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Network Switch Selection – How to Select a Network Switch

Overview

The network switch is the most common network device with most network infrastructure and as such selection of new switches or upgrading is a key part of most network design projects. Wireless designs will have switches interfacing with access points. That will in some cases have an affect on the switch such as increased utilization, assigned switch ports, access lists, trunking, Power over Ethernet (PoE) wattage draw or spanning tree protocol. The decision to buy new switches or upgrade will be determined after considering the network assessment and design features specified. The 5 network switch components include switch chassis, supervisor engine, switching modules, power supplies and IOS/Cat OS software.

Switch Chassis Features

The Switch Chassis features include - dimensions, number of slots, processor slot assignments, switching fabric, supervisor engines supported, supervisor engine diversity, power supplies, power supply failover, rack units.

Supervisor Engine Features

Switches are implemented with a Supervisor Engine (Switch Processor) for processing packets on a network segment. Routing is available with an onboard Multi Layer switch feature card (MSFC) or route processor running IOS code. The network switch Supervisor Engine running IOS code on the MSFC and the switch processor is in native mode, while those running Cat OS on the processor is in hybrid mode. Some engines won't support native and hybrid mode. The engine with no MSFC supports what is called Cat OS mode. Select the engine that matches design specifications. The MSFC module is integrated with the Supervisor Engine or upgradeable. You must implement a PFC module with any MSFC. Some Supervisor Engines have no MSFC module. The routing is integrated with the hardware and as such support native mode only.

The Supervisor Engine features include - supported switch chassis, uplink speed, processor memory, native IOS, Cat OS, PFC, MSFC, slot assignment, diversity.

- Supervisor Engine 720: 6500 series switches, 400 mpps, MSFC3, IOS, Cat OS

- Supervisor Engine 32: 6500 series switches, 15 mpps, MSFC2A, IOS, Cat OS

- Supervisor Engine 5: 4500 series switches, 72 mpps, Integrated Routing, IOS

- Supervisor Engine 4: 4500 series switches, 48 mpps, Integrated Routing, IOS

Switching Module Features

The Switching Module features include - supported switch chassis, interface speed, number of ports, media, cabling, connectors, throughput, Supervisor Engine supported, protocol features, Power over Ethernet, Cisco Prestandard or 802.3af.

- Media: Copper, Fiber

- Cabling: UTP Cat 5, CAT 5e, CAT 6, STP, MMF, SMF

- Connectors: RJ45, RJ21, SC, LC

- Transceivers: GBIC, SFP

Power Supply Features

The Power Supply features include - supported chassis, wattage ratings, Power over Ethernet, input/output amps, power cord type, IOS, Cat OS.

IOS/Cat OS Software

Cisco network switches can be deployed with IOS, IOS and Cat OS or exclusive Cat OS software. Design features will determine what mode and IOS or Cat OS version is selected. The software running on the Route Processor must be IOS while the Supervisor Engine switch processor will run IOS (native mode) or Cat OS (hybrid mode). Some Cisco equipment such as the 4507R deploy the Supervisor Engine IV with no MSFC onboard. The routing processor is integrated with the engine. With that design, the Supervisor Engine IV doesn't support Cat OS.

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Shaun Hummel - About the Author:

Shaun Hummel, CCNP, is a Senior Network Engineer with 11 years experience in enterprise network planning, design, and implementation. He has worked for various private and public companies in Canada and the United States improving infrastructure, security, and management. He has written Network Planning and Design Guide, Cisco Wireless Network Design Guide and Network Assessment Guide. http://www.ciscodesignbooks.com

Brainstorming to Collect Data in Designing the Corporate Computer Network

Suppose that you are appointed to lead a project of a computer network design in your organization that contains many sites that need to be integrated into a single corporate private network, what are you going to do? As a team leader, a time-frame project as general needs to be developed first that includes the brainstorming to collect data as much as possible, the blueprint project, budget forecasting, liaising with the third parties and so on.

It's quite difficult to start a project properly without knowing exactly what the strengths and weaknesses of supporting infrastructure which the system will base on. It is therefore, a computer network design should start by brainstorming to collect data as much as possible.

Assume this computer network design will involve three sites: one main headquarter office in Sydney, one main office in Jakarta, and one remote site – the gold mine in the middle of the Borneo jungle. The principal of the organization would like to have all the sites linked to a single corporate computer network to allow inter-sites communication including data, voice, or probably video conference and off course to allow easy communication with the whole world.

Telecommunication Requirements

The first data for your computer network design that needs to be collected is the telecommunication system requirements. The main question is how to link all of the sites to allow system communication to happen. The following questions can be used to collect the data for the telecommunication requirements.

1. How to arrange the Telecommunication service in remote site? We understand that both the main offices in Sydney and Jakarta are located in the area where you can find lots of communication services. What about the remote site – the site in the middle of the jungle? You should liaise with the third party company that can provide WAN services technology - probably uses the satellite link communication.
2. Collect the information what kinds of communication will be allowed for remote site to the Jakarta office: data only, voice, video, or combination of those. This information is important to help you determine how wide the satellite link bandwidth you need. This will relate to the budget since satellite link is expensive.
3. What kind of WAN technology to link data between Jakarta and Sydney, frame relay, ISDN network, VPN connection? Liaising with the third party – the telecommunication company will help.

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Ki Grinsing - About the Author:

Ki Grinsing was graduated from ITS technical college Surabaya with the addition of MCSE and CCNA certifications, he has long years of working experiences in IT. For complete articles, please visit: VPN connection

Wireless Networking – 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.

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

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Shaun Hummel - About the Author:

Shaun Hummel, CCNP, is a Senior Network Engineer with 11 years experience in enterprise network planning, design, and implementation. He has worked for various private and public companies in Canada and the United States improving infrastructure, security, and management. He has written Network Planning and Design Guide, Cisco Wireless Network Design Guide and Network Assessment Guide. http://www.ciscodesignbooks.com