Question And Solution Paper CCNA4 Chapter 2
Point-To-Point Connections 2024/2025
serial and parallel ports Answer: A common type of WAN connections is the point-to-point
connection. As shown in Figure 1, point-to-point connections are used to connect LANs to service
provider WANs, and to connect LAN segments within an enterprise network.
A LAN-to-WAN point-to-point connection is also referred to as a serial connection or leased-line
connection. This is because the lines are leased from a carrier (usually a telephone company) and are
dedicated for use by the company leasing the lines. Companies pay for a continuous connection
between two remote sites, and the line is continuously active and available. Leased lines are a
frequently used type of WAN access, and they are generally priced based on the bandwidth required
and the distance between the two connected points.
Understanding how point-to-point serial communication across a leased line works is important to an
overall understanding of how WANs function.
Communications across a serial connection is a method of data transmissions in which the bits are
transmitted sequentially over a single channel. This is equivalent to a pipe only wide enough to fit one
ball at a time. Multiple balls can go into the pipe, but only one at a time, and they only have one exit
point, the other end of the pipe. A serial port is bidirectional, and often referred to as a bidirectional
port or a communications port.
At one time, most PCs included both serial and parallel ports. Parallel ports were used to connect
printers, computers, and other devices that required relatively high bandwidth. Parallel ports were also
used between internal components. For external communications, a serial bus was primarily used to
connect to phone lines and devices that could potentially be further distance than a parallel transfer
would allow. Because serial communications are less complex and require simpler circuitr
Point-to-Point Communication Links Answer: When permanent dedicated connections are required,
a point-to-point link is used to provide a single, pre-established WAN communications path. This path
,goes from the customer premises, through the provider network, to a remote destination, as shown in
the figure.
A point-to-point link can connect two geographically distant sites, such as a corporate office in New York
and a regional office in London. For a point-to-point line, the carrier dedicates specific resources for a
line that is leased by the customer (leased line).
Note: Point-to-point connections are not limited to connections that cross land. There are hundreds of
thousands of miles of undersea fiber-optic cables that connect countries and continents worldwide. An
Internet search of "undersea Internet cable map" produces several cable maps of these undersea
connections.
Point-to-point links are usually more expensive than shared services. The cost of leased-line solutions
can become significant when used to connect many sites over increasing distances. However, there are
times when the benefits outweigh the cost of the leased line. The dedicated capacity removes latency or
jitter between the endpoints. Constant availability is essential for some applications such as VoIP or
video over IP.
Serial Bandwidth Answer: Bandwidth refers to the rate at which data is transferred over the
communication link. The underlying carrier technology will dictate how much bandwidth is available.
There is a difference in bandwidth points between the North American (T-carrier) specification and the
European (E-carrier) system. Optical networks also use a different bandwidth hierarchy, which again
differs between North America and Europe. In the U.S., Optical Carrier (OC) defines the bandwidth
points.
In North America, the bandwidth is usually expressed as a digital signal level number (DS0, DS1, etc.),
which refers to the rate and format of the signal. The most fundamental line speed is 64 kb/s, or DS0,
which is the bandwidth required for an uncompressed, digitized phone call. Serial connection
bandwidths can be incrementally increased to accommodate the need for faster transmission. For
example, 24 DS0s can be bundled to get a DS1 line (also called a T1 line) with a speed of 1.544 Mb/s.
Also, 28 DS1s can be bundled to get a DS3 line (also called a T3 line) with a speed of 44.736 Mb/s.
Leased lines are available in different capacities and are generally priced based on the bandwidth
required and the distance between the two connected points.
, OC transmission rates are a set of standardized specifications for the transmission of digital signals
carried on SONET fiber-optic networks. The designation uses OC, followed by an integer value
representing the base transmission rate of 51.84 Mb/s. For example, OC-1 has a transmission capacity of
51.84 Mb/s, whereas an OC-3 transmission medium would be three times 51.84 Mb/s, or 155.52 Mb/s.
WAN Encapsulation Protocols Answer: The following are short descriptions of each type of WAN
protocol:
HDLC - The default encapsulation type on point-to-point connections, dedicated links, and circuit-
switched connections when the link uses two Cisco devices. HDLC is now the basis for synchronous PPP
used by many servers to connect to a WAN, most commonly the Internet.
PPP - Provides router-to-router and host-to-network connections over synchronous and asynchronous
circuits. PPP works with several network layer protocols, such as IPv4 and IPv6. PPP is based on the
HDLC encapsulation protocol, but also has built-in security mechanisms such as PAP and CHAP.
Serial Line Internet Protocol (SLIP) - A standard protocol for point-to-point serial connections using
TCP/IP. SLIP has been largely displaced by PPP.
X.25/Link Access Procedure, Balanced (LAPB) - An ITU-T standard that defines how connections between
a DTE and DCE are maintained for remote terminal access and computer communications in public data
networks. X.25 specifies LAPB, a data link layer protocol. X.25 is a predecessor to Frame Relay.
Frame Relay - An industry standard, switched, data link layer protocol that handles multiple virtual
circuits. Frame Relay is a next generation protocol after X.25. Frame Relay eliminates some of the time-
consuming processes (such as error correction and flow control) employed in X.25.
ATM - The international standard for cell relay in which devices send multiple service types, such as
voice, video, or data, in fixed-length (53-byte) cells. Fixed-length cells allow processing to occur in
hardware; thereby, reducing transit delays. ATM takes advantage of high-speed transmission media
such as E3, SONET, and T3.
HDLC encapsulation Answer: HDLC is a bit-oriented synchronous data link layer protocol developed
by the International Organization for Standardization (ISO). The current standard for HDLC is ISO 13239.
HDLC was developed from the Synchronous Data Link Control (SDLC) standard proposed in the 1970s.
HDLC provides both connection-oriented and connectionless service.
