Structure and internal workings of the internet Flashcards
ARPANET 1967-72
ARPANET was a pioneering project funded by the U.S. Department of Defense, aimed at developing a wide-area network to connect diverse computers and serving as the precursor to the modern internet.
Primary challenge: enabling communication between heterogeneous machines, which led to the development of the Network Control Protocol (NCP), later replaced by TCP/IP.
ARPANET experimented with three modes of communication: telephone lines, satellites, and radio frequency (spectrum) communication.
Project successfully connected various computers, laying the groundwork for modern computer networking and the internet.
Also pioneered essential applications such as remote login and email, which remain integral components of digital communication today.
Internetworking (1973-1983)
This period focused on interconnecting various networks, including ARPANET and others, using the TCP/IP protocol suite. The term “Internet” emerged during this time, reflecting the global network of networks.
Demilitarization/Rise of NSFNET (1983-1995)
U.S. military separated its network from ARPANET, leading to the creation of MILNET. The National Science Foundation (NSF) established NSFNET, which became the backbone for academic and research networks, contributing to the expansion of the internet.
Privatization/Internet Boom (1995-2000)
During this period, NSFNET was decommissioned, and the internet infrastructure shifted to private entities. The World Wide Web (WWW) gained widespread adoption, spurring the internet boom and the dot-com bubble.
Modern Internet (2000–present)
Following the burst of the dot-com bubble, the internet continued to evolve, with significant developments such as social media, mobile internet, streaming services, cloud computing, and the Internet of Things (IoT) shaping the digital landscape.
Topology: Three Types of ISPs
Long-haul networks/backbone: Tier 1 ISPs
-Backbone of the Internet
-Connect a small number of interconnection points
-Originally made of phone lines, now fiber optics
-E.g., Verizon, Sprint, AT&T, Lumen/Level 3
-Ex: I-10
Middle-mile/regional networks: Tier 2 ISPs
-E.g., Cogent, Vodafone/Cable & Wireless, NTT, DT
-Ex: 288/Highway 6
Local/last-mile networks: Tier 3 ISPs
-E.g., Phone and cable companies (AT&T, Comcast)
-Ex: Farm Road/West House St.
-Campus, corporate, and municipal networks
-Existing last mile: telephone lines, dialup (56.6 kbps), DSL (100 Mbps), cable modem (1+ Gbps), 2G/3G (3 Mbps)
-New last mile
Fiber-to-the-home (FTTH) (1+ Gbps)
4G/5G mobile (1+ Gbps)
Satellite (50-500 Mbps)
Internet access technologies
(1) Dial-up
-Analog model converts data into sounds, required a change to network
-Max speed 56.6 kbps
-Local loop: connection from home to central office
(2) Cable modem (DOCSIS 1, DOCSIS 3)
-Generally, offers more bandwidth than DSL.
-Uses cable system (existing tech) so cheaper
-Coax cables to connect nodes to homes
-Provides gigabit speeds
(3) Digital Subscriber Lines (DSL)
-Asymmetric DSL (ADSL: 30 mbps)
-Very-high-speed DSL (VDSL: 100 mbps)
-Uses existing telephone system and same twisted pair wires from dialup
-Uses higher transmission frequencies to send data communications through the telephone line without interfering with voice communications (which occupy lower frequencies)
-Subject to extensive access regulation from which cable was largely immune
(4) Fiber
-Needs entirely new infrastructure. Put optical fiber to the premises
-Provides multiple gigabit speeds (v fast)
-Fast but very expensive, see $$ Verizon burned on FiOS rollout
(5) Mobile (3G, 4G LTE)
Mobile generations (e.g., 3G)
Generations:
1G: analog voice
2G: 20 kbps; personal communications systems (PCS); provided voice and minimal data (think pagers)
3G (GSM/HSPA+ or CDMA [technology for cell phone use w/o need for separate landline; in areas where no cable or DSL internet –> can still access internet thru cell phone]) –> Europe standardized to GSM but it later turned out CDMA was a better format, now 4G uses CDMA
4G LTE: 10-50 Mbps/LTE around 100+ mbps
5G: gigabit speeds
-Has become the dominant broadband internet access technology
-Growing evidence that consumers are beginning to rely entirely on wireless for broadband
-Mobile broadband poses challenges to which fixed broadband is not susceptible
-Bandwidth limited by government allocation (unlike fixed broadband, can’t just string additional cable to add capacity)
-Wireless more susceptible to local congestion and interference
Network components
TELEPHONE NETWORKS
-Handsets, fax machines, etc.; customer premises equipment (CPE)
-Physical connection: twisted pair, coaxial cable, fiber, spectrum
-Switches
BROADBAND NETWORKS
-Computers, smartphones, tablets: hosts
-Same physical connections
-Switches (internal) and routers (connecting outside of a network)
Two approaches to networking
Circuit Switching: Establishes a dedicated path for continuous data transmission between two endpoints, allowing only one user to use a link at a time, and requires all data to follow the same path, which can be less efficient and less robust against failures.
Packet Switching: Divides information into discrete packets and enables multiple users to share the same links, allowing different parts of a communication to take different paths, leading to more efficient use, better resilience against node failures or congestion, and overall increased network robustness.
IP protocol (shipping container analogy)
IP Protocol is like a shipping container: It provides a uniform format with essential information (destination address) in the header, allowing different technologies to handle it without examining the contents, while application layer formats (like email, web, file transfer, video) act as car carriers within the container.
Store-and-forward networking
OLD VERSION of Store-and-Forward Networking:
-Sequential Transmission: Data was sent as a whole from one node to another, often in a sequential manner, which required each intermediate node to receive and store the entire message before forwarding it to the next node.
-Less Efficient: This approach often led to delays and inefficiencies in the network, as the sender had to wait or retransmit the message if the next node was busy or unreachable.
-Limited Error-Checking: The error-checking capabilities in the old version were not as robust, making it more susceptible to data corruption during transmission.
MODERN APPROACH to Store-and-Forward Networking (Packet Switching):
-Packet-based Transmission: Data is divided into smaller units called packets, which are sent independently through the network to their destination, allowing each intermediate node to store and forward packets individually.
-Greater Efficiency: This approach allows for better utilization of network resources and reduces the impact of network congestion or node unavailability, as packets can be rerouted through alternate paths if needed.
-Improved Error-Checking: The modern approach includes more advanced error-checking mechanisms, ensuring that data corruption during transmission is less likely to occur.
SUMMARY: the modern approach to store-and-forward networking, which is an integral part of packet switching, provides greater efficiency, improved error-checking, and better utilization of network resources compared to the older version of store-and-forward networking.
Ports
Used by both TCP and UDP
When multiple apps run on the same machine, use port numbers to guide packets to right app
Some port numbers are preassigned; others are ad hoc
Protocol layering
All packets must contain all layers in order
Only equivalent actors should see that layer (any info necessary is placed in the header/no DPI)
