SONET Question

Answered Question
Feb 23rd, 2009

Is SONET a WAN technology? If not, what WANT technologies does SONET function at?

I have this problem too.
0 votes
Correct Answer by marikakis about 7 years 9 months ago

I will now post a short section of a book that might clarify things even further:

"SONET/SDH equipment was designed to efficiently and reliably transport 64kbps voice cicuits from the customer premises to (and beyond) the nearest exchange; however it was not intended to support the enourmously growing demand for IP bandwidth...With the vast installed base of SONET/SDH infrastructure and the desire to converge both voice and data transport, SONET/SDH was adapted to carry data more efficiently. Since data is not aligned on 64kbps boundaries as are voice signals, a new framing interface is needed at the data link layer to take IP packets and map them efficiently into SONET/SDH payloads. Packet over SONET/SDH (PoS/SDH) is a layer 2 technology that employs a couple of standard techniques to provide very efficient transport of data over SONET/SDH. PoS efficiently encapsulates the IP packets with a low overhead PPP header."

This is from Next-Generation Network Services by Robert Wood, and I hope he doesn't mind me advertising his book :-)

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4.3 (6 ratings)
Loading.
Giuseppe Larosa Mon, 02/23/2009 - 08:01

Hello Ray,

SONET/SDH is a WAN technology that allows to build a synchronous hierarchy of streams at different bit rates

STM-1 155 Mbps is the basis for higher speeds.

Actually Sonet/SDH allows to carry other TDM links like T1 by using ADM = add drop multiplexer in the sonet payload.

TDM = time division multiplexing

Sonet works at OSI layer1 but it has its own signalling plane for path protection.

see

http://www.iec.org/online/tutorials/sonet/topic01.asp

Sonet can provide stream transport services to ATM, FR or IP networks.

high end routers can use POS = packet over sonet interfaces to build cheap very high speed point-to-point links.

Nowdays in provider networks you find pos (from 155 Mpbs to 10 Gbps) and GE, 10GE links.

40 Gbps links are starting to be installed.

Hope to help

Giuseppe

rayroyaleverest Mon, 02/23/2009 - 08:07

Can SONET replace ATM and Frame Relay, or does SONET need another WAN technology to provide connectivity?

Giuseppe Larosa Mon, 02/23/2009 - 08:18

Hello Ray,

it depends :

on service provider backbone the trend is that having POS and ATM and FR had been moved to edge.

But they use Sonet to implement point-to-point links with protection.

an ATM 155 Mbps interface uses the SONET services for example so it is ATM that uses SONET for this speed and above.

POS have attracted interest because they are much simpler and less expansive then ATM at very high speed

in the enterprise WAN links in FR or ATM cannot be migrated to POS what we see is the advance of internet based VPN solutions used instead of FR with xDSL access links.

MPLS VPN solutions are also very attractive for enterprises and again access links are often LAN or E1 or DS3

Hope to help

Giuseppe

rayroyaleverest Mon, 02/23/2009 - 09:26

Giuseppe,

What do you mean by the term "POS?"

What is the functionality of POS?

In what way does POS replace ATM?

How is POS used with SONET?

What OSI network layer is POS at?

What OSI network layer is SONET at?

Thanks, Ray

Giuseppe Larosa Mon, 02/23/2009 - 09:51

Hello Ray,

POS = packet over Sonet/SDH

this is a technology that was developed for IP service providers:

they wanted only a subset of Sonet/SDH features and functions and they didn't want to be obliged to have an ATM layer in the middle.

So POS allows to place L2 frames with ppp or HDLC encapsulation (not sure FR is supported I don't think so) for building efficient point-to-point links

A POS link is simply a point-to-point link but it can be protected by Sonet network and convergence time is very fast as low as 50 msecs.

The router interfaces takes part in the Sonet signalling plane as a DTE and so POS can provide a big gain in routing convergence and this has been used in MPLS TE fast reroute features.

POS can replace ATM when the IP service provider just needs an high/very high speed pipe that spans over long distance.

Then all the IP QoS on the router tries to provide some QoS features over the link.

POS is layer1 and uses Sonet for transport.

Also Sonet is at Layer1 but it has its own signalling plane and some circuit based switching capability that is used for path protection.

Hope to help

Giuseppe

marikakis Mon, 02/23/2009 - 09:34

Guiseppe has posted useful information here. I just wanted to comment on some points that might not be straightforward.

Yes, SONET is a layer one technology. This means that you generally need a layer 2 encapsulation to transport frames. As Guiseppe already said, FR can be the encapsulation. ATM can also be an encapsulation and SONET was specified to be used for ATM for speeds 155Mbps and above. In the case of an ATM interface that uses SONET as the underlying transport, the encapsulation is implicitly ATM. A POS interface might support PPP, HDLC or FR, as is the case of PA-POS-OC3 for example (the supported encapsulations will depend on the adapter):

http://www.cisco.com/en/US/docs/interfaces_modules/port_adapters/install_upgrade/pos/pa-pos-oc3_install_config/3577over.html#wp1028627

Edit: I posted this before I saw your new questions :-) Hope I have answered some of them and I suppose Guiseppe can answer the rest since he did most of the work here.

marikakis Mon, 02/23/2009 - 10:19

I am tempted to answer this because I think I see the point that causes you confusion.

SONET was used in telco networks before it was used in the IP world at router interfaces. If you had a low speed leased line from a telco, the telco would use SONET inside its network and "put" your low speed circuit within SONET together with other circuits and transport those across its internal network, but this was not visible to the router endpoints. In this sense, SONET is independent of the payload it carries and doesn't care if you carry IP in it or anything else.

If you have SONET at the router endpoint interfaces, the router needs to make sense of the information carried in SONET. So, needs to use an encapsulation to distinguish the frames and eventually find the IP packet that needs to be forwarded.

Hope this helps.

Correct Answer
marikakis Mon, 02/23/2009 - 11:13

I will now post a short section of a book that might clarify things even further:

"SONET/SDH equipment was designed to efficiently and reliably transport 64kbps voice cicuits from the customer premises to (and beyond) the nearest exchange; however it was not intended to support the enourmously growing demand for IP bandwidth...With the vast installed base of SONET/SDH infrastructure and the desire to converge both voice and data transport, SONET/SDH was adapted to carry data more efficiently. Since data is not aligned on 64kbps boundaries as are voice signals, a new framing interface is needed at the data link layer to take IP packets and map them efficiently into SONET/SDH payloads. Packet over SONET/SDH (PoS/SDH) is a layer 2 technology that employs a couple of standard techniques to provide very efficient transport of data over SONET/SDH. PoS efficiently encapsulates the IP packets with a low overhead PPP header."

This is from Next-Generation Network Services by Robert Wood, and I hope he doesn't mind me advertising his book :-)

rayroyaleverest Mon, 02/23/2009 - 11:46

Is Packet over SONET/SDH a common layer 2 WAN technology? Is PoS/SDH comaparable to ATM and Frame Relay? What are the most commonly used layer 2 WAN technologies currently being used, and what is likely to be used in the future?

Thanks for the help. Ray

viyuan700 Mon, 02/23/2009 - 12:42

Packet over SONET is not a layer 2 WAN technology. SONET/SDH was not suitable to carry packets, POS made SONET/SDH to carry packet without any other technology in between. Its not doing any other thing apart from just carrying it.

No, POS/SDH is not comparable to ATM & Frame Relay.

Future is IP over DWDM, nothing in between.

viyuan700 Mon, 02/23/2009 - 12:04

I am still confused. Is SONET purely a Layer One technology, or does it provide the functionality of a Layer 2 WAN technology?

SONET is a Layer 1 or Physical layer Technology. Ealier if a client need more bandwidth than E1/T1 they have to buy DS3or was using a external modem to bond upto 4E1/T1.

But now SONET boxes have Ethernet termination where you can map more than 1 E1/T1 (e.g for FastEthernet itcan be mapped to 50E1) without any device in between. Similary for GigLinks. Few modification are done in SONET boxes to transport packet but SONET boxes are not doing any Layer 2 function. You can carry different protocols over it but still it is Layer 1.

Can SONET function independently of a protocol such as ATM or Frame Relay?

Yes SONET can work independently of a protocol such as ATM/FrameRelay.

If not clear we can discuss more.

marikakis Mon, 02/23/2009 - 16:22

The layering discussions usually have no end. Is RIP an L3 protocol since it uses a UDP port? A well known saying is that we can say MPLS is Layer 2 1/2 and be done with it. In a similar fashion, I would say SONET/SDH is Layer 1 1/2 and be done with it. OSI Layers are a reference model and hardly ever do protocols fit exactly an exact layer due to implementation choices and other factors. The practical view is to know how protocols work and how they can be made to function in a network.

dknov Fri, 03/27/2009 - 17:47

Hi guys,

Sorry to stir it up again :-)

If you have two devices with OCx POS interface in each and you want to interconnect them, so you need a service provider in the middle that will give you SONET service using OCx, then you will connect it two both interfaces run IP on top, right?

This is in case you use service provider for long haul connectivity. What if you are building your own Core, do you still need service provider to interconnect your P devices in the same way (using OCx SONET), or can you run SONET by yourself?

Thanks,

David

viyuan700 Fri, 03/27/2009 - 19:45

Hi David,

You have different option which depends on how far are your office and how much core bandwidth you need, i am wiritng few option you have

1. Your offices are close by you can connect POS cards directly (you dont need SONET box). Like your7600 router have POS card of OC 48 (2.5 Gbps). Here you dont need SONET boxes. I think you can get distances till 40-50 Km.

2 If your office are far away but core bandwidth requirement is not more than OC-12/OC 48 then service provider is easy or you need SONET boxes which can regenerate your signal.

3. If your office are within 60-70Km but your core bandwidth requirement are more than Oc48 then either can take 10Gb ethernet card or Gigabit ethernet card.

4. If your core bandwidth requirement are high then you can take your 10G Ethernet/OC 48 POS over DWDM either from service provider or your own.

Hope it is clear.

Actions

This Discussion