Almost finished a 3.5-year-long project to get our training courses available online, last major milestone accomplished today with the companion reference textbook now available on iTunes, Amazon Kindle and Google Play Books.
Learning all the material in the book took 25 years. Writing the book in Word took six months. Putting it in Adobe inDesign to export it in EPUB format (eBook) took three months.
Amazon took 10 minutes to open an account and upload the book to Amazon kindle. http://www.amazon.com/dp/B00F3KCDOS
You can read the book on pretty much any device
They take 70% commission and pay 30% to the author.
Apple took two weeks to get uploaded and online on iTunes iBooks. https://itunes.apple.com/us/book/telecom-datacom-networking/id705339315?mt=11
You can only upload the book from an Apple computer. Not a PC, iPhone, iPad or iPod.
You can only read the book on iPhone, iPad or iPod touch. Not on any computer.
They take 30% commission and pay 70% to the author.
They put the book on sale at a reduced price, but only pay 70% of the sale price to the author.
Why did I put Amazon first on the list?? They keep all the money! Google Play seems the best, since it is both the cheapest and you can read the book on any device. But does anyone actually buy books on Google Play Books? iTunes of course has the most users and so maybe the most people will see it there. Time will tell…
Here’s the latest free tutorial, with embedded video of yours truly and my favorite analogy: the FedEx Analogy to explain the OSI layers, what each layer does and how they work together in protocol stacks. Enjoy!
The term comes from the Institute of Electrical and Electronics Engineers (IEEE) 802 series of standards for LANs and MANs developed following the invention of Ethernet LANs by the Digital Equipment Corporation (now a part of HP), Xerox and Intel in 1979.
And people say Xerox never does anything original!
The first kind of LAN, Ethernet, employed a bus topology. The term bus comes from the Latin word omnibus, meaning “all”. It is used in electrical power systems, where a bus is a thick metal bar used to distribute electricity to many circuits.
The term “port” crops up in IP networking, particularly in the context of rules in routers and software firewalls. One hears about “opening a port on a firewall” and “TCP ports” and “UDP ports”.
So just what is a “port”, exactly?
Like about 40% of the words in English after the Norman invasion of southern England following the Battle of Hastings in 1066, the English word “port” is French. Une porte is a door.
Of course, the French got it from Latin: porta (gate, door). The Latin word portus (port, harbor, and earlier, entrance, passage) and the Greek word poros (journey, passage, way) are obviously related.
In the computer hardware business, a port is a doorway into the machine: a jack, where a cable can be connected. In days past, there were serial ports and parallel ports on PCs. Today, we have USB ports and LAN ports. Technicians talk about connecting customers to ports on access equipment, for example, equipment with banks of modems.
In the computer software business, a port can be thought of as a doorway into the software running on the machine, a passageway to a specific computer program running on the computer.
Why is this necessary? Since there can be many computer programs (a.k.a. applications, apps) running on the same computer at the same time, when trying to communicate to a particular program, we require a mechanism to identify it, a way of telling the host computer to which program to relay our communications.
For example, we all know that it’s possible to have multiple applications using the Internet connection on a computer at the same time. Think of an Outlook email program and a Chrome browser program running at the same time on a PC connected to the Internet.
When data arrives at this computer, how does the computer know whether this data is for the email program or for the browser program? And how does it convey the data to the correct program?
The answer: every program is assigned a number called a port number. Your browser is assigned port 80, for example.
Here’s how it works: the sending program creates a message and tags it with the port number identifying the program it wishes to communicate with on the destination computer. This is put in a packet that is tagged with the network address (IP address) of the destination host computer and transmitted. When the packet arrives at the destination computer identified by the IP address, this receiving computer looks at the destination port number and parks the message in a memory space associated with that port number. The program on the destination computer assigned that port number is constantly checking that memory space to see if there is anything new waiting for it.
The result is the ability for a computer program running on one computer to communicate with a specific computer program on another computer.
Visiting our warehouse service a couple of weeks ago, I was struck by the analogy possible between the idea of computer ports and a multi-tenant warehouse, so whipped out my Android smartphone and took a picture with the totally cool panoramic feature.
The warehouse is analogous to the host computer. It has a single street address. It handles goods for multiple users. Users have space allocated inside the warehouse. The warehouse has (on this side) six ports, also called loading docks. Each port has a number. A user can be assigned a port, either temporarily or permanently.
To communicate goods to that user, they’re carried in a shipping container (IP packet) on a truck (Ethernet frame) over a road (LAN cable) to the warehouse at its street address (IP address). To get the contents of the shipping container delivered to the correct user, the truck is backed up to the appropriate loading dock (port) identified by its door number (port number) and the contents of the container are unloaded to the space behind that port.
In computer communications today, the port number is 16 bits long, and the source and destination port number are populated at the beginning of the transport layer header, Layer 4 of the OSI model. The world’s most popular standard protocols for implementing the transport layer are the TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
Hence, one hears of “TCP ports” and “UDP ports”, particularly when configuring rules for packet forwarding on a router or firewall. When one “blocks” a port, that means that communication to a particular computer program is denied. When one “opens” a port, communication to that computer program is being allowed.
Standard practice is to allow communications only to specifically-identified ports and deny all other communications.
The port number of the application and the IP address of the host computer concatenated together is called a socket in UNIX and IP and is called a transport service in the OSI model. The result is the ability to identify the specific source computer program on one computer and the specific desired destination computer program on a different computer.
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The Internet connection at your office dies. Lights on your modem are flashing in a strange pattern. You call the ISP, and they quickly diagnose that the modem power supply has failed, and they will overnight you a replacement. Presumably you are not the first person to have this problem with that modem.
So how do you continue to operate while you are waiting for the replacement power supply? It’s hard to run your business without e-mail and ordering and administration systems, which are all accessed via the Internet.
A large business will be a station on a Metropolitan Area Network, which is a ring, meaning two connections to the Internet for that business and automatic reconfiguration in the case of one failing. But this is expensive… the second connection is not free.
Small and medium businesses usually have a single DSL or cable modem connection to the Internet. When that fails, connectivity to email, ordering and administration servers is impossible, and many businesses these days would be “dead in the water” until the ISP fixes the problem with their hardware.
Unless you have an Android smartphone, a good “data” plan and a laptop with WiFi running Windows.
The scenario described happened at our office last week. Since many of our customers might find themselves in a similar situation – even at home – I thought I’d share the quick and painless solution I came up with. Even if you’re not likely to need this solution, understanding how it works will no doubt sharpen your understanding of the devices involved and their functions.
In this tutorial, I will use the technology in our office: 16 Mb/s DSL, Android smartphone and Windows laptop. The solution is equally applicable to an Internet connection using a cable modem or if you are one of the lucky few, an Internet connection via fiber.
For the smartphone and laptop, there may be equivalent functions on Apple products, but as I am allergic to Apples, we don’t have any in the office. I’m posting this tutorial on our Facebook page, our Google+ page, or our blog; I invite someone better able to tolerate Apple products to leave a comment whether and how the iPhone and MacBook can perform the required functions.
Figure 1 illustrates the normal network setup in our office, a typical configuration for networking at a small or medium business. On the left is the access circuit to the Internet Service Provider (ISP), terminating on a modem in our office.
The modem is contained in a box that also includes a computer and an Ethernet switch. This box is more properly called the Customer Edge (CE).
The computer in the CE runs many different computer programs performing various functions: Stateful Packet Inspection firewall, DHCP server offering private IP addresses to the computers in-building, DHCP client obtaining a public IP address from the ISP, a Network Address Translation function between the two, routing, port forwarding and more.
In-building is a collection of desktop computers, servers and network printers. These are connected with Category 5e LAN cables to Gigabit Ethernet LAN switches, one of which is also connected to the CE.
When a desktop computer is restarted, its DHCP client obtains a private IP address and Domain Name Server (DNS) address from the DHCP server in the CE. The private address of the CE is configured as the “default gateway” for the desktop by Windows.
When a desktop computer wants to communicate with a server over the Internet, it looks up the server’s numeric IP address via the DNS, then creates a packet from the desktop to the Internet server and transmits it to its default gateway, the CE.
The NAT function in the CE changes the addresses on the packet to be from the CE to the Internet server and forwards the packet to the ISP via the modem and access circuit. The response from the Internet server is relayed to the CE, where the NAT changes the destination address on the return packet to be the desktop’s private address and relays it to the desktop.
The solution for restoring Internet access after the CE died is illustrated below.
An Android smartphone and a laptop running Windows were used to restore connectivity to the Internet without making any changes to the desktops, servers or network printers.
First, I took my Samsung/Google Nexus smartphone running Android out of my pocket and plugged in the charger.
Then on its menu under Settings > more > Tethering & portable hotspot > Set up Wi-Fi hotspot, I entered a Network SSID (“TERACOM”) and a password, clicked Save, then clicked Portable Wi-Fi hotspot to turn it on.
The smartphone is now acting as a wireless LAN Access Point, just like any other WiFi AP at Starbucks, in the airport or in your home.
At this point, the smartphone is the CE device, performing all of the same functions that the DSL CE device had been before it died: firewall, DHCP client to get a public IP address from the ISP (now via cellular), DHCP server to assign private IP addresses to any clients that wanted to connect (now via WiFi), NAT to translate between the two and router to forward packets.
Just as the DSL CE equipment “bridged” or connected the DSL modem on the ISP side to the Ethernet LAN in-building, allowing all the devices on the LAN to send and receive packets to/from the Internet via DSL, the smartphone “bridges” or connects the cellular modem on the ISP side to the WiFi wireless Ethernet LAN in-building, allowing all the devices on the wireless LAN to send and receive packets to/from the Internet via cellular radio.
The remaining problem was that none of the desktops or servers had wireless LAN cards in them, so they could not connect to the smartphone AP and hence the smartphone’s cellular Internet connection.
What was needed was a device to “bridge” or connect the wired LAN to the wireless LAN in-building. By definition, this device would need two LAN interfaces: a physical Ethernet jack to plug into the wired LAN, plus a wireless LAN capability.
Looking around the office, I spotted two devices that fit this description. One of them was my laptop, with both a LAN jack and wireless LAN.
I fired up the laptop, plugged it into an Ethernet switch with a LAN cable, and in the Network and Sharing Center, clicked Change Adapter Settings to get to the Network Connections screen that showed the two LAN interfaces.
I enabled both the wired and wireless LAN interfaces. Then right-clicking the Wireless Network Connection icon, selected the TERACOM wireless network and entered the password.
Once that was successfully connected, I selected the two adapters in the Network Connections screen, right-clicked and chose “Bridge Connections”. A message saying “Please wait while Windows bridges the connections” appeared, then an icon called “Network Bridge” appeared, and after a few seconds, “TERACOM” appeared as well.
My laptop was now acting as an Ethernet switch, connecting the wired LAN to the smartphone’s wireless LAN.
Each of the desktops, servers and network printers in the office had to be rebooted so they would run their DHCP client again, obtaining a private IP address and DNS address from the smartphone AP, and be configured so the smartphone was the “default gateway” in Windows.
After rebooting my desktop computer, it had Internet access over the wired LAN, through the wired Ethernet switch to my laptop, to the smartphone via WiFi then to the ISP over cellular.
After rebooting the other desktops and servers, all had Internet access again, with no changes to the configuration of the desktops or servers.
This took about 20 minutes to get up and running, and we were back in business. Running a bandwidth test on speedtest.net, I found we had exactly 5 Mb/s connection to the Internet via cellular.
Obviously my cellular service provider limited the connection to 5 Mb/s in software – but who’s complaining? 5 Mb/s is more than three times as fast as a T1, which cost $20,000 per month when I first started in this business 20 years ago.
I hope you found this tutorial useful, either as a template for your own emergency backup Internet connection, or simply as a way of better understanding the devices, their functions and relationships.– EC
Note 1: You must verify your billing plan for “data” on your cellular contract before doing this. I have 6 GB included, which means basically unlimited, and that includes the WiFi hotspot traffic. Make sure you have something similar, to avoid receiving a bill for $10,000 for casual “data” usage.
Note 2: As always, this tutorial is provided as general background information only. We do not guarantee it will work for you. Each situation is unique and requires professional advice to identify and resolve issues including but not limited to performance and security. This tutorial is not professional advice. But I hope you have found it valuable.
Note 3: I might have been able to implement this without the laptop. If you’d like to know that, or what was the other device I could have used to bridge the wired and wireless LAN in-building, or suggest how this could be done with Apple products, please leave a comment.
Happy birthday IP version 6 – you finally arrived!
World IPv6 Launch Day was June 6, 2012 (about 12 years later than originally planned).
Hundreds of companies permanently enabled IPv6 protocol stacks on their servers on June 6, allowing the small percentage of devices (primarily Android smartphones) that had applications, operating systems and carriers all supporting IPv6 to communicate IPv6 packets end-to-end.
The address fields in IPv6 packets are 128 bits long, meaning 2 to the power 128 addresses.
Forget about questions like “how long is eternity going to last for”, “how far is it to the other side of the universe?”, “what happened before the Big Bang”, “where did all that energy come from in the first place?”, “who is God’s God?, and “who is God’s God’s God?”; we humans are not capable of understanding 340,282,366,920,938,463,463,374,607,431,768,211,456.
Teracom Instructor Richard Olsen did some calculations to help us grasp this number, including calculating how many grains of sand there are in the Earth’s crust. (Can you tell Richard is an Engineer?)
I’ll let Richard tell the story in his own words:
“I was teaching at Motorola University circa 1998 and in discussing IPv6, a student said, ‘You know, there are enough IP addresses in IPv6 for every square inch of the Solar System.’ I thought, that’s crazy, he’s out of his mind. I just said, ‘Wow!'”
“Anyway, while flying home I thought, I wonder how many square inches there are in the Solar System anyway. I think I’ll figure that out when I get home.”
“First I had to decide what ‘square inches of the Solar System’ meant. I decided to use the surface area of all the planets in square inches. That didn’t even come close to the number of IP addresses in IPv6.
I decided to throw in the Sun because that sucker is really big. Didn’t even come close. Then I decided to use the square inches inside the orbit of Pluto (this was before Pluto got kicked out of the Planet Club – poor Pluto!). Still didn’t even come close.”
“Finally, I’d always heard “IPv6 has enough IP addresses for every grain of sand on all the beaches on Earth”. By this time, I knew that couldn’t be. So I finally decided to calculate IP addresses per grain of sand over the entire surface of the Earth, including under the oceans, one mile deep assuming 10,000 grains of sand per cubic inch.”
“Answer: an astounding 664 BILLION IP addresses per grain of sand. Now, that’s a big number!!”
“The most commonly quoted number of stars in a galaxy is 100 billion and the most commonly quoted number of galaxies in the Universe is 100 billion. Assuming there are 10 planets around every star, then there are 10 x 100 x 100 billion billion planets in the Universe.
So how many IP addresses per planet in the entire Universe? Answer: 3.4 quadrillion IP addresses per planet!”
“The number of IP addresses in IPv6 is truly a prodigious number.”
I’ve told Richard’s story many times in classes. Over the years, like all good stories, it became embellished, and the story became
“666 billion addresses per grain of sand in the Earth’s crust to a depth one mile deep”, and “more addresses than there are square inches on the sphere that encloses the solar system out to Pluto.”
After reading Richard’s story again recently, I figured I had better verify the last claim, so I asked Richard to calculate the number of square inches on the sphere that encloses the solar system out to Pluto and divide that into 2**128.
It turns out my embellishment was not wrong: there are 5 millon addresses per square inch on the sphere that encloses the solar system out to Pluto.
Hope this all helps you grasp the number 340,282,366,920,938,463,463,374,607,431,768,211,456.