My favorite: the FedEx Analogy to explain the OSI layers, what each layer does and how they work together in protocol stacks.
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!
What is a MAC address?
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.
Cisco VoIP phone vulnerability: continuously monitor and record all sound in people’s offices, boardrooms and bedrooms
A recent report of a Cisco VoIP phone vulnerability is very disturbing.
This is more serious than phone calls.
If the network world article is accurate, its first paragraph “vulnerability in its IP phones that allows hackers to access calls and call data” should read
“vulnerability in its IP phones that allows attackers to eavesdrop in people’s offices, boardrooms and bedrooms”
– or in fact, “continuously monitor and record all sound in people’s offices, boardrooms and bedrooms”.
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
|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.|
|I hope you’ve enjoyed this tutorial! This discussion is covered in the following Teracom training courses:
• Instructor-led Course 101: Telecom, Datacom and Networking for Non-Engineering Professionals, Lesson 12.17
• Instructor-led Course 110: IP, VoIP and MPLS for the Non-Engineering Professional, Lesson 8.25-8.27
• DVD-Video Course V4: Understanding Networking 1
• DVD-Video Course V5: Understanding Networking 2, Lesson 2.11
• Online Course L2112 The OSI Layers and Protocol Stacks, Lesson 8
• Online Course L2113 IP Networks, Routers and Addresses, Lessons 7 and 9
|Not only will you earn 20% of net proceeds from students who are referred from your site, becoming a Teracom Training affiliate adds prestige to your site, and may complement other content on your site or add to other training affiliations you may have, making your site in turn more valuable.|
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How to Use Cellular as Backup Internet Access When Your DSL, Cable or Fiber Internet Dies
|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-Engineers, 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|
|The diagram above 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 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.
|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.|
MPLS and Carrier Networks is a comprehensive training course designed to build a solid understanding of carrier packet networks and services, the terminology, technologies, configuration, operation and most importantly, the underlying ideas… in plain English.
This course can be taken by both those who need simply an overview and introduction to the fundamentals of carrier packet networks and MPLS, and by those who need to get up to speed and establish a solid base that project or job-specific knowledge can be built on.
We’ll cut through the buzzwords and marketing to demystify carrier packet networks and services, explaining Service Level Agreements, traffic profiles, virtual circuits, QoS, Class of Service, Differentiated Services, integration, convergence and aggregation, MPLS and other network technologies, and how they relate to TCP/IP without bogging down on details.
You will gain career- and productivity-enhancing knowledge of the structure, components and operation of carrier packet networks and services, how they are implemented, packaged and marketed by carriers and how they are used by government, business… and other carriers.
|Please click here to see the full tutorial on its web pagel, with the necessary diagram…|
|We’re getting ready to release another Online Course Module at the end of March: L2014 "MPLS and Carrier Packet Services."
As a sneak preview, this newsletter’s free tutorial is part of Lesson 11 "TCP/IP over MPLS" from that module.
NOTE: You may find this tutorial a bit overwhelming, landing smack on your computer screen with no preparation, like a parachutist whose chute didn’t open landing in a cow field.
In the Online Course module "MPLS and Carrier Packet Services", there are TEN lessons building up to this one. We’re actually going to be recommending at least two modules: "The OSI Layers and Protocol Stacks" and "IP Packet Networks, Addresses and Routers" as prerequisites… so that would be at least THIRTY-FIVE lessons building up to this one.
|So… if you are already familiar with the OSI Layers and protocol stacks, and IP packets and LANs, you’ll find the following lesson easier to follow. If you’re not already familiar with those pre-requisites, then you might want to watch some other free tutorials first: Video Tutorial VT-3 "Packets, Frames, Addresses and Routing", Video Tutorial VT-4 OSI Layers: The FedEx Analogy, and the "Datacom and Networking Fundamentals" section of our free online tutorials.|
|The following is part of the text and one graphic from Lesson 11 "TCP/IP over MPLS". The Online Course module when released at the end of March will have extensive animations following along with a voiceover of the text. Enjoy!|
Please click here to see the full tutorial on its web pagel, with the necessary diagram…