Locally Controlled Port Expansion

• The 10 Megabits to the backbone that is available at the wall jack (NAM) must be shared among all devices connected via the expansion device. This may occasionally impede performance. 
• All equipment connected via the expansion device must be on the same VLAN, as only one VLAN can be represented on each Network 21 port. 
• All equipment and cabling connected to the network expansion device must be within the same room as the expansion device. 
• Network Operations monitors and maintains the network only to the wall jack (NAM). Consequently, the department is responsible for troubleshooting the expanded network. Assistance is available from Network Operations for a fee. Troubleshooting of the Network 21 port to which the expansion device connects will be covered by monthly network fees. 

Types of Expansion Devices

A switching hub may be connected to a single Network 21 port in order to serve multiple computers. Such switches are available with port counts ranging between 8 and 24 and may also come with a 100BaseTx port for connecting a high traffic server. There are two speeds at which such a switch may be connected to the backbone, 10 Mbps and 100 Mbps. The 10 Mbps option will use a normal Network 21 port to carry traffic to the backbone. The 100 Mbps option will require the installation of an upgraded service level, including additional equipment within the Network 21 IDF, and therefore is substantially more expensive. Rates are being worked on. 

The limitations that apply to the dumb hub expansion approach and the shared 10 Mbps bandwidth, still apply to the switched hub expansion method, with the exception that a 100 Megabit connection to the backbone is a possible service upgrade option. 

This approach suggests itself in computer lab environments that also contain a server whose principal and dominant traffic is to or from the computers within that lab. It is also wise to note that the speed of the Network 21 port (10 Megabits vs. 100 Megabits) will have a large influence on the level of performance that the computers within the room achieve when accessing services outside of the room/lab. 

ThinNet Media Converter (Thinnet Connector) 

Another method of expansion is to use a media converter to connect a ThinNet segment to the NAM. This option is restricted to ThinNet segments within a single room. Although inexpensive and easy to use, the use of ThinNet for departmental LANs has at times been problematic due to several undesirable features of the ThinNet topology. These features include: the ease with which ThinNet segments can be extended beyond the specified maximum length and number of stations, poor quality cable connections, and that a disconnection anywhere in the segment breaks the network for all users on that segment. If the ThinNet segment is limited to one room, most of these problems are avoided. However, if an existing department-wide ThinNet is connected to a single NAM, the problems are likely to persist and the number of devices that the Network 21 port can support (20 on average) is likely to be a serious limitation. 

An excellent approach to gradually transition a departmental ThinNet to Network 21 is to connect a small dumb hub with a BNC port to a Network 21 NAM within each room and then to connect the ThinNet within each room to the BNC port on the hub. This avoids having to replace network interface cards, limits ThinNet segments to the size of each room, and provides 10BaseT ports that are reusable at the time the department desires to transition to one device per port. These small dumb hubs are quite inexpensive and can be ordered by the department. If desired, Information Technology/CR will establish a bulk buying arrangement for such hubs, thereby establishing a common hardware platform and a local stocking level for rapid procurement. 

AppleTalk/LocalTalk Gateways 

Devices such as the Shiva FastPath and Cayman GatorBox have been used on campus for some time to achieve two goals: media conversion from Ethernet to LocalTalk/PhoneNet, and AppleTalk to TCP/IP protocol conversion. Some Apple local area networks are implemented using TCP/IP only. These environments do not require FastPaths orGatorBoxes, just as they did not with UCDNet. 

AppleTalk to TCP/IP protocol conversion is necessary for AppleTalk traffic to transit between different VLANs. In those cases where a department's AppleTalk network uses Ethernet exclusively (also called EtherTalk) and all of the Apple computers are connected to Network 21 ports, either directly or indirectly through dumb or switched hubs or media converters, the protocol conversion can be accomplished by connecting a FastPath or GatorBox to a Network 21 port or to the expansion device. 

In those cases where departments have Apple computers connected via LocalTalk or PhoneNet networks, it will be necessary to use the FastPath or GatorBox as a physical gateway as well. This is because LocalTalk and PhoneNet transmit data at speeds much slower than Ethernet and use different signaling techniques. In these cases, it is recommended that the departments seriously consider converting to EtherTalk. In those cases where this is not practical because the computers are nearing the end of their life cycle or the department cannot afford the conversion, IT/CR will provide assistance to configure the department's FastPath or GatorBox in such a way as to preserve the function of the AppleTalk network. 

Centrally Controlled Port Expansion

• 10 Megabits to the NAM 
• VLAN flexibility 
• Electronics are housed, maintained, upgraded, and replaced by CR 
• Service Order Requests can be placed online.

Dedicated Lab Environment IDF (LabCab) 

This method, in essence, establishes a Network 21 IDF in the room, complete with a 155 Megabit ATM uplink, up to 15 VLANS per switch, and departmental access to the patch panels. The cabinet comes in either a 24 port or 48 port configuration. This method has the advantage of providing higher total throughput to the backbone, and troubleshooting, monitoring and maintenance to the individual local port level. This differs from the other expansion methods in that funding for maintenance, troubleshooting,and electronics upgrades will be handled through future network operation and maintenance fees. 

This approach suggests itself for those computer lab-like locations that have high backbone network traffic as well as high local traffic. While this approach requires a fairly high initial expenditure, it is a more cost-effective approach than installing individual NAMs and ports. 

SuperNAM 

The SuperNAM option presents a bulk NAM to room. The SuperNAM may be configured with 6, 12, 18, or 24 connections within the room. Each one of these connections is a full capability Network 21 connection. The SuperNAM is functionally equivalent to installing 6, 12, 18, or 24 individual connections, but has cost savings through the use of bulk cable between the room and the wiring closet. 

This method of expansion is best used in small computer labs. The distance from the NAM to the workstation is critical because the SuperNAM connections are subject to the same overall cable length restrictions as a typical Network 21 connection.

Network 21 Connectivity Options