Information Technology Reference
In-Depth Information
When ordering Frame Relay and AT M , a combination of access circuit charges, per-PVC
charges, and per-bandwidth committed information rate (CIR) charges are customary. CIR
is the rate that the provider guarantees it will provide. Some carriers set the CIR to half the
circuit's speed, thereby allowing customers to burst two times above the CIR. Frame Relay
speeds can be provisioned up to T3 speeds, but typically they are less than 10 Mbps.
MPLS VPNs have been competitive with ATM and Frame Relay rates. Service providers
are offering MPLS VPNs with higher bandwidth at lower rates to persuade their cus-
tomers away from traditional ATM and Frame Relay services. However, other service
providers see more value in MPLS VPNs and price them higher than ATM and Frame Re-
lay because of the added benefits of traffic engineering.
When you are selecting a standard carrier package, it takes about a month to contract a
WA N c i r c u i t . I f y o u w a n t t o n e g o t i a t e a d e t a i l e d S L A , e x p e c t t o t a k e a n o t h e r f i v e m o n t h s
or more, including discussions with the service provider's legal department. The bigger the
customer, the more influence it has over the SLAs and the contract negotiations.
Contract periods for most WAN services are one to five years. Contracts are usually not
written for longer durations because of the new emerging technologies and better offer-
ings from providers. An exception is dark fiber, which is usually contracted for a 20-year
term. In this case, you also want to have the right of non-reversion written in the SLA.
This means that no matter what happens to the service provider, the fiber is yours for the
20-year period. The process to repair fiber cuts needs to be defined in the SLA.
Ta r i ffe d c om merc i a l WA N s er v ic e s a re av a i l a ble a t pu bl i s he d r a te s bu t a re s u b j e c t to re -
strictions. However, carriers are moving toward unpublished rates to be more competitive
and to offer more options.
The PPDIOO methodology should be used when designing enterprise edge networks (PP-
DIOO) stands for Prepare, Plan, Design, Implement, Operate, and Optimize. Some keys to
PPDIOO are the processes of analyzing network requirements, characterizing the existing
network, and designing the topology:
Key
To p i c
Analyzing the network requirements
includes reviewing the types of applica-
tions, the traffic volume, and the traffic patterns in the network.
■
Characterizing the existing network
reviews the technologies used and the loca-
tions of hosts, servers, network equipment, and other end nodes.
■
Designing the topology
is based on the availability of technology, the projected
traffic patterns, technology performance, constraints, and reliability.
■
When designing the WAN topology, remember that the design should describe the func-
tions that the enterprise edge modules should perform. The expected service levels pro-
vided by each WAN technology should be explained. WAN connections can be
connect two or more sites together.
