A Madge Networks White Paper. Historical Documentation.

1. Deploying Hybrid Local
Area and Wide Area
Video Networks
A P P L I C A T I O N N O T E F O R N O R T H A M E R I C A
A U T H O R : G a v i n W a r n e s , M a d g e N e t w o r k s , A u g u s t 1 9 9 7

2. Deploying Hybrid Local Area and Wide Area Video Networks
3
Introduction
Over the past decade video conferencing has steadily grown as niche
communications tool adopted in certain vertical market segments. Medical and
educational establishments with distributed locations have embraced video
conferencing to meet their particular needs. At the same time videoconferencing has
found horizontal applications for general business communications. However,
despite the fact that the video codec market has grown to an annual size of $1.5B,
video conferencing has yet to become a routine form of business communication.
The reasons for this are several fold.
Codec cost
Videoconferencing requires extensive compression to obtain acceptable quality
video and the bandwidths used to date. This has required sophisticated hardware
costing between $10K-$50K for a rollabout system and $1.5-$5K for a desktop
codec.
Network restrictions
Two factors impact this area. First, the deployment of ISDN in North America has
been slow making it difficult to obtain a service to carry videoconferencing.
Second, the cost of running ISDN basic rate lines to the desktop has also been a
significant impediment for many organizations. The users that prefer higher quality
video must also incur increased usage cost of wide area bandwidth and equipment,
resulting in additional expenditures for multiplexing equipment and higher capacity
lines.
Standards
The ITU H.320 standard enabled vendors to interoperate at a minimum level for
video conferencing. Prior to this codec vendors has used their own communication
schemes.
Ease of Use
User interface and dialing methods are some of the limiting factors that sometimes
require a conferencing specialist to provide assistance. This limits the user’s ability
to spontaneously utilize videoconferencing as a routine part of their work.

3. Deploying Hybrid Local Area and Wide Area Video Networks
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Next Generation Videoconferencing
1997 will mark the beginning of shift in the cost and use of videoconferencing as a
business tool.
In December 1996 the ITU ratified the H.323 standard which describes how to
transmit voice and video data over local area and wide area networks using TCP/IP
as the transmission protocol. H.323 has the promise to significantly reduce the cost
of desktop video connections and enable video conferencing to become another
LAN application. The cost of hardware based desktop video codecs are decreasing
steadily, and software only video codecs such as Microsoft NetMeeting are
emerging. H.323 also provides ease of use enhancements such that end stations can
be addressed by names instead of numbers and in some cases video calls can be
launched from familiar web browsers.
For LAN based videoconferencing to fulfill its promise some infrastructural changes
will be required. To carry video traffic reliably switched LAN technologies will
need to be deployed to provide dedicated bandwidth to the desktop. Consolidating
multiple LAN sub-networks at a central router is likely to result in sufficient latency
to impair video communication and some office LANs will require redesigning to
carry video traffic. Video Gateways will be needed to enable LAN video users to
call others across the public network, and these will need to interoperate with H.323
and H.320 video equipment.

4. Deploying Hybrid Local Area and Wide Area Video Networks
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The Madge LAN Video Gateway
The Madge LAN Video Gateway provides call control for LAN video calls and
conversion between H.323 and H.320 video standards. It enables calls to be made
from LAN attached stations to public network connected H.320 video systems. LAN
to WAN speeds can range from 128Kbps to 384Kbps for high quality wide area
video conferencing. Each LAN Video Gateway supports up to four LAN to WAN
sessions, and multiple Gateways can be cascaded to provide extra capacity. The
LAN Video Gateway brings PBX features such as call forward and transfer to video
conferencing.
V.35BRI ETHERNET
LAN WAN LAN VIDEO
GATEWAY
1 2 3 4 1 2 3 4
Figure 1. The Madge LAN Video Gateway.

5. Deploying Hybrid Local Area and Wide Area Video Networks
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Hybrid LAN/WAN Video Networks
The Madge LAN Video Gateway is just one element of a video network. Although
video conferencing traffic can now be carried over the LAN at comparatively little
cost, video transmitted over the wide area is tariffed on a usage related basis. The
bulk of the cost of deploying videoconferencing has been found not be in the video
equipment itself but in the ongoing cost of wide area bandwidth. It is therefore very
important to focus on WAN access costs to reduce the cost of ownership of a video
network. Through connections to multiple carriers and leased lines controlled by
powerful dial plan capabilities, the Madge WAN AccessSwitch optimizes the cost of
WAN access for video applications. The AccessSwitch also provides connectivity
between existing room systems, BRI desktop systems and the LAN Video Gateway.
The advantages of LAN to WAN Video Conferencing are increased when multipoint
conferencing is added. The key benefit delivered by video conferencing has been the
avoidance of travel, so the addition of multipoint video communications enables
many people to avoid traveling to attend a traditional meeting. As video
conferencing becomes a spontaneous aspect of business communication the ability
to quickly establish multipoint conferences will become particularly important.
Madge WAN AccessSwitches with their integral multipoint controller units deliver
the functionality required to establish true LAN-WAN multipoint conferences and
make the perfect complement to a LAN Video Gateway.
LAN based video will require switched LAN architectures to ensure continuous
delivery of video information from desktop to desktop and from desktop to
Gateway. Traditional collapsed backbone router architectures are likely to
introduce unacceptable latency which will degrade the video quality and impair
communication. Combinations of Ethernet, Token Ring and ATM workgroup
switches linked by 3rd layer backbone switches provide the optimum architecture
for multiservice LAN traffic.
When designing LAN/WAN video networks it is important not just to concentrate on
LAN Video Gateways. The design should focus on video networks that provide
quality of service in the LAN, multipoint conferencing, connections to existing
video equipment, multicarrier access and control wide area network access costs.
The remainder of this document is devoted to example video networks illustrating
how to address all of these issues.

6. Deploying Hybrid Local Area and Wide Area Video Networks
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128Kbps LAN-WAN Video Solutions
While bandwidth for video conferencing calls between LAN attached stations is
essentially free, calls made across the public telephone network are not. Therefore,
some organizations may wish to limit their wide area video calls to 128Kbps. The
Madge LAN Video Gateway supports up to four ISDN Basic Rate lines per gateway.
The ISDN BRI interface supports multiple ISDN protocols including AT&T 5ESS,
NT DMS100, National ISDN 1 and EuroISDN ensuring compatibility domestically
and internationally. These ISDN trunks can be used for both outbound and inbound
video calls. LAN video users can place outbound calls by dialing a prefix just as they
would to gain an outside line on a voice PBX. By using multiple subscriber
numbering up to eight direct dial video telephone numbers can be provisioned per
BRI trunk to facilitate inbound calling. Alternatively each BRI trunk can be
associated with a default station to which any inbound calls on that trunk will be
delivered. The simplest of installations could consist of a single LAN Video Gateway
combined with a workgroup 10 Base T Ethernet switch.
4 xBRI
Madge LAN Video
Gateway
10 Base T
Desktop
Video
Desktop
Video
Desktop
Video
Desktop
Video
Workgroup
Switch
Room System
WAN
Desktop
Video
10 Base T
Server
Figure 2. A simple 128Kbps LAN to WAN Video Network.
The video network shown in figure 2 allows outbound and inbound calls to and from
the WAN at 128Kbps, while LAN to LAN calls can be run at codec limited speeds.
H.323 LAN Video codecs can operate at 128 to 768Kbps depending on the vendor.
By using a switched Ethernet hub LAN activity from others users does not interfere
with a video conference call. The single 10 Base T segment to the LAN Video
Gateway carries only video IP traffic and provides plenty of bandwidth (each
128Kbps video call generates about 350Kbps of IP traffic on the LAN).

7. Deploying Hybrid Local Area and Wide Area Video Networks
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The LAN Video Gateway used in conjunction with a WAN AccessSwitch enables
T1/ISDN PRI connections to the public network to be achieved. Using T1 access via
an AccessSwitch up to 40 direct dial video numbers can be provisioned per LAN
Video Gateway. These inbound numbers can be configured to hunt between the BRI
connections to the LAN Video Gateway until a free one is located. Assigning no
inbound numbers to a BRI trunk will effectively designate that trunk for outgoing
traffic only. The LAN Video Gateway can use its digit translation capabilities to
convert public ISDN direct dial video numbers to LAN video numbers, or in the
case of H.323 LAN video user names can be used. Combining a LAN Video
Gateway with an AccessSwitch enables the Gateway to be used in areas of North
America where ISDN basic rate is difficult to obtain but where switched T1 or ISDN
Primary Rate is readily available.
The VideoSwitch Express used in conjunction with the LAN Video Gateway
provides both T1/ISDN Primary rate connectivity and a multipoint video capability
(figure 3). In this configuration the VideoSwitch Express provides a 128Kbps MCU
accessible both to users on the LAN, over the WAN or mixtures of the two.
Room
System
Room
System
WAN
Primary Rate
ISDN or T1
MCU
Conf
VideoSwitch
Express MCU
4 xBRI
Madge LAN Video
Gateway
10 Base T
Desktop
Video
Desktop
Video

8. Deploying Hybrid Local Area and Wide Area Video Networks
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One LAN Video Gateway may not be sufficient in larger installations to cope with
the volume of video calls. In this case multiple Gateways can be used together, and
a Madge WAN AccessSwitch can be used to aggregate all of the WAN video traffic
onto T1 or ISDN primary rate trunks (figure 4). The trunks of each LAN Video
Gateway can be given the same outbound prefix number. This enables an outbound
call to hunt from one Gateway to another until a free outbound trunk is located.
10 Base T
Desktop
Video
Desktop
Video
Desktop
Video
Desktop
Video
Backbone
Switch
Room System
WAN
Desktop
Video
ISDN Primary Rate
or T1
4 X BRI
Madge LAN
Video Gateway
10 Base T
Madge Model 60 Access Switch
OBIU BRI card and MCU4 Card
4 X BRI
Madge LAN
Video Gateway
100 Base T
Server Server
Figure 4. Using two load sharing LAN Video Gateways to handle more calls.

9. Deploying Hybrid Local Area and Wide Area Video Networks
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384Kbps LAN-WAN Video Solutions
While video conferencing at 128Kbps offers the most economical use of WAN
bandwidth, the video quality and higher latency at this speed impose some
restrictions on the fluidity of human communication. For this reason many
companies will prefer to operate at 384Kbps for many of their videoconferences.
To make high quality video calls from the LAN to the WAN will require the use of
an inverse multiplexer to make multiple 56/64Kbps calls across the public telephone
network and aggregate them to provide a high bandwidth pipe. The Madge WAN
AccessSwitch can provide inverse multiplexing and when connected to the LAN
Video Gateway, LAN users can place 384Kbps video calls over the public network
(figure 5).
Room
System
Room
System
WAN
4xV.35
Primary Rate
ISDN or T1
Room
System
Madge LAN Video
Gateway
10 Base T
Desktop
Video
Desktop
Video
Desktop
Video
Desktop
Video
Workgroup
Switch
Madge Model 60
AccessSwitch
Server
Room System
2xV.35
Figure 5. The Madge AccessSwitch 60 acting as an inverse multiplexer to enable
384Kbps calls from the LAN to the public network.
Dialing of outbound video calls can be accomplished using either RS366 dialing
interfaces or V.25bis protocol. The Madge Model 20 AccessSwitch operates using
RS366 and can support up to four high bandwidth outbound videoconferencing calls.
For inbound calling each V.35 interface can be associated with a default LAN video
station and all incoming calls on that interface are sent to that user. The Madge
Model 60 and Model 200 AccessSwitches support V.25 bis which can allow inbound
high speed video calls to up to 100 LAN video stations (available Q1 1998).

10. Deploying Hybrid Local Area and Wide Area Video Networks
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10 Base T
Desktop
Video
Desktop
Video
Desktop
Video
Desktop
Video
Backbone
Switch
Room System
WAN
Desktop
Video
ISDN Primary Rate
or T1
4 X BRI
Prefix = 81
Madge LAN
Video Gateway
10 Base T
Madge Model 60 AccessSwitch
OBIU BRI card, QRVX V.35 card
and MCU4 Card
4 X V.35
Prefix = 80
Madge LAN
Video Gateway
100 Base T
Server Server
Figure 6. Using two LAN Video Gateways and an AccessSwitch 60 to support high
and low bandwidth calls to the public network.
The modular nature of the Madge Model 60 and 200 AccessSwitches allows
combinations of T1/PRI, BRI, V.35/RS366 and MCUs to be assembled with great
flexibility supporting simultaneous 128Kbps and 384Kbps video calls. One
AccessSwitch can provide access to the wide area for multiple LAN Video
Gateways. For instance, one LAN Video Gateway could be dedicated to 384Kbps
video calls while another handles only 128Kbps (figure 6). The LAN user can select
which type of call they wish to place by dialing a different prefix for the two speeds.
The dialing plan capability of the AccessSwitch allows inbound 384Kbps and
128Kbps calls to be routed to the correct LAN Video Gateway.

11. Deploying Hybrid Local Area and Wide Area Video Networks
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LAN Topologies for Video Networking
As video conferencing becomes another LAN application, the design of local area
networks will become particularly important. Congested LANs respond slowly but
are still usable for data applications. If video conferencing information is delivered
slowly and unpredictably it ceases to be a useful way to communicate. The
bandwidth of video conferencing traffic is not particularly high - 128Kbps and
384Kbps video calls require approximately 350Kbps and 1Mbps of LAN bandwidth
respectively. However, unlike data traffic, this bandwidth is required for the entire
duration of the video call and any pauses are immediately noticeable. Low latency
switched LAN architectures are required to make desktop LAN videoconferencing a
reality.
Over the past four years fully switched LAN architectures have emerged to provide
dedicated bandwidth connections to each desktop. Flat, layer 2 switched networks
also avoid the latency introduced by conventional layer 3 routers and allow the
network to be divided into virtual LANs. Network topologies such as this are very
well suited to carry video conferencing traffic 10BaseT connections provide
sufficient bandwidth to form links between the LAN Video Gateway and a backbone
switch, and 100BaseT links can be used for higher bandwidth connections to servers
and workgroup switches (figure 7).
Public
Network
100Mb 10Mb
100Mb
10Mb
4xV.35
T1 or
ISDN PRI
Madge LAN
Video Gateway
Model 60
AccessSwitch
Backbone
Switch
Workgroup
Switch
Figure 7. A router-less Video Network using 2nd Layer Switching.
An alternative approach to ensuring that LAN video traffic does not pass through a
router is to use third layer switching. Third layer switching offers the management
and segmentation benefits of a routed architecture but with the packet forwarding
rates and low latency of a switch (figure 8).

12. Deploying Hybrid Local Area and Wide Area Video Networks
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Public
Network
100Mb 10Mb
100Mb
10Mb
4xV.35
T1 or
ISDN PRI
Madge LAN
Video Gateway
Model 60
AccessSwitch
Backone
3rd Layer
Switch
Workgroup
Switch
Subnet #1
Subnet #2
Subnet #3
10Mb
10Mb
Figure 8 A router-less Video Network using Third Layer Switching.
Corporate networks that have deployed an ATM backbone can use LAN emulation
to run conventional protocols over this infrastructure. The LAN Video Gateway can
be easily integrated into networks such as this by using a 10 Base T to Ethernet
switch with an ATM uplink (figure 9).
155 Mbps
ATM Backbone
Workgroup
ATM Switch
Ethernet Edge Switch
with ATM Uplink
155 Mbps
ATM
155 Mbps
ATM
25 Mbps ATM
10 Mbps
Ethernet
Backbone
ATM Switches
Madge LAN
Video Gateway
Video Stations
with LANE Client
Public
Network
Private
Network
4 x V.35
Madge
AccessSwitch 60
Figure 9. Integrating the LAN Video Gateway with an ATM backbone.

13. Deploying Hybrid Local Area and Wide Area Video Networks
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Where switched Token Ring connections are used to the desktop, ATM is likely to
be form the backbone of the network. In this environment the LAN Video Gateway
can be connected to an ATM backbone using Ethernet edge switches that support
multiprotocol over ATM (MPOA). MPOA allows routable protocols such as IP to
be run over an ATM backbone without having to pass through a central ATM
attached router. A native Token Ring interface will be available for the LAN Video
Gateway in Q1 1998.
Public
Network
T1 or
ISDN PRI
Model 60
AccessSwitch
2xV.35
Backbone
ATM Switch
Madge LAN
Video Gateway
ATM 155
ATM 155
16 Mbps
Token Ring
Token Ring
Edge Switch
inc. MPOA
Token Ring
Edge Switch
inc. MPOA
Token Ring
Edge Switch
inc. MPOA
Room System
4xV.35
Ethernet
Edge Switch
inc. MPOA
10 BaseT
Figure 10. Integrating the LAN Video Gateway in a Token Ring and ATM
environment.

14. Deploying Hybrid Local Area and Wide Area Video Networks
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Optimizing Wide Area Bandwidth Costs
Although video calls within the LAN are effectively free of charge, calls over the
wide area will be delivered by carriers who will charge for the bandwidth used. De-
regulation of telecommunications markets has lead to an ever expanding range of
carrier services, many of which are suitable to carry switched video calls. The
Madge WAN AccessSwitch enables companies to take advantage of the multiple
service offering to minimize the money spent on video calls over the wide area.
Leased lines make a sensible choice between high video traffic site, and these can be
augmented by connections to public carriers for backup and over flow purposes
(figure 11). The sophisticated dial plan capabilities of the Madge AccessSwitch
enable leased line connections to be selected preferentially and transparently to the
LAN Video Gateway.
4xV.354xV.35
Madge LAN Video
Gateway
10 Base T
Desktop
Video
Desktop
Video
Desktop
Video
Desktop
Video
Visage 24T
Model 60
AccessSwitch
10 Base T10 Base T
Desktop
Video
Desktop
Video
Desktop
Video
Desktop
Video
Visage 24T
Madge LAN Video
Gateway
T1
Carrier 2
Model 60
AccessSwitch
Carrier 1
Figure 11. Using Madge AccessSwitches to connect to multiple carriers and leased
lines.

15. Deploying Hybrid Local Area and Wide Area Video Networks
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Delivering a Complete Solution
LAN video networks do not consist of LAN Video Gateways alone. To implement
LAN based video conferencing throughout an organization requires a combination
of LAN Video Gateways, LAN switches, ISDN switching, inverse multiplexing and
multipoint conferencing units. Madge Networks offers the technology, products and
expertise to construct and support video networks of all sizes.

16. Madge Networks
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