Network Services

The first real consideration for implementing frame relay is whether to utilize a public frame relay service, or to implement frame relay within an exisiting, or new private network. Then, some further considerations must be appreciated prior to purchasing frame relay network services. The following sections provide more details on some of the implications of running frame relay service:

The Public Services

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.

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 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 major issues to appreciate when considering a public service are:

How is service's pricing defined?

What are the physical interfaces/speeds and the CIRs that are offered?

Is there any guarantee of delivery?
 

The Private Services

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 knowledge of the leased circuits to be provided by the public service provider. For example:
  1. Is the traffic likely to pass over fibre optic lines?
  2. What error level is to be expected?
  3. What is the availability of a leased line?
There are basically three methods of implementing a private frame relay network:
  1. A complete private frame relay network with no other protocols involved.
  2. A partial frame relay network which utilizes existing network infrastructure.
  3. A frame relay network as a backbone to an existing 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:
  1. Is frame relay the dominant protocol for the network?
  2. Does the existing network offer a high enough level of service over which to pass the frame relay data?
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.
`

Further Considerations

Once a decision has been made as to whether public or private services would be used, it is then important to consider the different styles in which frame relay networks can be offered:
  • Additional capabilities within current packet switches
  • Additional capabilities within current circuit switches
  • Dedicated frame relay switches
Each of these approaches will have slightly different characteristics which may affect the user's networking requirements and which must be considered carefully prior to selection of a suitable vendor.
LAN data transportation is the main requirement for frame relay services. It's important to consider whether a frame relay based network is even required for this, or whether a network of point-to-point links would be suitable. The networking capabilities of LAN access devices must be considered, along with the functions, which may be required of the backbone network.

All of the above issues need to be considered when making the decision to implement frame relay services, either privately or via public offerings. There's no definitive answer as to which is the best method for implementation of frame relay.