T1: A Survival Guide

Conventions Used in This Book

Italic is used throughout the book to indicate Internet addresses, such as domain names and URLs, and new terms where they are defined.

I use the common industry term telco when referring to telecommunications service providers. I use it interchangeably with the term carrier.

Telco references to kilo- and mega- are used as power-of-ten modifiers. That is, a kilobit per second is 1,000 bits per second. For clarity, I abbreviate a 1,000 kilo (or “telephone company kilo”) as k (e.g., 64 kbps for 64,000 bits per second) and a conventional computer science power-of-two kilo as K (e.g., 4 KB for 4,096 bytes).

Standards documents often use the word octet for a sequence of 8 bits. I prefer the term byte, though it is not technically accurate in all cases. Now that most machines with bytes of non-8-bit lengths have been retired from service, I feel comfortable doing so.

I use the standard C convention of prepending 0x to a number to denote that it is hexadecimal. Unless otherwise noted, numbers in the text are decimal numbers.

ISO and ITU-T diagrams generally present bits in the order of transmission, which is usually least-significant first. In IETF diagrams, the fields are shown with the most-significant bytes first. Furthermore, IETF diagrams begin counting bits with zero, while other standards organizations begin with one. I shift between these two forms throughout the book. All diagrams use the bit order favored by the relevant standards organization, ...