Week Thirteen Agenda Attendance Announcements Final Exam composition Franklin Live presentation Mimic Simulator Lab Assignment 4-1-3 Review Week Eleven Information Current Week Information Upcoming Assignments
Final Exam Composition Drawings • IP Address Assignment in an Enterprise Network Questions asked: 11 Answer correctly: 10 • Routing in the Enterprise Architecture Questions asked: 6 Answer correctly: 5 • Dual-stacking Questions asked: 3 Answer correctly: 2 • Loop Free Path Questions asked: 1 Answer correctly: 1 • Telephone and Internet Paths Questions asked: 8 Answer correctly: 7
Final Exam Composition True/False questions: 100 Multiple choice questions: 25 Drawing questions: 25 Total points: 150
Week Thirteen Topics Review Week Twelve Power Point presentation Information Current Week Information
Definition of CODEC A codec is a device or computer program capable of encoding and/or decoding a digital data stream or signal. The word codec is a portmanteau of 'compressor-decompressor' or, more commonly, 'coder-decoder‘.
Voice Coding and Compression CODEC • A DSP (Digital Signal Processor is a hardware component that converts the analog signal to digital format • Codecs are software drivers that are used to encode the speech in a compact enough form that they can be sent in real time across a network using the bandwidth available • Codecs are implemented within a DSP • VoIP software or hardware may give you the option to specify the codecs you prefer to use • This allows you to make a choice between voice quality and network bandwidth usage, which might be necessary if you want to allow multiple simultaneous calls to be held using an ordinary broadband connection
Coding and Compression Algorithm • The different codecs provide a certain quality of speech • Advances in technology have greatly improved the quality of compressed voice and have resulted in a variety of coding and compression algorithms • PCM: The toll quality voice expected from the PSTN. PCM runs at 64 kbps and provides no compression, and therefore no opportunity for bandwidth savings • The other algorithms use compression to save bandwidth • Voice quality is affected
Which CODEC is most affective? G.729 is the recommended voice codec for most WAN networks (that do not do multiple encodings) because of its relatively low bandwidth requirements and high mean opinion score (MOS) (ITU-T P.800)
Reducing the Amount of Voice Traffic • The codecs chosen are a trade-off between bandwidth and voice quality • Technique used to reduce voice traffic: cRTP
cRTP • Every IP packet consists of a header and the payload (data, voice) • Although the payload of a voice packet is small (20 bytes when G.729 is used), the header is 40 bytes • cRTP compresses the header to 2 or 4 bytes • Use on slow WAN links, but it is CPU intensive
VAD Voice Activity Detection • On average, about 35 percent of calls are silent. • In traditional voice networks, all voice calls use a fixed bandwidth of 64 kbps regardless of how much of the conversation is speech and how much is silence • When VoIP is used, this silence is packetized along with the conversation. • VAD suppresses packets of silence, so instead of sending IP packets of silence, only IP packets of conversation are sent • Therefore,gateways can interleave data traffic with actual voice conversation traffic, resulting in more effective use of the network bandwidth
CAC –Call Admission Control • CAC protects voice traffic from being negatively affected by other voice traffic by keeping excess voice traffic off the network. • If a WAN link is fully utilized with voice traffic then adding more voice calls will degrade all the calls • CAC checks if the link is maximized and won’t allow new calls to go through until bandwidth is available • Callers will get a busy signal or “all circuits busy message”
LFI Link fragmentation and interleaving ensures that small voice packets don’t get stuck behind a large data packet The data packets are fragmented into smaller packets The voice packets can slip in between them because the are initially small.
Wireless Technologies • MMDS = Multichannel multipoint distribution services used for general purpose broadband networking. United States • LMDS = Local multipoint distribution service used for wireless cable television (TV), referring to premium wireless subscription TV rather than traditional free broadcast TV or cable TV.
Wireless Technologies • GSM = Global system for mobile communication is a cellular phone protocol. Used in many part of the world. • GPRS = General packet radio service is a radio technology for GSM networks. Europe and Asia. Not related to GPS • CDMA = Code division multiple access is a cellular phone protocol used for digital communication. United States
What is RF? • Radio frequency is a term that refers to alternating current (AC) having characteristics such that, if the current is input to an antenna, an electromagnetic (EM) field is generated suitable for wireless broadcasting and/or communications. • Frequencies of electromagnetic radiation in the range between 10 kHz and 300 MHz. • Many types of wireless devices make use of RF fields. Cordless and cellular phone , radio and television broadcast stations, satellite communications systems, and two-way radio services all operate in the RF spectrum.
Phenomena Affecting RF • Reflection: Occurs when the RF signal bounces off objects such as metal or glass surfaces. • Refraction: Occurs when the RF signal passes through objects such as glass surfaces and changes direction. • Absorption: Occurs when an object, such as a wall or furniture, absorbs the RF signal. • Scattering: Occurs when an RF wave strikes an uneven surface and reflects in many directions. Scattering also occurs when an RF wave travels through a medium that consists of objects that are much smaller than the signal’s wavelength, such as heavy dust. • Diffraction: Occurs when an RF wave strikes sharp edges, such as external corners of buildings, which bend the signal. • Multipath: Occurs when an RF signal has more than one path between the sender and receiver. The multiple signals at the receiver might result in a distorted, low-quality signal.
Power Consumption by WLANs • WLANs transmit signals just as radio stations do to reach their listeners • The transmit power levels for WLANs are in milliwatts (mW), whereas for radio stations the power levels are in megawatts (MW) • The amount of power that can be used in WLANs is set by the FCC • Wireless LANs operate in the unlicensed frequency bands, which is why they operate at very low power levels
Wireless LANs • 802.11 wireless LANs extend the 802.3 Ethernet LAN infrastructures to provide additional connectivity options. • In an 802.3 Ethernet LAN, each client has a cable that connects the client NIC to a switch. • The switch is the point where the client gains access to the network. • In a wireless LAN, each client uses a wireless adapter to gain access to the network through a wireless device such as a wireless router or access point. • The wireless adapter in the client communicates with the wireless router or access point using RF signals. • Once connected to the network, wireless clients can access network resources just as if they were wired to the network.
Wireless LAN Standard 802.11 wireless LAN is an IEEE standard that defines how radio frequency (RF) in the unlicensed industrial, scientific, and medical (ISM) frequency bands is used for the physical layer and the MAC sub-layer of wireless links. Data Rate: 802.11a: 54 Mbps at 5 GHz 802.11b: 11 Mbps at 2.4 GHz 802.11g: 54 Mbps at 2.4 GHz
Wireless LAN Standard Modulation technique: Direct Sequence Spread Spectrum (DSSS) 802.11b, 802.11g Orthogonal Frequency Division Multiplexing (OFDM). 802.11a, 802.11g, 802.11n Band: 2.4 GHz: 802.11b, 802.11g, 802.11n 5 GHz: 802.11a, 802.11n
IEEE 802.11a 802.11a OFDM modulation and uses the 5 GHz band. Less likely to experience interference than devices that operate in the 2.4 GHz band Because there are fewer consumer devices that use the 5 GHz band. There are some important disadvantages to using the 5 GHz band. The first is that higher frequency radio waves are more easilyabsorbed by obstacles such as walls, making 802.11a susceptible to poor performance due to obstructions. The second is that this higher frequency band has slightly poorer range than either 802.11b or g. Also, some countries, including Russia, do not permit the use of the 5 GHz band, which may continue to curtail its deployment.
IEEE 802.11n 802.11n The IEEE 802.11n standard is intended to improve WLAN data rates and range without requiring additional power or RF band allocation. 802.11n uses multiple radios and antennas at endpoints, each broadcasting on the same frequency to establish multiple streams. The multiple input/multiple output (MIMO) technology splits a high data-rate stream into multiple lower rate streams and broadcasts them simultaneously over the available radios and antennae. This allows for a theoretical maximum data rate of 248 Mb/s using two streams. The standard is now ratified
IEEE 802.11n Operates in the 2.4 GHz band or in the 5 GHz band The 2.4GHz band is more crowded with interference from lots of other devices and 802.11g networks The 5GHz band is less crowded but the range is less Terminology: • A “dual-frequency” or “dual-band” AP allows you to select which band 2.4GHz or 5 GHz • A “dual-radio” AP allows the AP to operate at both frequencies • You can allows your old 802.11g clients to connect on the 2.4 GHz band and your new 802.11n clients to connect on the 5GHz band
Wi-Fi Certification The 3 key organizations influencing WLAN standards are: • ITU-R ITU-R regulates allocation of RF bands. The ITU-R regulates the allocation of the RF spectrum. • IEEE IEEE specifies how RF is modulated to carry information. The IEEE developed and maintains the standards for local and metropolitan area networks. The dominant standards in the IEEE 802 are 802.3 Ethernet, and 802.11 Wireless LAN
Wi-Fi Certification • Wi-Fi Alliance (www.wi-fi.org) Wi-Fi ensures that vendors make devices that are interoperable. The Wi-Fi Alliance is to improve the interoperability of products by certifying vendors for conformance to industry norms and adherence to standards. Certification includes all three IEEE 802.11 RF technologies, as well as early adoption of pending IEEE drafts, such as 802.11n, and the WPA and WPA2security standards based on IEEE 802.11i.
802.11g and n (2.4GHz) Although there are 11 channels, these channels overlap each other You can have only use three APs in close proximity without interference. The APS will operate on channels 1, 6 and 11
802.11a and n (5GHz) • Twelve separate non-overlapping channels • As a result, you can have up to twelve access points set to different channels in the same area without them interfering with each other. • This makes access point channel assignment much easier and significantly increases the throughput the wireless LAN can deliver within a given area. • In addition, RF interference is much less likely because of the less- crowded 5 GHz band.
Wireless NICs • The device that makes a client station capable of sending and receiving RF signals is the wireless NIC. • Like an Ethernet NIC, the wireless NIC, using the modulation technique it is configured to use, encodes a data stream onto an RF signal. • Wireless NICs are most often associated with mobile devices, such as laptop computers. • In the 1990s , wireless NICs for laptops were cards that slipped into the PCMCIA slot. • PCMCIA wireless NICs are still common, but many manufacturers have begun building the wireless NIC right into the laptop. • Unlike 802.3 Ethernet interfaces built into PCs, the wireless NIC is not visible, because there is no requirement to connect a cable to it.
Wireless NICs Other options have emerged over the years as well. Desktops located in an existing, non-wired facility can have a wireless PCI NIC installed. To quickly set up a PC, mobile or desktop, with a wireless NIC, there are many USB options available as well.
Wireless Access Point (AP) • An access point connects wireless clients (or stations) to the wired LAN. • An access point is a Layer 2 device that functions like an 802.3 Ethernet hub. • Client devices do not typically communicate directly with each other; they communicate with the AP. • In essence, an access point converts the TCP/IP data packets from their 802.11 frame encapsulation format in the air to the 802.3 Ethernet frame format on the wired Ethernet network.
WLAN Operation • The coverage area of an AP is called the Basic Service Set (BSS). Otherwise known as a cell. • A Service Set Identifier (SSID) is an identifier name for a WLAN. • Roaming occurs when a wireless client moves from being associated to one AP to another AP. Basically, moving from one cell to another cell within the same SSID.
WLAN Security • Authentication: Only legitimate clients are allowed to access the network via trusted APs. • Encryption: Securing the confidentiality of transmitted data. • Intrusion detection and intrusion protection: Monitors, detects, and reduces unauthorized access and attacks against the network.
Wireless Network Technologies • Personal-area network (PAN): A persons personal workspace. • Local-area network (WLAN): A network design to be enterprise-based network that allows the use of complete suites of enterprise applications, without wires. • Metropolitan-area network (MAN): Deployed inside a metropolitan area, allowing wireless connectivity throughout an urban area. • Wide-area network (WAN): A wider but slower area of coverage, such as rural areas.
Autonomous AP • Originally in WLANs, all of the configurations and management was done on each access point • This type of access point was a stand-alone device • The term for this is a fat AP, standalone AP, intelligent AP, or, most commonly, an autonomous AP • All encryption and decryption mechanisms and MAC layer mechanisms also operate within the autonomous AP
Autonomous AP Autonomous AP require power in not traditional places. Two solutions: 1. Power of Ethernet (PoE) and power injectors. This power is inline with the Ethernet port, over the Category 5 coble. 2. Midspan power injectors is a stand alone unit, positioned into the LAN between the Ethernet switch and the device requiring power.
Autonomous AP • IEEE 802.1X is used for wireless client authentication, dynamic encryption keys can be distributed to each user, each time that user authenticates on the network. Wi-Fi Alliance also introduced Wi-Fi Protection Access (WPA) to enhance encryption and protect against all known WEP key vulnerabilities. The Wi-Fi Alliance interoperable implementation of 802.11i with AES is called WPA2.
Autonomous AP The autonomous AP acts as an 802.1Q translational bridge and is responsible for putting the wireless client RF traffic into the appropriate local VLAN on the wired network. Draw Autonomous AP / Traffic into VLANs.
Designing a Wireless Networks RF Site Survey is used for many reasons in a wireless network design, and the process to conduct such a survey. It is the first step in the design and deployment of a wireless network and the one to insure desired operation.