Module 2

1Version 3.0

Module 2WAN Technologies

WAN Technology

• A Wide Area Network (WAN) is used to interconnectLocal Area Networks (LANs) that are separated by alarge geographical distance.

• A Wide Area Network predominately operates at theOSI physical and data link layers.

• The WAN provides a data path between routers andthe LANs that each router supports.

2Version 3.0

• A Wide Area Network (WAN) is used to interconnectLocal Area Networks (LANs) that are separated by alarge geographical distance.

• A Wide Area Network predominately operates at theOSI physical and data link layers.

• The WAN provides a data path between routers andthe LANs that each router supports.

3Version 3.0

MAJOR CHARACTERISTICS OF WANS

The network operates beyond the local LAN’sgeographic scope. It uses the services ofcarriers such as Regional Bell OperatingCompanies (RBOCs).

WANs use serial connections of varioustypes to access bandwidth over wide-areageographies.

By definition, the WAN connects devicesseparated by wide areas.

4Version 3.0

MAJOR CHARACTERISTICS OF WANS

The network operates beyond the local LAN’sgeographic scope. It uses the services ofcarriers such as Regional Bell OperatingCompanies (RBOCs).

WANs use serial connections of varioustypes to access bandwidth over wide-areageographies.

By definition, the WAN connects devicesseparated by wide areas.

WAN DEVICES INCLUDE:

Routers that offer many services includinginternetworking and WAN interface ports. Switches that connect to WAN bandwidth for

voice, data, and video communication. Modems that interface voice-grade services;

Include channel service units/digital service units(CSU/DSU) that interface T1/E1 services;Terminal Adapters/Network Termination 1(TA/NT1) that interface Integrated Services DigitalNetwork (ISDN) services. Communication servers that concentrate dial-in

and dial-out user communication. WANS use the OSI layered approach for

encapsulation just like LAN's but are mainlyfocused on the physical and data link layers.

5Version 3.0

WAN DEVICES INCLUDE:

Routers that offer many services includinginternetworking and WAN interface ports. Switches that connect to WAN bandwidth for

voice, data, and video communication. Modems that interface voice-grade services;

Include channel service units/digital service units(CSU/DSU) that interface T1/E1 services;Terminal Adapters/Network Termination 1(TA/NT1) that interface Integrated Services DigitalNetwork (ISDN) services. Communication servers that concentrate dial-in

and dial-out user communication. WANS use the OSI layered approach for

encapsulation just like LAN's but are mainlyfocused on the physical and data link layers.

WAN Physical Layer

• WAN physical layer protocols describe how toprovide electrical, mechanical, operational, andfunctional connections for wide-area networkingservices.

• These services are most often obtained fromWAN service providers such as Regional BellOperating Companies (RBOCs), alternate carriers,and Post, Telephone, and Telegraph (PTT)agencies.

6Version 3.0

• WAN physical layer protocols describe how toprovide electrical, mechanical, operational, andfunctional connections for wide-area networkingservices.

• These services are most often obtained fromWAN service providers such as Regional BellOperating Companies (RBOCs), alternate carriers,and Post, Telephone, and Telegraph (PTT)agencies.

WAN Data Link Protocols

• WAN data link protocols describe howframes are carried between systems on asingle data path.

• They include protocols designed to operateover dedicated point-to-point, multipoint,and multi-access switched services suchas Frame Relay.

7Version 3.0

• WAN data link protocols describe howframes are carried between systems on asingle data path.

• They include protocols designed to operateover dedicated point-to-point, multipoint,and multi-access switched services suchas Frame Relay.

WAN Standards

• WAN standards typically describeboth physical layer deliverymethods and data link layerrequirements includingaddressing and flow controlencapsulation

8Version 3.0

• WAN standards typically describeboth physical layer deliverymethods and data link layerrequirements includingaddressing and flow controlencapsulation

describes the interface betweenthe data terminal equipment(DTE) and the data circuit-terminating equipment (DCE).

9Version 3.0

DTE & DCE• DTE - data terminal equipment. Device at the user end of a

user-network interface that serves as a data source,destination, or both. DTE connects to a data networkthrough a DCE device (for example, a modem) and typicallyuses clocking signals generated by the DCE.

• DTE includes such devices as computers, routers, andmultiplexers.

• DCE - Data communications equipment (EIA) or datacircuit-terminating equipment (ITU-T). The devices andconnections of a communications network that comprisethe network end of the user-to-network interface. The DCEprovides a physical connection to the network, forwardstraffic, and provides a clocking signal used to synchronizedata transmission between DCE and DTE devices. Ex:Modems and interface cards

10Version 3.0

• DTE - data terminal equipment. Device at the user end of auser-network interface that serves as a data source,destination, or both. DTE connects to a data networkthrough a DCE device (for example, a modem) and typicallyuses clocking signals generated by the DCE.

• DTE includes such devices as computers, routers, andmultiplexers.

• DCE - Data communications equipment (EIA) or datacircuit-terminating equipment (ITU-T). The devices andconnections of a communications network that comprisethe network end of the user-to-network interface. The DCEprovides a physical connection to the network, forwardstraffic, and provides a clocking signal used to synchronizedata transmission between DCE and DTE devices. Ex:Modems and interface cards

11Version 3.0

12Version 3.0

The WAN data-link protocols describe howframes are carried between systems on asingle path

13Version 3.0

The Data Link Layer: WAN ProtocolsHigh-Level Data Link Control (HDLC)—HDLC is an IEEE

standard. It might not be compatible between different vendorsbecause of the way each vendor has chosen to implement it.

• HDLC supports both point-to-point and multipointconfigurations with minimal overhead

Frame Relay - Frame Relay uses high-quality digital facilities.By using a simplified framing with no error correction

mechanisms, Frame Relay can send Layer 2 information muchmore rapidly than these other WAN protocols.

Point-to-Point Protocol - Described by RFC 1661. PPP containsa protocol field to identify the network-layer protocol.

Integrated Services Digital Network (ISDN) - ISDN is a set ofdigital services that transmits voice and data over existingphone lines.

14Version 3.0

High-Level Data Link Control (HDLC)—HDLC is an IEEEstandard. It might not be compatible between different vendorsbecause of the way each vendor has chosen to implement it.

• HDLC supports both point-to-point and multipointconfigurations with minimal overhead

Frame Relay - Frame Relay uses high-quality digital facilities.By using a simplified framing with no error correction

mechanisms, Frame Relay can send Layer 2 information muchmore rapidly than these other WAN protocols.

Point-to-Point Protocol - Described by RFC 1661. PPP containsa protocol field to identify the network-layer protocol.

Integrated Services Digital Network (ISDN) - ISDN is a set ofdigital services that transmits voice and data over existingphone lines.

Wide Area Networking

15Version 3.0

The WAN Cloud

• An overview of the WAN cloud organizes WANprovider services into:– Call setup service—Sets up and clears calls

between telephone users.– Also called signaling, call setup uses a separate

telephone channel not used for other traffic.– The most commonly used call setup is Signaling

System number 7 (SS7). SS7 is an out-of-bandsignaling system for the exchange of call controlinformation between network switching offices, insupport of voice and nonvoice services

16Version 3.0

• An overview of the WAN cloud organizes WANprovider services into:– Call setup service—Sets up and clears calls

between telephone users.– Also called signaling, call setup uses a separate

telephone channel not used for other traffic.– The most commonly used call setup is Signaling

System number 7 (SS7). SS7 is an out-of-bandsignaling system for the exchange of call controlinformation between network switching offices, insupport of voice and nonvoice services

17Version 3.0

• Information from many sources has bandwidth allocationon a single media.

• Circuit switching uses signaling to determine the callroute, which is a dedicated path between the sender andthe receiver.

• By multiplexing traffic into fixed time slots, TDM avoidscongested facilities and variable delays.

• Basic telephone service and ISDN services use TDMcircuits.

Time-division multiplexing (TDM)

18Version 3.0

• Information from many sources has bandwidth allocationon a single media.

• Circuit switching uses signaling to determine the callroute, which is a dedicated path between the sender andthe receiver.

• By multiplexing traffic into fixed time slots, TDM avoidscongested facilities and variable delays.

• Basic telephone service and ISDN services use TDMcircuits.

Time-division multiplexing (TDM)

• Transmits multiple signals simultaneously over a singletransmission path. Each lower-speed signal is time slicedinto one high-speed transmission.

• Example: Three incoming 1,000 bps signals (A, B and C)can be interleaved into one 3,000 bps signal(AABBCCAABBCCAABBCC).

• The receiving end divides the single stream back into itsoriginal signals.

19Version 3.0

• Transmits multiple signals simultaneously over a singletransmission path. Each lower-speed signal is time slicedinto one high-speed transmission.

• Example: Three incoming 1,000 bps signals (A, B and C)can be interleaved into one 3,000 bps signal(AABBCCAABBCCAABBCC).

• The receiving end divides the single stream back into itsoriginal signals.

20Version 3.0

21Version 3.0

• When your organization subscribes toan outside WAN provider for networkconnections, the provider assigns yourorganization the rules for connectingWAN calls.

• Your organization makes connectionsto destinations as point-to-point calls.

22Version 3.0

• When your organization subscribes toan outside WAN provider for networkconnections, the provider assigns yourorganization the rules for connectingWAN calls.

• Your organization makes connectionsto destinations as point-to-point calls.

Demarcation (or demarc)—• The point at which the CPE ends and the local

loop portion of the service begins.• Often occurs at the Point of Presence (POP)

of a building.Local loop (or “last-mile”)• Cabling (usually copper wiring) that extends

from the demarc into the WAN serviceprovider’s central office.

23Version 3.0

Demarcation (or demarc)—• The point at which the CPE ends and the local

loop portion of the service begins.• Often occurs at the Point of Presence (POP)

of a building.Local loop (or “last-mile”)• Cabling (usually copper wiring) that extends

from the demarc into the WAN serviceprovider’s central office.

Central office (CO) switch• A switching facility that provides the

nearest point of presence for theprovider’s WAN service.

24Version 3.0

Toll network• The collective switches and facilities (called

trunks) inside the WAN provider’s cloud.• The caller’s traffic may cross a trunk to a

primary center, then go to a sectional center,and then to a regional- or international-carriercenter as the call goes the long distance to itsdestination.

• Switches operate in provider offices with tollcharges based on tariffs or authorized rates.

25Version 3.0

Toll network• The collective switches and facilities (called

trunks) inside the WAN provider’s cloud.• The caller’s traffic may cross a trunk to a

primary center, then go to a sectional center,and then to a regional- or international-carriercenter as the call goes the long distance to itsdestination.

• Switches operate in provider offices with tollcharges based on tariffs or authorized rates.

26Version 3.0

• A key interface in the customer siteoccurs between the data terminalequipment (DTE) and the data circuit-terminating equipment (DCE).

• Typically, DTE is the router.

27Version 3.0

• A key interface in the customer siteoccurs between the data terminalequipment (DTE) and the data circuit-terminating equipment (DCE).

• Typically, DTE is the router.

• DCE is the device used to convert the userdata from the DTE into a form acceptable tothe WAN service’s facility.

• In the graphic, the DCE is the attachedmodem, channel service unit/data service unit(CSU/DSU) or Terminal Adapter/NetworkTermination 1 (TA/NT1).

28Version 3.0

• DCE is the device used to convert the userdata from the DTE into a form acceptable tothe WAN service’s facility.

• In the graphic, the DCE is the attachedmodem, channel service unit/data service unit(CSU/DSU) or Terminal Adapter/NetworkTermination 1 (TA/NT1).

Data communication over WANsinterconnects DTEs so they can shareresources over a wide area.

• The WAN path between the DTEs is calledthe link, circuit, channel, or line.

• The DCE primarily provides an interfacefor the DTE into the communication link inthe WAN cloud.

• The DTE/DCE interface acts as a boundarywhere responsibility for the traffic passesbetween the WAN subscriber and the WANprovider.

29Version 3.0

Data communication over WANsinterconnects DTEs so they can shareresources over a wide area.

• The WAN path between the DTEs is calledthe link, circuit, channel, or line.

• The DCE primarily provides an interfacefor the DTE into the communication link inthe WAN cloud.

• The DTE/DCE interface acts as a boundarywhere responsibility for the traffic passesbetween the WAN subscriber and the WANprovider.

DSU/CSU

30Version 3.0

• A pair of communicating devices that connect an in-houseline to an external digital circuit (T1). It is similar to amodem, but connects a digital circuit rather than ananalog one.

CSU

31Version 3.0

Terminates the external line at the customer premises.Provides diagnostics and allows for remote testing.If the customer's communications devices are T1 readyand have the proper interface, then the CSU is notrequired, only the DSU.

DSU

32Version 3.0

Does the actual transmission and receiving of the signaland provides buffering and flow control.DSU and CSU can be in the same unit.DSU may also be built into the multiplexor, (combinesdigital signals for high-speed lines).

Forms of WAN services with routers.The most common are:– Switched or relayed services.

• Frame Relay• ISDN (Integrated Services Digital Network)• ATM (Asynchronous Transfer Mode)• X.25

– Peer Devices• HDLC (High-level Data Link Control)• PPP (Point-to-Point Protocol)• DDR (Dial on Demand Routing)• LAPB - point to point and X.25

33Version 3.0

Forms of WAN services with routers.The most common are:– Switched or relayed services.

• Frame Relay• ISDN (Integrated Services Digital Network)• ATM (Asynchronous Transfer Mode)• X.25

– Peer Devices• HDLC (High-level Data Link Control)• PPP (Point-to-Point Protocol)• DDR (Dial on Demand Routing)• LAPB - point to point and X.25

34Version 3.0

Both Frame Rely and X.25 use the concept of virtualcircuits

X.25

• The first packet switched networks• X.25 provides a connection-oriented

technology for transmission over highly-errorprone facilities.

• Error checking is performed at each node,which can slow overall throughput and andtherefore would not make X.25 a choice forvoice and video

• X.25 can be very cost effective because tariffsare based on the amount of data deliveredrather than connection time or distance

35Version 3.0

• The first packet switched networks• X.25 provides a connection-oriented

technology for transmission over highly-errorprone facilities.

• Error checking is performed at each node,which can slow overall throughput and andtherefore would not make X.25 a choice forvoice and video

• X.25 can be very cost effective because tariffsare based on the amount of data deliveredrather than connection time or distance

Asynchronous Transfer Mode (ATM)

• Lower latency at higher bandwidths• Data rates beyond 155 Mbps• Cell-based rather than frame-based• Cell are a fixed length of 53 bytes• Also uses PVCs• Less efficient because of the small size

36Version 3.0

• Lower latency at higher bandwidths• Data rates beyond 155 Mbps• Cell-based rather than frame-based• Cell are a fixed length of 53 bytes• Also uses PVCs• Less efficient because of the small size

Digital Subscriber Line (DSL)

• Uses existing telephone lines• Uses multiple frequencies within the same

physical medium to transmit data• Bandwidth can vary• Distance of the local loop is a factor – must

be less than 3.5 miles

37Version 3.0

• Uses existing telephone lines• Uses multiple frequencies within the same

physical medium to transmit data• Bandwidth can vary• Distance of the local loop is a factor – must

be less than 3.5 miles

Cable Modem

• Two-way, high-speed data transmissionsusing the same coaxial lines that transmitcable television.

• Always on

38Version 3.0

• Two-way, high-speed data transmissionsusing the same coaxial lines that transmitcable television.

• Always on

WAN FrameEncapsulation Formats

39Version 3.0

WAN FrameEncapsulation Formats

40Version 3.0

41Version 3.0

42Version 3.0

43Version 3.0

44Version 3.0

Layer 2 Encapsulation• Each WAN connection type uses a Layer 2

protocol to encapsulate traffic while it iscrossing the WAN link.

• To ensure that the correct encapsulationprotocol is used, you will need to configurethe Layer 2 encapsulation type to use.

• The choice of encapsulation protocoldepends on the WAN technology and thecommunicating equipment.

45Version 3.0

Layer 2 Encapsulation• Each WAN connection type uses a Layer 2

protocol to encapsulate traffic while it iscrossing the WAN link.

• To ensure that the correct encapsulationprotocol is used, you will need to configurethe Layer 2 encapsulation type to use.

• The choice of encapsulation protocoldepends on the WAN technology and thecommunicating equipment.

46Version 3.0

PPP• Common for dialup single-user-to-LAN

(dialup and ISDN) or LAN-to-LAN(router-to-router) access.

• PPP is standardized, so it supportsvendor interoperability.

• It also supports the encapsulation ofmultiple upper-layer protocolsincluding IP and IPX.

47Version 3.0

PPP• Common for dialup single-user-to-LAN

(dialup and ISDN) or LAN-to-LAN(router-to-router) access.

• PPP is standardized, so it supportsvendor interoperability.

• It also supports the encapsulation ofmultiple upper-layer protocolsincluding IP and IPX.

HDLC• The Cisco default encapsulation type on

point-to-point links.• It is used typically when communicating with

another Cisco device.• If communicating with a non-Cisco device,

synchronous PPP is a viable option.• HDLC is normally proprietary between

vendors.

48Version 3.0

HDLC• The Cisco default encapsulation type on

point-to-point links.• It is used typically when communicating with

another Cisco device.• If communicating with a non-Cisco device,

synchronous PPP is a viable option.• HDLC is normally proprietary between

vendors.

LAPB (layer 2 of the X.25 protocol stack)• For packet-switched networks, the LAPB

protocol is used to encapsulate X.25 packets.• It can also be used over point-to-point links, if

the link is unreliable or there is an inherentdelay associated with the link, such as in asatellite link.

• LAPB provides reliability and flow control ona point-to-point basis.

49Version 3.0

LAPB (layer 2 of the X.25 protocol stack)• For packet-switched networks, the LAPB

protocol is used to encapsulate X.25 packets.• It can also be used over point-to-point links, if

the link is unreliable or there is an inherentdelay associated with the link, such as in asatellite link.

• LAPB provides reliability and flow control ona point-to-point basis.

50Version 3.0

51Version 3.0

HDLC

• HDLC is Cisco’s default encapsulation for seriallines.

• This implementation is very streamlined.• There is no windowing or flow control and only

point-to-point connections are allowed (nomultipoint).

• 2-byte proprietary type code is inserted after thecontrol field, which means that HDLC framing isnot interoperable with other vendors’ equipment.

52Version 3.0

• HDLC is Cisco’s default encapsulation for seriallines.

• This implementation is very streamlined.• There is no windowing or flow control and only

point-to-point connections are allowed (nomultipoint).

• 2-byte proprietary type code is inserted after thecontrol field, which means that HDLC framing isnot interoperable with other vendors’ equipment.

53Version 3.0

WAN Design Basics

54Version 3.0

55Version 3.0

56Version 3.0

57Version 3.0

58Version 3.0

When leased line connections are made:

•a router port is required for each connection,

•along with a CSU/DSU and

•the actual circuit from the service provider.

The cost of dedicated line solutions can become significantwhen deployed to connect many sites

59Version 3.0

When leased line connections are made:

•a router port is required for each connection,

•along with a CSU/DSU and

•the actual circuit from the service provider.

The cost of dedicated line solutions can become significantwhen deployed to connect many sites

Dedicatedconnectivity,also referred toas leased lines,provides full-timesynchronousconnections.

Dedicated, full-timeconnectivity isprovided bypoint-to-pointserial links.

60Version 3.0

Dedicatedconnectivity,also referred toas leased lines,provides full-timesynchronousconnections.

Dedicated, full-timeconnectivity isprovided bypoint-to-pointserial links.

61Version 3.0

Network Design

• Network designs tend to follow one oftwo general design strategies:

• mesh• hierarchical

62Version 3.0

• Network designs tend to follow one oftwo general design strategies:

• mesh• hierarchical

Mesh structure• Net topology is flat• All routers perform essentially the

same functions• Usually no clear definition of where

specific functions are performed.• Expansion of the network tends to

proceed in a haphazard, arbitrarymanner.

63Version 3.0

Mesh structure• Net topology is flat• All routers perform essentially the

same functions• Usually no clear definition of where

specific functions are performed.• Expansion of the network tends to

proceed in a haphazard, arbitrarymanner.

Hierarchical structure the network isorganized in layers that each have oneor more specific functions.

Benefits to using a hierarchical modelinclude the following:– Scalability– Ease of implementation– Ease of troubleshooting– Predictability– Protocol support– Manageability

64Version 3.0

Hierarchical structure the network isorganized in layers that each have oneor more specific functions.

Benefits to using a hierarchical modelinclude the following:– Scalability– Ease of implementation– Ease of troubleshooting– Predictability– Protocol support– Manageability

65Version 3.0

The three-layer model consists of:• core• distribution• access layers

66Version 3.0

Core layer -• Provides fast wide-area connections between

geographically remote sites, tying a numberof “campus” networks together in a corporateor enterprise WAN.

• Core links are usually point-to-point, andthere are rarely any hosts in the core layer.

• Core services are typically leased from atelecom service provider (for example, T1/T3,Frame Relay, SMDS, and so on).

67Version 3.0

Core layer -• Provides fast wide-area connections between

geographically remote sites, tying a numberof “campus” networks together in a corporateor enterprise WAN.

• Core links are usually point-to-point, andthere are rarely any hosts in the core layer.

• Core services are typically leased from atelecom service provider (for example, T1/T3,Frame Relay, SMDS, and so on).

Distribution layer -• Refers to the distribution of network

services to multiple LANs within acampus network environment.

• This layer is where the “campusbackbone” network is found, typicallybased on Fast Ethernet.

• This layer is implemented on sites thatare large and is used to interconnectbuildings.

68Version 3.0

Distribution layer -• Refers to the distribution of network

services to multiple LANs within acampus network environment.

• This layer is where the “campusbackbone” network is found, typicallybased on Fast Ethernet.

• This layer is implemented on sites thatare large and is used to interconnectbuildings.

Access layer -• Usually a LAN or a group of LANs, typically

Ethernet or Token Ring, that provide userswith frontline access to network services.

• The access layer is where almost all hosts areattached to the network, including servers ofall kinds and user workstations.

69Version 3.0

Access layer -• Usually a LAN or a group of LANs, typically

Ethernet or Token Ring, that provide userswith frontline access to network services.

• The access layer is where almost all hosts areattached to the network, including servers ofall kinds and user workstations.

• The three layers are bounded by Layer 3devices or other devices that provideseparation into broadcast domains.

Note: A three-layer model can usually meet theneeds of most enterprise networks.

• However, not all environments require a fullthree-layer hierarchy—a one- or two-layerdesign may be adequate.

• Even in these cases, however, a hierarchicalstructure should be maintained.

70Version 3.0

• The three layers are bounded by Layer 3devices or other devices that provideseparation into broadcast domains.

Note: A three-layer model can usually meet theneeds of most enterprise networks.

• However, not all environments require a fullthree-layer hierarchy—a one- or two-layerdesign may be adequate.

• Even in these cases, however, a hierarchicalstructure should be maintained.

The distribution layer would include the campusbackbone with all its connecting routers.

• Because policy is typically implemented atthis level, we can say that the distributionlayer provides policy-based connectivity.

• Policy-based connectivity means that thelayer 3 routers are programmed to only allowtraffic on the campus backbone that thenetwork manager has determined acceptable.

72Version 3.0

The distribution layer would include the campusbackbone with all its connecting routers.

• Because policy is typically implemented atthis level, we can say that the distributionlayer provides policy-based connectivity.

• Policy-based connectivity means that thelayer 3 routers are programmed to only allowtraffic on the campus backbone that thenetwork manager has determined acceptable.

73Version 3.0

The access layer connects users into LANs,and LANs into campus backbones or WANlinks.

• This approach enables designers to distributeservices across the CPU’s of devicesoperating at this layer.

• The access layer allows logical segmentationof the network and the grouping of usersbased on a function.

74Version 3.0

The access layer connects users into LANs,and LANs into campus backbones or WANlinks.

• This approach enables designers to distributeservices across the CPU’s of devicesoperating at this layer.

• The access layer allows logical segmentationof the network and the grouping of usersbased on a function.

• The one-layer design is typically implementedwhere:

• Only a few remote locations in the company• access to applications are mainly done via

the local LAN to the site file server.• Each site is its own broadcast domain.

76Version 3.0

• The one-layer design is typically implementedwhere:

• Only a few remote locations in the company• access to applications are mainly done via

the local LAN to the site file server.• Each site is its own broadcast domain.

In a two-layer design, a WAN link is used tointerconnect separate sites.

• VLANs may be implemented to createseparate logical networks without requiringadditional routers.

• Inside the site multiple LANs may beimplemented with each LAN segment beingits own broadcast domain.

• Router becomes a concentration point forWAN links.

78Version 3.0

In a two-layer design, a WAN link is used tointerconnect separate sites.

• VLANs may be implemented to createseparate logical networks without requiringadditional routers.

• Inside the site multiple LANs may beimplemented with each LAN segment beingits own broadcast domain.

• Router becomes a concentration point forWAN links.

79Version 3.0

• Remote sites can access the WAN core networkusing WAN technologies other than dedicatedlinks.

• Frame Relay or ISDN are two such alternatives.• If a remote site is small and has low demand for

access to services in the corporate network,ISDN would be a logical choice for thisimplementation.

• Perhaps another remote site cannot get accessto dedicate WAN links from their service providerbut has access to Frame Relay.

• In either case an entry point needs to beestablished for these types of WAN connectionsin to the WAN core.

80Version 3.0

• Remote sites can access the WAN core networkusing WAN technologies other than dedicatedlinks.

• Frame Relay or ISDN are two such alternatives.• If a remote site is small and has low demand for

access to services in the corporate network,ISDN would be a logical choice for thisimplementation.

• Perhaps another remote site cannot get accessto dedicate WAN links from their service providerbut has access to Frame Relay.

• In either case an entry point needs to beestablished for these types of WAN connectionsin to the WAN core.

81Version 3.0

• One of the advantages of hierarchical WANdesign is it provides a method for controllingdata traffic patterns by putting Layer 3routing points throughout the network.

• Since routers have the ability to determinepaths from the source host to destinationhosts based on Layer 3 addressing, datatraffic will flow up the hierarchy only as far asit needs to to find the destination host.

82Version 3.0

• One of the advantages of hierarchical WANdesign is it provides a method for controllingdata traffic patterns by putting Layer 3routing points throughout the network.

• Since routers have the ability to determinepaths from the source host to destinationhosts based on Layer 3 addressing, datatraffic will flow up the hierarchy only as far asit needs to to find the destination host.

• If Host A were to establish a connectionto Host B, the traffic from thisconnection would travel to Router 1and be forwarded back down to Host B.

• Notice that this connection did notrequire any traffic be placed on the linkbetween Router 1 and Router 2, thusconserving the bandwidth on that link.

84Version 3.0

• If Host A were to establish a connectionto Host B, the traffic from thisconnection would travel to Router 1and be forwarded back down to Host B.

• Notice that this connection did notrequire any traffic be placed on the linkbetween Router 1 and Router 2, thusconserving the bandwidth on that link.

• In a two-layer WAN hierarchy, the trafficpatterns are still governed by hostsource and destination addresses andpath determinations of the router.

• In this model again the traffic will onlytravel up the hierarchy as far as neededto get to the destination thusconserving bandwidth on other WANlinks.

86Version 3.0

• In a two-layer WAN hierarchy, the trafficpatterns are still governed by hostsource and destination addresses andpath determinations of the router.

• In this model again the traffic will onlytravel up the hierarchy as far as neededto get to the destination thusconserving bandwidth on other WANlinks.

88Version 3.0

89Version 3.0

90Version 3.0

Module 2

91Version 3.0

Module 2WAN Technologies