Chapter 1 - Network

Chapter 1:

Internet:
	hosts = end systems, running network apps
	communication links: fiber, copper, radio
						 transmission rate = bandwidth
	packet switch

	routers, link-layer switch -> route, path

	protocol

Internet: network of networks
		loosely hierarchical

		communication infrastructure: distrubute applications
		communcation services provided to apps:
			reliable data transfer
			best effort (unreliable)

		an infrastructure that provides services to applications

Protocol: format, order of message sent and received among network entities,
		  and actions taken on message transmission, receipt
		  TCP/IP


Network structure
	Network edge: applications and hosts
	Access networks, physical media: wired, wireless communcation links
	Network core: interconnected routers, network of networks

Network egdge: end systems (host),
				client/server model
				peer-peer model

Connect end systems to edge router:
	residential access nets
	institutional access network
	mobile access networks

Dial-up Modem:
	Existing telephony infrastructure
	Home is connected to central office
	up to 56Kbps direct access to router
	Cant surf and phone at the same time

DSL (Digital Subscriber Line)
	Existing telephony infrastructure
	up to 1Mbps upstream, 8Mbps downstream
	dedicated physical line to telephone central office

Residential access: cable modems:
	Does not use telephony infrastructure
	Use cable TV infrastructure
	HFC (hybrid fiber coax) 30Mbps down, 2Mbps up
	13Mbps down for cable access network
	network of cable and fiber attaches homes to ISP router
		home shares access to router (not dedicated access)

FTTH (Fiber to the Home)
	Optical links from central office to the home
	2 competing optical technologies:
		PON: Passive Optical network
		PAN: Active Optical Network
	Much higher Internet rates: fiber also carries TV and phone
	20Mbps down

Ethernet:
	companies, universities
	10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet
	end systems connect into Ethernet switch

Wireless access network:
	shared wireless access network connects end system to router
		(via access point)
	wireless LANs: 11 or 54 Mbps

	wider-area wireless access: provided by telco operator (3G, LTE)

Home networkss:
	DSL or cable modems
	router/firewall/NAT
	Ethernet
	wireless access point

Physical Media:
	Bit: propagates between transmitter/receiver pairs - Physical medium
	Physical link: lies between transmitter and receiver
	Guided media: signals propagate in solid media (copper, fiber, coax)
	Unguided media (propagate freely: radio)
	Twisted pair (TP): 2 insulated copper wires

	Coaxical cable (bidirectional, baseband): shared medium
	Fiber optic cable (high speed, low error rate)

	Radio:
		no wire,
		bidirectional,
		propagation environment effects
		signal carried in electromagnetic spectrum

		terrestrial microwave
		LAN (wifi)
		wide-area (cellular (3G))
		satellite

Network core:
	circuit switching: dedicated circuit per call
	packet switching: data sent through net in discrete chunks

Circuit switching:
	end-end resources reserved for "call"
		link bandwidth, switch capacity
		dedicated resources: no sharing
		circuit-like performance
		call setup required

	network resources divided into pieces
		pieces allocated to calls
		resource piece idle if not used by owning call (no sharing)
		dividing like bandwidth into bandwidth:
			Frequency division: FDM
			Time division: TDM

Packet switching:
	store and forward transmission
	each end-end data stream divided into packets
		full link bandwidth
		share network resources
		resources used as needed
	resource contention
		aggregate resource demand can exceed amount available
		congestion: packets queue, wait for link use
		store and forward: packets move one hop at a time

	statistical multiplexing:
		A, B have no fixed pattern, bandwidth shared on demand

	allow more users to use network

Packet switching vs. Circuit switching:
	packet switching great for bursty data:
		resource sharing
		simpler, no call setup
	excessive congestion: packet delay and loss
		protocols needed for rdt, congestion control

Internet structure: network of networks:
	roughly hierarchical
	Tier-1 ISP: center - provider
	Tier-2 ISP: smaller, regional - customer
	Tier-3 ISP and local ISP - customer

	a packet passes through many networks

Delay:
	packets queue in router buffers:
		packet arrival rate to link exceeds output link capacity
		packets queue, wait for turn

	nodal processing:
		check bits error, determine output link
	queueing delay:
		time waiting at output link for transmission
		depends on congestion level of router
	Transmission delay:
		L / R (time to send bits into link)
			R = link bandwidth (bps)
			L = packet length
	Propagation delay:
		d = length of physical link
		s = propagation speed in medium
		propagation delay = d/s

	d(nodal) = d(processing delay) + d(queueing delay)
			+ d(transmission delay) + d(propagation delay)

Queueing delay:
	R = link bandwidth (bps)
	L = packet length (bits)
	a = average packet arrival late

	traffic intensity = La / R
	La/R ~ 0: average queueing delay smaller
	La/R -> 1: delays become large
	La/R > 1: more work arriving than can be services,
				average delay infinite

Traceroute: provide delay measurement from source to router

Packet loss:
	queue (buffer) has finite capacity
	packet arriving to full queue dropped
	lost packet may be retransmitted by previous node

Throughput:
	rate (bits/time unit) and which bits transferred between sender/receiver
		instantaneous
		average
	bottleneck

Protocol "Layers"
	dealing with complex systems
	layered reference model for discussion
	ease maintenance, updating system

Internet protocol stack:
	application: network applications (FTP, SMTP, HTTP) - message
	transport: process-process data transfer (TCP, UDP) - segment
	network: routing of datagrams from source to destination (IP) - datagram
	link: data transfer between neighboring network elements (PPP, Ethernet) - frame
	physical (bits on the wire)

	ISO/OSI reference model
		application
		presentation: allow apps to interpret meaning of data
					encryption, compression
		session: synchronization, checkpointing, recovery of data
		transport
		network
		link
		physical

Encapsulation

Network security:
	not originally designed with much security in mind
	virus, worm, trojan, spyware, malware, botnet, self-replicating
	packet sniffing
	IP spoofing
	recored and playback

Internet history:
	61-72: Early packet switching principles
	72-80: Internetworking, new and proprietary nets
	80-90: new protocols, a proliferation of networks
	90, 2000: commercialization, the Web, new apps