Chapter 8 - Local Area Networks: Part 2

A)    Wireless Ethernet (233 – 266)

a.    Wireless LAN (Wireless Ethernet) – a local area network that is not based primarily on physical wiring but uses wireless transmission between workstations

                                          i.    Components of a wireless LAN

1.    User device must have a NIC that can receive and transmit wirelessly

2.    Wired local area network

3.    Access point – the interface device between the wireless user device and the wired local area network

                                         ii.    Configurations of a wireless LAN

1.    Single-cell wireless LAN – at the center of the cell is the access point which is connected to the wired LAN. All user devices communicate with this one access point and compete for the same set of frequencies. This standard is called Basic Service Set (BSS)

         

2.    Multiple cells are supports by multiple access points, as in a cellular telephone network. Users communicate with the nearest access point and may move from one cell to another

           

3.    Peer-to-Peer (Ad hoc layout) – no access point at the center of a cell, each user device communicates directly with the other user device

b.    Wireless LAN Standards

                                          i.    IEEE 802 suite of protocols was created to support the many different types of wireless local area networks in existence

IEEE 802.11b	11 Mbps using 2.4 GHz
IEEE 802.11g	54 Mbps using 2.4 GHz
IEEE 802.11a	54 Mbps using 5GHz
IEEE 802.11ac	Uses 5GHz

                                         ii.    Multiple input multiple output (MIMO) – technique in which both the mobile device and the access point have multiple, smart antennae that help to reduce signal interference and reflections

                                         iii.    Wired equivalent privacy (WEP) – security protocol for wireless LAN, not powerful enough to stop wiretapping and key was too small and not changeable

                              iv.   Wi-Fi Protected Access (WPA)

1.    Temporary Key Integrity Program (TKIP) – uses 128.bit key on each packet and it changes with each packet transmitted, making it nearly impossible for an unauthorized user with a wireless device to connect to a WPA-protected signal

                                         v.    Wi-Fi Protected Access II (WPA2) – uses CCMP (counter mode with cipher block chaining message authentication code protocol) instead of TKIP

c.    Wireless CSMA/CA

                                          i.    Carrier sense multiple access with collision avoidance (CSMA/CA) – if a user device wishes to transmit and the medium is idle, the device is not allowed to transmit immediately. Instead, the device is made to wait for a small period of time called the initerframe space (IFS). If the medium is still idle after this interframe space, the device is then allowed to transmit

B)    Network Operating Systems

a.    Operating System – program initially loaded into computer memory when the computer is turned on; it manages all the other programs (Applications) and resources (such as disk drives, memory, and peripheral devices) in a computer

                                          i.    Even after an application starts and is being executed, the application makes use of the operating system by making service requests through a defined application programming interface (API)

                                         ii.    Multitasking operating system – multiple programs can be running at the same time. In this case, the operating system schedules each task and allocates a small amount of time for the execution of that task

                                         iii.    Network operating system (NOS) – large, complex program that can manage the common resources on most local area networks, in addition to performing the standard operating system services mentioned previously

                            

C)    Network operating systems past and present

a.    Novell NetWare

                                          i.    NetWare Directory Services (NDS) – an intelligent system that authenticates users and includes a distributed database of information about every application, user, server, and resource on a network

                                         ii.    Redirection – when print requests are automatically forwarded to another printer on the network

                                         iii.    Bindery – structure (similar to a database) that contains the usernames and passwords of network users and group of users authorized to log in to that server; it consists of three linked, nonidentical files that are encrypted for security reasons

                                        iv.    Organizational unit (OU) – an object that is further composed of additional objects (examples of which include servers, printers, users, or groups of users)

                                         v.    Leaf objects – not composed of any objects and are usually entities such as the users, peripherals, servers, printers, queues, and other network resources

b.    Microsoft Windows NT and Windows Server

                                          i.    Windows NT Version 4

1.    Domain – container object that contained users, servers, printers, and other network resources

a.    Not hierarchical

                                         ii.    Windows Server 2000

1.    Active directory – stores information about all the objects and resources in a network and makes this information available to users, network administrators, and application programs

           

                                         iii.    Windows Server 2003

1.    Updates to the Active directory, including a new management tool that unifies all the tasks related to group policy

2.    Capability to interconnect (cluster) up to eight Windows 2003 servers for better user and application support

3.    New and improved file and printer support services, including increased reliability, wider range of supported printers, and remote document sharing

4.    Support for internet protocol version 6 (IPv6)

5.    Better security features for files, networks, servers, the operating system, and web-based transactions

                                        iv.    Windows Server 2008 and 2012

c.    UNIX – popular operating system that can be found on single-user workstations as well as on mainframe computers and servers. Most often found with a text-based interface

d.    Linux – based on UNIX concept and is a complete rewrite of the UNIX kernel and borrows additional functions from the well-established Free Software Foundation’s GNU toolset and from the even larger free software community

e.    Mac OS X Server – capable of supporting both Macintosh and Windows workgroups, and is based on software created by the open-source community

D)    Servers

a.    Server – the computer that stores software resources such as the network operating system, computer application, programs, databases, and performs one or more network-type services for attached clients

b.    Redundant Array of Independent Disks (RAID) – collection of techniques for interfacing multiple hard disk drives to a computer

                                          i.    RAID-0 – data is broken into pieces, and each piece is stored on different disk drives, known as stripping

                                         ii.    RAID-1 – data stored on at least 2 disk drives, in duplicate, disk mirroring

                                         iii.    RAID-3 – data is redundantly stored across multiple hard drives (stripping) and error-checking information concerning the stored data is kept on a separate disk. This error-checking is used to detect errors and possibly reconstruct the data should some of it become corrupted

                                        iv.    RAID-5 – data is broken into pieces (stripes) and stored across three or more disks. Parity information (error-checking code) is stored along with the stripped data, not on a separate disk

c.    Server virtualization – making one computer (or server) act as if it were multiple computers (or servers)

d.    Server appliance – single unit or box that supports many networking functions such as internet sharing, intranet Web serving, firewall security, FTP services, file and print serving, e-mail service, and virtual private network configurations

e.    Server blade – server that has no cabinet or box but resides on a single printed circuit card

f.      Peer-to-peer network – allows communications between workstations, as if the workstations were all equal

E)    Network support software

a.    Utilities – software programs that operate in the background and support one or more functions to keep the network running at optimal performance

                                          i.    Antivirus software – designed to detect and remove viruses that have infected the computer’s memory, disks, or operating system

                                         ii.    Spam – unsolicited commercial bulk e-mail

1.    Anti-spam software – used to block this unwanted e-mail

                                         iii.    Spyware – software that a user unknowingly downloads from the internet, and when this software is executed on the user’s machine, it begins spying on the user

1.    Anti-spyware software – can located and clean the spyware programs found in a computer’s memory and hard disk drive

                                        iv.    Backup software – allows network administrators to back up data files currently stored on a server’s hard disk drive

                                         v.    Crash protection software – performs crash stalling or to try to keep the operating system running long enough to perform a graceful exit

                                        vi.    Network-monitoring software – incorporates a fairly large number of network support tools

1.    Sniffers – can “listen” to traffic on a network and determine if invalid messages are being transmitted, report network programs such as malfunctioning NICs, and detect traffic congestion problems

                                       vii.    Remote access software – allows a user to access all of the possible functions of a personal computer workstation from a mobile or remote location

                                       viii.    Security assessment software – designed to scan an IP address or a range of IP addresses for any type of security weakness

1.    May include ports that are open, improperly designed shares and trusts, suspicious processes running in the background, and known vulnerabilities in the operating system that have not yet been corrected

                                        ix.    Uninstall software – works with the user to locate and remove applications that are no longer desired

b.    Internet software – toolset to support internet-related services

                                          i.    Web server software – application or set of programs that store web pages and allows browsers from anywhere in the world to access those web pages

F)     Software Licensing Agreements – legal contract that describes a number of conditions that must be upheld for proper use of the software package

a.    Single-user-single-station license – software package may be installed on a single machine and then only a single user at one time may use that machine

b.    Single-user-multiple-station license – designed for the user who might have a desktop machine at work and a laptop machine for remote sites, or another desktop machine at home

c.    Interactive user license – operating system user license, and controlled number of concurrent user’s license all refer to essentially the same situation. When a software package is installed on a multiuser system, it is possible for multiple users to execute multiple copies of a single program

d.    Server license – rarely a software counter controlling the current number of users

e.    Site license – allows a software package to be installed on any and all workstations and servers at a given site

f.      Corporate license – allows a software package to be installed anywhere within a corporation, even if installation involved multiple sites

g.    General Public License (GPL) – associated with software that is free to share and change

G)   Lan support devices

a.    Uninterrupted Power Supply (UPS) – a battery backup device that can maintain power to one or more pieces of equipment for short periods of time (usually less than one hour)

b.    Network attached storage (NAS) – computer-based device that provides a large amount of storage to users on a network

c.    Storage area network (SAN) – simpler storage device and uses network protocols such as iSCSI and Fibre channel to store and receive data

d.    Media converters – used for converting signals from one medium to another

e.    Thin client workstation – a computer with no disk drives of any kind, often with reduced memory, and some form of specialized and/or minimalized operating system. Can also be called zero-client workstation

Chapter 7 - Local Area Networks: Part 1

A)    Introduction (201 – 227)

a.    Local area network (LAN) – a communication network that interconnects a variety of data communications devices within a small geographic area and transmits data at high data transfer rates

B)    Primary Function of Local Area Networks

a.    File server – when a network performs file serving and is connected to a workstation with a large storage disk drive that acts as a central storage repository

b.    Print server – provides workstations with authorization to access a particular printer, accepts and queues print jobs, prints cover sheets, and allows users access to the job queue for routine administrative functions

C)    The First Local Area Network: The BUS/Tree

a.    Bus/tree local area network (bus LAN) – first physical design when LANs became commercially available. It is simply a linear coaxial cable which multiple devices or workstations tap

                                          i.    Tap – it is a passive device, as it does not alter the signal and does not require electricity to operate

                                         ii.    Network interface card (NIC) – electronic device, sometimes in the form of a computer circuit board or part of a larger circuit board, that performs the necessary signal conversions and protocol operations that allow the workstation to send and receive data on the network

                                         iii.    Baseband technology is bidirectional, meaning that when the signal is transmitted from a given workstation, the signal propagates away from the source in both directions on the cable

                                        iv.    Trees – splitting and joining broadband cables and signals to create configurations more complex than a single linear bus. These more complex bus topologies consisting of multiple interconnected cable segments are called trees

D)    A More Modern LAN

a.    Star-wired bus LAN – most popular configuration for a local area network today

                                          i.    Logical design – a network determines how the data moves around the network from workstation to workstation

                                         ii.    Physical design – pattern formed by the locations of the elements of the network, as it would appear if drawn on a sheet of paper

                                         iii.    Hub – nonintelligent device that simple and immediately retransmits the data it receives from any workstation out to all other workstations (or devices) connected to the hub

                                        iv.    Shared network – when two or more hubs are interconnected and a workstation transmits data, all the workstations connected to all the hubs receive the data. All devices on the network are sharing the one bandwidth

                                         v.    Medium access control protocol – software that allows a device to place data onto a hub-based local area network (as well as other networks that require their workstations to compete for access to the network)

1.    Contention-based protocols – carrier sense multiple access with collision detection

2.    Round-robin protocols – such as token passing

b.    Contention-based protocols – first come, first served protocol. The first station to recognize that no other stations is transmitting data and places it data onto the medium is the first station to transmit

                                          i.    Carrier sense multiple access with collection detection (CSMA/CD) – only one workstation at a time can transmit and because of this, it is a half-duplex protocol

                                         ii.    Collision – occurs when two or more workstations listen to the medium at the same moment, hear nothing, and then transmit their data at the same moment

                                         iii.    Collision window – a workstation will not hear a collision until its data has, on average, traveled halfway down the bus, collided with the other workstation’s signal, and then propagate back down the bus to the first workstation, this interval is the collision window

                                        iv.    Nondeterministic protocol – one in which you cannot calculate the time at which a workstation will transmit

E)    Switches – uses addresses and processing power to direct a frame out a particular port, thus reducing the amount of traffic on the network

a.    Components of a switch

                                          i.    Transparent – switches that learn by themselves which NICs are on their network

                                         ii.    Backward learning – observing the location from which a frame has come

                                         iii.    Backplane – the main hardware of the switch which must be fast enough to support the aggregate or total bandwidth of all the ports

                                        iv.    Hot swappable – possible to insert and remove cards while the power to the unit is still on

                                         v.    Cut-through architecture – the data frame begins to exit the switch almost as soon as it begins to enter the switch. It does not store the data frame, it just forwards it

                                        vi.    Store-and-forward device – holds in the entire frame for a small amount of time while various fields of the frame are examined, a procedure that diminishes the overall network throughput

                                       vii.    Shared segment network – a switch may be connected to a hub (or several hubs), which then connects multiple workstations, because they are connected to a hub, they are sharing one channel, thus limiting bandwidth

                                       viii.    Dedicated segment network – a switch may be directly connected to one or more workstations. Each workstation then has a private or dedicated connection

b.    Isolating Traffic patterns and providing multiple access

c.    Full-duplex switch – allow for a CSMA/CD network to simultaneously transmit and receive data to and from a workstation

d.    Virtual LAN (VLAN) – logical subgroup within a local area network created via switches and software rather than by manually moving wiring from one network device to another

e.    Link aggregation – allows you to combine two or more data paths, or links, into one higher-speed link

f.      Spanning tree algorithm – consists of four steps

                                          i.    First, designate a root switch

                                         ii.    Second, visit each switch, at each switch, identify the port/connection that leads you back to the root switch in the fewest number of hops

                                         iii.    Third, visit each local area network, at each network, identify the port/connection that leads you back to the root switch in the fewest number of hops

                                        iv.    Finally, the ports that remain without either an RP designation or a DP designation can be removed, which means updating it so that data is not passed through those ports

                                         v.    Rapid spanning tree protocol (RSTP) – can recompute the spanning tree algorithm in roughly a few seconds

g.    Quality of service

F)     Wired Ethernet

a.    Ethernet – first commercially available local area network system and remain the most popular today

b.    Power over Ethernet (PoE) – sending electrical power over the Ethernet connection

G)   Wired Ethernet Frame Format

a.    Medium access control (MAC) sublayer – works closely with the physical layer and contains a header, computer (physical) addresses, error-detection codes, and control information

b.    Logical link control (LLC) sublayer – responsible for logical addressing and providing error control and flow control information

c.    Runts (frame fragments) – frames that are shorter than 64 byes and are automatically discarded