Transcript Emerging Internet Technologies

Emerging Internet Technologies
Harish Sethu
Department of Electrical and Computer
Engineering
Drexel University
1
Introduction and History
 More rapid growth than any medium in
history
 New applications in education, business and
medicine
 Impact on entertainment, politics and the
day-to-day lives of people
 Internet still very young, and rapidly
evolving.
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Introduction and History (Cont’d)
The Origin
 Began as ARPANET in 1969 for the purpose of
sharing computing resources
 ARPANET was funded by the Department of
Defense
 Met with resistance even by university research
groups who did not wish to be linked to the
ARPANET
 Used packet switching as opposed to circuit
switching
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Introduction and History (Cont’d)
Circuit Switching
4
Introduction and History (Cont’d)
Circuit Switching
 Physical connection established between
communicating end-points.
 Requires setting up the connection before
communication
 Guaranteed bandwidth
 Predictable and bounded delay
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Introduction and History (Cont’d)
Packet Switching
 No physical connection established between
communicating end-points.
 Data is sent in blocks called packets
 Each packet is routed independently
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Introduction and History (Cont’d)
Packet Switching
Packet 1
Packet 2
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Introduction and History (Cont’d)
Packet Switching vs. Circuit Switching
 Packets may arrive out-of-order
 Packets may be dropped, since network does not
guarantee bandwidth
 Packet switching analogous to how we share road
space
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Introduction and History (Cont’d)
The origins of packet switching
 The roles of Leonard Kleinrock, Paul Baran and
Donald Davies
 BBN’s proposal to use packet switching for
ARPANET
 The travails of packet switching
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Introduction and History (Cont’d)
Milestones
 Ethernet
 TCP/IP
 E-mail
 Commercialization of the Internet
 World Wide Web
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Introduction and History (Cont’d)
Internet Organizations
 The Internet Society
 The Internet Architecture Board
 The Internet Engineering Task Force
 The Internet Engineering Steering Group
 ICANN
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Protocol Layering
 What is a protocol?
 What is protocol layering?
 The analogy to postal service.
 Why use protocol layering?
 Simplicity in design
 Flexibility in accommodating new technologies
 Compatibility of applications to systems
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Protocol Layering (Cont’d)
A common implementation
Application Layer
Application protocol, e.g., HTTP
Application Layer
Transport Layer
Application Layer
Transport protocol, e.g., TCP
Transport Layer
Transport Layer
Transport Layer
Network protocol, e.g., IP
Network Layer
Network Layer
Access Layer
Application Layer
Network access protocol, e.g., Ethernet
Network
Layer
Network
Layer
Access Layer
Access Layer
Access Layer
Physical Layer
Physical Layer
Physical Layer
Physical Layer
Physical medium, e.g. copper
System 1
System 2
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Switches and Routers
 What is a switch and what is a router?
 The problem with achieving performance
 The need for buffers
Packet headed to output 0
Packet headed to output 1
0
0
0
0
1
1
1
1
(a)
Before
After
0
0
0
0
1
1
1
1
(b)
Before
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After
Switches and Routers (Cont’d)
Input queueing and output queueing
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Switches and Routers (Cont’d)
Head-of-line blocking with input queueing
Packet headed to output 0
Packet headed to output 1
0
0
0
0
1
1
1
1
End of Cycle 1
End of Cycle 2
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Switches and Routers (Cont’d)
Output queueing and head-of-line blocking
Packet headed to output 0
Packet headed to output 1
0
0
0
0
1
1
1
1
End of Cycle 1
End of Cycle 2
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Switches and Routers (Cont’d)
Commercial switches and routers
 Use both input and output queueing
 Use shared buffer for output queueing
 Use complex buffer organizations and queue
management strategies
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Virtual Circuit Switching
 Establishes a virtual circuit
 Routes using a virtual circuit identifier on
each packet
 Packets with same identifier routed
identically by a switch
 Facilitates easy management of flows of
traffic
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Virtual Circuit Switching (Cont’d)
Asynchronous Transfer Mode (ATM)
 Uses virtual circuits
 Proposed for providing performance guarantees as
in circuit switching using the packet switching
technology
 Largely used today in the Internet backbone
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Routing
 What is routing?
 What is a route table?
 What is a “best” route?
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Routing (Cont’d)
Link State Routing
 Periodically measure cost to each neighbor
 Distribute measurements to all routers in the
network
 Each router has complete and current information on
the topology
 Each router independently computes the “best” path
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Routing (Cont’d)
Distance-Vector Routing
 Each router maintains a distance-vector, the cost to
reach each destination from itself.
 Exchanges distance-vectors with neighbors
 Determines the “best” path neighbor to reach
destination
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Routing (Cont’d)
Routing in the Internet
 Distance-vector routing used in the Internet core
(BGP)
 Link-state routing used within domains (OSPF)
 Border routers use both
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Flow Control and Congestion
Avoidance
 What is flow control?
 What is congestion avoidance?
 Design goals:
 responsiveness
 performance
 scalability
 simplicity
 fairness
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Flow Control and Congestion
Avoidance (Cont’d)
Flow control strategies
 Open loop flow control
 No feedback
 Pre-arranged self-regulation at the source
 Closed loop flow control
 Self-regulation based on feedback
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Flow Control and Congestion
Avoidance (Cont’d)
Open loop flow control
 Traffic descriptors
 Token bucket regulator
 token generation
 bucket capacity
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Flow Control and Congestion
Avoidance (Cont’d)
Token bucket regulator
Packets
Token
Bucket
Tokens
Network
Network
Before
After
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Flow Control and Congestion
Avoidance (Cont’d)
Closed loop flow control
 TCP uses closed loop flow control
 slow-start phase in TCP (exponential rate increase)
 congestion-avoidance phase in TCP (linear rate
increase)
 time-outs and back-off
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Flow Control and Congestion
Avoidance (Cont’d)
A typical saw-tooth graph of TCP sending rate
Time-out occurs
due to congestion
Linear
Increase
TCP
Send
ing
rate
Threshold
New threshold
Exponential
increase
Time
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Flow Control and Congestion
Avoidance (Cont’d)
Problems with TCP
 Does not avoid congestion, reacts only after
congestion
 Assumes time-outs are always due to congestion
 Always keeps pushing the network into congestion
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Flow Control and Congestion
Avoidance (Cont’d)
Random Early Detection (RED)
 Defines router actions designed to work with TCP
 Goal is congestion avoidance, at good performance
 Detects impending congestion based on queue
length
 Drops packets before congestion occurs
 Triggers TCP to cut down its rate before it causes
congestion
 Used in most Internet routers today
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Emerging Architectures and
Services
 Onslaught of multimedia traffic
 Need for service beyond best effort
 What is Quality of Service?
 throughput guarantee
 delay bound
 delay-jitter bound
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Fairness in Traffic Management
 The most basic guarantee: fairness.
 Why not just first-come-first-serve?
 Why not just packet-by-packet round-robin
scheduling?
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Fairness in Traffic Management
(Cont’d)
What is fair and how to be fair?
 All flows with unsatisfied demands should get an
equal share of the resource
 No flow should be allocated more resources than its
demand
 Fair queueing is a technique that achieves the above
two conditions for fairness to a satisfactory extent.
 Most Internet routers now implement some version
of a fair queueing discipline.
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The Integrated Services Model
 A new architectural framework to facilitate QoS in
the Internet.
 Applications describe their traffic to the network,
and their demand for QoS
 Network decides if the demand can be satisfied
before admitting the application traffic
 Routers reserve bandwidths and buffers necessary to
satisfy demand
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The Integrated Services Model
(Cont’d)
Flow specifications
TSpec




burst size
long-term average rate
maximum packet size
peak rate
RSpec
 service rate
 delay bound
 packet loss probability
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The Integrated Services Model
(Cont’d)
Service Classes
Guaranteed service
 Provides hard guarantees
 Requires per-flow management in the routers
 Suffers from scalability problems
Controlled Load Service




Service similar to best-effort in a lightly loaded network
Meant for applications that can tolerate some loss or delay
Requires application to specify traffic description
Network decides whether or not to admit a new flow for
controlled load service
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The Integrated Services Model
(Cont’d)
Signaling (RSVP)
 RSVP is an IP signaling protocol
 Uses two messages: Path and Resv
 Path messages go from the sender to the receiver,
containing traffic description
 Resv messages go from receiver to the sender,
containing QoS requirements
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The Integrated Services Model
(Cont’d)
Flow of Path and Resv messages
Path
Path
Receiver 1
Path
Resv
Sender
Resv
Resv
Path
Path
Path
Resv
Path
Resv
Resv
Path
Resv
Receiver 3
Resv
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The Integrated Services Model
(Cont’d)
Multicasting with RSVP
 RSVP explicitly designed for multicast
 Multicast method based on data replication in the
network
 Allows merging of Resv requests
 RSVP is a soft-state protocol
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The Differentiated Services Model
 Differentiated Serevices model is more scalable.
 Traffic is divided into classes
 Resources allocated on a per-class basis instead of a
per-flow basis
 Defines a set of Per-Hop Behaviors (PHBs)
 Service by the network based on the PHB carried in
the packet
 Standard PHBs
 Expedited Forwarding
 Assured Forwarding
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The Differentiated Services Model
(Cont’d)
Expedited Forwarding (EF-PHB)
 A request to forward the packet as quickly as
possible
 Meant for applications with stringent delay
requirements
 Requires strict regulation at source
 Requires careful capacity planning
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The Differentiated Services Model
(Cont’d)
Assured Forwarding (AF-PHB)
 Delivers with high assurance (a weaker guarantee)
 Consists of 4 classes and 3 drop precedence levels
 In-order delivery within each class
 Drop precedence defined at the source end
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The Differentiated Services Model
(Cont’d)
A potential DiffServ scenario
Drexel University DS Domain
Hosts
Border
router
ISP
router
Hosts
Internet backbone
network
Service Level
Agreement made
on aggregated rate
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Multi-Protocol Label Switching




Uses the concept similar to that of virtual circuits in IP
Uses fixed-size labels
Originally designed to facilitate sending IP packets over ATM
Packets are routed based on the label, instead of destination
address.
 Supported by high-end routers today
 Achieves lower header overhead
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Multi-Protocol Label Switching
(Cont’d)
Achieves separation of control and forwarding
components:
Control Component
Updates to/from
other routers
Routing
Protocols
Updates to/from
other routers
Routing
Tables
Forwarding
Tables
Packets with
labels
Forwarding
Fabric
Forwarding Component
Packets with
labels
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Multi-Protocol Label Switching
(Cont’d)
A limitation of traditional routing:
Point of
Congestion
1
4
A
A&B
A&B
3
2
B
6
5
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Multi-Protocol Label Switching
(Cont’d)
MPLS extends routing functionality:
1
4
A
A
A
3
2
B
6
B
5
B
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Concluding Remarks
 Internet is still evolving, and very rapidly.
 Service requirements of applications may
change; new solutions such as active
networking are emerging.
 Engineering the Internet continues to be both
challenging and rewarding.
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