II.

1 Wireline Broadband Access Technologies In the domain of wide area network access, there are
numerous wireline technology options that are presently competing for market share and acceptance.
These technology options originate from both the Area Network Wire (WAN) and Local Area Network
(LAN) environments and include, e.g. ISDN, ATM, switched Ethernet Frame Relay, several technologies
for data transmission over community antenna (CATV) cable, and the family of Digital Subscriber Line
technologies. II.1.1 DSL Technology Matrix The introduction of new services demanding digital signals
with higher and higher bit rates requires either to extend the usable bandwidth of existing subscriber
loops with sophisticated technologies or to replace the twisted pairs with broadband transmission
media such as, e.g. fibre / coaxial cables or wireless transmission. Report on Question 20-1/2 23
Historically wire subscriber loops contain twisted copper pairs assembled in multi-pair cables. Subscriber
loops have been under study for many years and are defined by cable type, cable length, loop structure
and noise sources. The spectrum of the subscriber loop which is normally used for voice frequency
signals of up to 4 kHz can be extended to about 1 100 kHz for the transmission of digital signals using
DSL technologies. The extensive cost related to the replacing of existing subscriber loops and at the
same time the development in the field of digital signal processing influenced the development of Digital
Subscriber Loop (DSL) technologies to achieve better utilization of the available bandwidth and, as a
result, the transmission of higher bit rates. The DSL technology allows the digital signals to share the
subscriber loop with the telephone voice signal (POTS). Typical DSL systems are: – High bit rate Digital
Subscriber Line (HDSL); – Asymmetrical Digital Subscriber Line (ADSL); – Very high-speed Digital
Subscriber Line (VDSL); – Single-pair High Speed Digital Subscriber Line (SHDSL); – ISDN based Digital
Subscriber Line (DSL ISDN). Figure 1 shows typical data rates and related ranges for systems using 1 pair
(not using any repeaters, i.e. regenerators). Figure 1 – Loop range related to various DSL systems 10 5.0
2.0 1.0 0.5 0.2 0.2 0.5 1.0 2.0 5.0 10 20 50 100 1 2 3 4 5 6 7 VDSL widl/xdsl1m Mbit/s (from subscriber to
central office) Mbit/s Downstream ADSL HDSL SHDSL km Loop range symm. asymm. (from central office
to subscriber) Upstream 24 Report on Question 20-1/2 The values shown in the table depend on many
parameters, such as, e.g. wire gauge, bridged taps, disturbances including crosstalk between pairs,
margins, etc. In addition, due to the continuous development of new technologies the values can
change. HDSL has been the most widely deployed of the DSL technologies and uses two or three copper
twisted pairs. Most implementations provide either 1.5 Mbit/s (T1) or 2 Mbit/s (E1) symmetrical at up to
3 000 m from the Central Office. This distance can be increased with Regenerators. ADSL holds the
greatest near term potential for providing broadband access to residential and small office, home office
markets. More bandwidth is allocated for traffic from the service provider to the subscriber
(downstream) than for the traffic from the subscriber to the service provider (upstream). The bandwidth
allocations permit simultaneous Plain Old Telephone Service (POTS) or ISDN traffic. Two ADSL versions
exist: Full-rate ADSL using about 1 MHz and ADSL Lite using about ½ MHz bandwidth. Full-rate ADSL
requires splitter filter installations, ADSL Lite works without splitter filters or requires simplified in-line
filter installations. VDSL is designed for much higher bit rates and extremely short subscriber loop
distances. VDSL often is used in conjunction with fibre installations, e.g. fibre to the Curb. With the aid of
splitter filters simultaneous POTs traffic is possible. SHDSL is expected in future to replace HDSL as the
system will normally operate across a single pair. Extended range is possible either using 2 pairs or/and
regenerators. The use of advanced coding limits bandwidth requirements leading to coexistence with
other DSL systems. The DSL family of technologies provides a wide variety of schemes to accomplish and
satisfy different market needs for present and future infrastructures. In the context of DSL, whether
single or two pairs, symmetric or asymmetric, rate-adaptive or multi-channel applications, DSL
technologies are tools to meet market challenges. Both market needs and DSL technologies are still
evolving. In addition to speed, DSL systems offer another key benefit: constant connectivity. Because
DSL modems use connectionless technology, much like in an office LAN, a subscriber’s PC is always
online with the network. Short list of References a) Report on DSL Technologies ITU-D Doc.
2/082(Rev.3)-E, 2002 Understanding Digital Subscriber Line Technology Thomas Starr e.a.
Communication Engineering b) Prentice Hall PTR, NJ 07458, 1999 DSL, Simulation Techniques and
Standards Dr Walter Y. Chen Macmillan Technical Publishing, Indianapolis, Indiana, 1998 II.1.2 Basic
Cable Matrix With near-ubiquitous coverage of broadband community antenna for cable TV in some
countries, community antenna connections provide a powerful platform for providing residences and
small business with high-speed data access. However, one-way cable television systems must be
upgraded into modern twoway networks to support advanced telecommunications services. Report on
Question 20-1/2 25 The study of “Cable TV Primer”, originating from ITU-T Study Group 9 could serve as
a useful introduction to the cable TV network. Further information on cable TV networks could be found
in ITU-D Study Group 2 Fascicule 4 in the following items: 5.3.9 Cable TV Distribution 5.3.9.1 Essential
components of cable TV system 5.3.9.2 HFC Cable systems 5.3.9.3 Interactive two-way TV services
5.3.9.4 High speed data using cable system Cable TV Primer Cable systems were originally designed to
deliver broadcast television signals efficiently to subscribers’ homes. To ensure that consumers could
obtain cable service with the same TV sets they use to receive overthe-air broadcast TV signals, cable
operators recreate a portion of the over-the-air radio frequency (RF) spectrum within a sealed
community antenna line and distributed to subscribers’ homes. Traditional community antenna systems
typically operate with 330 MHz or 450 MHz of capacity, whereas modern hybrid fibre/coax (HFC)
systems are expanded to 750 MHz or more. Logically, downstream video programming signals begin
around 50 MHz, the equivalent of channel 2 for over-the-air television signals. The 5 MHz-42 MHz
portion of the spectrum is usually reserved for upstream telecommunications from subscribers’ homes.
For example, countries using the National Transmission Standards Committee’s (NTSC, United States)
transmission standard, standard television channel occupies 6 MHz of RF spectrum. Thus a traditional
cable system with 400 MHz of downstream bandwidth can carry the equivalent of 60 analog TV channels
and a modern HFC system with 700 MHz of downstream bandwidth has the capacity for some 110
channels. Cable Modem Access Networks To deliver data services over a cable network, one television
channel (in the 50-750 MHz range) is typically allocated for downstream traffic to homes and another
channel (in the 5-42 MHz band) is used to carry upstream signals. A headend cable modem termination
system (CMTS) communicates through these channels with cable modems located in subscriber homes
to create a virtual local area network (LAN) connection. Most cable modems are external devices that
connect to a personal computer (PC) through a standard 10Base-T Ethernet external box or internal PCI
or PCMCIA card, or through a Universal Serial Bus (USB) connection. The cable modem access network
operates at Layer 1 (physical) and Layer 2 (media access control/logical link control) of the Open System
Interconnect (OSI) Reference Model. Thus, Layer 3 (network) protocols, such as IP traffic, can be
seamlessly delivered over the cable modem platform to end-users. A single downstream 6 MHz
television channel may support up to 27 Mbit/s of downstream data throughput from the cable
headend using 64 QAM (quadrature amplitude modulation) transmission technology. Speeds can be
boosted to 36 Mbit/s using 256 QAM. Upstream channels may deliver 500 kbit/s to 10 Mbit/s from
homes using 16 QAM or QPSK (quadrature phase shift key) modulation techniques, depending on the
amount of spectrum allocated for service. This upstream and downstream bandwidth is shared by the
active data subscribers connected to a given cable network segment, typically 500 to 2 000 homes on a
modern HFC network. 26 Report on Question 20-1/2 In addition to speed, cable modems offer another
key benefit: constant connectivity. Because cable modems use connectionless technology, much like in
an office LAN, a subscriber’s PC is always online with the network. Cable Internet Delivery To get into the
high-speed Internet business, cable operators must do more than simply install cable modem gear.
Rather, they must build a sophisticated end-to-end IP networking infrastructure in each community they
serve that is robust enough to support tens of thousands of data subscribers. That includes items like
Internet backbone connectivity, routers, servers, network management tools, as well as security and
billing systems. In essence, cable operators are faced with the task of building some of the world’s
largest “intranets”, a serious engineering and operations challenge. Cable operators are focused on
providing high-speed intranet access instead of straight Internet access for a simple reason: a network
connection is only as fast as its slowest link. Clearly, the benefit of a 1-Mbit/s cable link is lost if a
subscriber tries to access content stored on a Web server that is connected to the Internet through a 56-
kbit/s line. The solution to this dilemma is to push content closer to the subscriber, ideally right down to
the cable headend. This is done by recording or logging copies of popular Internet content on local
servers, so when a cable modem subscriber goes to access a Web page, he or she will be routed to the
server in the headend at top-speed, rather than being required to voyage out onto the congested
Internet. A number of companies are offering comprehensive networking and systems integration
services to cable operators entering the high-speed Internet needs. Shared Network Platform
Performance Most cable modem systems rely on a shared access platform, much like an office LAN.
Unlike circuitswitched telephone networks where a caller is allocated a dedicated connection, cable
modem users do not occupy a fixed amount of bandwidth during their online session. Instead, they
share the network with other active users and use the network’s resources only when they actually send
or receive data in quick bursts. So instead of 200 cable online users each being allocated 135 kbit/s, they
are able to grab all the bandwidth available during the millisecond they need to download their data
packets – up to many megabits per second. If congestion does begin to occur due to high usage, cable
operators have the flexibility to add more bandwidth for data services. A cable operator can allocate an
additional 6 MHz video channel for high-speed data, doubling the downstream bandwidth available to
users. Another option for adding bandwidth is to subdivide the physical cable network by running fibre-
optic lines deeper into neighbourhoods. This reduces the number of homes served by each network
segment, and thus, increases the amount of bandwidth available to end users. II.1.3 Fibre to the
Premises (FTTP) Matrix FTTP is becoming the Access Network architecture of choice given tremendous
reductions in both the costs of the equipment and the costs of outside plant (OSP) deployment. Several
of the largest US incumbent carriers have already announced plans to switch their Greenfield
deployments to FTTP. Similarly, the economics of copper network rehabilitation, where the copper plant
must be replaced due to degradation, Report on Question 20-1/2 27 make these “brownfield”
deployments increasingly attractive for FTTP deployments. Finally, given the significant expense
associated with extending the reach of copper-based networks to rural consumers given its distance-
limitations, FTTP is quickly becoming the Access Network architecture of choice for rural service
providers seeking to provide consumers with a “triple play” of voice, video, and data services. FTTP
Access Network equipment technologies can be primarily classified as active or passive solutions are
typically referred to as Passive Optical Networks or PONs. Active solutions have electronic components
deployed in the field and typically are capable of higher bandwidth while passive solutions have no
electronic components in the field and save both deployment and operations costs. These solutions can
further be classified as point-to-point (P2P) where there is a direct one-to-one link between the carrier’s
central office (CO) and/or head-end and the customer’s location or point-to-multipoint (P2MP) where
the signal from the carrier’s central office is split and sent to multiple customer’s locations. Typically,
P2P solutions are capable of higher bandwidth while P2MP solutions have lower deployment and
operations costs. Finally, within both active and passive and P2P and P2MP solutions, there is a range of
network protocol options available that further differentiates product offerings. For example, within the
PON solution space there are APON solutions (and its BPON variants) based on the traditional voice
telephony Asynchronous Transfer Mode (ATM) protocol; and EPON solutions based on the widely
deployed IP-based Ethernet protocol. BPON/APON is based on the ITU-T Recommendations G.983.3 and
its current version offers 622 Mbit/s downstream at 1 490 nm and 155 Mbit/s upstream at 1 310 nm
through a 1:32 split ratio (one signal split to 32 customers) with analog cable video offered at 1 550 nm
and is offered by vendors such as Optical Solutions, Alcatel, Hitachi, and others. The GPON standard
technology (offered by the same vendors) is based on the ITU-T G.984.2 standard and is also based on
the traditional ATM protocol but at higher speeds and offers either 2 422 or 1 244 Mbit/s downstream
at 1 490 nm and either 155, 622, 1 244 or 2 422 Mbit/s upstream at 1 310 nm with up to a 1:64 split
ratio and analog cable video at 1 550 nm. EPON solutions are based on the IEEE 802.3ah standard,
completed by IEEE P802.3ah Ethernet in the First Mile Task Force in 2004, and utilize IP for both voice
and data services and offer 1 000 Mbit/s downstream at 1 490 nm, 1 000 Mbit/s upstream at 1 310 nm
with a 1:32 split ratio and analog cable video at 1 550 nm (vendors include Alloptic, Calix, FlexLight, and
others). Figure 2 provides a graphic summary of the FTTP architectural options. Figure 2 – FTTP
Architectures: PON and P2P Passive Optical Network (PON) 1 or 2 fibers up to 32 subscribers up to 20
km Splitter(s) up to 1:32 OLT (in CO) ONT Point to Point (P2P) Switched Ethernet 1 - 10 fibers Ethernet
Switch(s) up to 1000 subscribers 300 m to 2 KM OLT ONT 1 or 2 fibers + No remote actives + 50% fewer
ports needed + Lower life cycle cost + Voice, Video, Data easy - Higher port cost - Lower data bandwidth
than P2P + Higher bandwidth + Possibly lower first cost + Greater security - Less reliable? - Higher
maintenance? - Voice and Video over IP unproven 10 KM 28 Report on Question 20-1/2 Beyond the
selection of Active and Passive and APON, BPON, GPON, EPON, there are significant technology
developments in outside plant solutions that can significantly affect the costs and benefits associated
with FTTP Access Network deployments. Proper fibre selection can greatly reduce network deployment
costs by allowing carriers to fit both the FTTP Access Network component along with their enterprise
and transport Edge Network component into a single fibre unit. Today’s advanced technology Zero
Water Peak Fibres (ZWPF) are displacing historic Standard Single Mode Fibre (SSMF) and enable the
deployment of 16-channel Coarse Wave Division Multiplexing (CWDM) Edge Networks on the very same
fibre carrying a 1:32 or 1:64 split FTTP network. CWDM channels are 60% less expensive than Dense
Wavelength Division Multiplexing (DWDM) channels, so such Access/Edge network deployments not
only allow carriers to deploy two networks on one infrastructure, but provide extremely cost effective
metro network architectures through the use of much less expensive CWDM channels. Figure 3 shows
such a CWDM over PON architecture and the benefits of providing network transport services or
premium business wavelength services over the same infrastructure carrying a PON Access Network.
Figure 3 – Zero Water Peak Fibre Enables Coarse Wave Division Multiplexing (CWDM ) over PON Two-
for-One Networks Enables Transport or Premium Business services using 1400 nm CWDM On Same Fiber
Carrying Your PON Access Network G.983 or EPON(Upstream) Data and Voice 1260 - 1360 nm G.983.3
or EPON (Downstream) Data and Voice 1480 – 1500 nm Video 1550 nm CWDM-PON 1 or 2 Fibers / End
User Premium Service CWDM Multiplexer 1360-1480 CWDM-PON OLT PS-PON 1 Fiber / End User
Standard Service E-Band Add/Drop E-Band Add/Drop Power Splitter for PS-PON <= 32 PS-PON
subscribers OLT •Low first cost using CWDM instead of DWDM • Commercially demonstrated with
Hitachi BPON, OFS ZWPF and Transmode CWDM •Low first cost using CWDM instead of DWDM •
Commercially demonstrated with Hitachi BPON, OFS ZWPF and Transmode CWDM CWDM-PON
businesses get dedicated channels, residences share PON Up to 20 KM CO/Head End 1250 1300 1350
1400 1450 1500 1550 1600 (ITU - Upgrade Band) Analog Video Isolation Bands Data/Voice Upstream
CWDM Businesses Data/Voice Downstream 1250 1300 1350 1400 1450 1500 1550 1600 (ITU - Upgrade
Band) Analog Video Isolation Bands Data/Voice Upstream CWDM Data/Voice Downstream 1250 1300
1350 1400 1450 1500 1550 1600 (ITU - Upgrade Band) Analog Video Isolation Bands Data/Voice
Upstream CWDM Businesses Data/Voice Downstream 1250 1300 1350 1400 1450 1500 1550 1600 (ITU -
Upgrade Band) Analog Video Isolation Bands Data/Voice Upstream CWDM Data/Voice Downstream
1370 1390 1410 1430 1450 1470 1370 1390 1410 1430 1450 1470 Wavelength (nm) Just as selecting the
right (ZWPF) fibre can provide the benefit of two networks for the price of one, the selection of low loss
fibre and components can allow carriers to reach up to twice the rated distance of commercial
equipment. This extended reach means carriers will able to serve up to twice as many customers for a
given investment in outside plant, will ensure that carriers will be able to connect all of their customers,
and will also allow carriers to realize up to a 30% system costs savings by more providing a more
efficient distribution/feeder fibre ratio. Report on Question 20-1/2 29 In some cases a number of copper
wire pairs are available between service provider and single subscriber. The pairs can be combined, i.e.
bundled, as described in the G series of ITU-T recommendations leading to a considerable increase of
single stream capacity. Two pairs offer a doubling, three pairs a threefold transmission capacity, up to 32
copper wire pairs can be bundled. The payload on the pairs can be ATM-based, Ethernet-based or
involve signals using time-division inverse multiplexing.