Network Communications
LTPH-SM-1052-04
68
July 14, 2002
HMS-358 List 5 and List 6
N
ETWORK
C
OMMUNICATIONS
N
ETWORK
P
ROTOCOL
ADC uses the standard Transmission Control Protocol/Internet Protocol (TCP/IP) on an Ethernet interface to send
internal management information between chassis. The HMS-358 can support up to 32 chassis using a low-cost
10BASE-T twisted pair or 10BASE-2 coaxial cable Local Area Network (LAN). If only TAO software is used
and there is no need to download multiplexer software, then either type of cable can be used. Systems that use TL1
or require download functions must use 10BASE-T. Additionally, larger systems using 10BASE-T require less
troubleshooting than larger systems using other LAN protocols.
ADC recommends placing the HMS-358 on its own 10BASE-T LAN. Any connection to a larger network should
be done through a router with the appropriate firewall protection. Selecting the IP address, subnet mask, TCP/IP
server address and trap addresses are basically arbitrary, but some understanding of these functions is still required
to make an informed choice.
H
ARDWARE
A
DDRESSES
AND
IP A
DDRESSES
To communicate, physical networks rely on 48-bit hardware addresses known as Media Access Control (MAC)
addresses. Every network interface adapter has a unique hardware address assigned by the manufacturer and
coded into the circuitry. On a local network, each piece of equipment picks up data which is addressed to it. In
order for one device to send data to another, it must know the hardware address of the destination device. This
works fine for small networks, where devices can easily broadcast their names and addresses on the network and
make it easy to find them, but it does not work well for large networks or for communication between devices on
different networks.
To solve this problem, a higher level of address, called an IP address, is used to identify each device in the internet.
IP addresses, unlike hardware addresses, are not burned into the electronics, but are configured in software after
a device is plugged into a particular network. Each IP address is associated with a particular hardware device. For
example, the HMU-319 in each HMS-358 shelf is programmed with a unique IP address that identifies each shelf.
The IP address is a 32-bit digital address arranged as four 8-bit words, each from 0 to 255, separated by a period.
The IP address consists of two parts: the network ID (netid) and the host ID (hostid). The subnet mask determines
which bits form the netid and hostid addresses. (See
Table 11.
Network Addressing
Subnet Mask
11111111 11111111 11111111 00000000
255.255.255.0
Class C
IP Address
110nnnnn nnnnnnnn nnnnnnnn hhhhhhhh
200.200.200.1
Class C
netid
hostid
