CHAPTER 4
1. Why is a focus on information systems insufficient in networking?
Because the network professionals often has to focus on the broader business system in which the information system is embedded.
2. Compare trends in network demand and network budgets.
The network demand is likely to grow rapidly in the future, just as it has always done in the past. The network budgets are growing very slow
3. What are QoS metrics? (Do not just spell out the acronym.)
QoS metrics stands for quality-of-service metrics that is metrics that is quantitative measures of network performance. For instance, companies use QoS metric to quantify their quality of service so that they can set targets and determine if they have met those taargets
4.
a. In what units is transmission speed normally measured?
Speed measured in factor of 1,000 not 1024
b. Is speed normally measured in bits per second or bytes per second?
Bits per second
c. Give the names and abbreviations for speeds in increasing factors of 1,000.
Kbps: kilobits per second- 1,000 bps
Mbps: megabits per second- 1,000 kbps
Gbps: gigabits per second- 1,000 Mbps
Tbps: terabits per second- 1,000 Gbps
d. What is 55,000,000,000 bps with a metric prefix?
55Gbps
e. Write out 100 kbps in bits per second (without a metric prefix).
100, 000 bps
f. Write the following speeds properly: 0.067 Mbps, 23,000 kbps, and 48.62Gbps.
0.067 Mbps= 67,000bps
23,000 kbps= 23,000,000 bps
48.62Gbps=48,620,000,000
5. Distinguish between rated speed and throughput.
A network’s rated speed is the speed it should achieve based on vendor claims or on the standard that defines the technology while a network’s throughput is the data transmission speed the network actually provides to users.
6.
a. What is availability?
The percentage of time that the network is available for use.
b. What is downtime?
The percentage of the time that the network is not available
c. What are the “five nines”?
The availability target is 99.999%. Data networks generally have lower availability but are under pressure to improve their availability given the cost of network downtime to firms today.
d. What are packets?
Host send data in small messages called packets.
e. When should error rates be measured? Why?
Error rates should be measured when network is overload, error rates can soar because the network has to drop the packet it cannot handle.
f. What is latency?
Latency is the amount of delay measured in milliseconds.
g. In what units is latency measured?
Measured in milliseconds
h. What is jitter?
Jitter occurs when the latency between successive packets varies.
i. For what applications is jitter a problem?
Make voice sound jittery.
7.
a. What are service level agreements?
Contracts that guarantee levels of performance for various metrics such as speed and availability. If a service does not meet the SLA guarantees, the service must pay a penalty to its customer.
b. Does an SLA measure the best case or the worst case?
Yes. Service will be no worse than a specific number.
8. Do a three-site traffic analysis. Site X attaches to Site Y, which attaches to Site Z. Site X is 130 meters east of Site Y. Site Z is 180 meters west of Site Y. Site X needs to be able to communicate with Site Y at 3 Gbps. Site Y needs to be able to communicate with Site Z at 1 Gbps. Site X needs to be able to communicate with Site Z at 700 Mbps. Supply your picture giving the analysis. You may want to do this in Office Visio or Windows Draw and then paste it into your homework. (Tip. Check page 151)
a. What traffic capacity will you need between Sites X and Y?
(700Mbps + 3Gbps) = 462.5 Mbps
b. Between Y and Z?
(700Mbps + 1Gbps) =212.5Mbps
[pic]
9. What is the purpose of redundancy in transmission lines?
To provide backup paths in case another line fails.
a. If the line between R and S fails in Figure 4-11, how much capacity will the line between Q and S need?
(300Mbps + 2Gbps) = 287.5Mbps [pic]
b. What about the line between Q and R?
(300Mbps + 2.04500Gbps) = 293.125000 Mbps
10.
a. What is a network topology?
Refers to the physical arrangement of network’s computers, switches, routers, and transmission line.
b. At what layer do we find topologies?
Physical layer concept
11.
a. What is the advantage of a full-mesh leased line network?
Provides direct connections between every pair of sites. It provides many redundant paths so that if one site or leased line fails, communication can continue unimpeded.
b. What is the disadvantage?
Prohibitively expensive if a company has many sites.
12. How long are momentary traffic peaks?
Lasting a fraction of a second to a few seconds are bound to occur
a. Distinguish between overprovisioning and priority.
Overprovisioning is adding more switching and transmission line capacity than will be needed most of the time. It will be rare for momentary traffic peaks to exceed capacity.
Priority assign high priority to latency-intolerant applications such as voice, while giving low priority to latency-tolerant applications, such as e-mail.
b. How is traffic shaping different from traditional approaches to handling momentary traffic overloads?
Only traffic shaping can dramatically reduce network cost and highly labor intensive.
13. Why is traffic shaping a more general tool than just being a way to handle momentary traffic peaks?
Traffic shaping is not just a tool of dealing with momentary traffic peaks. By eliminating some types of traffic entirely and by limiting other types of traffic to small percentages of total network traffic, traffic shaping can substantially reduce the overall traffic must handle at all times.
14. Should products that fail to meet minimum requirements be dropped from consideration?
Yes, specification that must be met. Noncompliant product that do not need a minimum requirement cannot be considered. Scalability is a concern.
15. We are considering products A, B, and C. Our criteria are price, performance, and reliability with weights of 20 percent, 40 percent, and 40 percent, respectively. Product A’s evaluation scores on these three criteria are 8, 6, and 6, respectively. For B, the values are 6, 8, and 8, respectively. For C, they are 7, 7, and 7, respectively. Present a multicriteria analysis of the decision problem in tabular form and showing all work. Interpret the table. (Tip. Check pages 163–164)
16.
a. Distinguish between the systems development life cycle and the systems life cycle.
System development Life Cycle (SDLC) Cost: -Hardware: full price: base price and necessary components -Software: Full price: base price and necessary components -Labor cost: Networking staff and user costs -Outsourcing development costs -Total development investment
System Life Cycle (SLC) Costs: -Total cost of Ownership Total cost over entire life cycle SDLC cost plus carrier cost Carrier pricing is complex and difficult to analyze Must deal with leases
b. What is the total cost of ownership (TCO)?
The cost of a system over its entire life cycle is called TCO
c. Why should operating and management costs be considered in addition to hardware, software, and transmission costs in purchasing decisions?
Because it is important to consider how much labor is involved in operating and managing the equipment and software.
17.
a. For what is OAM&P an abbreviation in ongoing management?
OAM&P= operations, administration, maintenance and provision is the most important and expensive part of the system life cycle.
b. Distinguish between operations and maintenance.
Operations: moment-by-moment traffic management; network operations center (NOC)
Maintenance: Fixing things that go wrong; preventive maintenance; and should be separate from the operations staff.
18. Assume that an average SNMP response message is 100 bytes long. Assume that a manager sends 40 SNMP Get commands each second. What percentage of a 100 Mbps LAN link’s capacity would the resulting response traffic represent?
.032%
CHAPTER 5
1.
a) Distinguish between LANs and WANs.
Local Area Network (LANs) exists within a company’s site, while Wide Area Network (WANs) connects different sites within an organization or transmits data between organizations.
b) What are rights of way?
Permission to lay wires in public area
c) What are carriers?
For transmission beyond its premises, a company use carrier that has received government right of way to lay wires in public locations or to send radio signal beyond the customer premises.
d) Why do you have more flexibility with LAN service than with WAN service?
For LANS, the company owns the property and can do what it wants and choose the technology it wishes.
e) What is the advantage of using carriers?
Since there are only few carrier in most communicates, each carrier typically only a few technologies and services options. The carrier operates and maintains the WANs, freeing companies of the need to staff the network.
2. Why are typical WAN speeds slower than typical LAN speeds? Give a clear and complete argument.
First, as the cost per gig increases; transmission lines get longer. Second, WAN connections are shared by many users.
3.
a) Distinguish between the two types of Ethernet switches in terms of what they connect.
Switches that connect host to the network are workgroup switches. Switches that connect switches to other switches are core switches.
b) Distinguish between the two types of Ethernet transmission link technologies in terms of what they connect.
Transmission links that connect host to workgroup switches are called access links. Transmission links that connect switches to other switches are called trunk links.
c) Why must core switches have more processing power than workgroup switches?
Because core switches must carry the frames of many conversations, so they must have high processing speeds while workgroup switches only carry the conversations of the host they serve directly. They can only operate much more slowly and still give adequate service.
4.
a) What is a MAN? (Don’t just spell out the acronym.)
Metropolitan Area network (MAN), it is a type of WAN limited to a large city and its surrounding communities. Distances are shorter for MANs than for National or international WANs.
b) What standards association creates most LAN standards?
The work of the 802 Committee is done in working groups. The terms Ethernet and 802.3 are interchangeable.
c) What is the name of its committee for developing LAN standards?
The 802.11 Working Group creates the wireless LAN standards.
d) What 802 working group creates Ethernet standards?
802.3 Working Group
e) What working group is likely to develop security standards to be used by multiple LAN/ WAN technologies?
802 LAN.WAN Standards Committee
f) When do vendors begin to develop products based on new 802.3 standards?
As soon as a standard comes out of 803.3 Working group vendors begin to build products using the standard.
5.
a) At what layers do single networks require standards?
Use standards at the physical layer and the data link layer
b) Is Ethernet processing executed in hardware or software?
Hardware
c) What circuit implements both of the physical and data link layer processes in Ethernet?
Network Interface Card (NIC)
6. What three things do physical layer standards govern?
Connector, Medium, Speed
7.
a) What must a sender do to send the bits of a frame over a transmission medium?
The sender must convert the 1s and 0s into physical signals. These signal will travel down the transmission link to the device at the other end of the physical link.
b) Distinguish between binary and digital signaling.
Binary has two states: 1 and 0 (high and low voltage)
Digital has a range of states (2, 4, 8 ... 256)
c) What is a state?
A certain number of bits, usually a multiple of 2.
d) Why is binary transmission error-resistant?
Because it has a wide range of accepted voltage, therefore even with attenuation, the signal will still transmit.
e) In Figure 5-7, how much could the signal attenuate before it became unreadable?
The attenuation does not cause an error in reading the signal. This is why binary transmission is error-resistant.
8.
a) What type of copper wiring is widely used in Ethernet?
4-pair UTP
b) How many wires are there in a UTP cord?
8
c) How many pairs?
4
d) What type of connectors and jacks does 4-pair UTP use?
RJ45
e) What is the advantage of parallel transmission compared to serial transmission?
faster transmission speeds
9.
a) List the three main propagation effects that can impair a signal travelling through UTP wire.
Attenuation (gets weaker)
Noise (random energy)
Terminal Crosstalk Interference (from other electronics, i.g. air conditioner)
b) List the two ways in which these effects are controlled.
Limit cord distance to 100 m
Limit the untwisting of the wires in each pair to 1.25 cm whe placing them in an RJ-45 connector.
c) Which types of propagation effects are controlled by which control method?
Attenuation and noise controlled by limiting the length of the cord. Crosswalk limited by limiting the untwisting of wires in each pair to ½ inch when connecting to RJ45
d) Why is terminal crosstalk interference the main type of interference problem?
It can produce errors or make signal unreadable.
10.
a) Of what wire characteristic is category a measure?
Cable quality is indicated by its category number.
b) What types of UTP wiring can carry signals 100 meters at 1 Gbps?
1000BaseBASE-T
c) What types of UTP wiring can carry signals in 10GBASE-T?
10GBASE-T
d) Which can carry 10Gbps Ethernet 100 meters?
10GBASE-T
11.
a) Does the signal travel through the optical fiber core, cladding, or both?
The signal travels out in the core, and back in the cladding.
b) Why can signals travel very far through optical fiber?
They won't attenuate traveling through the cord
c) Why does an optical fiber cord have two strands?
The ability to transmit in two directions simultaneously. Each strand carries the signal in one direction.
d) What is the ability to transmit in both directions simultaneously called?
Optical Fiber Cord with two strands for Full Duplex Communication
e) Why does modal dispersion happen?
The limiting factor in LAN fiber distance is modal dispersion. If modal dispersion is too large, parts of the light from sequential light pluses will overlap, making the signal unreadable.
f) When will modal dispersion be a problem?
Modal dispersion set a limit on LAN fiber distances.
12.
a) Comparing LAN and WAN fiber, what are distance limits?
Optical fiber in LANs uses 850 nm light core and diameters of 50 or 6.25 microns.
LAN Fiber required distance span 200 to 300m versus to carrier WAN Fiber 1-40 m.
b) What light wavelengths are used?
LAN Fiber: 850 nm
Carrier WAN Fiber: 1,310 t 1,550nm
c) What are the two diameters for multimode fiber?
LAN Fiber: 50 or 62.5 microns
d) What is the diameter of single-mode fiber?
8.3 microns
e) What are the principle distance limiting factors for LAN and carrier fiber?
Modal Dispersion and Absorptive Attenuation
f) Is modal bandwidth a quality measure for LAN fiber, carrier fiber, or both?
LAN Fiber
13. What is link aggregation?
Allows to increase trunk speed incrementally, by a factor of two or three, instead of by a factor of ten.
14.
a) What steps would you go through to use the information in Figure 5-12 and Figure 5-15 in network design?
Will shows what type of transmission link you can use. Because link aggregation is available on all core switches and have more choices.
b) If more than one type of Ethernet standard shown in Figure 5-12 and Figure 5-15 can span the distance you need, what would determine which one you choose?
There is no maximum end-to end distance (data link distance) between pairs of hosts in Ethernet network.
15.
a) What is the purpose of the preamble and start of frame delimiter fields?
The Preamble (7 bytes) and Start Frame Delimiter (SFD), also called the Start of Frame (1 byte), fields are used for synchronization between the sending and receiving devices. These first eight bytes of the frame are used to get the attention of the receiving nodes. Essentially, the first few bytes tell the receivers to get ready to receive a new frame.
b) Why are Ethernet addresses called MAC addresses or physical addresses?
Because physical devices NICs implement at the physical, MAC and LLC layers.
c) Convert 11000010 to hex.
0xA7D8CA
d) Convert 7F hex to binary.
0111 1111
16. Do switches know the entire data link between the source and destination host?
No. a switch only knows information in its switching table--what port to use to send the frame back out
17. What is the benefit of having a single possible path? Explain in detail.
The fact that there is only a single possible path between any two end hosts in an Ethernet hierarchy makes Ethernet’s switch forwarding simple and therefore inexpensive. This low cost has led Ethernet’s dominance in LAN technology.
18. Why is having a single possible path between any two hosts in an Ethernet network dangerous?
Because there's only a single path, Ethernet is vulnerable to single points of failure in which a single component such as a switch or trunk lines between switches can cause disruption. A single path does not allow for redundancy.
19.
a) What is a VLAN?
Virtual LANs (VLANs) are group of clients and servers that are allowed to communicate with each other but not with clients or servers on the VLANs.
b) How do VLANs bring security?
If clients on one VLAN cannot reach servers on other VLANs, they cannot attack these serves. Also, if client becomes infected with a virus, it can only pass the virus on the other clients and servers on its own VLAN.
c) When VLANs or priority are used, what two fields does the 802.1Q standard add to Ethernet frames?
Adds two optional tag fields
d) When VLANs are used, what does the Tag Protocol ID field tell a receiving switch or NIC?
The second tag field is Tag Control Information field-contains a 12 bit VLAN ID that sender senders sets to 0 if the firm does not use VLANs.
e) What information does the tag control information field tell the switch or receiver?
If the firm does use VLAINs, the frame is given a VLAN number.
20. How many priority levels are possible for Ethernet switches?
Three
21. What are managed switches?
Manage switches have sufficient intelligence to manage from a central computer called the manager and are more expensive than nonmanaged switches, but the reduce management labor in large networks enough to more than offset managed switched purchase costs.
22. What is POE?
Power over Ethernet-switches can supply power to devices connected by UTP (wired telephone system and USB ports already do this). This may be much less expensive than supplying power separately.
23. Assume that in an Ethernet Frame the Length field is 22. How long is the PAD?
22
CHAPTER 6
1.
a) At what layers do wireless networks operate?
Physical and data link layers
b) Are wireless network standards OSI standards or TCP/IP standards? Explain.
OSI Standards
2.
a) Why do wireless clients need access to the wired Ethernet LAN?
Wireless clients to access network resources it needs to be connect to wireless access point, which is usually connected to Ethernet LAN where resources such as Internet access router are usually located. 802.11 WLANs today are also primarily supplement wired LANs.
b) How can firms provide WLAN coverage throughout a large building?
Wireless clients to access network resources it needs to be connect to wireless access point, which is usually connected to Ethernet LAN where resources such as Internet access router are usually located.
802.11 WLANs today are also primarily supplement wired LANs.
3.
a) What is a hertz?
One cycle per second
b) At what range of frequencies do most wireless systems operate?
500 megahertz 10 gigahertz
4.
a) Distinguish between omnidirectional and dish antennas in terms of operation.
Omnidirectional can transmit three-dimensional signal transmission but short distance while dish antennas can point transmission of signals in one direction. Signals can also travel longer distances because of focus ability.
b) Under what circumstances would you use an omnidirectional antenna?
Short distances, three dimensional signal transmissions.
c) Under what circumstances would you use a dish antenna?
Good for longer distances because of their focusing ability but user need to know the direction of the other antenna.
d) What type of antenna normally is used in WLANs? Why?
Omnidirectional antennas are normally used in WLANs, because transmission of signal is equally strong in all direction, transmission signal spread in all three dimensions and receives incoming signal well from all direction. They are best for short distance.
5.
a) Which offers more reliable transmission characteristics—UTP or radio transmission?
Radio
b) Which attenuates more rapidly with distance—signals sent through wired media or radio signals?
Radio Signals
c) How are shadow zones (dead spots) created?
The radio waves are blocked by something they cannot penetrated
d) List some sources of EMI
High powered electrical wiring and florescent lights
6. In radio, how can you send multiple signals without the signals interfering with one another?
Different frequencies
7.
a) Does a signal usually travel at a single frequency, or does it spread over a range of frequencies?
Signals spread over a range of frequencies, this range is known as the Bandwidth
b) What is channel bandwidth?
The highest frequency in a channel minus the lowest frequency
8.
a) Do WLANs today use licensed or unlicensed bands?
Unlicensed
b) What is the advantage of using unlicensed bands?
The advantage of using unlicensed bands is there is no need for government approval, thus it is much less expensive.
c) What is the disadvantage?
There is no way to stop interference other than negotiating with others who are using the band and there is a limit to transmission power.
9.
a) In what two unlicensed bands does 802.11 operate?
802.11 operates in the 5-gigahertz and the 2.4 gigahertz bands
b) How wide are 802.11 channels usually?
Each channel in both of the 802.11 bands is usually 20 megahertz wide
c) Which licensed band is defined the same way in most countries around the world?
the 2.4 gigahertz band is the one standardized throughout most of the world. Diffrerent countries use different parts of the 5 gigahertz band.
d) Does the 2.4 GHz band or the 5 GHz band allow longer propagation distances for a given level of power? Justify your answer.
2.4GHz band=(lower frequency)
e) How many non-overlapping channels does the 2.4 GHz band support?
Three channels
f) How many non-overlapping channels does the 5 GHz band support?
11 and 24 non-overlapping channels
10. In normal radio operation, how does channel bandwidth usually relate to the bandwidth required to transmit a data stream of a given speed?
Bandwidth is no wider than required for the signals speed
11. What spread spectrum transmission method is used for the most recent 802.11 standards?
Use orthogonal frequency division multiplexing (OFDM.
12.
a) List the elements in a typical 802.11 LAN today.
Wired LANs Wireless access points Hosts with a wireless NIC
b) Why is a wired LAN usually still needed if you have a wireless LAN?
Because the server and internet access routers that mobile hosts need to use usually are on the wired LAN
13.
a) Why must the access point remove an arriving packet from the frame in which the packet arrives and place the packet in a different frame when it sends the packet back out?
Different networks require different frames.
b) Besides moving packets between wireless clients and the Ethernet network, what other control functions do access points have?
Access points also control hosts as wells as assigning transmission power levels to hosts within its range and other supervisory chores.
14.
a) What is a BSS? (Do not just spell out the acronym.)
Basic service set (BSS) A basic service set (BSS) consists of an access point and the set of hosts it serves
b) What is an SSID? (Do not just spell out the acronym.)
Service Set Identifier (SSID). Wireless hosts must know the SSID to associate with the access point.
c) Does the access point have an SSID?
The access point in a BSS has an identifier called the service set identifier (SSID). Wireless hosts must know the SSID to associate with the access point.
d) Why must wireless devices know the access point’s SSID?
So wireless devices knows how to associate the access point.
15.
a) What is a handoff in 802.11?
A handoff is when a user moves to a closer access point.
b) What is the relationship between handoffs and roaming in WLANs?
The ability to use handoff ins is called roaming in WLANs
c) What is an ESS? (Do not just spell out the abbreviations.)
An extended service set (ESS) is a group of BSSs that are connected to the same distribution system (network) and have the same SSID.
d) What feature do all access points in an ESS share?
Connected to the same distribution system (network) and have the same SSID.
e) How can access points communicate with each other?
Distribution system.
f) What is the purpose of the 802.11r standard?
Access points to contact one another when it deals with roaming.
16.
a) What is a collision?
Channel Sharing. The access point and all the hosts it serves transmit in a single channel. If two devices transmit at the same time, their signals will collide, becoming unreadable. If two devices transmit in the same channel at the same time, their signals will interfere with each other.
b) What is the purpose of media access control?
Media access control (MAC) methods govern when hosts and access points may transmit so that collisions can be avoided. The access point and all of the wireless hosts it serves transmit and receive in a single channel. When a host or the access point transmits, all other devices must wait.
c) Does media access control limit the actions of wireless hosts, the access point, or both?
MAC limits both the actions of wireless hosts and the access point.
d) What is the maximum rated speed for each standard?
802.11g = 54 Mbps
802.11n Single Band = 100 to 600 Mbps
802.11n Dual Band = 100 to 600 Mbps
802.11ac = 433 Mbps to 6.9 Gbps
802.11ad = 7 Gbps
e) Compare maximum speeds for 802.11g and 802.11n and the maximum distances at which each standard can provide these speeds.
802.11g, the maximum distance and speed are 30 m and 54 Mbps.
802.11n, distance and speed are much longer and faster at 70 m and 100-600 Mbps respectively.
f) Which can bring gigabit speeds to clients?
802.11ac & 802.11ad
g) What business application will gigabit transmission speed make feasible to do wirelessly?
Data backup, sharing data, and syncing data
17. What spread spectrum method do all four standards use as their main method?
OFDM
18. What frequency band or bands do 802.11g, 802.11n single band, 802.11n dual band, 802.11ac, and 802.11 ad use?
2.4, 5, 60 GHz band
19.
a) How does MIMO work?
By having the host or access point send two or more spatial streams (radio signals) in the same channel between two or more different antennas on access point and wireless hosts.
b) What is the main benefit of MIMO? What is its other benefit?
Greater transmission speed & greater transmission distance.
20.
a) What is beamforming?
Having multiple antennas and changing the phase of waves coming from different antennas, an access point can focus signals toward individual hosts instead of broadcasting them,]
b) Distinguish between MIMO and multiuser MIMO.
Multiuser MIMO is the possibility of simultaneously transmission in a single channel by multiple devices that are using a single access point as oppose to just one on MIMO. Beamforming can also bring multiuser MIMO, which is the possibility of simultaneous transmission in a single channel by multiple devices that are using a single access point. The 802.11n standard specified multiuser MIMO, but it did not specify a single multiuser MIMO technology. This led to a great deal of market confusion, and multiuser MIMO did not become popular with 802.11n. With 802.11ac, the Technical Group 802.11ac avoided market confusion by specifying a single multiuser MIMO technique. Beamforming is likely to be common in 802.11ac products.
21.
a) Distinguish between rated speed, aggregate throughput, and individual throughput.
Rated speed is the number of bits that the host or access point will transmit per second. Access point throughput is aggregate throughput, which is shared by all users of an access point. Suppose that the aggregate throughput is 100 Mbps per second and there are 10 users of an access point. Then individual throughput would be about 10 Mbps (actually somewhat less because of time lost in turn-taking). Of course, it would be rare for all stations to transmit simultaneously. However, even if there are sending and receiving simultaneously, the individual throughput they experience would be about 30 Mbps. Access point throughput is aggregate throughput. This must be shared by all stations currently sending or receiving individual throughput can be much lower than aggregate throughput
b) What factors influence individual throughput, given a certain level of aggregate throughput?
Another consideration is that speed is highest when a user is very near an access point. As the user moves away, speed falls. The problem is that at maximum transmission speed, there must be almost perfect propagation characteristics. As a user moves away from an access point, signal strength falls, errors. There are many other factors that will reduce individual throughput.
For example, there are still some wireless devices that use the old 802.11b standard, which only has a rated speed of 11 Mbps.
22. What is backward compatibility?
802.11g access point. In the same way, an 802.11n access point must be able to work with an older 802.11g access point. Of course, when an 802.11n device works with an 802.11g device, the transmission can take place only at 802.11g speeds. The 802.11n device must drop back to 802.11g operation. 