Point-To-Point Protocols

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