Frame Relay

Frame Relay is a very efficient packet-switching digital data transmission technique that is both quick and cheap. Data transmission occurs as a relay of frames between endpoints. This is the main reason why Frame Relay can send from one or many endpoints, to one or many endpoints, which is most definitely a big plus in Frame Relay’s favor.

Best-Effort Protocol

Frame Relay is a “best-effort” protocol. Whenever the Frame Relay protocol detects an error, it simply drops the frame, end of story. For applications; such as streaming videoconferencing and Internet AVIs, a few frames being dropped every now and then doesn’t really matter all that much. However; there still remain many scenarios, applications and production environment situations where this is just unacceptable.

Virtual Circuits

The key to frame relay is that it uses Virtual Circuits (VC). This is something it has in common with Asynchronous Transfer Mode (ATM). ATM is an OSI Reference Model, Data Link Layer (2) cell relay, circuit-switching protocol. Unlike ATM, which uses fixed-size packets, Frame Relay uses variable length packets, which are transported over a shared single point-to-point or point-to-multipoint link across a carrier internetwork using Virtual Circuits (VC). The older; now defunct, X.25 protocol was the packet-switching WAN connectivity protocol upon which Frame Relay was based/built.

Two Types of Frame Relays

From a functional production environment point of view, there are two types of Frame Relays that can be implemented:

1. Permanent Virtual Circuits (PVC) – It is in the formation of logical end-to-end links mapped over a physical network that PVCs are used.
2. Switched Virtual Circuits (SVC) – SVCs are much harder to implement and maintain. Not surprisingly, they are not very common.

Frame Relay Implementation Scenarios

Currently; there are a number of very similar Frame Relay implementations including Wide Area Network (WAN) and corporate WAN technologies. Each of these technologies/protocols has its pros and cons some of which I will discuss shortly.

Leased Line WAN Alternatives

WANs built using traditional leased lines tend to be very expensive. Circuit-switching and packet-switching technologies are far more efficient and economical which is where protocols like Frame Relay come in. Typically network protocols such as TCP/IP provide addressing and transport functions while ISPs use protocols such as Frame Relay and ATM to deliver the link.

Typical Frame Relay Deployment

The most common deployment scenario of Frame Relay consists of the end-user(s)/organization(s) leasing dedicated private lines. These lines ran from the customer’s premises to the Frame Relay node owned and operated by a major carrier. Here in Australia, this would include Telstra. The Telco’s Frame Relay network then handles the transmission over a frequently changing path that is all but transparent to all end-users.

Wide Area Networks (WAN)

When using frame relay as a Wide Area Network (WAN) protocol the most common scenario is to implement Frame Relay at the Data Link Layer (2) of the OSI Reference Model. For example, an Internet Service Provider (ISP) would commonly implement Frame Relay as an encapsulation technique for inter-LAN communications over a WAN. This includes both voice and data traffic alike.

Encapsulation

The importance of Frame Relay’s use of encapsulation cannot be underestimated as it is the mechanism that allows a Frame Relay WAN implementation to interconnect different LAN implementations in diverse geographical locations as well as the various different LAN segments that may exist at each geographical location. Each of these LANs may differ in architecture, hardware, logical aspects and/or the protocol implementations used.

So, by preserving the underlying individual LAN structures Frame Relay can leverage existing network infrastructures such as network hardware, security descriptors/policies and other logical aspects (addressing, permissions etc.) thereby greatly simplifying the administration of complex multi-LAN WANS.

Corporate WAN Technologies

Today; we find that many of the larger multi-branch companies have implemented corporate WAN technologies based around Frame Relay. The idea being to provide “big picture” connectivity and security solutions for geographically dispersed rural branches and thereby incorporating them into their corporate WAN.

Rural Areas

In many rural areas that lack DSL and cable modem services the least expensive type of "always-on" connection remains the 128-kilobit Frame Relay line.

Extrapolating into the Future

As a direct result of the recent dramatic increase in the deployment of Ethernet over longer distances using fiber optic cable we are seeing a corresponding marked decrease in the cost of the large fiber-optic bundle cables that the large Telecommunications companies are currently deploying. Not only are they being used for the Internet backbone, these cables are also seeing deployment as regional and local “trunk” lines in Metropolitan Area Networks (MAN) as well as WAN links rolled-out by regional Internet Service Providers (ISPs).

It therefore comes as no great surprise to discover that Frame Relay is currently being replaced by even cheaper IP-based technologies in applications and production environment scenarios once the sole proviso of Frame Relay.

Conclusions

Today: the biggest factors influencing the “useful” life expectancy of Frame Relay as a “live” production environment protocol are the massive increases in data transmission speeds that we are currently seeing in native IP-based networking. Much of these performance gains are in fact directly attributable to the improvements in transmission technologies such as fiber-optic cable and high-speed Ethernet over copper wire over longer distances (MANs & WANs).

Consumer and small business Internet access technologies such as cable, ADSL, ADSL2+ and regional ISP implementations of Digital Subscriber Line Access Multiplexer (DSLAM) have jointly made significant forward progress in increasing the bandwidth capabilities that can be offered to consumers and business alike. As a result they are no longer just consumer-level technologies. Larger organizations now consider them to be viable alternatives particularly when economic factors are taken into consideration.