by February 1, 2009 0 comments



We all know what a WAN is, or what a router is used for. So we don’t want to
unnecessarily fill up pages telling you all about them all over again. Instead,
we’ll focus on terms that you must be aware of and why they’re important in
today’s trying times.

Active/Active Connection: A mode where two devices are working
together in a load-balancing fashion. In case one fails, the other one
automatically takes over. In the WAN world, it is common for enterprises to have
Active/Active links between locations. This way, both links will do load
balancing while transferring data from one destination to another. In case one
link fails, the other one automatically takes over. The other type of connection
is called Active/Passive, wherein there’s a second connection that’s in hot
standby. It doesn’t do load balancing, but becomes alive if the primary link
fails.

Caching: This is again, not a new term, but is very much relevant for
WANs today. Caching basically refers to storing duplicate values of data in
places where the original data is very expensive to get. For instance, it’s
widely used in proxy servers, wherein the proxy server stores copies of
frequently accessed web pages. This way, when clients request for a web page,
the request is fulfilled from the local proxy cache instead of downloading the
web page again from the Internet. Similarly, various caching techniques are
being used in modern day WAN accelerators. This allows faster access to data
between two WAN accelerators.

Hub and Spoke Model: Think of a chariot or bicycle wheel when you
think of this model. Basically, data travels across the different spokes from
one end to the central hub. Many enterprises who use MPLS based connectivity for
instance, follow this model. In this, the various branch offices would be at one
end of the spoke, and the other end would terminate in a network aggregation
point or on the network operator’s MPLS ring. This ring would in turn connect to
the enterprise’s central hub. This allows for point-to-point connectivity
between an organization’s branch offices and the central head quarter, or the
data center.

ISDN BRI: The term ISDN doesn’t need any explanation. It’s an old and
well-known method of digital communication. BRI stands for Basic Rate Interface.
It’s one type of ISDN connection, which supports 128 Kbps transmission rate,
using two B-channels of 64 Kbps each, and one D-channel for sending control
information. The other kind of ISDN is PRI. This comprises of 23-B Channels (for
US) and 30-B channels (for Europe). Both support a D-Channel. Usually, most
enterprises tend to use an ISDN BRI connection as a backup link, which becomes
active if the primary link fails.

MPLS: Short for Multi-Protocol Label Switching. It’s basically an IETF
standard for data transmission in packet-switched networks. The technology works
between the data link and transport layer, and is therefore also known as a
Layer 2.5 protocol. The big benefit of a MPLS network is that it allows one to
move information around more efficiently, by providing traffic prioritization
and class of service tagging. Given that the traffic on most networks today
comprises of voice, video, and data, such a service proves very beneficial.
That’s why a lot of enterprises prefer to go to a network operator who provides
MPLS for their branch office connectivity.

PE/CE: Providers’ Edge/Customer’s Edge. These terms are used to
determine where the WAN equipment is located.

QoS: Short for Quality of Service, which comprises of different kinds
of techniques used to prioritize different kinds of traffic flowing over WAN
links. This is to ensure that high-priority, or time-sensitive traffic like
voice and video gets higher precedence over low-priority data traffic. QoS is
increasingly becoming important, thanks to the plethora of applications that
have hopped onto the WAN links. We have devoted a separate article in this story
to explain QoS in more detail.

SaaS: Software as a Service, which is a relatively new phenomenon when
we compare it against some of the other terms we’ve defined in this glossary.
Software as a Service essentially implies providing software applications over
the web as a service to customers. This is basically a re-avataar of the older
Application Service Provider model, in which the service provider would host
applications in his premise and offer it on ‘rent’ to different customers. Types
of services include email and messaging, and business applications like ERP and
CRM. It finds relevance in this glossary because SaaS is delivered over a WAN.
So whether it’s an enterprise that’s web-enabled its applications and provides
them to its various branch offices, or a service provider who sells applications
as a service, both have to ensure that their WAN links are optimized to provide
this service.

VDI: Short for Virtual Desktop Infrastructure. This is a hot new
buzzword, which unlike thin clients, hosts the entire desktop of a client on a
central server. The logic behind VDI is the same as thin clients. You don’t have
to manage a large and spread out desktop workforce. Instead, everything is
hosted centrally in the data center and accessed remotely over LAN or WAN links.

VPN: Virtual Private Network. Though this has been around for quite a
long time, today there are several different ways of deploying it. You could
deploy it over the Internet or an MPLS cloud. You could use it for connecting
branch offices to HO or for allowing mobile users to connect to the central
network. We’ve devoted a separate article on different kinds of VPNs.

WAN Accelerator: This is a device that can be used to get better
performance from a WAN link. These devices use various techniques such as
caching, compression, QoS, etc to speed up data transmission over WAN links.
Increasingly, enterprise WANs have started going beyond carrying basic data to
voice and video as well. Under such cases, having a WAN accelerator that can do
all these things definitely helps.

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