Wired Local Area Network (Ethernet)

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Vincent Jennings
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1 Chapter 13 Wired Local Area Network (Ethernet) IEEE Standards In 1985, the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication among equipment from a variety of manufacturers. Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols Topics discussed in this section: Data Link Layer (LLC and MAC) Framing Physical Layer 1

2 IEEE standard for LANs CSMA/CD Token Passing 13.3 IEEE 802 Series of LAN Standards name description IEEE Bridging and Network Management IEEE IEEE IEEE IEEE IEEE IEEE IEEE IEEE IEEE IEEE a/b/g/n IEEE IEEE IEEE Logical link control Ethernet Token bus Defines the MAC layer for a Token Ring Metropolitan Area Networks Broadband LAN using Coaxial Cable Fiber Optic TAG Integrated Services LAN Interoperable LAN Security Wireless LAN & Mesh (Wi-Fi certification) Cable modems Wireless PAN Bluetooth certification 13.4 IEEE Broadband Wireless Access (WiMAX certification) 2

3 Figure 13.2 HDLC frame compared with LLC and MAC frames 13.5 Ethernet It is the dominant LAN technology. Cheap First widely used LAN technology Simpler and cheaper than token LANs Kept up with speed race: 10, 100, 1000 Mbps Metcalfe s Ethernet sketch

4 Ethernet evolution 13.7 Ethernet Frame Format Sending adapter encapsulates network layer protocol packet such as IP datagram in Ethernet frame Preamble: 7 bytes with pattern followed by one byte with pattern Used to synchronize receiver, sender clock rates

5 Ethernet Frame Format Addresses: 6 bytes, frame is received by all adapters on a LAN and dropped if address does not match Type: indicates the higher layer protocol, mostly IP but others may be supported such as Novell IPX and AppleTalk) CRC: checked at receiver, if error is detected, the frame is simply pydropped 13.9 Minimum and Maximum Lengths Frame length: Minimum: 64 bytes (512 bits) Maximum: 1518 bytes (12,144 bits)

6 Addressing Figure 13.6 Example of an Ethernet address in hexadecimal notation Unicast and multicast addresses The least significant bit of the first byte defines the type of address. If the bit is 0, the address is unicast; otherwise, it is multicast or broadcast. The broadcast destination address is a special case of the multicast address in which all bits are 1s. (FF:FF:FF:FF:FF:FF)

7 Example 13.1 Define the type of the following destination addresses: a. 4A:30:10:21:10:1A b. 47:20:1B:2E:08:EE c. FF:FF:FF:FF:FF:FF Solution a. This is a unicast address because A in binary is b. This is a multicast address because 7 in binary is c. This is a broadcast address because all digits are F s Example 13.2 Show how the address 47:20:1B:2E:08:EE is sent out on line. Solution The address is sent left-to-right, byte by byte; for each byte, it is sent right-to-left, bit by bit, as shown below: B 2E 08 EE 47 is

8 Slot time Access method is CSMA/CD. Ethernet dose not provide any mechanism for acknowledging received frames( unreliable medium). Acknowledgments must be implemented at the higher layer. Slot time = round-trip time+ jam sequence time. It is defined in bits time. It is the time required for a station to send 512 bits depending di on the data rate, for traditional 10-Mbps Ethernet it is 51.2 microseconds. Max Length = propagation speed * (slot time/2) Max Length Max Length = propagation speed * (Slot time/2) Max Length=(2 x 10 8 )x(512x10 (51.2 x 10-6 /2)=5120 m Consider the delay times in repeaters and interfaces, and the jam sequence. Max Length= 2500m ( 48 % of the theoretical)

9 Physical layer implementations Categories of Standard Ethernet Encoding in a Standard Ethernet implementation

10 Figure Base5 implementation Base5 Ethernet Ethernet uses 1-persistent CSMA/CD on a coaxial cable at 10 Mbps (802.3 allows other speeds and medium) The maximum cable length allowed is 500m. Longer distances covered using repeaters to connect multiple segments of cable. No two stations ti can be separated by more than 2500m and 4 repeaters

11 Figure Base2 implementation Ethernet Technologies: 10Base2 10: 10Mbps; 2: under 200 meters max cable length Thin coaxial cable in a bus topology MAX 30 users on one segment. Repeaters are used to connect multiple segments Repeater repeats bits it hears on one interface to its other interfaces in both directions

12 10Base-T implementation Twisted-pair Ethernet Base-F implementation Fiber Ethernet

13 Summary of Standard Ethernet implementations Media 10Base 5 10Base2 10Base-T 10Base-F Thick coaxial cable Thin coaxial cable Two UTP 2 Fiber Maximum 500 m 185 m 100 m 2000 m length Topology Bus Bus Star star Standard Ethernet implementations use digital signaling( baseband) at a data rate of 10Mbps and Manchester for line coding CHANGES IN THE STANDARD The 10-Mbps Standard Ethernet has gone through several changes before moving to the higher data rates. These changes actually opened the road to the evolution of the Ethernet to become compatible with other high-data data-rate LANs. Topics discussed in this section: Bridged Ethernet Switched Ethernet Full-Duplex Ethernet

14 Bridged Ethernet Have two effects on an Ethernet LANs: The bandwidth is increased. Without bridges, all the stations share the bandwidth of the network. Collision domains are separated. Unbridged Ethernet network Bridged Ethernet: Raising the Bandwidth Bridges divide the network into two. Bandwidth-wise, each network is independent. With 2 port bridges, 10 Mbps network is shared only by half of the stations [actually bridge acts as one station]

15 Bridged Ethernet Separating Collision Domains: Using bridges, collision domain becomes much smaller and the probability bilit of collision i is reduced. d Switched Ethernet A layer 2 switch is an N-port bridge with additional sophistication that allows faster handling of the packets. kt

16 Full-Duplex Ethernet Limitation of 10Base5 and 10Base2 is that communication is half-duplex. Full-duplex doubles the capacity of each domain from 10 to 20 Mbps Full-Duplex Ethernet As there are two links, one for sending and one for receiving, we don t need CSMA/CD here. Connectionless (no ack); so no explicit flow or error control here. Flow and error control is provided by a new sublayer, called the MAC control, which is added between the LLC and MAC sublayer

17 13-4 FAST ETHERNET Fast Ethernet was designed to compete with LAN protocols such as FDDI. IEEE created td Fast Ethernet t under the name 802.3u. Fast Ethernet is backward-compatiblecompatible with Standard Ethernet, but it can transmit data 10 times faster at arate of 100 Mbps. Topics discussed in this section: MAC Sublayer Physical Layer MAC Sublayer Main consideration in the evolution of Ethernet from 10 to 100 Mbps was to keep the MAC sublayer untouched. Drop bus topologies and keep only the star topology. Star topology have two choices : Half-duplex approach: The stations are connected via a hub. The access method is CSMA/CD Full-duplex approach: The connection is made via a switch with buffers at each port. No need for CSMA/CD

18 MAC Sublayer Autonegotiation: Allows two devices to negotiate the mode or data rate of operation. To allow incompatible devices to connect to one another. To allow one device to have multiple capabilities. To allow a station to check a hub s capabilities Physical Layer More complicated than the one in Standard Ethernet. Topology: Two stations: point-to-pointto Three or more stations: star topology with a hub or a switch at the center

19 Physical Layer Implementation: Can be categorized as Two wire: Category 5 UTP (100Base-TX) Fiber-optic cable(100base-fx) four wire: Category 3 or higher UTP( 100Base-T4) Physical Layer Encoding: Manchester encoding needs a 200- Mbaud bandwidth for a data rate of 100 Mbps.(unsuitable for a medium such as TP cable). In Fast Ethernet, three different encoding schemes were chosen depending on the implementation: 100Base-TX 100Base-FX 100BAse-T

20 Encoding: 100Base-TX Uses two pairs of twisted-pair cable (either category 5 UTP or STP). Provide data rate of 100 Mbps MLT-3 scheme was selected since it has good bandwidth performance. (not self-synchronization line coding) So 4B/5B block coding is used to provide bit synchronization Encoding: 100Base-FX Uses two pairs of fiber-optic cables. Uses NRZ-I encoding scheme( bit synchronization problem.) To overcome this problem, 4B/5B block coding is used. Block coding increase the bit rate from 100 to 125 Mbps

21 Encoding: 100Base-T4 Uses four pairs of category 3 or higher UTP. Transmit 100 Mbps. -Encoding more complicated category 3 cannot easily handle more than 25 Mbaud. In this design one pair switches between sending and receiving 3 pairs handle only 75 Mbaud ( 25 each) Uses 8B/6T encoding scheme to convert 100 Mbps to 75 Mbaud Summary of Fast Ethernet implementations Media 100Base -TX 10Base-FX 10Base-T4 Cat 5 UTP or STP Fiber Cat 3 UTP or higher Number of wires Maximum length 100 m 400 m (2000 full 100 m duplex) Topology Star Star Star Data rate 100 Mbps 100 Mbps 100 Mbps Block encoding 4B/5B 4B/5B 8B/6T Line encoding MLT-3 NRZ-I NRZ

22 13-5 GIGABIT ETHERNET The need for an even higher data rate resulted in the design of the Gigabit Ethernet protocol (1000 Mbps). The IEEE committee calls the standard 802.3z. Topics discussed in this section: MAC Sublayer Physical Layer Ten-Gigabit Ethernet GIGABIT ETHERNET Use standard Ethernet frame format Allows for point-to-point links and shared broadcast channels In shared mode, CSMA/CD is used; short distances between nodes to be efficient Uses hubs, called here Buffered Distributors Full-Duplex at 1 Gbps for point-to-point links

Ethernet. Ethernet Frame Structure. Ethernet Frame Structure (more) Ethernet: uses CSMA/CD

Ethernet. Ethernet Frame Structure. Ethernet Frame Structure (more) Ethernet: uses CSMA/CD Ethernet dominant LAN technology: cheap -- $20 for 100Mbs! first widely used LAN technology Simpler, cheaper than token rings and ATM Kept up with speed race: 10, 100, 1000 Mbps Metcalfe s Etheret sketch