Multiservice Metro Networks
Moving towards more flexible architectures
interconnect its offices at different locations, Indian enterprises lease capacity
and infrastructure from service providers. But Multiservice Metro networks are
more beneficial than traditional SDH networks says Rajiv Ramaswami, CTO, Optical
Networking Group, Cisco Systems. He spoke to Brian Pereira about this
Why have Multiservice Metro networks suddenly gained significance
in the enterprise?
The trend (especially in the US) is that more enterprises are choosing Ethernet
over Optical instead of traditional leased lines. They either build their own
networks using leased capacity from a service provider or get a customized managed
service offering from a service provider.
What are the benefits of Multiservice Metro networks over
traditional SDH networks?
There are a couple of reasons why Multiservice Metro networks are favorable
Firstly, these networks support native data and storage protocols such as Ethernet,
and Fiber Channel, which are widely used in enterprises. Ethernet service offers
granularity of bandwidth. If you buy an E1 line you get 2 Mbps bandwidth. With
traditional SDH networks, if one wanted more bandwidth, it meant buying in multiples
of 2 Mbps. So you'd buy 2 E1 lines (for 4 Mbps). But what if someone wanted
So (with traditional SDH networks) you don't have this continuity of bandwidth.
But with Metro Ethernet networks, if the service provider offers an Ethernet
plugit's good enough for 100 Mbps. And it can be sliced from 1 to 100,
so there's very fine granularity. Then one can also get bandwidth on the fly,
without changing the pipe. So instead of buying a 2 Mbps private line or a leased
line, you'll be able to buy 1.5 Mbps bandwidth. The ability to have granularity
and also be able to change the granularity, is an advantage of Ethernet-based
The other major advantage is that on the Ethernet plug you can offer a host
of services, like Ethernet private line, simple Layer 2 VPN, Layer 2 VPN with
QoS (with a guaranteed bandwidth), or a service with Layer 3-aware SLA (such
as Voice over IP). So it presents significant benefits to both service providers
and enterprises. Service providers can offer a range of services (they can charge
differently for different services), and enterprises have more choice in getting
a service tailored for their needs.
Ethernet private line is being offered in India today, but more advanced services
(like Layer 2 VPN with QoS) will be provided soon.
Cisco sells equipment that supports all these services today on an optical platform.
Other vendors support TDM services and mostly offer Ethernet private lines.
An enterprise customer should be able to buy more bandwidth for the same price.
For the customer, connectivity costs are going down so they get lower cost per
megabit. Also, customers can buy more flexible services, with reliable SLAs
for each of the services.
Can you explain why Storage is a key driver for the adoption
of Metro Ethernet networks?
Most storage is going to be networked, and the amount of storage on the network
is going to go up.
Storage applications that support Business Continuance may not have taken off
in India in a big way. People are now focused on having multiple data centers.
There's a whole range of applications.
At the low-end, small businesses just need to create back-ups. But at the high
end, the banking and financial institutions need to have synchronous mirroring
and mirrored data centers. The data that's captured needs to be mirrored in
real-time locally, and at a remote site (as in stock exchange transactions).
What's your technique for transporting Ethernet and Storage
protocols? What are the emerging trends in this area?
Multi-service provisioning platforms are optical transport boxes that can transport
Ethernet and storage protocols efficiently in addition to being able to deliver
the traditional leased line services. Within our optical boxes we incorporate
packet multiplexing and a QoS engine. This is the same engine that sits inside
our routers. This enables us to offer the new services we talked about, as well
as reduce the cost of the transport infrastructure, compared to a purely circuit-switched
Finally, we have to make SDH more efficient to carry data.
There's more innovation in this area, like more efficient multiplexing mechanisms.
SDH deals with time slots. Each time slot offers a certain chunk of bandwidth.
Virtual concatenation enables you to utilize the time slots more efficiently.
The core of the network is realized using IP/MPLS routers. Now the SDH boxes
at the edge have to talk to the routers, particularly with respect to QoS. The
QoS that we have in the SDH boxes is exactly the same as that in the routers.
The software (Cisco IOS) in our routers and optical boxes is exactly the same.
On the storage side, the top companies have built their own DWDM networks as
disaster recovery is really crucial to them. This is for very high capacity
connections (10 gigabits or more). Then there are the companies in the mid-tier.
They will lease capacity from a service provider. On this SDH box we opt for
a native fiber channel plug. You can take a fiber channel fabric switch and
connect it to an SDH box. This is yet to happen here although it is happening
in the US.
So the service provider can sell you a fiber channel service
instead of selling you a private line. We are one of the few companies that
can offer native fiber channel on an SDH box. Though fiber channel and storage
is a niche or high-end of the market, every business will have Ethernet and
IP. So fiber channel over Ethernet/IP is what will really take off here.
The other trend coming in is managed services. Enterprises
are outsourcing the management of its network infrastructure, end-to-end. We
want to exploit the trend from moving away from private line or TDM services
to packet-oriented services.
Which technology are you in favor of: SDH or DWDM? What
are the limitations of each, and how are these being addressed?
We do both. They are complementary technologies catering to different capacity
requirements. Our optical box is called MSPP (Multi Service Provisioning Platform).
SDH is a very mature technology. The main limitation for SDH has to do with
how efficiently it could transport data. So it's a matter of optimizing SDH
to carry data.
On the WDM front, some of the things that are being addressed here are the flexibility
in the platforms. Right now we are talking about doing the multi-service platform
and the WDM, all in one. Earlier there were standalone platforms (separate box
for WDM, separate box for SDH.)
The second thing is being flexible with the distances. Previously
WDM was optimized for specific distances. Now you are seeing a broader spectrum
of applications. Earlier you had to buy one box for 50 Kms and another for 500
Kms. Now you get modular platforms that can operate over a range of distances
(up to 1,000 Kms for a metro system).
How have the new systems introduced flexibility in the
way the network is engineered?
Earlier with WDM you had to accurately predict the capacity, the channels to
be dropped, the lambdas to be dropped etc. But this could never be accurately
predicted. The older systems were very rigid.
The new systems have that capability. We are moving towards more flexible architectures
where you don't have to make that decision up front. You can add whatever channels
you want even later. Flexible Optical add-drop multiplexers make this possible.
WDM has multiple wavelengths. So for every wavelength you needed a different
line card. For 32 wavelengths you need 32 different line cards. This is difficult
to manage. Then you need to keep another set of spare line cards. The solution
to this is Tunable Laserslasers that can operate at multiple wavelengths.
This dramatically reduces all these costs. Today we sell 4 and 8 channel tunable
lasers. So I only need to stock 4 or 8 part numbers instead of stocking 32 different
Our routers and switches come with pluggable optical interfaces.
So you buy a switch or line card that does not have the optical transceiver
on it. When you want to enable ports you plug in the optical transceivers. The
advantages are a lower up-front cost, a more modular solution, and the ability
to customize the card by plugging in different types of tranceivers (different
distances, coarse or dense WDM).We recently introduced a DWDM pluggable.
Brian Pereira can be reached at firstname.lastname@example.org