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This article describes how to improve video performance over wireless networks. Many companies use various new technologies of today's video content such as streaming live video, webcasting, videoconferencing and Web conferencing. YouTube services and continues to be popular with more and more bandwidth, such as a video company to use for training purposes and marketing. Google translation service can now convert the text so that the English textvideo based on other countries. Note that with the proliferation of corporate VPN networks for security reasons, employees may use wireless at work seamlessly at home or in a public network. You can use the same video service access from anywhere. That's why wireless is so popular today and the need for video-grade performance wireless infrastructure.
Metro Wireless Cell Phone
The current 80.11a / g Wireless Access Point is easily overwhelmed when multiple clientsYou begin by downloading a large file size and video applications. The best way to ensure acceptable performance video is now the 802.11n wireless standard. According to a study by Cisco expects the number of wireless devices via the Internet by 2015 and more than 54% because of wired IP traffic. In addition to video traffic for 90% of Internet traffic consumption by 2015 a share.
Video Basics
Video and voice are real-timeTraffic flows through the nature, causes to be sensitive to network congestion, latency (delay). The video has both a date and an audio component. It should be noted that in order to influence the same performance as jitter, latency, packet loss, and throughput, video and voice traffic on the Internet and corporate networks. Packet loss has a greater effect on the video while the voice latency concerns even more. Guarantee certain levels of service for video on the network could include the implementationQOS, increases the bandwidth of the network changes the network design and equipment. All these improvements are for the purpose of the network "video ready." Companies are increasingly using web-conferencing, webcasts and video conferencing for meetings and training. Colleges use to deliver courses as well. It 'a very economical way to reduce business travel costs.
Types of video
It is worthwhile to discuss the various types of video services, populartoday and those of a network perspective, the source of the content of the consumer. Note that most services are available through the Internet.
Live video streaming via Internet webcast and TV companies usually shows on the desktop. Web conferencing to the desktop with applications like Skype and the very popular service for the meeting. Video Conferencing Service is running from and through the enterprise network with Cisco Telepresence and devices from companies such asTandberg and Polycom. Progressive download videos from companies such as YouTube on the desktop. Video transmitted by a multicast for multiple video streams such as Netflix.
Video Performance
H.323 defines a set of protocols for audio and video traffic, including H.264 and G.729 protocols. It is a framework for developing multimedia applications on a corporate network. The G.729 protocol is a popular audio compression codec for audio traffic at 8 Kbps with 10 msDelay. The H.264 video codec is the latest video compression standard adopted. There are frames 24, 30 and 60 per second (fps) high definition (HD) video conferencing with compression of the Gbps of video up to 4 Mbps with a resolution of 1920 x 1080 30 fps and 1.5.
It 'important to the performance metrics that affect the video performance, to understand, including packet loss, latency, jitter and throughput. The video is a constant flow of traffic instead of being directed toTraffic such as e-mail, which are relayed with a delay and have no significant impact on service levels. Traffic jams are a symptom of a core network that uses the experience and network performance problems. Queues are committed during periods of increased network activity. This leads to an increase in latency, jitter, packet loss, reduced throughput and retransmission of packets. The implementation of Quality of Service (QoS) is sometimes actually lead to dropped packets to avoidVoice / video packet loss. The packets are then retransmitted with a certain delay. The following defines the industry standard performance metrics.
Latency: time for a packet to travel from source to destination
Jitter: Number of average change in latency of each packet
Packet Loss: percentage of dropped packets from source to destination
Throughput: average number of packets during a specified period of
Each video service requires differentAmount of bandwidth. Some services such as video conferencing are affected by an increase in latency, jitter and packet loss, such as desktop applications. Acceptable performance for video conferencing, packet loss should not exceed 1%, the jitter of 30 ms and a one-way latency of 300 ms (latency of 150 ms for high-definition resolution video conferencing). If this can be overcome degrading the image. The bandwidth requirements for video are linked to the specific type of service,Level of resolution and frames per second. For example, a standard resolution of 704 x 576 video at 30 fps requires 768 Kbps - 1 Mbps of bandwidth, while a high-definition (HD) resolution of 1080 x 1920 at 30 fps requires 4 Mbps - 12 Mbps Service desktop as streaming video and Web conferencing requirements have lower bandwidth than video-conferencing, but the same problems of loss of latency, jitter and packet affect video performance. Also, with all the necessary servicesadd an average of 20% of overhead for the extra bandwidth Ethernet and IP protocol processing.
Video Quality of Service (QoS)
The implementation of Quality of Service (QoS) on a corporate network is an end to end, starting from the source video stream. Videoconferencing endpoints are often connected to a company an edge switch, and Internet streaming video on the desktop. The implementation process involves a QoS priority traffic and priority service.In the face video conferencing, the Cisco 3560 and 3750 edge switches for access are often used to connect video devices. The layer 2 frame of data is a header with three 802.1p bits can be set to 8 different class of service (CoS) values 0-7 For example, the video is assigned CoS of 4, while voice packets are assigned CoS 5 and the highest number becomes a better service. Data with the highest priority is often assigned CoS 2.
QoS DSCP is a Layer 3 protocol used to provide different types of services(ToS) for classes of data traffic, voice and video. DSCP values are Level 3, and as such in the first 6 bits of the IP precedence field set to the IP header. The recommendation of Cisco best practices for the identification of video is a DSCP AF41. The traffic is assigned a lower priority, such as AF21, while the entry is assigned a higher priority DSCP EF. Video traffic with access lists, video traffic and define a map class defines classified by the video that corresponds to an access listand refers to a specific policy map. The political map has the DSCP marking of video traffic and the DSCP value assigned to a queue. Class of Service (CoS) packets for a political map, however, is often marked on the access switches can be set with SRR and WRR distribution / core switches.
Shaped Round Robin (SRR) is a technology with hardware-based queues access switches are used. SRR provides Layer 2 class of service (CoS) and Layer 3 (ToS) to queue assignments. The distribution and coreNetwork layers are usually use 6500 switches from Cisco and Weighted Round Robin (WRR) queue hardware. WRR is the same idea, but the tail is slightly different architecture and only Layer-2 class of service values are assigned to queues.
WAN router with Low Latency Queuing (LLQ) and Class Based Weighted Fair Queuing (CBWFQ), video traffic has used the high priority queue with a priority, percentage to 15%. In this way all the video trafficYou get 15% of the bandwidth of the link. For example, a circuit 1 Gbps Metro Ethernet as part of the bandwidth of 150 Mbps for video traffic less protocol overhead. Company WAN connections as best practice should never be more than about 33% of the available bandwidth for all voice and video traffic. That leaves room for the overhead of the protocol and data packets. The traffic performance deteriorates as the packets are discarded and video traffic QOS less effective.
Desktop applications use the same QoS Tools, however, the Internet and the wireless network company in the design factor. In addition to public Wi-Fi network you are currently affecting the entire network performance videos. The bandwidth of the Internet connection at home and congestion affecting the performance and possible bottlenecks in the network. The wireless network is affected most frequently in video performance, especially on a public network 802.11b.
> Wireless Standard
These protocols describe wireless standards currently in use.
80.11b
This wireless standard approved in 1999 provides a maximum data rate of 11 Mbps in the 2.4 GHz license in the United States. The experience of band interference from commercial devices using this very often. The standard of the United States has 11 channels with a bandwidth of 5 MHz to 80 MHz per channel. The UnitedBeen awarded three non-overlapping channels 1, 6 and 11 with a center frequency separation of 25 MHz per channel. Modulation is used to minimize 802.11b Direct Sequence Spread Spectrum (DSSS) with CCK properties, the effects of interference. Further 802.11b data rates 1, 2 and 5.5 Mbps
802.11g
This wireless standard approved in 2003 provides a maximum data rate of 54 Mbps with the same 2.4 GHz band as 802.11b. The802.11g is popular with higher throughput and greater range. The same problems occur, however, with the band 2.4 GHz 802.11g is compatible with the 802.11b standard and has the same 11 channels 1, 6 and 11 as non-overlapping. The OFDM modulation is used with 802.11g, which means higher data transfer speeds. Further 802.11g data rates 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36 and 48 Mbps
802.11a
This wireless standard has beenapproved in 1999, indicating a maximum speed of 54 Mbps using the 5-GHz license in the United States. The advantage of 802.11a is higher throughput, but cell coverage is small and additional access points for the same coverage and 802.11g are needed. There is much less interference from devices such as cordless phones, Bluetooth devices, microwave devices, and trade with the 2.4 GHz band there are 23 non-overlapping channels with the current 802.11hSpecifications. Some Cisco devices support both 2.4 GHz and 5 GHz channels of the same Access Point. The OFDM modulation is used with 802.11a, with higher data transmission speeds and minimize the effects of noise. Each country determines the number of channels and allowing the 5-GHz frequencies.
802.16
It is a metropolitan area (MAN) wireless standard, the private and business customers provides wireless access anywhere. The line of sightThe technology is a distance of about 27 km and a speed of up to 120 Mbps point-to-multipoint specification is in the range 10-66 GHz 802.16a is a specific network topologies and non-visual connection with the licensed frequencies and unlicensed 2 GHz to 11 GHz with a speed of 70 Mbps The main problem for all construction MAN unlicensed frequency interference from similar units.
802.11n
The new 802.11n wireless standardapproved in 2009 has defined a data transfer speeds much faster than 300-600 Mbps and 1000 Mbps access point to the network switch to speed client-to-point and access point to access the network switch. It works on both 2.4 GHz and 5 GHz with effective performances of the new improvements, such as Multiple Input Multiple Output (MIMO) and channel bonding.
Wireless Contention
The access points are essentially a less efficient units with style shared media hubflat broadcast domain. Compare that has a Cisco Ethernet switch, 100/1000 Mbps of bandwidth per port and broadcast segmentation using VLANs. The switch uses a much more effective system of access to media contention as a wireless access point. The wireless network uses a Carrier Sense Multiple Access with older less efficient collision avoidance (CSMA / CA) process for managing client access to the network. The effect of CSMA / CA increases the utilization of bandwidth, packet loss andRetransmits packet with this shared media. In addition, it gives away the Wi-Fi interference problems with the 2.4 GHz band multipath and signal when the signal is distorted or the structure of the building occurs. From a practical point of view 15-25 wireless client can use a single point of access at any time assign and still maintain a good performance. This is, of course, changes more video and broadband applications are used. The 802.11n is actuallySimultaneous support of all these customers move live video streaming feature race with 14 of them high-definition video streams.
Data on the frequency, distance and frequency
So now you know that the speed with the warp threads. Data rate (speed) and performance metrics such as reducing the WLAN clients as far away from the access point. In addition to an average of 50-60 meters, the speed decreases and increases latency, packet loss and jitter. The wirelessNetwork Site Survey to determine where and how many access points should be used so that each cell (defined service area) with a signal strength should be 54 Mbps coverage area can be expanded with a stronger directional antenna. For example, these are valued about the specific distance, speed and frequency for the internal Cisco 1240AG Access Point. Note the distance is generally half of the 802.11a and 802.11g radios, but this assessment with a more powerful 3.5 dBi wasAntenna.
802.11a (5 GHz): 54 Mbps ft to 60 to 80 ft with 3.5 dBi omni antenna
802.11g (2.4 GHz): 80-100 ft ft at 54 Mbps with 2.2 dBi dipole antenna
Since the transmission rate increases effective network is smaller. Customers want to have a maximum bandwidth of continuous, multiple access points used for the design. Increasing power transmission network range actually decrease at higher speeds, increasing the flow of data rates lower, as in the case802.11g access point. The problem is associated with increased transmission power, the reduced sensitivity of the receiver via a process called error vector magnitude. This does not apply to wireless clients, where the transmission power should be set up to apply for best results. The maximum distance or wireless network length is about 100 meters from the client to the access point and Ethernet switch to wire designs to 100 meters from the access point. The campus project can be extended with additional switch- Switch connectivity, of course.
Speed wireless data transmission to provide maximum throughput, but this is not a practical value. As a mixed 802.11b and 802.11g environments reduce the rate for customers of the network segment. As mentioned, 802.11b and 802.11g clients are compatible and can use the same access point with the 2.4 GHz frequency band allocated. Speed is about 6 Mbps for 802.11b, but this varies with the type of antenna, the distance between accessPoint and transmit power. Configuring the Access Point 802.11g 54 Mbps for the customer base, and 11 Mbps for 802.11b clients. This prevents the access point, which is less than 11 Mbps access points to work Some dual-band 802.11a and 802.11g, but separate logical networks, and must have a separate wireless surveys. 802.11a Access Point uses the frequency of 5 GHz band. As frequency increases the wavelength decreases network. The version with802.11a covers distances much less than the same data rate 802.11g. The highest frequency (5 GHz) signals do not pass through the structure as simple as lower frequencies.
These are some average data throughput and standards associated with wireless. From the practical point of view are not all 24 channels with the 802.11a access points 802.11h standard invaded by interference channels available. Note the effect of mixed wireless environmentDevices such as 802.11b / g in the same network and throughput decreased. This also happens when 802.11n access points with older access points on the same network.
802.11g - 6 Mbps x 3 channels
802.11g - 22 Mbps x 3 channels
802.11b / g - 8 Mbps x 3 channels
802.11a - 25 Mbps x 21 channels
802.11n - 150 Mbps Mbps/300 x 21 channels
A reduction of transmission power of an access point to minimize interference. The network can effectivelyextended with repeater access points, increasing the transmit power or by setting the Access Point Access Point location. With a higher gain antenna on the Access Point is also an option. Cisco access points have a lot of options for the supply of antennas with higher gain and sensitivity. Note you must reduce the length of the antenna cable. The longer cable antenna will attenuate the signals. Some countries restrict the access point of maximum transmit power adjustment.
RF Propagation
Asattenuation of the signal mentioned is worse at high frequencies. However, there are a lot of environmental factors that bend, distort and minimize the signal strength. The result is the so-called multipath fading, where a signal takes multiple paths to a destination. These are just some examples.
• flexion - bending signal due to the structure of the building corner
• Refraction - Environmental factors such as humidity can cause the bow to signal
• Reflection - water, glass orsmooth surface can bounce a signal to distort or fade
• Absorption - Absorption signal structures (trees)
• EMI - cordless phones, microwave ovens, electric motors, Bluetooth devices
Fade margin is the amount that the power is diminished sensitivity of the receiver, while maintaining acceptable performance goal may be. This is a factor, with the use of off-wireless bridge, point-to-point topologies, such as buildings on a campus.Problems with the rain dampen the signals and the knowledge of the fade margin to avoid performance problems. Polarization is the orientation of the model from the aerial and radiated as a key must match the transmit and receive antenna. The most common access point for the linear polarization antenna is used. Antenna can transmit horizontally or vertically polarized signal.
The improvement of video-over-wireless performance
When it comes to bandwidth requirements andvarious video services is considered important that a wireless network will always require more bandwidth to the corporate LAN or the Internet connection at home for the same video service. One example is high-definition live video streaming, where the wireless bandwidth required today, much higher than the LAN or the Internet at home cable / DSL. The Internet connection at home would be 500 Kbps - 1 Mbps is not a problem, even to the Internet from home, where theCable download speed is 10 Mbps on average. The dispute over access to the wireless network problems and multipath fading are not efficient and would use an effective range of 5-10 Mbps. Also, note that packet loss is video-over-wireless performance, more latency and jitter, however, all the parameters with the following suggested improvements to improve compromised.
1 Distribute the new 802.11n access point client adapter
The new 802.11n standardWireless Access Point is now rated at 300 Mbps using the new extension. This is 6 times faster than standard 802.11g to the next. Deploying 802.11n in 5 GHz band and has 21 non-overlapping channels available. This allows higher data rates for each coverage area. The new enhancements include multiple-input multiple-output (MIMO), channel bonding, MAC block recognition and payload optimization of unicast QoS priority traffic classes.
MIMOHe explained
802.11n uses multiple input / output antennas on the Wireless Access Point and Client to increase and reducing the data re-sending and packet loss. They can send the access point and clients, while increasing the amount of data traffic and the expansion of the network (distance). The current most popular Cisco AP 1250 uses what is called MIMO 2T x 3R. That the two antenna on the access point and three receiving antenna on the client. The best results occurif all clients using 802.11n wireless network cards are all access points without 80.11n mixed environment of 802.11b / g access points.
Channel Bonding
The channel bonding technique to allow the combination of two non-overlapping channels in 5 GHz band, which dates back to 2 times the standard rate to send data to a theoretical 300 Mbps In practice, the average rate of 180 Mbps and 140 data tested Mbps for streaming video. And 'quite impressive compared to the average 802.11gThroughput of 22 Mbps
Payload Optimization
The function of the payload optimization or packet aggregation is basically putting more data in each packet sent to a more effective use of public transport.
MAC block recognition
Access points above requires that each MPDU MAC layer packet separately confirmed with an ACK packet. The new 802.11n standard now uses a single block ACK to acknowledge multiple MPDUs. This reduces the amount of the ProtocolOverhead and less bandwidth.
Multicast to unicast traffic
Video over Wireless offers a specific problem with multicasting, which is not the networked world. Wireless Access Point do not support multicasting, however, the conversion of unicast streams to multicast for 802.11n wireless client is at level 2
2 Design Network
Wireless access points must always be connected to a 100 Mbps full-duplex switch port.802.11n Access Points should be a 1-Gbps or 10 Gbps switch port to be connected. Video endpoints should be closer linked to the level and distribution of a line card is less busy. The video equipment source endpoint can be located on the edge of the network, as well, but you should choose a switch with all the features and preferably in the data center. Wireless Multiple SSID should always be defined on the segment of transport suitable and marked with the same VLAN schemeimplemented on the wired network.
Use a hierarchical structure, with each new wireless / wired implementations and, if possible, distributed across multiple access points and connect the network switch instead of a single switch. Consider doing some monitoring network performance in the media to eliminate the failure. For example, a network switch with Gigabit Ethernet switch with an uplink to 100 Mbps interface. In addition to WAN circuits are usually slower than the connectionSwitch infrastructure.
Take a proper wireless site survey done for each band to maximize signal coverage and minimize overhead. Distribute internal client instead of USB external style to your laptop for the best performance of the card. Provider of 802.11a/b/g access points (mixed environment) with 802.11n access point, it is better 802.11n Access Points and clients for the 5-GHz, where there are more non-overlapping channels and give less interference. Use all802.11n Access Points and clients, if possible, rather than mixed environment and at least 2T x 3R x 2S Streams space. Use access points more for each coverage area with 802.11n in 5 GHz band for high speed data transmission range (distance), the number of customers and network availability. Deploying the most advanced antennas, data rate and increase the range. Clean the problems with a sub-optimal routing of the network. Consider the use of WLAN Controllers WLC 4400. This requires aFirmware upgrade for all 1100 and 1200 series autonomous access points, but there are advantages, such as advanced RF management capabilities.
3-to-End Quality of Service (QoS) end
Any good quality of service provision must be either wired or wireless techniques to guarantee QoS end to end performance. The wire QOS here was already shared with Round Robin (SRR) and Weighted Round Robin (WRR) queues at the counters are discussed hardware. AlsoThere is Low Latency Queuing (LLQ) and Class Based Weighted Fair Queuing (CBWFQ) is implemented on the WAN router. DSCP and CoS packet marking is used for some types preferred to give priority to a queue of traffic. Now Wireless Extensions Wireless Multimedia (WMM) is that traffic is classified with four categories depending on the type of traffic. These include voice, video, best effort and background. This provides a guaranteed level of service for video traffic in the network timeCongestion.
Layer 2 data frames from the switch has a field 802.1p, where are the classes of service (CoS) bits. The access point checks the box and queues of traffic at a given setting CoS assigned to the queue. The voice traffic is the highest priority queue, and no traffic is waiting in the queue, the first video and data. All wireless clients will have priority to VoIP for the first video. Note that although three of the best effort queue has a CoS of 0 indicates that the queueeven higher priority than background traffic. Cisco Extension streaming video application layer enables the mapping of video traffic to a current priority for a VLAN or SSID mapping to favorite snake.
Priority Queuing access point:
Tail 1: voice traffic CoS = 6.7
Queue 2: video traffic CoS = 4.5
Queue 3: Best Effort (transactional data), cos = 0.3
Tail 4: The background traffic (email) cos = 1.2
Call Admission Control is a kind of QOS which limitsthe number of video sessions to avoid oversubscription of priority queue switches and routers. The use of a gatekeeper service controls the number of video sessions and refused further sessions of the adjustment of the bandwidth of the tail. The priority queue has sufficient bandwidth for a set number of meetings and requests for additional sessions will be refused if it exceeds the size of the tail.
4 band width
As mentioned, doing aTo identify the performance evaluation of the current network, where it is needed for additional bandwidth. WAN, the company is the most common cause of problems with the bandwidth. The cost and low prevalence of Metro Gigabit Ethernet circuits to make it today is a great opportunity to distribute it on the corporate network.
Copyright 2011 All rights reserved Shaun Hummel
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