N10-007.4 Flashcards
direct-sequence spread spectrum (DSSS)
Modulates data over an entire range of frequencies using a series of symbols called chips. A chip is shorter in duration than a bit, meaning that chips are transmitted at a higher rate than the actual data.
carrier-sense multiple access/collision avoidance (CSMA/CA)
Similar to how an Ethernet device listens to an Ethernet segment to determine whether a frame exists on the segment, a WLAN device listens for a transmission on a wireless channel to determine whether it is safe to transmit. In addition, the collision-avoidance part of the CSMA/CA algorithm causes wireless devices to wait for a random back-off time before transmitting.
Omnidirectional Antenna
Radiates power at relatively equal power levels in all directions (somewhat similar to the theoretical isotropic antenna). Omnidirectional antennas are popular in residential WLANs and SOHO locations.
Personal Mode
In the context of wireless networking, this refers to using a preshared key (PSK) instead of a centralized server, such as RADIUS, for authentication.
802.11ac
5 Ghz
Up to 1000ft range
Up to 1 Gbps Max Data Rate
Extended Service Set (ESS)
WLANs containing more than one AP are called ESS WLANs. Like BSS WLANs, ESS WLANs operate in infrastructure mode.
orthogonal frequency-division multiplexing (OFDM)
Whereas DSSS uses a high modulation rate for the symbols it sends, OFDM uses a relatively slow modulation rate for symbols. This slower modulation rate, combined with the simultaneous transmission of data over 52 data streams, helps OFDM support high data rates while resisting crosstalk between the various data streams.
802.11a
5 GHz
54 Mbps
400 ft
Independent Basic Service Set (IBSS)
A WLAN can be created without the use of an AP. Such a configuration, called an IBSS, is said to work in an ad hoc fashion.
802.11g
2.4 GHz
54 Mbps
450 ft
802.11n
2.4/5 Ghz
600 Mbps
825 ft
Basic Service Set (BSS)
WLANs that have just one AP are called BSS WLANs.
802.11b
2.4 GHz
11 Mbps
450 ft
Channel Bonding
With channel bonding, two wireless bands can be logically bonded together, forming a band with twice the bandwidth of an individual band. Some literature calls channel bonding 40MHz mode, which refers to the bonding of two adjacent 20MHz bands into a 40MHz band.
Frequency-Hopping Spread Spectrum (FHSS)
Allows the participants in a communication to hop between predetermined frequencies. Security is enhanced because the participants can predict the next frequency to be used but a third party cannot easily predict the next frequency. FHSS can also provision extra bandwidth by simultaneously using more than one frequency.
Enterprise Mode
In the context of wireless networking, this refers to using a centralized authentication server such as RADIUS for authentication, instead of a preshared key (PSK).
Classification
Classification is the process of placing traffic into different categories.
Incremental Backup
A backup job that only backs up the changed data since the last incremental backup.
Network Interface Card teaming
This technology permits multiple network interface cards to function as a single interface to the network. NIC teaming provides excellent redundancy.
Mean Time To Repair (MTTR)
The predicted time it takes to repair a network or network object.
Congestion Avoidance
If an interface’s output queue fills to capacity, newly arriving packets are discarded (or tail dropped). Congestion avoidance can prevent this behavior. RED (Random Early Detection) is an example of a congestion-avoidance mechanism.
Load Balancing
Distributing client requests among different network resources that can provide the same service or data.
Differential Backup
A type of partial backup of a data set. All data that has changed since the last full backup is targeted by the backup job.
Congestion Management
When a device, such as a switch or a router, receives traffic faster than it can be transmitted, the device attempts to buffer (or store) the extra traffic until bandwidth becomes available. This buffering process is called queuing or congestion management.
Latency
The measure of delay in a network.
Integrated Services (IntServ) (Strict)
Often referred to as hard QoS because IntServ can make strict bandwidth reservations. IntServ uses signaling among network devices to provide bandwidth reservations. Resource Reservation Protocol (RSVP) is an example of an IntServ approach to QoS. Because IntServ must be configured on every router along a packet’s path, a primary drawback of IntServ is its lack of scalability.
Policing
Instead of making a minimum amount of bandwidth available for specific traffic types, you might want to limit available bandwidth. Policing can drop exceeding traffic, as opposed to buffering it.
Link Efficiency
To make the most of the limited bandwidth available on slower speed links, you might choose to implement compression or link fragmentation and interleaving (LFI). These QoS mechanisms are examples of link efficiency mechanisms.
Committed Information Rate (CIR)
The CIR of an interface is the average traffic rate over the period of a second.
Jitter
The uneven arrival of packets.
Differentiated Services (DiffServ)
As its name suggests, DiffServ differentiates between multiple traffic flows. Specifically, packets are marked, and routers and switches can then make decisions (for example, dropping or forwarding decisions) based on those markings.
Full Backup
A backup job that ensures all data is backed up, regardless of when this data may have been backed up previously.
Traffic Shaping
Traffic shaping delays excess traffic by buffering it as opposed to dropping the excess traffic.
Common Address Redundancy Protocol (CARP)
An open standard variant of HSRP (Hot Standby Router Protocol), which provides first-hop router redundancy.
Clustering
Connecting systems together with the intent of delivering network services from the cluster to increase responsiveness and capacity. This solution also increases availability and redundancy.
