"Subsequently, the UTC timescale has marched backward relative to the TAI timescale exactly one second on scheduled occasions recorded in the institutional memory of our civilization."

"In TDMA, each user's timeslot ends with a guard period, to avoid data loss and to reduce interference to the following user, caused by propagation delay. Thus a user's timeslot is protected from interference from the preceding user, by the guard interval (guard period) at the end of that preceding user's timeslot. It is a common misconception that each TDMA timeslot begins with a guard interval, however the ITU Technical Specifications (such as GSM 05.05) clearly define the guard period as being at the end of each timeslot, thus providing protection against data loss within that timeslot, and protection against interference to the following timeslot. Longer guard periods allow more distant echoes to be tolerated. However, longer guard intervals reduce the channel efficiency. [...] Radio waves propagate at the speed of light, 5μs per mile. Ideally the guard interval is just longer than the delay spread of the channel."

Kibibytes, mebibytes and gibibytes!

"A byte is, formally, the smallest unit of data that can be read from or written to at one time in a computer system. In almost all cases today, that is indeed eight bits, but there are have been some systems where a byte was not eight bits. Some older 36-bit computers used 9-bit bytes, and there were also systems that had byte sizes of 6 or 7 bits, or even variable-sized bytes. For this reason, many people, especially techie professionals, prefer the term octet, which clearly and unambiguously implies “eight”."

"The term character is also used to express a set of eight bits. This use comes from the fact that computers often store alphanumeric characters, such as letters and numbers, one to a byte. The 16-bit word is fairly often used, but not nearly as much as “byte”."

"Normal Network Overhead: Every network has some degree of normal network overhead, which guarantees that you will never be able to use all of the bandwidth of any connection for data. Take as an example 10 Mbit/s Ethernet. Sure, the line may be able to transmit 10,000,000 bits every second, but not all of those bits are data! Some are used to package and address the data—data can't just be thrown onto the network in raw form. Also, many of those bits are used for general overhead activities, dealing with collisions on transmissions, and so on. There are natural inefficiencies in any networking technology."

"Metropolitan Area Networks (MANs): Another “intermediate” term that you may see sometimes is the metropolitan area network or MAN. As the name implies, this refers to a network that spans a particular small region or a city. Metropolitan area networks can be considered either as “small WANs” that cover a limited geographical area, or as “large LANs” that cover an area greater than that normally associated with a local network. Wireless metropolitan area networks are of course sometimes called WMANs; IEEE 802.16 is an example of a WMAN standard."

"The three basic type of addressing and message delivery in networking are illustrated in this simplified local area network. Device #6 is sending a unicast message to #2 shown in purple. Device #4 is sending a multicast message to multicast group “X”. In this case, that group includes devices #1 and #3, shown in green. Finally, Device #5 is sending a broadcast message, which goes to all other devices on the LAN."

"The ability to have many devices communicate simultaneously without dedicated data paths is one reason why packet switching is becoming predominant today."

"In a packet-switched network, no circuit is set up prior to sending data between devices. Blocks of data, even from the same file or communication, may take any number of paths as it journeys from one device to another."

"A packet-switched network is a digital communications network that groups all transmitted data, irrespective of content, type, or structure into suitably-sized blocks, called packets. The network over which packets are transmitted is a shared network which routes each packet independently from all others and allocates transmission resources as needed."

"The long-term average number of customers in a stable system L is equal to the long-term average arrival rate, λ, multiplied by the long-term average time a customer spends in the system, W; or expressed algebraically: L = λW."

"The service actually provided to the user by networks using packet switching nodes can be either connectionless (based on datagram messages), or virtual circuit switching (also known as connection oriented). Some connectionless protocols are Ethernet, IP, and UDP; connection oriented packet-switching protocols include X.25, Frame relay, Asynchronous Transfer Mode (ATM), Multiprotocol Label Switching (MPLS), and TCP. [...] Packet switching is used to optimize the use of the channel capacity available in digital telecommunication networks such as computer networks, to minimize the transmission latency (i.e. the time it takes for data to pass across the network), and to increase robustness of communication. The most well-known use of packet switching is the Internet and local area networks. The Internet is implemented by the Internet Protocol Suite using a variety of Link Layer technologies. For example, Ethernet and Frame Relay are common. Newer mobile phone technologies (e.g., GPRS, I-mode) also use packet switching."

For the "Web Resources" section.

Explains IP packets: "IP packets are composed of a header and payload. The IPv4 packet header consists of:"

A handy diagram; "A summary of the contents of the internet header follows:"

Symbols per second, or pulses per second. Not to be confused with bps. (You should ask youself, how many bits are used to convey a symbol?)