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Performance and Internet Architecture Networking CS 3470

This text explores performance, bandwidth, latency, and protocols in internet architecture and networking. It covers topics such as bandwidth, propagation speed, latency factors, protocol stacks, and encapsulation.

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Performance and Internet Architecture Networking CS 3470

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  1. Performance and Internet Architecture Networking CS 3470, Section 1 Sarah Diesburg

  2. Performance

  3. Bandwidth • Bandwidth • Width of the frequency band • Number of bits per second that can be transmitted over a communication link • 1 Mbps: 1 x 106 bits/second • 1 x 10-6 seconds to transmit each bit • Can imagine this on a timeline

  4. Bandwidth Bits transmitted at a particular bandwidth can be regarded as having some width: (a) bits transmitted at 1Mbps (each bit 1 μs wide); (b) bits transmitted at 2Mbps (each bit 0.5 μs wide).

  5. The length of bits • How wide/long is a bit in the network? • Propagation speed? • Electrons in copper: 2.3x108m/s • Light pulses in fiber: 2.0x108m/s • Transmission rates • 10Mbps • 100Mbps • 1Gbps • 10Gbps

  6. The length of bits • How wide is a bit in the network? • If your transmission rate is 10Mbps, how long does it take to put one bit on the line? 10Mbps = 10x106 bits in one second = 1 bit in 1/ 10x106 seconds = 1 bit in 1x10-7 seconds = 1 bit in 0.1 μs

  7. The length of bits • How long is a bit in the network? • 10Mbps = 1 bit every 1x10-7 seconds • In copper, electrons travel at 2.3x108 m/s • 2.3x108 m/s x 1x10-7 seconds ≈ 23 meters

  8. The length of bits • How long is a bit in the network? • What about wireless? • 2.4GHz spectrum (802.11b) • Transmission rate 11Mbps • Transmission medium is taken to be the speed of light • Unless there are physical considerations: • Wood,Glass, Plastic (low) • Water, Bricks, Living Animals (medium) • Ceramic, Paper, Bullet-proof glass, Concrete (high) • Metal (very high)

  9. Latency • Latency • How long it takes for a message to travel from the source to the destination • Always measured in time • Lots of factors can affect this – any ideas? • Latency = Propagation + Transmit + Queue

  10. Latency • Three main factors affect latency • Propagation delay deals with the speed of light over the medium • Electrons in copper: 2.3x108m/s • Light pulses in fiber: 2.0x108m/s • Propagation = Distance/SpeedOfLight

  11. Latency • Three main factors affect latency • Transmit time • Amount of time it takes to transmit a unit of data • Transmit = Size/Bandwidth

  12. Latency • Three main factors affect latency • Queue delay deals with delays in the network • E.g., switches that store and forward

  13. All Together… • Latency = Propagation + Transmit + Queue • Propagation = Distance/SpeedOfLight • Transmit = Size/Bandwidth • Sometimes, we are concerned with round-trip time (RTT) • Time it takes to send a message from source to destination and back to source • One-way latency time X 2

  14. The Delay x Bandwidth “Pipe” • Okay, so it takes “latency” seconds for a bit to go from one end to another (plus a fraction for the transmission of the bit!). • While that one bit is “on its way,” you can still send more bits. • How many bits can you stuff in the pipe?

  15. The Delay x Bandwidth “Pipe” • Think of the link as a pipe. • The “length” of the pipe as the latency • The cross-sectional area as the transmission rate • Then, the Delay x Bandwidth product is the volume (in bits) of the pipe.

  16. And yet another time • The transfer time refers to the amount of time sending the data plus the overhead in setup/teardown of the transfer. Transfer request Transmission Time Data Transmission Acknowledgment RTT

  17. Jitter • Packets that go through several congested routers must contend for transmission slots. • The result is that an application sending packets at a constant interval would be perceived by the receiver to have variations in the interpacket gap, or the time between successive packets. • This is observable by variations in latency, referred to as “jitter.”

  18. Internet Architecture

  19. Layered Architecture • Layering simplifies the architecture of complex system • Layer N relies on services from layer N-1 to provide a service to layer N+1 • Interfaces define the services offered • Service required from a lower layer is independent of it’s implementation • Layer N change doesn’t affect other layers

  20. Protocols • Protocols are rules by which network elements communicate • The format and the meaning of messages exchanged • Protocols in everyday life • Examples: traffic control, open round-table discussion etc

  21. Protocol Stacks and Layering • Layering leads to separation of tasks, which makes it easier for programmers and hardware vendors to implement the interface to the neighboring layers. • Protocols lead to standardization and well-defined behaviors and expectations.

  22. Encapsulation • Encapsulation refers to the embedding of a data representation at one protocol layer into the data representation of another layer.

  23. Fragmentation • Packets at one layer might be too large. • In this case, the packet might be fragmented into smaller pieces, encapsulated into the data representation of the underlying protocol, and then defragmented (reassembled) at the destination, or at a node later on in the link.

  24. Common Standards • ISO: • International Standards Organization • Defined reference model known as OSI (Open Systems Interconnection) • IETF • Internet Engineering Task Force • Defined the Internet Model

  25. The OSI Model • Also known as the seven-layer salad. • Application • Presentation • Session • Transport • Network • Data Link • Physical(All pizzas sent through Nick digest promptly)

  26. The Internet Model • Commonly four layers—with the physical layer implied. • Application • Transport • Network • Link • (Physical)

  27. ISO/OSI and Internet Reference Models

  28. ISO/OSI Reference Model • Application layer • Examples: http, ftp, smtp etc • Process-to-process communication • All layers exist to support this layer • Presentation layer (OSI only) • Conversion of data to common format • Example: Little endian vs big endian byte orders

  29. ISO/OSI Reference Model (cont’d) • Session layer (OSI only) • Session setup (authentication) • Recovery from failure (broken session) • Transport layer • Examples: TCP, UDP • End-to-end delivery • (Some typical) functions include reliable in-order delivery and flow/error control

  30. ISO/OSI Reference Model (cont’d) • Network layer • Examples: IP • Used to determine how packets are routed from source to destination • Congestion control • Accounting

  31. ISO/OSI Reference Model (cont’d) • Data link layer • Examples: Ethernet, PPP • Responsible for taking a raw transmission facility and transforming it into a line that appears free of undetected transmission errors. • Accomplished by sending data in frames, and transmitting frames in sequence. • Acknowledgment frames. • Special delineation bit patters used to distinguish frames.

  32. ISO/OSI Reference Model (cont’d) • Physical layer • Transmitting raw bits (0/1) over wire • Examples: 802.11 (2.4GHz wireless), Copper, Fiber

  33. More on Layers • The lower three layers are implemented on all network nodes • The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers

  34. Protocol Stacks and Layering The OSI 7-layer Model OSI – Open Systems Interconnection

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