Network Monitor
Overview
This write-up discusses the best way to increase video more than wireless performance. Quite a few firms are working with different new video content technologies currently including live video streaming, webcasting, video conferencing and internet conferencing. YouTube services continue to be well-liked and are working with increasingly a lot more bandwidth as firms use video for training and marketing and advertising purposes. Google language translation service can now convert text, creating the English text based videos obtainable to other countries too. Bear in mind that using the proliferation of corporation VPNs for security purposes, workers can use wireless at function as seamlessly as at property or on a public network. They are able to access exactly the same video services from anyplace. This is why wireless is so well-liked now plus the want for video grade wireless infrastructure performance.
The existing 80.11a/g wireless access point is very easily swamped when various customers begin downloading big files and running video applications. The most beneficial answer for guaranteeing acceptable video performance is now the 802.11n wireless regular. Based on a Cisco forecast study, the number of wireless devices will exceed wired devices online by 2015 and account for 54% of IP targeted traffic. Furthermore video visitors will account for 90% of the consumer net visitors by 2015.
Video Basics
Video and voice are real-time site visitors streams by nature which are sensitive to network congestion that causes latency (delay). Video has both a information and an audio component. It really should be noted that exactly the same performance metrics like jitter, latency, packet loss and throughput have an effect on video and also voice visitors across the world wide web and firm network. Packet loss has a higher impact on video whilst latency affects voice a lot more. Guaranteeing particular service levels for video on the network could involve implementing QOS, growing network bandwidth, network style adjustments and equipment adjustments. All these improvements are for the purpose of producing the network “video ready”. Firms increasingly use internet conferencing, webcasts and video conferencing for meetings and for training purposes. Colleges use it to deliver courses too. It’s a incredibly price efficient tool to reduce corporation travel expenses.
Sorts of Video
It’s worth discussing the numerous sorts of video services preferred currently and exactly where, from a networking perspective, customers source the content. Note how most of the services are across the world wide web.
Live Video Streaming more than the net of firm Webcasts and Television broadcasts normally delivered to your desktop.
Internet Conferencing to the desktop with applications like Skype along with the extremely common Go to Meeting service.
Video Conferencing service that runs from and across the firm network with Cisco Telepresence and equipment from businesses for instance Tandberg and Polycom.
Progressive Video download from businesses for instance YouTube to the desktop.
Broadcast Video multicast of 1 to numerous video streams for example Netflix.
Video Performance
H.323 defines a suite of protocols for audio and video site visitors such as H.264 and G.729 protocols. It’s a framework for creating multimedia applications on a organization network. The G.729 protocol can be a preferred audio codec for compressing audio site visitors at 8 Kbps having a 10 ms delay. The H.264 video codec regular will be the most present adopted video compression regular. It specifies 24, 30 and 60 frames per second (fps) for high definition (HD) video conferencing with compression from 1.five Gbps of video targeted traffic to 4 Mbps at a resolution of 1920 x 1080 and 30 fps.
It really is critical to realize the performance metrics that impact video performance such as packet loss, latency, jitter and throughput. Video is sent as a constant stream of site visitors in contrast to information site visitors for instance e-mail that may be re-transmitted with some delay and have no important impact on service level. Congestion may be the simple symptom of a network that’s busy and experiencing network performance troubles. The queues are busier for the duration of times of elevated network activity. This causes elevated latency, jitter, packet loss, decreased throughput and re-transmission of packets. Implementing high quality of service (QOS) will at times truly trigger dropped information packets to avoid voice/video packet loss. The information packets are then re-transmitted with some delay. The following defines these market regular performance metrics.
Latency: Quantity of time for a packet to travel from source to destination
Jitter: Quantity of typical variation in latency of every single packet
Packet Loss: Percent of packets dropped from source to destination
Throughput: Typical number of packets sent in the course of a fixed period of time
Each and every video service needs diverse amounts of bandwidth. Some services for example video conferencing are much more affected by elevated latency, packet loss and jitter than desktop applications. For acceptable video conferencing performance, the packet loss need to not exceed 1%, jitter 30 ms plus a one-way latency of 300 ms (latency of 150 ms for high definition video conferencing resolution). When these thresholds are exceeded the picture can deteriorate. Bandwidth specifications for video are linked to the certain form of service, quantity of resolution and frames per second. As an example a regular video conferencing resolution of 704 x 576 at 30 fps needs 768 Kbps – 1 Mbps of bandwidth even though a High Definition (HD) resolution of 1080 x 1920 at 30 fps calls for 4 Mbps – 12 Mbps. Desktop services like streaming video and internet conferencing have lower bandwidth specifications than video conferencing, nonetheless exactly the same latency, jitter and packet loss issues have an effect on video performance. Furthermore with all services, you might have to add an typical of 20% further bandwidth overhead for Ethernet and IP protocol processing.
Video Excellent of Service (QOS)
Implementing excellent of service (QOS) on a firm network is an end to end procedure beginning using the video stream source. Video conferencing end points are usually connected to a organization edge switch though video streaming to the desktop is world wide web based. The procedure of implementing any QOS entails prioritizing site visitors for preferential service. Thinking about video conferencing, the Cisco 3560 and 3750 access edge switches are typically employed to connect video equipment. The layer two information frame has an 802.1p header with three bits that could be set for 8 distinct class of service (CoS) values from 0 – 7. As an example video is assigned CoS of 4 although voice packets are assigned CoS of five plus the greater number gets greater service. High priority information is generally assigned CoS of two.
DSCP is actually a layer three QOS protocol applied to specify different forms of service (ToS) classes for information, voice and video visitors. DSCP values are layer three and as such are set inside the very first 6 bits of the IP Precedence field of the IP header. The most beneficial practice recommendation from Cisco for marking video can be a DSCP of AF41. Information visitors is assigned a lower priority like AF21 for example though voice is assigned a greater priority of DSCP EF. Video site visitors is classified with access lists that define video site visitors along with a class map is defined for video that matches an access list and points to a precise policy map. The policy map does the DSCP marking of video visitors as well as the DSCP value is assigned to a queue. Class of service (CoS) packets may be set using a policy map on the other hand it can be frequently marked at access switches with SRR and with WRR at distribution/core switches.
Shaped Round Robin (SRR) is really a hardware based queuing approach deployed with access switches. SRR permits layer two class of service (CoS) and layer three (ToS) mappings to queues. The distribution and core network layers generally have 6500 Cisco switches and they use Weighted Round Robin (WRR) hardware queuing. WRR will be the similar notion even so the queuing architecture is somewhat distinct and only layer two class of service values are mapped to queues.
WAN routers are deployed with Low Latency Queuing (LLQ) and Class Based Weighted Fair Queuing (CBWFQ) that assigns video site visitors to the high priority queue using a particular priority percentage including 15%. That guarantees all video site visitors will get 15% of the link bandwidth. As an example a 1 Gbps Metro Ethernet circuit will allocate 150 Mbps of bandwidth to video targeted traffic minus protocol overhead. Organization WAN links as a ideal practice really should by no means exceed roughly 33% of accessible bandwidth for all voice and video targeted traffic. That leaves room for protocol overhead and information packets. Information visitors performance worsens as packets are dropped and video site visitors QOS becomes much less efficient.
Desktop applications use exactly the same QOS tools nonetheless the firm net connection along with the wireless network factor into the style. Additionally the public wireless network you take place to be making use of affects the overall video network performance. The bandwidth of your property world wide web connection and congestion affects performance along with any congestion points across the network. The wireless network is most typically exactly where video performance degrades especially on an 802.11b public network.
Wireless Standards
These describe the business regular wireless protocols presently deployed.
80.11b
This wireless regular approved in 1999 specifies a maximum information rate of 11 Mbps utilizing the two.4 GHz unlicensed band inside the United States. The band experiences plenty of interference from commercial devices making use of that frequency. The regular inside the United States assigns 11 channels with bandwidth of about 80 MHz at five MHz per channel. The United States allocates three non-overlapping channels of 1, 6 and 11 having a center frequency separation of 25 MHz per channel. The modulation scheme employed with 802.11b is Direct Sequence Spread Spectrum (DSSS) with CCK with characteristics that reduce effects related to interference. The 802.11b further information rates incorporate 1, two, and five.five Mbps.
802.11g
This wireless regular approved in 2003 specifies a maximum information rate of 54 Mbps utilizing exactly the same two.4 GHz band as 802.11b. The 802.11g regular is common with greater throughput and elevated coverage. Exactly the same interference complications happen on the other hand using the two.4 GHz band. The 802.11g is compatible using the 802.11b regular and assigns exactly the same 11 channels with 1, 6 and 11 as non-overlapping. The modulation scheme utilized with 802.11g is OFDM that specifies greater information rates. The further 802.11g information rates consist of 1, two, five.five, 6, 9, 11, 12, 18, 24, 36 and 48 Mbps.
802.11a
This wireless regular was approved in 1999 specifying a maximum information rate of 54 Mbps working with the five GHz unlicensed band within the United States. The benefit of 802.11a is greater throughput nevertheless the cell coverage is smaller and further access points might be required for exactly the same 802.11g coverage. There’s considerably much less interference from devices including cordless phones, bluetooth devices, microwaves and commercial devices employing the two.4 GHz band. You will discover 23 non-overlapping channels using the present 802.11h specification. Some Cisco devices support both two.4 GHz and five GHz transmitters on exactly the same access point. The modulation scheme utilised with 802.11a is OFDM, with greater information rates and minimizing effects of interference. Every country specifies the number of channels and frequencies it enables using the five GHz band.
802.16
This is actually a metropolitan (MAN) wireless regular that supplies house and organization customers seamless wireless access from anyplace. The line of sight technologies specifies a distance of about 27 miles and speeds of as much as 120 Mbps. The point to multipoint specification operates within the 10-66 GHz range. There is certainly an 802.16a specification with mesh topologies and non-line of sight with frequencies from the licensed and unlicensed two GHz and 11 GHz band at a speed of 70 Mbps. The important difficulty with any MAN implementation making use of unlicensed frequencies is interference from comparable devices.
802.11n
The new 802.11n wireless regular approved in 2009 defines a lot quicker information rates of 300 – 600 Mbps and 1000 Mbps from access point to network switch growing throughput from client to access point and access point to network switch. It operates in both the two.4 GHz and five GHz bands with powerful new performance enhancements like numerous input various output (MIMO) and channel bonding.
Wireless Contention
Access points are basically a much less effective hub style shared media device having a flat broadcast domain. Contrast that having a Cisco Ethernet switch that has 100/1000 Mbps bandwidth per port and broadcast segmentation with VLANs. The switch utilizes a far more successful media access contention scheme than wireless access points. The wireless network employs an older much less helpful carrier sense numerous access with collision avoidance (CSMA/CA) approach to manage client access to the network. The impact of CSMA/CA is elevated bandwidth usage, packet loss and packet re-transmits with this shared media. Furthermore you can find the regular wireless complications using the two.4 GHz band interference and multipath signal fade that occurs when the signal bends or is distorted by the creating structure. From a practical perspective 15-25 wireless customers can associate using a single access point at anytime and nonetheless preserve superior performance. This obviously modifications as a lot more video and high bandwidth applications are employed. The 802.11n can really support all of those customers running simulataneous live video streaming with 14 of them running high definition video streams.
Information Rate, Distance and Frequency
So by now you realize there’s no warp speed with older wireless. Information rate (speed) and performance metrics reduce as the wireless customers move further from the access point. Beyond an typical of 50-60 feet, the speed decreases and latency, packet loss and jitter improve. The wireless network internet site survey determines exactly where and how quite a few access points needs to be deployed so every cell (defined coverage location) has a signal strength with 54 Mbps. The coverage location could be extended having a stronger directional antenna. As an example, these are approximate rated distance, speed and frequency specifications indoor for the Cisco 1240AG access point. Note the 802.11a distance is commonly half that of an 802.11g radio nevertheless this rating was having a stronger three.five dBi antenna.
802.11a (five GHz): 54 Mbps @ 60 ft – 80 ft with three.five dBi omnidirectional antenna
802.11g (two.4 GHz): 54 Mbps @ 80 ft – 100 ft with two.two dBi dipole antenna
As the information rate increases your powerful network range decreases. Customers that want a continuous maximum bandwidth will must deploy additional access points per style. Growing transmit energy will in fact reduce network range at greater information rates whilst growing the range with lower information rates like the case with 802.11g access points. The difficulty is with elevated transmit energy, the receiver sensitivity decreases using a approach named error vector magnitude. That does not apply to the wireless customers exactly where transmit energy must be set at maximum for greatest outcomes. The network length or wireless maximum distance is about 100 meters from client to access point, and with Ethernet wired designs 100 meters from access point to switch. The campus style could be extended with extra switch – switch connectivity not surprisingly.
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Wireless information rates specify maximum throughput nonetheless that is not a practical value. Mixed environments including 802.11b and 802.11g will reduce throughput for both customers on exactly the same network segment. As mentioned the 802.11b and 802.11g customers are compatible and can associate using the very same access point utilizing the two.4 GHz band spectrum. Throughput for 802.11b is about 6 Mbps on the other hand which will vary with antenna kind, distance from the access point and transmit energy. Configure the access point with 54 Mbps for 802.11g customers and fundamental 11 Mbps for the 802.11b customers. That prevents the access point from operating at much less than 11 Mbps. Some access points can operate with dual band 802.11a and 802.11g nevertheless they’re separate logical networks and ought to have separate wireless web site surveys. The 802.11a access point utilizes the five GHz frequency band. As frequency wavelength increases the network range will reduce. The style with 802.11a covers a lot much less distance compared with 802.11g in the very same information rates. The greater frequency (five GHz) signals do not pass by way of the constructing structure as uncomplicated as lower frequencies.
These are some typical bandwidth throughput values and connected wireless standards. From a practical perspective all 24 channels will not be readily available using the 802.11h regular and 802.11a access points as a result of channel overrun interference. Note the impact of mixed environment wireless equipment for example 802.11b/g on exactly the same network and decreased throughput. This occurs also when you will find 802.11n access points with older access points on exactly the same network.
802.11b – 6 Mbps x three channels
802.11g – 22 Mbps x three channels
802.11b/g – 8 Mbps x three channels
802.11a – 25 Mbps x 21 channels
802.11n – 150 Mbps/300 Mbps x 21 channels
Decreasing the transmit energy of an access point will decrease channel interference. The helpful network range could be extended with repeater access points, growing access point transmit energy or adjusting the access point position. Employing a greater acquire antenna on the access point is an choice too. Cisco access points have many selections for deploying antennas with greater acquire and sensitivity. Note it is best to reduce the cable length of any antenna. The longer antenna cabling will attenuate the signals. Some countries limit the maximum access point transmit energy setting.
RF Propagation
As mentioned signal attenuation is worse at greater frequencies. There’s nevertheless plenty of environmental variables that distort, bend and reduce signal strength. The result is some thing known as multipath fading exactly where a signal takes numerous paths to a destination. These are some examples.
? Diffraction – signal bending as a result of developing structure angles
? Refraction – environmental elements like humidity can trigger signal to bend
? Reflection – water, glass or any smooth surface can bounce a signal distorting or fading it
? Absorption – structures absorbing signal (trees)
? EMI interference – cordless phones, microwave ovens, electrical motors, bluetooth devices
Fade Margin may be the quantity of receiver sensitivity energy that may be decreased although sustaining acceptable network performance. That’s a factor with deployment of outside wireless bridges with point to point topologies like buildings on a campus. Complications with rain will attenuate signals and realizing the fade margin will stay away from performance concerns. Polarization will be the orientation of the radiated pattern from the antenna and like a important ought to match with transmitting and receiving antenna. Essentially the most usually polarization applied with access point antenna is linear. Antenna can transmit horizontal or perhaps a vertical polarized signal.
Enhancing Video more than Wireless Performance
When discussing bandwidth specifications and numerous video services it’s critical to note that a wireless network will often need a lot more bandwidth than your firm LAN or your property world wide web connection for exactly the same video service. An example is high definition live video streaming exactly where the actual wireless bandwidth necessary is a lot greater compared using the LAN or property cable/DSL net connection. The property world-wide-web connection would demand 500 Kbps – 1 Mbps. That’s not a challenge even for residence net exactly where the cable download speed is an typical 10 Mbps. The wireless network with access contention and multipath fading issues are not as effective and would use an efficient bandwidth of five – 10 Mbps. Furthermore, note that packet loss does have an effect on video more than wireless performance additional than latency and jitter on the other hand all metrics could be improved using the following suggested improvements.
1. Deploy the new 802.11n Access Point and Client Adapters
The new 802.11n wireless access point is now rated at 300 Mbps using the new feature enhancement. Which is 6x quicker than the nearest 802.11g regular. Deploying 802.11n within the five GHz band and you may have 21 non-overlapping channels offered also. That makes it possible for for greater information rates per coverage region. The new enhancements contain several input various output (MIMO), channel bonding, MAC block acknowledgment, payload optimization and unicasting and QOS prioritizing of site visitors classes.
MIMO Explained
802.11n utilizes various input/output antennas on the access point and wireless client to improve information rates and reduce re-transmits and packet loss. The access point and customers can send simultaneous visitors streams growing the quantity of information and extending the network range (distance). The existing most well-liked Cisco 1250 AP utilizes what’s known as a 2T x 3R MIMO. Which is two transmit antenna on the access point and three get antenna on the client. The most beneficial outcomes happen when all wireless customers use 802.11n adapters and access points are all 80.11n with no mixed environment of 802.11a/g access points.
Channel Bonding
The approach of channel bonding now makes it possible for combining of two non-overlapping channels inside the five GHz band to send information at 2x the regular information rate for a theoretical 300 Mbps. In practice the typical information rate has been tested at 180 Mbps and 140 Mbps for video streaming. Which is fairly impressive compared with 802.11g typical throughput of 22 Mbps.
Payload Optimization
The feature of payload optimization or packet aggregation is fundamentally putting additional information in every packet sent resulting in far more helpful use of the transport media.
MAC Block Acknowledgment
Prior access points necessary that every MAC layer MPDU packet was separately acknowledged with an ACK packet. The new 802.11n regular now utilizes a single block ACK to acknowledge many MPDUs. This decreases the quantity of protocol overhead and much less bandwidth necessary.
Multicast to Unicast Traffic
Video more than wireless presents a particular challenge with multicasting that the wired globe does not have. Wireless access points don’t support multicasting even so 802.11n can now convert multicast to unicast streams per wireless client at layer two.
two. Network Style
The wireless access points really should generally be connected to a 100 Mbps full duplex switch port. The 802.11n access points ought to be connected to a 1 Gbps or 10 Gbps switch port. Video end points ought to be connected closer to the distribution layer and on a much less busy line card. The end point video source equipment might be situated in the network edge also, even so you ought to choose a switch with all of the performance attributes and preferably situated inside the information center. Wireless many SSIDs must generally be defined to segment visitors and assigned VLANs to match exactly the same VLAN schema implemented on the wired network.
Use a hierarchical style with any new wireless/wired deployments and exactly where probable spread out and connect access points across many network switches as opposed to a single switch. Look at performing some performance monitoring on the network to remove media mismatches. For instance a network switch using a Gigabit port that’s uplinked to a switch using a 100 Mbps interface. Too WAN circuits are most typically the slowest link compared using the switch infrastructure.
Have a suitable wireless network website survey accomplished for every single band to decrease signal overrun and optimize coverage.
Deploy internal client adapters rather than external USB style at your laptop for finest performance.
When deploying 802.11a/b/g access points (mixed environment) with 802.11n access points, it’s far better to assign the 802.11n access points and customers to the five GHz band exactly where there is certainly additional non-overlapping channels and much less interference.
Use all 802.11n access points and customers exactly where doable as opposed to mixed environment and no less than 2T x 3R x 2S spatial streams.
Use further access points per coverage region with 802.11n at five GHz for elevated information rate, range (distance), number of customers and network availability.
Deploy far more effective extended range antennas to boost the information rate and range.
Clean up complications with any sub-optimal routing on the network.
Take into account deploying the WLC 4400 WLAN controllers. This demands a firmware upgrade on all 1100 and 1200 series autonomous access points, nevertheless you will find benefits including advanced RF management capabilities.
three. End to End Good quality of Service (QOS)
Any very good good quality of service deployment should contemplate both wired and wireless QOS methods for guaranteeing end to end performance. The wired QOS has already been discussed here with Shared Round Robin (SRR) and Weighted Round Robin (WRR) hardware queuing on switches. Too there is certainly Low Latency Queuing (LLQ) and Class Based Weighted Fair Queuing (CBWFQ) implemented on WAN routers. DSCP and CoS packet marking is employed to prioritize particular visitors varieties for preferential queuing. Wireless now has Wireless Multimedia Extensions (WMM) that classifies visitors with 4 categories based on targeted traffic kind. These consist of voice, video, finest effort and background. This supplies a guaranteed service level for video targeted traffic throughout times of network congestion.
The layer two information frame from the switch has an 802.1p field exactly where the class of service (CoS) bits are set. The access point examines that field and queues targeted traffic using a precise CoS setting to the assigned queue. The voice visitors queue could be the highest priority queue and any targeted traffic queued there’s serviced ahead of video and information. Any wireless customers not utilizing VoIP will have video prioritized initial. Note that even though queue three very best effort has a CoS of 0 that queue is nonetheless greater priority than background site visitors. Cisco VideoStream application layer enhancement enables assignment of video visitors to a priority stream based on a VLAN or SSID assignment for preferential queuing.
/>Access Point Priority Queuing:Queue 1: Voice Site visitors CoS = 6,7
Queue two: Video Site visitors CoS = 4,5
Queue three: Finest Effort (Transactional Information) CoS = 0,3
Queue 4: Background Targeted traffic (E-mail) CoS = 1,2
Call admission manage can be a form of QOS that limits the number of video sessions to keep away from oversubscription of the priority queue in the switches and routers. The use of a gatekeeper service monitors the number of video sessions and denies any extra sessions according to the bandwidth setting of the queue. The priority queue is configured with adequate bandwidth for a certain number of sessions and any requests for extra sessions are denied if that exceeds the queue size.
4. Bandwidth
As mentioned, performing a performance assessment of the present network will identify exactly where extra bandwidth is necessary. The organization WAN will be the most frequent source of difficulties with bandwidth. The prevalence and low expense of Metro Ethernet Gigabit circuits nowadays make it’s an awesome chance to deploy it on the corporation network.
Copyright 2011 Shaun Hummel All Rights Reserved
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Post # 5568ac2bcf1d43d1ff81 source: Rocky Lohmann is a Network Monitor specialist and he also can be asked for extra details in Network Monitor find out more on his well frequented blog © February 15, 2012, 4:13 pm
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