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Concentric Network Corporation White Paper, Outsourcing Remote Access Services

10/1/1998 10

The payload is then routed over the IP backbone to the endpoint of the tunnel that resides in the

gateway router. It is then forwarded to a specific Frame Relay Data Link Connection Identifier

(DLCI). There, the payload is re-encapsulated with a standard Frame Relay RFC 1490 header

and sent to the customers network via the Frame Relay connection.

Layer 3 Forwarding and Layer 2 Forwarding

The RemoteLink™ service carries only the Layer 3 (and above) payload through the IP tunnel.

Layer 2 Forwarding, on the other hand, tunnels the entire PPP frame over the Service Provider’s

IP backbone. This not only adds framing overhead, but introduces potential timing issues, since

PPP network control protocol negotiation are time sensitive. In many cases the endpoints of the

tunnel are separated by long distances and/or many router hops. Under these conditions, PPP

connections carried over tunnels based on Layer 2 Forwarding may be prone to timeouts and/or

frequent resets.

The IP tunnel is both created and terminated in Concentric’s network. The remote user’s PPP

session is terminated at the remote access server entry point into our network. This contrasts

with Layer 2 Forwarding technologies such as Point-to-Point Tunneling Protocol (PPTP), in which

the tunnel is created in the service provider’s network, but requires termination at an NT server

that usually resides at the customer’s premise.

The diagrams below depict examples of both Layer 3 and Layer 2 Forwarding. RemoteLink™ is

based on Layer 3 forwarding and therefore the tunnel is between the RAS and the gateway

router on Concentric’s network. Modifications in client laptop computer and corporate routers are

not required.

Concentric Network

GRE Encapsulated Tunnel

Gateway

Router

RAS

Laptop

computer

PPP session

Router

Frame Relay link

Layer 3 (Virtual Tunneling Protocol)

Tunnel

Mgt Sys

RADIUS

Authentication

Server

Concentric RemoteLink™ service - From edge to

edge of Concentric's Network

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Bay Networks Baystream 7 Bedienungsanleitung Seite 10