What is meant by LAN Architecture? 3 Major Components of LANs Media Access Control (MAC) Protocol Network Topology Network Operating System SoftwareMedia Access Control (MAC) Protocol – a protocol found at the media accesscontrol (MAC) sub layer of the OSI reference model’s data link layer. defines how a station gains access to the media for data transmission.Common MAC protocols Carrier Sense Multiple Access Collision DetectionNetwork Topology – the logical or physical arrangement of network nodes. – a model for the way in which network nodes are connectedLogical Topologies includes; Broadcast or Sequential (ring)Physical Topologies includes; Bus Ring Star
LAN Architecture – the overall design of a LAN. – includes hardware, software, topology and Media Access Control (MAC) Protocol. LAN TOPOLOGIES Topology – derives from a mathematics field that deals with points and surfaces in space. LANs 3 Basic Topologies Bus Star Ring Bus Topology – a physical network topology in which all network attached devices connect to a common communication pathway or channel. –in LANs the communication medium in a bus topology consist of a single wire or cable to which nodes are attached via connectors and/or transceivers.Figure 8-1 (a) BUS TOPOLOGY
LAN TOPOLOGIESEthernet – a LAN implementation using the CSMA/CD protocol on a busthe IEEE 802.3 standard is based on Ethernet. A popular LANimplementation.Institute of Electrical and Electronics Engineer (IEEE) – a professionalsociety that establishes and publishes documents and standards fordata communication. – has established several standards for both cable-based and wire less LANs including; IEEE 802.3 IEEE 802.5 IEEE 802.I IIEEE 802.3 Standard – the IEEE standard that addresses EthernetLANs. – It covers a variety of physical implementations of Ethernet all of which use CSMA/CD as the MAC protocol.
LAN TOPOLOGIESRing Topology – a LAN topology in which stations are attached to one anotherin a logical or physical circle. A weakness of this physical topology is thatcommunications for the entire network may be disrupted if one of themicrocomputer or network adapters malfunction. Figure 8-1 (b) A F B E C D RING TOPOLOGY In a physical ring the medium forms a loop to which workstations areattached. In both physical and logical rings, access to the medium is passed from onestation to the next; also, data are transmitted from one station to the next around thering. Generally, the access protocol used in a ring topology is token passing.
LAN TOPOLOGIES Figure 8-3 A G B F C E D Data FlowToken Passing Within a Ring Topology
LAN TOPOLOGIES Active node – a node capable of sending or receiving network messages. Inactive node – a node that may be powered down and is incapable of sending or receiving messages. IEEE 802.5 standard – an IEEE standard for token-passing networks including token ring LANs. Multistation Access Unit (MAU) – Figure 8-4 Workstation Ring Connection Connection Created by MAURing In InboundConnection Ring Out Outboundfrom other MAU Connection Multistation Access Unit (MAU) to other MAU
LAN TOPOLOGIES Star Topology – a physical network topology using a central station (typically a hub or a switch) to which all nodes have point-to-point in connections. -all communication among nodes occurs through the central station. - this is the most widely implemented LAN topology. That has been used today.Figure 8-1 (c) Wiring Hub Star Topology
HUBLAN TOPOLOGIESFigure 8-7 Star TopologyARCnet (Attached Resource Computer Network) – among the first LANimplementations capable of connecting up to 255 nodes in a star topology overtwisted-pair wires or coaxial cable.Logical Topology – a LAN’s logical topology is concerned with how messagesare passed from node to node within the network rather than with how thenodes are physically connected to form a network.Two logical LAN Topologies exist: Sequential Ring Broadcast
LAN TOPOLOGIES2 Logical LAN TopologiesSequential (Ring) – also called a ring logical topology because data ispassed from one node to another in a ring-like sequence. Each node in the ring examines the destination address field of each data packet receives in order to determine if it is the intended recipient.Broadcast – nodes in LANs that have a broadcast logical topologytransmit each packet to all the other nodes in the network. Each node receive all the packets transmitted by all other nodes and examines each packets that it receives to determine if it is the intended recipient.
DATALINK AND MEDIA ACCESS CONTROL PROTOCOL Data Link ProtocolsIn general, a data link layer protocol established the rules for gaining access tothe medium and for exchanging messages. Six Most Important Aspects of Data Link Protocol Delineation of Data – a data link layer protocol must define or delineate where the data portion of the transmitted message begins and ends. Octet- a group of 8 bits used in data communication protocol frame formats. Error Control – is used to detect transmission errors. Common error detection techniques are parity and cyclic redundancy checks. Addressing – communication between two network nodes is accomplished through the addressing scheme. Network addressing is similar to addressing used for postal mail. Transparency – in the data link protocol, transparency is the ability of the data link to transmit any bit combination.
Figure 8-9 Preamble Destination Source Type Field Data Field 32-Bit CRC Address Address (a) Original Ethernet II Frame Preamble Start Frame Destination Source Length Field Data Field 32-Bit CRC Delimeter Address Address (b) IEEE 802.3 Frame Preamble Start Destination Source Length IEEE 802.2 Data 32-Bit CRC Frame Address Address Field Control Field Delimeter (c) IEEE 802.2 Frame Preambl Destinati Source Length DSAP SSAP CTRL Data 32-Bit e on Address Field Field CRC Address (d) Ethernet SNAP (an 802.2 variant)Ethernet Message Formats
Code Independence – the ability to transmit data regardless of the code, such as ASCII or EBCDIC. - means that any data code, such as ASCII or EBCDIC, or Unicode, canbe transmitted. This codes used different bit patterns to represent many of thecharacter. Media Access – the way in which network device gains access to thecommunication medium . Thus is usually governed by a Media Access Control(MAC) protocol specifying how the device gains the right to transmit data on themedium.MAC PROTOCOLS LAN technology adheres to two primary data link protocols: Token Passing ContentionData Link layer is divided is divided into 2 sublayers: The LLC (Logical Link Control) – provides the function of a flow control , message sequencing , message acknowledgement, and error checkingThe MAC (Media Access Control) layer – describes token passing and contention.
LLC and MAC Sublayers of the OSI Reference Models Data Link Layer Application Layer Presentation Layer Logical Link Control Session Layer (LLC) Media Access Control Transport Layer (MAC) Network Layer Media Signaling Data Link Layer Bus Interface Unit Physical Layer OSI Reference Model Layers Communication Interface Unit Medium
MAC PROTOCOLS Contention - a media access control convention governing how devices obtain control of a communication link. - in contention mode, devices compete for control of the line either by transmitting directly on an idle line or by issuing a request for line control. - is typically follows a first-come, first -serve, methodology expect when two devices contend for the communication link at the same point in time. Collision – in the CSMA/CD media access control protocol and other contention-based communication protocols, a collision occurs when two stations attempt to send a message at the same time. The message interfere with each other, so correct communication is not possible. Carrier Sense Multiple Access and Collision Detection (CSMA/CD) - a media access control technique that resolves contention between two or more stations by collision detection. - it is used in Ethernet LANs and is often referred to as the “Ethernet protocol”. Carrier Sense Multiple Access and Collision Avoidance (CSMA/CA) - a LAN media access control method that attempts to avoid contention among stations and message collisions. It is widely used in wireless LANs.
MAC PROTOCOLS Token Passing - the second major MAC protocol. - a media access control protocol in which a string of bits called the token is passed from network node to network node in a logical ring. A computer that receives token is allowed to transmit data onto the network and after transmitting its data, the computer passes the token to the next computer in the ring. Active Monitor – in a token ring network, the active monitor is the station that controls the token. It maintains clock synchronization, detects and corrects errors in the token frame format, and generates a new token in the case of token loss. Kinds of Token Passing Token-Passing Ring – in a token-passing LAN with a physical or logical ring topology, the token can become loss if node holding the token fails or if transmission errors occur. Recovery in such problems involves the active monitor.
Token-Passing Bus - token passing is slightly different on a token-passingbus.On a bus, the token is passed from one workstation to another based on stationaddresses. As mentioned earlier , the token can be passed in ascending ordescending address order. Address 55 Address 72 Address 45 Lowest Address Passes to Highest Address Address 38 Address 10 Path of Token Based on Descending Station Address
Figure 8-12 MAU PORTS RI 1 2 3 4 5 6 7 8 RO Unused Unused A B C D E F Turned Malfunctioning Open Switch Off The 24-bit token is passed from node via circuits within the MAU. In Closed Switch this MAU, the token would be passed from node A to node C. Node C would the pass the token to node D. Node D would pass the token to F. the token would not be passed to nodes B or E. Switches within the MAU prevent the token from being passed to powered down or malfunctioning nodes; they also are used to bypass unused ports. Token Passing Within a Token Ring MAU
Table 8-3 MAC Protocol Comparison Token Passing CSMA/CD Access is equal for all nodes Access is equal for all nodes. Access window is predictable. Access window can be unpredictable. Maximum wait time to transmit is token Maximum time to transmit is unpredictable circulation time. and depends on collisions. Average wait time to transmit is predictable: Average wait time to transmit is half the maximum circulation time. unpredictable. Network congestion does not adversely affect Network congestion may result in collisions network efficiency. and reduce network efficiency. A node must wait for the token before being A node may be able to transmit immediately. able to transmit. One node cannot monopolize the network. A node may be able to monopolize the network Large rings can result in long delays before A node can transmit when the network is a node obtains token. quiet. Performance is consistent for large, busy Performance is unpredictable for large, busy networks. networks because of possibility of collisions.
Figure 8-13 1 1 0 1 0 0 1 1 a) Bit Stream b) Binary Encoded Bit System c) Manchester Encoding – Manchester encoding is used in 10- mbps Ethernet LANs and requires a low to high mid bit transition to represent a 1 and high to low to 1 and a high to low transition to represent a 0 bit. d) Differential Manchester Encoding – is used in token ring LANs. Like Manchester Encoding, Differential Manchester Encoding requires a mid bit transition. However, in this scheme, a 1 bit always starts at the same level as the previous bit ends ; a 0 bit always starts at the opposite level from where the previous bit ends. e) NRZI Encoding (Non-Return to Zero with Invert on Ones). NRZI Encoding is used in FDDI LANs. In this scheme, 1s have mid bit transitions, 0s do not. Both 1s and 0s start at the same level as the previous bit ends. Bit IntervalPhysical Layer Data Encoding Used in LANs
LAN Architectures Aspects of LAN architecture. These include the ; LAN’s physical topology LAN’s logical topology LAN’s MAC protocolEthernet Frame Formats Fast Ethernet – refers to 100BaseT Ethernet implementations that comply with the IEEE 802.3u standard. - 100BaseT transmits at 100 mbps. Like regular Ethernet, fast Ethernet is a shared media LAN that uses CSMA/CD as the media access control protocol. Gigabit Ethernet – evolved from ANSI’s X3TII Fibre Channel standard. Fibre Channel – gigabit Ethernet evolved ANSI’s X3I I specifications for Fibre Channel include a medium speed of 1 GHz and a data rate of 800 mbps. Fibre Channel often used to build storage area networks (SANs), and implementations that support speeds over 2 gbps. In the future, transmission speeds are expected to exceed 4 gbps.
Ethernet Frame Formats Isochronous Ethernet – enables 10BaseT Ethernet LANs located at different geographic locations to be connected via ISDN . The IEEE 802.9a specifications addresses Isochronous Ethernet; also called Iso- Ethernet. -This enhancement enables Ethernet to handle real-time voice and video by providing a total bandwidth of more than 6 mbps that can be used for video conferencing. - Isochronous Ethernet can be integrated into the existing network through the addition of the isochronous. Token Ring - networks use in a token-passing MAC protocol over a logical ring (sequential ) topology. Physically token ring networks look like a star. Multistation Access Unit (MAU) – a central hub in a token ring LAN.
Figure 8-14 Location 1 Iso-Ethernet Access ISDN Links ISDN Network Units (AU’s) with ISDN Interfaces Location 2Using Iso-Ethernet to Connect Ethernet Lans at two Locations via ISDN
FDDIFiber Distributed Data Interface (FDDI) – an ANSI standard token passing network that used optical fiber cabling and transmits at 100 mbps up to 2 kilometers. Its heyday as a LAN and MAN access method was the mid-1990’s . - FDDI, being pronounced as “Fiddy”Copper Distributed Data Interface (CDDI) – a version of FDDI that uses UTP (unshielded twisted pair) wires rather than optical fiber as the communication medium. - has also been recognized in the TP-PMD (twisted pair-physical media dependent) standard based UTP.
Figure 8-16 Minicomputer DAS (Dual FDDI Attachment Concentrator Station) SingleMinicomputer Attachment Station (SAS) Secondary Ring FDDI to Primary Ring Ethernet Bridge File Server Fiber Cable or STP FDDI Network Configuration and Key Technologies
Fiber Distributed Data Interface (FDDI) Single Attached Station (SAS) – some FDDI NICs enable a workstation to be attached only to the primary data ring, often via a concentrator; workstations that connect to FDDI network in this fashion are called single attached stations (SASs). Dual Attached Station (DAS) – workstations in FDDI networks that attached to both FDDI rings.
Figure 8-17 Z Node A Z Thas the token M Y Y E S S A A X Direction of X T A Direction of Token Token G Passing Passing E B B A - Token C T C T - Token (b) (a) Message Passing in a FDDI LAN
Figure 8-17 Node A receives message in Node B’s message acknowledgement continues to circulate. & removes it from the ring Message B Z Z Y Y Message A A A X Direction of X Direction of Token Token Passing Message A Passing B B T M C E C Message A T - Token S (d) S (c) Node X keeps A’s message and sends A it back to A. G ET -Token AMessage Passing in a FDDI LAN
Figure 8-18 Normal Operation Rerouted Traffic After Line Break Primary Primary Secondary Break in the line Between C and DFDDI’s Self-Healing Capability
100 G-AnyLAN 100 G-AnyLAN – an IEEE specification for twisted-pair wire or fiber optic cable Ethernet LANs with speed of 100 mbps. - is derived from a 100-mbps version of Ethernet developed by Hewlett-Packard that is capable of transporting both IEEE 802.3 and IEEE 802.5 (token ring) frames.
Figure 8-20 100VG Ethernet Hub In this 100VG-AnyLAN Implementation option, the 100VG 100VG router converts IEEE ROUTER 802.5 frames to IEEE 802.3 frames, and vice versa. 100 Mbps Token Ring 100VG LAN Token Ring MAUAn Example of a 100VG-AnyLAN Network
ATM LANs Another LAN architecture that has a good job of supporting multimedia traffic is ATM (asynchronous transfer mode). ATM is a switched network architecture that employs 53- octet cells to transmit data . ATM is also used in LANs. ATM LAN emulation – when ATM LAN emulation is employed, LAN MAC addresses are converted to ATM network addresses. - enables virtual LANs to be created across an ATM backbone by using ATM switches to handle message exchange among logical work-group members.
Figure 8-12 ATM Backbone Ethernet LAN ATM Network WAN ATM Switch 25-mps ATM ATM LAN Switch Switch Hub ATM Switch ATM Access Gateway/Switch MAUInterconnecting LANs via an ATM Backbone Token Ring LAN
Three-Tier Architectures and Virtual LANs Traditionally, LANs have been classified as having 2-tierred client/ server architecture which clients located on one tier and servers on second . Figure 8-22 Middle-Tier Server Application Server Data Server (e.g., Oracle) Client Backend Servers Data Server (e.g., Sybase)Three-Tier Client/Server Computing Architecture
Three-Tier Architectures Layer 2 switch – a network device that forwards traffic based on MAC layer (Ethernet or Token Ring ) Addresses . Most LAN switches are called Layer 2 switches because the switched connection is based on the MAC layer destination address included in data link layer frames transmitted between LAN-attached devices. Layer 3 Switch – a network device that forward traffic based on Layer 3 information. Layer 3 is the network layer of the OSI reference model. When network layer destination addresses (such as IP addresses) are used to establish switched connections instead of MAC layer addresses, the switch is called a layer 3 switch.
Three-Tier ArchitecturesFigure 8-23 LAN 1: 10 mbps LAN 3: 10 mbps 100 mbps 100 mbps Layer 2 Switch Layer 2 Switch Layer 3 Switch Layer 2 Switch LAN 2: 1 gbps 1 gbps 100 mbps Router Wide Area NetworkLayer 2 and Layer 3 Switches in LANs
Virtual LANs Virtual LANs are logical network designs that are dependent upon LAN switches to provide functionality. Special virtual LAN software, supported in Layer 2 and Layer 3 LAN switches, enables virtual LANs to be created and maintained. In essence , a virtual LAN is a logical grouping of work-group members that does not require each member of the group to be physically attached to the same switched.
WIRELESS LAN ARCHITECTURE Infrared LANs – LANs that rely on infrared lights as the communication medium transmits signals whose wavelengths fall between those of visible light and radio waves. Spread –Spectrum Radio (SSR) LANs – the primary application of SSR for data communication is wireless LANs. SSR has a long history military use because of its ability to provide reliable communication in battlefield environments where signal jamming and other kinds of signal interference are likely; Two Transmission Methods : Frequency-Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS)
Frequency-Hopping Spread Spectrum (FHSS) – FHSS continuouslychanges the center frequency of a conventional carrier several times per secondaccording to a pseudo-random pattern and set of channels.Data is transmitted at one frequency then, then the frequency is charged anddata are transmitted at once frequency, then the frequency is change and data isare transmitted at the new frequency , and so on.This makes very difficult to illegally monitor the spread spectrum signalsand increases the probability that the transmitted data will be successfullyreceived.Direct Sequence Spread Spectrum (DSSS) - sends data over severaldifferent spread spectrum radio frequencies simultaneously using the fullbandwidth of the communication channel.
Table 8-5 Frequency (Hz) Wavelength 1016 X rays, gamma rays 1015 Ultraviolet light 1014 Visible light 1013 Infrared light 1012 Millimeter waves 1011 Microwaves 1010 UHF television 109 VHF television 108 VHF TV (high band) FM radio 107 VHF TV (low band) Shortwave radio 106 AM radio 105 Very low frequency 104 Very low frequency 103 Very low frequency 102 Very low frequencyFrequency Spectrum Classification 1
Wireless LAN Topologies Wireless LANs are typically implemented as physical stars. Nodes connect to wireless hubs that are typically called access point. Access points can be stand-alone devices or can interface with cable-based networks in order to provide wireless segments for an otherwise wire-based called networks on order to provide wireless segments for an otherwise wire-based LAN.
Table 8-6 Important Wireless LAN Standard Standard Description IEEE 802.11 Original WLAN; supports 1- to 2-mbps transmission speeds IEEE 802.11b Currently the dominant WLAN standard; supports transmission speeds of 11mbps IEEE 802.11a High-speed WLAN standards for 5- to 6-GHz band; supports 54 mbps HiperLAN2 Competing high-speed WLAN standard for 5- to 6-GHz band; supports 54 mbps IEEE 802.11g High-speed WLAN standard for 2..4-GHz band; supports 20+ mbps transmission speeds IEEE 802.1x Comprehensive security framework for all IEEE networks including WLANs and Ethernet IEEE 802.11i Wireless-specific WLAN security standard that complies with IEEE 802.11x IEEE 802.11e Quality of Service (QoS) mechanisms that support all IEEE WLAN radio interfaces IEEE 802.11f Defines communication between WLAN access points IEEE 802.11h Defines spectrum management techniques for IEEE 802.11a WLANs WISPR Wireless ISP roaming standard recommended by the wireless Ethernet Compatibility Alliance to enable roaming among multiple public WLAN networks
MAKING THE DECISIONS Table 8-7 Major Factors Influencing LAN Selection Cost Number of workstations Type of workstations Number of concurrent Type of use Number of printers users Medium and distance Speed Applications Expandability Device connectivity Connectivity with other networks LAN software and Hardware Vendor Adherence to established standards Vendor Support Manageability Security In making the decision you need to consider; Cost - if cost were not a consideration, LAN selection would be easier. You could buy the fastest, biggest workstations and servers available and use the most comprehensive LAN network operating system and application software available .
MAKING THE DECISIONSTable 8-8 Immediate and Recurring LAN Costs Immediate Costs Equipment Costs Training (users, operators, administrators) Documentation Installation of cabling Site preparation System software installation Hardware installation Creative user environment Installing application Space required for new equipment Testing Supplies and spares Recurring Costs LAN management personnel costs Hardware and software maintenance Consumable supplies Training (new users, administrators) Total cost of ownership – includes all cost aspects of LAN/IT projects including ongoing cost for support, management, and maintenance over the entire expected life span of the network/system.
MAKING THE DECISIONSNumber of Concurrent Users and Type of Use The number of concurrent users expected during normal peak network usage periods is often an important factor in selecting among LAN alternatives. Overlay Module – a memory management technique wherein the program is divided into distinct segment types: resident or main segment overlay segments Overlay segments share the same memory area. Typically, only one of the overlays is in memory at any given time. When a different overlay segment is required, it replaces the memory resident overlay segment.
MAKING THE DECISIONS Communication Speed LAN speeds can be somewhat deceptive. A LAN speed quoted by the vendor is the speed in which data is transmitted over the medium. You cannot expect the LAN to maintain its speed at all times. Vendor and Support When you are selecting a LAN, you are selecting much more than hardware and software, You also are selecting a vendor/s with whom you expect to have a long-term relationship. Manageability Never underestimate the time and effort required to operate and manage LAN. Even small, static LAN requires some management once it has been installed and set up. Occasionally, a user might be added or deleted, applications must be added or updated, and so on.
MAKING THE DECISIONS Table 8-9 LAN Management TaskUser/Group Oriented Add, delete users and groups Set user/group security Set user environment Solve user problemsPrinter Oriented Install/removed printers Set-up user environment Maintain printersHardware/Software Oriented Add/change/delete software Add/change/delete hardware Diagnose problems Established connections w/ other networks Plan and implement changesGeneral Make backups Maintain operating procedures Carry out recovery as necessary Educate users Plan capacity needs Monitor the network Serve as a liaison with other networkadministrators
Security When stand-alone minicomputers, security generally is not an issue. Stand-alone microcomputer system usually single- user system, and system security features, such as passwords- controlled screen savers, are rarely used. As a result, access to the system is tantamount to access all data sorted on that system.
IEEE LAN STANDARDS The IEEE established a standards group called the 802 Committee during the 1970’s . This group is divided into subcommittees, each of which addresses specific LAN issues and architectures. The subcommittees and their objectives are summarized here. 802.1: High-Level Interface – high-level interface subcommittee addresses matters relating to network architecture, network management, network interconnection, and all other issues related to OSI layers above the data link layer, which are the network, transport, session, presentation, and application layers. 802.2; Logical Link Control - IEEE has divided the OSI data link layer into two sub layers: Logical Link Control (LLC) and MAC sub layer implements protocols such as token passing CSMS/CD. 802.3: CSMA/CD – the IEEE 802.3 standard covers a variety of CSMA/CD architectures that are generally based on Ethernet.
IEEE LAN STANDARDS 802.4: token Bus – the IEEE 802.4 standard subcommittee sets standard for token bus networks. 802.5: Token Ring – the IEEE standards subcommittee sets standards for token ring networks. 802.6: Metropolitan Area Networks (MANs) – as noted previously the FDDI family of technologies was proposed as a standard for metropolitan are networks. The IEEE 802 LAN standards committee, however, chose a competing set of specifications, IEEE 802.6, for a MAN. -The standard is also called the distributed queue dual bus (DQDB) standard. 802.7: Broadband Technical Advisory Group – this group provides guidance and technical expertise to other groups that are establishing broadband LAN standards, such as the 803.3 subcommittee for 10Broad36. 802.8: Fiber Optic Technical Advisory Group – this group provides guidance and technical expertise to other groups that are establishing standards for LANs using fiber optic cable.
Figure 8-24 Bus A, Unidirectional Bus B, UnidirectionalDistributed Queue Dual Bus MAN Architecture
IEEE LAN STANDARDS 802.9: Integrated Data and Voice Networks – this committee sets standards for networks that carry both voice and data. Specifically, it is setting standards for interfaces to ISDN networks. 802.10 LAN Security – this committee addresses the implementation of security capabilities such as encryption, network management, and the transfer of data. 802.11: Wireless LANs – these standards cover multiple transmission methods to include infrared light, as well as a variety of broadcast frequencies to include spread spectrum radio waves and microwaves. 802.12: Demand Priority Access Method – this subgroup developed the specifications for the data link layer protocol in 100VG- AnyLAN networks.