ARA-1 Operations Manual
6-2
INTEROPERABILITY NOW
Can I hook one ARA-1 directly to another via their Ethernet ports?
Yes, if you use a crossover Ethernet patch cable. A straight-through patch cable (such as the one
supplied with the unit) can only be used to attach the ARA-1 to network interface equipment
such as hubs, switches, or routers. You can directly connect a pair of ARA-1 units up to 100
meters apart using a CAT5 crossover cable.
What is the difference between a static IP address and a dynamic IP address?
On an IP network such as the Internet, the IP address is like a phone number. It is a unique
number that identifies the network device, and it allows connections to be made between network
devices. There are two kinds of IP addresses: those that are permanently assigned and those that
are assigned temporarily. Permanently assigned IP addresses are called static IP addresses, while
temporary IP addresses are called dynamic IP addresses. Static and dynamic IP addresses work
the same way, but a dynamic IP address is like having a telephone number that nobody else
knows; it effectively limits you to making outgoing calls only.
Why do we need static and dynamic IP addresses? Why not just assign addresses
permanently like phone numbers?
One problem with IP addresses is there are not enough to go around. There are "only" about 4
billion IP addresses available. On the surface that would appear to be enough, but some
companies use a lot of them, the military uses a lot of them, and all the millions of people using
the Internet use a lot of them. To ease this problem, many Internet providers only assign an IP
address to a computer when someone actually dials in to connect to the Internet. When they
disconnect, the IP address goes back into the pool of addresses so someone else can use it. This
makes sense in cases where computers might sit for a long time without needing to access the
Internet, as there is no point in tying up an IP address when it is not being used. There are plans
for an upgraded IP addressing system that will fix the problem of too few IP addresses, but for
now it is a limitation we must live with.
What kind of IP address does the ARA-1 need?
The ARA-1 will function properly with either a static or dynamic IP address. Which is better
depends upon your application. If the ARA-1 is being used with a SIP proxy, then a dynamic IP
address is fine. If the ARA-1 is being used in a standalone application where other devices are
issuing SIP invites to it, then a static IP address may be needed.
Who assigns IP addresses?
For Internet access, your ISP (Internet Service Provider) will assign IP addresses to you. If you
are on a private network (like a WAN or LAN), then your network administrator will assign IP
addresses. You should never program an IP address into an ARA-1 without checking with the
ISP or network administrator first.