New Tutorial: Wireless Spectrum and Radio Bands

Here’s the latest tutorial: Radio Spectrum and Radio Bands

This is taken from the new Teracom Training DVD-video course
DVD6 “Understanding Wireless” course book, pages 1.06 and 1.07.

The new DVD is due out in December.

Click the diagram to go to the full tutorial.


radio spectrum and radio bands

click here to go to the full tutorial

EC circa 1998 – The big prize is video on demand replacing movie rental stores

The video clip above is me talking about The Future. Shot in 1998. I was 36. I came across this by accident on a tape I was re-using.

The same day I came across this by accident, today, fourteen years later, I am getting Bell Fibe TV installed, which is exactly what I was talking about in the video clip!

Broadband high-speed Internet service (25 Mb/s) with IPTV over DSL over the phone line for content delivery.


– Eric Coll

Tutorial: How to Use Cellular as Backup Internet Access When Your DSL, Cable or Fiber Internet Dies

Cellular as Emergency Internet Connection Backup

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.

If you want availability, you need two connections to the Internet, so if one fails you are not out of business. We go over this in the lesson “Mature Competitive Carrier Network: Regional Rings, POPs and MANs”, slide 3.17 of Course 101, Telecom Datacom and Networking for Non-Engineering Professionals, and mention it in pretty much every other course.

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: Normal network setup

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.

Figure 2 Restored Internet Access via Cellular

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, 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.

New! Try the free Teracom Telecom, Datacom and Networking Quiz

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Do it as many times as you like – different questions every time!
Challenge your colleagues!


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Net Neutrality – Foolish, ignorant or disingenuous?

The popular press and news feeds have been full of stories about advocates of “net neutrality” testifying to congressional committees, lobbying the federal government and railing against the big ISPs over the past while.  Not much mention of arguments against net neutrality, though.  It’s hard to decide whether those arguing for net neutrality are foolish, ignorant or disingenuous.  
Let’s begin with some definitions. When someone demands “net neutrality”, they usually mean that the network must not discriminate between applications being carried in IP packets; that identical transmission characteristics (throughput, delay, number of errors, etc.) are to be provided for all packets regardless of what is being carried in them. They claim (correctly) that this is not the case at present, that the network service provider is “throttling” certain applications, “slowing down” or “shaping” traffic and that this, in their opinion, must stop. They sound the rallying cry “the net should be free”. 
What a load of hogwash.
But are these arguments foolish, ignorant or disingenuous?  Hard to decide: 

Continue reading “Net Neutrality – Foolish, ignorant or disingenuous?”

If you should know the answer to these questions about MPLS, but don't, this is the course for you:

Course 110 IP, VoIP and MPLS for the
Non-Engineering Professional
is the “next” course in our Core Training series, covering only newer technologies: virtually all aspects of IP networks and services.

Designed for non-engineers, this training course will give you the solid, vendor-independent foundation knowledge necessary to deal with IP telecom network projects and IP voice and data applications with confidence. 

If you want to know the answers to these questions, or you should know the answer to these questions, but don’t, this is the course for you: 
When an organization like AT&T or TELUS says it “has an MPLS network” and sells “MPLS services”,
– What exactly does that mean?
– Just what is an MPLS service anyway? What does it do? Who uses it? What for?
– Can you tell me two different ways MPLS service is different than Internet service?
– What benefit does that bring to the customer?
– Does it cost more? Better yet, is it costed the same way as Internet service?
– How do you connect to MPLS service?
– What is the technology and business environment for MPLS service going to in 2015?
I think you’ll agree that knowledge set is career-enhancing knowledge. We often tell people “if you want a guaranteed job, be an expert in MPLS”. Here’s a great place to start! 

And this is only one part of this intensive, three-day leadership and technology development course!
You will also learn the workings of SIP and softswitches; the nuts-and-bolts of packetized voice and its protocols; Layer 2, VLANs and 10 Mb/s – 40 Gb/s Ethernet services; IP routing; the ISP business and more.

In three days, you’ll get up to speed, demystify jargon and buzzwords, fill the gaps, understand the technologies, the underlying ideas and how it all fits together… knowledge you can’t get from trade magazines or salespeople. 

This investment will be repaid many times over, eliminating frustration at buzzword-filled meetings, increasing your efficiency, and helping ensure you make the right choices. IP, VoIP and MPLS is an essential knowledge set going forward in telecommunications. 

This professional training course will give you the solid, vendor-independent foundation necessary to deal with IP telecom network projects and IP voice and data applications with confidence. 

Get this career-enhancing knowledge today! more info

How ISPs connect to the Internet: peering vs. transit

This discussion is covered in Course 101, Chapter 16 “Understanding the Internet”,
and in more depth in Course 110, Chapter 16 “IP as a Business: Carrier Networks, Competition and Interconnect”

Originally, the only way to get on to the Internet was from a terminal connected to a computer at a university or research institute. The Internet was mostly circuits paid for by the taxpayers via the National Science Foundation. Today, commercial Internet access providers, called Internet Service Providers (ISPs) provide the capability for anyone to access and communicate over on the Internet. These ISPs are for the most part business units of facilities-based carriers, i.e. telephone companies and cable companies.

Such service providers have physical access circuits and circuit-terminating equipment on the customer side, plus routers, security and access control equipment to manage customer traffic. This is often organized with data centers in cities or regions, which are interconnected. This ensemble of interconnected routers controlled by an ISP is called an Autonomous System (AS).

The Internet is a vast, unregulated collection of interconnected Autonomous Systems. The connections between ASs are not specified by a central authority or world government, but are implemented on a case-by-case basis by the operators of an AS for business reasons. The Internet is not free. It is not a public utility. It is a business.

ISPs operating ASs will connect to competitors and content providers like Google to exchange traffic terminating on each other’s network (called peering), and will connect to larger organizations who will assure delivery of packets to other destinations (transit). The networks are physically connected at Internet Exchange (IX) centers such as Equinix Chicago at 350 E Cermak. These are buildings with equipment implementing network interconnection operated by a neutral third party. The ASs are responsible for paying for connectivity to the IX.

Course 101, page 16.09: Internet Service Providers

Internet Service Providers

Peering is settlement-free, i.e. no money is exchanged. Transit is a commercial service that costs money. Larger ISPs charge smaller ISPs for transit services. The largest networks are sometimes called Tier-1 service providers… but “Tier-1” is not an officially defined term. Some claim that it means a network “close to the center of the Internet” or a network that does not pay for transit. However, there is no “center” to the Internet, and virtually all networks employ a mix of peering and transit agreements to connect to other networks… and the nature of such connections is non-disclosed confidential business information. A “Tier-1 network” might best be thought of as one operated by a very big facilities-based carrier that has presence in most or all IXs and sells transit services to smaller networks and ISPs.

The ISPs build the access network and peering or transit connections to other networks, then charge the users for access. It’s a pyramid scheme. The end users end up paying for all.

In addition to access services, the ISP usually provides a Web server to host your website, a Domain Name Server, and an e-mail server.
Back in the Flintstones era when dial-up Internet access was first available, telcos were a bit slow to react, so for a while, companies like Netcom, MindSpring, Portal, Pipeline, iStar and others had their day in the sun. These organizations were resellers, leasing circuits from a carrier and reselling them to users under per-minute or per-month billing plans.

The carriers eventually began competing with resellers, who for the most part went out of business, selling their customers to the carriers. For example, Netcom is now part of Earthlink, which is majority owned by Sprint. AOL and MSN are the biggest remaining reseller-type ISPs. For the most part, it is business units of the companies that own the cables coming into your home: the LEC and the cable TV company that are the dominant ISPs today.

If you do choose to use a reseller-type ISP, particularly for a business or organization, questions regarding customer service, capacity and availability should be asked. Another is redundancy – do they have a single point of failure? Do they have multiple connections to different Tier-1 providers? What capacity are those connections?

This discussion is covered in Course 101, Chapter 16 “Understanding the Internet”,
and in more depth in Course 110, Chapter 16 “IP as a Business: Carrier Networks, Competition and Interconnect”

The Mature Competitive Environment: Regional Rings and MANs

Competition today means much more than the 1984 idea of LECs, competitive IXCs and switched access charges or subcontracted dedicated access lines. Competition today includes competitors providing various services to residences and business customers using a mix of switched access, subcontracted dedicated access, plus colocation and bypass on the “last mile”. Continue reading “The Mature Competitive Environment: Regional Rings and MANs”

4G Cellular, OFDM and LTE – the "GSM vs. CDMA" Standards War Ends!

This tutorial is part of the most recent update to Course 101, Chapter 6, October 2008.

After more than 20 years, it appears that an almost universally-accepted standard for mobile radio may finally be implemented, bringing to an end the standards war between carriers that deployed TDMA/GSM for second generation and carriers that deployed CDMA for second generation. Those two factions continued the standards war for the third generation (UMTS and 1X respectively); but now carriers from both of the factions are supporting the GSM/UMTS faction’s Third Generation Partnership Project (3GPP) release 8, known as Universal Terrestrial Radio Access Network Long Term Evolution (LTE). Continue reading “4G Cellular, OFDM and LTE – the "GSM vs. CDMA" Standards War Ends!”

Soft Switches

The term soft switch is not defined in a standard… meaning that marketing departments at different equipment and software manufacturers use the same term to describe different things.

A switch, in its simplest form, is a device that causes communications to happen from one point to one other particular point, often when there are multiple “other” points to choose from.

A traditional Central Office (CO) telephone switch might be called a “hard” switch, since it has physical line cards that terminate loops. The switching software running on the computer which is the CO switch directs traffic between a line card and a trunk or between two line cards during a phone call.

The term soft switch is used to mean a computer running switching software that does not have telephone line cards – the communications are instead directed to the correct destination by routers routing packets, a software function.

softswitch diagram

Continue reading “Soft Switches”