ASCOM Myco 3 - 4 The Handset as a WLAN Wireless Client; Vowifi Handset Protocol Layers

The Handset as a WLAN Wireless Client
TROUBLESHOOTING GUIDE
Ascom Myco 3
4 The Handset as a WLAN Wireless Client
A handset is designed to be a part of a VoWiFi system that enables voice communication across RF
channels. RF channels are provided by APs connected to a wired LAN. Before a handset can access the
network, it must have been authenticated by the AP to verify that it is allowed to connect to the network. If
the verification is successful, the handset forms an association with the AP and communications may begin.
A Basic Service Set (BSS) is an AP and the clients that are in communications range of that AP. A client, or
handset, in the context of a WLAN becomes a member of the BSS when it becomes associated with the AP.
In the usual implementation of a permanent, or infrastructure, WLAN, a BSS can only have one AP. The MAC
address of the AP is used to uniquely identity the BSS and thereby provide the BSS identity (BSSID).
4.1 VoWiFi Handset Protocol Layers
The handset uses protocols defined in a 4 layer TCP/IP protocol stack, which has similarities to some of the
layers defined in the Open Systems Interconnection (OSI) 7 layer protocol model. A thorough understanding
of the protocols at each level is essential to understanding how data is moved across a network. A support
engineer with a good understanding of the media and the data structures and devices involved at each
level of the protocol will have a systematic view of where problems may be occurring and a methodological
approach to solving them. In addition, he or she will have a considerable armory of tools and utilities at
hand for investigating sources of trouble.
The TCP/IP protocol stack is all about data communication across a WLAN and the use of protocols such as:
• Application layer. For applications that interface with the transport layer, including Private Branch
Exchange (PBX9, Unite, Dynamic Host Name Configuration Protocol (DHCP) and Domain Name Server
(DNS).
• Transport layer. Transports User Datagram Protocol (UDP) and TCP packets. TCP ensures secure and
correct delivery of TCP packets through retransmission of lost packets, congestion throttling and error
free transmission.
• Internet layer. Assigns each networked device its logical IP address.
• Link layer (consisting of MAC and physical sublayers specified in 802.11). Defines the physical character-
istics of the carrier medium and access protocols.
The role of the handset in moving data across the network between different physical and logical entities
defined by the protocols is summarized below:
Layers Sublayers Entity Sending or
Receiving Info
Functions
Application layer - Application data packets It depends on the type of
application that is installed on the
handset:
If VoIP is used, the VoIP application
will most likely use the SIP and RTP
protocols.
Transport layer - TCP/UDP packets The handset uses TCP, or UDP as
the protocol to address packets to
be delivered to other devices like a
SIP PBX.
8 TD 93297EN / 19 December 2019 / Ver. B