Traffic engineering
180 Avaya Application Solutions IP Telephony Deployment Guide
Table 34: IP LAN bandwidth usages (Erlangs) for Example 6: IP bandwidth considerations
on
page 179 and
Table 35: IP WAN bandwidth usages (Erlangs) for Example 6: IP bandwidth
considerations
on page 179 express bandwidth usages in Erlangs, because each such usage
actually represents the average number of simultaneous bidirectional media streams through
the IP network in question. To convert those usages into bandwidth requirements in units of
kilobits per second (kbps), one must know how many kbps each call requires. To answer that
question, a closer look at IP packet structure is necessary.
An IP packet consists of a payload and some amount of overhead. The payload consists of
actual sampled voice, and the overhead represents headers and trailers, which serve to
navigate the packet to its proper destination. The overhead due to IP, UDP, and RTP is 40
bytes, while the Ethernet overhead is between 18 and 22 bytes (18 is assumed in this example).
This represents a total overhead of 58 bytes (464 bits), regardless of the nature of the payload.
For this example, Layer 2 (Ethernet) overhead is included in that total. At every router boundary,
because Ethernet overhead is included in this example, our calculations are for bandwidth on a
LAN. Because WAN protocol (for example, PPP) Layer 2 headers are generally smaller than
Ethernet headers, WAN bandwidth is slightly less than LAN bandwidth.
The size of the payload depends on certain parameters that relate to the codec that is used.
The two most common codecs that are used with Avaya products are uncompressed G.711 and
compressed G.729. The transmission rates that are associated with those codecs are 64 kbps
for G.711 (this is the Nyquist sampling rate for human voice) and 8 kbps for G.729.
The packet “size” is sometimes expressed in units of time (specifically, in milliseconds). The
following formula yields the packet size, expressed in bits:
Calls from site
3 to site 2
0
0
2.0
Totals
24.0
10.0
4.0
Table 35: IP WAN bandwidth usages (Erlangs) for
Example 6: IP bandwidth
considerations
(continued)
Endpoints
WAN bandwidth
(Erlangs) between
Sites 1 and 2
WAN bandwidth
(Erlangs) between
Sites 1 and 3
WAN bandwidth
(Erlangs) between
Sites 2 and 3
2 of 2
Number of bits of
payload per packet
Transmission Rate
(kbps)
ms per Packet
(
)
×
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Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...