PSIJan2017

NETWORKING
Beat bandwidth bottlenecks
The amount of data being generated
in modern surveillance systems is
increasing all of the time especially
with higher resolution cameras
continually coming to the market.
What is the impact of high rates of
data on bandwith and what can be
done to improve performance?
IP CCTV systems transmit vast amounts of video
data over networks. Video data is continually
transmitted between the IP cameras,
processing servers and storage devices. It
includes live viewing, reviewing and recording, as
well as data used for network system
communications. As the camera count in a system
increases, so too does the amount of data being
transmitted, creating network bandwidth
bottlenecks. This has an adverse impact on the
efficiency of the CCTV system, causing it to underperform.
Paul Scott, Technical Director at the Security
Buying Group, explains to PSI what the common
network bandwidth restrictions encountered in IP
CCTV systems are and explores how a welldesigned,
IT infrastructure and deployment, using
an intelligent video management software (VMS)
solution, can contribute to reducing negative
bandwidth effects and dramatically increase
system performance for users.
System bandwidth
The system bandwidth requirements of an IP
CCTV system are easy to calculate and can be
split into three prime categories:
1. Camera live viewing bandwidth. This is the
total bandwidth required for live camera viewing
and is typically assumed to be D1 resolution, as
viewing is usually in multi-screen formats. A
calculator suggests a "worst case" figure based
on a fully unicast system: one where every
camera in the system will be viewed
simultaneously by a combination of clients. In
real applications, this amount of traffic is rarely
so high.
2. Recording bandwidth. This is the total
bandwidth required for the camera video
recording streams. A typical 2MP IP camera,
operating in real-time (25 IPS) and producing
good quality video, generates around 3 Megabits
of data per second (Mbps).
3. Client reviewing bandwidth. This is the total
bandwidth needed by each client when reviewing
the system. It assumes concurrent live display
and play back of HD video from multiple cameras.
Each client viewing the IP CCTV system, from a PC
or central monitoring position, will typically
demand 30Mbps of data.
The total system bandwidth comprises the
sum of all three bandwidth types.
As an example, a system of 100 x 2MP cameras
operating in real-time (25FPS) for 31 days and
viewed by four concurrent clients would demand
the following:
• Camera live viewing bandwidth = 100Mbps
• Recording bandwidth = 300Mbps
• Client reviewing bandwidth: 4 x Clients (max
30Mbps each) = 120Mbps
Total system network bandwidth requirement
is 520 Mbps.
Total required storage is therefore
(approximately) 100TB.
Bandwidth usage
A network does not reserve 100% of its available
bandwidth for video data. Some bandwidth is
required for protocol and communication
demands. As a result, a Gigabit connection will
normally offer just over 90% of its bandwidth for
the actual data payload.
Most networks use copper Ethernet cabling,
capable of transmitting up to 1 Gigabit of data per
second (Gbps) or 1000 Megabits per second
(Mbps).
Using the example system above, bandwidth
usage would be nearly 60% of what is available. If
the system uses variable bit rate (VBR)
compression, to ensure the best detail and
quality, the actual bandwidth requirement will
feature peaks and troughs of higher and lower
bandwidth demand.
Ethernet cables and
connections
The simplest way to reduce bandwidth
bottlenecks is to create more routes, larger
capacity routes, or alternative routes for data
within the network but also in creating different
networks for different purposes.
When it comes to Ethernet connectivity then
the more available NIC ports the better, allowing
teaming and virtual LAN (VLAN) support.
VLANs offer a good method of segregating
video traffic so that all data is not transmitted
across the entire network. For instance, separate
VLANs can be used for recording traffic, live
A network does not
reserve 100% of its
available bandwidth
for video data. Some
bandwidth is required
for protocol and
communication
demands
www.psimagazine.co.uk
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