Tài liệu Basic Networking Technologies docx

1 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ 4 Basic Networking Technologies Terms you’ll need to understand: ✓ Media Access Control (MAC) addressing ✓ Ethernet 802.3 ✓ Ethernet_II ✓ Fast Ethernet ✓ Gigabit Ethernet ✓ Token Ring 802.5 ✓ Fiber Distributed Data Interface (FDDI) ✓ Copper Distributed Data Interface (CDDI) ✓ Carrier Sense Multiple Access with Collision Detect (CSMA/CD) ✓ Beaconing ✓ Ring insertion ✓ Ring monitor ✓ Dual homing ✓ H.323 ✓ Signaling System 7 (SS7) ✓ Realtime Transport Protocol (RTP) ✓ RTP Control Protocol (RTCP) ✓ Quality Of Service (QOS) Techniques you’ll need to master: ✓ Describing layer 2 MAC addresses ✓ Working with Ethernet, Token Ring, and FDDI characteristics and limitations ✓ Understanding basic multiservice theory 2 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Chapter 4 This chapter concentrates on the characteristics and limitations of the different types of Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI) technologies. After reviewing each of these technologies, the chapter briefly turns to voice and video communications that can be delivered over existing data net- works. These topics are called Multiservice Services by Cisco. The following CCIE blueprint objectives as determined by the Cisco Systems CCIE program are covered in this chapter: ➤ Data Link layer—MAC addressing and IEEE 802.2 standards ➤ Ethernet/Fast Ethernet/Gigabit Ethernet—Encapsulation, Carrier Sense Mul- tiple Access with Collision Detect (CSMA/CD), topology, speed, controller errors, limitations, and the IEEE 802.3 standards ➤ Token Ring—Token passing, beaconing, active monitor, ring insertion, soft and hard errors, topology, maximum transmission unit (MTU), speed, limitations ➤ FDDI/CDDI—Dual ring, encapsulation, class, redundancy, dual homing, medium (including copper and fiber), claims, station management (SMT), limitations ➤ Voice/Video—H.323, codecs, Signaling System 7 (SS7), Realtime Transport Protocol (RTP), RTP Control Protocol (RTCP), Quality Of Service (QOS) Additional information is provided for completeness and in preparation for addi- tional subjects as the CCIE program expands. We will begin by discussing what makes up a MAC address. MAC Addressing All devices that operate over a physical LAN medium require a unique address, called the Media Access Control (MAC) address. The MAC address is also some- times referred to as the physical address, burned-in address (BIA), or hardware address. A MAC address is assigned to each hardware device that connects to a LAN, such as an Ethernet NIC. In Token Ring networks, the MAC address can be set in software. In IEEE 802 networks, the Data Link Control (DLC) layer of the OSI reference model is divided into two sublayers: the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. Figure 4.1 displays the location of the LLC sublayer and the MAC sublayer in relation to the OSI model. LLC Sublayer Functions The LLC sublayer provides networks with connection or connectionless enviroments. The LLC sublayer simply sits on top of all 802.x protocols and provides a service to the Network layer. 3 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Basic Networking Technologies Using IP as an example, we know that IP is a connectionless service, but the role of the LLC sublayer is to identify that an IP packet is carried in the data portion of the frame. The IP software then looks further into the frame to locate the header information and the IP address. MAC Sublayer Functions The MAC sublayer simply provides access to the Physical layer, whether Ethernet or any other medium is in use. To allow this communcaition each device must have a unique address. To enable all devices to have a unique address or MAC address, the network interface cards have a unique MAC address located in Read Only Memory (ROM). This unique address allows communication between devices regardless of the physical medium. Let’s now describe the format of the MAC address. MAC addresses are 48 bits long, and they are expressed primarily in two formats: ➤ 0060.7015.5e4d ➤ 00-60-70-15-5e-d4 The first byte, or octet, of a MAC address also contains two reserved bits that are used to identify what destination device or devices are intended to be the recipent of the frame: ➤ I/G—Individual/Group ➤ L/G—Local/Global Layer 2 frames can be directed to one (I bit) or more devices (G bit). The Local/ Global bit defines whther the address is the burned in address or a locally as- signed address. OSI Model IEEE 802 Network Network Data Link Physical Logical Link Control Media Access Control Figure 4.1 IEEE 802 DLC. 4 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Chapter 4 Canonical vs. Non-Canonical The IEEE refers to MAC addresses as Universal Addresses. The IEEE also specified that when the bits are sent across the Ethernet Physical layer the least significant bit is transmitted first. This is referred to as non-canonical . Token Ring is canonical, which means that the most significant bit is transmiited first. Let’s look at a simple example of sending the number 1 (decimal) across an Ethernet network. The num- ber 1 in binary is 00000001. The non-canonical format of this is 10000000. This means that on the Ethernet wire the bits 10000000 will be reversed by the receiving device back to 00000001. The majority of modern networks use a 48-bit addressing scheme or plan. MAC addresses are represented using the hexadecimal numbering system. The first 24 bits represent the manufacturer’s identification, vendor’s code, or the organiza- tion unique identifier (OUI). The next 24 bits typically provide a serial number assigned by the vendor. To illustrate, here is an example of a Cisco MAC address: 006070-155e4d In the preceding address, 00-60-70 (24 bits) identifies Cisco as the manufacturer or vendor code, and 15-5e-4d (24 bits) identifies the serial number assigned by Cisco. Manufacturers such as Cisco may have more than one OUI. For instance, Cisco Systems has more than 20 OUIs from the IEEE. Frames sent to MAC addresses can be classified as being sent to either unicast, multicast, or broadcast addresses: ➤ Unicast Frame—A frame destined for a specific device. In the destination address, a unicast frame will appear as 0xxxxxxx in the first byte. ➤ Multicast Address—A special address reserved for communication among a group of devices. For example, 1xxxxxxx in the first byte. ➤ Broadcast Address—An address destined for all devices on the wire. For ex- ample, FF-FF-FF-FF-FF-FF in the destination field indicates all devices must read the frame. Note that all frames will have their source MAC address as a single node (unicast). Ethernet, Fast Ethernet, and Gigabit Ethernet Ethernet is one of the most popular local area network (LAN) technologies used today. Ethernet can operate at three speeds: 5 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Basic Networking Technologies ➤ Ethernet—Allows transmission speeds of 10Mbps ➤ Fast Ethernet—Allows transmission speeds of 100Mbps ➤ Gigabit Ethernet—Allows transmission speeds of 1,000Mbps 10 Gigabit Ethernet is coming soon. The networking industry has formed a coalition to make 10G a reality. Originally, Ethernet started when the Xerox Corporation released a method of allowing devices to share a common medium and communicate together. Table 4.1 shows a summary of Ethernet’s recent evolution. In this section, we’ll review the three main Ethernet types, starting with a discus- sion about traditional Ethernet. Ethernet 802.3 and Ethernet_II Ethernet has two versions available—Ethernet 802.3 and Ethernet_II. The main difference between Ethernet 802.3 and Ethernet_II can be found within the frame formats, as discussed later in this section. Original Ethernet and then the second version called Ethernet_II was jointly developed by the Digital Equip- ment Corporation, Intel, and Xerox Corporation, also know as the DIX Consor- tium. Ethernet 802.3 is the standard defined by the IEEE. The Ethernet specifications also define the frame sizes as follows: ➤ Minimum Ethernet Frame Size—64 bytes ➤ Maximum Ethernet Frame Size—1,514 bytes Table 4.1 Ethernet history. Date Timeline Event 1972 Work begins on Ethernet by Xerox 1980 Ethernet released 1982 Version II released by DIX (Digital, Intel, and Xerox) 1985 IEEE 802.3 Ethernet Standard is released 1994 Transmission of Ethernet over twisted pair wiring is released 1995 Fast Ethernet 1998 Gigabit Ethernet 6 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Chapter 4 When running IP, Ethernet_II is the default transmission method for Cisco Routers. Both Ethernet 802.3 and Ethernet_II are shared physical media technologies. This means that when an end device on an Ethernet network needs to send data, it first must wait to see if the physical medium is not being used before transmis- sion can commence. The end device will listen to the wire using its ability to carrier sense, which is part of the CSMA/CD. (CS stands for carrier sense.) Further, while the data is transmitting, the end device must ensure no other de- vice has transmitted at the same time on its receive interface. The sending station will also listen to see if received data is different from the transmitted data. If it is different, a collision occurred. Specifically, the end device is listening for a change in voltage on the wire. When a collision occurs, the sending end device transmits a jam signal (a random signal used to inform all devices that a collision has been detected) and backs off for a random value calculated with the back off algorithm. This method is called Collision Sense Multiple Access with Collision Detection (CSMA/CD). As a result of Ethernet’s shared-medium properties, Ethernet is sometimes referred to as undeterministic. This is because end devices don’t know when they can send data (that is, when the wire is clear), and end devices aren’t aware that another device will transmit at the same time. A deterministic device is able to calculate the maximum time that will pass before any end station will be able to transmit. What is half-duplex and full duplex Ethernet? Half duplex Ethernet al- lows only one device to send data or receive data at a time. Full duplex Ethernet allows the capability of simultaneous data transmission be- tween two devices. Full duplex Ethernet allows for better use of the available bandwidth because both devices can send and receive data at the same time. To illustrate CSMA/CD in action, Figure 4.2 shows an Ethernet network with four PCs (end devices) trying to communicate. The following occurs: 1. PC-1 listens and determines that no one else is sending data. 2. PC-1 starts to transmit information if the wire is clear. At exactly the same time, PC-2 decides to send data after also determining that no other device was using the media to send data. 7 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Basic Networking Technologies 4. At some point, the bits will collide, a collision will be detected by the colli- sion detection circuitry within each PC’s NIC, and both devices will send a jam signal and then back off for a random amount of time before attempting to retransmit. 5. PC-1 sends data once more after completing Step 1 again. This will be tried up to 15 times before an error is sent to the user applications. When using a shared media, such as Ethernet, collisions are a part of Ethernet’s operation, and they are considered normal. However, excessive collisions can cause delays and reduce available bandwidth to end devices. Typically, after network utilization goes above 12 percent, you will start to see excessive collisions. Exces- sive collisions will result in time delays, and end user performance will be im- pacted. When utilization reaches 30 percent, Ethernet networks will start to experience longer delays and excessive collisions. As mentioned earlier, there are two types of Ethernet—Ethernet 802.3 and Ethernet_II. There are four frame type formats that are supported in Ethernet. The frame formats vary for each of these Ethernet types. Figure 4.3 displays the PC-1 has data to send PC-2 has data to send PC-3 has no data to send PC-4 has no data to send Collision occurs Figure 4.2 Using Ethernet devices to send data using CSMA/CD. 8 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Chapter 4 four Ethernet frame formats, which can contain the Ethernet_II, Ethernet 802.3, Ethernet 802.2, and the SNAP Ethernet frame. Note: Previously, we mentioned that the minimum size of an Ethernet frame is 64 bytes. Now that we have introduced the preamble, it is crucial to note that while the preamble is part of the Ethernet frame, it is not considered when determining size. Thus, an Ethernet frame with a size of 64 bytes (minimum) or 1518 bytes (maximum) has a preamble that is not counted in the frame size. We will now cover what each field is responsible for in the four Ethernet frame types. Ethernet_II has the following frame format parameters: ➤ Preamble (8 bytes)—The preamble is used to synchronize all stations. ➤ Destination Address (6 bytes)—The destination address can be unicast (spe- cific device), multicast (group of addresses), or broadcast (all devices). ➤ Source Address (6 bytes)—The source address identifies the sender. ➤ Type (2 bytes)—The type field describes the protocol been carried in the frame. ➤ Data (46 to 1,500 bytes)—The data field carries end user information, such as an email message. ➤ Frame Checksum (4 bytes)—This frame checks sequence and calculates all fields, except the preamble and the frame checksum (FCS), to make sure the frame is not corrupted. (All lengths in bytes) Ethernet_II Frame Preamble 8 DA 6 SA 6 Type 2 Data 46 to 1500 FCS 4 Ethernet 802.3 Frame Preamble 8 DA 6 SA 6 Length 2 802.2 or SNAP Header (see below) 46 to 1500 FCS 4 Ethernet 802.2 Frame Preamble 8 DA 6 SA 6 Length 2 802.2 Field DSAP 1 SSAP 1 CTRL 1 Data 46 to 1497 FCS 4 Ethernet SNAP Frame Preamble 8 DA 6 SA 6 Length 2 AA 1 AA 1 CTRL 1 Data 46 to 1496 Ethernet Type 1 FCS 4 SNAP Fields Figure 4.3 Four Ethernet frame types. 9 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Basic Networking Technologies The total length of an Ethernet frame must never exceed 1,518 bytes, or a frame called a giant will be generated. The smallest frame size is 64 bytes. A frame smaller than 64 bytes is called a runt . Ethernet 802.3 has the following frame format parameters: ➤ Preamble (8 bytes)—The preamble is used to synchronize all stations. ➤ Destination Address (6 bytes)—The destination address can be unicast (spe- cific device), multicast (group of addresses), or broadcast (all devices). ➤ Source Address (6 bytes)—The source address identifies the sender. ➤ Length (2 bytes)—The length field describes data length. ➤ Data (46 to 1,500 bytes)—The data field carries end user information, such as an email message. ➤ Frame Checksum (4 bytes)—This frame checks sequence and calculates all fields, except the preamble and the frame checksum (FCS), to make sure the frame is not corrupted. The main difference between Ethernet_II and Ethernet 802.3 is that Ethernet_II has a type field and 802.3 has a length field. If the contents of this field exceed a value of 1,518, devices will know they are in possession of a Ethernet_II frame and read the field as a type field. If the value is less than 1,518, the field is treated as a length field. Ethernet 802.2 has the following frame format parameters: ➤ Preamble (8 bytes)—The preamble is used to synchronize all stations. ➤ Destination Address (6 bytes)—The destination address can be unicast (spe- cific device), multicast (group of addresses), or broadcast (all devices). ➤ Source Address (6 bytes)—The source address identifies the sender. ➤ DSAP (1 byte)—The Destination Service Access Point field together with the SSAP define the source and destination protocol of the frame. ➤ SSAP (1 byte)—The Source Service Access Point field together with the DSAP define the source and destination protocol of the frame. ➤ CTRL (1 byte)—The control field. ➤ Data (46 to 1,497 bytes)—The data field carries end user information, such as an email message. 10 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Chapter 4 ➤ Frame Checksum (4 bytes)—This frame checks sequence and calculates all fields, except the preamble and the frame checksum (FCS), to make sure the frame is not corrupted. Note: With an IPX packet, the 802.2 header is set to E0 E0 03. Ethernet SNAP header has the following frame format parameters: ➤ Preamble (8 bytes)—The preamble is used to synchronize all stations. ➤ Destination Address (6 bytes)—The destination address can be unicast (spe- cific device), multicast (group of addresses), or broadcast (all devices). ➤ Source Address (6 bytes)—The source address identifies the sender. ➤ DSAP (1 byte)—The Destination Service Access Point field together with the SSAP define the source and destination protocol of the frame. For a SNAP frame, this field is set to AA. ➤ SSAP (1 byte)—The Source Service Access Point field together with the DSAP define the source and destination protocol of the frame. For a SNAP frame, this field is set to AA. ➤ CTRL (1 byte)—The control field. ➤ Data (46 to 1,496 bytes)—The data field carries end user information, such as an email message. For a SNAP frame will include a type field that will iden- tify the payload type like IP for example. ➤ Frame Checksum (4 bytes)—This frame checks sequence and calculates all fields, except the preamble and the frame checksum (FCS), to make sure the frame is not corrupted. In the Control Fields (CTRL), 03 indicates Logical Link Control Type I or datagram service. In Ethernet_II, the type field identifies the payload or end user data . Some common type field examples include the following: ➤ 0x0800 —TCP/IP ➤ 0x6004 —Local Area Transport (LAT) ➤ 0x8037 —IPX Table 4.2 summarizes a number of standards for Ethernet. Notice that Ethernet 802.3 and Ethernet_II run at 10Mbps. This was found to be too slow for today’s networks, so a new standard was developed, called Fast Ethernet. Table 4.2 displays three different physical Ethernet standards used in Ethernet networks. The first two digits display the speed (in this case 10, it could be 100 or [...].. .Basic Networking Technologies 11 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Table 4.2 Ethernet (802.3) characteristics Ethernet Standard Characteristic 10BaseT 10Mbps over... assigned ➤ packets input—Total number of error-free packets received by the system ➤ bytes—Total number of bytes received by the interface (Note that this is on the same line as packets input.) Basic Networking Technologies 13 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ➤ no buffers—Number of packets discarded because the router had no available buffers to store the... modify the ring speed on a Cisco router, you use the following IOS command: ring-speed In summary format, the main characteristics of Token Ring 802.5 are: ➤ Star topology ➤ Star cabling Basic Networking Technologies 15 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ This PC has the free token Possession of token permits data transfer Token frame Token Ring Figure... bits are copied, because there is no redundancy check or CRC made on this field An important fact is that Token Ring supports two broadcasts frame types—FF-FF-FF-FF-FF-FF and C0-00-FF-FF-FF-FF Basic Networking Technologies 17 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Figure 4.5 illustrates a variety of bit combinations and serves as a very handy diagram for troubleshooting... The steps involved in the ring insertion process are as follows: 1 Phase 0: Lobe Media Check/Physical Insertion—The device runs a loopback test to ensure that any frame that is sent is received Basic Networking Technologies 19 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ 2 Phase 1: Monitor Check—The device sends a signal (called a phantom voltage) to flip the old mechanical... 0 ignored, 0 abort 2589508 packets output, 2212474871 bytes, 0 underruns 0 output errors, 0 collisions, 5 interface resets 0 output buffer failures, 0 output buffers swapped out 6 transitions Basic Networking Technologies 21 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Notice the preceding display is similar in some respects to an Ethernet display (shown earlier in... FDDI’s properties and limitations There are a number of devices that can reside on an FDDI ring Figure 4.6 shows a diagram that represents the types of stations that can exist on an FDDI ring Basic Networking Technologies 23 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ FDDI Property Limitation Speed 100Mbps MTU 4,500 bytes Distance 100km for each ring Frame format Similar... to occur Before a station can enter a ring, the station must go through a number of states before connection is guaranteed Table 4.6 describes the initialization states in order of operation Basic Networking Technologies 25 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Table 4.6 Station initialization procedure Initialization States, in Order of Operation Description... summary of the H.323 standard is as follows: ➤ Delivers high-quality and scalable multimedia-based conferencing ➤ Can be used over existing networks (IP) ➤ Can be used for long-distance voice calls Basic Networking Technologies 27 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ➤ Allows more cost-effective use of ISDN ➤ Supports intranets and can provide more reliable connections... expand on H.323, SS7, RTP, and QOS, refer to the references listed in the “Need To Know More?” section at the end of this chapter for some excellent information freely available on the Internet Basic Networking Technologies 29 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Practice Questions Question 1 Gigabit Ethernet is specified by which IEEE standard? ❍ a 802.2 ❍ . network (LAN) technologies used today. Ethernet can operate at three speeds: 5 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Basic Networking Technologies ➤. service to the Network layer. 3 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Basic Networking Technologies Using IP as an example, we know that IP is a connectionless