Ch 7 WAN

Created by mike_carter 

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Customer premises equipment (CPE)

Customer premises equipment (CPE) is equipment that's owned by the service provider but located on the subscriber's (your) property

CSU/DSU

Channel service unit/data service unit (CSU/DSU) is a Layer 1 device that connects your serial ports on your router to the provider's network and connects directly to the demarcation point (demark) or location.

These devices can be external or internal cards on the router. The CSU/DSU provides clocking of the line to the CPE (your router, in this case) and provides other important options, like voltage regulation.

extended demark

cableing from the telco box to the CPE, which is usually a connection to a CSU/DSU or ISDN interface.

Local loop

A cable consisting of a pair of copper wires called the local loop connects the demarc to the closest switching office known as a central office (CO).

Central office

A phone company building that connects the customer's network to the provider's switching network. Good to know is that a CO is sometimes referred to as a point of presence (POP).

Toll network

The toll network is a trunk line inside a WAN provider's network. This network is a collection of switches and facilities owned by the ISP

Leased lines

These are usually referred to as a point‐to‐point or dedicated connection. A dedicated leased line is a pre‐established WAN communications path that goes from the CPE through the DCE switch and then over to the CPE of the remote site. The CPE enables DTE networks to communicate at any time with no cumbersome setup procedures to muddle through before transmitting data. When you've got plenty of cash, this is the way to go because it uses synchronous serial lines up to 45Mbps. High‐Level Data Link Control (HDLC) and Point to Point Protocol (PPP) encapsulations are frequently used on leased lines.

-circuit switched-army

Circuit switching

When you hear the term circuit switching, think phone call. The big advantage is cost—you only pay for the time you actually use. No data can transfer before an end‐to‐end connection is established. Circuit switching uses dial‐up modems or ISDN and is used for low‐bandwidth data transfers. Circuit switching can be used in some of the newer WAN technologies as well.
X.25, PSTN

Packet switching

This is a WAN switching method that allows you to share bandwidth with other companies to save money. Packet switching can be thought of as a network that's designed to look like a leased line yet charges you more like circuit switching does. Packet switching will only work for you if your data transfers are not continuous.
-Frame Relay, DSL, cable and the super‐old X.25 are packet‐switching technologies with speeds that can range from 56Kbps up to T3 (45Mbps).

T-carrier

-method of signaling.
-physical layer.
-TDM over two wire pairs. (time division multiplexing)
The term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s.

T‐Series Connections speeds(# of T1)

T1

T1C (2)

T2(4)

T3(28)

T4(168)

T5(240)

T1
1.544Mbps------24 channels------DS1

T1C
3.152Mbps---48 channels-----DS1C

T2
6.312Mbps---96 channels----DS2

T3
44.736Mbps ---672 channels-----DS3

T4
274.176Mbps---4032 channels---DS4

T5
400.352Mbs-----5760 channels--DS5

The T1 Connection

A 1.544Mbps connection uses DS1 and aggregates 24 discrete, 64Kbps channels that use DS0. Each channel can carry either voice or data.

The T3 Connection

A 44.736Mbps connection uses DS3 that is generally delivered over fiber‐optic cable. Many local ISPs have T3 connections to their next‐tier ISPs. Also, very large multinational companies use T3 connections to send voice and data between their major regional offices.

Synchronous Optical Network (SONET)

SONET defines a base data rate, or throughput, of 51.84Mbps, and multiples of this rate are known as optical carrier (OC) levels like OC‐3, OC‐12, and so on., an optical transmission interface originally proposed by BellCore. Intended to provide the specification for taking advantage of high speed digital transmission capability of optical fiber. The basic SONET building block is the STS-1 frame which is 810 octets transmitted once every 125 us for overall data rate of 51.84Mbps. Ch 17 PG 504

Optical Carrier Levels

OC‐1

OC‐3

OC‐12

OC‐48

OC‐192

OC‐1
51.84Mbps

OC‐3
155.52Mbps

OC‐12
622.08Mbps

OC‐48
2.488Gbps

OC‐192
9.953Gbps

frequency hopping spread spectrum

Bluetooth uses this radio technology, which chops up the data being sent and transmits chunks of it through the air on up to 75 different frequencies.

Microwave radio relay

a technology for transmitting digital and sometimes even analog signals between two locations on a line‐of‐sight radio path through the atmosphere.

A communications satellite (comsat)

A comsat is an artificial satellite stationed in space for telecommunications purposes.

Modern communications satellites use a variety of orbits. List them:

Geostationary orbits

Molniya orbits, named after a series of communications satellites from Russia (Molniya means lightning in Russian)

Low‐polar and non‐polar Earth orbits from which the satellite can first boost communications signals and then send them back to earth

DSLAM

A DSLAM is the device located at the providers' CO (central office) that concentrates connections from multiple DSL subscribers.

High bit‐rate digital subscriber line (HDSL)

HDSL was the first DSL technology to use a higher‐frequency spectrum of copper twisted‐pair cables. It was typically used to interconnect local‐exchange carrier systems and to carry high‐speed corporate data links and voice channels using T1 lines.

Symmetric digital subscriber line (SDSL)

SDSL provides T1/E1 type speeds symmetrically for both uploading and downloading data but doesn't allow low‐frequency phone calls on the same line like asymmetric digital subscriber line (ADSL) does.

Asymmetric digital subscriber line (ADSL)

DSL focuses on providing reasonably fast upstream transmission speeds (768Kbps) and very fast downstream transmission speeds (up to 9Mbps, although usually slower). The best part is that ADSL works on a single phone line without losing voice call capability.

Very high data‐rate digital subscriber line (VDSL)

(VHDSL) provides faster data transmission over single, flat, untwisted or twisted pairs of copper wires.
Second‐generation VDSL2 systems utilize bandwidths of up to 30MHz to provide data rates exceeding 100Mbps simultaneously in both the upstream and downstream directions. The maximum available bit rate is achieved at a range of about 300 meters

Headend

This is where all cable signals are received, processed, and formatted. The signals are then transmitted over the distribution network from the headend.

Distribution network

These are small service areas that usually range in size from 100 to 2,000 customers. They're typically composed of a mixed, fiber‐coaxial, or hybrid fiber coaxial (HFC) architecture, with optical fiber substituting for the distribution network's trunk portion. The fiber forms both the connection from the headend and an optical node that changes light to radio frequency (RF) signals that are then distributed through a coaxial cable throughout the specific service area ‐ i.e. your home or office.

Data over cable service interface specification (DOCSIS)

This specification provides the interface requirements for a data over cable system, including that of high‐speed data transfer to an existing Cable TV (CATV) system.

Integrated Services Digital Network (ISDN)

ISDN is a digital, point‐to‐point WAN technology capable of maximum transmission speeds of about 2Mbps (Primary Rate Interface [PRI]), although speeds of 128Kbps (Basic Rate Interface [BRI]) are more common in a SOHO environment.

advantages of ISDN

It has a fast connection.

It offers higher bandwidth than POTS. BONDING yields 128Kbps bandwidth.

There is no conversion from digital to analog.

ISDN disadvantages

It's more expensive than POTS.

Specialized equipment is required at the phone company and at the remote computer. Needs PSTN!

Not all ISDN equipment can connect to every other type of equipment.

Why use ISDN if you can get DSL or cable?

Frame Relay Technology

Frame Relay is a WAN technology in which variable‐length packets are transmitted by switching

Packet switching

Packet switching involves breaking messages into chunks at the sending device. Each packet can be sent over any number of routes on its way to its destination. The packets are then reassembled in the correct order at the receiver. Because they are packet‐switched and the exact path is unknown, a cloud is used when creating a diagram to illustrate how data travels throughout this service.

There are two separate bandwidth specifications with Frame Relay:

Access rate The maximum speed at which the Frame Relay interface can transmit.

CIR The maximum bandwidth of data guaranteed to be delivered. In reality, it's the average amount that the service provider will allow you to transmit, based on what you purchased.

Permanent virtual circuits (PVCs)

Permanent virtual circuits (PVCs) are by far the most common type in use today. What permanent means here is that the telco creates the mappings inside their gear and as long as you pay the bill, they'll remain in place.

Switched virtual circuits (SVCs)

Switched virtual circuits (SVCs) are more like phone calls. The virtual circuit is established when data needs to be transmitted, and it's taken down when the data transfer is complete.

Multi Protocol Label Switching (MPLS)

MPLS is referred to as residing on Layer 2.5. and is a mechanism in high-performance telecommunications networks which directs and carries data from one network node to the next with the help of labels. MPLS makes it easy to create "virtual links" between distant nodes. It can encapsulate packets of various network protocols.

BRI (Basic Rate Interface)

A variety of ISDN that uses two 64-Kbps bearer channels and one 16-Kbps data channel, as summarized by the notation 2B+D. BRI is the most common form of ISDN employed by home users.

Primary Rate Interface (PRI)

A type of ISDN that is a full T-1 line, carrying 23 B channels (totaling approximately 1.5 Mbps).

ATM

asynchronous transfer model. data link layer. ITU prescribes both network access and signal multiplexing.
-he common speeds of ATM networks today are 51.84Mbps and 155.52Mbps.

DSL

-digital subscriber line
-WAN connection method. limited distances w/out repeaters. supports multiple data and voice channels over a single line. physical layer.

Integrated Services Digital Network

ISDN, international standard. connects WANs locations to exchange both data and voice signals. layers 1-2, 4.

SONET

synchronous optical network. high bandwidth WAN signaling technique. physical layer. integrates many other WAN technologies. fast data transfer rates. high fault tolerance.
-uses the ATM protocol

virtual private networks

VPN. WANs that are logically defined over public transmission systems. allows access to only authorized users.

WAN

-wide are network
-wider geographical area. usually use point to point communication. uses protocols of layer 3 and higher in OSI model.

x.25

analog. packet switched technology designed for long distance data transmission. connects clients and servers with WAN. uses protocols from layers 1-3.

Which of the following WAN topologies comes with the highest availability and the
greatest cost?

Full mesh

Which of the following elements of the PSTN is most likely capable of transmitting only
analog signals?

Local loop

A customer calls your ISP's technical support line, complaining that his connection to
the Internet usually goes as fast as 128 Kbps, but today it is only reaching 64 Kbps. He
adds that he has tried dialing up three different times with the same result. What type of
connection does this customer have?

ISDN

What is the purpose of ISDN's D channel?

To carry call session information

Suppose you work for a bank and are leasing a frame relay connection to link an
automatic teller machine located in a rural grocery store with your bank's headquarters.
Which of the following circuits would be the best option, given the type of use this
automatic teller machine will experience?

SVC

On an ISDN connection, what device separates the voice signal from the data signals at
the customer premises?

Terminal adapter

Which of the following WAN technologies operates at Layer 3 of the OSI model?

d. None of the above

What technique enables DSL to achieve high throughput over PSTN lines?

a. Data modulation

Suppose you establish a home network and you want all three of your computers to
share one broadband cable connection to the Internet. You decide to buy a router to
make this sharing possible. Where on your network should you install the router?

c. Between the cable modem and the workstations

How does ATM differ from every other WAN technology described in this chapter?

c. It uses fixed-sized cells to carry data.

You work for an Internet service provider that wants to lease a T3 over a SONET
ring. What is the minimum Optical Carrier level that the SONET ring must have to
support the bandwidth of a T3?

OC1

Which two of the following are asymmetrical versions of DSL?

VDSL ADSL

What technique does T1 technology use to transmit multiple signals over a single
telephone line?

b. Time division multiplexing

Where on the PSTN would you most likely find a DSLAM?

a. In a remote switching facility

The science museum where you work determines that it needs an Internet connection
capable of transmitting and receiving data at 12 Mbps at any time. Which of the
following T-carrier solutions would you advise?

c. Ten T1s

What part of a SONET network allows it to be self-healing?

a. Its double-ring topology

Which of the following may limit a DSL connection's capacity?

b. The distance from the customer to the carrier's switching facility

Why is broadband cable less commonly used by businesses than DSL or T-carrier
services?

c. Because most office buildings are not wired with coaxial cable

Flickr Creative Commons Images

Some images used in this set are licensed under the Creative Commons through Flickr.com. Click to see the original works with their full license.

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