A/B Copper Network Backup Switches - A perfect originate Guide

Introduction:
However uncomplicated the term A/B switch may sound, A/B switches are not necessarily uncomplicated to design. Following is a view process with examples that can aid any network boss with the amelioration of the exact switch to meet his or her requirements.

1. Location - Where are you going to put the switch?:
A) Desktop - A desktop A/B switch may look like a black box with a knob, but that is not the total story. An example is the Model 8050 Rj45 A/B Switch that is Cat5 compliant. This manual switch enables access to two 10/100 Base-T networks (up to 100 Mbps) and incorporates a high-quality sealed switch with self-wiping low-impedance contacts. The switch is transparent to data speed and format. The anodized enclosure provides Emi/Rfi shielding which enables the switch to achieve well in noisy environments. A desktop switch can be compact, full-featured and sit right on a desk.

B) Computer Room Rack - Following are two examples of rackmount A/B switches.
i. Switch Modules - Model 9740 switching ideas includes switch modules and a rack that can accommodate up to 40 channels in only 8.75 inches of panel height. The A, B and coarse connections are on the rear panel. The 2-position rotary switches are neatly lined up on the front panel. All 8 pins are switched which allows compatibility with all Rj45 interfaces. Systems are available to accommodate both Cat5 and Cat5e high-speed requirements. Forty channels of A/B switching in a compact rack may meet your enterprise requirements.

ii. Switch Box - A switch box instead of a module may be a better fit for some requirements. The Model 9716 16-Channel Rj45 Cat5e Compliant A/B Switch, with manual operation, fits into a proper 19" rack (2U high). Sixteen front-panel knobs contribute private control of each channel. This switch configuration is rated for 10/100/1000 networks (up to Cat5e).

C) Process control System - Din rail mounting is an ideal method of mounting switches for use in process control systems. The Model 9080 Rj45 A/B/Offline Switch allows the user to access two Rj45 devices linked to its A and B ports with one Rj45 gismo linked to its coarse port, or to separate all ports by switching to the Offline position. This unit is a manually operated keylock switch requiring no power. The switch is literally integrated as a ideas component by utilizing its rear panel Din rail mounting bracket. A grounding screw is mounted on the front panel.

D) Nuclear Power Plant or other Rough Environments - The Model 4503 is a Seismic-Proof Db9 A/B switch. This manual switch has been ruggedized to withstand vibrations. The switch and its feed-through connector have successfully passed the careful seismic testing of the galvanic Power research produce (Epri) Seismic Qualification Reporting and Testing Standardization Squrts Program, qualifying it for use in nuclear power plants. The Model 4503 is ideal for factory floors, energy facilities, and any other harsh environment application.

E) Ship or other Mobile/Motion Application - The manual Model 4504 Ruggedized Db25 A/B switch is designed to withstand vibrations encountered in mobile and appeal applications. This switch has also passed careful seismic testing. The optional mounting ears allow firm attachment.

F) In the Wall - The Model 7190 is a manually operated duplicate gang wall box Online/Offline switch. When in the Online position, the switch connects the coarse gismo to gismo A. In the Offline position, the switch disconnects the coarse gismo from gismo A. There are two Rj45 Cat5e ports on the bracket inside the wall box. The Rj45 network cables must be run into the box and bracket before installing in the wall.

2. Connectors - Types of Connectors/Ports
The coarse types of connectors and ports include: Db9, Db15, Db25, Db37, Hd15, Bnc, Rj45, Rj11/12, Mini-Din and Usb.

3. Rj45 Connector/Port - If the switch has Rj45 ports, is Cat5, Cat5e, or Cat6 required?
A) Cat5 is a type of twisted pair cabling. Twisted pair cabling is categorized agreeing to its transmission capability. Category 5 (Cat 5) cabling transmits data at speeds up to 100 Mbps.
B) Cat5e is a incompatibility of Cat5 that supports short-run Gigabit Ethernet (1000 Mbps) networking by utilizing all four wire pairs in a Cat5 cable.
C) Cat6 is a cable proper for Gigabit Ethernet and includes stringent specifications for crosstalk and ideas noise. The Cat6 cable proper provides doing of up to 250 Mhz and is suitable for 10Base-T, 100Base-Tx (Fast Ethernet), 1000Base-T/1000Base-Tx (Gigbit Ethernet) and 10Gbase-T (10-Gigabit Ethernet). Most high capability Cat6 cables will exceed the proper and literally contribute doing of up to 550 Mhz.

4. Controls - How do you want to control the switch?
Our four categories include: Local Manual, Remotely Controllable, Automatic, or any combination.

A) Local Manual - All of the network switch examples above are manually operated. They can highlight pushbuttons or rotary knobs and they want no power.

B) Remotely Controllable Network Switches - This switch group includes Rs232 Serial Control, experience Closure, Ip Addressable, and any combination of the three.

i. Rs232 Serial Control - The Remote connector accepts Rs232 serial data Ascii commands. An example of a switch with Rs232 Serial control is the Model 7356 6-Channel Rj45 Cat5 A/B Switch with Local and Remote private Channel Control. Each channel maintains its current position in the event of a power loss and continues to pass data. The unit fits into a proper 19" rack and is 1U high. The Supervisory Remote Port consists of a Db9 female connector that accepts Rs232 serial data. Switch positions can be prime locally via front panel controls or remotely via Rs232 Ascii command via the Remote port.

ii. experience Closure - An example of a experience Closure switch is the Model 7359 Tri-Channel Rj45 Cat5 A/B Switch with Remote control via experience Closure. The switch is controlled manually via pushbuttons or remotely via the Db9 female connector on the rear panel that accepts experience closure signal switch commands.

iii. Ip Addressable - An example of an Ip Addressable switch is the Model 7465 8-Channel Rj45 A/B Switch with 10/100 Base-T Lan Telnet access. The 8 channels on this switch can be independently controlled via pushbuttons. Remote access can be accomplished via the Rj45 Female connector on the rear panel that accepts 10/100 Base-T Lan access Ethernet for remote control operation. Remotely pick switch position, query switch position, and lockout the front-panel pushbuttons. During power loss, the Model 7465 continues to pass data in the lost position.

iv. Graphical User Interface (Gui) - The remote Gui interface allows the user to control the switch remotely with uncomplicated point and click operation. The Model 7358 Rj45/48 T1 Interface A/B Switch features both Telnet and Gui remote control. This switch allows quick association to any one of two Rj45/48 T1 interface devices from one coarse device. Local control is via a front-panel pushbutton. The remote control Rj45 port is an Ip addressable, 10/100 Base-T port. Remote control Telnet command interface or the Graphical User Interface allow the user to control the switch position, lockout the front panel operations and procure switch status. The software features allow the user to access the switch via any proper Web browser. With uncomplicated point and click doing the user can control and monitor the Model 7358. The user can also turn the switch's Ip address. Lan access gives users over the Lan or over the Internet access to control the switch.

v. Code Operated - The switch position and lockout status can be changed through the data stream on the coarse port. The Model 4406 Rj45 Code-Operated A/B Switch shares one Rj45 interface gismo between two other devices. The switch may be controlled via a front-panel pushbutton or remotely by sending a trigger character sequence to the unit via the Remote port. Switch position status is displayed by front-panel Leds or can be queried by the Pc linked to the Remote Rs-232 serial port.

5. Safety Concerns - Keylock, Lockout and Offline Positions
A) Keylock - The benefit of a keylock is the Safety of knowing that only the person with the key can turn the switch position. The Model 8076 Dual-Channel Rj45/110-Block, Cat5e 100 Base-T Network access Keylock Switch accepts two 8-conductor Cat5e cables Input via two Rj45/110-Block punch-down connectors. This switch allows the user to switch-through or break-from two yield Rj45 exit ports. The user can take off the top cover of the switch and punch down the connections inside the unit.

B) Lockout - The benefit of the lockout highlight is that the user can lockout the switch position remotely and be assured that the switch is operating as prescribed. The Model 7348 Tri-Channel Rj45 Cat 5 A/B Switch may be controlled manually via pushbuttons or remotely from an Rs232 serial port. Each channel is an private switch that is independently controlled. Remote commands can switch each channel individually or all channels simultaneously as well as lockout the front panel control. Remote commands allow monitoring of channel switch position and lockout status.

C) Offline and Cutoff Positions - With remote and self-acting switches, the switch can automatically switch to an offline position before switching between ports A and B. manual and remotely controllable switches are also available with a bodily offline position that can be prime to stop the switch from passing data. The Model 7246-Esl Dual Channel Rs530 Switch and Rj45 Secure/Non-Secure Switch with Cutoff position provides two-channel switching in a low profile, 19-inch 1U rack unit. Channel one shares a singular Db25(M) interface gismo linked to the coarse port among two other Db25(F) devices linked to the procure and Non-Secure Db25 ports. Channel two shares an Rj45 gismo linked to the coarse port among two other Rj45 devices linked to the procure and Non-Secure Rj45 ports. Both channels allow the user to set the switches to the Cutoff position which stops any and all data throughput for the switch. If power to the Model 7246-Esl is removed, both switches will automatically move to the Cutoff position. When power is restored, each switch will move to the programmed default position.

6. Power Loss - How do you want to deal with a power loss?
Which position should the switch be in? Should the switch continue to pass data?

A) Last Position, Pass Data - The Model 4421 Cat5 Rj45 A/B Switch with Password Serial Remote Port includes an Rs232 serial Safety enhanced Supervisory Remote Port requiring a password login to access. Upon permissible authentication, a final or computer in final mode linked to this port can chronicle with the unit, determine its status, turn the switch position as desired, and/or lockout the front panel switching capability. The Model 4421 retains the last switch position in the event of a power loss and continues to pass data.

B) Default Position - The Model 4515 8-Channel A/B singular experience Relay Port Switch, Rj11 Interface with 10/100 Base-T Lan access and Serial Remote access shares a gismo linked to a singular pin of each Rj11 interface port between two other devices linked to the A and B pins for each port. Remote access can be via a Web-based Gui interface through 10/100 Base-T Ethernet association or using Ascii commands sent to the unit via an Rs232 connection. Each port has (4) active contacts: commonly Open, commonly Closed, the Wiper experience of the relay, and a pin for Sg (signal ground referenced to the switch unit). The Model 4515 defaults to the commonly accomplished position in the event of a power loss to the unit.

C) Switch Evaluates and Determines Power Up Position - The Model 7387 Rs232 Db25 A/B Switch with Fallback and Remote Port shares a singular port interface gismo linked to the coarse port among two other devices linked to the A and B ports. This switch can sense Rd action or Dcd nearnessy on the ports and switch accordingly. The switch can also be controlled manually via pushbutton or remotely via experience closure. All switched signals are passed via latching copper experience relays that profess their position and continuity in the event of a power loss. When power is restored, the Model 7387 loads the former position and mode of doing and checks Dip switch settings and the remote port to determine the exact startup configuration.

7. Whole of Channels per Chassis - From singular channel A/B switches to complicated channel switches, the technology exists to deal with specific requirements.

A) Combining singular Channel Switch Modules - Up to eight single-channel Model 7009 Rj45 Cat5e A/B/Off-Line Remotely Controllable Switch Modules compactly fit into a Model 9030 Rack. This modular expandable ideas allows the user to add switching capacity as required. Channels are switched individually.

B) 4 Channels in Slim Rackmount Configuration - The Model 7234 Quad-Channel Rj45 A/B Switch with Remote control Port is slim, only 1U high, and fits into a proper 19" rack. All four channels are switched simultaneously. This switch allows local switching via pushbutton. Remote switching is accomplished via the transition from open to accomplished or accomplished to open via a singular set of contacts linked over pins 1 & 2 of the Db9/Female Remote connector port. Upon initial power to the unit, the unit will read the Remote port to determine the power up position state. If there are no connections to the Remote port connector, pins 1 & 2 are open, thus the unit will default to all four channels in the A position. All four channels are switched simultaneously.

C) 8 Channels in a Rackmount Configuration - Model 9066 8-channel Rj45 (2 Pair) 10Base-T manual A/B Switch enables access to two 10 Base-T networks. The operator can reroute data between two networks with a uncomplicated push of a button. Switch each channel individually.

D) 16 Channels of Auto-Controlled Switching in Rackmount Configuration - The Model 7435 Auto-Controlled 16-Channel Rj45 A/B Switch ideas allows sharing a singular port Rj45 interface gismo linked to the coarse port among two other devices linked to the A and B ports for each of the switch's 16 channels. The port position, A or B, of private channels in the Model 7435 is user-configurable to be determined either manually, via the Gui, or automatically per the programming. In the self-acting mode, the position of the private channels is controlled by sensing incoming data on ports A and B. All switched signals are passed via gold clad silver relays that profess their position and continuity even in the event of a power loss. All channels can be switched simultaneously or independently.

E) Up to 40 Channels of A/B Switching - Model 9741 handles up to 40 channels of A/B switching in a high-density switch ideas that takes up only 8.75 inches of panel height. The A, B and coarse connectors are on the rear panel. The 2-position rotary switches are on the front panel. All 8 pins are switched allowing compatibility with all Rj45 interfaces. This trustworthy switch ideas is manually operated and requires no power. Each channel is switched individually.

8. Channel control - Simultaneous, private Remote control or Both. How do you want to switch your channels?
The examples above contribute a collection of control systems:
Model 7009: private switching
Model 7234: Simultaneous switching
Model 9066: private switching
Model 7435: private or simultaneous switching
Model 9741: private switching

9. Power Requirements
Most remotely controllable and self-acting switches want an external power supply.
A) Ul beloved 120Vac, 60Hz wall mount power module that supplies 12 Vdc, 500mA to the unit.
B) Ce and Ul listed wall mount wide range power module, 100Vac, 240Vac, 50Hz/60Hz supplies 12 Vdc, 1.5A to the unit.
C) Exceptions: Some switches want customer supplied voltage to the power input connectors.

10. Summary
The data networks of today are approximately as diverse as snowflakes. Managers have huge tasks: trying to backup data, procure the network, deal with fiber to copper conversions and so much more. This white paper was developed to be used as a guide to help in the produce of an A/B copper network backup switch.

A/B Copper Network Backup Switches - A perfect originate Guide

How to make Homemade Yogurt

Read More

Build Your Own Fiber Optic Network Like a professional Network Engineer

What does an firm fiber optic network consist of?

The basic doctrine of modern Lan wiring is the view of structured cabling. The entire networking theory is broken up into chunks that allow workstation wires to be concentrated.

In a typical firm Lan system, the fiber optic network consists of telecommunication rooms, backbone wiring, work areas and horizontal wiring.

Let's interpret this with a 3 stories building.

On each floor, there will be a telecommunication room sitting on top of each other. These telecommunication rooms hold all network equipment such as routers, servers and switches. Telecommunication rooms are linked together with fiber optic cables passing through vertical shafts which are called backbone wiring/cabling or vertical wiring/cabling.

The backbone fiber optic cables typically run at 10Gbps Ethernet speed to furnish sufficient bandwidth for the whole enterprise.

Work areas are work stations (Pcs) divided into cubicles. These work areas are linked to each floor's telecommunication room with horizontal cabling. These horizontal copper/fiber optic cables typically run at 1Gbps Ethernet speed.

How to pull the fiber optic cable through vertical shaft

The backbone cabling used to be twisted pair copper cables. But now it is typically multimode fibers or even singular mode fibers.

There are many tools ready to pull the vertical backbone fiber cables. These contain Gopher poles, cable caster pulling tools or fish tapes. And usually you need to setup a pulling eye to protect the fiber cables and connectors while pulling the fiber cables.

How to desist a backbone vertical fiber optic cable?

The backbone fiber optic cables come in without termination (connector). You usually need to desist these fibers with fiber optic connectors such as St, Sc or Lc connectors.

The termination steps are not very difficult but it does need some thorough training before you can do a fairly good job.

Fiber optic termination tools

The tools needed for fiber terminations are fiber optic cable strippers, Kevlar cutters, fiber cleavers, St, Sc, Lc or Mtrj fiber optic connectors, fiber connector hand polishing puck, fiber polishing films and fiber inspection microscope.

Fiber optic cable termination steps

1. Strip the fiber

Fiber cables come with 3mm jacket, Kevlar vigor member and 0.9mm buffer coating. To get to the 0.125mm fiber cladding, you need to remove the 3mm jacket with a fiber jacket stripper, then cut the Kevlar fibers with a Kevlar cutter, finally strip the 0.9mm buffer down to 0.125mm cladding with a fiber optic stripper.

2. Cleave the fiber

After stripping the fiber down to 0.125mm cladding, you insert the fiber into a Sc, St or Lc connector, and then inject some fiber optic epoxy into the connector with a syringe.

You will then lay the connector into a hot oven to cure the fiber epoxy so it can hold the fiber tightly.

After the curing process, you Cleave extra fibers from the connector tip with a fiber optic cleaver.

3. Hand polishing the fiber

In the next step, you put the connector (already with fiber fixed inside) into a hand polishing puck, which serves as a fixture while you polish the end face of the connector to get a high capability mirror like finish.

You then hold the polishing puck and polish the connector on a connector lapping film in a frame 8 shape for 10~15 times.

Repeat the hand polishing steps stepping from 12um, 3um to 0.5um lapping films.

4. Fiber termination capability inspection

The final step is to peruse the capability of your work. You insert the terminated connector into a fiber optic inspection microscope which zooms to 200 to 400 time level to show you all the scratches and pits that may exist on the connector end face. If everything looks perfect, then you can join together your fiber into the network.

This only touches the outside of building a fiber optic network. We have tons of facts on our web site. Ensue the links below to peruse even more!

Build Your Own Fiber Optic Network Like a professional Network Engineer

Clips Video Guide by Clipzaa Absolute Encoders Zune MP3 Players

Read More

Improving Video Over Wireless Network Performance

Overview

This article discusses how to improve video over wireless performance. Many companies are using various new video content technologies today such as live video streaming, webcasting, video conferencing and web conferencing. YouTube services continue to be popular and are using increasingly more bandwidth as companies use video for training and marketing purposes. Google language translation service can now convert text, making the English text based videos available to other countries as well. Keep in mind that with the proliferation of company VPNs for security purposes, employees can use wireless at work as seamlessly as at home or on a public network. They can access the same video services from anywhere. This is why wireless is so popular now and the need for video grade wireless infrastructure performance.

50 Ft. Usb Cables

The current 80.11a/g wireless access point is easily swamped when several clients start downloading large files and running video applications. The best solution for guaranteeing acceptable video performance is now the 802.11n wireless standard. According to a Cisco forecast study, the number of wireless devices will exceed wired devices on the internet by 2015 and account for 54% of IP traffic. In addition video traffic will account for 90% of the consumer internet traffic by 2015.

Video Basics

Video and voice are real-time traffic streams by nature that are sensitive to network congestion that causes latency (delay). Video has both a data and an audio component. It should be noted that the same performance metrics such as jitter, latency, packet loss and throughput affect video as well as voice traffic across the internet and company network. Packet loss has a greater effect on video while latency affects voice much more. Guaranteeing specific service levels for video on the network could involve implementing QOS, increasing network bandwidth, network design changes and equipment changes. All these improvements are for the purpose of making the network "video ready". Companies increasingly use web conferencing, webcasts and video conferencing for meetings and for training purposes. Colleges use it to deliver courses as well. It is a very cost effective tool to decrease company travel costs.

Types of Video

It is worth discussing the various types of video services popular today and where, from a networking perspective, consumers source the content. Note how most of the services are across the internet.
Live Video Streaming over the internet of company Webcasts and TV broadcasts typically delivered to your desktop. Web Conferencing to the desktop with applications such as Skype and the very popular Go to Meeting service. Video Conferencing service that runs from and across the company network with Cisco Telepresence and equipment from companies such as Tandberg and Polycom. Progressive Video download from companies such as YouTube to the desktop. Broadcast Video multicast of one to many video streams such as Netflix.

Video Performance

H.323 defines a suite of protocols for audio and video traffic including H.264 and G.729 protocols. It is a framework for developing multimedia applications on a company network. The G.729 protocol is a popular audio codec for compressing audio traffic at 8 Kbps with a 10 ms delay. The H.264 video codec standard is the most current adopted video compression standard. It specifies 24, 30 and 60 frames per second (fps) for high definition (HD) video conferencing with compression from 1.5 Gbps of video traffic to 4 Mbps at a resolution of 1920 x 1080 and 30 fps.

It is important to understand the performance metrics that affect video performance including packet loss, latency, jitter and throughput. Video is sent as a constant stream of traffic in contrast to data traffic such as email that can be re-transmitted with some delay and have no significant effect on service level. Congestion is the basic symptom of a network that is busy and experiencing network performance problems. The queues are busier during times of increased network activity. This causes increased latency, jitter, packet loss, decreased throughput and re-transmission of packets. Implementing quality of service (QOS) will sometimes actually cause dropped data packets to prevent voice/video packet loss. The data packets are then re-transmitted with some delay. The following defines these industry standard performance metrics.

Latency: Amount of time for a packet to travel from source to destination

Jitter: Amount of average variation in latency of each packet

Packet Loss: Percent of packets dropped from source to destination

Throughput: Average number of packets sent during a fixed period of time

Each video service requires different amounts of bandwidth. Some services such as video conferencing are more affected by increased latency, packet loss and jitter than desktop applications. For acceptable video conferencing performance, the packet loss should not exceed 1%, jitter 30 ms and 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 requirements for video are linked to the specific type of service, amount of resolution and frames per second. For example a standard video conferencing resolution of 704 x 576 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. Desktop services such as streaming video and web conferencing have lower bandwidth requirements than video conferencing, however the same latency, jitter and packet loss problems affect video performance. In addition with all services, you have to add an average of 20% additional bandwidth overhead for Ethernet and IP protocol processing.

Video Quality of Service (QOS)

Implementing quality of service (QOS) on a company network is an end to end process starting with the video stream source. Video conferencing end points are often connected to a company edge switch while video streaming to the desktop is internet based. The process of implementing any QOS involves prioritizing traffic for preferential service. Considering video conferencing, the Cisco 3560 and 3750 access edge switches are often used to connect video equipment. The layer 2 data frame has an 802.1p header with 3 bits that can be set for 8 different class of service (CoS) values from 0 - 7. For instance video is assigned CoS of 4 while voice packets are assigned CoS of 5 and the higher number gets better service. High priority data is often assigned CoS of 2.

DSCP is a layer 3 QOS protocol used to specify various types of service (ToS) classes for data, voice and video traffic. DSCP values are layer 3 and as such are set in the first 6 bits of the IP Precedence field of the IP header. The best practice recommendation from Cisco for marking video is a DSCP of AF41. Data traffic is assigned a lower priority such as AF21 for instance while voice is assigned a higher priority of DSCP EF. Video traffic is classified with access lists that define video traffic and a class map is defined for video that matches an access list and points to a specific policy map. The policy map does the DSCP marking of video traffic and the DSCP value is assigned to a queue. Class of service (CoS) packets can be set with a policy map however it is often marked at access switches with SRR and with WRR at distribution/core switches.

Shaped Round Robin (SRR) is a hardware based queuing technique deployed with access switches. SRR allows layer 2 class of service (CoS) and layer 3 (ToS) mappings to queues. The distribution and core network layers typically have 6500 Cisco switches and they use Weighted Round Robin (WRR) hardware queuing. WRR is the same idea however the queuing architecture is somewhat different and only layer 2 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 traffic to the high priority queue with a specific priority percentage such as 15%. That guarantees all video traffic will get 15% of the link bandwidth. For instance a 1 Gbps Metro Ethernet circuit will allocate 150 Mbps of bandwidth to video traffic minus protocol overhead. Company WAN links as a best practice should never exceed approximately 33% of available bandwidth for all voice and video traffic. That leaves room for protocol overhead and data packets. Data traffic performance worsens as packets are dropped and video traffic QOS becomes less effective.

Desktop applications use the same QOS tools however the company internet connection and the wireless network factor into the design. In addition the public wireless network you happen to be using affects the overall video network performance. The bandwidth of your home internet connection and congestion affects performance as well as any congestion points across the network. The wireless network is most often where video performance degrades particularly on an 802.11b public network.

Wireless Standards

These describe the industry standard wireless protocols currently deployed.

80.11b

This wireless standard approved in 1999 specifies a maximum data rate of 11 Mbps using the 2.4 GHz unlicensed band in the United States. The band experiences a lot of interference from commercial devices using that frequency. The standard in the United States assigns 11 channels with bandwidth of around 80 MHz at 5 MHz per channel. The United States allocates 3 non-overlapping channels of 1, 6 and 11 with a center frequency separation of 25 MHz per channel. The modulation scheme used with 802.11b is Direct Sequence Spread Spectrum (DSSS) with CCK with characteristics that minimize effects associated with interference. The 802.11b additional data rates include 1, 2, and 5.5 Mbps.

802.11g

This wireless standard approved in 2003 specifies a maximum data rate of 54 Mbps using the same 2.4 GHz band as 802.11b. The 802.11g standard is popular with higher throughput and increased coverage. The same interference problems occur however with the 2.4 GHz band. The 802.11g is compatible with the 802.11b standard and assigns the same 11 channels with 1, 6 and 11 as non-overlapping. The modulation scheme used with 802.11g is OFDM that specifies higher data rates. The additional 802.11g data rates include 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36 and 48 Mbps.

802.11a

This wireless standard was approved in 1999 specifying a maximum data rate of 54 Mbps using the 5 GHz unlicensed band in the United States. The advantage of 802.11a is higher throughput however the cell coverage is smaller and additional access points will be needed for the same 802.11g coverage. There is much less interference from devices such as cordless phones, bluetooth devices, microwaves and commercial devices using the 2.4 GHz band. There are 23 non-overlapping channels with the current 802.11h specification. Some Cisco devices support both 2.4 GHz and 5 GHz transmitters on the same access point. The modulation scheme used with 802.11a is OFDM, with higher data rates and minimizing effects of interference. Each country specifies the number of channels and frequencies it allows with the 5 GHz band.

802.16

This is a metropolitan (MAN) wireless standard that provides home and business clients seamless wireless access from anywhere. The line of sight technology specifies a distance of around 27 miles and speeds of up to 120 Mbps. The point to multipoint specification operates in the 10-66 GHz range. There is an 802.16a specification with mesh topologies and non-line of sight with frequencies from the licensed and unlicensed 2 GHz and 11 GHz band at a speed of 70 Mbps. The key problem with any MAN implementation using unlicensed frequencies is interference from similar devices.

802.11n

The new 802.11n wireless standard approved in 2009 defines much faster data rates of 300 - 600 Mbps and 1000 Mbps from access point to network switch increasing throughput from client to access point and access point to network switch. It operates in both the 2.4 GHz and 5 GHz bands with effective new performance enhancements such as multiple input multiple output (MIMO) and channel bonding.

Wireless Contention

Access points are essentially a less efficient hub style shared media device with a flat broadcast domain. Contrast that with a Cisco Ethernet switch that has 100/1000 Mbps bandwidth per port and broadcast segmentation with VLANs. The switch uses a much more effective media access contention scheme than wireless access points. The wireless network employs an older less effective carrier sense multiple access with collision avoidance (CSMA/CA) process to manage client access to the network. The effect of CSMA/CA is increased bandwidth usage, packet loss and packet re-transmits with this shared media. In addition there are the standard wireless problems with the 2.4 GHz band interference and multipath signal fade that occurs when the signal bends or is distorted by the building structure. From a practical perspective 15-25 wireless clients can associate with a single access point at anytime and still maintain good performance. This of course changes as more video and high bandwidth applications are used. The 802.11n can actually support all of those clients running simulataneous live video streaming with 14 of them running high definition video streams.

Data Rate, Distance and Frequency

So by now you know there is no warp speed with older wireless. Data rate (speed) and performance metrics decrease as the wireless clients move further from the access point. Beyond an average of 50-60 feet, the speed decreases and latency, packet loss and jitter increase. The wireless network site survey determines where and how many access points should be deployed so each cell (defined coverage area) has a signal strength with 54 Mbps. The coverage area can be extended with a stronger directional antenna. For instance, these are approximate rated distance, speed and frequency specifications indoor for the Cisco 1240AG access point. Note the 802.11a distance is typically half that of an 802.11g radio however this rating was with a stronger 3.5 dBi antenna.

802.11a (5 GHz): 54 Mbps @ 60 ft - 80 ft with 3.5 dBi omnidirectional antenna

802.11g (2.4 GHz): 54 Mbps @ 80 ft - 100 ft with 2.2 dBi dipole antenna

As the data rate increases your effective network range decreases. Clients that want a continuous maximum bandwidth will need to deploy more access points per design. Increasing transmit power will actually decrease network range at higher data rates while increasing the range with lower data rates such as the case with 802.11g access points. The problem is with increased transmit power, the receiver sensitivity decreases with a process called error vector magnitude. That doesn't apply to the wireless clients where transmit power should be set at maximum for best results. The network length or wireless maximum distance is around 100 meters from client to access point, and with Ethernet wired designs 100 meters from access point to switch. The campus design can be extended with additional switch - switch connectivity of course.

Wireless data rates specify maximum throughput however that isn't a practical value. Mixed environments such as 802.11b and 802.11g will decrease throughput for both clients on the same network segment. As mentioned the 802.11b and 802.11g clients are compatible and can associate with the same access point using the 2.4 GHz band spectrum. Throughput for 802.11b is around 6 Mbps however that will vary with antenna type, distance from the access point and transmit power. Configure the access point with 54 Mbps for 802.11g clients and basic 11 Mbps for the 802.11b clients. That prevents the access point from operating at less than 11 Mbps. Some access points can operate with dual band 802.11a and 802.11g however they are separate logical networks and must have separate wireless site surveys. The 802.11a access point uses the 5 GHz frequency band. As frequency wavelength increases the network range will decrease. The design with 802.11a covers much less distance compared with 802.11g at the same data rates. The higher frequency (5 GHz) signals don't pass through the building structure as easy as lower frequencies.

These are some average bandwidth throughput values and associated wireless standards. From a practical perspective all 24 channels won't be available with the 802.11h standard and 802.11a access points due to channel overrun interference. Note the effect of mixed environment wireless equipment such as 802.11b/g on the same network and decreased throughput. This occurs as well when there are 802.11n access points with older access points on the same network.

802.11b - 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/300 Mbps x 21 channels

Decreasing the transmit power of an access point will minimize channel interference. The effective network range can be extended with repeater access points, increasing access point transmit power or adjusting the access point position. Using a higher gain antenna on the access point is an option as well. Cisco access points have a lot of options for deploying antennas with higher gain and sensitivity. Note you should minimize the cable length of any antenna. The longer antenna cabling will attenuate the signals. Some countries limit the maximum access point transmit power setting.

RF Propagation

As mentioned signal attenuation is worse at higher frequencies. There is however a lot of environmental factors that distort, bend and minimize signal strength. The result is something called multipath fading where a signal takes several paths to a destination. These are some examples.

• Diffraction - signal bending due to building structure angles

• Refraction - environmental factors such as humidity can cause 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 is the amount of receiver sensitivity power that can be decreased while maintaining acceptable network performance. That is a factor with deployment of outside wireless bridges with point to point topologies such as buildings on a campus. Problems with rain will attenuate signals and knowing the fade margin will avoid performance issues. Polarization is the orientation of the radiated pattern from the antenna and like a key must match with transmitting and receiving antenna. The most often polarization used with access point antenna is linear. Antenna can transmit horizontal or a vertical polarized signal.

Improving Video over Wireless Performance

When discussing bandwidth requirements and various video services it is important to note that a wireless network will always require much more bandwidth than your company LAN or your home internet connection for the same video service. An example is high definition live video streaming where the actual wireless bandwidth needed is much higher compared with the LAN or home cable/DSL internet connection. The home internet connection would require 500 Kbps - 1 Mbps. That is not a problem even for home internet where the cable download speed is an average 10 Mbps. The wireless network with access contention and multipath fading problems aren't as efficient and would use an effective bandwidth of 5 - 10 Mbps. In addition, note that packet loss does affect video over wireless performance more than latency and jitter however all metrics can be improved with the following recommended 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 with the new feature enhancement. That is 6x faster than the nearest 802.11g standard. Deploying 802.11n in the 5 GHz band and you have 21 non-overlapping channels available as well. That allows for higher data rates per coverage area. The new enhancements include multiple input multiple output (MIMO), channel bonding, MAC block acknowledgment, payload optimization and unicasting and QOS prioritizing of traffic classes.

MIMO Explained

802.11n uses multiple input/output antennas on the access point and wireless client to increase data rates and decrease re-transmits and packet loss. The access point and clients can send simultaneous traffic streams increasing the amount of data and extending the network range (distance). The current most popular Cisco 1250 AP uses what is called a 2T x 3R MIMO. That is 2 transmit antenna on the access point and 3 receive antenna on the client. The best results occur when all wireless clients use 802.11n adapters and access points are all 80.11n with no mixed environment of 802.11a/g access points.

Channel Bonding

The technique of channel bonding now allows combining of 2 non-overlapping channels in the 5 GHz band to send data at 2x the standard data rate for a theoretical 300 Mbps. In practice the average data rate has been tested at 180 Mbps and 140 Mbps for video streaming. That is pretty impressive compared with 802.11g average throughput of 22 Mbps.

Payload Optimization

The feature of payload optimization or packet aggregation is basically putting more data in each packet sent resulting in more effective use of the transport media.

MAC Block Acknowledgment

Previous access points required that each MAC layer MPDU packet was separately acknowledged with an ACK packet. The new 802.11n standard now uses a single block ACK to acknowledge multiple MPDUs. This decreases the amount of protocol overhead and less bandwidth required.

Multicast to Unicast Traffic

Video over wireless presents a specific problem with multicasting that the wired world doesn't have. Wireless access points do not support multicasting however 802.11n can now convert multicast to unicast streams per wireless client at layer 2.

2. Network Design

The wireless access points should always be connected to a 100 Mbps full duplex switch port. The 802.11n access points should be connected to a 1 Gbps or 10 Gbps switch port. Video end points should be connected closer to the distribution layer and on a less busy line card. The end point video source equipment can be located at the network edge as well, however you should select a switch with all the performance features and preferably located in the data center. Wireless multiple SSIDs should always be defined to segment traffic and assigned VLANs to match the same VLAN schema implemented on the wired network.

Use a hierarchical design with any new wireless/wired deployments and where possible spread out and connect access points across multiple network switches instead of a single switch. Consider doing some performance monitoring on the network to eliminate media mismatches. For example a network switch with a Gigabit port that is uplinked to a switch with a 100 Mbps interface. As well WAN circuits are most often the slowest link compared with the switch infrastructure.
Have a proper wireless network site survey done for each band to minimize signal overrun and optimize coverage. Deploy internal client adapters instead of external USB style at your laptop for best performance. When deploying 802.11a/b/g access points (mixed environment) with 802.11n access points, it is better to assign the 802.11n access points and clients to the 5 GHz band where there is more non-overlapping channels and less interference. Use all 802.11n access points and clients where possible instead of mixed environment and at least 2T x 3R x 2S spatial streams. Use additional access points per coverage area with 802.11n at 5 GHz for increased data rate, range (distance), number of clients and network availability. Deploy more powerful extended range antennas to increase the data rate and range. Clean up problems with any sub-optimal routing on the network. Consider deploying the WLC 4400 WLAN controllers. This requires a firmware upgrade on all 1100 and 1200 series autonomous access points, however there are advantages such as advanced RF management features.

3. End to End Quality of Service (QOS)

Any good quality of service deployment must consider both wired and wireless QOS techniques 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. As well there is Low Latency Queuing (LLQ) and Class Based Weighted Fair Queuing (CBWFQ) implemented on WAN routers. DSCP and CoS packet marking is used to prioritize specific traffic types for preferential queuing. Wireless now has Wireless Multimedia Extensions (WMM) that classifies traffic with 4 categories according to traffic type. These include voice, video, best effort and background. This provides a guaranteed service level for video traffic during times of network congestion.

The layer 2 data frame from the switch has an 802.1p field where the class of service (CoS) bits are set. The access point examines that field and queues traffic with a specific CoS setting to the assigned queue. The voice traffic queue is the highest priority queue and any traffic queued there is serviced before video and data. Any wireless clients not using VoIP will have video prioritized first. Note that although queue 3 best effort has a CoS of 0 that queue is still higher priority than background traffic. Cisco VideoStream application layer enhancement allows assignment of video traffic to a priority stream according to a VLAN or SSID assignment for preferential queuing.

Access Point Priority Queuing:

Queue 1: Voice Traffic CoS = 6,7

Queue 2: Video Traffic CoS = 4,5

Queue 3: Best Effort (Transactional Data) CoS = 0,3

Queue 4: Background Traffic (Email) CoS = 1,2

Call admission control is a type of QOS that limits the number of video sessions to avoid oversubscription of the priority queue at the switches and routers. The use of a gatekeeper service monitors the number of video sessions and denies any additional sessions based on the bandwidth setting of the queue. The priority queue is configured with enough bandwidth for a specific number of sessions and any requests for additional sessions are denied if that exceeds the queue size.

4. Bandwidth

As mentioned, doing a performance assessment of the current network will identify where additional bandwidth is needed. The company WAN is the most common source of problems with bandwidth. The prevalence and low cost of Metro Ethernet Gigabit circuits today make it is a great opportunity to deploy it on the company network.

Copyright 2011 Shaun Hummel All Rights Reserved

Improving Video Over Wireless Network Performance

Insect Lore Live Butterfly Garden Bed Bug Baby

Read More