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Networking Glossary
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Bridge | Dark Fiber |
DWDM | FDDI |
HFC | ICMP |
IGMP | IP |
ISDN | MPLS | OC |
OSI Model | Packet Switching
| PON | Router |
SDH | SONET |
Switch | TCP/IP |
UTP | VCSEL Lasers |
VLAN | VPN |
WDM | 100BASE-T
- Bridge
- A device that connects two local-area networks (LANs), or
two segments of the same LAN. The two LANs being connected can
be alike or dissimilar. For example, a bridge can connect an
Ethernet with a Token-Ring network. Unlike routers, bridges
are protocol-independent. They simply forward packets without
analyzing and re-routing messages. Consequently, they're
faster than routers but also less versatile.
- Dark Fiber
- Dark fiber refers to unused fiber-optic cable. Often,
companies lay more fiber lines than what's needed at the
moment to curb costs. The dark strands can be leased to
individuals or other companies that want to establish optical
connections among their own locations. Under such a scenario,
the fiber is neither controlled by nor connected to the local
phone company. Instead, the company or individual provides the
necessary components to make it functional.
- DWDM
- Dense Wavelength Division Multiplexing is an optical
technology used to increase bandwidth over existing
fiber-optic backbones. DWDM works by combining and
transmitting multiple signals simultaneously at different
wavelengths on the same fiber. In effect, one fiber is
transformed into multiple virtual fibers. A key advantage of
DWDM is that it's protocol and bit-rate independent.
DWDM-based networks can transmit data in IP, ATM, SONET/SDH,
and Ethernet, and handle bit-rates between 100 Mb/s and 2.5
Gbps.
- FDDI
- Fiber Distributed Data Interface is a set of ANSI
protocols for sending digital data over fiber optic cable.
FDDI networks are token-passing networks, and support data
rates of up to 100 Mbps. FDDI networks are typically used as
backbones for wide-area networks. An extension to FDDI, called
FDDI-2, supports the transmission of voice and video
information as well as data. Another variation of FDDI, called
FDDI Full Duplex Technology (FFDT) uses the same network
infrastructure but can potentially support data rates up to
200 Mbps.
- HFC
- Hybrid Fiber Coax is a way of delivering video, voice
telephony, data, and other interactive services over coaxial
and fiber optic cables. An HFC network works consists of a
head-end office, distribution center, fiber nodes, and network
interface units. The head-end office receives information such
as television signals, Internet packets, and streaming media,
and then delivers them through a SONET ring to distribution
centers. The distribution centers then send the signals to
neighborhood fiber nodes, which convert the optical signals to
electrical signals and redistributes them on coaxial cables to
residents' homes where network interface units send the
appropriate signals to the appropriate devices (i.e.
television, computer, telephone).
- ICMP
- Internet Control Message Protocol is an extension to the
Internet Protocol (IP) defined by RFC 792. ICMP supports
packets containing error, control, and informational messages.
The PING command, for example, uses ICMP to test an Internet
connection.
- IGMP
- Internet Group Management Protocol is defined in RFC 1112
as the standard for IP multicasting in the Internet. It's used
to establish host memberships in particular multicast groups
on a single network. The mechanisms of the protocol allow a
host to inform its local router, using Host Membership
Reports, that it wants to receive messages addressed to a
specific multicast group. All hosts conforming to level 2 of
the IP multicasting specification require IGMP.
- IP
- Abbreviation of Internet Protocol, pronounced as two
separate letters. IP specifies the format of packets, also
called datagrams, and the addressing scheme. Most networks
combine IP with a higher-level protocol called Transport
Control Protocol (TCP), which establishes a virtual connection
between a destination and a source. IP by itself is something
like the postal system. It allows you to address a package and
drop it in the system, but there's no direct link between you
and the recipient. TCP/IP, on the other hand, establishes a
connection between two hosts so that they can send messages
back and forth for a period of time. The current version of IP
is IPv4. A new version, called IPv6 or IPng, is under
development.
- ISDN
- Abbreviation of Integrated Services Digital Network, an
international communications standard for sending voice,
video, and data over digital telephone lines or normal
telephone wires. ISDN supports data transfer rates of 64 Kbps
(64,000 bits per second). Most ISDN lines offered by telephone
companies provide two lines at once, called B channels. One
line can be used for voice and the other for data. Both lines
can be used for data to reach data rates of 128 Kbps, more
than twice the speed of today's fastest modems. The original
version of ISDN employs baseband transmission. Another
version, called B-ISDN, uses broadband transmission and is
able to support transmission rates of 1.5 Mbps. B-ISDN
requires fiber optic cables and is not widely available
- MPLS
- Multiprotocol Label Switching is an IETF initiative that
integrates Layer 2 information about network links (bandwidth,
latency, utilization) into Layer 3 (IP) within a particular
autonomous system — or ISP in order to simplify and improve
IP-packet exchange. MPLS gives network operators flexibility
to divert and route traffic around link failures, congestion,
and bottlenecks.
- OC
- Short for Optical Carrier, used to specify the speed of
fiber optic networks conforming to the SONET standard. The
table shows the speeds for common OC levels.
| OC-1 |
= |
51.85 Mbps |
| OC-3 |
= |
155.52 Mbps |
| OC-12 |
= |
622.08 Mbps |
| OC-24 |
= |
1.244 Gbps |
| OC-48 |
= |
2.488 Gbps |
|
- OSI Model
- Short for Open System Interconnection, an ISO standard for
worldwide communications that defines a networking framework
for implementing protocols in seven layers. Control is passed
from one layer to the next, starting at the application layer
in one station, proceeding to the bottom layer, over the
channel to the next station and back up the hierarchy.
| |
|
|
| Layer |
Name |
Function |
| 7 |
Application Layer |
Program-to-program communication. |
| 6 |
Presentation Layer |
Manages data representation
conversions. For example, the Presentation Layer
would be responsible for converting from EBCDIC to
ASCII. |
| 5 |
Session Layer |
Responsible for establishing and
maintaining communications channels. In practice,
this layer is often combined with the Transport
Layer. |
| 4 |
Transport Layer |
Responsible for end-to-end
integrity of data transmission. |
| 3 |
Network Layer |
Routes data from one node to
another. |
| 2 |
Data Link Layer |
Responsible for physical passing
data from one node to another. |
| 1 |
Physical Layer |
Manages putting data onto the
network media and taking the data off. |
|
- Packet Switching
- Refers to protocols in which messages are divided into
packets before they are sent. Each packet is then transmitted
individually and can even follow different routes to its
destination. Once all the packets forming a message arrive at
the destination, they are recompiled into the original
message. Most modern Wide Area Network (WAN) protocols,
including TCP/IP, X.25, and Frame Relay, are based on
packet-switching technologies. In contrast, normal telephone
service is based on a circuit-switching technology, in which a
dedicated line is allocated for transmission between two
parties. Circuit-switching is ideal when data must be
transmitted quickly and must arrive in the same order in which
it's sent. This is the case with most real-time data, such as
live audio and video. Packet switching is more efficient and
robust for data that can withstand some delays in
transmission, such as e-mail messages and Web pages. A new
technology, ATM, attempts to combine the best of both worlds —
the guaranteed delivery of circuit-switched networks and the
robustness and efficiency of packet-switching networks.
- PON
- Passive Optical Network is a high bandwidth point to
multipoint optical fiber network based on the asynchronous
transfer mode protocol (ATM). PONs generally consist of an OLT
(Optical Line Termination), which is connected to ONUs
(Optical Network Units), using only fiber cables, optical
splitters and other passive components (do not transmit
signals using electricity). Up to 32 ONUs can be connected to
an OLT. The OLT is located at a local exchange, and the ONU is
located either on the street, in a building, or even in a
user's home. PONs rely on lightwaves for data transfer. In a
PON, signals are routed over the local link with all signals
along that link going to all interim transfer points. Optical
splitters route signals through the network; optical receivers
at intermediate points and subscriber terminals tuned for
specific wavelengths of light direct signals intended for
their groups of subscribers. At the final destination, a
specific residence or business can detect its specified
signal. PONs are capable of delivering high volumes of
upstream and downstream bandwidth (up to 622 Mbps downstream
and 155 Mbps upstream), which can be changed on-the-fly
depending on an individual user's needs.
- Router
- A device that connects any number of LANs. Routers use
headers and a forwarding table to determine where packets go,
and they use ICMP to communicate with each other and configure
the best route between any two hosts.
- SDH
- Short for Synchronous Digital Hierarchy, an international
standard for synchronous data transmission over fiber optic
cables. The North American equivalent of SDH is SONET.
- Single Mode Fiber
Yellow and labeled
62.5/125 Core and Cladding
- Multi-Mode
Orange and Gray exterior
- ST Fiber connecter that is like a BNC bayonette
connection
- SC This is the fiber type connector that is push-pull
connectors
- SONET
- Short for Synchronous Optical Network, a standard for
connecting fiber-optic transmission systems. SONET was
proposed by Bellcore in the middle 1980s and is now an ANSI
standard. SONET defines interface standards at the physical
layer of the OSI seven-layer model. The standard defines a
hierarchy of interface rates that allow data streams at
different rates to be multiplexed. SONET establishes Optical
Carrier (OC) levels from 51.8 Mbps (about the same as a T-3
line) to 2.48 Gbps. Prior rate standards used by different
countries specified rates that were not compatible for
multiplexing. With the implementation of SONET, communication
carriers throughout the world can interconnect their existing
digital carrier and fiber optic systems. The international
equivalent of SONET, standardized by the ITU, is called SDH.
SDH defines a standard rate of transmission at 155.52 Mbps,
which is referred to as STS-3 at the electrical level and
STM-1 for SDH. STM-1 is equivalent to SONET's Optical Carrier
(OC) levels -3.
- Switch
- In networks, a device that filters and forwards packets
between LAN segments. Switches operate at the data link layer
(layer 2) of the OSI Reference Model and therefore support any
packet protocol. LANs that use switches to join segments are
called switched LANs or, in the case of Ethernet networks,
switched Ethernet LANs.
- TCP/IP
- Abbreviation for Transmission Control Protocol/Internet
Protocol, the suite of communications protocols used to
connect hosts on the Internet. TCP/IP uses several protocols,
the two main ones being TCP and IP. TCP/IP is built into the
UNIX operating system and is used by the Internet, making it
the de facto standard for transmitting data over networks.
Even network operating systems that have their own protocols,
such as Netware, also support TCP/IP.
- UTP
- Short for Unshielded Twisted Pair, a popular type of cable
that consists of two unshielded wires twisted around each
other. Due to its low cost, UTP cabling is used extensively
for local-area networks (LANs) and telephone connections. UTP
cabling does not offer as high bandwidth or as good protection
from interference as coaxial or fiber optic cables, but it is
less expensive and easier to work with.
- VCSEL Lasers
- Vertical-cavity surface emitting lasers. Of the two types
of diode lasers, the vertical-cavity surface emitting lasers (VCSELs)
have advantages over the traditionally used edge-emitting
lasers. The laser beam from a VCSEL is circularly symmetric
and hence can be very tightly focused, in contrast with the
highly asymmetric output beam of an edge-emitting laser. The
tighter focusing makes a VCSEL easier to couple to an optical
fiber. VCSELs can also be produced in two-dimensional arrays,
which cannot be achieved using the edge-emitting lasers.
Fabricating VSCELs in a two-dimensional array would allow for
the possibility of parallel or phased transmission.
- VLAN
- Short for virtual LAN, a network of computers that behave
as if they are connected to the same wire even though they may
actually be physically located on different segments of a LAN.
VLANs are configured through software rather than hardware,
which makes them extremely flexible. One of the biggest
advantages of VLANs is that when a computer is physically
moved to another location, it can stay on the same VLAN
without any hardware reconfiguration.
- VPN
- Short for Virtual Private Network, a network that is
constructed by using public wires to connect nodes. For
example, there are a number of systems that enable you to
create networks using the Internet as the medium for
transporting data. These systems use encryption and other
security mechanisms to ensure that only authorized users can
access the network and that the data cannot be intercepted.
- WDM
- Wavelength Division Multiplexing, a type of multiplexing
developed for use on optical fiber. WDM modulates each of
several data streams onto a different part of the light
spectrum. WDM is the optical equivalent of FDM. Also see DWDM.
- 100BASE-T
- A networking standard that supports data transfer rates up
to 100 Mbps (100 megabits per second). 100BASE-T is based on
the older Ethernet standard. Because it is 10 times faster
than Ethernet, it is often referred to as Fast Ethernet.
Officially, the 100BASE-T standard is IEEE 802.3u.
Like Ethernet, 100BASE-T is based on the CSMA/CD LAN access
method. There are several different cabling schemes that can
be used with 100BASE-T, including:
- 100BASE-TX: two pairs of high-quality twisted-pair wires
- 100BASE-T4: four pairs of normal-quality twisted-pair
wires
- 100BASE-FX: fiber optic cables. All Ethernet interfaces
are multi-mode fiber and use 1300nm
- 10BASE-FX is 850nm
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