NT1210 Introduction to Networking - · PDF fileLAN i ht b i l Eth tLAN might be simple Ethernet-onlLANly LAN ... Topologies PitPoint-to-PitT l ... Earlier standards used 64-Kbps

NT1210 Introduction to Networking

Unit 7:Chapter 7, Wide Area NetworksChapter 7, Wide Area Networks

ObjectivesObjectives

Identify the major needs and stakeholders for y jcomputer networks and network applications.Identify the classifications of networks and how they are applied to various types of enterprises.Explain the functionality and use of typical network protocolsprotocols.Analyze network components and their primary functions in a typical data network from both logicalfunctions in a typical data network from both logical and physical perspectives.

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Differentiate among major types of LAN and WAN g j yptechnologies and specifications and determine how each is used in a data network.Explain basic security requirements for networks.Use network tools to monitor protocols and traffic characteristicscharacteristics.Use preferred techniques and necessary tools to troubleshoot common network problemstroubleshoot common network problems.Differentiate among WAN technologies available from service providersp

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Evaluate how WAN devices functionDefine and describe WAN protocolsEvaluate troubleshooting techniques for WANEvaluate troubleshooting techniques for WAN connections

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Introducing Wide Area Networks: BasicIntroducing Wide Area Networks: Basic Telco Services

T l h T l d i th t fTelephone, Telcos, and companies that grew from original Bell System impact how today’s WANs work

Telcos built huge networks to support voice traffic longTelcos built huge networks to support voice traffic, long before computers could create and send bits

Figure 7-1Timeline Comparison of Inventions Compared to Telephone5

Introducing Wide Area Networks: BasicIntroducing Wide Area Networks: Basic Telco Services – Circuit Switching

S it h d A l Ci it f V i I l d fSwitched Analog Circuits for Voice: In early days of telephones, voice call required one analog electrical circuit between two phonesp

Telco installed 2-wire cable into each home: Local loopOther end connected equipment sitting in nearby TelcoOther end connected equipment sitting in nearby Telco office: Central Office (CO)

When user called number, Telco created electrical circuit from one telephone to other (source to destination)

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Figure 7-2Early Voice: Telco Creates One Analog Electrical Circuit Between Phones7


S it h d A l Ci it f D t T t fi t WANSwitched Analog Circuits for Data: To create first WAN connections, early computing devices had to act like telephonesp

One computer device would “make phone call” to other computer, encoding its bits using analog electrical signals

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Figure 7-4Connecting from a PC to an ISP, Using Modems and an Analog Telco Circuit9


B i i id 20th t T l t f dBeginning mid-20th century Telcos transformedInvention and commercialization of computers: Started with few computers being rare and unusual to world where mostfew computers being rare and unusual to world where most companies owned computers

Migration from Telcos as government monopolies to free-market competition: Governments started removing monopolymarket competition: Governments started removing monopoly status from different parts of Telcos’ business so allowed competition

C fComputerization of Telco’s own network: Revolutionized how Telco built its internal network to create better services at lower cost

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Di it l Ci it dDigital Circuits and Leased Lines: Telcos started offering service gthat used digital circuit between customer devicescustomer devices

Endpoints still had circuit between them but could encode signal as bits with different electrical signals that followed encoding rules

Figure 7-5More Modern Routers Using a Digital Leased Line11


S it h d Ci itSwitched Circuits and Circuit Switching: When user calls phone number, various circuit switches connectswitches connect circuit on both sides of switch ( d li )(see arrowed lines)

Circuit switches create effect of end-to-end circuit by switching/connecting circuits on various linksswitching/connecting circuits on various links

Figure 7-6Circuit Switching12


T t it h d i it S it h d tTo create switched circuits: Switches and customer devices (telephones and modems) use signaling to setup and tear down circuitp

Signaling messages allow switches to choose which switch-to-switch links (trunks) to use for particular call

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Ci it C i ti th b t t d i tCircuit: Communication path between two endpoints

Circuit Switching: Logic used by Telco network and devices called “circuit switches” that allows them todevices called circuit switches that allows them to switch circuits in and out of different physical trunks to create end-to-end circuit through network

Switched Circuit: End-to-end circuit through Telco that changes over time because user calls number, hangs up calls another number and so onup, calls another number, and so on

Dedicated Circuit (leased line): Circuit between two specific devices Telco never takes downspecific devices Telco never takes down

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Introducing Wide Area Networks: BasicIntroducing Wide Area Networks: Basic Telco Services – Packet Switching

P k t S it hi T l t t t d ff i WANPacket Switching: Telcos next started offering WAN services using packet switching services

Figure 7-7General Timeline: Circuit Switching, Digital Circuits, and Packet Switching15

Introducing Wide Area Networks: BasicIntroducing Wide Area Networks: Basic Telco Services – Packet Switching

All t d i d di t ti t WAN iAll customer devices need direct connection to WAN via circuit to packet switching service

Customers: All devices can send data to every otherCustomers: All devices can send data to every other device connected to packet switched service

Telco (service provider): Must look at meaning of bits inTelco (service provider): Must look at meaning of bits in customer’s headers and make forwarding decision per packet

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Introducing Wide Area Networks: BasicIntroducing Wide Area Networks: Basic Telco Services – Packet SwitchingPacket Switching ExamplePacket Switching Example

Figure 7-8Example of Packet Switching Service17

Introducing Wide Area Networks: Routers

C t LAN t WANConnect LANs to WANs

Figure 7-9Layer 3 IP Forwarding Logic18


LAN i ht b i l Eth t l LANLAN might be simple Ethernet-only LAN

LAN might be simple 802.11 WLAN

LAN i ht b l LAN ith b th i dLAN might be more complex campus LAN with both wired and wireless LANs

Figure 7-10Example Enterprise Network, With LAN and WAN Details Revealed19


E l ti d D l tiEncapsulation and De-encapsulation

Figure 7-11Encapsulation that Happens During the IP Packet Forwarding Process20

Introducing Wide Area Networks: Topologies

P i t t P i t T l B i WAN iPoint-to-Point Topology: Basic WAN serviceLAN with10BASE-T or 100BASE-T cable has 2-pair: 1 pair for sending data in each directionsending data in each direction

Both LAN and WAN topologies allow full duplex operation and can share 1 link

Figure 7-12Point-to-Point Topologies in WAN and LAN21


Hub and Spoke TopologiesHub and Spoke TopologiesReduces number of leased lines

Provides way for packets to reach all sitesProvides way for packets to reach all sites

Connects one router (hub router) to all other routers using leased lines

Figure 7-13WAN Hub and Spoke Topology Vs. LAN Star Topology22


H b d S k T l lHub and Spoke Topology exampleRouters in Enterprise network and how many leased lines required to connect every router to every other routerrequired to connect every router to every other router

Number of Routers

Number of Leased Lines Formula: N(N 1)/2Routers Leased Lines Formula: N(N-1)/2

20 190 (20 x 19) / 2 40 780 (40 x 39) / 260 1770 (60 x 59) / 280 3160 (80 x 79) / 2100 4950 (100 x 99) / 2

Table 7-1Number of Leased Lines to Connect Every Pair of Routers

( )

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M lti i t t l i H b d k t l hMultipoint topologies: Hub-and-spoke topology has some disadvantages

Uses leased lines that might have to run hundreds orUses leased lines that might have to run hundreds or thousands of miles at large expense

Packets that go from one spoke site to th k it h tanother spoke site have to

cross multiple WAN links

Figure 7-14WAN Multipoint Topology24

Understanding Leased Line WAN Links

C t t t t b i i f di bitCustomer expects to get basic service of sending bits between two devices

Customer buys right to send X number of bits perCustomer buys right to send X number of bits per second constantly between two sites

Figure 7-15Leased Line in Concept25


Di t li it ti N i l i it t d tiDistance limitations: No single circuit extends entire distance between two routers

“Point to point” circuits really series of circuitsPoint to point circuits really series of circuits

Figure 7-16Leased Line: Shorter Electrical Circuits, Knitted Together26


T l i USA ff l d li d i lti l fTelcos in USA offer leased line speeds in multiples of 64 Kbps: 64, 128, 192, 256, etc., up to 24 times 64 (1.536 Mbps)( p )

Speeds above 1.5 Mbps offered in multiples of 1.544 Mbps up to 28 times (around 43 Mbps)

Incremental Speed Value Speed Increment

Up to this Many Increments

Speed RangeBased on…

Increments

DS0 64 Kbps 24 64 - 1536 Kbps DS1 (T1) 1.536 Mbps 28 1.536 - 43.008 Mbps

Table 7-2Leased Line Speed Options, USA27

( ) p p


Telcos built networks to support digital transmission ofTelcos built networks to support digital transmission of voice in mid-20th centuryEarlier standards used 64-Kbps b ildi bl k ll d di it l i lbuilding block called digital signallevel 0 (DS0): Combined bits from slower speed links into single higher p g gspeed physical link using multiplexingBits from 24 DS0s (plus some overhead) combined onto singleoverhead) combined onto single physical link called digital signal level 1 (DS1, T1)Physical links combined bits from 28 DS1s (plus y (poverhead) to create DS3 (T3) lines

Figure 7-17Visual Comparison of Speeds: DS0, DS1, DS328


T l i t ll h i l bl b t i t i COTelco installs physical cable between equipment in CO to customer site

2 pair cable typically runs underground into customer2-pair cable typically runs underground into customer buildings terminating near customer’s router

Figure 7-18Cables in a Relatively Short Leased Line29


C t d t l f bli t d f T l ’Customer needs to plan for cabling at end of Telco’s leased line cable

Example: Customer’s router connects to cable installedExample: Customer s router connects to cable installed by Telco

Figure 7-19Components and Responsibilities on One Side of a Leased Line30


L d li h Ch l S i U it/D t S iLeased line has Channel Services Unit/Data Services Unit (CSU/DSU) function on each side of line at customer site

Each site uses either internal or external CSU/DSU Internal CSU/DSU sits inside router as part of serial interface pcard

Figure 7-20Customer Equipment and Cabling with External CSU/DSU31


E t l CSU/DSU t k l i N d t kExternal CSU/DSU takes more planning: Need to know which connectors used by router and CSU/DSU device and then use correct serial cable to connect them

Figure 7-21Drawings of Some of the Short Serial Cables (Router to CSU/DSU)32


E l Ci t ith t l t f blExample: Cisco router with two slots for removable router interface cards (WICs) where serial cards are install

Serial card on left has built-in CSU/DSU and uses RJ-48 connectorSerial card on right does not have CSU/DSU so relies on external e es o e te aCSU/DSU

1921 router… http://www.cisco.com/en/US/prod/collateral/voicesw/ps6789/ps7290/ps10589/data_sheet_c78-598389.htmlWIC-1CSU: http://www.cisco.com/en/US/prod/collateral/routers/ps221/product_data_sheet09186a00801a9184.html

Figure 7-22Photos of Router and Removable WAN Cards

http://www.cisco.com/en/US/prod/collateral/routers/ps5853/data_sheeet_serial_high_speed_waniInt_cards_for_1861.html

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K t f i t lli l d liKey steps for installing leased lines1. Order leased line from Telco; include specs on line speed, cable

connectors required, and exact location where cable should be installed (address, floor, identifying information for exact room)

2. Install router and serial interface cards in router as needed by leased line

3. If interface card does not have internal CSU/DSU, choose CSU/DSU and matching cable

4. Physically connect all cablesy y5. Configure devices (beyond scope of this chapter)

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Break

Take 10

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Understanding Leased Line WAN Links:Understanding Leased Line WAN Links: Multiplexing

T C i t d lti l i h ll TT-Carrier system and multiplexing challenge: Too many trunks between sites

Example: 3 customers (A B C) who each have offices in sameExample: 3 customers (A, B, C) who each have offices in same two towns about 15 miles apart and each has DS1 or T1 leased line between each site

Figure 7-23Conceptual View, Three T1 Leased Lines, Three Customers (A, B, C)36


P ibl l ti T l ld i t ll th T1 t k liPossible solution: Telco could install three T1 trunk lines between CO switches

Figure 7-24Telco Switching Connecting Incoming Customer T1s to T1 Trunks37


M ffi i t l ti Ti Di i i M lti l iMore efficient solution: Time Division Multiplexing (TDM) uses TDM switches and one T3 trunk

Telco connects cable using T3 card in each TDM switch to useTelco connects cable using T3 card in each TDM switch to use T3 link (43.736 Mbps—28 times T1 speed)

Figure 7-25CO Switches Multiplexing T1 Bits onto Faster T3 Circuit38


Top: 3 routers continually send bits to switch CO1 via 3Top: 3 routers continually send bits to switch CO1 via 3 separate T1 lines

Middle: Switch CO1 combines (“plexes”) bits onto single T3 for transmissiontransmission

Bottom: Switch CO2 demultiplexes incoming signal back intodemultiplexes incoming signal back into original bit streams, sending bits for customer A’s T1 to router A2, and B’s and C’s likewiseC s likewise

Figure 7-26A Three Part Drawing of the TDM Example39


Link types in T-carrier system (DS0 DS1 DS3) defineLink types in T-carrier system (DS0, DS1, DS3) define timing of when TDM switch can send bits over link

Example: On customer A’s T1 connection, CO1 and CO2 p ,TDM switches give A’s traffic “turn” on T3 on regular basis

As long as number of bits allocated to A’s traffic totals 1.544 million every second, TDM switches can send all traffic for A’s T1

Figure 7-27A View into a Longer Time Period over a T3 Link40


TDM it h id T3 t k h i l i l li kTDM switch considers T3 trunk as physical serial link with 28 logical T1 channels

Physically T3 line uses 2-pairPhysically, T3 line uses 2 pair cable that sends and receives bits serially (one at a time) at )43.736 Mbps

Logically, TDM switch views T3 asswitch views T3 as 28 T1 channels numbered 1 through 28

Figure 7-28Matching TDM T3 Port and T1 Logical Channel on Both Ends of the T3 Trunk41


T l it h d CSU/DSU i bit fTelco switches and CSU/DSUs view bits as frames

Figure 7-31A T1 Frame, Shown as Sent Serially Over a T142


T1 f t f 193 bit th t fl li kT1 frames are set of 193 bits that flow over link

T1 equipment uses data in extra 193rd bit for several functions includingfunctions, including framing (can’t be used for customerdata bits)

Figure 7-30193-Bit T1 Frame43


C t b T1 li t h it ith f ll T1 dCustomer buys T1 line at each site with full T1 speed (1.536 Mbps)

What happens if customer router can only transmit atWhat happens if customer router can only transmit at 768 Kbps?

Figure 7-29Speed Differences on a 768-Kbps Leased Line WAN44


Example: Serial cable connecting CSU/DSU and routerExample: Serial cable connecting CSU/DSU and router includes wires that set clocking (speed of link)

CSU/DSU signals router when to send or receive 1 bitCSU/DSU signals router when to send or receive 1 bit

If CSU/DSU configured to make router run at 768 Kbps, CSU/DSU sends clocking signal 768,000 times per second

Figure 7-33CSU/DSU View of Serial Cable and Router, with Clocking45


H t ti T1 d Adj t d t d iHow to use entire T1 speed: Adjust data speed using CSU/DSU

CSU/DSU looks at T1 line as 24 separate DS0 channelsCSU/DSU looks at T1 line as 24 separate DS0 channels plus overhead bits (framing)

Every 1/8000th of second, each frame gets to send andEvery 1/8000 of second, each frame gets to send and receive one byte of data (i e each DS0(i.e., each DS0 channel gets 64 Kbps of the capacity of the T1)

Figure 7-32CSU/DSU Channel View of the T1 Line from Customer to Local CO46


C t b ht 1 536 Mb f T1 b t tCustomer bought 1.536 Mbps of T1 between routers (full capacity of 24 DS0 channels)

So CSU/DSU must clock router at slightly slower rate ofSo CSU/DSU must clock router at slightly slower rate of 1.536 Mbps

Figure 7-34Full T1 with CSU/DSU: 1.536 Mbps to the Router, 1.544 Mbps to the CSU/DSU47


Wh t ki bit f t CSU/DSU t fit thWhen taking bits from router, CSU/DSU must fit them into 24 DS0 channels in T1 frame

Figure 7-35Role of the CSU/DSU in a Full T1 Leased Line48


F ti l T1 O T1 li di id d i t DS0Fractional T1: One T1 line divided into numerous DS0 channels

Example: 256 Kbps (4 times 64-Kbps speed of DS0 channel)Example: 256 Kbps (4 times 64-Kbps speed of DS0 channel) uses 4 DS0 channels on T1 line

Figure 7-36Role of the CSU/DSU in a Fractional T1 Leased Line (256)49


Type of Line Geography Speed Number of ChannelsType of Line Geography Speed Number of ChannelsDS0 USA 64 Kbps N/A

DS1 (T1) USA 1.544 Mbps 24 DS0

DS3 (T3) USA 43.736 Mbps 28 DS1E0 Europe 64 Kbps N/A

E1 E 2 048 Mb 32* E0E1 Europe 2.048 Mbps 32* E0

E3 Europe 34.368 Mbps 16 E1J0 Japan 64 Kbps N/Ap p

J1 Japan 1.544 Mbps 24 J0

J3 Japan 32.064 Mbps 20 J1

Table 7-3Summary of Carrier TDM Line Standards

* 30 E0 channels are available for customer data; 2 E0 channels are for other functions.

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D t Li k P t lData Link Protocols1. PC1 sends IP packet encapsulated in Ethernet frame to router R12. R1 receives frame, removes header/trailer, makes decision to send2. R1 receives frame, removes header/trailer, makes decision to send

packet to R2; R1 adds header/trailer based on WAN Data Link protocol

3. R2 receives WAN frame, removes header /trailer, makes decision to3. R2 receives WAN frame, removes header /trailer, makes decision to send packet to host PC2; R2 adds Ethernet header/trailer so frame arrives at PC2

Figure 7-37Encapsulation in a Serial WAN Data Link Protocol between Two Routers51


Hi h l l D t Li k C t l (HDLC) t l h 2High-level Data Link Control (HDLC) protocol has 2 main purposes:

Deliver encapsulated data from sender to correct receiverDeliver encapsulated data from sender to correct receiver

Perform error detection

Figure 7-38HDLC Frame Format52


Sh th d Si il tField Description Shorthand Reminder

Similar to Ethernet…

Flag 1-byte (7E) that signals beginning of frame

Here comes the frame! Preamble + SFD frame the frame!

Address Identifies destination device To there Destination MAC

Control Defines many subfields used by older devices Old; ignore N/A

Data Data plus all headers from upper layers The actual data pa load Data p pp y data payload

FCSFrame Check Sequence used for error checking (to see if any bits changed during transmission)

Check for errors FCS

Table 7-4HDLC Header and Trailer Fields53

during transmission)


P i t t P i t P t l (PPP) D i d f TCP/IPPoint-to-Point Protocol (PPP): Designed for TCP/IP networks and multiprotocol routers

Figure 7-39PPP Frame Format54

Understanding Packet Switching and Multi-Understanding Packet Switching and MultiAccess WANs

P k t it hi TDM l T l h i t ll dPacket switching vs. TDM example: Telco has installed 28 T1 leased lines for customers near two COs

Each T1 mapped to one of 28 T1 channels in T3 trunkEach T1 mapped to one of 28 T1 channels in T3 trunk

All 28 channels of T3 used

Figure 7-40Single T3 Trunk Consumed by Supporting 28 Customer T1s55


28 T1 l d li t t h f t CO28 T1 leased lines stretch from two COs

Leased lines run through total of four TDM switches and total of three T3 trunkstotal of three T3 trunks

T1s take up entire capacity on all three TDM trunks

Figure 7-41Multiple T3 Trunks Completely Used by Supporting 28 Customer T1s56


H k t it hi k D i TDMHow packet switching works: Devices use same TDM physical link types as T-carrier system

Use Data Link protocol that identifies destination addressUse Data Link protocol that identifies destination address using hex code

Telco packet switches must know location of each destination, typically using table

Figure 7-42Packet Switching Concept: Telco Node Receives, Queues, Forwards Packets57


With k t it hi li k it b t it hWith packet switching, link capacity between switches used to forward packets as needed or available

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Understanding Packet Switching and Multi-Understanding Packet Switching and MultiAccess WANs: Frame Relay

F R l All d i t d t t kFrame Relay: Allows any device connected to network to communicate with any other network and details of Frame Relay design do not mattery g

Figure 7-44Typical Drawing of a Frame Relay Design, One Customer, Ignoring Details59


F R l h i l li k Ed b t tFrame Relay physical links: Edge between customer site and Frame Relay network

Point of Presence (PoP): Where Telco devices/cablesPoint of Presence (PoP): Where Telco devices/cables interface with customer premises

DTE (Data Terminal Equipment): Customer device (e.g., router)

Frame Relay switch: Telco device that forwards customer frames (also called DCE [Data Communications Equipment])

Access link: Physical link between DTE and DCEAccess link: Physical link between DTE and DCE

DLCI: Data Link Control Identifier, used instead of IP address

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F R l tFrame Relay terms

Figure 7-45One Possible Telco Implementation of the Frame Relay Network61


Vi t l Ci it (VC) Vi t l l d li b t CO dVirtual Circuit (VC): Virtual leased line between CO and customer

Telco has to permanently configure VCs so also calledTelco has to permanently configure VCs so also called Permanent Virtual Circuits (PVCs)

Example: R1 is HQ router, Branch are routers at other p ,locations, leased lines connect R1 to each Branch router

Figure 7-46Four Physical Circuits Between Routers62


S d i i PVC i F R l t kSame design using PVCs in Frame Relay network

Figure 7-47Frame Relay Virtual Circuit (VC) Concept; Partial Mesh63


P ti l d f ll h F R l f ll h d iPartial and full mesh: Frame Relay full mesh design makes sense when most sites send lots of IP packets to every other sitey

Full mesh: PVC between every pair of Frame Relay routers

Figure 7-48Full Mesh of Frame Relay PVCs64


E k t it hi t h l d fi t lEvery packet switching technology defines protocols used to deliver data

Link Access Procedure Frame (LAPF): Frame RelayLink Access Procedure Frame (LAPF): Frame Relay protocol; often just called Frame Relay

LAPF defines header/trailer

Header includes LAPF address called Data Link ConnectionIdentifier (DLCI)Identifier (DLCI)

Figure 7-49Frame Relay Header/Trailer: Link Access Procedure Frame (LAPF)65


E l 4 t h R1 i t HQ ith ti l hExample: 4 routers where R1 is at HQ with partial mesh of PVCs connected to 3 remote routers (R2, R3, R4)

Uses 3 DLCIs that uniquely identifying Frame RelayUses 3 DLCIs that uniquely identifying Frame Relay PVCs to each connection

Figure 7-50Example: Three DLCIs, Three PVCs, All Using a Single Access Link 66


E l f DLCI R1 i IP k t f LANExample of DLCI use: R1 receives IP packet from LAN (not shown) and decides to forward packet to router R2

Figure 7-51Example: Frame Relay Frame with DLCI 102 (R2) 67


P k t S it hi S i SONET dPacket Switching Services: SONET speeds

(Rounded) Line Speed (in

NameLine Speed (in

Mbps)OC-1 52OC-3 155OC-12 622OC-24 1244OC 24 1244OC-48 2488OC-96 4976OC 192 9952

Table 7-5SONET Optical Carrier (OC) Names and (Rounded) Line Speeds

OC-192 9952

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Ti li f WAN t h l i (d t l dTimeline for WAN technologies (dates are general and only meant for comparing some of technologies)

Figure 7-52Comparison Timeline of WAN Technologies Mentioned in this Chapter 69

Summary, This Chapter…Compared switched circuits as used for a typical homeCompared switched circuits as used for a typical home telephone call with two computers sending data over a similar switched circuit using modems.

Explained the basic differences between a circuit switching WAN service and a packet switching WAN service from the customer’s perspectiveservice from the customer s perspective.

Illustrated the reasons why IP routers work well at forwarding data between different types of LANs and g ypWANs.

Drew common WAN topologies.

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Summary, This Chapter…Drew and contrasted the different customer-site cablingDrew and contrasted the different customer site cabling for a leased line WAN installed between two routers.

Listed the types of physical links in the US T-carrier yp p yhierarchy, their approximate speeds, and the specific number of slowed-speed channels that fit in the next higher-speed linehigher-speed line.

Explained how Telcos use CSU/DSUs to match a leased line speed to a physical DS1 line, using an p p y , gexample of a 768 Kbps fractional T1 leased line between two routers.

Compared and contrast the HDLC and PPP standards.

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Summary, This Chapter…Explained the differences between packet switchingExplained the differences between packet switching and circuit switching from the Telco perspective.

Used an example network, explain how with Frame p , pRelay, a router can have one physical link connected to the WAN, but send data to many other destination routersrouters.

Listed the other WAN packet switching services, and show whether they were introduced before or after yFrame Relay.

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Questions? Comments?

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Documents

NT1210 Introduction to Networking - · PDF fileLAN i ht b i l Eth tLAN might be simple Ethernet-onlLANly LAN ... Topologies PitPoint-to-PitT l ... Earlier standards used 64-Kbps