After last week’s talk explaining networking from the real basics, Wayne Pecena is back to look at “where the good stuff is” in the next two layers of the OSI model.
Much of what live production needs happens in layers 2 and 3. At layer 2 we have Ethernet which defines how data is passed from switch to switch. Then at layer 3 we have the IP protocols, UDP and TCP which do nearly all of the heavy lifting getting our data from one place to another.
Wayne Pecena from Texas A&M University builds this talk around layer 2 specifically and starts by looking at the underlying protocols of Ethernet including collision detection. Given that the cabling is bi-directional, it’s possible for both ends to be sending data at the same time. This needs to be avoided, so the sending devices need to sense what’s happening on the wire and allow time for the other interface to finish.
Famously Ethernet has MAC addresses which is the way that this Layer 2 protocol deals with addressing the correct end point. Wayne shows the format these addresses follows and looks at the makeup of the frame which houses the data payload. The length of each segment of data is set with a maximum, but there is a high-throughput option called Jumbo Frames which increases efficiency for high bit rate applications by reducing the number of frames needing to be sent and therefore reducing the amount of header data sent.
A switch is an Ethernet device for connecting together multiple devices to communicate over Layer 2 and has a number of functions like learning MAC addresses, filtering frames and forwarding frames from one interface to another one. Switches can provide not only data but power to avoid having to run more than one cable. Usefully, Wayne walks us through the steps taken for one computer to send to another. Stepping through this mixture of ethernet and IP address is very useful to understand how to fault find, but also to see how layer 2 and 3 work so closely together.
Knowing the innards of a switch is vital to a full understanding of network behaviour. Wayne talks through a diagram of the what’s inside a switch showing that each NIC has its own set of buffers, a backplane (also known as ‘switch fabric’) and shared resources like a CPU. We see then how the switch learns the MAC addresses of everything connected to it and we see that, with the CPU and separating MAC address lists, a switch can create virtual lans, known as VLANs which allow a logical separation of interfaces that are on the same switch. It has the effect of creating multiple networks, that can’t speak to each other by default, on the same hardware and then allows the flexibility to add certain interfaces to multiple networks. VLANs are highly utilised in enterprise computing.
The talk finishes with a full description of how VLANs work and interact and 802.1Q VLAN tagging.
IP explained from the fundamentals here in this in this talk from Wayne Pecena building up a picture of networking from the basics. This talk discusses not just the essentials for uncompressed video over IP, SMPTE ST 2110 for instance, but for any use of IP within broadcast even if just for management traffic. Networking is a fundamental skill, so even if you know what an IP address is, it’s worth diving down and shoring up the foundations by listening to this talk from the President of SBE and long-standing Director of Engineering at Texas A&M University.
This talk covers what a Network is, what elements make up a network and an insight into how the internet developed out of a small number of these elements. Wayne then looks at the different standards organisations that specify protocols for use in networking and IP. He explains what they do and highlights the IETF’s famous RFCs as well as the IEEE’s 802-series of ethernet standards including 802.11 for Wi-Fi.
The OSI model is next, which is an important piece of the puzzle for understanding networking. Once you understand, as the OSI model lays out, that different aspects of networking are built on top of, but operate separately from other parts, fault-finding, desiring networks and understanding the individual technologies becomes much easier. The OSI model explains how the standards that define the physical cables work underneath those for Ethernet as separate layers. There are layers all the way up to how your software works but much of broadcasting that takes place in studios and MCRs can be handled within the first 4, out of 7 layers.
The last section of the talk deals with how packets are formed by adding information from each layer to the data payload. Wayne then finishes off with a look at fibre interfaces, different types of SFP and the fibres themselves.
In IP networks multicast flow subscription is usually based on a combination of IGMP (Internet Group Management Protocol) and PIM (Protocol Independent Multicast) protocols. While PIM allows for very efficient delivery of IP multicast data, it doesn’t provide bandwidth control or device authorisation.
To solve these issues on SMPTE ST 2110 professional media networks the NMOS IS-06 specification has been developed. It relies on a Software-Defined Networking, where traffic management application embedded in each single switch or router is replaced by a centralised Network Controller. This controller manages and monitors the whole network environment, making it bandwidth aware.
NMOS IS-06 specification provides a vendor agnostic Northbound interface from Network Controller to Broadcast Controller. IS-06 in conjunction with IS-04 (Discovery and Registration) and IS-05 (NMOS Device Connection Management) allows Broadcast Controller to automatically set up media flows between endpoints on the network, reserve bandwidth for flows and enforce network security. Broadcast Controller is also able to request network topology information from Network Controller, which can be used to create a user friendly graphic representation of the flows in the network.
In this presentation Rob Porter from Sony Europe explains the basics of NMOS IS-06, showing in details how setting up media flows with this specification fits into the IS-04 / IS-05 workflow. Rob emphasise that all AMWA NMOS specifications are completely open and available to anyone, allowing for interoperability between broadcast and network devices from different manufacturers.
The next speaker, Sachin Vishwarupe from Cisco Systems, focuses on the future works on IS-06, including provisioning feedback (such as insufficient bandwidth, no route available from sender to receiver or no management connectivity), flow statistics, security and grouping (similar to ”salvo” in SDI world).
There is also a discussion on extension of IS-06 specification for Network Address Translation (NAT), which would help to resolve problems caused by address conflicts e.g. when sharing resources between facilities.
“OTT over the air” – ATSC 3.0 deployment has started in the US and has been deployed in Korea. Promising to bring interactivity and ‘internet-style’ services to broadcast TV, moreover allowing ‘TV’ to transition to mobile devices. To help understand what ATSC 3.0 enables, NABShow Live brings together Sinclair’s Mark Aitken, Bill Hayes from Iowa Public Television and SMPTE’s Thomas Bause Mason all of which are deeply involved in the development of ATSC 3.0.
The panelists dive in to what ATSC 1 was and how we get to 3.0, outlining the big things that have changed. One key thing is that broadcasters can now choose how robust the stream is, balanced against bandwidth. Not only that but multiple streams with different robustnesses are possible for the same channel. This allows ATSC 3.0 to be tailored to your market and support different business models.
ATSC 3.0, as Bill Hayes says was ‘built to evolve’ and to deal with new standards as they come along and was at pains to point out that all these advancements came without any extra spectrum allocations. Thomas outlined that not only is SMPTE on the board of ATSC, but the broadcast standards upstream of distribution now need to work and communicate with downstream. HDR, for instance, needs metadata and the movement of that is one of the standards SMPTE has formed. As Mark Aitken says ‘the lines are blurring’ with devices at the beginning of the end of the chain both being responsible for correct results on the TV.
The session ends by asking what the response has been from broadcasters. Are they embracing the standard? After all, they are not obliged to use ATSC 3.0.
Thomas say that interest has picked up and that large and small networks are now showing more interest with 50 broadcasters already having committed to it.