Chapter 9: Network Requirements and Preparation Understanding the Requirements for Toll-Quality Voice
ShoreTel 8 Planning and Installation Guide 103
9.4.2.3 Bandwidth in the LAN
For LAN calls using the voice switches, 10 msecs of voice samples are encapsulated in a
Real Time Protocol (RTP) packet before being transmitted onto the LAN. For IP phones
and SoftPhones, 20 msecs of voice samples are encapsulated in an RTP packet before being
transmitted onto the network.
The protocol overhead consists of 12 bytes for the RTP header, 8 bytes for the UDP header,
20 bytes for the IP header, and 26 bytes for the Ethernet framing. When ADPCM voice
encoding is used, an additional 4 bytes are added to the voice data for decoding purposes.
This yields an effective LAN bandwidth as shown in Table 9-4.
HQ/
Director
Server
Distributed
Voice Mail
TCP 25 SMTP -
Voice Mail
transport
HQ/
Director
Server
Voice Mail
Notification
TCP 25
SMTP
HQ/
Director
Server
CDR TCP 3306 -
CDR
archive on
remote
server
Other Call Control UDP 5060
SIP
Other Media Stream UDP 1024-
65535
RTP - for SIP
Other Configuration
Control
UDP 68
DHCP Client
UDP 68
DHCP Client
TCP 80
HTTP - Director
Other Maintenance TCP 23
Telnet
UDP 161
SNMP
TCP 23
Telnet
TCP 80
HTTP - Quicklook
Linear
Broadband Linear G.711 ADPCM G.729a G.729a
Voice data (10
msec)
320 160 80 40+4a20 (20 msec)b30 (30 msec)
RTP header 12 12 12 12 12 12
UDP header 8 8 8 8 8 8
IP header 20 20 20 20 20 20
Ethernet header
and framingc
26 26 26 26 26 26
Total bytes per
packetd
386 226 146 110 86 (20 msec) 96 (30 msec)
Bandwidth for
voice onlye
256 Kbps 128 Kbps 64 Kbps 32 Kbps 8 Kbps 8 Kbps
Bandwidth with
overhead
309 Kbps 181 Kbps 117 Kbps 88 Kbps 34 Kbps 34 Kbps
Table 9-4 LAN Bandwidth—Bytes
Originating
Device Traffic Type
Destination Device
Switch IP Phone Desktop SoftPhone DVM Server
HQ/Director
Server Other
Table 9-3 Port Usage
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