Ethernet in the First Mile
For engineers struggling with the IEEE standard 802.3, this book annotates and explains the dense language of the standard document, taking particular care how to explain how the EFM dovetails with other standards.
TABLE OF CONTENTS Ethernet in the First Mile
Chapter 5: The Long-Reach Solution: 2BASE-TL
"Like it or not, the business environment is where long reach EFM is needed now."
-THE 2BASE-TL BASELINE PROPOSAL [26]
Introduction to SHDSL
Synchronous Digital Hierarchy
The Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SDH/SONET) specify different levels of multiplexing for data transport. T1 and E1 links are first-order multiplexes of digitized telephone lines, used for trunking between a private exchange and a central office (CO). Each digitized telephone line has an uncompressed bit rate of 64 kbps, corresponding to 8000 audio samples per second, with a size of 8 bits each. [1]
The American variant T1 has a rate of 24 64 kbps = 1536 kbps. The European variant E1 has a rate of 32 64 kbps = 2048 kbps. The original implementations of T1/E1 links used a robust but spectrally inefficient modulation scheme, generating particularly nasty crosstalk.
High-Speed Digital Subscriber Line (HDSL), Synchronous Digital Subscriber Line (SDSL), and their successors Single-Pair High-Speed Digital Subscriber Line (SHDSL) and HDSL2 were introduced to offer T1 and E1 services more efficiently and with less crosstalk.
Pulse Amplitude Modulation
Pulse Amplitude Modulation (PAM) codes a set of bits into the amplitude of a pulse. In SHDSL, 16-level PAM is used. [2] Before being mapped onto PAM symbols, the serial bit stream of user data is first scrambled and then sent through a convolutional encoder. The convolutional encoder transforms m input bits into m+1 output bits. This implies that the 4-bit PAM symbol carries the equivalent of...
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