Skype - 2.0 Uživatelská příručka stáhnout pdf (Strana 11)

Page 11 IT Administrators Guide

it can use TCP for the media stream (with the additional overhead due to TCP being

stateful).

Before a user places their call, the client communicates with the peer network to test

connectivity. It checks whether the outgoing UDP port is available and the type of

address translation used by your network. Status checking and updating is also carried

out through P2P architecture to identify a contact’s Status.

Users can make calls to another Skype user or by entering a mobile or landline number

into the Skype dialer. The Skype client then selects, from multiple standby connection

paths, the one with the lowest latency and optimal bandwidth.

Calling a Skype user can generate a search through various supernodes, some of which

reply, giving the recipient’s possible network addresses, along with their associated

supernodes. If found, the caller can then ask the recipient to let them connect.

Alternatively, you can determine your users’ access by selecting authorized Skype IDs.

Nodes communicate various networking parameters and information. They establish

a session (for a chat, call, le transfer, avatar update or authorization request), either

directly or through a P2P relay. Users can then activate a tool, like IM, voice, or video.

2.2 Network conguration considerations

The greatest challenge in deployment is in traversing the border between a corporate

network and the public internet. Firewalls, NATs, and proxy servers can all complicate

how network software is deployed. Skype should work natively with these devices. In

particular, using a SOCKS5 or HTTPS proxy for Skype can improve performance (for more

information, please see 2.2.3 HTTPS/SOCKS5 proxies).

2.2.1 Firewall and NAT traversal

Enabling communications with a remote user or a user behind a NAT or rewall is one

of the most difcult challenges you’ll face. Since NATs change the outgoing IP address,

there’s no simple way for Skype clients to nd one another. Additionally, rewalls are

congured to reject new incoming sessions.

Skype offers three techniques for connecting to ordinary nodes separated by a rewall or

NAT:

Native rewall NAT traversal

A SOCKS5/HTTP proxy server

TCP/UDP relays

Native NAT traversal is the best solution, as it causes the least delay. Next best is a proxy

server. SOCKS5 proxies use UDP, so introduce less delay than HTTP proxies. Finally, relays

almost always work, but cause the most delay, particularly TCP relays.

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Skype - 2.0 Uživatelská příručka Strana 11