Computer Network LAN Features & Purposes 40 units (45 minutes/unit) Part - LOCAL AREA NETWORK 1.LAN Features & Purposes 2.Topology 3.Layered Model of LAN 4.Media Access Control: CSMA/CD | Ethernet 5.LAN Devices Belongs to own an organization Building and development depending on organization’s requirements and budget No cost to users but being controlled References: Data- Computer Communication handbook- William Stallings TCP/IP Illustrated, Volume I - W.R Stevens CCNA- semester1-2-3-4 Purposes Sharing resources • Hardware (CPU; RAM; Storages; primters…) • Soft ware (applications: MS-offices; antivirus, OS) • Organization’s Information -> database (file server) • Communication facilities – ADSL / Wireless / RAS / mail… Communication to customers, partners, staff… Topology E- management (Lotus note) • Business Process Reengineering • CRM- Customer Relationship Management Broadcast the image of organization (web server) • Interconnecting large systems: • Main-frame • Storage network - SAN Physical & Logical Topologies • Physical topologies – Define the actual layout of the wire (media) • Logical topologies – Define how the media is accessed by the hosts • The path that the data flow transmitted and received Internal Using in ptithcm Physical Topologies Bus Ring Star Extended Star Hierarchical Mesh Physical Topology: Ring • No backbone • A host is directly connected to each of its neighbors Physical Topology: Extended Star • Connects individual star topologies together • At the center of the star is a hub or a switch • Extends the length and size of the network Internal Using in ptithcm Physical Topology: Bus • Single backbone • All hosts directly connected to backbone • Each end of the bus must be properly terminated Physical Topology: Star • All devices connected to a central point • Center of star is usually a hub or a switch Physical Topology: Hierarchical • Like the extended star except a computer controls traffic (not a hub or a switch) Physical Topology: Mesh • Each host has its own connection to every other host • Used in situations where communication must not be interrupted Logical Topologies Broadcast Token Passing Logical Topology: Broadcast • Each host on the LAN sends its data (or broadcasts its data) to every other host • First-come, first-serve Internal Using in ptithcm Logical Topology: Token Passing • Access to media is controlled by an electronic token • Possession of the token gives the host the right to pass data to its Back… destination Layered Model of LAN Data-link and Physical layers Data- • Layered Model of LAN Physical Layer in LAN Model • The Institute of Electrical and Electronic Engineers • LAN standards: – 802.1d: Spanning tree – 802.2: LLC – 802.3: MAC ~ Ethernet – 802.5: MAC ~ Token ring – 802.11: Wireless LAN Coaxial Cable Internal Using in ptithcm • Media with wire link and wireless – Wire-link: cable types • Twisted pair (shielded and unshielded) • Co-axial cable: think and thick • Fiber optical cable – Wireless: the frequency used for transmission • 802.11a/ 802.11b/ 802.11g… • Media with relevant connectors – RJ-45 – AUI-15 / AUI-9 – RS-232C – 25pin “Thinnet” Cable “Thick-net” Connections Twisted Pair Media Any wire passing an electrical signal creates a surrounding magnetic field If the wires are aligned parallel, interference can occur called Crosstalk Twisted Pair Media To help eliminate crosstalk, wires are twisted together IEEE 802.11 Architecture Fast Ethernet The original fast Ethernet cabling • IEEE 802.11 is MAC protocol and physical medium specification for wireless LANs Gigabit Ethernet • There are two type of WLAN: – Infrastructure network – Ad - h network oc • Internal Using in ptithcm 802.11 Ad Hoc Networking 802.11 infrastructure Networking •Station (STA) • Peer t p network - o eer • Set up temporarily to meet some immediate need 802.11 LAN STA1 • E.g group of employees, each with laptop or palmtop, in business or classroom meeting • Network for duration of meeting 802.x LAN – terminal with access mechanisms to the wireless medium and radio contact to the access point •Basic Service Set (BSS) BSS1 Portal Access Point •Access Point Distribution System Access Point ESS – station integrated into the wireless LAN and the distribution system •Portal – bridge to other (wired) networks BSS2 STA2 – group of stations using the same radio frequency •Distribution System 802.11 LAN STA3 – interconnection network to form one logical network (ESS: Extended Service Set) based on several BSS Ethernet introduction MAC • Ethernet is the most widely used local area network (LAN) technology Media Access Control • Ethernet was designed to carry data at high speeds for very limited distances • Ethernet is well suited to applications where a local communication medium must carry sporadic traffic, occasionally heavy traffic at high peak data rates Ethernet history • 1960s, the University of Hawaii • 1970s, Xerox developed the first system • 1980, IEEE released 802.3 specification • 1980s, Digital, Intel and Xerox jointly developed and released an Ethernet specification (v2.0), Compatible with 802.3 • Today, the term Ethernet is often used to refer to Ethernet specifications, including IEEE 802.3 Internal Using in ptithcm Layer • Layer uses framing to organize or group the bits • Layer uses an addressing process to identify computers • Layer uses Logical Link Control (LLC) to communicate with the upper-level layers • Layer uses Media Access Control (MAC) to decide which computer will transmit Shared media environment • Multi-access • Base-band – => collision problem • MAC- address- 48bits flat address – Ex: 3a:23:4e:ef:10:33 Collisions Contention- Collisions Contention- • More than one node attempts to transmit at the same time • Collisions occur in broadcast topology (physical layer): – Ethernet LAN technology Ethernet technology: • Collision Problem : – Base-band environment allow only one data packet to access the cable at any one time – Sharing media environment with collision problem due contention causing for collision • A collision happens when two bit are on a point of media at the same time • Collision domain: Collision Domains are the area where collisions occur Collisions domain: Share access • Ethernet Frame Format • Limits the number of computers Internal Using in ptithcm Ethernet Frame Format Ethernet Frame Structure Ethernet Frame Structure • Addresses: bytes • Sending interface encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame – Each adapter is given a globally unique address at manufacturing time • Type: bytes • Preamble: bytes – – Indicates the higher layer protocol, mostly IP 101010…1011 • Address space is allocated to manufacturers but others may be supported clock rates – Used to synchronize receiver, sender such as Novell IPX – 24 bits identify manufacturer and AppleTalk) • CRC: bytes – E.g., 0:0:15:* – Checked at receiver, if error is detected, the frame is simply dropped 3com adapter • Frame is received by all adapters on a LAN and dropped if address does not match – Special addresses • Broadcast – FF:FF:FF:FF:FF:FF is “everybody” • Range of addresses allocated to multicast – Adapter maintains list of multicast groups node is interested in CSMA/CD (cont.) CSMA/CD • When a station wishes to transmit, it checks the network to determine whether another station is transmitting • If network is free, the station proceeds with the transmission • While sending, the station monitors the network to ensure that no other station is transmitting • If a transmitting node recognizes a collision, it transmits a jam signal so that all other nodes recognize collision • All transmitting nodes then stop sending for a backoff time (randomly 2n - of 51.2μs) CSMA/CD Algorithm Ethernet’s CSMA/CD (more) Back… Jam Signal: make sure all other transmitters are aware of collision; 48 bits; Exponential Backoff: • If deterministic delay after collision, collision will occur again in lockstep • If random delay with fixed mean – Few senders Calculating Backoff Given Internal Using in ptithcm needless waiting – Too many senders t too many collisions • Goal: adapt retransmission attempts to estimated current load – heavy load: random wait will be longer Devices function at Layers LAN DEVICES LAN Media Symbols LAN Device: Transceiver UTP Ethernet Line Token Ring Serial Line FDDI Ring 10Base-T: Transceiver 10Base- AUI BNC • Connect different media technologies • Layer device LAN Device: Repeater • Expanding the capacity of communication distance • Regenerates and repeats the signal with the determinate level of voltage • Layer device Internal Using in ptithcm 10/100 Base-T: Repeater Base- • Regenerates signals: • Enables cables to extend farther to reach longer distances • Increase number of nodes that can be connected to a network • Cannot filter traffic LAN Device: Hub • A multi-port repeater • • • • • Layer device Multi port repeater Center of a star topology network Allows many devices to be inter-connected Receives signals from only a port then broadcasts to others Shared bandwidth Cannot filter traffic 10Base-T: Hub 10Base- Layer Devices • NIC (Network Interface Card) • Connect your computer with network • Provide MAC addresses to each connection • Implement CSMA/CD algorithm • Bridge • Forward or filter frame by MAC address • Switch • Multi-port bridge LAN Device: NIC NIC • Network interface of hosts • Build-in physical address • Layer device Internal Using in ptithcm 10 NIC (cont.) • Provides ports for network connection • When selecting a network card, consider: Type of network: • Ethernet • Token Ring • FDDI Type of media • Twisted-pair • Coaxial • Fiber-optic Type of system bus • PCI • ISA Bridge NIC: Layer functions • Logical link control (LLC): communicates with upper layers in the computer • Naming: provides a unique MAC address identifier • Framing: part of the encapsulation process, packaging the bits for transport • Media Access Control (MAC): provides structured access to shared access media • Signaling: creates signals and interface with the media LAN Device: Bridge • Connects network segments • Make intelligent decisions about whether to pass signals on to the next segment • Improve network performance by eliminating unnecessary traffic and minimizing the chances of collisions • Divides traffic into segments and filters traffic based on MAC address • Often pass frames b/w networks operating under different Layer protocols • Keeps traffic local by filtering traffic based on physical addresses • Layer device Segmentation with bridges Internal Using in ptithcm LAN Segmentation 11 Segmentation with routers LAN Device: Switch • A multi-port bridge • Layer device LAN Switch: MAC table Benefits of LAN Switch • No collision domain, because of micro-segmentation • Low latency levels and a high rate of speed for frame forwarding • Increases the bandwidth available on a network • Is performed in hardware instead of in software, it is significantly faster Issues of LAN Switch • All hosts connected to the switch are still in the same broadcast domain • Security problem within a broadcast domain • Solutions ? • VLAN? • How does it work? VLAN & Implementation • Each port can be assigned to a VLAN • Ports assigned to the same VLAN share broadcasts • Ports that not belong to that VLAN not share these broadcasts • Two methods that can be used to assign a switch port to a VLAN: • Static • Dynamic Internal Using in ptithcm 12 Transport of VLANs Benefits of VLAN • Reduce administration costs – moves, additions changes • Controlled broadcast activity • Workgroup and network security • Save money by using existing hubs Static VLAN Static VLAN • Ports on switch that is statically assigned to a VLAN • Require administrator to make changes • Secure • Easy to configure • Straightforward to monitor • Works well in which moves are controlled and managed Dynamic VLAN Dynamic VLAN • Ports on switch automatically determine their VLAN assignments • Based on MAC addresses, logical addressing etc… • Less administration with in wiring closet when a user moves or new one added • Centralized notification when an unrecognized user is added • More administration is required to initially set up database Internal Using in ptithcm 13 ... of WLAN: – Infrastructure network – Ad - h network oc • Internal Using in ptithcm 802.11 Ad Hoc Networking 802.11 infrastructure Networking •Station (STA) • Peer t p network - o eer • Set up temporarily... used local area network (LAN) technology Media Access Control • Ethernet was designed to carry data at high speeds for very limited distances • Ethernet is well suited to applications where a local. .. bridge to other (wired) networks BSS2 STA2 – group of stations using the same radio frequency •Distribution System 802.11 LAN STA3 – interconnection network to form one logical network (ESS: Extended