NEC UNIVERGE SV9100 Manual page 10

10
2.8 Layer 2 Protocol?
All VoIP packets are encapsulated into a Layer 2 protocol (e.g. Ethernet, PPP, Frame Relay) for
transmission over the data network. Every Layer 2 protocol has different characteristics and header
sizes. This means that the amount of bandwidth will vary dependant on the protocol used.
The bandwidth graph
requirement. Unfortunately it is rarely possible to change the Layer 2 protocol to a less bandwidth-
intensive protocol. The protocol is usually fundamental to the data network design and it is unlikely
that this can be changed.
2.9 Type of data connection
The type of data network used will have a big affect on the voice quality. The reasons for this are
described above (e.g. Bandwidth, delay, etc).
A brief description of some of the typical data network types is shown below.
Name
Leased line
- Kilostream
- Megastream
LES
(LAN Extension Service)
Frame Relay
ADSL
(Asymmetric Digital Subscriber
Line)
above shows the affect of different Layer 2 protocols on the bandwidth
Typical
Bandwidth
(may vary)
64Kbps –
768Kbps 1Mbps
– 2Mbps
10Mbp
s
100Mb
ps
1Gbps
Up to 2Mbps (UK)
Upstream
512Kbps
Downstream
8Mbps
Advantages
- Guaranteed bandwidth
- No contention
- Reliable
- Guaranteed bandwidth
- High throughput
- Reliable
- No contention
- Widely available
(commonly used for
international
connections)
- Inexpensive
Disadvantages
- Expensive
- Distance limitations
- Both ends must be
located on same
Telephone Exchange
- Expensive
- Expensive
- Contention
(shared
bandwidth)
- No bandwidth guarantees
- Delay varies dependant
on Internet conditions
- Unreliable
- Asymmetric bandwidths