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Chapter 6 Wide Area Networking
Wide area networks (WANs)  <ul><li>Provide data communications that traverse a broad geographic area.  </li></ul><ul><li>W...
Point-to-point WANs <ul><li>A point-to-point connection in a WAN is not a typical direct connection. Rather, it’s a pre-es...
Switching Methods  <ul><li>Circuit switching </li></ul><ul><li>Packet switching </li></ul><ul><li>Cell switching </li></ul>
Circuit Switching <ul><li>Circuit-switched networks use temporary paths created through the network along which to transmi...
Circuit Switching <ul><ul><li>Permanent virtual circuits (PVC) </li></ul></ul><ul><ul><ul><li>dedicated path between two p...
Packet Switching  <ul><li>The carrier creates virtual circuits, a system that specifies a path between specific sites, wit...
Packet Switching  <ul><li>Each packet is transmitted in a store-and-forward process.  </li></ul><ul><ul><li>When a router ...
Packet Switching  <ul><li>Because packet-switched protocols provide for error checking and flow control, packet switching ...
Cell Switching <ul><li>Cell switching is a form of packet switching.  </li></ul><ul><li>The main difference between a pack...
Cell Switching <ul><li>An example of a cell-switched network is Asynchronous Transfer Mode (ATM). </li></ul><ul><li>The ce...
ISDN  <ul><li>developed as the digital offering by the telephone companies to run over the existing telephone copper wirin...
ISDN  <ul><li>Basic Rate Interface (BRI): Used for home and small office connectivity.  </li></ul><ul><li>BRI services inc...
ISDN  <ul><li>Primary Rate Interface (PRI): Used for WANs and runs across leased lines.  </li></ul><ul><li>The PRI service...
ISDN  <ul><li>A computer with an ISDN line is able to connect to any other computer that also uses ISDN simply by dialing ...
Using Fiber Optics with FDDI  <ul><li>Light signals are capable of traveling long distances, and fiber optics aren’t subje...
Using Fiber Optics with FDDI  <ul><li>Both multimode and single mode fiber optics transmit light signals.  </li></ul><ul><...
Using Fiber Optics with FDDI  <ul><li>FDDI’s dual ring structure enables traffic to flow on each ring, but in opposite dir...
Using Fiber Optics with FDDI
Using Fiber Optics with FDDI  <ul><li>FDDI is a physical and data-link layer protocol.  </li></ul><ul><li>Upper-layer prot...
Gaining WAN Speed with ATM  <ul><li>WANs are typically slow. They are transmitted across long distances over networks that...
Gaining WAN Speed with ATM <ul><li>ATM is a network made up of a series of ATM switches (also called ATM routers) and ATM ...
Gaining WAN Speed with ATM
Gaining WAN Speed with ATM <ul><li>ATM is a connection-oriented protocol in which the two ATM end points must establish a ...
The ATM Model <ul><li>Three layers in the ATM networking model map roughly to the physical and data-link layers of the OSI...
ATM physical layer <ul><li>The ATM physical layer is concerned with transmission of bit-stream data on the physical media....
The ATM layer <ul><li>Creates the virtual connection between the sending and receiving node and then switches the ATM cell...
The ATM layer
The ATM adaptation layer <ul><li>Receives the packets from upper-layer processes and translates them into ATM cells.  </li...
Frame Relay <ul><li>Widely applied WAN protocol that uses packet switching.  </li></ul><ul><li>Originally designed to run ...
Frame Relay <ul><li>Even though frame relay was designed to transmit across ISDN, it has since been updated to transmit da...
Frame Relay <ul><li>Frame relay supplies data-link and physical layer services. </li></ul><ul><li>Both permanent virtual c...
Frame Relay
Frame Relay <ul><li>Data Link Connection Identifiers (DLCI) are key to frame relay connections.  </li></ul><ul><li>The DLC...
Frame Relay <ul><li>Controlling Congestion </li></ul><ul><ul><li>Congestion is one problem that can occur in a cloud netwo...
Frame Relay <ul><li>The frame relay protocol includes 3 bits in the address of each frame relay frame header to manage con...
Frame Relay <ul><li>Given that congestion does exist in the frame relay network, the carrier provides a guaranteed minimum...
Frame Relay <ul><li>Not only is frame relay flexible because of its ability to burst extra traffic, but its data transmiss...
SONET/SDH <ul><li>The Synchronous Optical Network (SONET), or Synchronous Digital Hierarchy (SDH) as it’s known in Europe,...
SONET/SDH <ul><li>SONET is a global standard focusing on synchronous communications that are multiplexed.  </li></ul><ul><...
SONET/SDH <ul><li>SONET’s basic transmission rate, Synchronous Transport Signal level 1 (STS-1), also considered Optical C...
SONET/SDH
T-Carrier System  <ul><li>The T-carrier system is a series of data transmission formats developed by Bell Telephone for us...
T-Carrier System  <ul><li>T1/E1  </li></ul><ul><ul><li>T1 and E1 lines are each multiples of DS0 signals. The T1 line prov...
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Chapter 6

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Chapter 6

  1. 1. Chapter 6 Wide Area Networking
  2. 2. Wide area networks (WANs) <ul><li>Provide data communications that traverse a broad geographic area. </li></ul><ul><li>WANs typically utilize the transmission infrastructure provided by a third party such as a telephone company. </li></ul><ul><li>WAN technologies function at the lowest three layers of the OSI reference model. </li></ul><ul><li>WANs consist of physical media and connectors at the physical layer, physical addressing and media access at the data-link layer, and routing at the network layer. </li></ul>
  3. 3. Point-to-point WANs <ul><li>A point-to-point connection in a WAN is not a typical direct connection. Rather, it’s a pre-established path from one site to another that passes through a carrier network. </li></ul><ul><li>A point-to-point connection, including wiring and hardware, is usually rented from a carrier and thus called a leased line . </li></ul>
  4. 4. Switching Methods <ul><li>Circuit switching </li></ul><ul><li>Packet switching </li></ul><ul><li>Cell switching </li></ul>
  5. 5. Circuit Switching <ul><li>Circuit-switched networks use temporary paths created through the network along which to transmit data. </li></ul><ul><li>There are two types of virtual circuits: </li></ul><ul><ul><li>permanent virtual circuits (PVC) </li></ul></ul><ul><ul><li>switched virtual circuits (SVC) </li></ul></ul>
  6. 6. Circuit Switching <ul><ul><li>Permanent virtual circuits (PVC) </li></ul></ul><ul><ul><ul><li>dedicated path between two points used when data communications must take place 24 hours a day, 7 days a week. A PVC is similar to a telephone call that never ends. (more expensive option) </li></ul></ul></ul><ul><ul><li>Switched virtual circuits (SVC) </li></ul></ul><ul><ul><ul><li>SVCs are established on demand and ended when the communication is complete. SVCs are often called a dialup service because the SVC is established just like a telephone call and terminated in the same way. SVCs are used when the need to transfer data is sporadic. (circuit must be established & terminated each time data is sent, requiring some overhead) </li></ul></ul></ul>
  7. 7. Packet Switching <ul><li>The carrier creates virtual circuits, a system that specifies a path between specific sites, within its network. </li></ul><ul><li>The path is not dedicated, however, and data can flow across different routers but still arrive at the same destination. </li></ul><ul><ul><li>FLASH VIDEO </li></ul></ul>
  8. 8. Packet Switching <ul><li>Each packet is transmitted in a store-and-forward process. </li></ul><ul><ul><li>When a router receives a packet, it stores the packet temporarily. After reviewing the packet’s address information, the router forwards the packet. </li></ul></ul><ul><ul><li>The time that it takes to store the packet causes a slight latency in the transmission. </li></ul></ul>
  9. 9. Packet Switching <ul><li>Because packet-switched protocols provide for error checking and flow control, packet switching is very efficient. </li></ul><ul><li>The virtual circuit minimizes the connection time between any two systems, reducing the load on the network. </li></ul><ul><li>Because virtual circuits are closed after each packet is forwarded, a router is available to accept information from a router for a different virtual circuit. </li></ul><ul><ul><li>Voice over IP (VoIP) phone calls use this </li></ul></ul>
  10. 10. Cell Switching <ul><li>Cell switching is a form of packet switching. </li></ul><ul><li>The main difference between a packet-switched network and a cell-switched network is the size of the cell. </li></ul><ul><li>Cells are extremely small and do not vary in size. Their size makes them fast and provides for a network with a low latency. </li></ul>
  11. 11. Cell Switching <ul><li>An example of a cell-switched network is Asynchronous Transfer Mode (ATM). </li></ul><ul><li>The cell in an ATM network is 53 bytes in length, including the data portion. </li></ul><ul><li>Because a cell does not vary in size, each router in the cell-switched network knows how much data to expect with each cell and is built to take advantage of it. </li></ul><ul><li>The tiny cell is small enough to be stored in random access memory, whereas a packet-switching router must store a packet to disk. </li></ul><ul><li>Because the router need only switch the cell in and out of its fastest memory, there is little latency in a cell-switched network. </li></ul>
  12. 12. ISDN <ul><li>developed as the digital offering by the telephone companies to run over the existing telephone copper wiring. </li></ul><ul><li>ISDN allows subscribers to transmit data, voice, and multimedia. </li></ul>
  13. 13. ISDN <ul><li>Basic Rate Interface (BRI): Used for home and small office connectivity. </li></ul><ul><li>BRI services include two B channels and a single D channel. </li></ul><ul><li>A B channel offers 64 Kbps and carries user data. A BRI D channel operates at 16 Kbps and carries control and signaling information. </li></ul><ul><li>Through these two channels, a home connection can reach 128 Kbps of data throughput. </li></ul>
  14. 14. ISDN <ul><li>Primary Rate Interface (PRI): Used for WANs and runs across leased lines. </li></ul><ul><li>The PRI service is composed of 23 B channels at 64 Kbps each for user data, along with a single D channel, also operating at 64 Kbps to handle control information. </li></ul><ul><li>Overall, the PRI service provides a throughput rate of 1.544 Mbps. </li></ul>
  15. 15. ISDN <ul><li>A computer with an ISDN line is able to connect to any other computer that also uses ISDN simply by dialing its ISDN number. </li></ul><ul><li>Terminal adapter (TA): Also called an ISDN modem, this is either an internal or external adapter to connect equipment to an ISDN line. </li></ul><ul><ul><li>Question: Why is this device not really a MODEM? </li></ul></ul>
  16. 16. Using Fiber Optics with FDDI <ul><li>Light signals are capable of traveling long distances, and fiber optics aren’t subject to either electromagnetic interference or radio frequency interference. </li></ul><ul><li>Fiber Distributed Data Interface (FDDI) is the American National Standards Institute (ANSI) specification for a 100-Mbps token-passing dual ring network over fiber optic cable and is often used as a backbone for a campus network because it can attain distances up to two kilometers with multimode fiber or farther with single-mode fiber. </li></ul>
  17. 17. Using Fiber Optics with FDDI <ul><li>Both multimode and single mode fiber optics transmit light signals. </li></ul><ul><ul><li>Multimode fiber uses a light emitting diode (LED) to transmit the signals. </li></ul></ul><ul><ul><li>Single mode fiber depends on lasers. </li></ul></ul>
  18. 18. Using Fiber Optics with FDDI <ul><li>FDDI’s dual ring structure enables traffic to flow on each ring, but in opposite directions </li></ul><ul><ul><li>one runs clockwise and the other counterclockwise. </li></ul></ul><ul><li>One of the rings is considered primary, the other secondary. </li></ul><ul><li>The primary ring is used for data transmission. </li></ul><ul><li>Because fiber optic cables are brittle, the secondary ring acts as a backup in case of a break in the primary ring. </li></ul>
  19. 19. Using Fiber Optics with FDDI
  20. 20. Using Fiber Optics with FDDI <ul><li>FDDI is a physical and data-link layer protocol. </li></ul><ul><li>Upper-layer protocols such as TCP/IP and IPX/SPX can run across a FDDI ring. </li></ul><ul><li>The FDDI frame is similar to a token ring frame format. There are two frames: the token frame and the data frame. </li></ul><ul><li>The FDDI data frame can become as large as 4500 bytes in length. </li></ul>
  21. 21. Gaining WAN Speed with ATM <ul><li>WANs are typically slow. They are transmitted across long distances over networks that traditionally were unreliable. </li></ul><ul><li>As a result, the oldest WAN technologies were loaded with failsafe measures, such as error checking, and were clocked to match the slowest expected link. </li></ul><ul><li>Demand for greater data throughput was one of the driving forces behind Asynchronous Transfer Mode (ATM). </li></ul>
  22. 22. Gaining WAN Speed with ATM <ul><li>ATM is a network made up of a series of ATM switches (also called ATM routers) and ATM nodes. </li></ul><ul><li>The ATM nodes can be routers that connect the ATM network to another type of network, such as an Ethernet LAN. </li></ul><ul><li>Any ATM node can communicate with any other ATM node by transmitting data across the ATM network. </li></ul>
  23. 23. Gaining WAN Speed with ATM
  24. 24. Gaining WAN Speed with ATM <ul><li>ATM is a connection-oriented protocol in which the two ATM end points must establish a connection before transferring data. </li></ul><ul><li>Each ATM cell consists of 53 total bytes, including the data. The header is 5 bytes in length, with 48 bytes of data. </li></ul>
  25. 25. The ATM Model <ul><li>Three layers in the ATM networking model map roughly to the physical and data-link layers of the OSI reference model: </li></ul><ul><ul><li>ATM physical layer </li></ul></ul><ul><ul><li>ATM layer </li></ul></ul><ul><ul><li>ATM adaptation layer </li></ul></ul>
  26. 26. ATM physical layer <ul><li>The ATM physical layer is concerned with transmission of bit-stream data on the physical media. </li></ul><ul><li>This layer is divided into logical sublayers. </li></ul><ul><ul><li>The physical medium sublayer commands the sending and receiving of the bit stream and uses timing information to synchronize the transmitted data. </li></ul></ul><ul><ul><li>The physical medium sublayer is dependent on the type of cabling used. ATM can transmit across SONET and T3/E3, fiber optics, shielded twisted pair (STP), and unshielded twisted pair (UTP). </li></ul></ul>
  27. 27. The ATM layer <ul><li>Creates the virtual connection between the sending and receiving node and then switches the ATM cells through the virtual path. </li></ul><ul><li>When two virtual connections temporarily share the same path, the ATM layer will multiplex the cells to be able to transmit them as a single bit stream, and then demultiplex the cells when the virtual connections split off into two different directions. </li></ul>
  28. 28. The ATM layer
  29. 29. The ATM adaptation layer <ul><li>Receives the packets from upper-layer processes and translates them into ATM cells. </li></ul><ul><li>These upper-layer packets can come from AppleTalk, TCP/IP, or IPX/SPX. </li></ul>
  30. 30. Frame Relay <ul><li>Widely applied WAN protocol that uses packet switching. </li></ul><ul><li>Originally designed to run across ISDN interfaces. </li></ul><ul><li>The frame relay protocol provides an efficient data transmission, even though the packets vary in length. </li></ul><ul><li>The variable length of the packets makes data transmission very flexible. </li></ul>
  31. 31. Frame Relay <ul><li>Even though frame relay was designed to transmit across ISDN, it has since been updated to transmit data across a variety of different protocols. </li></ul><ul><li>Most of the data transmission takes place within the carrier’s network, also called a cloud, which provides for congestion signaling, physical media, and switching. </li></ul>
  32. 32. Frame Relay <ul><li>Frame relay supplies data-link and physical layer services. </li></ul><ul><li>Both permanent virtual circuits (PVC) and switched virtual circuits (SVC) can be used. It is most common to find frame relay with PVCs. </li></ul>
  33. 33. Frame Relay
  34. 34. Frame Relay <ul><li>Data Link Connection Identifiers (DLCI) are key to frame relay connections. </li></ul><ul><li>The DLCI identifies the point-to-point link that begins the virtual circuit to the cloud. </li></ul><ul><li>It is a logical connection, because a single interface can transmit to different DLCIs. </li></ul><ul><li>It’s easiest to think of a DLCI as a phone number. When transmitting data across frame relay, the interface into the cloud will specify the destination by its DLCI in the same way that a telephone call identifies the recipient by that recipient’s telephone number. </li></ul>
  35. 35. Frame Relay <ul><li>Controlling Congestion </li></ul><ul><ul><li>Congestion is one problem that can occur in a cloud network shared by multiple customers. Because the switches can participate in any number of virtual circuits, they can become overloaded by traffic. </li></ul></ul>
  36. 36. Frame Relay <ul><li>The frame relay protocol includes 3 bits in the address of each frame relay frame header to manage congestion. </li></ul><ul><li>The first bit is called the Forward Explicit Congestion Notification (FECN). When this bit is set to a one (1) value, it means that the frame encountered congestion. A router that receives a frame with the FECN bit set to 1 will send a reply frame with a different bit named the Backward Explicit Congestion Notification (BECN). Both the FECN and BECN bits are used to notify upper-layer protocols of congestion so that they can initiate flow-control mechanisms to reduce data transmissions. </li></ul><ul><li>The third congestion control bit, the Discard Eligibility (DE) bit, is assigned to unimportant frames. Frames with the DE bit set to 1 are discarded when there is congestion on the network. This is an additional method to help manage high-traffic situations within the frame relay cloud. </li></ul>
  37. 37. Frame Relay <ul><li>Given that congestion does exist in the frame relay network, the carrier provides a guaranteed minimum data transmission speed: the committed information rate (CIR). </li></ul><ul><li>A benefit of frame relay is that bursts of speed up to double the CIR level are generally allowed by the carrier network, but only for short periods of time. </li></ul><ul><li>Bursting is available only during non-congested time periods when extra bandwidth is available. </li></ul>
  38. 38. Frame Relay <ul><li>Not only is frame relay flexible because of its ability to burst extra traffic, but its data transmission rates are also dependent solely on configuration. </li></ul><ul><li>A frame relay link can be installed and configured at a lower speed (and at a lower cost) using the same equipment that is used for a much faster link. </li></ul><ul><li>If a link needs to be upgraded because of an increased need for bandwidth, or downgraded because bandwidth is no longer required, the carrier needs only to make a configuration change. </li></ul>
  39. 39. SONET/SDH <ul><li>The Synchronous Optical Network (SONET), or Synchronous Digital Hierarchy (SDH) as it’s known in Europe, offers the ability to construct large-scale, high-speed IP networks over fiber optics. </li></ul><ul><li>The SONET topology can be either a dual ring architecture or a star. The dual ring is preferable because it can be reconfigured in case of a break in the fiber optic cable to ensure the network’s survivability. </li></ul><ul><li>SONET is often used for Internet and large internetwork backbone services. </li></ul><ul><li>Using time division multiplexing (TDM), SONET is capable of providing high-bandwidth capacity for data transmission as well as voice traffic and even cable television. </li></ul>
  40. 40. SONET/SDH <ul><li>SONET is a global standard focusing on synchronous communications that are multiplexed. </li></ul><ul><li>In synchronous networking, all the clocks are synchronized to the same time. </li></ul><ul><li>The time division multiplexing enables signals from slower networks to be intermingled directly with SONET signals as they are moved onto the SONET network. </li></ul><ul><li>This is also partially because of the advanced network management and maintenance features inherent in SONET. </li></ul>
  41. 41. SONET/SDH <ul><li>SONET’s basic transmission rate, Synchronous Transport Signal level 1 (STS-1), also considered Optical Carrier 1 (OC1), is 51.84 Mbps. The SONET multiplexing scheme can transmit at rates that are multiples of 51.84 Mbps. </li></ul>
  42. 42. SONET/SDH
  43. 43. T-Carrier System <ul><li>The T-carrier system is a series of data transmission formats developed by Bell Telephone for use in the telephone network system in North America and Japan. </li></ul><ul><li>The base unit of a T-carrier is DS0, which is 64 Kbps. </li></ul><ul><li>The T-carrier system uses in-band signaling, a method that actually robs bits from being used for data and uses them instead for overhead. </li></ul><ul><li>This reduces the transmission rates used for T-carrier signals. The E-carrier system used in Europe doesn’t perform bit-robbing and as a result has a higher throughput rate. </li></ul>
  44. 44. T-Carrier System <ul><li>T1/E1 </li></ul><ul><ul><li>T1 and E1 lines are each multiples of DS0 signals. The T1 line provides 1.544 Mbps, while the E1 line provides 2.048 Mbps. The difference in data rates results from the T-carrier system’s method of bit-robbing. </li></ul></ul><ul><ul><li>Customers can purchase fractional-T1 lines, which are actually multiples of the DS0 signal. With Frac-T1, the customer rents a number of the 24 channels within a T1 line. The remaining channels go unused. For example, a Frac-T1 line can be 128 Kbps, 256 Kbps, 512 Kbps, and so on. </li></ul></ul><ul><li>T3/E3 </li></ul><ul><ul><li>T3 lines are digital carriers, equivalent to 28 T1 lines, that can transmit at the rate of 44.736 Mbps. E3 lines provide 16 E1 lines, with a transmission rate of 34.368 Mbps. </li></ul></ul>

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