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specification, coming out of the work of the Metro
Ethernet Forum, is used primarily for core and distribu-
tion network services over fiber and is not relevant to
SMO and cell site target segments under consideration
here. The last category, Pre-Standard Ethernet over
Copper, refers to the proprietary technology for Ethernet
on bonded copper loops that was originally developed by
a small company named Net to Net in the late 1990s and
acquired by Zhone in 2005. A number of Zhone custom-
ers continue to use this technology quite successfully.
One other term with some currency in the industry is
"carrier Ethernet" — used variously as an umbrella term
to refer to the services that operators can offer with any
of these technologies, or sometimes more specifically to
refer to Ethernet services in the core or distribution
networks. Our focus for the balance of this discussion is
on EFM over Copper, which in practice is usually short-
ened to just EFM.
How EFM Works
In simplest form, EFM is a straightforward combination
of packet data in Ethernet frames carried over an SHDSL
physical layer on one or more last-mile twisted pair
copper loops. An EFM connection is made between an
Ethernet access device (EAD) at the customer premise
and typically an EFM aggregation platform in the central
Choices for Ethernet in the Access Network
A quick reference guide to the four common technology categories
Ethernet
over
Fiber
Category
Category
Metro Ethernet
Metro Ethernet
Standard
Standard
MEF* 10 Technical
MEF* 10 Technical
Specification
Specification
Physical
Physical
1 single-mode optical
1 single-mode optical
Medium
Medium
fiber with WDM
fiber with WDM
Topology
Topology
Ring, star
Ring, star
Physical
Physical
1000/10000 Base T
1000/10000 Base T
Layer
Layer
Data
Data
1–10 Gbps
1–10 Gbps
Rates
Rates
Reach
Reach
10–40 km (6–25 mi.)
10–40 km (6–25 mi.)
depending on optics
depending on optics
Target
Target
Large enterprises
Large enterprises
Segments
Segments
Z H O N E T E C H N O L O G I E S
Ethernet in the First Mile (EFM)
Active Ethernet
Active Ethernet
IEEE 802.3ah EFM
IEEE 802.3ah EFM
1 single-mode optical
1 single-mode optical
fiber
fiber
Point to point
Point to point
10/100/1000 Base T
10/100/1000 Base T
10/100/1000 Mbps
10/100/1000 Mbps
10–40 km (6–25 mi.)
10–40 km (6–25 mi.)
depending on optics
depending on optics
SM 0
Small/medium
enterprises (SME)
Residential triple play
Residential triple play
*MEF = Metro Ethernet Forum
E T H E R N E T O V E R C O P P E R
office, or in some cases directly with an EAD at another
premise. EADs deliver WAN connectivity on the premise
through an Ethernet port to a standalone device or a
LAN switch, and they may also provide emulated legacy
interfaces (POTS, T1/E1) as well.
The IEEE 802.3ah standard incorporates a number of
advances in Ethernet over last-mile twisted pair, includ-
ing:
• use of the SHDSL physical layer for high symmetric
data rates per twisted pair (up to 15 Mbps)
• direct connection between the Ethernet MAC layer and
the SHDSL PHY layer, avoiding latency and frame
overhead associated with prior approaches that
retained ATM encapsulation and adaptation in the
process
• support for multiple twisted pairs in a bond group that
are combined to form one virtual Ethernet connection
with higher speeds and resiliency — as shown in the
diagram on the facing page, individual inbound
Ethernet frames are divided by EFM devices into
fragments optimized for current loop performance
before being sent in parallel over the bond group, one
fragment to a pair, and then re-assembled on the
receiving end.
Ethernet
over
Copper
EFM over Copper
EFM over Copper
Pre-Standard
Pre-Standard
Ethernet over Copper
Ethernet over Copper
IEEE 802.3ah EFM
IEEE 802.3ah EFM
None
None
(Net-to-Net protocol)
(Net-to-Net protocol)
1 to 8 voice-grade
1 to 8 voice-grade
1 to 8 voice-grade
1 to 8 voice-grade
Cat-3 copper pairs
Cat-3 copper pairs
Cat-3 copper pairs
Cat-3 copper pairs
Point to point
Point to point
Point to point
Point to point
SHDSL.bis
SHDSL.bis
T1, E1, SHDSL.bis
T1, E1, SHDSL.bis
Up to 5.7 Mbps per
Up to 5.7 Mbps per
1.5–5.7 max Mbps
1.5–5.7 max Mbps
pair (max 45 Mbps)
pair (max 45 Mbps)
per pair (to 45 total)
per pair (to 45 total)
Up to 7 km (4.5 mi.)
Up to 7 km (4.5 mi.)
Unlimited for T1/E1;
Unlimited for T1/E1;
< 7 km / 4.5 mi. for
< 7 km / 4.5 mi. for
SHDSL.bis
SHDSL.bis
SM O
SM O
SME
SME
(inc. T1/E1 or frame
(inc. T1/E1 or frame
(inc. T1/E1 or frame
(inc. T1/E1 or frame
relay replacement)
relay replacement)
relay replacement)
relay replacement)
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