Network Architectures
If a 3.2MHz upstream channel is using 16 QAM at a symbol rate of 2.560 millions of symbols per second (MS/s), what is the amount of data bandwidth available in Mbps?
10.24 16 QAM delivers 4 bits x = 2.56 x 4 x = 10.24
How many 6 MHz RF channels are in a 750 MHz system?
117
Per wavelength what is maximum number of home passed in a fiber deep system?
128
What is the symbol rate of 256 QAM?
5.36 MS/s @ 6mhz, 6.95 MS/s @ 8mhz
top-split frequencies
900 to 1050 mhz
multiplexing point
A multiplexing point (MP) is a location in the outside plant that de-multiplexes optical signals. Also known as a virtual hub or field splice enclosure.
what is frequency related to signal?
A signal's frequency describes the rate at which the signal alternates over a given period of time. The faster the rate of alternation, the higher the frequency.
analog intensity modulation (AIM)
Analog Intensity Modulation (AIM) is a laser modulation scheme that uses varying intensity of the light in direct proportion to the analog electrical signal that is applied to the optical transmitter.
drop cable
Drop Cable: Drop cables are used to connect the taps to individual subscriber's homes. They are generally made of smaller diameter coax than that used in the feeder such as series 6 or series 11.
ethernet passive optical network
Ethernet Passive Optical Network (EPON) is based on the Ethernet standard 802.3, EPON 802.3ah specifies a similar passive network with a range of up to 20 km. It uses WDM with the same optical frequencies as GPON and TDMA.
feeder
Feeder: The feeder section of the transmission plant distributes signals in a specific serving area such as a neighborhood or subdivision. The feeder is sometimes referred to as distribution. It typically consists of smaller diameter coax such as .500 inch or 13 mm. It also contains amplifiers that are generally referred to as line extenders (LE).
gigabit passive optical network
Gigabit passive optical network (GPON) uses optical wavelength division multiplexing (WDM) so a single fiber can be used for both downstream and upstream data.
headend
Headend: This is the origination point for all downstream signals in the network. These signals may come from satellite receivers (sometimes called TV Receive Only or TVRO) or microwave links. Some signals may originate at the headend. The headend also houses a launch amplifier that provides adequate RF signal level for transmission over the network.
hub star topology
In the hub star topology, a single optical transmitter sends the same signals to all receivers. In the hub distributed technology, secondary hubs are used to modify signals, if necessary, before transmission to the final receivers. In the optical bus technology, a single optical transmitter sends an optical signal through an optical bus. Optical couplers located periodically along the bus tap off small amounts of this optical signal for individual optical receivers.
line power supply and power inserter
Line Power supply and Power Inserter: Both the trunk and feeder contain line power supplies and power inserters. These devices provide power for the active devices in the network. Power is carried over the coaxial cable along with the RF signals.
On top of DOCSIS, what other technologies can remote PHY handle?
OOB
what are the upstream and downstream bands utilized for RFoG communications?
Per the SCTE/ISBE standard, RFoG uses the 1610 nm band for upstream communication. Per the SCTE/ISBE standard, RFoG uses the 1550 nm band for downstream communication. An alternate upstream wavelength in the 1310 nm band is included in the standard and may be used as a less expensive option as long as EPON or GPON wavelengths will not be using an optical overlay on the same fiber as the RFoG signals.
This device converts the downstream optical signal to an electrical RF signal and converts the upstream RF signal into an optical signal?
R-ONU
subscriber electronics
Subscriber Electronics: The final portion of the network consist of the subscriber electronics. These are located inside the subscriber's home and may include set-top converters and cable modems.
tap
Tap: The tap is used to extract an appropriate amount of RF signal from the network and supply it to the individual subscriber. Taps are typically configured with 2, 4 or 8 subscriber ports.
core and access network
The core network uses digital fiber to connect a headend to multiple hubs. Hubs use analog intensity modulated optical fiber to connect to multiple optical nodes. The node converts downstream optical signals to RF signals for transmission over the coaxial portion of the network. The node also converts upstream RF signals from the coaxial plant into optical signals for transmission to the hub.
point to multipoint/broadcast topology
The point to multipoint or broadcast optical network consists of a single optical transmitter and many optical receivers. The losses in such a network consist of not only the loss of the optical fiber but also the loss of the optical splitters and optical couplers. This loss limits the reach of such networks to a relatively short distance.
conventional coax network
This type of network distributes radio frequency (RF) signals to individual network subscribers. The network is made up of several distinct parts.
transmission plant
Transmission Plant: The section of the network that carries signals from the headend to the subscriber is called the transmission plant or access network in modern terms. This portion of the plant can be further divided into trunk and feeder.
trunk
Trunk: The trunk carries signals from the headend to a general serving area. It typically contains larger coax diameter such as .750 inch or 19 mm. It also contains amplifiers known as mainstations, trunk stations or trunk amplifiers. These amplifiers are used to compensate for the loss of the coaxial cable in the network.
wavelength
Wavelength is related to frequency. It is a measure of the distance that a signal travels during one cycle.
Dense Wavelength Division Multiplexing (DWDM)
a form of wavelength division multiplexing where the wavelengths are spaced close to each other
outside plant (OSP_
another nae for an HFC or ODN network
fiber deep
another term that is used and may include technologies such as FTTx, xPON, RFoG, as well as others. reduces the number of amps in the field, length of coax legs, power requirements and access network maintenace. additional fiber links divide subs into small groups, with each group served by a separate node. each node may serve 85 subs or fewer. runs at a mid-split design.
EPON and GPON networks use ________________ of the optical signal rather than the analog intensity modulation that is used by RFoG networks.
baseband digital modulation
optical fiber network
comprised of the supertrunk, regional access and HFC distribution sections
centralized split architecture
dedicated fibers leave this splitter and feed individual customer homes. the optical tap near the sub is simply a location for optical connectors to attach individual optical drops. the tap does not contain any directional couplers or splitters, as is the case in a coax directional tap. this approach is preferred as it provides a central location for maintenance and troubleshooting
Which type of optical distribution network (ODN) uses a single fiber to feed all the subscriber homes?
distributed tap architecture
True or False: As the frequency increases the wavelength increases.
false; frequency and wavelength are inversely proportional
An HFC network is typically designed with:
fewer active devices compared to tree and branch architectures
In an architecture where fiber replaces the coax and amplifiers, producing a node + 0 architecture, coax is retained in the 'last mile (meter).' What is the name of the architecture?
fiber deep
radio frequency over glass (RFoG)
fttx design that allows rf signals to ravel over fiber optics.
Which return/forward split offers the most amount of upstream bandwidth?
high split
what is a disadvantage of using hubs within an architecture?
increased power requirements
distributed tap architecture
like the tapped feeder in conventional HFC networks. single fiber is used to feed the network. multiple optical taps are along this single line. unlike the two preferred methods, these taps contain optical directional couplers and/or splitters. each tap has a main optical input, output and connectors to attach drops for individual customers.
distributed split architecture
multiple splitters are distributed at various locations in the OSP. ie for a 32-home serving station, there could be one 8 way splitter feeding 8 4 way splitters.
What network topology has every point in a network is directly connected to every other point in the network using a separate optical fiber?
multipoint to multipoint
The reliability of an HFC architecture increases ___. (Choose 2)
number of customers decreases number of active devices decreases
supertrunk hub communication style
often a headend is intended to serve an area larger than what contentional access can. the headend would be connected to multiple access networks by means of an optical fiber transport ring, called the supertrunk ring.
what two challenges in deployment does an RFoG system face?
optical loss and optical transmission in the upstream loss mainly due to splitters the issue with upstream is that many optical xmitters are deployed in different sub homes/businesses
An architecture in which a common signal source is distributed to many municipalities is referred to as:
point to multipoint
hybrid fiber coax
replacing portions of the trnuk cascade with optical fiber link - this can replace up to 30 trunk amps and coax cable spans. trunk cascade is replaced with a dual optical link, for up and down communication, in a 2 way system
Repeaters (amplifiers) are used in an optical system for:
signal loss compensation
frequency division multiplexing (FDM)
technique used to divide an RF spectrum into non-overlapping channels, each to be used to transmit a separate RF signal
What part of the network has an optical reciever and a RF transmitter?
the node
True or False: The number of amplifiers after the node is limited by the amount of distortion and noise they produce.
true
True or False? RFoG may be deployed with no changes to all of the existing RF devices in the hub or headend.
true
The channel data rate = symbol rate x the number of bits per symbol.
true x = MS/s x QAM bits per symbol
The_________carries signals from the headend to the general serving area?
trunk
high split frequencies
up - 5 to 200 mhz down - 258 mhz to 1.2 ghz
Sub-Split frequencies
up - 5 to 42 mhz down - 54 to 1000 mhz
mid-split frequencies
up - 5 to 85 mhz down - 108 mhz to 1.2 ghz
node
used to interface between fiber and coax. contains downstream optical receivers, RF amps, and upstream optical xmitters as required. "node" can mean the piece of hardware that interfaces between fiber and coax or the actual coax portion of the plant that is served by a single optical link.
passive optical network (PON)
uses fiber optics ad no active devices to service cable subs. main components are optical fibersm splitters and taps
what are the capacity differences for 6 mhz of space on the spectrum for digital vs for analog?
with 6 mhz of space, analog produces 1 SD channel digital has 42.88 mbps of data capacity, or 9 SDTV/2HDTV channels
