overview notes

Questions?

What happens when I go to example.com or google.com home page?

What do I need to send a request packet?

What is an address?

How do I get example.com address?

How do I get DNS's address?

How do I get my address?

How do I get DHCP's address?

What if I have more than one window or tab to the same google.com? How would return from google goes back to the correct tab?

room number of the same address ( aka port number)

Components of the Internet, core/edge/access/host

Core Network

Circuit switching versus Packet switching

What is it? How it works? Advantage/Disadvantage?

Circuit switching:

dedicated path, fixed bandwidth => ++ predictable delay, ++ predictable quality,

-- poor bandwidth utilization, -- limited number of simultaneous users

Different ways of multiplexing a circuit -- TDM, FDM, mixer of TDM/FDM, CDM

Packet switching:

dynamic path, shared bandwidth => ++ more users, ++ flexible bandwidth , ++ burst data,

-- random delay, -- packet loss, -- congestion

A store-n-forward network, based on statistical multiplexing

bottom line : control (quality, security) vs. utilization (efficiency, flexibility)

Try to get the best of both worlds:

virtual circuit -- create circuit switching environment in a packet switching network

Multi-tier ISP, peering, private peering, POP, CDN (content delivery network)

Internet service model - client/server, peer to peer

Throughput/Bandwidth and Delay

four packet delay sources .. processing, queuing, transmission, propagation

• processing: CPU decides where the packet goes next and puts it in the corresponding interface queue

• queuing: packet waits its turn to get to the front of interface queue

• transmission: packet is put on the wire, bit by bit. Wire clock speed (e.g. 10 Mbps) and the number of bits (e.g. 2KB packet) determine the delay

• propagation: the time 1 bit takes to go from one end of the wire to the other end. It is determined by wire distance and the speed of electron (constant) on wire

examples of low throughput & high delay ..light traffic, slow speed

low throughput & low delay ..light traffic, fast speed

high throughput & low delay .. heavy traffic, fast speed

high throughput & high delay ..heavy traffic, slow speed (congestion)

Packet loss

Where/How can it happen?

queue overflow / overrun

router crash

router drop (e.g. TTL expired, checksum error)

wire error (radiation, california wild fire :-)

malicious hack

OSI 7 layer models

TCP/IP layers

what are they?

where are they in the packet? Can I see it in wireshark?

why layering?

Internet Architecture principles

no strict layering

hourglass design philosophy

IP is the focal point .. many app, many transport on top, many link / physical network on bottom

working implementation

believe in rough consensus and running code