The HKU Gigabit Ethernet Campus Network Backbone

The HKU campus network backbone has been using the ATM (Asynchronous Transfer Mode) technology since 1997 to provide a faster network and to implement the ACEnet roaming network.

As the vendor supplying our existing ATM network equipment is backing out of the highly competitive network equipment market and is phasing out the customer support, Computer Centre has to resort to other network equipment providers in order that we get the most cost-effective supplier and support for our network.  In the past few months, Computer Centre was searching for a substitution solution that can meet our network backbone requirements.

The Gigabit Ethernet (G.E.) technology is found to be one of the best solutions available as its price has dropped drastically and it would meet the large bandwidth requirement of our current campus network. Besides the bandwidth requirement, inter-operability with existing network equipment is also a major factor to consider. The Virtual Local Area Network (VLAN) technology is being used in the existing ATM campus backbone to facilitate the linking together of geographically dispersed users. Now the Ethernet-based VLAN technology has become mature enough to be deployed. With all these advantages, the G.E.-based network infrastructure was selected to inter-operate with our ATM-based campus network.

Two high-density G.E. backbone switches had been installed in October serving as the new G.E. backbone.  These two G.E. backbone switches have a very compact design that each switch can provide integrated functions of router, ATM switch and G.E./F.E. switch within a single box. The router function provides additional network traffic routing capacity to the existing network, so that the existing backbone routers can be off-loaded and network resiliency is increased. The ATM switch function provides connectivity to the existing ATM backbone and thus the two backbone networks can be linked up. For the G.E. switch itself, it can be configured to use VLAN-based network topology to join the existing VLAN-based ATM network. Therefore the overall new backbone can be fully inter-operable with the existing network. We have already performed many tests with positive results before actual implementation.

The entire implementation plan has different phases and we are working with the vendor closely. At the current phase, the two G.E. backbone switches were installed and running.  One of the switches is installed in Computer Centre and the other is in the Kadoorie Biological Sciences Building as a backup. The new G.E. backbone switches are connected to each other by two G.E. links with load-sharing function enabled. Each G.E. backbone switch has a ATM OC-12 (622Mbps) link to connect to the existing ATM backbone network. In this backbone design, there should be no single-point-of-failure between the backbone switches. Several network segments had been switched over to the new backbone and they are running normally without any problems.  Some network traffic on the old backbone had been re-routed to the new backbone to off-load the old backbone routers.

In the next phase, we are going to install 15 to 20 high-density F.E. switches with dual G.E. fiber uplinks to different buildings to serve as a building concentration switch for that building. To cope with the increased need of fiber connections between building in the main campus, additional fibers are being installed. We shall report further on the progress of the GE backbone upgrade project as it develops.


Asynchronous Transfer Mode

ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronous relative to other related cells and is queued before being multiplexed over the transmission path. Multiplexing is sending multiple signals of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end. Our ATM backbone has a transmission speed of 622 Mbps.

Gigabit Ethernet

Gigabit Ethernet (GE) is a local area network transmission standard that provides a data rate of 1 billion bits per second (one gigabit). Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a Gigabit Ethernet backbone.

Fast Ethernet

Fast Ethernet is a local area network transmission standard that provides a data rate of 100 megabits per second (100BASE-T). Workstations with existing 10 megabit per second (10BASE-T) ethernet cards can be connected to a Fast Ethernet network.

virtual LAN

A virtual LAN is a local area network with a definition that maps workstations on some other basis than geographic location (for example, by department, type of user, or primary application). The virtual LAN controller can change or add workstations and manage load balancing and bandwidth allocation more easily than with a physical LAN.


Ethernet is the most widely-installed local area network (LAN) technology. A local area network (LAN) is a group of computers that share a common communications line and the resources of a single processor or server within a small geographic area (e.g. within an office building).  An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires providing transmission speeds up to 10 Mbps (10BASE-T).

Ronald Leung
Tel: 2857 8593

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