OVERVIEW
Ø What is Frame Relay?
Ø How does Frame Relay differ from other techniques?
Ø What is Frame Relay useful for?
ØMixing Frame Relay with other technologies
Originally Frame Relay was conceived to run over ISDN. The initial proposals went to the Consultative Committee on International Telephone and Telegraph (CCITT) in 1984. As mentioned in the initial chapters, CCITT is now known as ITU-T, for international standards, whereas American National Standards Institute (ANSI) is still known for American standards.
Frame Relay is a fast packet−switching technology introduced in 1992. Its installed base has skyrocketed since its development and introduction in the industry. No one could have ever predicted just how popular this technique would become, but the final outcome is that Frame Relay has become the "bread and butter" service for many carriers. The reason is not as simple as one might believe; therefore, this chapter will explore the details of what has led to the popularity in Frame Relay installations.
Frame relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packets switching methodology. Originally designed for transport across integrated Services Digital Network (ISDN) infrastructure, it may be used today in the context of many network interfaces.
Network providers commonly implement Frame Relay for voice (VoFR) and data as an encapsulation technique, used to between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line (or leased line) to a Frame Relay node. The Frame Relay network handles the transmission over a frequently-changing path transparent to all users.
Frame Relay has become one of the most extensively-used WAN protocols. Its cheapness (compare to leased lines) provided one reason for its popularity. The extreme simplicity of the configuring user equipment in a Frame Relay network offers another reason for the Frame Relay population.
TERMINOLOGY:
TERMINOLOGY:
Terminology figure:
Frame relay is used between the customers premises equipment (CPE) and the Frame Relay
switch, but the complete path is known up front. Figure illustrates the LMI signaling
(keepalives) that occurs from your router to local frame switch. the Frame Relay connection
from r1 to r2 and r3 are through PVCs. Local DLCIs are layer 2 connection identifiers by the
service provider.
WHAT IS FRAME RELAY?
Frame relay is a technique used to transport data from locations to location, just like T-1 lines or ISDN connections do. In frame relay, there are a number of locations on the network that can send and receive data. These connections are known as Ports. Each location that needs access to the frame system, needs to have one of these ports.
Frame relay is used between the customers premises equipment (CPE) and the Frame Relay
switch, but the complete path is known up front. Figure illustrates the LMI signaling
(keepalives) that occurs from your router to local frame switch. the Frame Relay connection
from r1 to r2 and r3 are through PVCs. Local DLCIs are layer 2 connection identifiers by the
service provider.
WHAT IS FRAME RELAY?
Frame relay is a technique used to transport data from locations to location, just like T-1 lines or ISDN connections do. In frame relay, there are a number of locations on the network that can send and receive data. These connections are known as Ports. Each location that needs access to the frame system, needs to have one of these ports.
Every port in a Frame Relay system has an Address. This address is Unique to the port at that specific location. The port is connected to the equipment that handles the Data on one side, to the Frame Relay Cloud on the other side.
The equipment that handles the data can send data out the frame relay port. This happens in the form of Packets, or Frames. Each frame is built up of two parts; the actual Data and the Control block. These frames are sent over Virtual Connections.
The frame network itself should be imagined as a cloud. Every Frame Relay Access Port runs into this Cloud. Inside the cloud, there are a lot of different ways to get from one port to another. These ways are all interconnected by Frame Switches. These switches can make informed decisions on the traffic flow over each part of each route. Together, they figure out what router to send a packet over to get it fast and reliable from the source to the destination port.
Let's for example say that we have two sites connected to a frame relay network, and we wish to send data from site A to site B. The diagram would look like this:
What happens INSIDE the Frame Cloud is not known, and does not matter to us. What we do is simply address data as Going to B or Going to A. So, at this point, things work pretty much the same as they would on a dedicated line between A and B. When we add a Location C, things get more interesting: 
Now, the three sites can simply talk to each other by passing packets with the correct addresses. In a conventional setup with leased or dialup lines, this would have meant that either each site would have to have two lines, or that traffic would have to pass through two sites. Not in frame relay, the cloud takes care of all of this!
What the cloud does for us, is form 'Virtual Connections'. The way this is done, is simple. Each connection from one site to another is defined. For example, we say there is a connection from site A to site B. From site A to site C, etc. Each end of each connection is given a number that identifies it, this is called a Data link Connection Identifier, or DCLI. For everyone in the above diagram to be able to talk to everyone directly, these are the virtual connections that would be needed:
This means that everyone can talk to each other by simply stating the address and DLCI number of the line they want to talk over. This will get the data across the Virtual Connection.
What Can Frame Relay Bring to the Table?
Frame Relay in itself is merely a communications protocol designed to eliminate the overhead
discussed previously. What one can expect from Frame Relay services is the use of the higher−speed communications, the basis of the newer fiber−based Wide Area Networks (WANs). Taking advantage of the capacity improvements, Frame Relay can use the bandwidth on demand concept to get faster data across the network.
How does Frame Relay differ from other Techniques?
The biggest difference in frame Relay from other techniques is the use of Virtual Connections rather than Static Connections. As shown before, each location can have one port into a Frame Relay Network. From this port, it can have multiple Virtual Connections to various locations. It can make multiple redundant connections possible through the use of PVC's between various routers, without having to use multiple physical links.
Also, since Frame relay is not media specific, and offers a way to buffer speed differences, it can make a good interconnect medium between various devices that run at various speeds.
The multiplexed nature of Frame Relay facilitates especially the transmission of Bursty Traffic. In a traditional fixed-bandwidth multiple connection scenario, a lot of bandwidth will be wasted at most times, since it is not actually being used. The bandwidth on frame is shared, allowing for multiple bursts to be handled sequentially, therefor allowing better utilization of bandwidth. The chance of congestion is however also greater, since the bandwidth in the Frame Relay Port may become a bottleneck.
What is frame relay useful for?
Frame Relay can be used for various types of connections. It should be seen as a flexible protocol that lies on the Data Level of the Connections between routers. It can currently be used effectively for carrying all sorts of data, up to speeds of about 4 megabits per second.
Due to the implementation and cost of frame relay, it is most suitable for permanent or semi-permanent connections. It is not desirable as of yet to access frame relay on a dialup basis for economical purposes.
Where People Use Frame Relay
Frame Relay is designed as a WAN technology primarily for data. When the deployment began, endusers and carriers alike all felt that digital voice (data) could ride on Frame services. However, that aside, the network and protocols were designed to carry data traffic across the WAN. More specifically, Frame Relay was developed to carry data traffic across the WAN and link Local Area Networks (LANs) to other LANs, as shown in Figure1-1 .
Figure 1-1:
Figure 1−2 shows theconnection at T−3 speeds on one end and Synchronous Optical Network (SONET) OC−1 on the other end of the connection. Note this was still used just for data transmission across the network. A higher−end router is installed on each end of the connection to facilitate the data throughput of up to 50 Mbps.
Figure 2-2:
Mixing Frame Relay with Other Technologies
Frame Relay is nearly a protocol that describes how packets of data move from one location to another; it does not concern itself with the issues of how packets get to and from the frame network.
Overall Frame Relay Core Protocols
When the Frame Relay specification was developed, the primary goal was to carry data over the
WAN. To handle this form of wide area communications, the core protocols for Frame Relay were established using the revised version of the data link protocols. Instead of using the network layer protocols, Layer 3 was gleaned down to efficiently carry the traffic while performing the same function as the network layer. Moreover, the data link layer was also streamlined to offer less overhead and processing on a link−by−link basis. Because the circuits across the wide area are much more reliable and error−free (thanks to fiber optics), the ACK and NAK functions can be eliminated. Furthermore, the use of PVCs in the connection eliminates the need for the sequence numbering on the link. One can assume that if we send multiple frames onto a circuit between two end points (even if it is a virtual circuit), the data will come out in the same sequence that it went in on the other end. Unless a frame is discarded, there should be no way that the data will arrive out of sequence. Because the data should not arrive out of sequence, there should not be a need to do the counting.
Sources:
Broadband Telecommunications Handbook Second edition
I think Frame Relay has acquired a bad reputation in some markets because of excessive bandwidth.
ReplyDeleteFrame relay is a technique used to transport data from locations to location, just like T-1 lines or ISDN connections do.
ReplyDeleteThe frame rally help the communication fast an less cost....nice job
ReplyDeleteNice Entry. hehehe. as what you have discussed, frame relay was really conceived to run over ISDN. this is due to the fact that ISDN has its own limitations. its just amazing how the development of this technology evolved very fast.
ReplyDeletethanks for your entry. hehehe
The Cisco IOS creates a broadcast queue for interfaces running frame-relay. This queue performs 2 functions: it ensures routing traffic is dealt with as a priority but it also limits the bandwidth that can be consumed by such traffic. great work!! =)
ReplyDeleteframe relay help our communication system to be come fast and cost effective.
ReplyDeletei just hope that you give more example of how the frame relay functions.
ReplyDeleteFrame Relay can be used for various types of connections. It should be seen as a flexible protocol.
ReplyDeleteCan you site some difference among the two T-1 lines or ISDN?
ReplyDeleteT1 lines are used for both home and commercial use and come in a variety of different types of connections to accommodate voice and data transmission.
DeleteA T1 line is comprised of a series of digital channels that allow transmission for voice and data at a speed that is much faster than a standard Internet connection.
Therefore a T1 connection is generally used for larger business networks instead of home or small office settings.