Transcript Small Office Service

Small Office Service
• Serial Router Connects Internal Stations to
Shared Broadband Access Service
Serial Router
Shared
Broadband
Line
Small
Office
ISP
Small Office Service
• Serial Routers are Very Simple
– One or more ports to connect the serial port to the LAN
– One port to connect to the high-speed access line,
which is serial
– Much less expensive than general-purpose routers
because no complex router forwarding decision caused
by multiple possible output ports
Serial Router
Small Office Service
• Serial Router Connects Internal Stations to
Shared Broadband Access Service
– Companies with several stations pay much more for
line than when connecting a single PC
– Each machine gets its own IP address via DHCP
– Serial router may be a user PC with added software
– Often, router is called a gateway (the old name for
router)
Connecting Two PCs at Home
• Physically, One PC (the Gateway PC)
Connects to the Hub or Switch and to the
Broadband Line
– Gateway (router) PC needs two Network Interface
Cards, one for hub, one for broadband modem
Hub or Switch
NIC
ADSL/Cable
Modem
Gateway
PC
Broadband
Line to ISP
Connecting Two PCs at Home
• Gateway PC Needs Gateway Software
– On NIC to broadband line, acts like a single station
– Gets temporary IP address from ISP DHCP
– Sends and receives to ISP using this IP address
Gateway
PC
Send, Receive with
Temporary
IP Address
Connecting Two PCs at Home
• Gateway PC Needs Gateway Software
– Each PC is set up with a permanent IP address
– So gateway PC has two addresses, one bound to each
NIC
Gateway
Program
Permanent
IP Address
Permanent
IP Address
Temporary
IP Address
Connecting Two PCs at Home
• Gateway Software Does Network Address
Translation (NAT)
– When a PC sends using permanent IP address
– Gateway software replaces source IP permanent address
with temporary IP address ISP expects
Gateway
PC
Permanent
IP Address
Permanent
IP Address
Temporary
IP Address
Connecting Two PCs at Home
• Gateway Software Does Network Address
Translation (NAT)
– When a PC receives
– Gateway software replaces ISP temporary IP
destination address with receiver’s permanent IP
address, passes on to PC
Gateway
PC
Permanent
IP Address
Permanent
IP Address
Temporary
IP Address