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WANs operate at what layer of the OSI model?
The physical and data link layers of the OSI model. WANs interconnect LANs that are seperated by geographical distance. The datalink layer defines the WAN layer 2 encapsulation (Frame Relay, ATM, PPP)
What is the largest WAN in the world?
The internet.
What is the size of an ATM cell?
An ATM cell is 53 bytes. This includes a 5-byte header and 48 bytes of payload.
What are the four available WAN connection types?
Dedicated (leased line)
Circuit-Switched
Packet-Switched
Cell-Switched
Define customer premise equipment (CPE), and give an example.
CPE is equipment that is located on the customer's or subscribers premises.
What is a demarcation (demarc) point?
Demarc is the point where the CPE ends and the local loop begins. It is the last responsibility of the service providor and is usually a NID (Network Interface Device). 
What is the local loop?
The physical cable that extends from the demarc to th providors central office switch.
Define the central office (CO)
This is where the local loop terminates and where circuit switching occurs.
What is WAN signalling?
The process of sending a transmission signal over a physical medium. in north america the signaling standard is called DS1 an has a transmission rate of 1.544 Mbps.
What are WAN data link layer protocols?
They are designed to work over dedicated lines, multipoint services, and multiaccess-switched services such as Frame Relay.

HDLC, PPP, and Frame Relay
What is the differance between baseband and broadband?
Baseband is a network technology in which only one carrier frequency is used (such as ethernet). Broadband is a network technology in which several independant channels are multiplexed into one cable (Such as a T1 or Cable TV).
What is serial transmission?
A method of data transmission in which bits of data are transmitted sequentially over a single channel. WANs use serial connections.
In WAN communications, what is clocking?
Clocking is the method used to synchronize data transmission among devices on a WAN. The CSU/DSU (DCE device) controls the clocking of transmitted data.
How many channels (time slots) are in a full point-to-point or Frame Relay T1 line?
A T1 line has 24 channels or time slots. Each channel is 64 kbps.
WANs use a technology called multiplexing. What is multiplexing?
Multiplexing is a technology that enables multiple logical signals to be transmitted simultaneously accross a single physical channel and then be combined into a single data channel at the source.
On what layer of th OSI model does multiplexing occur?
Multiplexing occurs on the physical layer. Because multiplexing combines signals accross a singal physical channel, it occurs at the physical layer of th OSI model.
What typ of data can an ATM network transfer?
An ATM network can transfer voice, video and data. ATM uses a cell-switched network, and the cells that transfer voice, video, and data are always a fixed size of 53 bytes.
How many DS0s are bundled to create a T1 line?
Twenty-four DS0s are bundled to create a T1 line. One DS0 is 64 kbps. (perfect example of multiplexing 24 DS0s are combined to make one WA line with a transfer rate of 1.544 Mbps)
Describe packet-switched WAN connections.
Packet-switched connections use virtual circuits (VC) to provide end-to-end connectivity. Packet-switched connections are simular to leased lines, except that the line is shared by other customers. A packet knows how to reach its destination by the programming of switches. Frame Relay and X.25 are examples of packet switched networks. 
Your company has its headquarters in San Jose and regional offices in different cities throughout the region. As the network administrator, you want to connect the reigional offices to headquarters. You want each regional office to connect to HQ in a hub-and-spoke topology using a packet-switching technology. What WAN technology should you use to accomplish your goal?
You should use Frame Relay. FR is a packet-switched technology that functions in a hub-and-spoke topology. (AKA star topology)
What are circuit -switched WAN connections?
Circuit-switched WAN connections are connections dedicated for only the duration of the call of the time required to transmit data. The telephone system is an example of a circuit-switched network.
What type of WAN link is a leased line?
A leased line is a point-to-point link that provides a single. preestablished WAN communication path from the customer to the remote network.
Describe DSL.
Digital subscriber line (DSL) is a modem technology that uses existing twisted-pair telephone lines to transfer high-speed data.  ADSL provides higher downstream speed than upstream. SDSL provides the same speed for both upstream and downstream traffic.
On what layer of the OSI model does DSL operate.
DSl operates at the physical layer (layer 1) of the OSI model. DSL relies on upper-layer protocols to encapsulate the data at the CO. It uses ATM, Ethernet, or PPP at the data link layer and IP and the network layer.
Define the following Cisco NAT terminology:

Inside local address
Inside global address
Outside local address
Outside global address
Inside local address: The IP address assigned to a host on the inside, private network. This is usually a private (RFC 1918) IP address.

Inside global address: A registered, Internet-routable IP address that represents one or more inside local IP addresses to the outside world.

Outside local address: The IP address of an outside host as it appears to the inside, private network.

Outside global address: The IP address assigned to a host on the outside network by the host's owner. This is usually a routable IP address.
What is overload NAT?
Overload NAT is another term for Port Address Translation. It has a many-to-one mapping.
What are three benefits of NAT?
Eliminates readdressing overload of hosts that require external access

Conserves IP addresses through application port-level multiplexing.

Hides the internal network, providing a small level of network security.
How many internal hosts can be translated to one routable IP address through PAT?
Theoretically, 65,536 internal hosts can be translated by PAT using one routable IP address.
What Cisco command clears all the NAT mappings in the NAT table?
The clear ip nat translation command clears all the NAT translations in the NAT table.
How do you view the active NAT translations in the NAT table?
To view the active NAT translations in the NAT table, use the show ip nat translations command.
Describe HDLC.
HDLC is the default encapsulation type on a point-to-point dedicated link and circuit -switched connections between Cisco routers. HDLC is a connection-oriented protocol that has little overhead.
What is the default encapsulation on a cisco serial interface?
HDLC is the default encapsulation on a Cisco serial interface.
By default, Cisco uses HDLC as its default encapsulation method accross synchronous lines (point-to-point links). If a serial line uses a different encapsulation method, how do you change it back to HDLC?
To change a serial link back to HDLC, use the following interface command on the serial interface you want to change.

encapsulation hdlc
What is the Point-to-Point ptotocol (PPP)?
PPP is an industry-standard protocol that provides router-to-router or router-to-host connections over synchronous and asynchronous links.
What IOS command enables PPP on a Cisco router serial interface?
To enable PPP encapsulation on a serial interface, enter the encapsulation PPP interface command.
What communication protocol allows you to connect your computer to the Internet using a standard telephone line, and can transmit multiple protocols?
PPP.  PPP offers the following features:

Control of data link setup.

Provides dynamic IP address assignment.

Link configuration and link quality testing.

Error detection.

Network-layer address negotiation and data compression.

Supports several network-layer protocols.
What features does LCP offer to PPP encapsulation?
LCP offers authentication, callback, compression, error detection, and multilink to PPP encapsulation.
What types of physical interfaces can you configure PPP on?
You can configure PPP on the following interface types.

Asynchronous serial

Synchronous serial

High-Speed Serial Interface (HSSI)
Name the WAN encapsulation that can be configured on an asynchronous serial connection.
PPP can be configured on an asynchronous serial connection.
What two protocols are available for compression on PPP links?
Stacker and Predictor. Predictor uses more memory and stacker is more  CPU intensive.
What two methods of authentication can be used with PPP links?
(PAP) Password Authentication Protocol. Passwords sent in clear text.

(CHAP) Challenge Handshake Authentication Protocol. CHAP uses MD5 for password encryption.
Does CHAP uses two-way or three-way handshake for authentication?
Chap uses a three-way handshake for authentication.
If PPP is enabled on an interface, how do you view th LCP and NCP states of the interface?
Issue the show interface serial number command:

sh interface s0
What is Frame Relay?
FR is a switched data link layer protocol that uses virtual circuits to identify the traffic that belongs to certain routers. It provides dynamic allocation and congestion control.
Is Frame Relay a circuit-switched or a packet-switched network?
FR is a packet-switched network that creates virtual circuits (VC) between DTE devices on a network to enable bidirectional communication. The virtua circuits can be either Permanent or Dynamically switched virtual circuits.
In Frame Relay, what identifies a virtual circuit?
The data-link connection identifier (DLCI) locally identifies a VC.
Is a DLCI locally or globally significant?
It is locally significant.
Which encapsulation type is appropriate to use in a Frame Relay network that has routers from two different vendors?
You should use IETF.

Frame Relay encapsulation defines the Layer 2 frame format used by both ends of a Frame Relay link, Cisco routers support two types of Frame Relay encapsulation: Cisco and IETF.


List four devices used to connect to or used on a WAN?
Routers: Used to connect the LAN to the WAN. They provide network layer services: they route data from one network to another.

WAN switches / Networking devices: Multiport devices that switch Frame Relay, X.25, or ATM traffic.

Modems or DSUs/CSUs: CSU/DSU convert one form of digital format to another form of digital format.

Communication Servers: Concentrate dial-in and dial-out user comm.
What are the four types of multiplexing?
Time-Division (TDM): Each datd channel is allocated bandwidth based on time slots, regardless of whether data is transferred; thus bandwidth is wasted when there is no data to transfer.

Frequency-Division (FDM): Information of each data channel is allocated bandwidth based on the signal frequency of the traffic. FM radio is a good example. 

Wave-Division (WDM): Each data channel is allocated bandwidth based on wavelength (Inverse of frequency).

Statistical-Division (SDM): Bandwidth is dynamically allocated to data channels.
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