Ccent/ccna Icnd1 Chapter 4

Front 1

[401] Define and describe the terms LAN, MAN, and WAN.

Back 1

[401] LAN = local area network. MAN = metropolitan area network. WAN = wide-area network. LANs are typically within a building, MANs within a city, and WANs are between cities and countries.

Front 2

[402] What does PTT stand for?

Back 2

[402] Public Telephone and Telegraph (company)

Front 3

[403] Which network devices connect different types of layer 1 and 2 technologies?

Back 3

[403] Routers

Front 4

[404] What does CO stand for?

Back 4

[404] Central Office

Front 5

[405] What is a CSU/DSU?

Back 5

[405] Channel Service Unit/Data Service Unit. Usually owned by the telco or ISP. It sits between the telco's leased lines and the customer's router. The telco's underground cable usually connects to the CSU/DSU with an RJ48 connector.

Front 6

[406] Describe a typical point-to-point leased line setup, including all network devices and relative cable lenths.

Back 6

[406] The customer's router connects to the CSU/DSU with a relative short cable (usually less than 50 feet). The CSU/DSU connects to the service provider's network, which eventually terminates in the CO (central office) at a WAN switch.

Front 7

[407] What is a demarc point?

Back 7

[407] The demarc (short for demarcation point) is the point at which the telco's responsibility ends - usually where their long 4 wire line terminates and where the CSU would be plugged in. Usually the CSU and the cable connecting to the router is owned by a separate company and so those are outside the demarc.

Front 8

[408] What does CPE refer to?

Back 8

[408] Customer Premises Equipment. This includes the router, cables, and usually the CSU - it is all equipment NOT owned by the telco.

Front 9

[409] What type of interface do routers use to connect to CSUs?

Back 9

[409] Serial interface.

Front 10

[410] Name 5 common CSU connectors and the number of pins used by each.

Back 10

[410] EIA/TIA-232 (25 pins). EIA/TIA-449 (37 pins). EIA/TIA-530 (25 pins). V.35 (34 pins). X.21 (15 pins).

Front 11

[411] What is the TIA? What is the ITU?

Back 11

[411] Telecommunications Industry Association - responsible for development of telecommunication standards in the US. International Telecommunication Union - international standards body.

Front 12

[412] What type of connector is typically used for the cable connecting the CSU to the telco's CO?

Back 12

[412] RJ48 - same size and shape as RJ45.

Front 13

[413] List the cable lengths necessary to achieve each of the following data speeds when using an EIA/TIA-232 connector for your CSU: 2400 bps; 4800; 9600; 19,200; 38,400; 115,200; 1.544 Mbps.

Back 13

[413] In meters - 60, 30, 15, 15, 15, 3.7, and T1 is not possible.

Front 14

[414] List the cable lengths necessary to achieve each of the following data speeds when using an EIA/TIA-449, V.35, X.21, or EIA-530 connector for your CSU: 2400 bps; 4800; 9600; 19,200; 38,400; 115,200; 1.544 Mbps.

Back 14

[414] In meters - 1250, 625, 312, 156, 78, 115,200 is not possible, and 15.

Front 15

[415] What are three common ways to refer to the speed of a leased circuit?

Back 15

[415] clock rate, bandwidth, and link speed.

Front 16

[416] What does DTE stand for?

Back 16

[416] Data terminal equipment.

Front 17

[417] What does DCE stand for?

Back 17

[417] Data communications equipment.

Front 18

[418] In the context of clocking, what are the different roles played by the DTE and the DCE?

Back 18

[418] The device that provides clocking is the DCE - usually the CSU; the device that receives clocking is the DTE - usually the router.

Front 19

[419] Is the serial cable connecting the router the same in every case?

Back 19

[419] No - you need to buy either a DTE or a DEC serial cable, depending on which function the router is performing.

Front 20

[420] Is a DTE serial cable straight-through or crossover?

Back 20

[420] Straight-through.

Front 21

[421] Is a DCE serial cable straight-through or crossover?

Back 21

[421] Crossover.

Front 22

[422] Describe a back-to-back serial connection.

Back 22

[422] Two routers, one configured as a DCE and one as a DTE, connected with a DCE (female) cable plugged into a DTE (male) cable.

Front 23

[423] What was the original standard for converting analog voice to a digital signal? How many bits were required to represent 1 second of voice?

Back 23

[423] PCM, or pulse code modulation. It defined that an incomming voice signal should be sampled 8000 times per second, and that each sample should be represented by an 8-bit code. So 64,000 bits were required to represent 1 second of voice.

Front 24

[424] What is a DS0 channel?

Back 24

[424] DS0 stands for Digital Signal level 0 and referred to the original 64kbps lines required to transmit audio signals (64,000 bits per second was the PCM-required speed for transmitting voice).

Front 25

[425] Why are some DS0 channels actually 56kbps lines instead of 64kbps?

Back 25

[425] The telco's needed some of the bandwidth for management and overhead. When most of the traffic was voice, changing a bit every once in a while was fine, but when it changed to data they had to lower the advertised speeds and reserve 1 bit out of every 8 for that purpose. 7/8 of 64,000 is 56,000.

Front 26

[426] What are the common types of point-to-point WAN line, the names of the signalling types, and the speeds for each?

Back 26

[426] 1. 56/DS0/56 kbps 2. 64/DS0/64 kbps 3. T1/DS1/1.544 Mbps (24 DS0's, plus 8 kbps) 4. T3/DS3/44.736 Mbps (28 DS1's, plus overhead) 5. E1/ZM/2.048 Mbps (32 DS0's) 6. E3/M3/34.064 Mbps (16 E1's, plus overhead) 7. J1/Y1/2.048 Mbps (32 DS0's; Japanese standard).

Front 27

[427] What are the two common layer 2 point-to-point protocols?

Back 27

[427] HDLC, or High-level data link control. PPP, or Point-to-Point Protocol.

Front 28

[428] Which of the 4 Layer 2 functions does HDLC perform?

Back 28

[428] On a point-to-point link each device can send over the 4-wire circuit at any time, so there is no need for arbitration. HDLC framing does include an address field, even though it is not really necessary. It also defines an FCS field for error detection. The original standard did not include a protocol type field, but Cisco added one making their implementation of HDLC proprietary.

Front 29

[429] What is LCP?

Back 29

[429] Link Control Protocol.

Front 30

[430] What are the 4 main functions of LCP?

Back 30

[430] 1. Link Quality Monitoring (LQM) 2. Magic Number - detects looped links 3. Multilink PPP - allows multiple serial links between two devices with load balancing 4. PAP and CHAP - used to authenticate and verify identity of endpoint devices.

Front 31

[431] Describe SDLC.

Back 31

[431] SDLC = Synchronous Data Link Control. Error correction = yes. Type Field = no. Supports multipoint links. Assumes that an SNA header occurs after the SDLC header.

Front 32

[432] Describe LAPB.

Back 32

[432] LAPB = Link Access Procedure Balanced. Error correction = yes. Type Field = no (although Cisco's implementation does). Used mainly with X.25.

Front 33

[433] Describe LAPD.

Back 33

[433] LAPD = Link Access Procedure on the D Channel. Error correction = no. Type Field = no. Used by ISDN lines for signaling to bring circuits up and down.

Front 34

[434] Describe LAPF.

Back 34

[434] LAPF = Link Access Procedure for Frame Mode Bearer Services. Error correction = no. Type Field = yes. Used over Frame Relay links.

Front 35

[435] Describe HDLC.

Back 35

[435] HDLC = High-Level Data Link Control. Error correction = no. Type Field = no (although Cisco's implementation does). Cisco's default on serial links.

Front 36

[436] Describe PPP.

Back 36

[436] PPP = Point-to-Point Protocol. Error correction = supported but not enabled by default. Type Field = Yes. Only protocol meant for multiprotocol interoperability from inception.

Front 37

[437] Define synchronous.

Back 37

[437] Synchronous means there is an imposed time ordering at the link's sending and receving ends. In order to achieve this, one device is set to be the master and provide clocking. The slave then listens and makes small adjustments to its own clock until the speeds match.

Front 38

[438] Define asynchronous.

Back 38

[438] No clocking or speed adjustment is performed. Only 1 byte per transfer is sent, so slight differences don't matter. A start bit is used to signal the beginning of a byte.

Front 39

[439] How does a Frame Relay Switch know where to send frames?

Back 39

[439] Each frame header holds an address field called a DLCI (data-link connection identifier).

Front 40

[440] In the context of a Frame Relay network, what do the terms DTE and DCE refer to?

Back 40

[440] The device providing the frame switching service (Frame Relay Switch) is the DCE, and the customer equipment is the DTE.

Front 41

[441] What is the logical path between two routers on a Frame Relay network called?

Back 41

[441] A virtual circuit (VC).

Front 42

[442] What is a PVC?

Back 42

[442] Often, the telco preconfigures all the required details of a VC - these are called permanent virtual circuits, or PVC's.

Front 43

[443] What does CIR stand for? What is it?

Back 43

[443] Committed information rate. It is the minimum bandwidth guaranteed by the telco for each VC.

Front 44

[444] What are the benefits of using Frame Relay over point-to-point WAN links?

Back 44

[444] Frame Relay allows multiple devices to be connected to the network just once and uses VC's to route traffic directly between them, eliminating the need for a separate physical leased line between every WAN site. Because it is so much more efficient and easier to implement, it is usually much cheaper when connecting many WAN endpoints.

Front 45

[445] What does ATM stand for?

Back 45

[445] Asynchronous Transfer Mode.

Front 46

[446] What does SONET stand for?

Back 46

[446] Synchronous Optical Network.

Front 47

[447] What is the standard used outside the US, instead of SONET?

Back 47

[447] SDH - Synchronous Digital Hierarchy.

Front 48

access link

Back 48

in frame relay, the physical serial link tha connects a frame relay DTE device, (ex router) to a Frame Relay switch - same physical standards as point to point leased lines

Front 49

back-to-back link

Back 49

serial link between 2 routers without CSU/DSUs - connect DTE cable to one router and DCE cable to the other - used in labs

Front 50

clocking

Back 50

process of supplying a signal over a cable, either on a separate pin on a serial cable or as part of the signal transitions in the transmitted signal so that receiving device can keep synchronization with sending device

Front 51

DS1

Back 51

digial signal level 1.A 1.544-Mbps line from telco - 24 DSO channels of 64 kbps each, plus an 8-kbps management and framing channel - also called a T1

Front 52

Frame Relay

Back 52

international standard data-link protocol that devines capabilities to create a frame-switched service - allowing DTE devices (like routers) to send data to many other devices using a single physicla connection to the frame relay service

Front 53

leased line

Back 53

serial communications circuit between two points - provide by some service provider - telco doesn't sell the physical cable - charges a fee to send bits between two sites

Front 54

packet switching

Back 54

reference to network services (like WAN) in which the service examines the contents of the transmitted dta to make some type of forwarding decision - contrasts circuit swtiching (layer 1 circuit between 2 devices, no interpreting of meaning of bits)

Front 55

serial cable

Back 55

type of cable with many different styles of connectors used to connect a router to an exteranl CSU/DSU on a leased line installation

Front 56

T1

Back 56

line from telco - allows data at 1.544 Mbps, treats the line as 24 different 64-kbps DS0 channles (plus 8 kbps of overhead)

Front 57

virtual circuit

Back 57

in packet-switched services like Frame Relay, VC is ability of two DTE devices to send and receive data directly to each other - same function as physical leased line, does so without physical circuit (contrast leased line, or leased circuit)