3Com PathBuilder S200 Series Manual de usuario
3Com®Corporation
PathBuilder™S200 Series Switch
Voice Over IP
Notice
©1998 3Com Corporation
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Part No. T0008-48, Rev. B
First Printing October 1998
Manual is current for Release 5.2M.
Voice Over IP 1
Voice Over IP
Overview
Introduction This document describes the Voice Over IP (VoIP) feature for 3Com’s PathBuilder
S200 series switch Products.
Note
Parameters and applications for voice traffic are discussed in the manual. For
information on SoTCP and serial data applications, refer to the IP and LAN
Feature Protocol documentation.
In This Manual Topic See Page
About Voice over IP (VoIP) .......................................................................... 2
Network Topology ................................................................................... 3
SoTCP Operation ..................................................................................... 4
Establishing a Call ................................................................................... 5
VoIP Applications ......................................................................................... 8
Example VoIP Configuration ................................................................... 9
Configuring VoIP .......................................................................................... 11
SoTCP Parameters ................................................................................... 12
Route Selection Table Parameters ............................................................ 15
SoTCP Map Table Parameters ................................................................. 16
Statistics ........................................................................................................ 18
SoTCP Statistics ....................................................................................... 19
SoTCP Detailed Statistics ........................................................................ 20
Glossary of Terms These terms appear throughout this document:
• ACP - Adjacent Channel Protocol
• VoIP - Voice over IP
• SVC - Switched Virtual Circuit
• UDP - User Datagram Protocol
• SoTCP - Serial Protocol Over TCP
2 Voice Over IP
About Voice over IP (VoIP)
About Voice over IP (VoIP)
What is VoIP? PathBuilder S200 series switch products support Voice over IP (VoIP) to provide
termination and encapsulation of voice and fax traffic for transport over an IP
network (see to Figure 1). 3Com’s proprietary protocol, Serial Protocol over TCP
(SoTCP), provides the encapsulation mechanism for carrying voice traffic over an IP
network.
Figure 1. Voice over IP Network
VoIP Applications VoIP provides new and cost effective solutions for a company’s telephony
communication including:
• Long distance calling over an Intranet or the Internet
• Remote location dial-in and telecommuting
Features Key features include:
• real-time voice and fax over IP networks
• multiple SVCs over a single UDP session
• call management and signalling using TCP
Product Support These PathBuilder S200 series switches support VoIP:
• PathBuilder S21x switch
• PathBuilder S24x, 26x, and 27x switch
PBX
IP Network
Fax
modem
Fax
Fax
Voice Over IP 3
T0008-48/B Revision 5.2
About Voice over IP (VoIP)
Network Topology
Introduction This section describes a typical network topology for the application of VoIP.
Network Topology Figure 2 illustrates a typical network topology for voice traffic.
Figure 2. Example Network Topology
Node Conventions The node conventions described below refer to Figure 2 and are used throughout this
document.
IP Network
PB S200
Source IP Node PB S200 Destination
IP Node
PBX
Voice Device
Voice
Network
Voice Device
Voice
Network
Convention Description
Voice Device or Network The voice device or network sends voice to
the voice port on the source IP node.
Source IP Node The source IP node is a PathBuilder S200
series switch that
• connects directly to the voice device.
• connects directly to the IP network.
• connect directly to a frame relay network
supporting voice.
• encapsulates voice received from the
voice device or network using 3Com’s
SoTCP protocol.
• initiates calls to the peer, the destination
IP node.
Destination IP Node The destination IP node is a PathBuilder
S200 series switch that receives SoTCP
packets sent from the source IP node over the
IP network. The destination IP node
un-encapsulates SoTCP packets and sends
voice traffic to the PBX.The PBX may also
connect to a frame relay network supporting
voice.
PBX The PBX connects to the destination IP node
and receives voice traffic from it.
4 Voice Over IP
About Voice over IP (VoIP)
SoTCP Operation
Introduction This section describes the operation of SoTCP protocol. SoTCP provides the
encapsulation method for carrying voice traffic over an IP network.
SoTCP Packet
Format The SoTCP protocol terminates voice traffic received from a voice device and
prefixes the traffic with a 3-byte SoTCP header or 4-byte SoTCP header, depending
on the version of SoTCP protocol. Figure 3 illustrates the SoTCP packet.
Figure 3. SoTCP Packet Format
The SoTCP header contains information that will allow a destination IP node to
reconstruct the voice packet at the remote end.
Transport
Mechanism To carry voice traffic over IP, SoTCP uses two Transport layer protocols, the
Transport Control Protocol (TCP) and User Datagram Protocol (UDP).
Each TCP or UDP session may carry multiple switched virtual circuits (SVCs).
SoTCP uses SVC call setup and routing procedures to establish voice SVCs.
3 or 4 Byte SoTCP Header Data
Transport
Layer
Protocol
Traffic Carried Description
TCP Voice Signalling Traffic SoTCP uses TCP to carry voice signalling
traffic because TCP provides reliable,
sequenced packet delivery. Voice
signalling traffic encapsulated by SoTCP
must arrive at the destination node without
error or delay. TCP implements error
recovery for duplicate or lost packets.
UDP Audio and Fax SoTCP transports audio and fax traffic
over UDP session. Unlike TCP, UDP
provides fast and simple transaction
services with minimal protocol overhead.
UDP provides a best-effort, transport
mechanism only and does not ensure
reliable delivery.
Voice Over IP 5
T0008-48/B Revision 5.2
About Voice over IP (VoIP)
Establishing a Call
Introduction This section describes call establishments. Figure 4 shows the packets exchanged for
session and connection establishment and finally, voice transfer.
Figure 4. Session and Connection Establishment
Voice Port Voice Port
ACP call request
TCP call request
TCP Call accept
SoTCP internal call request
ACP call request
ACP call accept
SoTCP internal call accept
ACP call accept
Source IP Node Destination IP Node
Session Setup
Connection Setup
Voice
Voice
Voice
Data Transfer
Open UDP channel
6 Voice Over IP
About Voice over IP (VoIP)
Establishing a
Session Before voice traffic can pass between the voice ports over the network, the source IP
must establish a TCP and UDP session with the destination IP node. Each session is
uniquely identified by a source IP address, destination IP address, source port
number, and destination port number. The source and destination node exchange the
following call packets to establish a session:
Establishing a
Connection After opening a TCP and UDP session, the source node must establish an SoTCP
connection with the destination IP node. Each TCP session support multiple
connections or SVCs. A unique connection identifier identifies each connection
multiplexed on a TCP session. The source and destination IP nodes exchange the
following call packets to establish a connection:
Stage Packet Transferred Description
1ACP Call Request The voice port sends an ACP (Adjacent
Channel Protocol) Call Request to inform
the source IP node that it wishes to send
voice over the network to the destination
voice port.
Open UDP When a voice port attempts to make a call,
the Source IP node opens a UDP channel.
2TCP Call Request To open a session, the source IP node sends a
TCP call request to the destination IP node.
TCP Call Accept The destination IP node responds to the Call
Request by sending a Call Accept, and
establishes a TCP session.
Stage Packet Transferred Description
1SoTCP Internal Call
Request The source IP node sends an internal
SoTCP call request packet with the UDP
port number included, to the destination IP
node. The destination IP node examines the
facilities field in the header to determine
the presence of voice traffic. If voice traffic
is present, the destination IP node opens a
UDP channel.
The destination IP node uses the UDP port
number in the internal SoTCP call request
packet to identify the destination port for
UDP packets.
2ACP Call Request The destination IP node sends an ACP call
request to the remote voice port.
ACP Call Accept To accept the call, the voice port responds
with an ACP Call accept packet.
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