For Dummies CCNA Certification All-In-One
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1. tions Even though serial communications may seem to have a disadvantage compared to parallel transmissions serial communications methods are often faster than parallel communications Cisco uses a 60 pin serial connec tor for one end of the serial transmission cable while the other end of the cable may be EIA TIA 232 EIA TIA 449 EIA TIA 530 V 35 or X 21 ISDN connections Digital technology that transmits integrated voice and data over a publicly switched network ISDN was originally designed to provide private customers and small businesses with high speed Internet access over existing communications infrastructures ISDN BRI Basic Rate Interface is a service that uses two 64 Kbps bearer channels 2B plus one 16 Kbps data channel D used for clocking and is called out of band signaling This basically means that two encapsulation methods are used between the signaling and data channels Console connections A DTE terminal session is established and used to deliver commands to the router via a console connection A rollover cable with an RJ 45 connector is used to connect the PC or terminal to the console port of the Cisco device Introducing Cable Connections Connecting Cisco routers using a DCE to DTE crossover cable Although Cisco routers are considered DTE devices Cisco serial interfaces are DTE by default you can create a simulated lab DCE to DTE WAN environment using two Cisco routers and a DCE to DTE crosso2. 7 and 8 are not used Crossover RJ 45 cable used to connect a source and destination interface directly to one another without the need for a hub or switch The crossover cable cross connects two pairs of wires meaning that each end of the cable is wired differently The white orange and orange solid set of wires is swapped with the white green and green solid set of wires on one end of the cable Pin 1 crosses over to pin 3 and pin 2 crosses to pin 6 This means that one end of the cable is defined as T568A the other specified as T568B A crossover cable may be used to connect pairs of computers hubs switches or routers to one another Rollover Cisco proprietary cables used to connect into the console port of a router or a network switch In an RJ 45 rollover cable the colored wiring on one end of the cable becomes reversed on the other end Pin 1 on one end of the cable connects to pin 8 at the other end of the cable Similarly pin 2 is wired to pin 7 at the other end and so on RJ 45 to DB 9 female Management cable provided with Cisco 600 800 1600 and 1700 series routers Some common uses for unshielded twisted pair cabling in a Cisco wide area networking environment include the following Serial transmission A WAN serial transmission over a single channel consist ing of a single 1 bit data transmission Each bit is transmitted one bit at a time compared to the multiple 8 bit transmission nature of parallel communica
3. Error Control HEC Field used in checksum calculations to determine whether problems exist in the header WAN circuits are categorized into two kinds of connection types Permanent virtual circuits PVCs PVCs establish direct connections between sites and function similarly to a dedicated leased line The MBER KV amp Introducing Cable Connections 815 persistent nature of PVC connections allows for a permanent mode of communications where call setup and termination is not required A PVC connection guarantees an always on communications availabil ity using a manual static setup method Switched virtual circuits SVCs SVCs dynamically generate connections and terminate them after data has been completely transferred function ing similarly to a telephone call A signaling protocol is used between the ATM endpoint and the ATM switch to dynamically control the connection SVCs provide flexibility and call setup to networking devices but require additional time and overhead to set up the connection Both PPP and ATM WAN encapsulation types support asynchronous communications X 25 This is an international WAN protocol family standardized by the ITU s Telecommunication Standardization Sector ITU T that defines how connections are established and maintained between end user devices and networking equipment X 25 network devices are categorized into three types Data terminal equipment DTE DTE devices
4. are customer owned com puters terminals and routers that communicate across the X 25 network Data circuit terminating equipment DCE DCE devices are modems and packet switches that reside between DTE devices and PSEs Packet switching exchange PSE PSEs transfer data between DTE devices over the X 25 network X 25 was designed before the conception of the OSI layer and has been generally replaced by the more efficient Frame Relay technology although X 25 is still used in some ISDN scenarios Introducing Cable Connections Cisco routers use either RJ 45 or DB 25 connectors for DCE DTE console and AUX ports A terminal DTE device or DCE modem may be connected to these ports using an RJ 45 cable and an RJ 45 to DB 25 or RJ 45 to DB 9 connector RJ 45 cabling Unshielded twisted pair UTP cable uses four pairs of eight individual wires twisted together to eliminate electrical interference known as crosstalk UTP cables feature RJ 45 connectors that contain eight connector pins per con nector RJ 45 cables are categorized into these main types Book VII Chapter 1 soiseg Bupjomjay ealy apIM 816 Introducing Cable Connections Straight through Standard network cable used to connect source and destination interfaces between hubs and switches The eight individual wires on both ends of the 8 pin connector are identical Pins 1 and 2 are used for sending data and pins 3 and 6 are used for receiving data Pins 4 5
5. expensive communications methods The most popular types of DSL connections are as follows Asymmetric digital subscriber line ADSL The most common method of DSL communication that transfers both analog and digital information over a pair of copper wires using either POTS or ISDN signals Since a typical home user requires less upstream bandwidth than down stream bandwidth ADSL allocates the majority of the telephone line frequencies to downstream traffic This provides a much larger capacity for Internet downloading while restricting a users upload bandwidth considerably This means data downloads to the end user will occur much faster than data being uploaded from the user to the Internet ADSL line speeds may approach 24 Mbps downstream and 3 5 Mbps upstream with data transmission rates fluctuating based on the Internet service provider ISP and line quality of the link Distance also plays a factor in data rates By using a splitter an ADSL subscriber may simul taneously access both the public switched telephone network PSTN and the Internet on the same twisted pair copper cabling The splitter provides a means to filter between high and low frequencies Two DSL modems or ADSL transceiver units ATUs are used to establish a link One unit located at the service provider s central office is called the ATU C the remote transceiver unit located at the home or business customer is called the ATU R The location where the t
6. number of methods to connect to remote sites such as dedicated telephone lines ATM Frame Relay and satellite links Private WANs may also use public networks to communicate Setting up an encrypted VPN over a local ISP s DSL service or dialup connection is another cost friendly alternative for secure communications 808 Introducing WANs Figure 1 1 WAN Corporate Headquarters Office WAN Mobile User Purpose of WANs A wide variety of options exist to interconnect remote LAN sites LANs are brought together into WANs for the purpose of sharing network resources between authorized users and devices Collaborative data and resource sharing between corporate sites and business partners allows WANs to globally interconnect any business Data terminal equipment DTE and data communications equipment DCE Basic WAN connectivity between the subscriber and provider relies on two types of serial communications devices Data terminal equipment DTE Data communications equipment DCE also known as data circuit terminating equipment A DCE device is typically a modem known as either e Terminal adapter network termination 1 TA NT1 e Channel service unit data service unit CSU DSU Figure 1 2 DTE and DCE devices Introducing WANs 809 These hardware devices are used to establish the WAN communications link and are responsible for translating frames between the local LAN and the ISP or phone company D
7. protocol used to frame and transmit IP datagrams over serial connections See Encapsulation Types B HSSI High Speed Serial Interface HSSI is a proprietary smart serial DTE DCE interface that uses a male subminiature 50 pin connector with a maximum cable length of 50 feet Examine Cisco serial interfaces B E POTS and ISDN The two types of serial circuit switched connections are asynchronous plain old telephone system POTS dialup and synchronous Integrated Services Digital Network ISDN Look over Connection Types Wide Area Networking Basics B D Frame Relay and X 25 are known as packet switched technologies and provide higher bandwidth and cost compared to ISDN and dialup alternatives Check out Connection Types S S amp S A N OVa i i SS D Dedicated leased line A dedicated leased line establishes a permanent link using a point to point serial connection which provides guaranteed bandwidth to remote networks Review Connection Types C ATM Asynchronous Transfer Mode establishes a point to point cell switched WAN that transmits 53 byte packets called cells Refer to Connection Types
8. Book VII Chapter 1 soiseg Hun om yN eaay aPIM 812 Encapsulation Types Cell switched connection A type of point to point packet switched connection that uses digital circuits to transmit 53 byte packets called cells Asynchronous Transfer Mode ATM is an example of a cell switched WAN Encapsulation Types Encapsulation is the wrapping of data in a particular protocol header to suc cessfully transport the data Because IP is a network layer protocol it must be encapsulated when traversing a WAN data link physical layer link Cisco devices support many WAN encapsulation types Each encapsulation type must be manually assigned to a router s serial interface while identically matching the corresponding point to point link on the other end of the connection The configured encapsulation type must be identical between both end points on a single link otherwise communications will not be possible The following sections describe the most popular encapsulation types used on Cisco devices HDLC High Level Data Link Control Cisco s default encapsulation type for serial interfaces HDLC is used to encapsulate packets into frames over established dedicated point to point leased lines HDLC packets are small and use low overhead thus making them quite efficient HDLC also verifies link integrity and communications by implementing keepalives and sequence numbering A downside of HDLC is that it provides no means for authen
9. CE units are located between the DTE device and the transmission link or circuit such as a dedicated leased line The transmission link is the WAN path the data travels to reach other networks DCE devices also control the clock rate for DTE devices DCEs allow the timing for all network devices to remain synchronized by maintaining an accurate bit rate This ensures that all network data is time synchro nized and readable between DCE and DTE devices WAN connectivity would not be possible without the services of both DCE and DTE devices DTEs are known as user side devices usually routers or com puters that interconnect packet switching LANs converting user data into signals that can be interpreted by DCE devices Customer devices that con nect to the telephone company s telco s equipment are known as customer premises equipment CPE The site location where the customer equipment DTE and telephone equipment DCE meet is called the demarcation point demarc An example of the DCE and DTE arrangement is shown in Figure 1 2 f LEON ecco Router Modem A cs DTE DCE Transmission DCE Computer Terminal Medium Telecom DTE Switch Cisco serial interfaces All wide area networks use serial interfaces as a means of transmission Serial transmission allows traffic to flow 1 bit at a time over a single channel or link A few questions must be raised when selecting a serial interface Will the interface
10. Chapter 1 Wide Area Networking Basics Exam Objectives Defining wide area networking y Explaining WAN connection types Describing WAN protocol encapsulation methods Introducing Cisco router cabling standards Identifying AUX and COM port connectors Understanding popular DSL technologies Recognizing the differences between DCE and DTE devices Introducing WANs A wide area network WAN is a connection between two or more local area networks LANs spanning across a large spread out geographical area A single LAN is usually considered to be confined to the same building or office that does not communicate over public transportation methods A metropolitan area network MAN limits its communications to a specific city function or campus area while a WAN uses dedicated leased lines from telephone companies to establish links between geographically dispersed LANs and or MANs WAN technologies are generally represented by the three lower layers of the OSI model namely the network data link and physical layers The Internet is the best example of a WAN and is the largest public network on the planet As you can see in Figure 1 1 private WANs are used to establish permanent communications links between company sites and branch offices Using routers traffic is managed and sent to the proper destination LAN The traffic is then transferred to LAN switching devices until the data reaches the intended recipient Private WANs may use a
11. Point to Point Tunneling Protocol PPTP found in virtual private networks For this reason PPPoE consumes additional bandwidth and resources Cisco Long Range Ethernet LRE A proprietary broadband Ethernet protocol developed by Cisco Systems that connects LANs or individual computers to LRE enabled switches over POTS LRE is based on VDSL technology and supports distances up to 1 5 kilometers over standard phone lines enabling simultaneous voice video and data transfers Cisco LRE products are designed to share lines with analog Integrated Services Digital Network ISDN and digital private branch exchange PBX switch telephones using the 0 to 700 kHz frequency range delivering data rates of 5 15 Mbps This allows Cisco LRE to offer Ethernet like performance using lower quality and older Category 1 2 3 cabling LRE is considered a metropolitan area network protocol and is easy to install and manage Cisco LRE also provides huge speed advan tage over standard Internet dialup connections Router 60 pin serial port connector CSU DSU or other DCE Serial transition cable EIA TIA 232 EIA TIA 449 V 35 X 21 or EIA 530 connector Book VII Chapter 1 soiseg Bupjomjay ealy apIM Prep Test 1 Which types of devices control the clock rate and timing synchronization for WAN interfaces Choose two A O DTE B O ATM C O MTF D O DCE 0 O CSU DS
12. U 2 Which type of cable is required to configure a simulated WAN environment between two routers A O 50 pin HSSI cable B O 60 pin DCE to DTE crossover cable C O CAB 449MT cable D O RJ 45 straight through cable E O RJ 45 to DB 9 female cable 3 What is the name for WAN equipment not located at but connected to the telephone company A O PBX B O Demarc C O Cisco LRE D O Customer premises equipment CPE E O MAN Wide Area Networking Basics 4 Which protocol would be used by an ISP to establish an authenticated customer dialup session A O ATM B O HDLC C O PPPoE D O Frame Relay E O SLIP 5 Which technology uses separate channels for data and signaling A O ISDN B O ADSL C O ATM D O HDLC 6 10 11 Which simplistic nonstandard protocol is used to frame and transmit IP datagrams over serial connections A O ATM B O HDLC C O SLIP D O X 25 Which proprietary interface was developed by Cisco Systems and T3plus Networking for use in high speed WAN link communications A O HDMI B O HSSI C O 60 pin DCE to DTE D O RJ 45 to DB 9 Which technologies are examples of circuit switched connections Choose two A O Dedicated leased line B O POTS C O Frame Relay D O ATM E O ISDN Which technologies are examples of packet switched connections Choose two A O ATM B O Frame Relay C O ISDN D O X 25 Which WAN type provides guaranteed bandwidth over an always on connection A O Packet switc
13. be used by a DTE or a DCE device Which signaling standard does the serial interface require What type of connector is required A DTE device typically has a male connector with pins A DCE device typically has a female connector with holes The two types of proprietary Cisco WAN connectors are as follows Proprietary 60 pin serial connection A WAN connection using a 60 pin serial interface developed by Cisco Systems The opposite end of the Book VII Chapter 1 soiseg Hun om y eaay aPIM 810 Introducing WANs 60 pin serial cable may be EIA TIA 530 EIA TIA 449 EIA TIA 232 V 35 or X 21 standard connectors which I examine in the following section High Speed Serial Interface HSSD A proprietary smart serial DTE DCE interface developed by Cisco Systems and T3plus Networking for use in high speed WAN link communications HSSI operates at the physical layer of the OSI model and uses a male subminiature 50 pin connector with a maximum cable length of 50 feet HSSI provides data transmission rates approaching 52 Mbps by employ ing differential emitter coupled logic ECL ECL technology enables low noise and high speed data communications HSSI uses a series of four loopback tests and two control signals to validate the communications process These communication checks provide handshaking internal self testing and high reliability features DCE serial interfaces Several types of serial interface standards for WAN commu
14. elephone company s copper wires terminate is called the main distribution frame MDF The MDF connects incoming public or private lines to the internal telephone company s network inside a wire rack The digital subscriber line access multiplexer DSLAM is connected to the line at the telephone service provider via the MDF and is used to connect multiple customer DSL con nections to the Internet backbone using multiplexing The DSLAM acts as a Layer 2 switch that collects multiple customer DSL streams and multiplexes the data into a single signal This multiplexed traffic is then sent over the Internet backbone switch called the Network Service Provider NSP at speeds up to 10 Gbps Figure 1 3 shows an example of a typical ADSL setup Figure 1 3 ADSL setup Introducing Digital Subscriber Line DSL Connections 819 PPPoE Point to Point Protocol over Ethernet An OSI Layer 2 protocol used to encapsulate PPP frames inside Ethernet frames PPPoE is typically used by Internet service providers ISPs to allow customers to log on to DSL services using broadband modems Based on the older Point to Point Protocol PPP ISPs use PPPoE to track an IP address to a specific customer s authenticated username and password This allows users to establish a virtual point to point WAN dialup session over Ethernet networks and securely transmit data between endpoints PPPoE uses tunneling for security purposes and is similar to the
15. er data which is processed individually asynchro nously ATM cells are queued before being multiplexed over the connection oriented transmission path Packaging data into smaller fixed size cell units allows jitter reduction and prevents data queuing delays known as contention By preventing contention in applications where timely delivery of data is crucial such as voice and video applications jitter is reduced and overall performance is improved Book VII Chapter 1 soiseg BupjomjaN ealy apIM 8 14 Encapsulation Types ATM is a popular Layer 2 WAN protocol that establishes data link layer com munications over physical Layer 1 circuits The link between endpoints must be established before data transmission may begin Data bit rates of 155 Mbps over CAT5 cable and 622 Mbps using fiber optic cable are possible with ATM network speeds approaching 10 Gbps ATM is more expensive compared to Frame Relay technology An ATM network is comprised of multiple ATM switches interconnected by point to point links which transmits data cells to destination ATM network interface adapters known as the ATM endpoints Examples of ATM end points include CSUs routers switches computers and video coder decod ers codecs Two types of ATM switch interfaces are known as either UNI or NNI UNI interfaces interconnect ATM end systems to ATM switches NNI interfaces connect ATM switches UNI and NNI interfaces are also classified by the owner
16. hed network connection B O Cell switched network connection C O Circuit switched network connection D O Dedicated leased line connection What is the best example of a cell switching technology A O X 25 B O CST C O ATM D O Ethernet g bulysomayy vary apiy sais Answers 1 D E DCE and CSU DSU Data communications equipment DCE also referred to as a channel service unit data service unit CSU DSU controls the timing synchronization for WAN devices Review Data terminal equipment DTE and data communications equipment DCE B A 60 pin DCE to DTE crossover cable is used to establish a simulated DCE to DTE environment using the serial interface between Cisco routers See Cisco serial interfaces and Introducing Cable Connections D Customer premises equipment CPE connects to equipment provided by the telephone company at the demarcation point Refer to Data terminal equipment DTE and data communications equipment DCE C PPPoE Many Internet service providers use PPPoE to authenticate customers using a username and password over dialup connections Take a look at Encapsulation Types A ISDN ISDN BRI Basic Rate Interface is a service using two 64 Kbps bearer channels 2B plus one 16 Kbps data channel D used for clocking and is called out of band signaling Read ntroducing Cable Connections C SLIP Serial Line Internet Protocol is a very simplistic nonstandard
17. ling and adapters The types of cabling and adapters used for Cisco routers are categorized into these main types RS 232 straight through cable Standard serial cable known as CAB R23 This Cisco router cable uses a female DB 25 connector on one end and a male DB 25 connector on the other end Either end may be used by the network or Cisco device depending on DCE or DTE device designation and assignment If the Cisco router is designated as a DCE device the female DB 25 connector is the Cisco end of the cable If the router is des ignated as a DTE device the male DB 25 connector is the Cisco end RJ 45 to DB 9 adapter Connects a router to a PC through a 9 pin COM port 817 Book VII Chapter 1 soiseg Hun om y eaay aPIM 818 Introducing Digital Subscriber Line DSL Connections RJ 45 to DB 25 adapter Connects a router to a PC through a 25 pin serial port Introducing Digital Subscriber Line DSL Connections Digital subscriber line DSL data transfer is the high speed transmission of digital data over standard telephone lines The digital data is transmitted over analog carrier signals using copper wiring DSL technology enables home and small business customers to use the same phone line for both high speed Internet access and telephone services This combination of new DSL technol ogy with older analog signaling POTS allows high speed Internet access with out requiring the installation of newer and more
18. nications have been defined by the Electronic Industries Alliance Telecommunications Industry Association EIA TIA The following connectors may be used to connect to a router s serial port EIA TIA 530 The standard for synchronous balanced and unbalanced serial interfaces using inexpensive DB 25 connectors EIA TIA 530 defines a cabling interface standard between a DTE and DCE device Differential signaling is used to send high speed data over long cable using a combination of send receive clocking control and hand shaking signals to send high speed data over long cabling Even though the EJA TIA 530 standard reduces the amount of signal pins used from a 37 pin connector to a 25 pin connector the most critical electrical sig nals are carried over and maintained on the 25 pin connector EIA TIA 449 A synchronous serial interface standard used for data net working communications that uses a smaller and less expensive connec tor than V 35 types EIA TIA 449 signals may travel greater distances than the EIA TIA 232 standard and support data transfer rates up to 2Mbit s The Cisco CAB 449MT cable uses a male DB 60 pin connector Cisco end to a male DB 37 pin connector network end EJA TIA 232 An asynchronous serial interface that uses 9 pin DB 9 and 25 pin DB 25 connectors popular on all types of DCE DTE equipment per sonal computers modems terminals and older printers The EIA TIA 232 standard is used to transfe
19. of the interface The telephone company is assigned publicly owned interfaces with private equipment being assigned to the end user and is known as customer premises equipment CPE The ATM cell headers are defined in either UNI or NNI format depending on the type of interface used Some of the ATM cell header fields are as follows Generic Flow Control GFO Field used to identify two or more devices on an ATM network that are using the same ATM interface multiplexing Virtual Path Identifier VPD and Virtual Channel Identifier YCD Fields used in determining the ATM cell destination while in transit through an ATM switched network Cells are tagged with VPI and VCI values A local translation table determines the port address of a particular destination based on the VPI and VCI values Payload Type PT Field used to show the type of data carried Data may be either user data or control data If the cell is transporting user data the first bit is always set to 0 The bit value changes to 1 when control data is used The second bit in the payload type is assigned for congestion A 0 bit value represents no congestion and a 1 bit is used to register network congestion If the third bit is on a 1 bit the cell is marked as the last cell in a frame Cell Loss Priority CLP Field responsible for management of buffering If the CLP bit equals 1 the cell will be dropped when congestion on the network is discovered Header
20. otocol LCP Manages initial link setup handshake negotiations and ongoing connections during PPP communications LCP also manages the termination of point to point links SLIP Serial Line Internet Protocol SLIP is a very simplistic nonstandard protocol used to frame and transmit IP datagrams over serial connections Due to its inflexible design SLIP does not provide additional features such as encryption authentication or error detection and has been widely replaced by PPP Frame Relay Frame Relay is a high performance packet switching WAN protocol originally designed for use with ISDN which has superseded X 25 Frame Relay uses HDLC encapsulation between connected devices at T 1 1 544 Mbps and T 3 45 Mbps speeds but is relatively inexpensive compared to ATM or dedicated leased lines Frame Relay is an OSI Layer 2 protocol that relies on the upper layer protocols to handle flow control and error correction responsibilities Frame Relay uses virtual circuits to multiplex multiple connections over a single transmission link between DTE and DCE devices Service providers assign connection i dentifiers to customer DTE devices and map them to outgoing ports ATM Asynchronous Transfer Mode ATM is packet switching digital transmission technology that sends voice video and data signals using 53 byte fixed length cell relay between end points over a virtual circuit An ATM cell contains a 5 byte header anda 48 byte payload us
21. r binary data between a DCE and DTE device Generally computer serial ports use DTE male pins and DCE devices such as modems and other networking equipment employ female connectors Male to female and female to male gender changers are available EIA TIA 232 cable lengths are restricted to 50 feet 15 meters Connection Types 811 V 35 The OSI physical layer ITU partially balanced standard that sup ports high speed data rates up to 2 048 Mbps but used mostly for 56kbps and 64kbps communications V 35 is a standard for synchronous serial interfaces that has become obsolete in favor of EIA TIA 449 but it continues to be used and remains popular today V 35 eliminates line noise by separately twisting the indi vidual wires carrying data and clock information Connection Types Various connection types are available when designing a WAN connection Each type provides advantages and disadvantages that must be understood prior to implementation Defining an organization s WAN traffic flow requirements is crucial to the success of the WAN design The four common types of WAN connections available are as follows Dedicated leased line connection An individual point to point serial connection that uses a permanently established link to provide guar anteed bandwidth between remote networks These dedicated circuits provide up to 44 736 Mbps speeds over a public carrier s T 1 or T 3 lines These types of high speed connections a
22. re always on and have the advantage of minimum overhead compared to other connection types Also this persis tent connection does not require continuous setup and tear down between communication phases The disadvantage of dedicated leased lines is cost fac tored by distance between links and the amount of bandwidth assigned to the single link because they are more expensive that other connection types Circuit switched connection The most popular type of WAN connection in which a physical circuit is established as needed between two endpoints for the duration of the connection This type of connection requires call setup of the link to occur before any communications may begin The physi cal lines remain unavailable for other users until the connection is dropped The two types of serial circuit switched connections are e Asynchronous plain old telephone system POTS dialup e Synchronous Integrated Services Digital Network ISDN Packet switched connection A point to point virtual circuit connection established using a public carrier s network allowing multiple customers to share carrier resources The sharing of packet switched connections between customers remains transparent to the end user Packet switched connections provide high bandwidth and reduced cost compared to dedicated leased lines but are more expensive than ISDN and dialup connections Frame Relay and X 25 are known as packet switched technologies
23. tication The original HDLC specification outlined by the International Organization for Standardization ISO did not provide simultaneous support for multiple net work layer protocols Independent vendors took it upon themselves to make improvements to the HDLC protocol which introduced new functionality and incorporated the use of multiple Layer 3 protocols Cisco s proprietary ver sion of HDLC known as cHDLC is a synchronous bit oriented protocol which adds a new frame field in the packet header to allow for multi protocol sup port cHDLC uses a link keepalive method called Serial Line Address resolu tion Protocol SLARP to verify connection availability and integrity HDLC encapsulation is the default assignment for serial interfaces If a non HDLC encapsulation type is required for link establishment it must be manu ally configured by the network administrator on both sides of the link PPP Point to Point Protocol PPP encapsulates network layer packets and transmits frames over Layer 2 connections used by point to point dedicated circuits and asynchronous Encapsulation Types 8 13 dialup and ISDN links PPP features include connection authentication encryption and compression Two basic PPP sublayers are as follows Network Control Protocol NCP Encapsulates heterogeneous network layer protocols over PPP This allows multiple dissimilar protocols to be transmitted by NCP over the PPP link Link Control Pr
24. ver cable Because channel service unit data service unit CSU DSU devices DCEs control the timing clocking for synchronous serial interfaces one Cisco router must be configured as a DCE device Each router s serial interface should be configured depending on which end of the DB 60 cable is plugged in One interface configured as a DCE and the other end as the DTE device Make sure that both routers serial interfaces are configured with the no shutdown command and the proper IP addressing information and then configure clocking on the DCE device RouterDCE config if clock rate 64000 Before connecting a terminal to the console port configure the terminal to match the router console port settings typically 9600 baud 8 data bits This command sets the clock rate to 64 000 bits per second Because no error message was generated by the router the command executed successfully What would happen if the same clocking command was mistakenly executed on the DTE device RouterDTE config if clock rate 64000 Error This command applies only to DCE interfaces oe The show controllers command display output allows an administrator to view which interfaces are set up for DCE or DTE operation RouterDTE show controllers serial 0 inD wane il alg OR EDON driver structure at 0x124140 buffer size 1524 HD unit 1 V 35 DTE cable no parity and either 1 or 2 stop bits depending on the router model DB 25 cab
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