Generic selectors
Exact matches only
Search in title
Search in content

Reply To: PABX System

#11943
SANJAY BANGROO
Guest

Hi Sanjay,

I think u really have hit the nail on the head and without any doubt u are ABSOLUTELY correct. There are packet overheads in case of VOIP as well as FR. The only difference is that for VOIP the packet overhead size is around 7 Kbps and for FR it is around 2Kbps,per 8Kbps compressed voice.

PLEASE REMEMBER THE GOLDEN RULE :
‘FOR PURE VOICE NETWORK,TDM IS THE BEST SOLUTION’
Let me explain and compare various technologies in a small tabular form and this will explain everything to u very clearly :

BANDWIDTH EFFICIENCY COMPARISON
(FOR A 64KBPS LINK )

TDM VOFR VOIP
CODEC B/W 8KBPS 8KBPS 8KBPS

PACKET 2KBPS 7KBPS
OVERHEAD

TOTAL B/W 8KBPS 10KBPS 15KBPS

LESS 6KBPS 9KBPS
SILENCE

NET AVG. 8KBPS 4KBPS 6KBPS
B/W

MAX. 8 6 4
ACTIVE
VOICE
CHANNELS

NETWORK DELAY AND JITTER
Key ingredient for good voice is
low delay
Delay can be measured as
Average length of time for packet to move

Variability in the arrival of packets
A jitter buffer nullifies the effect of variation
Latency is sum of above two
A latency of 200 – 250 msec makes a bad voice
Example consider network with 50 ms avvg delay but some part goes as high as 200-250 msec
A Jitter buffer of 10 msec will have low delay but will miss delayed packets
A jitter buffer of 200 msec will compensate for late packets but increase latecy
Hence Dynamic Jitter Buffering is a must criterion for Bandwidth Managers

COMPARING TECHNOLOGIES
TDM
Quality of Voice : HIGHEST
Provides predictable and consitent quality of voice
Does not suffer from effects of Latency, Jitter

Bandwidth Efficiency :
Very High for a pure voice network
Poor for a multiservice network
Cost : Cheapest
Effictive support for Multiservices: Poor

FRAME RELAY
Quality of Voice :HIGH
Provides very good quality of voice under optimal conditions
Does not lower efficiency on implementing solutions for Latency, Jitter

Bandwidth Efficiency :
High for a pure voice network
Very efficient for a voice/ data network
Cost :Medium
Effictive support for Multiservices: Good

VOIP
Quality of Voice : Optimal to poor
Provides very good quality of voice under optimal conditions
lowest efficiency on implementing solutions for Latency, Jitter

Bandwidth Efficiency :
Very Low for a pure voice network
Not very efficient for a voice/ data network
Most efficient for data Networks
Cost : Medium
Effictive support for Multiservices: Low

TECHNOLOGY FOR PURE VOICE NETWORK
Dynamic Bandwidth Allocation is not an issue
Voice Quality is of paramount importance
Bandwidth efficiency is significantly important

TDM is the best choice to meet the above requirement

TECHNOLOGY FOR VOICE /DATA NETWORK
Dynamic Bandwidth Allocation is an important issue
Voice Quality is of significant importance
Bandwidth efficiency is paramount importance important
FRAME RELAY is the best choice to meet the above

DELAY OR LATENCY
Caused By:
algorithmic processing delay
frame delay (size of frame)
transmission delay
General Rule:
Delay approaching 32 ms requires echo cancellation
Delay is a function of transport technology also

Choice of Technology has bearing on

1.Bandwidth Efficiency
2.Delay
3.Jitter

AND HENCE ON VOICE QUALITY

Choice of Technology is also governed by
Type of traffic running viz voice only or multiservices
Whether Dynamic Bandwidth allocation desired
QOS Requirement in multiservices

SOLUTIONS FOR JITTER
Variation in delay for Packet voice due to Network Congestion

Does not apply to Circuit Switched TDM

Happens when a large packet has already transmitted resulting in a voice packet waiting
Solved using techniques like fragmentation etc.

BUT
EFFECTS OF FRAGMENTATION ON EFFICIENCY
Fragmentation results in creation of large no. of data packets
Each packet has to have a packet overhead
Packet overhead of FR is much lesser than IP

IP overhead reduces WAN Efficiency by 10 – 15 %
FR overhead reduces by 2-4 %

COMPARING PACKET TECHNOLOGIES ON QOS :
FR offers higher levels of prioritization

ATM offers highest levels

IP is very limited in this aspect

TECHNOLOGY FOR PURE VOICE NETWORK
Dynamic Bandwidth Allocation is not an issue
Voice Quality is of paramount importance
Bandwidth efficiency is significantly important

TDM is the best choice to meet the above requirement

I hope I have answered all your queries. In case u require any further clarification or have more queries, please feel free to get in touch with me on sanjay_bangroo at Yaho.

Cheers!!!!!!!
Sanjay Bangroo