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Fundamentals of WANs


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WANs
LANs typically include nearby devices, while __ connect devices that can be far apart, potentially hundreds or thousands of miles apart.
WAN
To connect the new building’s LAN to the rest of the existing corporate network, you need some kind of a __.
Leased line
WAN needs to be able to send data from the remote LAN back to the rest of the existing network and vice versa. __ WANs do exactly that, forwarding data between two routers.
crossover
From a basic point of view, a leased line WAN works a lot like an Ethernet __ cable connecting two routers, but with few distance limitations.
router
To connect LANs together using a WAN, the internetwork uses a __ connected to each LAN, with a WAN link between them.
WAN link
The enterprise’s network engineer would order some kind of __. A router at each site connects to both the __ and the LAN.
crooked line
Note that __ between the routers is the common way to represent a leased line when the drawing does not need to show any of the physical details of the line.
Ethernet
The wired LAN world basically has one major option today__, because it won the wired LAN battle in the marketplace back in the 1980s and 1990s.
two pair full-duplex
The leased line uses __ of wires, one pair for each direction of sending data, which allows __ operation.
telco
The __ network creates a service that acts like a crossover cable between two points, but the physical reality is hidden from the customer.
leased line
The term __ refers to the fact that the company using it does not own the line, but instead pays a monthly lease fee to use it.
service provider
Many people today use the generic term __ to refer to a company that provides any form of WAN connectivity, including Internet services.
Leased circuit
The words line and circuit are often used as synonyms in telco terminology; circuit makes reference to the electrical circuit between the two endpoints.
Serial link, Serial line
Refers to the fact that the bits flow serially, and that routers use serial interfaces.
Point-to-point link, Point-to-point line
Refers to the fact that the topology stretches between two points, and two points only.
T1
A specific type of leased line that transmits data at 1.544 megabits per second (1.544 Mbps).
Private line
Refers to the fact that the data sent over the line cannot be copied by other telco customers, so the data is **.
central offices
Telcos put their equipment in buildings called __. The telco installs cables from the ** to most every other building in the city.
Customer Premises Equipment
A telco term that refers to equipment on-site at the telco customer site (the enterprise’s site) that connects to the WAN service provided by the telco.
CSU/DSU
A device that connects a physical circuit installed by the telco to some CPE device, adapting between the voltages, current, framing, and connectors used on the circuit to the physical interface supported by the DTE.
RJ-48
The four-wire cable from the telco plugs into the CSU/DSU, typically using an __ connector that has the same size and shape as an RJ-45 connector.
64 kbps 1.5 Mbps
Telcos offer a wide variety of speeds for leased lines. You must pick from a long list of predefined speeds. Slower-speed links run at multiples of __, while faster links run at multiples of about __.
data terminal equipment
The serial cables normally used between a router and an external CSU/DSU are called __ cables.
DCE DTE
The __ cable has a female connector, while the __ cable has a male connector, which allows the two cables to be attached directly.
DCE
The __ cable also does the equivalent task of an Ethernet crossover cable by swapping the transmit and receive wire pairs.
DTE
The __ serial cable acts as a straight-through cable, and does not swap the transmit and receive pair.
clocking
The CSU/DSU normally provides a function called __, in which it tells the router exactly when to send each bit through signaling over the serial cable.
bits
A leased line provides a Layer 1 service. In other words, it promises to deliver __ between the devices connected to the leased line.
High-Level Data Link Control Point-to-Point Protocol
The two most popular data link layer protocols used for leased lines between two routers are __ and __.
Flag
Lists a recognizable bit pattern so that the receiving nodes realize that a new frame is arriving.
Address
Identifies the destination device.
Type
Identifies the type of Layer 3 packet encapsulated inside the frame.
FCS
A field used by the error detection process; it is the only trailer field in this table
Ethernet
To send the IP packet to router R1 next, PC1 encapsulates the IP packet in an __ frame that has the destination MAC address of R1.
HDLC
Router R1 deencapsulates (removes) the IP packet from the Ethernet frame, encapsulates the packet into an __ frame using an header and trailer, and forwards the frame to router R2 next.
Ethernet
Router R2 deencapsulates (removes) the IP packet from the HDLC frame, encapsulates the packet into an __ frame that has the destination MAC address of PC2, and forwards the frame to PC2.
WAN
In summary, a leased line with HDLC creates a __ link between two routers so that they can forward packets for the devices on the attached LANs.
point of presence
The (fiber) Ethernet link leaves the customer building and connects to some nearby SP location called a __.
emulation
Ethernet __ is a general term, meaning that the service acts like one Ethernet link.
EoMPLS
__ refers to Multiprotocol Label Switching (MPLS), which is one technology that can be used inside the SP’s cloud.
Ethernet
The EoMPLS link uses __ for both Layer 1 and Layer 2 functions. That means the link uses the same familiar *** header and trailer.
Internet
As a network of networks, the __ is actually owned by countless companies and people.
Internet core
The middle of the Internet, called the __, exists as LANs and WANs owned and operated by Internet service providers.
Internet access link
All of these lines connecting an enterprise or home to one of the ISPs represent some kind of WAN links.
DSL cable
Consumers often use technologies like __ and __ for Internet access links.
analog phone cable TV
DSL uses the __ lines that are already installed in homes, while cable Internet uses the __ cable.
Digital subscriber line
__ creates a relatively short (miles long, not tens of miles) high-speed link WAN between a telco customer and an ISP.
DSL
__ just provides a short physical link from a home to the telco’s network, allowing access to the Internet.
switch Public Switched Telephone Network
At the CO, each line connects to a port on a telco __. This switch supports the ability to set up voice calls, take them down, and forward the voice through the worldwide voice network, called the __.
DSL modem
The __ follows the DSL physical and data link layer standards to send data to/from the telco.
DSL Access Multiplexer
The home-based router on the left needs to be able to send data to/from the Internet. To make that happen, the telco CO uses a product called a __.
data voice signals
The DSLAM splits out the __ over to the router and also splits out the __ over to the voice switch.
asymmetric speeds downstream upstream
DSL supports __, meaning that the transmission speed from the ISP toward the home (__) is much faster than the transmissions toward the ISP (__).
coaxial cable
In Cable Internet the telephone line has been replaced with __ cable from the CATV company, and the DSL modem has been replaced by a __ modem.
faster lower
Cable Internet typically runs at __ speeds than DSL, with DSL providers keeping their prices a little __ to compete.
Level 4