PPP and MLPPP
PPP is a point to point protocol primarily associated with the
Internet. PPP supports both asynchronous and synchronous serial lines and provides a
point-to-point connection across a variety of media. PPP was first proposed as a standard
in 1990 to replace an older de facto standard known as SLIP (Serial Line Internet
Protocol) that requires links to be established and torn down manually. However, unlike
SLIP, PPP offers significant flexibility. This explains its widespread use for Internet
communication.
Multilink PPP (MLPPP) is a method for splitting, recombining and
sequencing PPP Datagrams across multiple logical data links. This protocol was originally
designed to exploit multiple B-channels in ISDN, but is equally applicable to any
situation in which multiple serial PPP links connect two systems.
X.25
Packet-switched protocols have long been an alternative to point to
point protocols such as PPP, with X.25 being the best of these alternatives.
Packet-switched connections are "virtual", in that connected sites are not
physically linked. Whereas point to point protocols are analogous to a direct pipeline
between two sites (point to point), a packet-switched service is analogous to a delivery
service sending packages between sites via intermediate hubs and couriers.
For this reason, a single physical link to the X.25 network can support
multiple concurrent connections to different sites. X.25 is available almost universally,
supporting transmission speeds ranging from 9.6 KBPS to 512 KBPS, with guaranteed global
delivery. Because X.25 is a mature technology, it supports numerous access methods. You
can connect to an X.25 network (a network where all traffic is X.25 packets) through a
dial-up telephone link, ISDN, or a dedicated leased line. X.25 pricing is usage based, but
not very distance sensitive.
Over long distances, it is far less expensive than using a point to
point protocol. These characteristics make X.25 suitable for both LAN-LAN and LAN-SNA host
connections–especially for global corporations, which need reliability and universal
availability. X.25 is not, however, suited to high-bandwidth applications, especially
those sensitive to latency introduced by X.25 networks.
X.25 is also suitable for remote user connectivity. Remote users
worldwide can simply dial into a local X.25 networks using a standard modem. The X.25
service provider’s Packet Assembler/ Disassembler (PAD), converts the asynchronous
data stream coming from the modem into X.25 packets. This enables affordable and reliable
remote access to corporate LANs from anywhere in the world.
Frame Relay
Frame Relay is a packet-switched protocol, which has replaced many
point to point leased line applications. It was designed to take advantage of the higher
reliability offered by modern telecommunications systems. Frame Relay can be viewed as a
streamlined version of X.25. It offers greater speed and reduced latency, at the cost of
less error checking. Frame Relay availability is steadily growing, however, it may not be
available in countries with unreliable communications infrastructures (in which case,
X.25, with its advanced error checking, will usually be available).
Applications requiring meshed connectivity are especially
cost-effective using Frame Relay, since multiple virtual connections can exist on a single
physical link. An added benefit of Frame Relay is that it allows bandwidth on demand up to
the allowable clock speed of the line, making it suitable for bursts applications.
Growing confidence in Frame Relay networks is making it a popular
choice for SNA access (SNA over Frame Relay). It is also gaining favor for remote access,
as service providers begin to offer dial-up access into Frame Relay networks via POTS and
ISDN. ISDN access into Frame Relay networks will also enable them to easily back up the
permanent Frame Relay links currently in use. It seems likely that Frame Relay will
eventually enjoy the same degree of flexibility as X.25 provides today.
Remember, in a WAN setup the major chunk of the money goes in to the
communication links and WAN hardware is not even 20 percent of the total cost. So a
reseller must discuss the Wide Area Networking requirement of the customer first in detail
and then choose the appropriate WAN media and communication protocol which best suits the
customer need.
Differentiate your services and your solution with others in a
cost-effective way by choosing the right WAN media and communication protocol for your
customer and by doing so I am sure you will have the cutting edge over your competition.
V Srivathsan is the Business Development Manager, Eicon Technology
Corporation. He can be contacted at wan_isdn@yahoo.com