fundamentals

Video: IP Fundamentals For Broadcast Seminar IV

Posted on by Russell Trafford-Jones

“When networking gets real”, perhaps, could have been the title of this last of 4 talks about IP for broadcast. This session wraps up a number of topics from the classic ‘TCP Vs. UDP’ discussion to IPv6 and examines the switches and networks that make up a network as well as the architecture options. Not only that, but we also look at VPNs and firewalls finishing by discussing some aspects of network security. When viewed with the previous three talks, this discusses many of the nuances from the topics already covered bringing in the relevance of ‘real world’ situations.

Wayne Pecena, President of SBE, starts by discussing subnets and collision domains. The issue with any NIC (Network Interface Controller) is that it’s not to know when someone else is talking on the wire (i.e. when another NIC is sending a message by changing the voltage of the wire). It’s important that NICs detect when other NICs are sending messages and seek to avoid sending while this is happening. If this does’t work out well, then two messages on the same wire are seen as a ‘collision’. It’s no surprise that collisions are to be avoided which is the starting point of Wayne’s discussion.

Moving from Layer 2 to Layer 4, Wayne pits TCP against UDP looking at the pros and cons of each protocol. Whilst this is no secret, as part of the previous talks this is just what’s needed to round the topic off ahead of talking about network architecture.

“Building and Securing a Segmented IP Network Infrastructure” is the title of the next talk which starts to deal with real-world problems when an engineer gets back from a training session and starts to actually specify a network herself. How should the routers and switches be interconnected to deliver the functionality required by the business and, as we shall see, which routers/switches are actually needed? Wayne discusses some of the considerations of purchasing switches (layer 2) and routers (layer 3 & 2) including the differing terms used by HP and Cisco before talking about how to assign IP addresses, also called an IP space. Wayne takes us through IP addressing plans, examples of what they would look like in excel along with a lot of the real-world thinking behind it.

Security is next on the list, not just in terms of ‘cybersecurity’ in the general sense but in terms of best practice, firewalls and VPNs. Wayne takes a good segment of time out to discus the different aspects of firewalls – how they work, ACLs (Access-control Lists), and port security amongst other topics before doing the same for VPNs (Virtual Private Networks) before making the point that a VPN and a firewall are not the same. A VPN allows you to extend a network out from a building to be in another – the typical example being from your work’s address into your home. Whilst a VPN is secured so that only certain people can extend the network, a firewall more generally acts to prevent anything coming into a network.

As an addendum to this talk, Wayne explains IPV4 depletion and how IPv6 addressing works. In practice, for broadcasters deploying within their company in the year 2020, IPv6 is unlikely to be a topic needed. However, for people who are distributing to homes and working closer with CDNs and ISPs, there is a chance that this information is more relevant on a day-to-day basis. Whilst IP address depletion is a real thing, since every company has a 10.x.x.x address space to play with, most companies use internal equipment with an IPv4 address plan.
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Speaker

Wayne Pecena Wayne Pecena
Director of Engineering, KAMU TV/FM at Texas A&M University
President, Society of Broadcast Engineers AKA SBE

Video: Timing Tails & Buffers

Posted on by Russell Trafford-Jones

Timing and synchronisation have always been a fundamental aspect of TV and as we move to IP, we see that timing is just as important. Whilst there are digital workflows that don’t need to be synchronised against each other, many do such as studio productions. However, as we see in this talk from The Broadcast Bridge’s Tony Orme, IP networks make timing all the more variable and accounting for this is key to success.

To start with Tony looks at the way the OBs, also known as REMIs, are moving to IP and need a timing plane across all of the different parts of production. We see how traditionally synchronisation is needed and the effect of timing problems not only in missed data but also with all essences being sent separately synchronisation problems between them can easily creep in.

When it comes to IP timing itself, Tony explains how PTP is used to record the capture time of the media/essences and distribute through the system. Looking at the data on the wire and the interval between that and the last will show a distribution of, hopefully, a few microseconds variation. This variation gives rise to jitter which is a varying delay in data arrival. The larger the spread, the more difficult it will be to recover data. To examine this more closely, Tony looks at the reasons for and the impacts of congestion, jitter, reordering of data.

Bursting, to make one of these as an example, is a much overlooked issue on networks. While it can occur in many scenarios without any undue problems, microbusting can be a major issue and one that you need to look for to find. This surrounds the issue of how you decide that a data flow is, say, 500Mbps. If you had an encoder which sent data at 1Gbps for 5 minutes and no data for 5 minutes, then over the 10 minute window, the average bitrate would have been 500Mbps. This clearly isn’t a 500Mbps encoder, but how narrow do you need to have your measurement window to be happy it is, indeed, 500Mbps by all reasonable definitions? Do you need to measure it over 1 second, 1 millisecond? Behind microbursting is the tendency of computers to send whatever data they have as quickly as possible; if a computer has a 10Gbe NIC, then it will send at 10Gbps. What video receivers actually need is well spaced packets which always come a set time apart.

Buffers a necessary for IP transmission, in fact within a computer there are many buffers. So using and understanding buffers is very important. Tony takes us through the thought process of considering what buffers are and why we need them. With this groundwork laid, understanding their use and potential problems is easier and well illustrated in this talk. For instance, since there are buffers in many parts of the chain to send data from an application to a NIC and have it arrive at the destination, the best way to maximise the chances of having a deterministic delay in the Tx path is to insert PTP information almost at the point of egress in the NIC rather than in the application itself.

The talk concludes by looking at buffer fill models and the problems that come with streaming using TCP/IP rather then UDP/IP (or RTP). The latter being the most common.

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Speakers

Tony Orme Tony Orme
Editor,
The Broadcast Bridge

Video: IP Fundamentals For Broadcast Seminar Part III

Posted on by Russell Trafford-Jones

‘IP’ is such a frequently used term, that is real meaning and context easily gets lost. As we saw from Wayne’s first and seminars, IP stands on top of ethernet and the cabling needed to support the whole network stack. But as we see from the subtitle, this where we get to virtual addressing which, as an abstraction layer, offers us a lot of flexibility. IP, the Internet Protocol, is where much of what we refer to as ‘networking’ happens, so it’s important to understand.

Wayne Pecena, long-standing staff member at Texas A&M University, goes straight into to IPV4 packet types. In the world of SMPTE ST-2110 and SMPTE ST-2022, this is important as much media traffic is sent multicast which is different to unicast and broadcast traffic. These three methods of sending data each have pros and cons. Unicast is the most well-known whereby packets are sent directly from the sender to a specific receiving device. Broadcast is, as the term suggests, a way of sending from one computer to all computers. This is great when you’re shouting out to another device to find out some key information about the network, but it can lead to disaster if all senders are doing this. For media use, multicast is where it’s at, allowing a sender to send to a group of receiving devices each of which opt in to this stream, just like you can opt in to a newsletter.

Wayne digs in to how an IPv4 packet is constructed looking at all parts of the header including the source and destination IP addresses. This leads us into looking at how an IP address is constructed. The trick with IP addresses and moving data from one network to another, we learn is in understanding which machines are on your local network (in which case you can use layer 2 Ethernet to send them data) and those that aren’t (in which case you need to use IP to pass on your message to the other network). This is done using subnets which is explained along with classes of addresses and class-less notation.

Once you know how to tell which network an address is in, this leads to the need to pass information from one to another opening up the topic of Network Address Translation (NAT). The typical example of NAT is that a message might come in to a public IP address on port 3000 which would then be sent to the internal network to a defined internal address on port 80. Wayne explains how this works and runs through examples.

For a network to keep track of which physical interfaces are where and have which IP address requires an ARP table which has been mentioned in previous seminars because it bridges both layer 2 and layer 3. Now we’re at layer 3, it’s time to go in for another look ahead of examining how DHCP workshop it assigns DNS addresses and how DNS itself works.

The next section steps into the world of diagnosis with ping and the ICMP protocol on which it is based. This leads in to explaining how trace route works, based on changing the TTL of the packet. The TTL is the Time To Live, which one way that a network knows it can drop a packet. This exists to protect networks from having packets which live forever and are constantly circling the network. However the TTL, in this situation, can be used to probe information about the network. Wayne explains the pros and the cons of ping and traceroute.

The seminar finishes by a look at routers, routing tables, routing protocols like IGP, EGP, OSPF, EIGRP and their peers.

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Speaker

Wayne Pecena Wayne Pecena
Director of Engineering, KAMU TV/FM at Texas A&M University
President, Society of Broadcast Engineers AKA SBE

Video: IP Fundamentals For Broadcast Part II

Posted on by Russell Trafford-Jones


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.

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Wayne’s previous talk
Speaker

Wayne Pecena Wayne Pecena
Director of Engineering, KAMU TV/FM at Texas A&M University
President, Society of Broadcast Engineers AKA SBE