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Chapter 1: Introduction

• Provides the "feel" for the "big picture" and introduces key terminology.
• More depth and detail on the topics covered will follow later in the course.

Overview/Roadmap

• Topics covered include:
  • What is the Internet and what is a protocol
  • Network Edge
  • Network Core
  • Performance
  • Protocol Layers
  • Service Models
  • Security and History

The Internet

• It is comprised of billions of connected computing devices called hosts or end systems which run network applications at the Internet's "edge".
• Packet switching is used to forward data in chunks.
• It uses:
  • Routers and switches
  • Various communication links like fiber, copper, radio, and satellite with transmission rates measured as bandwidth
• It is a network that has devices, routers and links managed by orgs
• Internet-connected devices include:
  • Amazon Echo
  • Internet Refrigerator
  • Security Camera
  • Internet Phone
  • IP Picture Frame
  • Gaming Devices
  • Pacemaker and Monitor
  • Web-enabled Toaster and Weather Forecaster
  • Sensorized Bed, Mattress
  • Fitbit

Internet Structure: Network of Networks

• The Internet is a "network of networks" comprised of interconnected Internet Service Providers(ISPs).
• Protocols govern sending and receiving messages, including HTTP, streaming video, Skype, TCP, IP, WiFi, 4G, 5G, and Ethernet.
• Internet standards are defined in RFCs and maintained by IETF.
• The Internet is the infrastructure that provides services to applications like Web browsing, streaming video, multimedia teleconferencing, email, games, e-commerce, social media etc.

Protocols

• govern all communication activity in the Internet.
• Define the format and order of messages sent and received among network entities, and the actions taken on message transmission and reception

Network Edge

• Includes hosts that are clients or servers.
• Servers are often located in data centers.
• Includes wired and wireless communication links
• Provides a connection from end systems to the edge router and includes:
  • Residential access networks
  • Institutional access networks
  • Mobile access networks

Access Networks: Cable-Based Access

• Frequency Division Multiplexing (FDM) is the key technology here.
• A hybrid fiber coaxial (HFC) setup provides asymmetric transmission.
  • Downstream rates of 40 Mbps to 1.2 Gbps
  • Upstream rates of 30-100 Mbps
• Homes share access network to cable headend.

Access Networks: Digital Subscriber Line (DSL)

• Uses existing telephone lines to connect to the central office DSLAM.
• Provides dedicated downstream transmission rates of 24-52 Mbps.
• Upstream transmission rates of 3.5-16 Mbps.
• Data and voice are transmitted at different frequencies over the dedicated line.

Access Networks: Home Networks

• Combine wireless and wired devices via a single box.
• WiFi wireless access point (54, 450 Mbps)
• A router, firewall, and NAT
• Wired Ethernet (1 Gbps)

Wireless Access Networks

• Shared wireless access networks connect end systems to a router via a base station "access point".
• Wireless Local Area Networks (WLANs) operate within or around buildings (~100 ft).
  • Based on 802.11b/g/n (WiFi) with transmission rates of 11, 54, 450 Mbps.
• Wide-Area cellular access networks cover 10's of Km and are provided by mobile network operators.
  • 4G networks can reach 10's of Mbps and 5G is faster

Access Networks: Enterprise Networks

• Found in companies and universities.
• Integrate wired and wireless technologies, connecting switches and routers.
• Wired Ethernet access at 100Mbps, 1Gbps, and 10Gbps.
• Wifi wireless access points operate at 11, 54, and 450 Mbps.

Access Networks: Data Center Networks

• High-bandwidth links, 10s-100s Gbps, connect hundreds to thousands of servers together and to the internet

Host Sending Data

• An application message will be broken down into smaller chunks, and the breaks are labeled as packets with a length of L bits.
• The packet will then transmit into an access network with a transmission rate that is labeled as R
• Packet Transmission Delay is the equal to L/R

Links: Physical Media

• The "bit" propogates between transmitter/receiver pairs
• The "physical link" lies between the transmitter and reciever
• Guided media propagates in solid media, copper, fiber, etc
• Unguided media propagates freely

Twisted Pair

• This media uses to insulated copper wires
• Category 5: transmits at 100 mbps, 1 Gbps Ethernet
• Category 6: transmits at 10 Gbps Ethernet

Coaxial Cable

• Uses 2 concentric copper conductors
• Broadband that has multiple frequency channels on cable
• Transmitts 100's Mbps

Fiber Optic Cable

• Uses glass fiber carrying light pulses, each pulse representing a bit
• High speed operation over 10's-100's Gbps
• immune to electromagnetic noises

Wireless Radio

• Signal carries various "bands" in electromagnetic spectrum
• It broadcasts via "half-duplex", sender to reciever
• Causes:
  • Reflection
  • Obstruction
  • Interference/Noise

Wireless LAN

• 10-100's Mbps in 10's of meters

Wide-Area

• 10's Mbps over -10 km

Bluetooth

• Used for short distances, limited rates

Satellite

• up to 45 Mps, 270 msec end-end delay

Network Core

• Packet switching enables hosts to break application-layer messages into packets.
• The network forwards packets from router to router across links from source to destination.
• It provides interconnection between routers as a "network of networks".

Key Network Core Functions

• Forwarding: The local action of moving arriving packets from a router's input link to the appropriate router output link
• Routing: The process of determining the source destination paths taken by packets

Packet-Switching: Store-and-Forward

• Packet transmission delay: The time it takes to transmit an L bit packet into a link measured as L/R
• Store and Forward: The time it takes for the packet to arrive until it can be transmitted on the next link

Packet-Switching: Queueing

• Queueining takes place if arrival rate to link (in bps) exceeds the transmission rate (bps)
• Packets will queue while memory is used to transmit on output link
• Packets are dropped if memory cannot hold them

Circuit Switching

• End to end calls are allocated and reserved between source and desitnation
• dedicated resources are used
• circuit segments are idle is a call is not using them FDM and TDM can also be used.
• FDM has optical frequencies divided into bands where each call transmits at the max rate
• TDM has time alloted into slots, were each call uses a maximum rate of each bands time When using FDM you continuously get a fraction of the bandwidth where TDM gets bandwidth over time

Switching vs Circuit Switching

• Circuit switching*: has a fixed rate over bandwidth
• Packet switching*: Probability that most users are on the same time

Internet Structure

• Hosts attach to the Internet via access Internet Service Providers (ISPs)

• Access ISPs must interconnect so any 2 hosts can send packets to each other

• The resulting network that comes form these connects is complex Connecting each Access ISP to each other does not scale

• This would result in multiple connection depending on number of access

• It would be easier to connect each access ISP to one global transit

Due to bussiness ISP's compete causing multiple global providers:

• Having regional ISP can connect access to connect ISP's

Stepwise Internet Structure

• At the top are Tier 1 ISP commercial networks that service national and international range with well connected large networks
• Content service providers are private network that connects data centers for tier 1 use to connect to other ISP to bypass usage

Packet Delay

• Delay occurs in router queues as transmission happen, as queue length temporarily exceed link capacity

• The delay will be the transmission and time waiting in the output line The nodal processing is the checking of bit errors to detemine output time

• To calculate queue delay R - link transmission, L = packet Length, with the forumal of "dtrans" the transmission can be calculated

• Propogation delay is is calculated with * d = / s / d (distance) s (speed)

Packet Loss

• Loss happens by queues from a buffer with finite capacity, resulting in being "full"
• This retransimtted and not always recieved

Theoughput

• Rate at with "bits" are being sent
  • Instantanous: Rate at a given point in an instance of time
  • Average: Rate over a long time period
• It happens when the bottlenect from path constraints cause throughput in end to-end transmition

Network Security

• The Internet was not created with original security in mind:
  • Open Vision with mutally trusting users as transparant network We now need to consider safety in mind
• We now need to consider
  • How bad guys can attack
  • How we can defend access
  • How to design architecture

What Bad Guys Can Do

• Bad guys can preform -Packet Sniffing: Broadcast media with proisous network
  • IP Sniffing: Preform IP sniffing to inject false packets with false addresses

Lines of Defence

• Lines of Defence: -Authentication Proving who you are
• Confidentiality*: To Encrypt
• Integrity Checcks*: Digital signatures preventing detecting of hammering
• Access Restrictions*: Password protected VPC's and private network connections
• Fiiirewalls*:Specialized middeboxes in access

Protocol Layers and Service Models

• Networks are complex, with many hosts, routers, links and media to work with A protocol layes creates the ability to ORAGANIZE the srtucture of networks that create: HOsts, Routers etc

why Layering?

• Layering creates: Structure and Modularity Where in Layed Network they can change, implement without affectig anything else

Here are the Layers that exist

• The application layer with applications like: HTTP, IMAP, DNS, SMTP
• The transport layer with applications: UDP, TCP
• The Network Layer: IP (routing protocol)
• Data can be sent through the top and encapsule, to make more layers