1 Introduction to Networking • What is a computer network? • Why do you want to take Csci 5211? • Internet Architecture • Statistical multiplexing and packet switching • Connection-oriented vs Connectionless • Fundamental issues in computer networking • Readings – Sections 1.1-1.5
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Introduction to Networking - University of Minnesota · • Store-and-forward approach: packets buffered before transmission ... Item Circuit-switched Packet-switched ... Connection-Oriented
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1
Introduction to Networking
• What is a computer network?
• Why do you want to take Csci 5211?
• Internet Architecture
• Statistical multiplexing and packet switching
• Connection-oriented vs Connectionless
• Fundamental issues in computer networking
• Readings
– Sections 1.1-1.5
2
What is a Computer Network?
• Network provides connectivity
– A set of computers/switches connected by communication links
•“A domain characterized by the use of electronics and the electromagnetic spectrum to store, modify, and exchange data via networked systems and associated physical infrastructure.”
Inside the ‘Net: A Different Story…
• Closed equipment
– Software bundled with hardware
– Vendor-specific interfaces
• Over specified
– Slow protocol standardization
• Few people can innovate
– Equipment vendors write the code
– Long delays to introduce new features29
Do We Need Innovation Inside?•Many boxes (routers, switches, firewalls, …) with different interfaces and not programmable.
Proposed SDN Solution
•Control Plane
•Data Plane
•Standard API to Enable
Programmable
•Separation of Control Plane and Data Plane
•Logically Centralize
d Controller
•Open API
Seamless Mobility• See host sending traffic at new location
• Modify rules to reroute the traffic
32
Server Load Balancing• Pre-install load-balancing policy
• Split traffic based on source IP
•src=0*,
•dst=1.2.3.4
•src=1*,
•dst=1.2.3.4
•10.0.0.1
•10.0.0.2
Example SDN Applications
• Seamless mobility and migration
• Server load balancing
• Dynamic access control
• Using multiple wireless access points
• Energy-efficient networking
• Adaptive traffic monitoring
• Denial-of-Service attack detection
• Network virtualization
34•See http://www.openflow.org/videos/
Network Function Virtualization (NFV)
•Slide from: http://
Use Case: vWOC (virtualized
WAN Optimization Controller)
6 September 2015 37
Future Internet Requirements
Be worthy of our society’s trust
– Especially for managing and operating critical infrastructures
Provide a bridge between physical and virtual worlds
– Via instrumented and managed sensorized physical environment
Support pervasive computing
– From netted smart devices to supercomputers
– From wireless channels to all optical light-paths
Enable further innovations in S&E research
– Seamless access to networked instruments, supercomputers, storage,
databases, collaboratories, etc.
Create a social world in which we would want to live
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Multiplexing Strategies
• Sharing of network resources among multiple users
• Common multiplexing strategies
• Time Division Multiplexing (TDM)
• Frequency Division Multiplexing (FDM)
• These two strategies are circuit switching technology
39
Circuit Switched Networks
• All resources (e.g. communication links) needed by a call
dedicated to that call for its duration
– Example: telephone network
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Statistical Multiplexing
• Time division, but on demand rather than fixed
• Reschedule link on a per-packet basis
• Packets from different sources interleaved on the link
• Buffer packets that are contending for the link
• Buffer buildup is called congestion
• This is packet switching, used in computer networks
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Packet Switched Networks
• Data entering network is divided into chunks called “packets”
• Store-and-forward approach: packets buffered before transmission
• Packets traversing network share resources with other packets
– On demand resource use: statistical resource sharing
• Fewer resources: queuing delay, packet loss
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Why Statistically Share Resources
• Efficient utilization of the network
• Example scenario
– Link bandwidth: 1 Mbps
– Each call requires 100 Kbps when transmitting
– Each call has data to send only 10% of time
• Circuit switching
– Each call gets 100 Kbps: supports 10 simultaneous calls
• Packet switching
– Supports many more calls with small probability of contention
• 35 ongoing calls: probability that > 10 active is < 0.0017!
43
Circuit Switching vs Packet Switching
Item Circuit-switched Packet-switched
Dedicated “copper” path Yes No
Bandwidth available Fixed Dynamic
Potentially wasted bandwidth Yes No
Store-and-forward transmission No Yes
Each packet follows the same route Yes No
Call setup Required Not Needed
When can congestion occur At setup time On every packet
Effect of congestion Call blocking Queuing delay
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Connection-Oriented Service
• Sender
– Requests “connection” to receiver
– Waits for network to form connection
– Leaves connection in place while sending data
– Terminates connection when no longer needed
• Network
– Receives connection request
– Establishes connection and informs sender
– Transfers data across connection
– Removes connection when sender requests
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Connectionless Service
• Sender
– Forms packet to be sent
– Places address of intended recipient in packet
– Transfers packet to network for delivery
• Network
– Uses destination address to forward packet
– Delivers the packet to destination
46
Connection-Oriented vs Connectionless
• Connection-Oriented• Telephone System, Virtual Circuit Model
– Path is setup before data is sent
– Data identifies the connection
– All data follows the same path
• Connectionless• Postal System, Datagram Model
– No path setup before transmitting data
– Packet contains identification of destination
– Each packet handled independently
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Connection-Oriented vs. Connectionless
• Connection-Oriented
– Connection setup overhead
– State in packet switches
– Can reserve bandwidth
• Connectionless
– Stateless and less overhead
– Resource reservation not possible
– Allows broadcast/multicast
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Fundamental Issues in Networking
• Naming/Addressing
– How to find name/address of the party (or parties) you would like
to communicate with
– Address: byte-string that identifies a node
– Types of addresses
• Unicast: node-specific
• Broadcast: all nodes in the network
• Multicast: some subset of nodes in the network
• Routing/Forwarding: process of determining how to send
packets towards the destination based on its address
– Finding out neighbors, building routing tables
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Fundamental Problems in Networking
• What can go wrong?
– Bit-level errors: due to electrical interferences
– Packet-level errors: packet loss due to buffer overflow/congestion
– Out of order delivery: packets may takes different paths
– Link/node failures: cable is cut or system crash
• What can be done?
– Add redundancy to detect and correct erroneous packets
– Acknowledge received packets and retransmit lost packets
– Assign sequence numbers and reorder packets at the receiver
– Sense link/node failures and route around failed links/nodes
• Goal: to fill the gap between what applications expect and what underlying technology provides