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WAN Encapsulation Protocols

WAN Encapsulation Protocols

Network layer passes the data to the data link layer for transmission over the physical layer. The Data Link layer creates frames by adding the necessary checks and controls around the Network layer data. The encapsulation on a router serial interface must be configured to guarantee the correct encapsulation method is used. Different WAN technologies use different encapsulation methods. So, the selection of WAN encapsulation protocol depends on the WAN technology and the communicating equipment.

Each WAN encapsulation protocols usually accompany a certain connection type. The important WAN encapsulation protocols are Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), Frame Relay, Asynchronous Transfer Mode (ATM), X.25, and Serial Line Internet Protocol (SLIP). HDLC is the most common encapsulation protocol type and most framing protocols are based on it. The following are short descriptions of each type of WAN protocol. In the coming articles, we would discuss the protocols in detail.

High-Level Data Link Control (HDLC)

HDLC is the default encapsulation protocol type on point-to-point connections, dedicated links, and circuit-switched links when the link uses two Cisco devices. It is a synchronous Data Link layer bit-oriented protocol originally developed from the Synchronous Data Link Protocol (SDLC) and became standardized by ISO as ISO 13239. It provides both connection-oriented and connectionless service. HDLC also provides flow control and error control by using acknowledgements. Cisco uses a proprietary version of the HDLC protocol known as Cisco HDLC (cHDLC).

Point-to-Point Protocol (PPP)

Point-to-Point Protocol (PPP) is another WAN encapsulation protocol of the data link layer that is used to send and receive multiprotocol data between two directly connected computers or network devices. PPP is used between synchronous and asynchronous circuits. It supports several network layer protocols, such as IPv4 and IPv6. It uses HDLC encapsulation protocol, but also has built-in security mechanisms such as PAP and CHAP. PPP is a byte-oriented protocol widely used in broadband network communications. PPP is also known as RFC 1661.

Frame Relay

Frame Relay is a high-performance WAN encapsulation protocol working at the physical layer and data link layers of the OSI reference model. It was originally designed for use across Integrated Services Digital Network (ISDN) interfaces. It is an industry-standard, packet-switched protocol that handles multiple virtual circuits simultaneously. Frame Relay overcomes the time-consuming processes (such as error correction and flow control) employed in previous X.25 protocol. Today, it is used over a variety of network interfaces.

X.25/Link Access Procedure, Balanced (LAPB)

X.25 is a WAN encapsulation protocol suite defined by ITU-T in 1976 for packet-switched communications over WAN. In 1980 it was the most popular WAN encapsulation protocol. It allows several logical channels to use the same physical line and allow data exchange between terminals with different communication speeds.  It defines how connections between a DTE and DCE are maintained for remote terminal access and computer communications in public data networks. X.25 specifies LAPB, a data link layer protocol. It is a predecessor to Frame Relay. It is the oldest packet-switching technique available and was commonly used before the Open System Interconnection (OSI) reference model became standard.

Serial Line Internet Protocol (SLIP)

SLIP uses a standard protocol for point-to-point serial connections using TCP/IP. It is an industry-standard protocol developed in 1984 that supports TCP/IP networking over serial transmission lines. The protocol is used for TCP communication between two machines that are previously configured for communication with each other.  The older dial-up connection to the server is typically the example of the serial line. It provides TCP/IP hosts with dial-up access to the Internet by using SLIP servers located at Internet service providers (ISPs).

Asynchronous Transfer Mode (ATM)

Asynchronous Transfer Mode (ATM) is an international standard for cell relay in which multiple service types are conveyed in fixed-length cells. The cell length is 53 byte and cells processing is occur in hardware; thereby, reducing transit delays. ATM takes advantage of high-speed transmission media such as E3, SONET, and T3.

What is Frame Relay? Exclusive Introduction

What is Frame Relay? Exclusive Introduction

Frame relay is a packet-switching telecommunication service designed for interconnecting enterprise LANs. Being a student of networking, it is important that you know about all the emerging WAN technologies. To stay up-to-date with emerging and developing technologies, you may know the following alternate options available for WAN connectivity.

  • Frame Relay
  • Broadband DSL
  • Broadband cable modem
  • GigaMAN
  • VPN
  • MPLS

WAN technologies are constantly developing to keep pace with the network demands of today and those of tomorrow. Each network administrator wants to offer the best quality, low-cost WAN network services for their companies. So, it should be your aim to gather information about these alternate WAN options to intelligently discuss the future goals of your network with your business manager and other network administrators.

Frame Relay is a layer2 non-broadcast multiaccess (NBMA) WAN technology. It allows for a single serial interface on the router to connect multiple remote sites with the help of permanent virtual circuits (PVCs) or switched virtual circuits (SVCs).

Frame Relay uses X.25 protocol across Integrated Services Digital Network (ISDN) interfaces as well as with other network interfaces. Network providers apply Frame Relay to support voice and data traffic between LANs over a WAN.

Each end-user gets a leased line, to a Frame Relay node. The Frame Relay deals with the transmission over a repeatedly changing path transparent to all end users. Frame relay is also the solution to permit the communications between multiple sites using a single access circuit to the provider. The figure below illustrates the Frame relay network.

Frame Relay

Basically, Frame Relay is a low-cost WAN protocol as compared to committed leased lines. Equipment configuration in a Frame Relay network is very simple and easy. Frame Relay connections are contained customer premise equipment (CPE) routers or Data Communication Equipment (DCE) i.e. switches and modems.

PVCs have dedicated connection without having to pay for a full-time leased line, but the service provider can monitor each frame travels to its destination and can charge based on usage. PVCs can bring both voice and data traffic between a source and destination, and support data rates up to 4 Mb/s, with some providers offering higher data speed.

A customer can select a level of service quality, for example, they can prioritize some traffic and can make some traffic less important. Frame relay create switched virtual circuit (SVCs) when data is available for sending and then close these SVCs when there is no more data available for sending.

Data-link Connection Identifier (DLCI)

Data-link connection identifier (DLCI) is used to uniquely identify the frame relay PVCs. PVC and DLCI both are responsible for bidirectional communication from DTE to another device. DLCI may be the router configured with frame relay or provided by the service provider in both cases, the endpoints are configured as DLCI number to identify uniquely. DLCI number is necessary on both sides of the frame relay as the source and destination.

Frame Relay Devices

It is used, Data Terminal Equipment (DTE) and Data Circuit terminating Equipment (DCE) for data transmission. this is usually the customer’s side equipment and can include routers, bridges, and personal computers. DCEs are service provider side equipment providing switching and associated services.

Advantages and Disadvantages

At the presence of broadband services such as DSL and cable modem, Ethernet WAN, VPN, and MPLS, Frame Relay is no famous solution for accessing the WAN. But, there is still the importance of the Frame Relay for connectivity to the WAN. Frame Relay provides better bandwidth, reliability, and resiliency than private or leased lines.

Advantages

  • Cost Savings: Cost saving is the first advantage of Frame Relay over other WAN technologies. It offers a low cost of physical local loops over a private line network as the frame uses a virtual circuit (VCs) for each new connection
  • Higher circuit utilization: FrameRelay uses a physical circuit by statistically multiplexing multiple PVCs over a single physical circuit, that increased circuit utilization.
  • Higher network availability: FrameRelay network switches support automatic routing of PVC around in case of failure, which improves network availability.
  • Extended Technology Life Duration: Back-word compatibility is another advantage of Frame Relay that make possible communication with older technologies such as X.25 and forward compatible with newer technologies like ATM and MPLs
  • Networks Overhead: FrameRelay network overhead is less due to the incorporation of a congestion control mechanism.
  • Protocol Independence: FrameRelay allows a frame size of 9000 bytes which is enough for all the frame types therefore it supports a wide variety of application transports and meets the throughput requirements.
  • Performance: FrameRelay  services offer higher speed with lower delay as compared to X.25
  • Security: FrameRelay provides a secure connection because it is difficult to break into PVCs between the sites.

 Disadvantages

  • The FrameRelay does not provide flow control and error control. This should be taken care of by upper-layer protocols.
  • The FrameRelay provides a 44.736 Mbps data rate which is not enough for protocols with higher data rates
  • It creates varying delays for different users, therefore it is not suitable to send sensitive data like real-time voice or video.
  • Not suitable for sending delay-sensitive data such as real; time voice or video or teleconferencing.
  • It is more expensive compare to internet service.
  • It involves data overhead and processing overhead with every packet.
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