Ccna4 M2 Wan Technologies
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CCNA – Semester4
Module 2 WAN Technologies
Objectives
• Identify the devices used in a WAN and list standards • Differentiate between packet-switched and circuitswitched WAN technologies • Describe equipment involved in the implementation of various WAN services • Compare and contrast WAN design models
WAN Technology Overview
Parts of a WAN service
Modem
• In order for the local loop to carry data, a device such as a modem is needed to prepare the data for transmission.
DTE and DCE
• Devices that put data on the local loop are called data circuitterminating equipment, or data communications equipment (DCE). • The customer devices that pass the data to the DCE are called data terminal equipment (DTE).
WAN Line Types and Bandwidth
WAN Devices
WAN Devices: Modem
• •
A modem is needed if the local loop is analog rather than digital. Modems transmit data over voice-grade telephone lines by modulating and demodulating the signal.
WAN Devices: CSU/DSU • The communications link needs signals in an appropriate format. • For digital lines, a channel service unit (CSU) and a data service unit (DSU) are required. • The CSU/DSU may also be built into the interface card in the router.
WAN standard organizations
WAN standard • WANs use the OSI reference model, but focus mainly on Layer 1 and Layer 2. • WAN standards typically describe both physical layer delivery methods and data link layer requirements, including physical addressing, flow control, and encapsulation.
WAN physical layer
•
Describe how to provide electrical, mechanical, operational, and functional connections to the services provided by a communications service provider.
Physical Connectors
WAN data link layer
• The data link layer protocols define how data is encapsulated for transmission to remote sites, and the mechanisms for transferring the resulting frames.
WAN encapsulation • • • •
The choice of encapsulation protocols depends on the WAN technology and the equipment. Most framing is based on the HDLC standard. The address field is not needed for WAN links, which are almost always point-to-point. The control field indicates the frame type: – Unnumbered frames carry line setup messages. – Information frames carry network layer data. – Supervisory frames control the flow of information frames and request data retransmission in the event of an error.
WAN Data-link Protocols
Circuit Switching • Fixed capacity may not be efficient due to access bursts. • Generally an expensive way of moving data. • The data bits are automatically delivered to the far end because the circuit is already established.
Packet Switching
Packet Switching • Two approaches: connectionless or connection-oriented. • Connectionless systems carry full addressing information in each packet. • Connection-oriented systems predetermine the route for a packet, and each packet need only carry an identifier.
WAN link options
WAN Technologies
Analog dialup •
• •
•
When intermittent, low-volume data transfers are needed, modems and analog dialed telephone lines provide low capacity and dedicated switched connections. The advantages are simplicity, availability, and low implementation cost. The upper limit is around 33 kbps. The rate can be increased to around 56 kbps if the signal is coming directly through a digital connection. The disadvantages are the low data rates and a relatively long connection time, not proper for voice or video traffic.
ISDN • The connection uses 64 kbps bearer channels (B) for carrying voice or data and a signaling, delta channel (D) for call set-up. • ISDN is used to provide additional capacity or backup for leased-line. • ISDN tariffs are based on a per-B channel basis and are similar to those of analog voice connections.
ISDN • Basic Rate Interface (BRI) ISDN is intended for the home and small enterprise. • For larger installations, Primary Rate Interface (PRI) ISDN is available.
Leased line • The dedicated capacity gives no latency or jitter between the endpoints. • These dedicated circuits are generally priced based on bandwidth required and distance between the two connected points.
X.25
• • •
Packet-switched networks using shared lines to reduce costs, tariffs are based on the amount of data . Switched or permanent virtual circuits can be established through the network and data packets are subject to delay. X.25 networks are usually low capacity
Frame Relay
• • • •
Frame Relay is a much simpler protocol with no error or flow control The simplified handling of frames leads to reduced latency Most Frame Relay connections are PVCs rather than SVCs It can operate at much higher bit rate that provides permanent shared medium bandwidth connectivity that carries both voice and data traffic.
ATM • ATM provide very low latency and jitter at much higher bandwidths. • ATM has data rates beyond 155 Mbps, capable of transferring voice, video, and data. • It is built on a cell-based architecture rather than on a frame-based architecture. ATM cells are always a fixed length of 53 bytes including 5 bytes header.
DSL • • • •
Digital Subscriber Line (DSL) technology is a broadband technology Use existing twisted-pair telephone lines to transport high-bandwidth data. Broadband refers to a technique which uses multiple frequencies within the same physical medium to transmit data. The transfer rates are dependent on the actual length of the local loop and the type and condition of its cabling.
Cable modem • Network access is available from some cable television networks allows greater bandwidth than telephone local loop. • Enhanced cable modems enable two-way, highspeed data transmissions up to 6.5 times that of T1 leased lines. • It is an attractive medium for transferring large amounts of digital information quickly, including video clips, audio files, and large amounts of data.
WAN Design
WAN design • Approaching the design in a systematic manner can lead to superior performance at a reduced cost. • It is necessary to know what data traffic must be carried, its origin, and its destination.
Traffic Characteristics • For each pair of end points and for each traffic type, information is needed on the various traffic characteristics.
Steps in WAN design •
•
Several modifications may be necessary before a design is finalized. Continued monitoring and re-evaluation are also required after installation of the WAN to maintain optimal performance.
Designing a WAN • Designing a WAN essentially consists of the following: – Selecting an interconnection pattern or layout for the links between the various locations – Selecting the technologies for those links to meet the enterprise requirements at an acceptable cost
WAN topologies • Knowing the various end points allows the selection of a topology or layout for the WAN. • The topology will be influenced by geographic considerations but also by requirements such as availability
WAN Technologies • With the end points and the links chosen, the necessary bandwidth can be estimated. • Type of traffic on the links may have varying requirements for latency and jitter. • With the bandwidth availability already determined, suitable link technologies must be selected.
Three-layer design model • A systematic approach is needed when many locations must be joined. A hierarchical solution with three layers offers many advantages. • This three-layer model follows the hierarchical design used in telephone systems.
Advantages of the hierarchical approach
Advantages of the hierarchical approach
Three-layer design model
Other layered design models
• Many networks do not require the complexity of a full three-layer hierarchy. Simpler hierarchies may be used.
Summary • Identify the devices used in a WAN and list standards • Packet-switched and circuit-switched WAN technologies • Overview of analog dialup, ISDN, leased line, X.25, Frame Relay, cable modem and ATM services • Steps in WAN design and WAN design requirements • Advantages offered with a three-layer hierarchical WAN design
CCNA4 – Module2
Module 2 WAN Technologies
Objectives
• Identify the devices used in a WAN and list standards • Differentiate between packet-switched and circuitswitched WAN technologies • Describe equipment involved in the implementation of various WAN services • Compare and contrast WAN design models
WAN Technology Overview
Parts of a WAN service
Modem
• In order for the local loop to carry data, a device such as a modem is needed to prepare the data for transmission.
DTE and DCE
• Devices that put data on the local loop are called data circuitterminating equipment, or data communications equipment (DCE). • The customer devices that pass the data to the DCE are called data terminal equipment (DTE).
WAN Line Types and Bandwidth
WAN Devices
WAN Devices: Modem
• •
A modem is needed if the local loop is analog rather than digital. Modems transmit data over voice-grade telephone lines by modulating and demodulating the signal.
WAN Devices: CSU/DSU • The communications link needs signals in an appropriate format. • For digital lines, a channel service unit (CSU) and a data service unit (DSU) are required. • The CSU/DSU may also be built into the interface card in the router.
WAN standard organizations
WAN standard • WANs use the OSI reference model, but focus mainly on Layer 1 and Layer 2. • WAN standards typically describe both physical layer delivery methods and data link layer requirements, including physical addressing, flow control, and encapsulation.
WAN physical layer
•
Describe how to provide electrical, mechanical, operational, and functional connections to the services provided by a communications service provider.
Physical Connectors
WAN data link layer
• The data link layer protocols define how data is encapsulated for transmission to remote sites, and the mechanisms for transferring the resulting frames.
WAN encapsulation • • • •
The choice of encapsulation protocols depends on the WAN technology and the equipment. Most framing is based on the HDLC standard. The address field is not needed for WAN links, which are almost always point-to-point. The control field indicates the frame type: – Unnumbered frames carry line setup messages. – Information frames carry network layer data. – Supervisory frames control the flow of information frames and request data retransmission in the event of an error.
WAN Data-link Protocols
Circuit Switching • Fixed capacity may not be efficient due to access bursts. • Generally an expensive way of moving data. • The data bits are automatically delivered to the far end because the circuit is already established.
Packet Switching
Packet Switching • Two approaches: connectionless or connection-oriented. • Connectionless systems carry full addressing information in each packet. • Connection-oriented systems predetermine the route for a packet, and each packet need only carry an identifier.
WAN link options
WAN Technologies
Analog dialup •
• •
•
When intermittent, low-volume data transfers are needed, modems and analog dialed telephone lines provide low capacity and dedicated switched connections. The advantages are simplicity, availability, and low implementation cost. The upper limit is around 33 kbps. The rate can be increased to around 56 kbps if the signal is coming directly through a digital connection. The disadvantages are the low data rates and a relatively long connection time, not proper for voice or video traffic.
ISDN • The connection uses 64 kbps bearer channels (B) for carrying voice or data and a signaling, delta channel (D) for call set-up. • ISDN is used to provide additional capacity or backup for leased-line. • ISDN tariffs are based on a per-B channel basis and are similar to those of analog voice connections.
ISDN • Basic Rate Interface (BRI) ISDN is intended for the home and small enterprise. • For larger installations, Primary Rate Interface (PRI) ISDN is available.
Leased line • The dedicated capacity gives no latency or jitter between the endpoints. • These dedicated circuits are generally priced based on bandwidth required and distance between the two connected points.
X.25
• • •
Packet-switched networks using shared lines to reduce costs, tariffs are based on the amount of data . Switched or permanent virtual circuits can be established through the network and data packets are subject to delay. X.25 networks are usually low capacity
Frame Relay
• • • •
Frame Relay is a much simpler protocol with no error or flow control The simplified handling of frames leads to reduced latency Most Frame Relay connections are PVCs rather than SVCs It can operate at much higher bit rate that provides permanent shared medium bandwidth connectivity that carries both voice and data traffic.
ATM • ATM provide very low latency and jitter at much higher bandwidths. • ATM has data rates beyond 155 Mbps, capable of transferring voice, video, and data. • It is built on a cell-based architecture rather than on a frame-based architecture. ATM cells are always a fixed length of 53 bytes including 5 bytes header.
DSL • • • •
Digital Subscriber Line (DSL) technology is a broadband technology Use existing twisted-pair telephone lines to transport high-bandwidth data. Broadband refers to a technique which uses multiple frequencies within the same physical medium to transmit data. The transfer rates are dependent on the actual length of the local loop and the type and condition of its cabling.
Cable modem • Network access is available from some cable television networks allows greater bandwidth than telephone local loop. • Enhanced cable modems enable two-way, highspeed data transmissions up to 6.5 times that of T1 leased lines. • It is an attractive medium for transferring large amounts of digital information quickly, including video clips, audio files, and large amounts of data.
WAN Design
WAN design • Approaching the design in a systematic manner can lead to superior performance at a reduced cost. • It is necessary to know what data traffic must be carried, its origin, and its destination.
Traffic Characteristics • For each pair of end points and for each traffic type, information is needed on the various traffic characteristics.
Steps in WAN design •
•
Several modifications may be necessary before a design is finalized. Continued monitoring and re-evaluation are also required after installation of the WAN to maintain optimal performance.
Designing a WAN • Designing a WAN essentially consists of the following: – Selecting an interconnection pattern or layout for the links between the various locations – Selecting the technologies for those links to meet the enterprise requirements at an acceptable cost
WAN topologies • Knowing the various end points allows the selection of a topology or layout for the WAN. • The topology will be influenced by geographic considerations but also by requirements such as availability
WAN Technologies • With the end points and the links chosen, the necessary bandwidth can be estimated. • Type of traffic on the links may have varying requirements for latency and jitter. • With the bandwidth availability already determined, suitable link technologies must be selected.
Three-layer design model • A systematic approach is needed when many locations must be joined. A hierarchical solution with three layers offers many advantages. • This three-layer model follows the hierarchical design used in telephone systems.
Advantages of the hierarchical approach
Advantages of the hierarchical approach
Three-layer design model
Other layered design models
• Many networks do not require the complexity of a full three-layer hierarchy. Simpler hierarchies may be used.
Summary • Identify the devices used in a WAN and list standards • Packet-switched and circuit-switched WAN technologies • Overview of analog dialup, ISDN, leased line, X.25, Frame Relay, cable modem and ATM services • Steps in WAN design and WAN design requirements • Advantages offered with a three-layer hierarchical WAN design
CCNA4 – Module2
