Video Share – the work ahead
October 17, 2007
The first interoperability event for the IMS Activity Group, and now the real work begins. We know where we are and what we want to achieve.
There were 6 of us there. Companies with implementations of video share. It seems like each one has interpreted what are the requirements on the SIP level a bit differently, and this caused some issues. We had issues in various messages that were sent as well as with accessing and registering to a P-CSCF (a SIP server). I wouldn’t delve here into details, but I’d like to say that we’ve made some good progress this week.
The general feeling in the group is that now we have substance to talk about, and a lot of work ahead of us.
So what’s next?
- We need to start drafting out the baseline scenario test case with as much detail as possible – especially in the areas where we found issues between companies. Having that would assist us in our next steps and will provide a good starting point for new members.
- Outline the requirements from operators and IMS core networks. We had some issues with the 3G network we used and its firewall configurations. As we plan to have more events in the future, we better get these requirements into an official working document for our group.
- See if we can somehow find a solution that would allow our group to test not only during face to face events, but also remotely throughout the year.
- We’re already planning the next event. We’re targeting the beginning of 2008 for it. I am sure we will make good progress there.
Technorati Tags: IMTC, IMS, Video Share, Interoperability, Tsahi Levent-Levi, F2F
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The First IMS AG Face2Face Event is Here
September 25, 2007
It’s about time this happened. We’ve been working for several months now in the IMTC IMS AG for this moment – the first face-to-face interoperability event of our group.
Why is this important?
Up until today, no real IMS testing was done for the client side in any methodical way. Sure, the IMS Forum is doing PlugFest events and the GSMA is also doing some basic interoperability testing for their specification. Nevertheless, there’s no real place where handset vendors and middleware/software providers for handsets can gather around on a regular basis and deal with interoperability. The IMS AG is just that place.
What do we focus on?
We currently deal with Video Share as an IMS service that we are testing, focusing on the client itself. Not what is required on the network side and how billing is done but rather how two mobile clients can call each other, negotiate the parameters they will use for the call and share a video session between each other. We will be moving on to additional client-side service aspects as they develop – we started with Video Share simply because it seems like one of the services of IMS that will be deployed first – I believe AT&T is the first of many operators that will focus on Video Share in the next couple of months.
What do we do?
We talk once a week or two, depending on availability. Companies in the group join a conference call to discuss matters at hand. In these calls we discuss a wide range of topics:
- Drafting out our test case document
- Establishing and discussing liaison connections with other organizations (GSMA, IMS Forum, OMTP and others)
- Scheduling interoperability events
Our goal?
To make sure that once operators decide to deploy services such as Video Share, they will be able to choose any phone vendor they want and be confident of the level of interoperability provided. This means that operators would rather take handsets from vendors who are actually test interoperability in the IMTC IMS AG.
October interoperability event
Our first event is scheduled for October 10-12 this year. RADVISION, my company, is hosting this event along with the 3G-324M AG, which will do their own interoperability testing there.
We are planning to convene after the event and publish the first official test cases document for Video Share from the IMTC. As usual, I am sure we will have some comments to the 3GPP and the GSMA that might require some clarifications or changes to the specifications – that happens when an activity group in the IMTC starts doing interoperability and places a specification under its magnifying glass…
If you do develop communication products, you must know that interoperability is important. What do you do to close this gap of interoperability in your products?
Technorati Tags: IMTC, IMS, IMS Client, Video Share, GSMA, IMS Forum, OMTP, 3GPP, Interoperability, 3G-324M, Tsahi Levent-Levi
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H.323 versus SIP: An (un)objective Comparison
September 18, 2007
I came across an interesting comparison between H.323 and SIP in a Cisco related blog. They make a pretty good technical analysis, but the comparison lacks in its completeness.
Both H.323 and SIP are used today for VoIP, and they are considered interchangeable solutions. The comparison made covers the following issues:
- Philosophy – H.323 does calls, SIP does sessions
- Reliability – H.323 reliable by design, SIP by responsible user agents
- Message Definition – H.323 uses ASN.1, SIP uses ABNF
- Message Encoding – H.323 is binary, SIP is mostly textual
- Media Transport – both use RTP/RTCP and SRTP
- Extensibility – H.323 extensible by design, SIP breaks interoperability with extensibility
- Scalability – H.323 scalable by design, SIP by implementation or by additional IETF standards
- Addressing – H.323 supports multiple addressing schemes, SIP has only URIs
- Billing – H.323 has billing by design, SIP by implementation
And the list goes on to other issues. It seems strange to me that in all, H.323 either excels or does as good as SIP. This being the case, why does every new developer looking for SIP?
I have been working with H.323 and SIP for several years now, and I can say that both have their advantages and both are broken in some places. H.323 is a lot better today in issues of interoperability – a lot of it can be easily attributed to the IMTC’s work in this area. I also have a warm place in my heart for this particular protocol – I have been working and dealing with it for many years. That said, the comparison above lacks two main points:
IMS
The 3GPP’s next generation network, which has been adopted by the Tispan and CableLabs (making it the de-facto network in the world in the future). This happened as the 3GPP added interfaces scenarios and call flows to SIP, giving more advantages to it.
H.323 is not part of IMS and is irrelevant for IMS.
SIP is at the core of IMS.
Market
H.323 is dominant today and has large deployments around the world. It is a lot better where it comes to video conferencing, and can be found a lot more in the enterprise.
SIP is the protocol of choice for most developers today – it is quite strong in the consumer and service provider markets. If you are a company about to develop a communication product, you will probably be selecting SIP. It is not as good for video conferencing, but it is getting there.
Services
There is another parameter that is important, and that is what services are part of the protocol and what new services can be offered easily?
H.323 focuses on multimedia calls in all of their flavors. Voice only, video, data collaboration, conferences and a rich set of telephony services.
SIP doesn’t seem to focus on anything in particular. You can use sessions to make calls with it (voice, video – whatever), you use it for presence and instant messaging, and you can use it for a large array of additional services as well.
That said, these services can be added to H.323 as well – this statement would be true to trying to add new services to SS7 though…
Now, if you opened a company now, which protocol would you decide use? What would be your decision looking only on technical aspects, and what would it be looking only on market aspects?
Technorati Tags: Cisco, IMS, IMTC, H.323, SIP, VoIP, Interoperability, Tsahi Levent-Levi
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IMS, 3GPP and IETF: A standardization complexity
September 3, 2007
How do we get those specifications for IMS? In a complex way.
It started off as a set if requirements for a Next Generation Network (NGN). The 3GPP wanted an all-IP network for its mobile infrastructure, calling it IMS (IP Multimedia Subsystem). As there’s no need to reinvent the wheel, the 3GPP decided to select an existing standard to do the work, and SIP was there – all young and fresh. But SIP is an RFC. It is handled and standardized by the IETF. This need not be changed.
So what does an organization like the 3GPP does at this point in time? Use the IETF as a subcontractor.
Have you ever worked with a subcontractor? I have never heard of anyone who liked the experience… you provide requirements for a rocket to space, and you get a fire cracker. You want a match, and you get a rocket instead. Time is not time, effort estimations are far from true (sounds like regular development, but it is always harder with a subcontractor).
So we have the 3GPP providing the requirements, while the development of new RFCs (=standards for IMS) done by the IETF, including modifications to RFCs when needed.
The result?
- We have a whole lot of RFCs coming from the IETF. Some colliding each other, others solving the same problems, but a bit differently.
- We have a bunch of 3GPP specifications, which point to RFCs (and a lot of drafts!) that are used by the 3GPP’s IMS network – in a way, a selection of the RFCs that are needed.
- But then, it is not always understood which features from the IETF, or the 3GPP you really need to build an application. And as usual, I haven’t covered GSMA, GCF, OMTP and other organizations.
We at the IMTC IMS AG are actually facing these issue each day. We are currently unraveling the set of specifications required for the implementation and interoperability of the Video Sharing service that is gaining momentum.
Technorati Tags: IMS, IETF, SIP, SigComp, 3GPP, Standardization, Tsahi Levent-Levi
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IPSec – transport and tunnel modes
July 9, 2007
Remember my post about IMS access?
I talked about how a user is authenticated on the network using a key exchange mechanism (AKA-MD5 or IKE) and IPSec to ensure privacy.
We were left with this one nagging issue derived from the fact that IPSec is used differently with different types of access. These are:
- Transport mode, when we use IPSec with AKA-MD5, and we have a USIM.
- Tunnel mode, when we use IPSec with IKE, and we don’t have a USIM.
- Transport over tunnel mode, when we use IPSec twice, since we’re outside an operator network.
Why is there a difference? Why not have IPSec in a single mode (like IP VPN) and be done with it?
Well, let’s start with tunnel mode. In tunnel mode, the data that you want to send is going to be passed “as is”, with the key exchange done using either IKE or MOBIKE. That’s not good enough for our USIM (the one that requires AKA-MD5, as it makes more sense to manage the data in front of the operator’s HSS). AKA requires exchanging keys and tweaking some internal parameters of IPSec. So we need to use a different mode for IPSec in this case. The problem is, some of the operating systems most commonly used in mobile handsets do not support this mode. So there is no real solution today for developers. Hopefully, solutions will become available soon.
Doing IPSec twice is sort of like peeling the layers of an onion. The external layer is tunnel mode, where you use IKE in front of your wireless network’s access, but then tunnel the IPSec packets generated using transport mode, which were generated with AKA-MD5 to authenticate the USIM you have with the mobile network (since you don’t have direct access to it) inside it.
So IPSec alone is also an issue.
Do you think this post was written just to make you developers despair? Nah… I know you guys. I am one of you. We developers love challenges. We thrive on them. And IMS is a doozie!
Technorati Tags: IMS, SIP, IPSec, Tsahi Levent-Levi
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AT&T and Video Share
June 21, 2007
I totally missed this one!
I’ve been to NXTcomm. I sniffed around. I searched for IMS. I came back empty handed.
But then – AT&T actually announced their Video Sharing service during the show. And on the same day I was there…
I first found out about it in MobileCrunch blog – good I’m reading others. Two days after it was posted there, my Google alerts went jiggling happily about this service. It’s so good to know that operators are going to offer Video Sharing as their first IMS service.
To those of you who don’t know what Video Sharing is and those who would like to understand what can be done with this technology, AT&T were kind enough to have some mockup demos in their site – they’re quite good.
The interesting this is that they will be doing that over their WCDMA network and not CDMA2000 EV-DO one. The reason for that is the way these two technologies differ from one another.
In WCDMA, you can utilize both the circuit switched and the packet switched networks at the same time. This means that you can do an audio call over the circuit switched connection (as it is done for every audio call today), and then you add the video over the packet switched network (the data capability of the network).
But in EV-DO, this is impossible. You either do voice calls over circuit switching or data of some kind which would be packet based. So to do Video Sharing over EV-DO would require doing the voice over IP as well – and that’s a whole different ballgame.
So Video Sharing it is.
Let’s see which operators jump on this one next.
Additional coverage – Wired News, AT&T Site
Technorati Tags: NXTcomm, Video Sharing, IMS, Tsahi Levent-Levi
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NXTcomm and IMS
June 21, 2007
This week I had a business trip. As part of my day job, I joined a panel discussing the IPTV experience at NXTcomm. While there, I had the time to walk around the show floor and see what companies are doing.
I can definitely say that this year, the main theme of NXTcomm is IPTV.
The second coolest acronym in the show was IMS.
First question out there, is what does IPTV has to do with IMS? Probably everything and nothing at the same time… But I’ll be leaving this one to a future post sometime.
What I really want to discuss here is still IMS.
Walking the floor and talking to companies in NXTcomm means you are meeting a lot of sales people from different companies. So IMS is what I do here, and I decided to go check what these people know of the IMS offering of their companies (you know – it’s not that easy).
Here’s a short roundup of the answers I got:
- “It’s essentially SIP”
- “We’re doing SIP, connecting it with Alcatel-Lucent’s thing, and we support IMS this way”
- “We’re IMS-ready” (heard that one before)
So nobody really knows what IMS exactly is there and don’t know how to chew it. Hopefully, this will change with time… especially when they all have IMS written all over their booth…
Technorati Tags: NXTcomm, IMS, IPTV, SigComp, Tsahi Levent-Levi
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IMS and access
June 11, 2007
Let’s explore the issue of access (how IMS clients register on the network and gain access to services) in the world of IMS. Today, the way this is done over UMTS is simply by using the USIM (that small card hiding behind the battery of your handset. You know; the little bugger that falls out of the phone and onto the floor sometimes).
The USIM card is what holds the information that links your identity with the mobile operator’s database. And that’s what it does on an IMS network too.
So what do we need to do? Connect a mobile handset that has a USIM to the network. The technique used is asymmetric keys, exchanged in SIP, using a procedure called AKA-MD5. And since we want the actual exchange of the information to be secure, we send everything on top of IPSec, in a mode called transport mode.
Sounds OK. But that’s the 3GPP way of doing things. IMS has been adopted by all sorts of networks, and all types of Wireless LANs (WLANs) will now used as access to IMS infrastructure.
But wait – WLAN devices don’t have USIMs. And no asymmetric keys you can use directly. And you still need authentication. Maybe the solution is to use IKE! — not AKA-MD5. And why not use IPSec – we have that already. And once we are doing that, we should use a different mode of IPSec (tunnel mode if you’re really into details).
Let’s see… can we make it even more complicated? What about all those mobile devices that have both USIM and WLANs. OK, here’s a neat solution. Let’s do IPSec twice (yes – twice!) on each and every packet we send. One will provide access to our WLAN network, and this will tunnel IPSec packets that are targeted directly at the IMS core of the mobile operator. So lo and behold, now we are going to have transport level over tunnel for IPSec!
Confused? Well, so am I.
And as if all this wasn’t enough, I haven’t even gotten into all the veritable alphabet soup of other issues like MOBIKE, EAP-AKA or EAP-SIM. Ouch!
To make a long story short, this may sound and look unwieldy. But it works.
When you are developing new products, don’t forget that gaining access to IMS can be quite a complex task. It depends on which transport you are using and what network you are trying to access. So roll up your sleeves, get out your acronym glossary and get to work!
Technorati Tags: IMS, SIP, 3GPP, IPSec, Tsahi Levent-Levi
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Compression and IMS, Part 2: ROHC
June 1, 2007
In my last post, I discussed SigComp and how it relates to the wonderful world of IMS. SigComp though is only part of the IMS compression story. There is more. Much more.
Just in case you forgot – messages are big. We would all like to shrink them so that they use less of operators’ precious bandwidth. We tackled the big message problem by compressing the content using SigComp.
But there is one “minor” issue I left out last time – the issue of IP. IP is a nice enough protocol, and is required for IMS (you remember the IP Multimedia Subsystem…).
SIP messages are sent over TCP or UDP, which in turn are sent over IP. RTP packets (you know, that media we want to see or use) are sent over UDP, which again means it is over IP.
Last time, we dealt with the SIP message issue. But what about the IP, UDP, TCP and RTP?
All these have their own headers that add lots of overhead to the messages themselves. We’re talking about 40 bytes for an IPv4 packet sent over RTP (UDP and IP included). And if we have to send 50 of those packets every second just to keep our audio running, we have some pretty heavy packets to deal with!
The solution to this problem is ROHC (Robust Header Compression). It is defined in various RFCs, with different modes of operation. I won’t delve into the technical details, but would like to point out one very interesting thing: it’s in the operating system.
Since ROHC is used to tweak the size of IP, UDP and TCP headers and compress them to be 1 or 3 bytes, it requires support from the operating system itself. By operating system, I mean your “average” IP stack that you get for free with it.
What all this means to us, is very simple. To implement IMS – and on a client no less – requires not only application implementation but also an operating system with support for all the architecture’s special needs.
Technorati Tags: IMS, SIP, SigComp, 3GPP, Tsahi Levent-Levi, IMTC
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Compression and IMS: SigComp
May 4, 2007
I have been promising to touch on the different aspects of technology related to IMS, and if there is one thing I am good at – it is keeping promises! This time I will start with one of these – compression.
For all you history buffs, let me take you back in time a bit. Once upon a time, there was a great protocol named SIP. It was simple (yeah, sure!) and easy to use. It was text based (Look Mom… you can see messages!), so it was easy to implement, maintain and debug. Many people started to use it and promote it big time. And it did have some great routing and filtering criteria capabilities. So at some point, the 3GPP decided to adopt it for IMS.
So the world was a better place with a nice, simple, text-based protocol, used for signaling purposes over mobile networks. And since it’s signaling, and you don’t have a lot of information you need to convey, it should work. But as time went on, people saw that the messages and the amount of information were actually quite large. When you start adding routing information, authentication and authorization information, billing information and some more – each message becomes REALLY big.
At the end of the day, we had a text-based protocol, with large messages, running over mobile networks. Our problem: mobile networks have lower bandwidths than fixed IP networks (mostly). Also operators out there have to actually pay for the bits you use. For them, more bandwidth required per user for simple calls means less capacity in their cells… and more power consumed by the handset which means a shorter battery life. What to do?
Zip!
You take those messages; you somehow “zip” them and then send them on their way when they take up less space. Since it’s text, it zips quite well.
The secret behind this “zipping” is with a compression protocol called SigComp (RFC 3220, and more) – Signaling Compression.
Everyone agrees: SigComp is nice. It’s general purpose, and it can use different compression algorithms. You can optimize it for the exact messages and scenarios you use. But it’s complex…
By complex I mean that SigComp actually uses bytecode methodology. When you compress messages, you can send along the code that is used to uncompress the messages with the compressed data. This is done using the predefined UDVM (Universal Decompressor Virtual Machine) instructions set (hence bytecode) that outlines the different atomic operations allowed in SigComp.
The process is fairly easy. To compress, you choose an algorithm, use it for your compression, send the compressed data along with the algorithm, and the other side uses the algorithm you sent to decompress.
To make things even more interesting, there’s also a dynamic version of SigComp, which lets you update the SigComp states used in mid-session to provide optimized compression as well.
But then, what could you use as a compression algorithm? Would you go for an LZSS or a Deflate one? Would you do the dynamic optimizations with it? Do you go to patented compressions? Have you thought how much MIPS will this thing take on your mobile???
Lots of questions, huh?
So we have the IMS (3GPP that is). 3GPP means mobile networks. It also means limited bandwidth and the need to compress.
Remember though… there are other standards bodies that do not necessarily need compression, but have adopted IMS architecture. TISPAN and PacketCable, for example, are focused on the wireline and cable telephony networks. So our efforts in this area really are a wider attempt to build a single paradigm for all types of telephony and services! A virtual Utopia! Where everything looks the same.
But our friends who are adopting TISPAN and Packet Cable took a peek at our SigComp in IMS and said, “Sorry. We don’t need it.” Their networks can handle large messages, for them, adding SigComp just adds complexity and requires even more resources.
So, on top of everything else, you are faced with the million dollar compression question: Do you need SigComp or not?
Oh yeah… and what about WiMAX?
So you see, SigComp is only part of the compression story. Next time, we’ll discuss other IMS compression issues.
