Broadcast News

Bookmark and Share
05/06/2018

Introduction To Network Topologies For IP – Part 2

News Image
In the first part of this article, dB Broadcast looked at the 'big switch' and three-tier tree network topologies as applied to IP-based broadcast systems. Limitations on scalability in particular were identified. In this part, another architecture is considered with an examination of the spine-leaf system of network design.

Clos crossbar networks (after researcher Charles Clos), originated in telecoms networks in the 1950s. The big advantage of this architecture in telecom applications was that multiple switching paths allowed telephone calls always to be connected, and not blocked by another call.

In the context of data centre applications, two-tier Clos networks, which are commonly referred to as spine-leaf networks (Figure 2), are inherently non-blocking. Hosts are connected to leaf switches (analogous to the access switches in a tree network) and each leaf switch is connected to every spine switch in a full mesh topology. As a result, the spine layer acts as a network backbone, providing interconnection between all the leaf switches.

Equal-Cost-Multi-Path (ECMP) Layer 3 routing or Layer 2 switching allows all links to remain forwarding (non-blocking), meaning that multiple paths are available, minimising bottlenecks and oversubscription. In Layer 2 leaf-spine designs, Transparent Interconnection of Lots of Links (TRILL) or Shortest Path Bridging (SPB) commonly take the place of the spanning tree. In Layer 3 designs, the path is explicitly routed, often using a shortest path routing algorithm such Open Shortest Path First (OSPF).

In both Layer 2 and Layer 3 implementations, whatever path is used, the payload hops to a single spine and then to another leaf, making latency predictable (the exception being where both hosts are connected to same leaf switch, where no hops are needed). As the forward and reverse paths always have the same number of hops, the network has far less asymmetry than a three-tier tree network.

Spine-leaf networks are highly scalable. If the network is danger of becoming oversubscribed, an additional spine can be added with links to every leaf. Likewise, if port capacity becomes an issue, an additional leaf can be added with links to every spine.

There are some disadvantages with the spine-leaf topology. The first is the large amount of cabling needed to connect every spine with every leaf. This becomes an increasing issue as the network is scaled up. This does mean that careful consideration should be given to the location of the spine switches within the data centre, to minimise cable lengths.

If a layer 3 design is used, then spine-leaf VLANs are limited to each individual leaf switch, making leaf to leaf VLAN access not possible, even within the same location. However, "VLAN Everywhere" is not restricted if a layer 2 design is used. Alternatively, the use of Virtual Extensible LAN (VXLAN) provides a virtual layer 2 overlay over layer 3, making leaf to leaf VLAN mobility then possible.

The inherent non-blocking characteristics of the spine-leaf topology along with its built-in scalability make it likely that it will eventually become the norm in high-bandwidth IP video applications.

dB Broadcast has accumulated unique knowledge in designing and implementing IP solutions for broadcasting, and has systems experience with technology from several different switch manufacturers, including solutions from Arista, Cisco and Evertz. Over the last three years, dB Broadcast has completed a major programme for Bloomberg Television, and for the next two years will be working with BBC Wales. This landmark project features a spine-leaf network deploying SMPTE ST 2110, and will deliver the first BBC facility to use IP technology across both its production and broadcast operations.

This article is also available in the June edition of Broadcast Film & Video.
Solidmate Ltd Memory Card Hire London

Top Related Stories
Click here for the latest broadcast news stories.

15/05/2017
Improved Workflow From iBroadcast At Broadcast Asia 2017
Following a successful Broadcast Asia event last year, Astec will be once again co-exhibiting alongside leading systems integrator Ideal Systems on st
12/05/2017
Pixel Power 'Offers The Future Today' At Broadcast Asia
Pixel Power has announced a demonstration of its innovative solutions using the StreamMaster Media Processing and Gallium Workflow Automationplatforms
09/05/2017
Christy Media Solutions Is At Broadcast Asia: Stand 6J4-05
Christy Media Solutions is exhibiting at Broadcast Asia for the first time this year. As a regular visitor to the show and with a growing customer bas
18/09/2017
Marquis Broadcast Transforms Its Business With Hybrid Cloud Production
The company aims to decouple people and operations from infrastructure and technical complexity. There's been a big shift in the industry recently, fr
15/09/2017
Densitron Introduces 'Technical Excellence, Tailored For Broadcast'
Leader in display, monitor and embedded computing solutions, Densitron will be making its IBC debut with a stunning range of high quality, HD and 4K m
13/09/2017
ES Broadcast Announces New Appointments
ES Broadcast has announced the appointment of Chris Williams and Jonathan Lyth as company directors to lead its systems integration division. Lyth joi
08/09/2017
TVLogic To Exhibit New Broadcast Monitors
TVLogic will have four new broadcast monitors on display at IBC2017, Stand 10.C27, it has been revealed. The monitors will include the company's 5.5-i
04/09/2017
dB Broadcast Announces IBC Line Up
dB Broadcast will be showing a range of its products at IBC and visitors will be able to meet experts from the company to discuss their applications.
01/09/2017
Gearhouse Broadcast Involved In Shure Radio Microphone Platform Launch
Gearhouse Broadcast has launched the new Shure Axient Digital radio microphone platform. The company's Australian-based, in-house Event Communications
22/08/2017
Digigram: Building Advanced Broadcast Solutions
In 2017, after 32 years of sustained history in the radio broadcast arena, Digigram will gain new momentum through a major change to its management bo
18/08/2017
BT's Media & Broadcast Division
Getting content from glass to glass – from capture to end audiences – may sound like an easy thing to deliver, but for those in the media and broadcas
08/08/2017
Further Expansion For Gearhouse Broadcast France
Gearhouse Broadcast France has announced a multi-million technology investment in order to support its growing business. With this latest expansion, t
26/07/2017
DTC Domo Broadcast To Launch AEON-TX At IBC 2017
Announcing their upcoming IBC 2017 showcase, DTC Domo Broadcast Sales Director JP Delport, said: "It is exciting to watch the development and possibil
21/07/2017
Marquis Broadcast Transforming Disaster Recovery
The ever-increasing capacity of Avid shared storage has completely transformed production processes, with faster networks, greater storage and more co
22/03/2017
ES Broadcast Adds To Portfolio
ES Broadcast has announced that it is to take delivery of Canon's new UHD DIGISUPER 27 (UJ27x6.5B IESD) 4K studio and field broadcast lens. It will be