Three Key Design Considerations of IP Video Surveillance Systems

Three Key Design Considerations of IP Video Surveillance Systems Copyright Notice 2012 Moxa Inc. All rights reserved. Trademarks The MOXA logo is a registered trademark of Moxa Inc. All other trademarks or registered marks in this manual belong to their respective manufacturers. Disclaimer Information in this document is subject to change without notice and does not represent a commitment on the part of Moxa. Moxa provides this document as is, without warranty of any kind, either expressed or implied, including, but not limited to, its particular purpose. Moxa reserves the right to make improvements and/or changes to this manual, or to the products and/or the programs described in this manual, at any time. Information provided in this manual is intended to be accurate and reliable. However, Moxa assumes no responsibility for its use, or for any infringements on the rights of third parties that may result from its use. This product might include unintentional technical or typographical errors. Changes are periodically made to the information herein to correct such errors, and these changes are incorporated into new editions of the publication. Technical Support Contact Information www.moxa.com/support Moxa Americas Toll-free: 1-888-669-2872 Tel: +1-714-528-6777 Fax: +1-714-528-6778 Moxa Europe Tel: +49-89-3 70 03 99-0 Fax: +49-89-3 70 03 99-99 Moxa China (Shanghai office) Toll-free: 800-820-5036 Tel: +86-21-5258-9955 Fax: +86-21-5258-5505 Moxa Asia-Pacific Tel: +886-2-8919-1230 Fax: +886-2-8919-1231

Table of Contents CCTV Becoming a Deprecated Solution... 1-4 Advantages of IP-based Video Surveillance... 1-4 IP Video Surveillance Design Considerations... 1-5 Network Architecture... 1-5 Bandwidth Requirements... 1-6 QoS... 1-7 Begin Every New Network with the Right Plan... 1-11 7

CCTV Becoming a Deprecated Solution In the past, video surveillance systems were built using closed circuit television (CCTV) technology, which has been used for many years. In the CCTV system, the video image is transmitted from camera to monitor in a purely analog signal, and uses coaxial cable to transmit the analog data. A multiplexer is used to interconnect the video camera, CRT monitor, VCR recorder, and control joystick. This technology was in use for many years. However, CCTV is a closed system, so it is difficult to be integrate with other systems. Also, CCTV requires high installation and cabling costs, especially for system maintenance or system expansions. For this reason CCTV technology is increasingly becoming displaced by more capable IP-based video surveillance technology. Advantages of IP-based Video Surveillance In an IP-based system, video streams are converted to digital data and shared through the IP network. The benefits of IP surveillance are: Remote Accessibility: IP-based video encoders and IP cameras use an IP network to deliver the video stream, so as long as there is an access to the network, the video image can be easily obtained and restored. Also, most video encoders/ip cameras are web based, which provides a user-friendly way to access and configure the video devices. Scalability and Flexibility: IP networking is a widely used and understood standard, and IP-based video devices can freely exchange data on this network as long as they have network access. This provides a convenient way to combine many different type of devices on one IP network. An IP video surveillance can easily be integrated with an existing IP network-based system by using the same network resources, and the system is highly scalable because it uses standard networking architecture. Cost-Effective: Thanks to the integration of IP and video technology, the video surveillance system can save a substantial amount of time and money by using existing IP network infrastructure to build the video surveillance system. No separate cabling or infrastructure is needed. In addition, Video streams encoded in IP data can even be transmitted wirelessly, through WLAN devices, which is a substantial cost and time-saver in environments that are difficult to cable.

IP Video Surveillance Design Considerations There are many ways to implement an IP network, and there is no single best way design a perfect IP network. As mentioned above, any digital data can be exchanged within an IP network. For IP networks that need to support IP video surveillance applications, keep the following key design considerations in mind Network Architecture Your network should optimize the network architecture for efficient bandwidth utilization. Some network architectures are less efficient, and consume more bandwidth. For example, figure 1 illustrates a network with bus topology. The PC is placed at the edge of the network to monitor the video images from all cameras. All video data will flow to the PC eventually. Each section of the bus will increase the bandwidth load on the network, until in the rightmost network segment the network much support data coming from all four cameras. For this reason, bus architectures are usually inefficient network topologies and not recommended for IP video. In the Figure 2, the PC is placed in the middle of the network. Compared to the figure 1, the total bandwidth load of four cameras is split between the two halves of the network. There is never a network segment that needs to support data from more than two cameras at once. This architecture distributes the bandwidth more evenly and decreases the possibility of network issues.

Bandwidth Requirements In IP video surveillance, the communications model is typically server-client or host-client communication. The server is the IP camera, and the client is the PC or storage hard disk. The IP camera will generate a video stream as long as there is a client request. The number of clients in the system depends on the type of connection. Depending on the specific network and system requirements, sometimes a unicast communication model is sufficient, but in other circumstances a multicast communication model is required. Unicast: Unicast is one-to-one communications. In unicast transmissions, the packets are sent from one node to another individually. The network uses the unicast address to identify the source and destination addresses. When many clients request unicast transmissions from one host, the host will generate multiple duplicate packets of that transmission. This will increase the load on the host, and the bandwidth requirements on the network. Multicast: Multicast transmission is one-to-many communications. In multicast transmissions, the host sends the packets to a special address that represents a group clients or destination receivers. When a client wants to request the multicast transmission, it must join the multicast group. The host sends just one copy of the multicast data to the multicast address, and all members of the multicast group will receive the packets at the same time. Even if many clients request a packet from the host, the host needs to send just one copy of the packet. This minimizes the impact to the performance of the host, and the load on the network. The L3 multicast IP addresses are between 224.0.0.0 and 239.255.255.255, and the L2 multicast MAC addresses are from 01.00.5e.00.00.00 to 01.00.5e.7f.ff.ff. In order to send multicast packets, the network devices must support multicast and a multicast protocol. For IP cameras, which are the host in the network, look for multicast support that enables them to send traffic to a multicast group. For L2 switches and L3 routers, look for IGMP snooping and IGMP, so these network devices can understand the multicast process and deliver multicast traffic to group members. In addition, multicast traffic has an additional restriction in that it usually can be transmitted within one subnet only. If you need to send multicast traffic from one subnet to another subnet, the L3 router must support a multicast routing protocol such as DVMRP to route multicast traffic between subnets.

In a system that only has one client that needs the video stream, as illustrated in the figure below where there is only one control room monitoring all the cameras, then unicast communication is sufficient. On the other hand, if a system possesses multiple clients, such as illustrated in the figure below where the control room and two other remote sites are monitoring the cameras, then multicast communications is a superior solution. Determine the right traffic type for your network based on the number of video streams required in order to minimize device load and bandwidth requirements. QoS QoS, or Quality of Service, is a mechanism that ensures higher quality network performance for critical applications. Traditionally, without QoS, all traffic will be processed equally by the network, and transmissions will be based on the network s best-effort. The QoS assigns different network traffic different priority. The traffic with higher priority will be processed before lower priority traffic. This ensures the network performance is reserved for the most critical applications, and can guarantee that these critical applications will experience more reliable communication. Therefore, the transmission of critical applications will be optimized by QoS to reduce frame loss, stabilize the jitter and minimize the latency. Layer 2 devices use 802.1p and Layer 3 devices mostly use DSCP to prioritize traffic.

In order to ensure that the traffic is prioritized from sender all the way to receiver, all network devices must support QoS. For video surveillance systems, this means the IP camera should have the ability to generate packets with a priority tag.the priority tag identifies the packet to the L2 switch or L3 router, so that it can be assigned the appropriate level of priority. Of course, the L2 switches and L3 routers themselves should also support QoS, in order to process the priority tags. If any devices do not support QoS, then the traffic wil simply by processed in First In First Out (FIFO) order. The following figure is an example of QoS configuration of an IP camera and L2 switch(es). The IP camera should have a field where the user can configure the DSCP value, which is the priority tag in the IP header. When the video stream is generated by the camera, the DSCP value will be attached to the IP header of the outgoing packets. When the L2 switch receives the packets on its incoming port, the switch will check the value of the DSCP field in the IP header, and map to its DSCP mapping table. The switch will then process the packet according to the priority queue. QoS can be helpful to optimize the performance of video application. There are many network performance issues that can be reduced or minimized by QoS, such as: Frame Loss: The L2 switch can handle multiple types of traffic at the same time. The figure below illustrates a scenario where there are multiple incoming streams to one port. In normal operations, the L2 switch would have no problem handling this setup. With 100 Mbps of bandwidth available, the switch can easily support the typical bandwidth usage rate of the three attached devices. The problem only arises when all three devices

experience a bandwidth spike simultaneously. This sudden burst in outgoing traffic can create up to 300 Mb of traffic, overwhelming the port. Packets will be dropped, creating frame loss. With the QoS, the traffic is prioritized, and the switch will process the traffic in priority order. Each stream will be processed one by one based on priority, which reduces the risk of packet loss, as illustrated in the figure below. Latency: Network latency is the transmission time of a packet from a sender all the way to receiver. In IP video systems, there is usually some latency between the actual event being captured, and when the image appears on a monitor. This video latency comes from a combination of three sources: Time spent processing the image on the camera, or video processing delay Time spent transmitting data through the network, or propagation delay Time spent processing the image on the computer or monitor, or decoding/buffering delay

With QoS, users can configure the video traffic as higher priority traffic. When the video stream is delivered through the network, the switches and routers will process the video stream prior to other traffic. This reduces the latency in the switch and router, minimizing the propagation delay component of video latency. Jitter: When the video packets are generated by the camera, the packets are delivered one by one with gaps between each packet. During the transmission through the network, the packets might be processed differently in a switch or router, e.g. a switch might handle multiple streams in different order. This causes the gaps between packet to vary when they finally reach the network destination. This phenomenon is called jitter, and creates intermittent video streams. the different gaps between packets when arrives to the destination, this is called jitter, and it will result the intermittent video image display. To prevent jitter, the video application attempts to buffer the video by collecting and consolidating many incoming packets. After a certain number of packets ar stored in the buffer, the application will process the packets so the video image will display smoothly. QoS can help to reduce the jitter. When the video stream is set to high priority, the switch or router will process the video stream prior to other data streams. This will maintain consistent gaps between packets.

Begin Every New Network with the Right Plan Every network is different, and each network must be designed to meet the specific requirements and variables of each specific application. However, for any network, it s useful to review the three key design considerations outlined in this guide. Identifying the right network architecture, bandwidth requirements, and quality of service settings for an IP video network are the important first step to building a data network that will successfully become a consistent, dependable communications platform that empowers IP video surveillance systems.