In most fiber optic systems, optical fiber and waveguides are coupled to and from bulk optical devices, creating hybrid optical devices. In this tutorial article, the authors explain in detail how to successfully collimate, focus, and align hybrid optics, including polarizing and polarization maintaining optics.

Glossary
Mode field diameter (MFD): A measure of the intensity profile of light traveling within a fiber. In Gaussian optics, this diameter is measured at the point where the light intensity drops to 13.5% (1/e2) of the peak intensity. In single-mode fibers, it is typically about 15% larger than the actual core size.

Numerical Aperture (NA): A measure of the maximum angle at which a given optical system can receive light. If a system can receive light within a cone having a half angle q, then the NA of that system is equal to sin q.

Understanding VPN
A truly private network is a network where a single entity (e.g., a company) owns all the wires from point A to point B. In a Virtual Private Network (VPN), some part of the path from A to B is a public network (e.g., the Internet or the public telephone system). VPN software technology creates a private “tunnel” through the public network system for your sensitive traffic. Using encryption and authentication methods, a VPN provides security over unsecured media.

VPN Benefits
VPNs provide a very cost-effective means of private communication by using inexpensive local call ISDN or telephone connections (with the Internet as the backbone).

VPN Limitations
Obviously, when a technology incorporates portions of the network that are physically not in its control, there are Quality of Service (QoS) limitations. With a true private network, users can demand a guaranteed QoS from the telephone company or provider. However, this is not as clear-cut with VPNs.

VPN protocols

• Cisco IPSec
• L2TP/IPSec
• PPTP

Authentication methods

• Password (MSCHAPv2)
• RSA SecurID
• CRYPTOCard
• X.509 digital certificates
• Shared secret

VPN Deployment Scenario
The example depicts a typical deployment with a VPN server/concentrator as well as an authentication server controlling access to enterprise network services.

1. iPhone requests access to network services (typically over a PPP connection).
2. The VPN server/concentrator receives the request and then passes it to the authentication server.
3. In a two-factor token environment, the authentication server would then manage a time-synchronized token key generation with the key server. If a certifi cate authentication method is deployed, an identity certifi cate needs to be distributed to iPhone prior to authentication. If a password method is deployed, the authentication process proceeds with user validation.
4. Once a user is authenticated, the authentication server validates user and group policies.

In this user guide, the term Cisco VPN device refers to the following Cisco products:
• Cisco VPN 3000 Series Concentrators
• Cisco Secure PIX Firewall devices
• IOS platform devices, such as the Cisco 7100 Series Routers

The Cisco VPN Client for Windows (referred to in this user guide as VPN Client) is software that runs on a Microsoft® Windows®-based PC. The VPN Client on a remote PC, communicating with a Cisco Easy VPN server on an enterprise network or with a service provider, creates a secure connection over the Internet. Through this connection you can access a private network as if you were an on-site user.

Thus you have a Virtual Private Network (VPN). The server verifies that incoming connections have up-to-date policies in place before establishing them. Cisco IOS, VPN 3000 Series Concentrators, and PIX central-site servers can all terminate VPN connections from VPN Clients. As a remote user (low speed or high speed), you first connect to the Internet. Then you use the VPN Client to securely access private enterprise networks through a Cisco VPN server that supports the VPN
Client.

What is this Guide?
This guide provides information to help you understand how to manage Skype in the context of an enterprise environment.

Who should read this guide?
This Network Administrator’s Guide is for IT personnel (system and network administrators) who are responsible for managing the deployment of software applications, specifically on the Microsoft Windows Platform.

This Network Administrator’s Guide assumes you are familiar with enterprise deployment issues, editing the Windows registry, Windows Group Policy Administration, basic XML syntax, as well as other things related to networking and operating system environments.

Important legal information
Copyright
This document is the property of Skype Limited and its affiliated companies (Skype), and is protected by copyright and other intellectual property rights laws.

Skype makes no representation or warranty as to the accuracy, completeness, condition, suitability, or performance of this document or related documents or their content, and shall have no liability whatsoever to any party resulting from the use of any of such documents.