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”

Is the Internet a Public Utility?

Reading articles and blogs about Net Neutrality, one often sees the justification for government interference in the operation of IP networks to allow people stealing copyrighted works to consume bandwidth 24/7 at line speed “because the Internet is a public utility.”

It ain’t. The Internet is a business.

Reading articles and blogs about Net Neutrality, one often sees the justification for government interference in the operation of IP networks to allow people stealing copyrighted works using bittorrent (the net neutrality advocates) to consume bandwidth 24/7 at line speed “because the Internet is a public utility.”

It ain’t. The Internet is a business.

Continue reading “Is the Internet a Public Utility?”

Net neutrality – not. VideoTutorial on Service Level Agreements, traffic shaping and traffic policing

This video tutorial explains Service Level Agreements, traffic profiles, transmission characteristics, and how Differentiated Services (Diff-Serv) is implemented to be able to provide different transmission characteristics for different kinds of traffic – the EXACT OPPOSITE of net neutrality.

watch on youtube

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 (the correct term is “policing”) and that this, in their opinion, must stop.

This video tutorial explains Service Level Agreements, traffic profiles, transmission characteristics, and how Differentiated Services (Diff-Serv) is implemented to be able to provide different transmission characteristics for different kinds of traffic – the EXACT OPPOSITE of net neutrality.

It is taken from Teracom’s DVD video V9 Understanding Voice over IP 2: Voice Packetization • Voice Quality • Codecs, Jitter and Packet Loss • Diff-Serv • Network QoS with MPLS

 

ALL “NET NEUTRALITY” ARTICLES:

Net Neutrality – Foolish, ignorant or disingenuous?

Net Neutrality II: If the power company allowed this, your electrical bill would double

Net neutrality – not. VideoTutorial on Service Level Agreements, traffic shaping and traffic policing

Is the Internet a Public Utility?

 

Visit Teracom Training Institute for more information on telecommunications training and voip training

Net Neutrality II: If the power company allowed this, your electrical bill would double.

If “net neutrality” principles were applied to electricity, it would be like having no electricity meter. Everyone pays the same, regardless how much power they use. The problem: if you’re one of the 99% of normal users, you would have to pay DOUBLE what you normally would, to cover the costs of the 1% of users constantly drawing 200 amps 24 hours a day, 7 days a week, 365 days a year.

Following up on a previous discussion, a demand for “net neutrality” usually means a demand 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.

But a demand for “net neutrality” is usually also wrapped together with a demand by these same people for no metering, no usage charges. This would mean that users who are continuously transmitting and receiving packets would pay the same flat rate as someone who is paying only for a typical traffic profile.

If this principle were applied to electricity, it would be like having no electricity meter. Everyone pays the same, regardless how much power they use. The problem: if you’re one of the 99% of normal users, you would have to pay DOUBLE what you normally would, to cover the costs of the 1% of users constantly drawing 200 amps 24 hours a day, 7 days a week, 365 days a year.

Here’s how that would work:
Continue reading “Net Neutrality II: If the power company allowed this, your electrical bill would double.”

Digitally-Signed Email: Authentication and Digital Signatures

E-mail was one of the first “killer apps” on the Internet, and has been a major contributor to increases in productivity over the past ten years. Of course, along with email came the scourge of spam. Criminals infect computers with trojan horse programs, creating collections of machines they control remotely to send millions of unsolicited offers for fake watches, pirated software, phony medications and ecard invitations to infect your computer.

As spam reaches 30, 40 or even 100 unwanted messages per day on a targeted account, it is becoming essential to automatically separate legitimate messages from spam. One tool available to senders of legitimate emails to aid the recipient in this process is to digitally sign their messages, allowing the recipient to establish a level of comfort that the message actually came from the indicated sender.

Continue reading “Digitally-Signed Email: Authentication and Digital Signatures”

Offshored tech support from the phone company… so bad it's funny + $240 per year for an email address ?!

We usually feature articles on technical fundamentals in the newsletter – but this related topic might lighten up your day… a “help” desk so bad, it’s almost funny.

Recently, a relative asked me to help them sort out an issue with their ISP. They were paying for two internet access services, one old dial-up plan and one DSL plan. They wanted to go to a new 802.16 WiMax broadband wireless plan from the same ISP. They question they were trying to sort out was whether they could move their email addresses from the two existing services to the new one… or if they would lose those email addresses.

So I agreed to contact the ISP’s email “help” desk to find out the answer. One would think that the question: “Can I migrate my email address from one service provided by your company to another?” would be a frequently-asked question at an ISP email help desk, and could be answered “yes” or “no” in a few seconds.

However, it turned out that the ISP, a subsidiary of Bell Canada, has outsourced most of its customer service, and what could have been answered in a few seconds turned into a 20-minute waste of time. Here’s a transcript of the online chat session:

Continue reading “Offshored tech support from the phone company… so bad it's funny + $240 per year for an email address ?!”

The IP-PSTN

The Packet-Switched Telecommunications Network

Over the past fifty years, several attempts have been made to develop converged networks: networks with “dial tone” that supports all communications: speech, music, text, graphics, images and video. For a number of reasons, convergence strategies employing ISDN and ATM were unsuccessful and did not gain critical mass. This time, it appears that packet-switched network service using IP will gain enough momentum to become the new kind of plain ordinary telecommunications service.

Continue reading “The IP-PSTN”

TCP/IP over MPLS

Following is a section from the new third edition of the Telecom 101 textbook, tracing the flow of information from server to client over a TCP/IP/MPLS protocol stack.

18.8 TCP/IP Over MPLS

MPLS is deployed for managing traffic on IP networks, and in conjunction with other technologies like VPNs covered in Chapter 19, will end up replacing all other services, including dedicated T1s, Frame Relay, ATM and ISDN.

Since MPLS is a virtual circuit technology, the packet flow from server to client over an MPLS network is similar to the Frame Relay flow examined earlier.

Starting with the server on the right, which is downloading a file to the client on the left, we take a chunk of the file and give it to the TCP software running on the server. That puts a sequence number, error check and application port number on the chunk of the file, passes this to the IP software on the server and starts a timer. The IP software adds the source and destination IP addresses to form an IP packet, which is put in an 802.3 LAN frame (that uses the 802.2 logical link layer protocol), with the MAC address of the premise router on the right pasted on the frame. The frame is then broadcast onto the Gigabit Ethernet over copper (1000BASE-T) LAN on the right and directed to the premise router by the LAN switch.

The premise router on the right brings in the LAN frame, extracts the packet and passes it to the routing software on the premise router, which makes a routing decision, puts the packet in a LAN frame, changes the MAC address, recalculates the error check and sends it over the Gigabit Ethernet over fiber (1000BASE-LX) access circuit to the service provider’s MPLS network.

diagram of TCP/IP/MPLS protocol stack

FIGURE 153  TCP/IP OVER MPLS

The service provider receives this packet with an ingress Label Switching Router (LSR). That device examines the IP address on the packet and along with other factors, decides what Forwarding Equivalence Class the packet belongs to, and implements its decision by labelling the packet with a 20-bit label identifying the FEC. It then does a table lookup to determine what network device packets with this label are forwarded to, and transmits the labelled packet in a frame on the appropriate circuit.

Each LSR in the middle of the network (not shown) brings in the frame, extracts the packet then only looks at the label and performs a table lookup to determine where to forward it and what priority to give it.

Eventually the labelled packet is delivered to the network’s egress LSR on the left. This device removes the label from the packet and uses conventional IP routing to send the packet in an Ethernet frame to the customer’s premise router on the left. 

The premise router on the left brings in the packet, and looks in a table to find out what MAC address (what LAN card) is currently assigned that IP address. If it does not find an entry, it broadcasts an address resolution request on the LAN at the left using the Address Resolution Protocol (ARP), asking “who owns this IP address?” The client responds with its MAC address. The premise router puts the packet in a LAN frame with that MAC address on the front, and broadcasts the frame onto the LAN at the left. The LAN switch on the left directs the frame to the client on the left. 

The client pulls in the frame, extracts the packet and gives it to the IP software on the client. Seeing that the destination IP address on the packet is the same as its address, the client’s IP software extracts the data out of the packet and gives it to the TCP software on the client. This checks the error check, and if it fails, discards the data. 

Shortly after, the TCP timer on the server times out, so the TCP software on the right retransmits the data. Let’s say the second time, it passes the error check at the client, so the client TCP software sends an acknowledgement to the server, then extracts the data from the TCP protocol data unit and parks it in a memory space for the application identified by the port number on the TCP header… the file transfer application, which picks up the data shortly after.

Meanwhile, we’re sending the next one.

 

Want more ?
There is, of course, much more to the story than this brief tutorial.

This discussion is actually the final discussion in a whole chapter that leads up to it, starting with bandwidth on demand and packet network fundamentals, ideas like virtual circuits and jargon like connectionless network services, then going through the technologies: X.25, Frame Relay, TCP/IP over Frame Relay, understanding what is needed for voice over packet networks, how Frame Relay doesn’t do it, but ATM was supposed to, then MPLS and how QoS is implemented with MPLS and finally the discussion above.

This topic is covered in more detail in Teracom instructor-led courses, DVD video Computer-Based Training courses, and textbooks.
Telecom 101 textbook, 3rd edition: Chapter 18 (26 pages)

Course 101 Telecom, Datacom and Networking for Non-Engineers
: Chapter 15
Course 110 Understanding IP Telecom: IP, VoIP and MPLS for Non-Engineers: Chapters 5, 8 and 13
DVD 4 Understanding Networking 1: Part 3

 



GSM vs. UMTS… and the CDMA tipping point finally reached

Recently, we’ve noticed there is confusion regarding GSM cellular technology, and how it relates to CDMA. Not a big surprise given the wealth of jargon, buzzwords and semi-informed “analysts” in this area, but worth straightening out.

First generation: analog
In the beginning was analog cellular mobile radio. This was the first generation (1G) of cellular, an improvement on the previous Mobile Phone System (MPS) that provided better coverage, more capacity and allowed mobility: the possibility of the user moving, and being handed off from one base station [antenna] to another without dropping the call.

Various flavors were deployed by operators in different countries, including AMPS in North America, TACS in England and NMT in Scandanavian countries. These 1G systems are Frequency-Division Multiple Access (FDMA), meaning that the spectrum [radio band] allocated to the operator is divided into smaller bands called channels, and channels are allocated to users.

Second generation: digital and the warring factions
Problems with capacity and data communication led us to second generation (2G) cellular. Two warring factions emerged, with radically different views on sharing spectrum amongst users: the TDMA faction and the CDMA faction.

TDMA, Time-Division Multiple Access, means sharing one radio channel amongst a number of users by taking turns, one after another, in time. In North America, systems conforming to the IS-136 standard implement eight time slots on 30 kHz channels, allowing three users (one time slot for each direction for each user, plus time slots for control information). In the Rest Of The World, systems conforming to the Global System for Mobile Communications (GSM) standard implement sixteen time slots on 200 kHz channels, allowing seven users. Modems transmit 1s and 0s that are digitized speech (or digitized silence), or data (or idle patterns) at 9.6 kb/s between the phones and the base station over the radio channel.

CDMA, Code-Division Multiple Access, means not dividing spectrum into narrow channels, and not implementing time-sharing on those channels, but instead having all users transmit in the same carrier [wide frequency band], all at the same time. However, instead of transmitting 1s and 0s directly, the users transmit codes to represent 1s or 0s, and only transmit when they have something to say. Codes are binary numbers – strings of 1s and 0s – chosen so that if some users transmit and some do not, the base station can determine which transmitted. In North America and in limited places in the Rest of The World, a solution from Qualcomm Incorporated called CDMAOne and standardized as IS-95 was deployed. Qualcomm has patents on several functions necessary for cellular CDMA.

GSM/TDMA is the most popular today
GSM/TDMA became far more popular than IS-95, and so the market for selling phones and collecting money from GSM users is currently the largest. But, GSM/TDMA assigns 9.6 kb/s time slots to users, and even with band-aids and add-ons like GPRS and HSCSD, bandwidth like that is not useful for data communication (email, text messaging, Internet browsing, Google maps and location-based advertising, video) in any meaningful way. Further, GSM/TDMA reserves bandwidth for users whether they have anything to transmit or not – a very wasteful and inefficient use of scarce radio spectrum.

Third generation broadband: the factions continue to disagree
So we needed a third generation (3G). Because of the 2G schism, it was desired to have a global standard for 3G mobile radio. A group called International Mobile Telecommunications 2000 (IMT-2000) was formed to come up with a single world standard – and failed. They produced a document that had five incompatible variations. The two serious variations both were CDMA, since it is the most flexible and most efficient way of sharing the radio spectrum.

The warring factions did not make peace, they just changed what they were arguing about.

The 2G CDMA faction supported the variation called IMT-Multi Carrier, known as CDMA2000, basically a software upgrade from IS-95. A version called 1X using 1.25 MHz carriers was immediately deployed. 1X Evolution – Data Optimized (1XEV-DO) allows high-bitrate data communications.

The GSM/TDMA faction supported the variation called IMT-Direct Spread, known as Wideband CDMA and now marketed as Universal Mobile Telecommunications System (UMTS), which uses 5 MHz carriers and allows high-bitrate data communications using technologies like High-Speed Packet Access (HSPA).

The CDMA tipping point in the GSM/UMTS faction
After numerous false starts, the tipping point between 2G and 3G in the GSM/UMTS camp was finally reached in the summer of 2007, when more new activations on GSM/UMTS carriers’ networks were UMTS (3G CDMA) instead of GSM (2G TDMA).

What to take away from this discussion

  • The 2G TDMA technology GSM at present has far more users, but like 1G analog, GSM will eventually disappear.
  • Two incompatible competing 3G CDMA-based technologies: IMT-MC (CMDA2000 1X) and IMT-DS (UMTS) will go forward.
  • Qualcomm sells a chip or gets a patent license royalty for every handset and base station sold, for both 1X and UMTS.
  • Many users, salespeople and semi-informed analysts and reporters will erroneously refer to IMT-DS (UMTS) as “GSM”.
  • Want more ?
    There is, of course, more to the story than this brief tutorial. This topic is covered in more detail in Teracom instructor-led courses, DVD video Computer-Based Training courses, and textbooks:
    Course 101 Telecom, Datacom and Networking for Non-Engineers: Chapter 6
    Course 120 Understanding Wireless: Chapters 8, 9 and 10
    DVD 6 Understanding Wireless 1: Parts 2, 3 and 4
    Telecom 101 textbook, 3rd edition: Sections 8.2 – 8.7 (21 pages)