ)
• Motivations: no end-to-end signaling and per-flow state, for scalability, complexity and quick-to-deploy reasons.
• Diff-Serv approach: use the TOS field to sort packets into classes and treat them differently.– e.g., one TOS bit to indicate the delay
requirement of the packet, and another to indicate the drop precedence
IP Header (V4)8 bits
19
Type of Service (TOS) Routing
“low delay”
“high throughput”
Originally does not support real QoS
Principles of DiffServ• Connectionless mode• QoS for aggregates of traffic, such as
primary/premium, assured and best-effort• Keep the forwarding path simple to
allow easy and early deployment; push complexity to network edge
• Avoid strong assumptions about traffic types; assume the dominant Internet traffic will be the best-effort traffic in a massive amount, so there is ample headroom to provide priority for a relatively small set of packets
How to describe a service• What is provided to the customer
– E.g., 1 Mbps, continuously available
• To where is this service provided– A single destination– A group– All nodes on local provider– Everywhere
• Level of assurance provided to service– What level of performance uncertainty can
user tolerate
Premium service
• Provides guaranteed peak bandwidth service with negligible delay/jitter
• “Virtual leased lines”: don't waste bandwidth when circuits are unused
• Useful for voice• is given its own high-priority queue in
routers; takes a small portion of network bandwidth
• Shaped and hard-limited to its provisioned peak rate
Mechanism for premium service
Host First-hop
Intra-network
Router
H-Q: premium, no dropping L-Q: best effort, dropping on
congestion
Assured service
• Provides an expected level of bandwidth with delay
• Characteristic slightly better than best-effort
• Useful for e.g., connections to search engines
• Permits flows to use any additional available bandwidth
• Requires buffer management, e.g., RED
Mechanism for assured service
Host First-hop Cou
nte r
Cou
nte r
Out- and in- dropper
RIO scheme, packets are treated preferentially
Marking packets according to the service profile
RIO algorithm
• RED - Random Early Detection– Packets dropped with low but
increasing probability as queue grows; instead of waiting until it is full and dropping all new packets
• RIO– Run two RED algorithms for “in” and
“out” with different dropping frequencies
Usage Example of DiffServ
Components of DiffServ
(1) Edge node algorithmsClassification, policing, shaping,
metering, marking, etc.
(2) Router algorithmsPacket discard algorithms: RED-like methods for in-profile and outof-
profile trafficPriority, low-latency queueing
Forwarding Path
Access Router
• Packet Classifier: classifies the packets based on their flow-id
• Marker:– being implemented as tocken bucket– checks the conformance of arriving packets and marks
them accordingly
Marker Implementation
Premium Marker Assured Marker
Core Router
Illustration of Discard Policy
Closure
• DiffServ is sort of a gamble. It may actually work in the market place. We are all learning!
• Initially, probably only few traffic classes will need to be deployed. Deployment can start when ISP routers have been made TOS aware
• Access and boundary routers need processing power per packet
• Network management is needed for resource control (on-going work)
Assignment
• Compare ATM’s CBR with DiffServ’s Premium Service
• Compare ATM’s ABR with DiffServ’s Assured Service
We are all learning, so keep improving your knowledge