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QoS on SkyWay 7000
David Gell
VP Engineering
New Applications
The Internet and private enterprise intranets have been
evolving steadily over the last 5-10 years and are
responsible for the effective communication of ever-growing
applications.

Three of the fastest growing are real time voice, video and
wireless communication.

Video
Tremendous gains in standardized video compression and IP
conversion technologies has created an important, but difficult to
implement purpose for IP networks – real time video transport.

Applications include CCTV and IP camera-based surveillance,
video conferencing and video streaming.

While the technology to convert video to and from IP packets is
highly standardized (e.g. – Motion JPEG, MPEG2, MPEG4, H.264),
the ability to transport such IP packets in a timely manner has been
left to other technologies.

VoIP
International groups (ITU, IETF) have standardized a series of
end-to-end protocols for IP based telephony. Such standards

encompass and address necessary functions at OSI layer 4 and
above (e.g. – H.323, SIP, RTP, H.245, G.711, G.72x)
Like with real-time video, the technology to convert voice to and
from IP packets is highly standardized but the ability at layer 3 and
below to deliver IP packets in a timely manner has been left to
other technologies.

The need for QoS…
It is clear that in both voice and video standardization, the means
to assure timely and error free packet delivery is left to other, QoS

technologies.
When combined with Broadband Wireless systems, it becomes
clear that an effective mechanism is needed…

‘Typical’ Enterprise BWA application
Satellite Office A
…
…
…
…
…
…
Main Site
Satellite Office B
PSTN
Internet
In this example, how can VoIP intranet performance
be properly managed?....
Congested Networks

Despite gains in throughput performance, a long-distance,
fixed wireless system can often become a network bottleneck during
peak times of network usage.
At such times, latency and packet-loss sensitive payload, such as
voice or video can suffer significant degradation.

Priority Queuing

Conceptually simple, priority queuing uses multiple queues
to allow higher priority traffic to ‘jump ahead’ of lower priority traffic.
6 5 4 3 2 1
Input
traffic
High
Priority
Queue
5
Low
Priority
Queue
4
6
2
3
1
Priority
Engine
Output
traffic
5 4 6 2 3 1
Priority Tagging
Multiple approaches are available to tag frames with desired
priority:

Ethernet frame tagging (802.1q)
Ethernet Frame
PRE
SFD
Dest
Addr.
Src Addr
TPID
Priority
3 bits: 0-7
TCI
CFI
Len
Data
VID
FCS
Priority Tagging, cont.
IP frame tagging via ToS (RFC 791)

Ethernet Frame
PRE
SFD
Dest
Addr.
Src Addr
TPID
TCI
Len
Data
FCS
IP Packet
Vers
IHL
ToS
Len
Iden
Flags
Frag
TTL
3 priority bits: 0-7
Protocol
H Cksm
Src
Dest
Opt
Data
Priority Tagging, cont.

IP frame tagging via DiffServ (RFC 2474)

Redefines ToS byte as DS byte. Supercedes ToS definition
Ethernet Frame
PRE
SFD
Dest
Addr.
Src Addr
TPID
TCI
Len
Data
FCS
IP Packet
Vers
IHL
DS
Len
Iden
Flags
Frag
TTL
6 priority bits: 0-63
Protocol
H Cksm
Src
Dest
Opt
Data
SkyWay 7000 QoS Features

Priority Queuing System

4 Queues. From highest priority to lowest: Voice, Video, Best Effort,
Background

Line speed packet inspection supports the three most common
tagging methods:
1) 802.1p VLAN tag priority bits
2) IP ToS field
3) IP Diffserv

Note: QoS requires end-to-end network support. SkyWay 7000 will
prioritize traffic but will not actually tag the data. Endpoint
devices/appliances are responsible for tagging data.
SkyWay 7000 Queue mapping
Voice
802.1q bits:
IP ToS/Diffserv Byte:
Video
Best Effort
Background
0x1, 0x2
0x6, 0x7
0x3, 0x4,
0x5
0x0
0x30, 0xe0
0x28, 0x88,
0xa0
Default
0x08, 0x20
Note: If a frame has multiple tags, then the tag with the highest
priority will establish queue assignment
SkyWay 7000 System Design for QoS

The SkyWay 7000 provides support for QoS, but the proper, end-toend network design is critical for QoS performance.

Tagging device: the closer to the data source the better. Ideally, the
voice or video generation device itself will tag frames.
Examples:
Uniden VoIP phones
Vbrick CCTV/IP converter
Polycom Video Conferencing systems

QoS-enabled network. For best results all switches, routers and
gateways should be QoS enabled.