Local Area Network – Wired LAN

Local Area Network – Wired LAN

1. Local Area Network – Wired LAN LAN is a computer network that is designed for a limited geographical area such as building or campus. In 1980 and 1990s several different type of LANs were used. All of these LAN used a media –access method to solve the problem of sharing the media. The Ethernet used the CSMA/CD approach. The token ring, Token BUS, and FDDi used token passing approach. Almost every LAN except Ethernet has disappeared from the market place because Ethernet was able to update itself to meet the need of time .

2. Wired LAN has six essential components to function. Network Adapter : A network adapter is usually the only component within a computer for interfacing or connecting with a network. Typically, it is built on a printed circuit board with jumpers that connect it with the computer’s motherboard. A network adapter for wired networks has an RJ-45 port that uses twisted or untwisted pair cable for network connectivity .\ Network Medium Wired networks need cable. The most common form of cable used in networks is called the "Unshielded Twisted Pair." I

3. Cable Connectors In wired networks, the most common form of connector is the RJ45. Every computer with networking capabilities has an RJ45 port. This is sometimes called a "network port" or an "Ethernet port." Power Supply Both wired and wireless networks need a power supply. A wireless network uses the current to generate radio waves. A cabled network sends data interpreted as an electronic pulse

4. Hub/Switch/Router – connecting devices Software: is the intelligence that causes all of the components to function together. The most popular network software today uses what is known as the TCP/IP protocol suite, or stack. The suite is constructed from actual layers of software, where each has its own function. 

5. ETHERNET Ethernet is most widely used LAN Technology, enabling devices to communicate with each other via a  protocol  -- a set of rules or common network language . which is defined under IEEE standards 802.3. The reason behind its wide usability is Ethernet is easy to understand, implement, maintain and allows low cost network implementation . Engineers at Xerox first developed Ethernet in the 1970s. Ethernet initially ran over  coaxial cables , while a typical Ethernet LAN today uses special grades of  twisted pair  cables or fiber optic cabling. Early Ethernet connected multiple devices into network segments through  hubs  -- Layer 1 devices It usually transmits at 10 Mbps and relies on CSMA/CD to regulate traffic on the main cable segment.  

6. The Institute of Electrical and Electronics Engineers Inc.  (IEEE)  specifies in the family of standards called  IEEE 802.3  that the Ethernet protocol touches both Layer 1 -- the physical layer -- and  Layer 2  -- the data link layer -- on the  OSI  network protocol model

7. In IEEE 802.3 Ethernet Data link layer is split into two sublayers : Bottom part: MAC The frame is called IEEE 802.3 Handles framing, MAC addressing, Medium Access control Specific implementation for each LAN p rotocol Defines CSMA/CD as the access method for Ethernet LANs and Token passing method for Token Ring. Implemented in hardware Top part: LLC (Logical Link Control) The subframe is called IEEE 802.2 Provides error and flow control if needed It makes the MAC sublayer transparent Allows interconnectivity between different LANs data link layers Used to multiplex multiple network layer protocols in the data link layer frame Implemented in software

8. Figure 13.1 IEEE standard for LANs

9. IEEE Project. Project 802 is a set of networking standards and procedures for implementing networks, and creating network related equipment.  The IEEE (institute of Electrical and Electronics Engineers) designed Project 802 and it became a standard in 1983 . The project mostly covers physical media aspects of networking, such as cabling, attachments, hardware recommendations, and some logical networking aspects as well.

10. A list of the 802 Networking Standards and uses: 802.1: Internetworking. Covers routers, bridging, switches, and other internetworking communications standards and equipment. 802.2: Logical Link Control. Covers the properties and standards of physical media interoperability, such as with network interface cards, attachment and cabling media. 802.3: Ethernet: Covers standards and specifications of implementing Ethernet networks. 802.4: Token Bus LAN: Covers forms of physical media that work with the Token Bus Networking topology. 802.5: Token Ring LAN: Covers forms of physical media that work with the Token Ring Topology

11. 802.6: Metropolitan Area Networks: Covers the procedures and implementation procedures for managing large networks. 802.7: Broadband Technical Advisory Group: Covers broadband networking media concepts and procedures. 802.8: Fiber Optic Technical Advisory Group: Covers the standards and procedures for Digital Optical networking. 802.9: Integrated Voice and Data Networks: Covers the procedures for integrating voice and data over networks. 802.10 : Network Security: Covers the standards and procedures for securing networks logically (software level), and physically (Hardware level). 802.11 : Wireless Networking: Covers the procedures, specifications, and implementation of wireless networks.

12. Ethernet Evolution / Types of Ethernet

13. Standard Ethernet ( 10 Mbps) All Ethernet connections are limited by the slowest component, be that the hub, the Ethernet card or the Ethernet cable. While 10Mbps Ethernet long remained the standard for local-area networking and wide-area networking, it was ultimately held back by the type of cable it used. “Manchester encoding” cable could only handle as many bits as 10 million per second, so as long as the cabling standard remained the same, so would the throughput on the network .

14. Ethernet Standards and Cable Designation Supported Media Maximum Segment Length Transfer Speed Topology 10Base-5 Coaxial 500m 10Mbps Bus 10Base-2 ThinCoaxial (RG-58 A/U) 185m 10Mbps Bus 10Base-T Category3 or above unshielded twisted-pair (UTP) 100m 10Mbps Star,using either simple repeater hubs or Ethernet switches

15. Fast Ethernet The Fast Ethernet standard (IEEE 802.3u) has been established for Ethernet networks that need higher transmission speeds. This standard raises the Ethernet speed limit from 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure. Fast Ethernet provides faster throughput for video, multimedia, graphics, Internet surfing and stronger error detection and correction.

16. 100Base-TX Category5 UTP / STP 100m 100Mbps Star,using either simple repeater hubs or Ethernet switches 100Base-FX Fiber-optic- two strands of multimode 62.5/125 fiber 412 meters (Half-Duplex), 2000 m (full-duplex) 100 Mbps, (200 Mb/s full-duplex mode) Star(often only point-to-point) 100Base –T4 UTP 100 m 100 Star

17. Gigabit Ethernet Gigabit Ethernet was developed to meet the need for faster communication networks with applications such as multimedia and Voice over IP (VoIP). Also known as “gigabit-Ethernet- overcopper ” or 1000Base-T, GigE is a version of Ethernet that runs at speeds 10 times faster than 100Base-T. It is defined in the IEEE 802.3 standard and is currently used as an enterprise backbone. Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a Gigabit Ethernet backbone to interconnect high performance switches, routers and servers.

18. 1000Base-SX Fiber-optic- two strands of multimode 62.5/125 fiber 260m 1Gbps Star,using buffered distributor hub (or point-to-point) 1000Base-LX Fiber-optic- two strands of multimode 62.5/125 fiber or monomode fiber 440m (multimode) 5000 m ( singlemode ) 1Gbps Star,using buffered distributor hub (or point-to-point) 1000Base-CX Twinax,150-Ohm-balanced, shielded, specialty cable 25m 1Gbps Star(or point-to-point) 1000Base-T4 Category5 100m 1Gbps Star

19. Ethernet Frame / or Working

20. Preamble: The first field of the 802.3 frame contains 7 bytes (56 bits) of alternating 0s and 1s that alerts the receiving system to the coming frame and enables it to synchronize its input timing. Start of frame delimiter (SFD) –  This is a 1-Byte field which is always set to 10101011. SFD indicates that upcoming bits are starting of frame, which is destination address.  Destination Address –  This is 6-Byte field which contains the MAC address of machine for which data is destined. Source Address –  This is a 6-Byte field which contains the MAC address of source machine. As Source Address is always an individual address (Unicast), the least significant bit of first byte is always 0.

21. type   : a two byte value representing either the length of the frame or the specific  protocol  type ). Protocol can be IP, ARP, OSPF. Data –  This is the place where actual data is inserted, also known as  Payload . Both IP header and data will be inserted here, if Internet Protocol is used over Ethernet. The maximum data present may be as long as 1500 Bytes. In case data length is less than minimum length i.e. 46 bytes, then padding 0’s is added to meet the minimum possible length . Cyclic Redundancy Check (CRC) –  CRC is 4 Byte field. This field contains 32-bits hash code of data, which is generated over Destination Address, Source Address, Length and Data field. If the checksum computed by destination is not same as sent checksum value, data received is corrupted.

22. CSMA/CD Algorithm To understand how CSMA/CD works, it makes sense to break down the individual components of the term: Carrier sense  (CS): The carrier state detection makes sure that all network participants check whether the medium is currently free – only then does the protocol initiate data transmission Multiple access  (MA): Several participants (computers connected to the network) share a transmission medium Collision detection  (CD): The collision detection is an extension of the original protocol and regulates how to proceed in case data packets happen to collide

23. In   Ethernet network (IEEE 802.3) , all network participants usually meet on a common transmission medium – a cable. This meeting must be regulated to avoid chaos during data transmission, which could lead to data loss or damage.  CSMA/CD  algorithm offers a method that organizes data transmission properly . In this method, a station monitors the medium after it sends a frame to see if the transmission was successful. If so, the station is finished. If, however, there is a collision, the frame is sent again.

24. How CSMA/CD works? Step 1:  Check if the sender is ready for transmitting data packets. Step 2:  Check if the transmission link is idle? Sender has to keep on checking if the transmission link/medium is idle. For this it continuously senses transmissions from other nodes. Sender sends dummy data on the link . If it does not receive any collision signal, this means the link is idle at the moment . If it senses that the carrier is free and there are no collisions, it sends the data. Otherwise it refrains from sending data.

25. Step 3:  Transmit the data & check for collisions. Sender transmits its data on the link. CSMA/CD does not use ‘acknowledgement’ system. It checks for the successful and unsuccessful transmissions through collision signals. During transmission, if collision signal is received by the node, transmission is stopped. The station then transmits a jam signal onto the link and waits for random time interval before it resends the frame. After some random time, it again attempts to transfer the data and repeats above process Step 4:  If no collision was detected in propagation, the sender completes its frame transmission and resets the counters.

26. IEEE 802.4 (Token Bus) This standard, 802.4, describes a LAN called a token bus. Physically, the token bus is a linear or tree - shaped cable onto which the stations are attached. Logically, the stations are organized into a ring, with each station knowing the address of the station to its “right” and “left”.

27. Token Bus was a 4 Mbps  Local Area Networking  technology created by IBM to connect their terminals to IBM mainframes. Token bus utilized a copper coaxial cable to connect multiple end stations (terminals, wokstations , shared printers etc.) to the mainframe . The coaxial cable served as a common communication bus and a token was created by the Token Bus protocol to manage or 'arbitrate' access to the bus. Any station that holds the token packet has permission to transmit data. The station releases the token when it is done communicating 

28. MAC Sublayer Function  • When the ring is initialized, stations are inserted into it in order of station address, from highest to lowest.  • Token passing is done from high to low address. Whenever a station acquires the token, it can transmit frames for a specific amount of time. • If a station has no data, it passes the token immediately upon receiving it.

29. Preamble (PRE) - 1 bytes. The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the frame-reception portions of receiving physical layers with the incoming bit stream. SDEL / EDEL - Starting Delimiter / Ending Delimiter. These fields are used to mark the frame boundaries. Both of these fields contain analog encoding of symbols other than 0s and 1s, so that they cannot occur accidentally in the user data. As a result, no length field is needed. FC - Frame control field indicates whether the frame contains data or control information Destination address - Destination station address. Source address - Source station address. Data – The actual information that needs to be transferred. Its range is between 0-8182 bytes. Checksum – This field is used to detect transmission errors.

30. IEEE 802.5 token ring Token Ring is a LAN protocol defined in the IEEE 802.5 where all stations are connected in a ring and each station can directly hear transmissions only from its immediate neighbor. Permission to transmit is granted by a message (token) that circulates around the ring. Token Ring as defined in IEEE 802.5 is originated from the IBM Token Ring LAN technologies. A ring consists of a collection of ring interfaces connected by point-to-point lines  i.e.  ring interface of one station is connected to the ring interfaces of its left station as well as right station. Internally, signals travel around the Communication network from one station to the next in a ring.

31. Token Ring and IEEE802.5 are based on token passing MAC protocol with ring topology. They resolve the uncertainty by giving each station a turn on by one. Each node takes turns sending the data; each station may transmit data during its turn. The technique that coordinates this turn mechanism is called Token passing ;

32. Whenever a station wants to transmit a frame it inverts a single bit of the 3-byte token which instantaneously changes it into a normal data packet. Because there is only one token, there can atmost be one transmission at a time. Since the token rotates in the ring it is guarenteed that every node gets the token with in some specified time. So there is an upper bound on the time of waiting to grab the token so that starvation is avoided. There is also an upper limit of 250 on the number of nodes in the network .

33. SDEL / EDEL - Starting Delimiter / Ending Delimiter. Alerts arrival of a token / data / control frame. AC - Access control field Contains the Priority fields. FC - Frame control field indicates whether the frame contains data or control information  Destination address - Destination station address. Source address - Source station address. Route information - The field with routing control, route descriptor and routing type information. Information - The Information field may be LLC (logical link control) or MAC (Media Access Control). FCS - Frame check sequence. Frame status - Contains bits that may be set on by the recipient of the frame to signal recognition of the address and whether the frame was successfully copied.