CCNA

CCNA Study Guide
online cisco ccna training guide – collection of high quality CCNA tutorials.
These tutorials are prepared with single slogan; “provide best online CCNA training absolutely free”. This comprehensive collection of CCNA Study material is exactly; what you need to prepare for following exams CCNA Routing and Switching; Cisco Certified Entry Networking Technician (CCENT), Interconnecting Cisco Networking Devices – part 1 (ICND-1); Interconnecting Cisco Networking Devices – part 2 (ICND-2). CCNA certificate is a goal in your career journey. So to get this goal we arranged this exclusive CCNA training program in such a way that you get advantage from these CCNA tutorials in exam and after getting certificate in your job life.

DB9 to DB25 serial cable

Serial Cable

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Serial cable is used to interconnect DTEs and DCEs. The DCEs are data communication equipment that generated or received data, and the DCEs are data communication equipment that only relayed data. There are two different types of cables, one for connecting a DTE to a DCE, and another for connecting two DTEs directly to each other. The DTE/DCE interface for a particular standard defines the standards including the number of pins and connector types, voltage levels for 0 and 1, defines the function for each of the signalling lines in the interface and sequence of events for transmitting data.

Serial Cable

Figure-1 illustrates the original RS-232 standard that was defined as the connection between DTEs and DCEs (modems). However, we have also the requirement to connect two DTEs, for example, two routers or two computers. For this purpose, a special cable called a null modem can be used which eliminates the requirement of DCEs. With a null-modem connection, the Trans and receive lines are cross-linked between both ends of the cable. Figure 2 illustrates the null-modem cable.

Serial Cable
STDM

Statistical Time-Division Multiplexing (STDM)

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Statistical time-division multiplexing (STDM) is sharing a communication like TDM but like the TDM the time slots are not allocated to any channel. In the case of TDM, time slots are allocated to channels and reserved even if there is no data to send.  This allocation is just wastage of the bandwidth and Statistical time-division multiplexing overcome this inefficiency of standard TDM.  Statistical time-division multiplexing achieved this with the use of intelligent devices that are capable of identifying when a terminal is idle.

STDM was specially developed to overcome the inefficiency of TDM. It uses a variable time slot length allowing channels to use any free slot space for sending their information. It uses a buffer memory for temporarily stores the data during periods of peak traffic. STDM requires each transmission to carry identification information or a channel identifier.

Statistical time-division multiplexing is mainly the same as TDM except that every signal is assigned a slot based on priority and demand. Standard TDM and various other circuits switching technique are executed at the physical layer in the OSI and TCP/IP model but Statistical time-division multiplexing is executed at the data link layer and above.

The STDM is used to transport multiple data, audio and video streams with different data rates to be broadcasted across a bandwidth-limited channel. The example is the Frame relay packet-switching and X.25 protocols, in which the packets have different lengths. The STDM is the example of Asynchronous Transfer Mode packet-switched protocol.

In the Asynchronous Transfer Mode, single streams are classified in variable time segments and subsequently transmitted using the asynchronous time-division multiplexing procedure. There no define the order for the bit transmission in this mode. Each time slot carries channel information to separate the packet in the demultiplexer procedure. The figure below illustrates the STDM process.

STDM

TDM

Time Division Multiplexing (TDM)

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Multiplexing is a technique that allows multiple logical signals to share a single physical channel. The two common types of multiplexing are time-division multiplexing (TDM) and statistical time-division multiplexing (STDM). In this article, I am going to discuss the time-division multiplexing.

Time Division Multiplexing (TDM) transmits more than one streaming digital signals over a common channel. Time Division Multiplexing differentiates between synchronous and asynchronous multiplexing.

Incoming signals are divided into equal fixed-length time slots. The multiples signals are transmitted over a shared medium.  At the receiving end, the signals are de-multiplexed and reassembled into their original format. Time-division multiplexing (TDM) is also known as a digital circuit switched technique. Before multiplexing, each telephone call required its physical medium. Bell Laboratories invented TDM to decrease the physical medium needs for every telephone call.

TDM is working in the physical layer. It is independent of the Layer 2 protocol that has been used by the input channels. It is not caring about the nature of the information that is multiplexed on to the output channel.

TDM Multiplexing

Figure 1 illustrates the function of the multiplexer (MUX). The multiplexer at transmitting end accepts three separate signals from three different sources and breaks each signal into segments. After breaks, the signals into segments the MUX puts each segment into a single channel by inserting each segment into a time slot.

A MUX at the receiving end receives the stream and reassembles it into three separate output signals based on the arrival timing of each bit. A MUX keeps every bit interleaving number and sequence from each specific transmission so that they can be quickly and efficiently reassembled it into their original form when received. Byte interleaving do the same functions, but there are eight bits in each byte, so, the process required a bigger and longer time slot. The T1/E1 and ISDN telephone lines are common examples of synchronous TDM. In the synchronous method, single data streams are classified in defined time segments for subsequent transmission in a predetermined order.

Point to Point Links

Point to Point Communication Links

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Usually, a point to Point links is used when permanent dedicated connections are required. It is a pre-established WAN communications path connection, which can securely connect two or more locations for private data services. The point to point links is available with different standards and different speed including T1 lines, Ethernet or DS3.

Enterpriser usually used point-to-point links to provide reliable and secure data service for applications including credit card processing, file sharing, data backup, VOIP, and video conferencing. All the above mention services can be configured together over the same point to point connection. We also know Point-to-Point links link as Private Line, Leased Line, or Data Line. Point-to-point connections can communicate over vast distances either through audio or video with maintaining high quality throughout the call. The example is the undersea fibre-optic cables that connect countries and continents worldwide over thousands of miles with a high quality of service. The figure below illustrates the point-to-point links.

point to point link

V.35 and HSSI

Serial Communication

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Serial communication is the famous and broadly used technique to transfer data between processing equipment and peripherals. Serial communication is used to transfer data across the WANs. The sending router encapsulates the data using a communication protocol. The encapsulated data is sent on a physical medium to the WAN and receiving router de-encapsulates the encapsulated data back.

Serial communication uses Binary One for representing logic HIGH or 5 Volts and binary zero for representing a logic LOW or 0 Volts. It can take many forms depending on the type of transmission mode and data transfer. The transmission modes are Simplex, Half Duplex, Full Duplex, Synchronous and Asynchronous. The source is known as a sender and the destination is known is a receiver for each transmission mode.

Some well-known interfaces used for the data exchange are RS-232, RS-422, RS-423, V.35, HSSI, RS-485, etc. Each one is using a different signalling method. The three most important serial communication standards are affecting LAN-to-WAN connections. We should discuss these most important methods.

Asynchronous Data Transfer – In the Asynchronous Data Transfer the bits of data are not synchronized by a clock pulse. The clock pulse is a signal used for synchronization.

Synchronous Data Transfer – In the synchronous mode the bits of data are synchronized using a clock pulse.

RS-232 

RS-232 is referring to the Interface between data terminal equipment (DTE) and data communications equipment (DCE) using serial binary data exchange.  The data terminal equipment (DTE) is usually the user computer, while data communications equipment (DCE) is the modem. RS-232 was introduced in the 1960s and originally known as EIA recommended standard 232.  It is the oldest serial communication standard.

Most of the serial ports on personal computers are RS-232C or newer standards RS-422 and RS-423. All the standards use both 9-pin and 25-pin connectors. Modems, mice, keyboards and printers were uses serial port but now these types of peripheral devices have been replaced by new and faster standards such as USB and RJ-45 connectors.

RS-232 are commonly available with 4, 9 or 25-pin wiring. The 25-pin Rs232 known as DB-25 connects every pin while the 9-pin Rs232 known as DB-9 does not connect many of the uncommonly used connections.  The 4-pin Rs232 cables provide the minimum connections for data transferring.

Most RS-232 devices can operate with a minimum of 3 signal cables: Transmit (TX), Receive (RX) and Ground (GND). The TX cable of one device must be connected with the RX cable of other device and vice versa and the ground cable must be connected.

A 25 pin RS-232 port on a PC transmits on pin 2 and receives on pin 3, and Ground is pin 7.  In the 9-pin RS-232 port on a PC transmits on pin 3, receives on pin 2 and Ground is pin 5. We cannot connect simply two devices with a serial cable because the connectors fit. It is important to verify the functions of each pin on each device, as well as verify whether or not the cable is a straight-through or null-modem cable.

V.35

The V.35 interface was originally specified by CCITT as an interface for 48kbps line transmissions. It has been adopted for all line speeds above 20kbps and seems to have acquired a life of its own. It was discontinued by CCITT in 1988, and replaced by recommendations V.10 and V.11.

It is an International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) specification standardized as an interface for 48 kbps line transmissions. The standard is used for modem-to-multiplexer communication. The standard is used for high-speed, synchronous data exchange combines the bandwidth of several telephone circuits.  The standard provides high data transfer rates (DTR) and connectivity between DCE and DTE over digital lines. In the U.S., this is used by most routers and DSUs that connect to T1 carriers.

The V.35 interface is working on layer 1 of the Open Systems Interconnection (OSI) model. V.35 interface is usually used for 56 kbps and 64 kbps data rates. It has balanced data and clock leads including handshake leads.  The V.35 has a 34 pin connector that combines the bandwidth of several telephone lines. The combined telephone lines provide a high-speed interface between DTE and channel service units.  Both balanced and unbalanced voltage signals on the same interface provide better speed and distance.  We can travel the V.35 cable up to 1200 meters with 100 Kbps speed.

The V.35 plug is standard with black plastic cover about 20mm by 70mm size, often with gold-plated contacts and built-in hold down and mating screws. The V.35 plug is 20 to 40 times the price of a DB25. Financially the RS-232 option is economical than the V.35 option.

HSSI

HSSI is the abbreviation of High-Speed Serial Interface, which is used for short-distance communications. Usually, HSSI is used to interconnect routing and switching devices on local area networks (LANs) with the higher-speed lines of a wide area network (WAN) such as T3 lines.  It is a serial interface that supports data transmission up to 52 Mbps.  HSSI is developed by Cisco system for DTE and DCE. HSSI can transmit data up to a distance of 52 feet. HSSI is working at the physical layer of the OSI model. HSSI is used as a 50-pin connector. It is used ECL technology for transmission.

parallel port

Parallel port

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Parallel ports usually used for connecting printers, computers, and other devices that required high bandwidth. The port is also used for interconnection between interior components of the devices. Parallel ports can be transmitted simultaneously over multiple wires. Theoretically parallel port is eight-time faster than a serial port. The serial port sends one bit while at the same time parallel ports send eight bits.

Parallel ports have an issue of crosstalk, especially with long wires.  Due to transfers a data over multiple wires the clock skew has also occurred which is creating synchronization issues.  Mostly the parallel port support data transfer only into one direction.  The common parallel port is a printer port also known as the Centronics port.

The latest version of parallel ports supports bi-directional data transfer. The standard for the bi-directional parallel port is IEEE 1284. The parallel port is now largely changed with the USB ports. Over a parallel cable, we can transmit data up to the length of 6 to 10 feet. If the cable is long then this length, the integrity of the data can be lost.

The cable Centronics Data Computer Corporation introduced the cable in 19970s. The data transfer rate at the time was 300 Kbits per seconds. The cable was introduced for the printer port and known as standard printer port (SPP). In 1987, the PS/2 port was introduced. The PS/2 was a bi-directional port and mostly was used for mouse, keyboard and games handles. The PS/2 was known as the bidirectional parallel port (BPP).  In 1994 the Enhanced parallel port(EPP) and The Extended capabilities port (ECP) was introduced.

The EPP was faster port than older parallel ports, which is supporting 500 KBps to 2 MBps data transfer speed. The ports are also used for printer connectivity. During this time, the five modes of operation were also specified as ECP mode, EPP mode, byte mode, nibble mode and compatibility mode. All the modes must carry data transfer in the forward direction, backward direction or bidirectional. The parallel ports are usually known as LPT1, LPT2, etc. The figure below illustrates the parallel port (DB-25). The parallel port is in the shape of the letter D.

Parallel port 1

Parallel port Pin Detail

The parallel port connector has an 8-bit data bus with a maximum recommended cable length of 10-feet. Cable long than recommended length can create poor connection and data signals. The pin information from pin 1 to pin 25 is the following:

  • Pin 1 – Strobe
  • Pin 2 – Data bit 0
  • Pin 3 – Data bit 1
  • Pin 4 – Data bit 2
  • Pin 5 – Data bit 3
  • Pin 6 – Data bit 4
  • Pin 7 – Data bit 5
  • Pin 8 – Data bit 6
  • Pin 9 – Data bit 7
  • Pin 10 – Ack
  • Pin 11 – Busy
  • Pin 12 – Paper End
  • Pin 13 – Select
  • Pin 14 – Auto Feed
  • Pin 15 – Error
  • Pin 16 – Initialize Printer
  • Pin 17 – Select Input
  • Pin 18 –Bit 0 Return (Ground)
  • Pin 19 –Bit 1 Return (Ground)
  • Pin 20 –Bit 2 Return (Ground)
  • Pin 21 –Bit 3 Return (Ground)
  • Pin 22 –Bit 4 Return (Ground)
  • Pin 23 –Bit 5 Return (Ground)
  • Pin 24 –Bit 6 Return (Ground)
  • Pin 25 –Bit 7 Return (Ground)

Pin1 – It is used for acknowledgement when the signal is low.

Pin 2 to 9 – It is used for data transfer.

Pin 10 – It is providing acknowledgement when data has finished processing. The pin has two states high and low when the pin signal is on the high state, it’s mean ready for more.

Pin 11 – When the signal state is on high, it means that the printer has accepted the data and is processing it. When this signal becomes low and Pin 10 goes high then the connected device will accept additional data.

Pin 12 – When printer jams a paper, the pin signal goes high and the printer stopped working.
Pin 13 – When the signal is high on pin 13, the printer is indicating that it is on-line and ready to print.

Pin 14 – When pin 14 has low signal, then the PC has indicated that the printer inset a line feed after each line.

Pin 15 – In case of an error the printer sends data to the computer that an error has occurred.
Pin 16 – When the signal goes low on pin 16, then the PC initiate request for internal reset.
Pin 17 – When the signal is low on that pin the PC has selected the printer and should in return prepare for data being sent.
Pin 18-25 – Ground.

Serial Port

Serial Port

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A serial port allows a PC or network devices to transmit or receive data one bit at a time. A serial interface is the oldest types of an interface that was also used to connect printers and external modems to a PC at that time. Modern serial ports are used in scientific instruments such as cash registers and applications like industrial machinery systems. The data transfer rate is very slow then the parallel port.

The serial port is used for point-to-point connection such as LAN-to-WAN connection. The LAN-to-WAN connection over a serial interface is also known as leased line connection because the line is usually leased from the telephone companies and the subscribers pay for those lines to hold the continuous connection between two sites.

Usually serial port is a male port and system resource configurations are chosen for each port and are recognized by COM1, COM2, COM3, COM4, and so forth. Each COM position represents an input/output (I/O) and an interrupt request (IRQ) address. The I/O address sends and receive packets to and from a peripheral device such as a mouse or keyboard or any network devices.

Using the serial connection on the network, we can send and receive data bits sequentially over a single channel. The serial port is bidirectional, and usually known as a bidirectional port or a communications port.

A serial connection was primarily used for signal exchange because of their bidirectional ability. Serial communications are less costly to implement because it is used fewer wires, cheaper cables, and fewer connector pins. On most computers, parallel ports and serial ports have been replaced by the higher speed serial Universal Serial Bus (USB) interfaces. Though, for long-distance communication, many WANs still uses serial transmission. This standard used for serial transmission between devices is RS 232 and usually called data communications equipment (DCE) and data terminal equipment (DTE). The serial port uses a nine-pin connector which is known as DB-9 connector.

Today the Higher speed communication port Universal Serial Bus (USB) and FireWire introduced faster interfaces; therefore, the serial port is hardly ever used but can be found as a communication device for Radios, GPS receivers, LED and LCD text displays, bar-code scanners and flat-screen monitors.

Serial Port DB-9 Connector

The figure below illustrates the serial connector DB-9. The figure shows each of the pins located on the DB9 connector. The Pin 1 starts from the top left and pin 9 is in the bottom right.

Serial Port

The serial ports carry data signals and control signals. To support these signal types including ground signals, RS-232 standard defines a 25-pin connection known as a parallel port. However, most PC’s and UNIX platforms use a 9-pin connection.  Actually, only three pins are needed for serial port communications: pin for sending data, pin for receiving data, and pin for the signal ground. The table below illustrates the signals associated with the DB-9 pin connectors.

Serial Port 2

The RTS and CTS Pins

The RTS and CTS pins transmit signals that the devices are ready to send or receive data. It is providing hardware handshaking and control data loss during transmission. The TD pin is used to send data between DCE and DTE.

The DTR and DSR Pins

These Pins are used for showing that the device is connected and powered. These pins provide an alternative method of hardware handshaking.

The CD and RI Pins

The CD and RI pins are used to show different signals during modem to modem connections. The modem gets indication from CD pin that it is connected to another modem. RI is used to indicate the presence of an audible ringing signal.

VPN

VPN Technology

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VPN is the abbreviation of a virtual private network. A VPN technology creates a safe and encrypted connection over an unsecured network, such as the internet. It extends a private network using a public network such as the internet. A virtual private network is using virtual connection known as VPN tunnels instead of using a dedicated Layer 2 connection, such as a leased line.

The virtual connection is routed through the Internet from the private network of the company to the remote site or employee host. To get access to controlled resources through a VPN, the user must provide authentication factors, such as security token or user name and password. There are two types of VPN:

Remote-access VPN

Remote access VPN enables an individual user to connect to a private network and access its resources and services remotely. A corporate employee uses a VPN to connect to their company’s private network and remotely access files and resources on the private network while they are away from their offices.

VPN Technology

Each employ typically has VPN client software installed on their android and laptop. They can also use a web-based client for remote access and remote management. The users also use a VPN service to bypass regional restrictions on the Internet and access blocked websites. Users aware of Internet security also use VPN services to improve their Internet security and privacy.

Site-to-site VPN

A Site-to-Site VPN is mostly used by corporate companies in their offices in different geographical locations. The site-to-site VPN connects the network of one office location to the network at another office location. It is also known as Router-to-Router VPN.

The example usage of Site-to-site VPNs can connect a branch office network to a company headquarters network. Each site is equipped with a VPN gateway. The gateway may be a router, firewall, or VPN concentrator. It is based on Router-to-Router communication, so, one router acts as a VPN Client and another router as a VPN Server. The communication between the two routers starts only after authentication is validated between them. There are two types of site-to-site VPNs:

Intranet-based

When one or more remote offices of the same company are connected using Site-to-Site VPN type, it is called an Intranet-based VPN.

Extranet-based

When companies use Site-to-site virtual private networks type to connect to the office of another company such as a supplier or partner).  It is called an Extranet based VPN. Extranet-based Site-to-site VPN can create a virtual bridge between the networks at geographically isolated offices and connect them through the Internet and maintain secure and private communication between the networks.

Advantages of VPN

The VPN technology was developed for the security of the peoples and especially for sending encrypted data over an unsecured or less secured network. Besides the VPN technology has many other advantages:

  • Cost savings– VPNs is a cost-saving because once it is created, the maintenance cost is very low. Companies can use Internet services to connect remote offices and remote users to the main corporate site, which also eliminate the expenses of the companies.
  • Enhanced Security– Using VPNs we can get the highest level of security because of advanced encryption and authentication protocols. The encryption and authentication kept securing the data from unauthorized access.
  • Scalability– Due to the use of the internet it is easy to add new users to the VPN. The companies can add large amounts of users to the capacity without adding major infrastructure.
  • Compatibility – Mobile workers and telecommuters can access their corporate network using their high-speed Internet service because VPN technology is supported broadband services such as DSL and cable.
  • Unblock websites & bypass filters. Using a VPN we can access the blocked websites or we can bypass the internet filters.
Cellular Network

Cellular Network

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Cellular networks are the type of wireless WAN technologies. Cellular networks provide services to connect users and remote locations where no other WAN access technologies are available. Millions of users use their smartphones and tablets to email, surf the web, download apps, and watch videos. We can easily connect computers, laptops including routers with the cellular network using cellular technology.

The cellular devices communicate to the nearby cellular tower using radio waves. The devices at the user end use a small antenna while the service provider uses a large antenna installed on the top of the tower to provide a line of sight connectivity to the subscriber devices. The common type of cellular networks is 2G, 3G, 4G, LTE and the latest one is 5G.

Cellular Network

2G Networks

2G is the second generation and it is the first digital standard of cellular networks introduced in the 1990s.  It is included Global System for Mobile (GSM), General Packet Radio Service (GPRS), and Enhanced Data Rate for Evaluation (EDGE). It is allowed call and text encryption as well as SMS, picture messaging and MMS. The maximum theoretical data speed of GSM for upstream was 14.4 Kbps and for downstream also 14.4 Kbps. The theoretical data speed of GPRS for upstream was 26.8 Kbps and for downstream was 53.6 Kbps.  The theoretical speed of EDGE for upstream is 108.8 Kbps and for downstream is 217.6 Kbps.

3G Network?

3G is the abbreviation for 3rd generation cellular access. With the start of 3G network standard HTML pages including photos and videos are more accessible for remote users. Comparatively, it is faster than 2G standards; which is the protocol used before the introducing of 3G but it is pretty slow compared to a 4G network. 3G networks provide 168.8 Mbps download speed and 23 Mbps upload speed.

LTE

LTE is the abbreviation of Long-Term Evolution. The LTE technology considered to be the part of fourth-generation (4G) network technology. It is considered pre-4G and offers more benefits compared to a 3G network. LTE is allowing the maximum download speed of 100 Mbps and upload speed of 50 Mbps but a big change when compared to a 3G network.

4G Network?

4G is the abbreviation for 4th generation cellular access. It is a faster network than the previous 3G network. The 4G services provide 1000 Mega Bits Per Second (Mbps) speed for downstream and 500 Mbps for upstream.  4G is also known as Long-Term Evolution (LTE-A).

Wireless Internet

Wireless internet

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Wireless internet uses wireless connectivity via radio waves instead of wires on a personnel computer, laptop, smartphone etc. Initial wireless technologies lack the high speed of broadband internet connection e.g cable and DSL, but the latest wireless technologies cover the gap.  Wireless Internet service providers (WISP) typically provide wireless internet services to home users and organizations. The services are provided using radio waves or satellite signals.  Wireless internet connection required a wireless internet modem, wireless access card or internet dongle. WiMax and EV-Do are a common example of wireless internet.

Usually, wireless technologies use the unlicensed radio spectrum for communication which is accessible to anyone who has a wireless router and wireless technology in the device they are using. The main limitation of wireless access is the range which is typically less than 100 feet. The latest developments in broadband wireless technologies are the following.

Wireless internet

Municipal Wi-Fi

Municipal Wi-Fi networks are started in many cities in the world. These networks provide high-speed Internet services for free or for considerably on very fewer prices of other broadband services. Usually, the subscriber needs a Wi-Fi modem with a directional antenna to connect to the municipal Wi-Fi networks. The service providers provide the necessary equipment both for free or for a fee.

Worldwide Interoperability for Microwave Access (WiMAX )

The IEEE standard 802.16 describes WiMAX technology. It provides high-speed broadband internet service with wireless access. It is also provided cell phone services through small Wi-Fi hotspots. The WiMAX provides similar service like Wi-Fi, but at higher speeds including greater distances coverage. The WiMAX uses towers that are similar to cell phone towers. To avail the service of WiMAX the subscribers must subscribe to an ISP with a WiMAX tower within 30 miles of their location including the WiMAX receiver and a special encryption code to get access to the base station.

Satellite Internet

Satellite internet is usually used in remote areas where cable and DSL are not available. A VSAT can be used both for uploading and downloading data. To used satellite Internet services, the user required a satellite dish, two modems for uplink and downlink including the coaxial cables between the dish and the modem.

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