(C) Ho-Won Jung, Korea University 1 Chapter 7: LAN topologies and media access control College of Business Administration Korea University Fall, 2000 Ho-Won Jung, office B309 ( ) College of Business Administration Korea University

(C) Ho-Won Jung, Korea University 2 Decision points for selecting LAN  Topology (a model for the way in which network nodes are connected)  Star, bus, ring, tree  Media access control (MAC)  CSMA/CD, token passing (the way in which a network node gains access to the medium and transmits data)  Medium  Twisted pair cable, coaxial cable, fiber optic  Software : Chapter 8  (Hardware : Chapter 6 에서 다룸 )

(C) Ho-Won Jung, Korea University 3  Media sharing LAN : 여러 PC users 가 media share "how to control access to the media"  Solution : IEEE 802 series (IEEE : Institute of Electrical & Electronic Engineers)

(C) Ho-Won Jung, Korea University 4 IEEE 802.x: A family of standards for Local & Metropolitan Area Networks

(C) Ho-Won Jung, Korea University 5 IEEE 802.x series  IEEE 802 : Overview and Architecture  IEEE : Glossary, Network Management, and Internetworking  Address matters relating to network architecture, network management, network interconnection, and all other issues related to the OSI layers above the data link layer.  IEEE : Logical Link Control  forms the interface between the network layer and the media access control protocols. LLC (Logical Link Control) is a sublayer of the data link layer (layer 2)  IEEE : CSMA/CD Access Method and Physical Layer Specifications  IEEE : Token-Passing Bus Access Method and Physical Layer Specifications  IEEE : Token-Passing Ring Access Method and Physical Layer Specifications

(C) Ho-Won Jung, Korea University 6  IEEE : Metropolitan Area Network Access Method and Physical Layer Specifications  DQDB (Distributed Queue Dual Bus) standard: 45 Mbps over coaxial cable and 156 Mbps over fiber optic cable. Note that the definition of MAN (upto 200 miles and order of 100 Mbps)  IEEE : Broadband Technical Advisory & Physical Layer Topics & recommend Practices  IEEE : Fiber Optic Technical Advisory and Physical Layer Topics  IEEE : Integrated Voice/Data Access Method and Physical Layer Specifications  Setting standards for interfaces to the ISDN (Integrated Services Digital Networks).  IEEE : Security and Privacy Access Method and Physical Layer Specifications  IEEE : Wireless Access Method and Physical Layer Specifications  IEEE : Demand priority access method

(C) Ho-Won Jung, Korea University 7 LAN topologies and standards  LAN topologies (corresponds to the OSI physical layer)  Bus topology (p.185, Fig 7-1; p.186, Fig 7-2)  IEEE : contention protocol (Ethernet implementation)  IEEE : token-passing protocol  Ring topology (p.185, Fig 7-1, p.187, Fig 7-3, p.189, Fig 7-4)  IEEE  generally token passing  IBM token passing ring : 4 Mbps or 16 Mbps  FDDI (Fiber Distributed Data Interface) : 100 Mbps (200 Km)  CDDI (Copper Distributed Data Interface) : use STP or UTP  Star topology (Fig 7-5, 7-6(a and b)  Star-wired LAN: use wiring hub to form the connection between network nodes  example ARCnet : 2.5 Mbps and 20 Mbps [p.191, Fig 7-6(b)] –de facto microcomputer LAN standard –token-passing bus StarLAN : 1 Mbps and 10 Mbps

(C) Ho-Won Jung, Korea University 8 Data link layer and Media access control protocol  Data link protocol (layer 2) ① delineation of data  Framing the data with a certain control characters (ch 11)  Using a standard message format  see Figure 7-12 (p.198) ② Error control  Parity and CRC ③ Addressing : uniqueness of network node addressing

(C) Ho-Won Jung, Korea University 9 ④ Transparency: the ability to send any bit string as data in a message. The data bits are not interpreted as control characters. ⑤ Code independence: The ability to successfully transmit data regardless of the data code, such as ASCII or EBCDIC.  Media access: the way in which a deive gains access to the medium.

(C) Ho-Won Jung, Korea University 10 Media access Protocol m LAN 은 OSI 의 Data link layer 의 분할해 사용 ê (LLC) Logical Link Control Sublayer Þ flow control Þ message sequencing Þ Message acknowledgement Þ Error checking ê (MAC) Media Access Control Sublayer : Access method Þ Contention Þ Token ring

(C) Ho-Won Jung, Korea University 11 Contention CSMA/CD (Carrier Sense Multiple Access with Collision Detection) 1. Listen to the medium to see whether a message is being transmitted. 2. If the medium is quiet, transmit message. If the medium is busy, wait for the signal to clear and then send. 3. If a collision occurs, wait for the signal to clear, wait a random interval, and then retransmit.  저가의 단순한 protocol  contention 이 비교적 적은 경우에 유용한 기술  data 전송의 요청이나 허락이 필요 없으므로 overhead 감소  Data collision 증가 --> retransmission (performance 저하 )  Real time 이 요구되는 전송에는 부적합

(C) Ho-Won Jung, Korea University 12 Token passing 1. Wait for transmit token 2. If transmit token is received and there is no message to send, send the token to the next node. 3. If transmit token is received and there is a message to send, then; a) transmit message; b) wait for acknowledgement; c) when acknowledgement is received, pass token to the next node.  Token-passing ring: A LAN architecture using a ring topology and token passing MAC protocol  Token-passing bus: a protocol where a token is passed from one workstation to another based on station address. m P.205 (Table 7-4), Please read the table.

(C) Ho-Won Jung, Korea University Repeaters  Layer 1 support  To repeat the digital signal by regenerating, retiming, and amplifying the incoming signal  To not read destination address of data packets  To allow for the connection of different types of media

(C) Ho-Won Jung, Korea University Bridges  Layer 2 support  Connecting two LANs using the same protocols  The medium does not have to be the same on both LANs  Basic bridge functions  Packet routing function  Accept packet from LAN A  Examine address of packet  If packet address is a LAN A address, allow the packet to continue on LAN A  If packet address is a LAN B address, transmit the packet onto the LAN B medium.  Do the equivalent for LAB B packets.

(C) Ho-Won Jung, Korea University 15  Data 나 resource 공유  only connect LANs of similar MAC sublayer protocols  Ethernet-to-Ethernet or Token ring to token ring  source address 를 check 해서 local node table 에 추가  destination address 를 읽어 local node table 과 비교해 destination 의 local 여부 판단  Bridge 는 frame segmentation 기능이 없음  : 1518 bytes/frame  : 8191 bytes/frame  : variable bytes/frame  Brouter 는 frame 의 segmentation 기능이 있음

(C) Ho-Won Jung, Korea University Routers  Layer 3 support  connect LANs to LANs, WANs to WANs, and LANs to WANs  Most common: TCP/IP  delivery of data packets to destination address across multiple LANs and perhaps over WAN links  functionality (bridges 와 routers 의 차이점 비교를 통해 )  examine data packets specifically addressed to it. (Bridge 는 data packet 의 address 를 읽음 )  choose the best path for the data packet to reach its destination (based on the latest traffic condition) and send the packet on its way  The destination address on an Ethernet or token ring packet must be the address of the router. The router handles further internetworking forwarding.  A router is addressed in the data-link layer destination address field.  How to find the best path: best path = (hops, circuit speed, protocol used)

(C) Ho-Won Jung, Korea University Gateways  Protocol converter  Connect networks that use different protocols, such as the protocols used in a LAN and those used in a WAN  Conversion of header and trailer of the packet  Support over layer 3

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(C) Ho-Won Jung, Korea University 23 Passive star coupler and Active star coupler