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

Announcements Project 1 Due in two weeks Start now, if you haven’t already Will go over missing pieces and answer questions on Friday Assignment 1 Due in one week Hand in during class (instead of e. Learning)

Performance

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

Bandwidth Bits transmitted at a particular bandwidth can be regarded as having some width: (a) bits transmitted at 1 Mbps (each bit 1 μs wide); (b) bits transmitted at 2 Mbps (each bit 0. 5 μs wide).

The length of bits How wide/long is a bit in the network? Propagation speed? Electrons in copper: 2. 3 x 108 m/s Light pulses in fiber: 2. 0 x 108 m/s Transmission rates 10 Mbps 100 Mbps 1 Gbps 10 Gbps

The length of bits How wide is a bit in the network? If your transmission rate is 10 Mbps, how long does it take to put one bit on the line? 10 Mbps = 10 x 106 bits in one second = 1 bit in 1/ 10 x 106 seconds = 1 bit in 1 x 10 -7 seconds = 1 bit in 0. 1 μs

The length of bits How long is a bit in the network? 10 Mbps = 1 bit every 1 x 10 -7 seconds In copper, electrons travel at 2. 3 x 108 m/s x 1 x 10 -7 seconds ≈ 23 meters

The length of bits How long is a bit in the network? What about wireless? 2. 4 GHz spectrum (802. 11 b) Transmission rate 11 Mbps 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)

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

Latency Three main factors affect latency 1. Propagation delay deals with the speed of light over the medium Electrons in copper: 2. 3 x 108 m/s Light pulses in fiber: 2. 0 x 108 m/s Propagation = Distance/Speed. Of. Light 11

Latency 2. Three main factors affect latency Transmit time Amount of time it takes to transmit a unit of data Transmit = Size/Bandwidth 12

Latency 3. 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/Speed. Of. Light 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? That is, how many bits can be “in transit” that the sender knows have been sent, but the receiver has not yet been made aware of?

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.

And yet another time Transmission Time The transfer time refers to the amount of time sending the data plus the overhead in setup/teardown of the transfer. We'll see a lot of these when we talk about TCP, but for now, look at it like this: RTT Transfer request sion Data Transmis Acknowledgment

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. ”

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 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 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.

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

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)

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

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. 4 GHz 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