Network Implementation Frame Relay can be used as an interface to either a publicly available carrier-provided service or to a network of privately owned equipment. A typical means of private network implementation is to equip traditional T1 multiplexers with Frame Relay interfaces for data devices, as well as non-Frame Relay interfaces for other applications such as voice and video-teleconferencing. The configuration is shown below
A public Frame Relay service is deployed by putting Frame Relay switching equipment in the central offices of a telecommunications carrier. In this case, users can realize economic benefits from traffic-sensitive charging rates, and are relieved from the work necessary to administer and maintain the network equipment and service.
In either type of network, the lines that connect user devices to the network equipment can operate at a speed selected from a broad range of data rates. Speeds between 56 kbps and 2 Mbps are typical, although Frame Relay can support lower and higher speeds. Implementations capable of operating over 45-Mbps (DS3) links are expected to be available soon.
Whether in a public or private network, the support of Frame Relay interfaces to user devices does not necessarily dictate that the Frame Relay protocol is used between the network devices. No standards for interconnecting equipment inside a Frame Relay network currently exist. Thus, traditional circuit-switching, packet-switching, or a hybrid approach combining these technologies can be used.
A common private Frame Relay network implementation is to equip a T1 multiplexer with both Frame Relay and non-Frame Relay interfaces. Frame Relay traffic is forwarded out the Frame Relay interface and onto the data network. Non-Frame Relay traffic is forwarded to the appropriate application or service, such as a private branch exchange (PBX) for telephone service or to a video-teleconferencing application.
A typical Frame Relay network consists of a number of DTE devices, such as routers, connected to remote ports on multiplexer equipment via traditional point-to-point services such as T1, fractional T1, or 56 K circuits.
A simple Frame Relay network connects various devices to different services over a WAN.
Public Carrier-Provided Networks
In public carrier-provided Frame Relay networks, the Frame Relay switching
equipment is located in the central offices of a telecommunications carrier.
Subscribers are charged based on their network use but are relieved from
administering and maintaining the Frame Relay network equipment and service.
Generally, the DCE equipment also is owned by the telecommunications provider.
DCE equipment either will be customer-owned or perhaps owned by the
telecommunications provider as a service to the customer.
The majority of today's Frame Relay networks are public carrier-provided
networks.
Private Enterprise Networks
More frequently, organizations worldwide are deploying private Frame Relay
networks. In private Frame Relay networks, the administration and maintenance of
the network are the responsibilities of the enterprise (a private company). All
the equipment, including the switching equipment, is owned by the customer.
The first companies to operate frame relay networks were the public network operators. These companies saw frame relay as a potential new market opportunity supplementing their existing data services: the data services include leased line services, packet switching services, circuit switching services, and ISDN.
These are the major similarities and differences between the public network services :
Frame relay offers the network service provider the ability to provide a service which is tariffed according to the bandwidth required and with very small network delays. It has the on-demand nature of packet switching bandwidth, and the low delay and traffic independent tariffing of a leased line.
The tariffing of the public frame relay services will be the major influencing factor in their success, and initial indications show these tariffs to be extremely aggressive and cost effective. According to today's rates, it's clear that for short distances frame relay is only a viable proposition compared to leased lines. Over medium to long distances frame relay is always the most cost effective option. As for the actual physical access rate into the frame relay service, it is possible to utilize a higher speed access into the network even with a CIR (see Glossary) of 64 kbps - hence reducing the transit delay. This alone is a sufficient reason to justify the use of a public frame relay service over a leased line.
The private network represents an extremely high level of investment. Frame relay has a part to play within large corporations as a protocol which needs to be integrated within an existing network infrastructure. The benefits which a private frame relay network can offer over the public services are :
Control
over the CIRs and the burst conditions
Control
over the network design
Integration
of non-frame relay traffic.
An important issue that one must consider for a private frame relay network is a knowledge of the leased circuits to be provided by the public service provider. For example :
There are basically three methods of implementing a private frame relay network :
Apart from the 1st method, which is a complete stand-alone frame relay network, the two other methods reflect two possible ways of implementing a mixed frame relay and 'other services' network. The major difference between frame relay as the overlay network and frame relay as the backbone network is the handling of congestion and discards: within the overlay network these issues are dealt with at the access point to the network. However, for a frame relay backbone network, the congestion management strategies exist mainly within the backbone network rather than at the access layer.
The choice of the way to add frame relay to an existing private network depends on the following issues :