GPRS Architecture with Viola Systems
Arctic and M2M Gateway Products
Jari Lahti, CTO
GPRS architecture
ARCTIC GPRS DEVICE
10.10.10.31
ARCTIC GPRS DEVICE
10.10.10.12
GPRS SUBNETWORK
10.10.*.*
•GPRS devices attaches to APN
Acess point
Router 62.1.24.13
DATA NETWORK
(INTERNET)
CORPORATE 1
SUBNETWORK
Router
131.220.33.*
LAN 172.16.*.*
Server
131.220.33.1
CORPORATE 2
SUBNETWORK
Router
145.111.55.*
LAN 172.16.*.*
GPRS originated connection
GPRS DEVICE
10.10.10.31
GPRS DEVICE
10.10.10.12
GPRS SUBNETWORK
10.10.*.*
•GPRS designed for client use!
OK!
APN ”Router”
62.1.24.13
DATA NETWORK
(INTERNET)
CORPORATE 1
SUBNETWORK
Router
131.220.33.*
LAN 172.16.*.*
Server
131.220.33.1
CORPORATE 2
SUBNETWORK
Router
145.111.55.*
LAN 172.16.*.*
GPRS terminated connection
ARCTIC GPRS DEVICE
10.10.10.31
ARCTIC GPRS DEVICE
10.10.10.12
GPRS SUBNETWORK
10.10.*.*
•Private GPRS IP address
•Dynamic GPRS IP address
•Operator NAT
?
•Operator Firewall
•Solution: Private APN or Tunneling
with Viola M2M Gateway!
CORPORATE 1
SUBNETWORK
DATA NETWORK
(INTERNET)
Router
131.220.33.*
LAN 172.16.*.*
Server
131.220.33.1
APN ”Router”
62.1.24.13
CORPORATE 2
SUBNETWORK
Router
145.111.55.*
LAN 172.16.*.*
Private APN
•Operator contract, special SIM card, access router
•Private, unique APN name (e.g. viola.fi)
•Fixed virtual IP addresses to GPRS devices
•Two-way connection establishment
•Secure communication (VPN)
•GPRS devices part of company LAN
•Full routing usually not possible (D-NAT)
INTERNET OR •Requires
CLOSED NETWORK
roaming on foreign countries
GPRS
VPN router
(from operator)
LAN
VPN
Operator
APN:COMPANY.FI
GPRS
Destination NAT (D-NAT)
ARCTIC
GPRS IP: 11.22.33.44
Ethernet IP: 10.10.10.1
2
Ethernet
1
Connect to 11.22.33.44 port 888
GPRS
Forward to 10.10.10.2 port 80
Reply from 10.10.10.2 port 80
Reply from 11.22.33.44 port 888
3
4
•
•
•
•
•
Requires fixed GPRS IP address (Private APN)
Arctic forwards defined (protocol,port) connections from GPRS to
Ethernet by replacing the destination IP address of packet
The reply contains Arctic's GPRS IP as source address
Makes it possible to access Ethernet devices behind GPRS
The Ethernet devices use Arctic as default gateway
•
The Arctic uses GPRS connection as default route
Tunneling
•Operator independent, any operator - any SIM card
•Requires SW on GPRS devices
•Fixed virtual IP addresses to GPRS devices
•Two-way connection establishment
•Secure end-to-end communication (SSH-VPN)
•Subnetting - GPRS devices part of company LAN
•Full routing - connect remote networks together
•Easy to scale from local to global - no roaming costs
INTERNET
Viola
M2M GW
SCADA
TUNNEL
GPRS
Operator
APN:INTERNET
GPRS
Tunnel establishment
•Start situation
GPRS
INTERNET
APN
LAN IP: 172.16.2.1/24
GPRS IP: ?
TUNNEL IP:?
GPRS
GPRS
WAN IP: 62.236.160.171
LAN IP:172.16.1.4/16
REMOTE NET:Not active
•Arctic uses GPRS connection
to connect to Viola M2M GW
INTERNET
APN
LAN IP: 172.16.2.1/24
GPRS IP: 192.168.12.3
TUNNEL IP:10.10.10.2
•Arctic forms GPRS
connection to APN and gets
GPRS IP address
INTERNET
APN
LAN IP: 172.16.2.1/24
GPRS IP: 192.168.12.3
TUNNEL IP:?
GPRS
LAN IP: 172.16.2.1/24
GPRS IP: 192.168.12.3
TUNNEL IP:10.10.10.2
WAN IP: 62.236.160.171
LAN IP:172.16.1.4/16
REMOTE NET:Not active
WAN IP: 62.236.160.171
LAN IP:172.16.1.4/16
REMOTE NET:Not active
INTERNET
APN
•Viola M2M GW has fixed and
public WAN IP address
•Arctic gets Tunnel IP address
from Viola M2M GW
•Tunnel is formed between
Viola M2M GW and Arctic
•Arctic LAN seems to be part
WAN IP: 62.236.160.171
LAN IP:172.16.1.4/16
of Viola M2M GW LAN
REMOTE NET:172.16.2.1/24 address space
Proxy-ARP
Who is 172.16.2.2
I am (00:06:70:11:22:44)
Data to 172.16.2.2 (00:06:70:11:22:44)
Tunnel
LAN IP:172.16.2.2
Subnet 172.16.2.*
•
•
•
•
•
•
LAN IP: 172.16.2.1/24
GPRS IP: 192.168.12.3
TUNNEL IP:10.10.10.2
Data from 172.16.2.2
WAN IP: 62.236.160.171
LAN IP:172.16.1.4/16
LAN MAC: 00:06:70:11:22:44
LAN IP:172.16.1.3
Network 172.16.*.*
Method for dividing network to subnetworks
On the picture above the subnet 172.16.2.* of main network 172.16.*.* is behind
GPRS
When Viola M2M GW recognizes an ARP request targeted to 172.16.2.2 it
responds whit it's own MAC address and therefore "cheats" the device on LAN.
This is proxy-ARP operation on Viola M2M GW.
The LAN device thinks the remote device to be on it's local LAN and sends data to
172.16.2.2 by using Viola M2M GW's MAC address
The Viola M2M GW forwards the data to tunnel
By using proxy-ARP the remote GPRS devices appear as a part of local LAN
without the need to use Viola M2M GW as default gateway!
L2TP Tunnel
• Plain tunneling without strong authentication or encryption
•
•
•
•
•
•
•
– Viola M2M Gateway authenticates the Arctic only by
user/password combination
– Data is not encrypted
Very fast data transfer and small delays when compared to other
tunnels
Very fast tunnel establishment
Suitable for bringing full routing to private-APN systems
Suitable for applications not requiring strong security
Extra GPRS data caused by L2TP Tunnel ~ 30-40 bytes/packet
Available on Arctic versions >= 4.0
Currently available as add-on for M2M GW
– standard feature on Series 5 release Q1/2006
L2TP Tunnel notes
• L2TP uses UDP
– UDP is connectionless protocol - possible NAT devices
(APN, firewall) between Arctic and M2M GW may
maintain the NAT binding only 30-60 seconds
– In order to keep the NAT binding valid additional
keepalive data may be required
– Ask the NAT binding timeout from operator!
UDP data from 192.168.12.3
UDP data from 64.12.33.44
UDP data to 192.168.12.3
UDP data to 64.12.33.44
NAT on operator
UDP data from 192.168.12.3
UDP data from 64.12.33.44
UDP data to 64.12.33.44
• NAT timeout not reached, data
flows normally
•Data arrives after NAT timeout, data
is discarded by NAT
NAT on operator
UDP data from 192.168.12.3
UDP data from 64.12.33.44
Keepalive from 192.168.12.3
Keepalive from 64.12.33.44
UDP data to 192.168.12.3
UDP data to 64.12.33.44
NAT on operator
•Keepalive packets are sent in order
to keep NAT binding valid, data flows
normally
SSH-VPN
• Secure and authenticated VPN tunnel
– Uses SSH protocol
– Authentication with 1024 bit RSA keys
• Each device has two keys (asymmetric keypair)
– private key (must be kept hidden)
– public key (can be given to anyone)
– Message crypted with a private key can be decrypted
only with a public key of the same asymmetric keypair
– Message crypted with a public key can be decrypted
only with a private key of the same asymmetric keypair
• Communicating parties must know each other's public
keys in order to be able to authenticate
• Extra GPRS data caused by SSH-VPN ~ 50-60
bytes/packet
SSH-VPN notes
• Tunnel establishment takes more time and data than with
L2TP-Tunneling
– Operators usually drop GPRS connections after X hours
• SSH uses TCP protocol
– TCP is connection oriented protocol - possible NAT devices
between Arctic and M2M GW maintains NAT binding without
keepalive data
– Each packet must be acknowledged by receiver with ACK
packet
– If the "tunneled" data also uses TCP this leads situation
where multiple ACK packets are sent. This increases the
amount of data transmitted and decreases performance on
interactive applications
Usually combined to a single packet
USER TCP DATA OVER SSH
SSH ACK
USER TCP ACK OVER SSH
SSH ACK
Private APN vs. Tunneling
FEATURE
PRIVATE APN
TUNNELING (Viola M2M GW)
Operator
Fixed
Any
APN
Unique
Any
Routing
Limited (D-NAT)
Full routing
Security
Good (VPN from LAN to operator)
Good (end-to-end)
QOS on GPRS
Good
Good/Standard
Additional Components
VPN router (from LAN to operator)
Tunnel client & M2M Gateway
Delivery time
~1-4 weeks
Instant
Maximum GPRS devices
Depends on contract
Unlimited
Initial investment
Depens on operator
Viola M2M Gateway + static IP
address form M2M GW
Cost per SIM/month
Normal + x/month
Normal
Communication costs
Normal
Normal
Foreign countries
Roaming
Roaming or local operator
Maintenance
Operator
Own/ASP