Skype For Business Online - Types of traffic and Protocols

Skype For Business Online - Types of traffic and protocols

Skype for business in O365  - One platform for calling, conferencing, video, and sharing.

As per the current trend 70% of onprem lync/Skype servers are now migrated to the cloud service called Skype for Business online in O365.

All of us are using it in our daily life but do you think whether all media traffic are always send via internet to reach the other end ?  in-fact not always, it depends upon where you are and how you communicate.

In this article we will see a brief about the basics of Skype traffic and  protocols used in the Skype online communication.

Type of traffic

1) Signalling - Set of protocols that helps to establish connection between caller and callee.

2) Media - Audio, video, desktop/program sharing and file transfer are all examples of media traffic.

Types of protocols used in the Skype communications

ICE - Interactive Connectivity Establishment (ICE)is a technique used in computer networking to find ways for two computers to talk to each other as directly as possible in peer-to-peer networking using technique that uses SDP, STUN, and TURN to discover a network path between peers on the Internet.

SIP - The Session Initiation Protocol (SIP) is a communications protocol for signalling, for controlling multimedia communication sessions.

These are set of control signals to initiate and process communication connection establishment.

SDP - The Session Description Protocol (SDP) is a format for describing streaming media initialization parameters. (Candidates - IP addresses, ports & CODECS)

This protocol identify the IP addresses, ports and protocols used by the caller and callee.

STUN - Session Traversal Utilities for NAT To determine the most direct media path possible between endpoints

This protocol helps to identify the most direct path to send the media between caller and callee by analyzing SDP.

TURN - Traversal Using Relays around NAT

 Discovery of paths between peers and exchange of media stream packets using media relay server 

This protocol helps in case no direct connectivity is available between caller and callee, the media traffic exchange happens with the help of Skype Media Relay server in the cloud. This method is opted only when there is no direct path between the caller and callee.

Five Phases of ICE

1) During Sign-in: Requesting token from Media Relay Authentication Service (MRAS)

 Call establishment: 

2) Candidate discovery - Identify the IP addresses, ports and protocols between the peers

3) Candidate exchange - Exchange the identified IP addresses, ports and protocols between peers

4) Connectivity check - Check the connectivity between peers

5) Candidate promotion - Promote the shortest/direct path identified to reach the peer.

When User01 try to call User02, the signalling traffic will do the following.

Identify the unicast IP address of O365 cloud server and then request a token from Media Relay Authentication Service (MRAS) server in O365 cloud.

SDP Collects the details of IP addresses, ports and protocols used by User01 and collect the same details from the User02 upon the invite request received on callee's end.

These SDP details are then exchanged between the User01 and User02.

Establish direct path between User01 and User02 to exchange media traffic with the help of protocol "STUN".

Here both Users are in the same LAN network, hence the media packet exchange happens between them via locally, that is via local switches & LAN cables.

Signalling traffic is required to keep the connection but it is lightweight and not much consume your internet bandwidth.

In your infrastructure the Skype for business online calls happens with in the LAN will not eat up the internet bandwidth but internet connectivity is required to establish and keep the Skype communications.

In the next article i will explain more about how the Skype traffic flows when a user call from internet to LAN, internet to internet, WAN (VPLS/MPLS) networks and conference calls.

 Hope this is informative for you and thank you for reading.

Cheers😊