Multiprotocol Label Switching (MPLS) VPNs - Everyone-to-Everyone Links

When customers sign up for MPLS VPN service they give their provider a list of the Internet protocol (IP) addresses associated with each site they want included in the VPN. The carrier uses this list to define a closed group of users allowed to communicate with each other using the VPN service.

Classes of Service - To Prioritize Particular Traffic
The customer chooses from a list of four or five classes of service. These classes of service are used to define the priority given to traffic for each class. For example, there may be two or three classes for data, one for voice, and another (the most expensive) for video. Voice and video have higher priorities than data. Some organizations use the lowest priced class of service for most data and higher-priced classes of service for database lookups. Often customers choose MPLS for its capability to treat voice differently than data. They initially use the network exclusively for data but plan to add voice traffic at a later time. Examples of voice traffic include:
Worldwide voice mail functionality such as broadcasting lists made up fo staff at diverse sites

Audio conferences
Sending call center traffic to remote sites based on time-of-day or staffing levels
Transmitting voice calls between international and domestic sites
Electronic Tags on MPLS Packets

MPLS attaches electronic tags to packets. Routers read the tags and assign levels of priority. The tags also enable routers to forward packets more quickly because they don't have to look up addresses in tables for each packet.

Most carriers offer service level agreements (SLAs) for an additional fee in conjunction with MPLS VPNs. These agreements offer guarantees on issues like the following:

Uptime, the percentage of time that the service operates
Latency, the amount of delay in milliseconds between when packets are sent and when they are received. This is important for voice and video
Restoral time per failure
Packet loss
Access line (the line from the customer to the carrier) uptime
Carriers that do not meet these SLAs generally give agreed-upon credits to customers.
Service Components

Customers that order MPLS use access lines between their network and the carrier. These lines are typically T-1, 1.54 Mbps or less. Most customers have a separate access line for MPLS traffic and a different line for their Internet traffic. They feel their MPLS traffic is from trusted sources at branches. The public Internet traffic requires higher levels of security.

They also specify the following:

A port speed at the provider's point of presence, often at a lower speed than their access line, perhaps 1 Mb

A committed access rate (CAR) - also referred to as committed data rate (CDR), and committed information rate (CIR). The bandwidth charge is the fee charged by many carriers for guaranteeing a particular speed between the carrier's edge and the carrier's high-speed core network. Some carriers charge a higher rate for international traffic. These speeds vary from 64 kilobits to 44 megabits (T-3)

Access charge for the circuit connecting the customer to the provider's network
They can "burst" send data at up to the speed of the port and access line they lease
Service level agreements
Classes of service; classes with a lower priority cost less than those with a higher priority (see above)

Managed Service - Provider Monitor Onsite Routers
Customers have the option of managing their own router or paying their provider to manage it. Carrier management of the router is referred to as managed service. With managed service, carriers monitor the router 24 hours per day, 7 days a week for service disruptions, denial of service attacks indicated by unusual traffic levels, and viruses. For medium-size companies, it may cost less to depend on a pool of specially trained provider technicians than to train and hire their own technical staff for these functions. As part of the service, carriers provide activity reports that track the level of traffic so that customers can ensure there is adequate capacity.

MPLS Advantages for Carriers - Revenue Sources and Administrative Efficiency
Carriers are eager to migrate customers to MPLS to save money on administration and as a platform for new services. Administratively, carriers have the capability to add classes of service for higher-priced voice and videoconferencing. These changes can be made in real time by programming requested modifications. Making changes to frame relay service is more complex because each path between sites must be programmed separately. Other potential sources of revenue for carriers are hosting, and access to hosted data storage (backup storage of customer files on the network).

However, carriers still have investments in asynchronous transfer mode (ATM) network infrastructure that is not fully depreciated. The transition to MPLS as the single network will take place gradually.