Sketch The Internet & an Ethernet
Here are dot-points to go along with the 'sketch of the internet' the instructor scrawls on
the board. Some graduates report that their technical interviewer, or the receptionist,
asked them to 'sketch The Internet' or 'name the important features of The Internet'
as part of an interview or test given before the tech interviewer wastes time talking to
somebody without enough enough technical skills and knowledge to warrant an interview...
How to learn this stuff: Google is our friend on most IT topics and 'Internet Infrastructure' is one of them.
Search with any of the acronyms or new words,
clusters of them get the best results, and learn to pick out those links pithy with what you need to know.
Sometimes, googling the _images_ gets your eyes on the right topics the quickest. If there's
an image that makes sense there's usually good content behind it...
Seek out good study guides, websites or books, for the some entry-level certificates like A+, Security+, or Network+
and get one or more.
Our textbook is very 'high level', so are the links on the class' page,
and there are few of the nitty-gritty details that help develop deep technical skills needed
to work in IT and IS.
- The Internet has long been depicted as a 'cloud' because there are many routes possible
for packets of data as they are dispatched across The Internet by IP Routers. Internet and
Ethernet are 'packet switched' networks where the nodes are connected to the media all the time
and 'listen' for packets addressed to them. On packet-switched networks all the devices attached to the network share the
bandwidth available and throughput is never equal to the bandwidth. Traffic on an Internet may
take more than one route to the destination.
Telephone Companies and Long-Distance Carriers' networks are more like 'pipelines' than clouds.
'Telco Switches' handle 'circuit-switched' or 'dedicated connections'
that carry a mostly error-free, full-time, full-duplex, 'stream' of data
between the equipment (telephone, CSU/DSU, frame relay) at each end of the switched circuit.
Bandwidth on these 'traditional telephone company circuits' is not shared and throughput is equal to the bandwidth.
A dedicated circuit may lead to a
switch, router, or other device that does share bandwidth.
Rates for internet connections are usually a fixed, monthly amount for a full-time
connection to the ISP, ranging from $19 for a cheap DSL through $179+ for a good DSL,
$300+ for a T1, $1200+ for a T3, and several thousand or more for faster OC circuits.
- ISPs - Internet Service Providers are at 'the edge of The Internet cloud' and
connect customers on their networks to The Internet Backbone with industrial-strength IP Routers servicing
multiple high-speed fiber circuits, the more the better, and
there are seldom enough. ISPs connect to their customers' sites using
several technologies from analog and digital dial-up and cellular through DSL, cable, FIOS, and other
optical circuits that may be available in a business or residential neighborhood.
ISPs and large organizations that connect directly to backbone circuits
are assigned AS-Autonomous System addresses and can route their customers' internet traffic
among thousands and thousands of OC - Optical Carrier networks worldwide, their own, and their peers'.
ISPs rent big blocks of IP addresses from
their RIR - Regional Internet Registry
and make them available to their customers either dynamically when they connect, or as fixed IPs singly or in smaller blocks.
ISPs on The Internet
agree to carry their competitors' traffic, an agreement that fosters competition and coopetition at their best.
'Internet Neutrality' is related to this, is a very current topic...
- The Internet Backbone
isn't owned by any one company, is truly global in scope, with dozens and dozens of companies providing
the high-speed optical circuits and industrial-strength routers that make up
the infrastructure. Russ Haynal has been maintaining this next link for a decade or more,
is a collection of links to websites of the major, and many minor,
Internet Backbone Providers.
Check out this detailed gallery about
Submarine Cables that carry Internet traffic around the world.
Thousands of companies are assigned the AS-Autonomous System addresses that it takes
to control traffic in this HUGE backbone network of high-speed optical networks, and serve as
their own ISP. Mr Haynal shows us the ones
that provide Internet Services to customers who need an ISP.
- WAN - Wide Area Network media connects a residence, SOHO - Small Office/Home Office or SMB - Small to Medium-sized Business
to an ISP via a 'Last Mile' connection, which is usually 5 miles or less.
Several types of circuits are used:
POTS - Plain Old Telephone Service (rarely these days), a 'broadband' service like DSL - Digital Subscriber Line, Cable,
FIOS - FIber Optic Service, Google Fiber or another FTTP - Fiber To The Premises provider in markets lucky to have them,
WiMax (similar to WiFi except for a large area) or
a 'traditional telco service' like ISDN - Integrated Services Digital Network, T1, T3,
OC3, OC12, or even faster optical circuits. Businesses that need a lot of
bandwidth must be located in neighborhoods, or office parks, embued with high-speed
- On traditional telco circuits 'bandwidth = throughput'. These networks were built on
'Telco Switches' that
carry conversations 'real time' and are 'circuit switched', dedicated channels that do not
share bandwidth. They use 'time division multiplexing' to ensure that each channel gets its
bandwidth all the time.
circuits like DSL or cable typically lead to devices that are 'packet switched' or use 'statistical multiplexing'
that can lead to traffic jams when traffic is heavy since bandwidth is shared with other customers on the circuit.
If a carrier oversells their services,
throughput can be a tiny fraction of the advertised maximum bandwidth.
Care must be taken when provisioning internet circuits to get the Quality of Service needed
to run a business or keep a household happy. Customers of a company that advertises big numbers like
10 to 30 Mbps for their DSL service, or Gigabit for Cable, might find their effective throughput during periods of peak use
is more like 50 to a couple hundred Kbps.
- 'The Box' at the customer's end of the circuit to the ISP might be: some kind of Modem, Router,
ISDN, or even a Smartphone acting as an access point;
a CSU/DSU is used for digital telco circuits;
a PBX that can handle a mix of analog and digital circuits and mix voice, fax, and data
an ISDN or other Router; some kind of Transceiver for 'Wimax',
or some hybrid that serves to mash up WAN and LAN in one box or software --
like the typical 'wireless router' attached to a DSL or Cable circuit in a home that has a router, wifi, and wired ethernet
all in one convenient package.
- An Ethernet Switch moves packets through a LAN using MAC - Media Access Control addresses.
An IP Router or other border device uses ARP - Address Resolution Protoccol
to memorize the MAC/IP/Port combination of all the nearby devices so it can direct internet traffic
to the correct MAC address.
- IP Addresses are classified as private and public.
Private IP addresses are not carried on The Internet, are only used on
LAN - Local Area Networks. One of the pillars of Internet security is to use
private IP addresses for devices within a LAN that don't need to be 'outfacing' to The Internet.
NAT - Network Address Translation is used to hide the devices from The Internet while providing them Internet access.
Private IP addresses are in the ranges
10.0.0.0 - 10.255.255.255, 172.16.0.0 - 172.31.0.0, and 192.168.0.0 - 192.168.255.255.
Network managers can assign the private addresses on the networks they manage.
- Firewalls, which may be integral with a border router, separate devices, or implemented in software
help shield networked resources from pillage and theft over the internet or within an ISP's networks
- A SOHO router (not industrial strenth and not necessarily 'wireless')
usually connects to one WAN media (the 'last mile') to one ISP
and to one ethernet switches on the LAN in the home or small office. Industrial-strength routers may connect to dozens of WAN media
and other routers in the exchange.
- The router uses ARP - Address Resolution Protocol to keep track of which
IP address is assigned to which MAC address in the LAN. Routers often use
NAT - Network Address Translation, masquerading, mangling, or filtering to help protect
internal IP addresses used in a LAN. They may log activity and identify and warn of probes and exploits.
When using NAT, a router keeps track of the private IP address and port assigned to a computer that requests a remote service on the Internet and
substitutes it's own public IP -- when the remote device replies to the assigned port, the router sends the packets to
the local IP that made the request.
- IP addresses and protocols like RIP - Router Interface Protocol, OSPF - Open Shortest Path First,
IP - Internet Protocol,
and TCP - Transmission Control Protocol are used to determine routes and
carry internet packets locally or globally.
- Additional firewalls may be needed within the LAN to protect servers and storage systems from pillage and theft by employees
or others using the LAN. Bad guys 'on the internet' are bad enough, but a dishonest or disgruntled employee
on a LAN can do even more damage.
- Take a quick look at the 7 'layers' of the OSI-Open Systems Interconnect Model
Routers function at Layer 3 - Networking of the OSI model and are used to interconnect networks.
In an SOHO network a router connects the LAN to the ISP's network.
Switches function at Layer 2 - Data Link of the OSI model, are used to connect the devices in a LAN.
The wires, fiber optic cables, and radio frequencies that carry the data are Layer 1 - Physical
of the OSI model. Hubs (not quite obsolete yet) are also Layer 1 devices, don't do anything with the MAC address
except include it in the packets it repeats to all connected devices.
Layers 1 2, & 3 are traditionally implemented with 'hardware' and the upper layers are 'software' that
runs within the client or server.
Blog About OSI that does a good job explaining OSI's functions and protocols.
'All People Seem To Need Data Processing' is a polite
Memory Aid for
naming the 7 layers from top to bottom: Application,
Presentation, Session, Transport, Network, Data Link, and Physical). 'Please Do Not Take Sales People's Advice'
is good advice and pegs the layers from the bottom up.
- If there are WAPs (Wireless Access Points) in the LAN, BEWARE! Wireless networks require constant effort to keep them secure.
The ordinary WiFi can be cracked in a few minutes if it's running WEP,
or several hours even if 'security is turned on' and it runs on of the WPA flavors. Something like half of them
have no security involved, or keep the default 'admin' password,
so their LAN can be invaded with the click of a mouse or tap of a screen.