AA ReviewReview ofof KeyKey NetworkingNetworking ConceptsConcepts
Dr. Arjan Durresi Louisiana State University Baton Rouge, LA 70810 [email protected] These slides are available at: http://www.csc.lsu.edu/~durresi/csc4601-04/
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Overview
Telecommunications – tools to improve communications ISO/OSI Reference Model Ethernet/IEEE 802.3 LANs Interconnecting Devices
Louisiana State University 2- Networking Key Concepts - 2 CSC4601 F04 A Motivating Example Requirements of an e-Commerce site Performance
# of current transactions Usability
Easy to follow GUIs, convenience (cookies?) Security
Secure transmission and storage of costumer financial/personal data
Protect the Web servers and the enterprise network from illegitimate access
Provide continuous/uninterrupted services
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Networking Technologies
Louisiana State University 2- Networking Key Concepts - 4 CSC4601 F04 Trends: by Application Demands
Hunger for bandwidth Hardware (Physics) breakthroughs seem to come easier than software Wider spectrum of application sophistication: Best-effort to guaranteed Built-in security? Drive for ubiquitous access Economics/profitability
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Quest for Better Services
Real-time audio/video requires guaranteed end-to-end delay and jitter bounds. Adaptive multimedia application requires minimum bandwidth and loss assurance. Intelligent application demands reliable feedback from the network. Security.
Louisiana State University 2- Networking Key Concepts - 6 CSC4601 F04 Quest for Ubiquitous Access ...
Information age is a reality. Everything depends on reliable and efficient information processing. Quality of our everyday life. Development of national/world economy. Security of national defense/world peace. Networking is one critical part of this underlying information infrastructure!
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Economic Pressure
Service providers want the most bang on their buck - the most profitable technology? Cautious adoption of new technologies
Even for security Emphasis on leveraging deployed technologies Increased utilization of existing facilities
Louisiana State University 2- Networking Key Concepts - 8 CSC4601 F04 Security Implications
Vulnerabilities - from weak design, to “feature-rich” implementation, to compromised entity Heterogeneous networking technologies adds to security complexity But improves survivability Higher-speed communication puts more information at risk in given time period Easier to attack than to defend Ubiquitous access increases exposure to risks
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The Good News ...
Plenty of basic means for end-user protection - authentication, access control, integrity checking Intensive R&D effort on security solutions (government sponsored research & private industry development) Increasing public awareness of security issues New crops of security(-aware) researchers and engineers YOU!
Louisiana State University 2- Networking Key Concepts - 10 CSC4601 F04 The Bad News ...
(Existing) information infrastructure as a whole is very vulnerable, which makes all critical national infrastructure vulnerable e.g., Denial-of-service attacks are particularly dangerous to the Internet infrastructure Do we continue to band-aid or re-design? Serious lack of effective technologies, policies, and management framework
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Communication
Exchange of Information (Communication), makes possible the Human society and the civilization Improvements in communication - milestones in the history of civilization Language Writing Books Electronic communication, Internet
Louisiana State University 2- Networking Key Concepts - 12 CSC4601 F04 Communication with computers Tools created to increase and enhance our capabilities: Cars, Airplanes, Microscopes, Telescopes Telegraph , Telephone to communicate Computers born to store and process information Computers to communicate; Network - more than two computers Each epoch in human history is dominated by one tool: Industrial Revolution: Steam engine Information Age: Computers and networks
The Internet is the universal medium of communication
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Evolution of Networks In 1890 simple telephone networks with manually operated switches – circuit switching Operators replaced by mechanical switches and 100 years later by electronic switches
Electronic switches and exchange control information using the common channel signaling (CCS)
Louisiana State University 2- Networking Key Concepts - 14 CSC4601 F04 Evolution of Networks Since 1980s Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) for the transmission links of the telephone networks Integrated Services Digital Network (ISDN) – integration of data and voice Asymmetric Digital Subscriber Line (ADSL) > 1.5 Mbps downstream
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RS-232C
Up to 38kbps over short distances (less than 30m) Serial transmission one character at a time Each character => 7 bits + 1bit parity
Louisiana State University 2- Networking Key Concepts - 16 CSC4601 F04 Synchronous Transmission
The first computer networks designed to share large- scale computers HDLC family Packet based => header + data + CRC
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Store-and-forward Packet Switching
To interconnect many computers Statistical multiplexing – more efficient than time- division multiplexing ARPNET late 1960s The network is peripheral
Louisiana State University 2- Networking Key Concepts - 18 CSC4601 F04 Evolution of Networks
Emergence of LANs In the 1990s Internet becomes a commercial success Internet has been doubling is size every nine months From “If a company is important it is online” to “If a company is not on line it doesn’t exist” The impact of Internet: Economic, Education, Government, etc.
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Local Area Networks
Emergence of LANs Ethernet 10Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet everywhere: LAN and WAN
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Token Ring – better performance than Ethernet Avoid collisions Handle priorities FDDI up to 100Mbps Data + Real time traffic
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Asynchronous Transfer Mode
Switched technology – total throughput much larger than shared medium ones 53 bytes cell. Integration of data and voice. Very good QOS Complex, less scalable than Ethernet and IP, no native applications
Louisiana State University 2- Networking Key Concepts - 22 CSC4601 F04 Always more speed DWDM
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Cable Television Networks
CATV delivers TV in more than 50% of US households High Speed Internet Access. Cable modems: 45 Mbps downstream, 1.5 Mbps upstream Sharing ⇒ Security issues No cable in offices But new revenue for providers
Louisiana State University 2- Networking Key Concepts - 24 CSC4601 F04 Historical Maps of Computer Networks
http://www.cybergeography.org/atlas/historical.html The pioneering research of Paul Baran in the 1960s, who envisioned a communications network that would survive a major enemy attacked. Donald Davies, a pioneer in networking in the 1960s A good book Where Wizards Stay Up Late: The Origins of the Internet, by Katie Hafner and Matthew Lyon
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Trend: Convergence Entertainment Video Games Publishing News Advertising Cable TV Telephone Computer
Digital Digital Media Video Voice Media Storage/ Transport Transport Production Handling
Louisiana State University 2- Networking Key Concepts - 26 CSC4601 F04 Convergence (Cont) Content
Computing Communications Merging of Content Providers and Content transporters Phone companies, cable companies, entertainment industry, and computer companies Single department for telephone and computer networking LAN/WAN convergence
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Social Impact of Networking
From : “To be important should be online” to: “ To exist should be online”
No need to get out for Virtual Schools Office Virtual Cash Shopping Virtual Workplace Entertainment 165 Million US online Education users
Louisiana State University 2- Networking Key Concepts - 28 CSC4601 F04 Cave Persons of 2050
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Networking Trends ?
Networking Bottleneck – Bandwidth bps more important that CPU speed Networking Age - Internet-based Economy Internet Growth - High Data > Voice ⇒ Networking and Telecom Merger Quality of Service – “Holy Grail” for the research Optical Networks – The promise for unlimited bandwidth The Internet - the universal medium of communication Louisiana State University 2- Networking Key Concepts - 30 CSC4601 F04 How Fast is the Internet Growing? IP Traffic Growth will slow down from 200-300% per year to 60% by 2005 - McKinsey & Co and JP Morgan, May 16, 2001 98% of fiber is unlit - WSJ, New York Times, Forbes (Fiber is a small fraction of cost. Laying is expensive.) Nortel blamed sales decline on falling IP traffic Carriers are using only avg 2.7% of their total lit fiber capacity - Michael Ching, Marril Lynch & Co. in Wall Street Journal
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The Bubble
Dot Coms CLECs Networking Y2K Spending
1997 1998 1999 2000 2001 Sidgmore: Internet Traffic doubling every 40 days, 30 days, …⇒ Over-projection data networking equipment Nearly 1/3 of all tech IPOs over the last 21 years happened in 1999 and 2000. Source:Morgan Stanely/Chi at Opticomm CLEC - Competitive Local Exchange Carrier ILEC - Incumbent Local Exchange Carriers
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Demand on 14 of 22 most used routes exceeds 70% -Telechoice, July 19, 2001 Traffic grew by a factor of 4 between April 2000- April 2001 -Larry Roberts, August 15, 2001
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Total U.S. Internet Traffic
20 Largest Tier 1 U.S. Internet Service Providers 60
3.0/yr Average Growth Rate 50
40 Total U.S. Internet Traffic 30
PetaBytes/month 20
10 ISPs
0 Jan 00 Apr 00 Jul 00 Oct 00 Jan 01 Apr 01 Jul 01 Oct 01 Jan 02 Source: Roberts et al., 2002
Louisiana State University 2- Networking Key Concepts - 34 CSC4601 F04 Moore’s Law is Too Slow
70.0 Traffic 60.0 50.0 40.0 30.0 20.0 10.0 Moore's Law Years 0.0 123456 Moore’s Law: Factor of 2 every 1.5 years ⇒ 60%/year Internet Traffic: Factor of 4 per year ⇒ Need for more Networks, QoS, Optical Switching
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Voice vs Data: Traffic vs Revenue 100%
80%
IP Traffic IP Revenue 60% Aug 2000 Aug 2002 40% Voice Traffic Voice Revenue 20%
0% Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05
Source: L. Roberts at Opticomm 2001
Louisiana State University 2- Networking Key Concepts - 36 CSC4601 F04 Trend: Traffic > Capacity
"You can never be too rich, too thin, or have too much bandwidth" Expensive Bandwidth Cheap Bandwidth Sharing No sharing Multicast Unicast Virtual Private Networks Private Networks Need QoS QoS less of an issue Likely in WANs Possible in LANs
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Is Technology only technical stuff ? Technology depends on the Socio-technical System Social, Political, Economic, Institutional Not simply the rational product of scientists and engineers. Technology makes sense when seen as part of the society Examples: Automobile engines: Internal combustion vs. steam Network technologies:
OSI vs. TCP/IP vs. ATM, Ethernet vs. Token Ring, ISDN vs. fax
Future: Quality of Service mechanisms over the Internet Louisiana State University 2- Networking Key Concepts - 38 CSC4601 F04 The right Trade off in Networking Need
Cost Complexity
User is the King => Pays the bill What does the user really need? Killer applications are key for the success of a particular technology In today’s Internet the driving need is connectivity Email and web browser – killer applications, which don’t need more QOS Future Internet, new applications + more QOS ?
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Dealing with Network Complexity Network complexity: Many technologies with different features Not all standards are compatible, from different organizations Multiple technologies to interconnect the networks No single underlying theory that explains the relationship among the parts How to learn about the networking ? Focus on the concepts, go beyond the details When needed is easy to go from concepts to details Concepts are “borrowed” among technologies.
Louisiana State University 2- Networking Key Concepts - 40 CSC4601 F04 ISO/OSI Reference Model
Application File transfer, Email, Remote Login 3 Presentation ASCII Text, Sound Session Establish/manage connection Transport 2 End-to-end communication: TCP Network Routing, Addressing: IP Datalink Two party communication: Ethernet 1 Physical How to transmit signal: Coding
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TCP/IP Reference Model
TCP = Transport Control Protocol IP = Internet Protocol (Routing) TCP/IP Ref ModelTCP/IP Protocols OSI Ref Model Application Application FTP Telnet HTTP Presentation Session Transport TCP UDP Transport Internetwork IP Network Host to Ether Packet Point-to- Datalink Network net Radio Point Physical
Louisiana State University 2- Networking Key Concepts - 42 CSC4601 F04 Layered Packet Format
Nth layer control info is passed as N-1th layer data. FTP FTP Data Header TCP TCP Data Header IP IP Data Header Ethernet Ethernet Ethernet Data Header Trailer
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Internet Protocol IP Hour-glass model: Glue of the Internet, Everything over IP, and IP over everything The single common language Implemented at both hosts and routers Accommodating heterogeneity Minimalist approach. Best effort datagram service One of the main reasons of the Internet’s success TCP,UDP
IP
ATM,Ethern.
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Defined by Internet Engineering Task Force (IETF) Hourglass Design Application vs. Application Protocol (FTP,
HTTP) FTP HTTP NV TFTP
TCP UDP
IP
… NET 1 NET 2 NET n
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TCP/IP Networking Architecture
Router = Intermediate Node
End host A End host B FTP Protocol FTP Application
TCP TCP Protocol Transport
IP IP IP IP IP Network Protocol Protocol
Ethernet Ethernet Ethernet Ethernet Driver Driver Driver Driver Ethernet Ethernet Protocol One or more nodes Protocol within the network Louisiana State University 2- Networking Key Concepts - 46 CSC4601 F04 OSI/ISO Networking End host End host
Application Architecture Application
Presentation Presentation
Session Session
Transport Transport
Network Network Network Network
Data link Data link Data link Data link
Physical Physical Physical Physical
One or more nodes within the network Louisiana State University 2- Networking Key Concepts - 47 CSC4601 F04
OSI vs TCP Reference Models OSI introduced concept of services, interface, protocols These were force-fitted to TCP later ⇒ It is not easy to replace protocols in TCP. In OSI, reference model was done before protocols. In TCP, protocols were done before the model OSI: Standardize first, build later TCP: Build first, standardize later OSI took too long to standardize. TCP/IP was already in wide use by the time. OSI became too complex. TCP/IP is not general. Ad hoc.
Louisiana State University 2- Networking Key Concepts - 48 CSC4601 F04 Coding Terminology Pulse +5V 0 -5V Bit
Signal element: Pulse Modulation Rate: 1/Duration of the smallest element =Baud rate Data Rate: Bits per second Data Rate = Fn(Bandwidth, signal/noise ratio, encoding)
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Channel Capacity
Capacity = Maximum data rate for a channel Nyquist Theorem: Bilevel Encoding: Data rate = 2 × Bandwidth
5V 1 0 0 Multilevel coding: Data rate = 2 × Bandwidth × log2 M 10 11 01 00 Example: M=4, Capacity = 4 × Bandwidth
Louisiana State University 2- Networking Key Concepts - 50 CSC4601 F04 Channel Capacity (Cont)
Bilevel Encoding: Worst case: 1010101010 Cycle time = 2 × Bit time ⇒ Data rate = 2 × Bandwidth
5V 1 0 0 Multilevel coding: Worst case 0011001100110011 Cycle time = 4 × Bit time
⇒ Data rate = 2 × Bandwidth × log2 M 11 11 11 11 11 00 00 00 00 00
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Channel Capacity (cont.)
Bilevel Coding: Worst case: 1010101010
5V 1 1 1 0 0 0 0 0 3F Time Frequency
Bilevel Coding: not worst case: 111000111000 5V 1 1 1 0 0 0 0 0 F Time Frequency
Louisiana State University 2- Networking Key Concepts - 52 CSC4601 F04 Shannon's Theorem Bandwidth = B Hz Signal-to-noise ratio = S/N
Maximum number of bits/sec CMAX = B log2 (1+S/N) Application of Second Law of Thermodynamic
When more than CMAX, information becomes noise Example: Phone wire bandwidth = 3100 Hz
S/N = 30 dB, 10 Log 10 S/N = 30 3 Log 10 S/N = 3, S/N = 10 = 1000 Capacity = 3100 log 2 (1+1000) = 30,894 bps Compression : Code repetitive patterns with a shorter data set Example: Code “XXXXXX” (6 bytes) with 2 bytes
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Nyquist’s vs. Shannon’s Theorem
Nyquist’s Theorem: Explore ways to encode bits Clever encoding allows more bits to be transmitted per unit time, for example multilevel encoding Shannon’s Theorem: No amount of clever encoding can overcome the laws of physics
Louisiana State University 2- Networking Key Concepts - 54 CSC4601 F04 Data vs Signal Data Signal Data T R 1010
Data: Analog (Music), Digital (files) Signal: Analog (POTS, Radio), Digital (ISDN) Data Signal Examples Analog Analog Modulation AM, FM Digital Analog Coding/Keying ASK, FSK, PSK Analog Digital Modulation PCM, ADPCM Digital Digital Coding Manchester, NRZ
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Bit Stuffing
Delimit with special bit pattern (bit flags) Stuff bits if pattern appears in data Remove stuffed bits at destination
0 11111 11111 11111 10010
Transmitter
01111110 0 111110 111110 111110 10010 01111110 Flag Receiver
0 11111 11111 11111 10010
Louisiana State University 2- Networking Key Concepts - 56 CSC4601 F04 What Goes Wrong in the Network?
Bit-level errors (electrical interference) Packet-level errors (congestion) Link and node failures Messages are delayed Messages are deliver out-of-order Third parties eavesdrop The key problem is to fill in the gap between what applications expect and what the underlying technology provides.
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Flow Control
Flow Control = Sender does not flood the receiver, but maximizes throughput Sender throttled until receiver grants permission Methods: Stop and wait Sliding window
Louisiana State University 2- Networking Key Concepts - 58 CSC4601 F04 Error Control
Error Control = Deliver frames without error, in the proper order to network layer Error control Mechanisms: Ack/Nak: Provide sender some feedback about other end Time-out: for the case when entire packet or ack is lost Sequence numbers: to distinguish retransmissions from originals ARQ: Stop and Wait, Selective Reject, Go-back n
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Packet Switched Data entering network divided into chunks called "packets'' packets traversing network share network resources (e.g., link bandwidth, buffers) with other packets. Resource use: statistical resource sharing Resource demands may exceed available resources :
A and B packets arrive at R1, destined for C : resource contention: queuing (waiting), delay are random
A R1 R2 C B
Louisiana State University 2- Networking Key Concepts - 60 CSC4601 F04 Circuit Switched
All resources (e.g. communication links) needed by the call dedicated to that call for duration example: telephone network Resource demands may exceed available resources; A and B want to call C: resource contention: blocking (busy signal)
A R1 R2 C B
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Addressing and Routing
Address: byte-string that identifies a node usually unique Routing: process of forwarding messages to the destination node based on its address Types of addresses unicast: node-specific broadcast: all nodes on the network multicast: some subset of nodes on the network
Louisiana State University 2- Networking Key Concepts - 62 CSC4601 F04 Multiplexing
Time-Division Multiplexing (TDM) Frequency-Division Multiplexing (FDM)
L1 R1
L2 R2
Switch 1 Switch 2 L3 R3
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Statistical Multiplexing
On-demand time-division Schedule link on a per-packet basis Packets from different sources interleaved on link Buffer packets that are contending for the link Buffer (queue) overflow is called congestion
…
Louisiana State University 2- Networking Key Concepts - 64 CSC4601 F04 Why statistically share resources? Save/make money! Example: 1 Mbit/sec link; each user requires 100 Kbits/sec when transmitting; each user has data to send only 10% of time. circuit-switching: give each caller 100 Kbits/sec capacity. Can support 10 callers. packet-switching: with 35 ongoing calls, probability that 10 or more callers simultaneously active < 0.0004! Can support many more callers, with small probability of` "contention.''
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Inter-Process Communication
Turn host-to-host connectivity into process-to- process communication. Fill gap between what applications expect and what the underlying technology provides.
Host Host Application
Host Channel Application
Host Host
Louisiana State University 2- Networking Key Concepts - 66 CSC4601 F04 Network Support for Applications
Network supports common process-to-process channels; Request/Reply: for file access and digital libraries Message Stream: for video applications video: sequence of frames
resolution: 1/4 TV-size image = 352 x 240 pixels; 24-bit color: frame = (352 x 240 x 24)/8 = 247.5KB; frame rate: 30 fps = 7500KBps = 60Mbps video on-demand versus video-conferencing
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Design Issues for Layers Duplexity: Simplex: Transmit or receive Full Duplex: Transmit and receive simultaneously Half-Duplex: Transmit and receive alternately Error Control: Make "channel" more reliable; Error detection and recovery Flow Control: Avoid flooding slower peer Fragmentation: dividing large data chunks into smaller pieces; reassembly Multiplexing: several higher level session share single lower level connection Addressing/naming: locating, managing identifiers associated with entities
Louisiana State University 2- Networking Key Concepts - 68 CSC4601 F04 Performance Metrics-Important Concepts Throughput Bandwidth Bandwidth vs. throughput Amount of data that can be transmitted Delay per time unit link versus end-to-end Notation: KB = 210 bytes, Mbps = 106 bits per second Bandwidth related to “bit width”
B = 1 Mbps Link 1 1 bit 1 microsecond B = 10 Mbps Link 2
10 bits Louisiana State University 2- Networking Key Concepts - 69 CSC4601 F04
Performance Metrics-Important Concepts Latency (delay) time to send message from point A to point B one-way versus round-trip time (RTT) Latency = Propagation_time + Transmit_time + +Queuing _time
Propagation_time = Distance/SpeedOfLight
Transmit_time = SizeOfData/Bandwidth
Queuing _time = Processing time in routers, long in case of network congestion when routers buffer the data
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Speed of light 3.0 x 108 meters/second in a vacuum 2.3 x 108 meters/second in a cable 2.0 x 108 meters/second in a fiber
No queuing delays in direct link Bandwidth not relevant if Size = 1 bit Process-to-process latency includes software overhead Software overhead can dominate when Distance is small
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Performance Metrics (cont.) Relative importance of bandwidth and latency small message (e.g., 1 byte): 1ms vs 100ms dominates 1Mbps vs 100Mbps With bandwidth = 100Mbs => transmit_time = 0.08 micros With bandwidth = 1Mbs => transmit_time = 8 micros large message (e.g., 25 MB): 1Mbps vs 100Mbps dominates 1ms vs 100ms With bandwidth = 1Mbs => transmit_time = 200 s With bandwidth = 100Mbs => transmit_time = 2 s High speed networks RTT dominates
Throughput = TransferSize / TransferTime
TransferTime = RTT + 1/Bandwidth x TransferSize 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link
Louisiana State University 2- Networking Key Concepts - 72 CSC4601 F04 Performance Metrics (cont.)
Delay x Bandwidth: amount of data “in the pipe”, important concept in network design Example: 100ms x 45Mbps = 560KB
Bandwidth
Delay
Application Needs Bandwidth requirements: burst versus peak rate Jitter: variance in latency (inter-packet gap)
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Connection-Oriented vs Connectionless
Connection-Oriented: Telephone System Path setup before data is sent Data need not have address. Circuit number is sufficient. Connectionless: Postal System. Complete address on each packet The address decides the next hop at each router
Louisiana State University 2- Networking Key Concepts - 74 CSC4601 F04 Multiple Access Protocols
(a) Multiple Access
(b) Carrier-Sense Multiple Access with Collision Detection
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Multiple Access Protocols
Aloha at University of Hawaii: Transmit whenever you like Worst case utilization = 1/(2e) =18% CSMA: Carrier Sense Multiple Access Listen before you transmit CSMA/CD: CSMA with Collision Detection Listen while transmitting. Stop if you hear someone else. Ethernet uses CSMA/CD. Standardized by IEEE 802.3 committee.
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The diagram was drawn by Dr. Robert M. Metcalfe in 1976 to present Ethernet to the National Computer Conference in June of that year
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Interconnection Devices
Repeater: PHY device that restores data and collision signals Hub: Multiport repeater + fault detection and recovery Bridge: Datalink layer device connecting two or more collision domains. MAC multicasts are propagated throughout “extended LAN.” Router: Network layer device. IP, IPX, AppleTalk. Does not propagate MAC multicasts. Switch: Multiport bridge with parallel paths These are functions. Packaging varies.
Louisiana State University 2- Networking Key Concepts - 78 CSC4601 F04 Interconnection Devices
LAN= H H B H H Collision Router Domain Extended LAN =Broadcast domain Application Application Gateway Transport Transport Network Router Network Datalink Bridge/Switch Datalink Physical Repeater/Hub Physical
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IEEE 802 Address Format
48-bit:1000 0000 : 0000 0001 : 0100 0011 : 0000 0000 : 1000 0000 : 0000 1100 = 80:01:43:00:80:0C Organizationally Unique Identifier (OUI) 24 bits assigned by Individual/ Universal/ OUI Owner Group Local 11 22 24 Multicast = “To all bridges on this LAN” Broadcast = “To all stations” = 111111....111 = FF:FF:FF:FF:FF:FF
Louisiana State University 2- Networking Key Concepts - 80 CSC4601 F04 Summary
ISO/OSI reference model has seven layers. TCP/IP Protocol suite has four layers. Ethernet/IEEE 802.3 uses CSMA/CD. Addresses: Local vs Global, Unicast vs Broadcast.
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