| Your business intends to make extensive use of video | | | | Remember unless this is a greenfield then baseline, |
| conferencing and multi-media applications. How do you | | | | baseline, baseline! |
| determine what bandwidth solution (T1, DS3, OCx | | | | When it comes to streaming video, bi-directional - you |
| Sonet, etc.) would best meet your needs and | | | | are going to have to consider the quality of the |
| incorporate that decision into your network cover | | | | compression you are planning to use. If you are |
| these applications? | | | | planning on using high definition video 1 direction it is |
| I'd say that it depends on what kind of service and | | | | recommended to have at least 2MB in the direction of |
| QoS you are looking at. For example, when you say | | | | the video being accessed. |
| "video" you mean video conferencing and not | | | | So if you are streaming video to your computer then |
| something like VoD. The Bandwidth requirements will | | | | you need to make sure that you get 2MB download |
| vary according to your service requirements. | | | | capacity. Also, another thing to keep in mind is latency |
| For example: For IPTV services, the image quality | | | | and loss of packets. I would recommend staying away |
| depends on the encoding deployed: MPEG-2 | | | | from wireless for this type of application as it will add |
| consumes approx. 3.75 Mbps, whereas MPEG-4 | | | | latency and cause issues later. DS3 bandwidth and |
| needs approx. 2 Mbps for the same high-quality image | | | | anything higher may be over kill, but would easily be |
| production. Also broadcast TV is delivered using IP | | | | able to handle your demands. |
| Multicast which makes the bandwidth required | | | | Without knowing specifics, it is hard to provide a |
| dependent on the number of channels offered and the | | | | precise answer, but, one can still specify a systematic |
| encoding rate. 200 channels of MPEG-2 in standard | | | | method for calculating required bandwidth. Once you |
| definition will take approx. 750 Mbps of bandwidth. | | | | know the bandwidth requirement, then it is all about |
| VoD, on the other hand, is a unicast per-viewer | | | | negotiating the most economical way to order that |
| channel. 1000 standard definition VoD users will need | | | | bandwidth from a network provider in the area. |
| appro. 3.75 Mbps. | | | | Here is what I would suggest: |
| The QoS requirements for video conferencing using | | | | 1. Calculate the peak external link bandwidth |
| H.323 (SIP could be different again) can be planned on | | | | requirements (inter-office data transfer, video |
| the "Rule of 75" as follows: Calculate the minimum | | | | conferencing, email transfers. With attachments running |
| bandwidth required by each of your applications ( e.g., | | | | in tens of megabytes, email traffic can't be ignored |
| video, voice, data). The total of this bandwidth is the | | | | these days.). |
| minimum requirement for any given link and it should | | | | 2. Real time applications being mostly jitter and delay |
| consume NO MORE than 75% of the total available | | | | sensitive - so you have to make sure that you will |
| bandwidth on the link. The 75% rule makes allowances | | | | have enough bandwidth when they need it. The |
| for bandwidth required for over head traffic, such as | | | | bandwidth of video depends on the mpeg profiles |
| routing, Layer 2 keepalives and other applications, such | | | | used (without going into specific, generally 1.5 Mbps can |
| as, email, HTTP etc. | | | | give you very good video on a PC (equal to VCD |
| So, Capacity planning for H.323, should look like | | | | quality). HDTV images can take about 20 Mbps - but |
| something as follows: | | | | that is domain more reserved for IP TV service |
| Video data + 20% = bandwidth required. | | | | providers). Most current users of interactive video |
| Example: | | | | communications will be happy with the images coded |
| Video data rate: Bandwidth Required: | | | | and transmitted @ 512 Kbps. This includes audio and |
| 512 kbps = 614 kbps | | | | video as well as control signaling. So, one should |
| 1.5Mbps = 1.8 Mbps ... | | | | provision at least 512 Kbps per video stream, and |
| For issues such as number of concurent users and | | | | more the better (I would say 1.5 Mbps is the good if |
| more stuff on video conferencing you can perhaps | | | | you are a big organization and use a large TV for |
| consider looking into Cisco's solutions offered and also | | | | video conferences)). So, multiply bandwidth for a single |
| TANDBERG boxes. | | | | stream by the number of parallel streams required. |
| Cisco considers anything 766Kb to be a "slow link" for | | | | Now that determines the total peak real time usage. |
| VOIP. Also you need to consider the criticality of the | | | | 3. There is no specific rule - but wise men with |
| sites so you may need two separate connections. All | | | | experience advise to keep the peak real time within 60 |
| multi-media applications run on top of your other | | | | to 75% of network bandwidth available leaving the |
| applications so QoS only allows a preference of who | | | | remaining capacity for background traffic. In a small |
| goes first. | | | | organization of 5 people - it is easy to tell people not to |
| You need a good baseline of non-multi-media | | | | download gigabyte attachments when video |
| applications (VOIP). So bandwidth needs to be able to | | | | conferencing is going on , but in larger organizations it is |
| handle all necessary applications in the network. | | | | hard to enforce such things except with router policies |
| Also, you'll need to remember that the bandwidth | | | | (assuming they have QoS support), and you can deal |
| aggregation at the Data Center needs to meet or | | | | with occasional unhappy users. |
| exceed all inbound remote site traffic. In other words, if | | | | 4. Now, once you know your bandwidth requirements, |
| I have three remote sites all with T1s. I'll need more | | | | it is time to talk to the network operator how they can |
| than one T1 at the Data Center to manage the traffic. | | | | provide that bandwidth in the most cost effective way. |