TCP/IP procedures and application for the GTS
Geoff Molloy
Communications and Computing
Branch
Bureau of Meteorology
Australia
TCP/IP procedures and application for the GTS
Agenda
•
•
•
•
•
•
•
GTS Comms Evolution
Network Topologies
Overview of TCP/IP
GTS IP Addressing
Routing
Data Transfer - TCP and FTP
WMO standards – Sockets and FTP
TCP/IP procedures and application for the GTS
GTS Comms Evolution
• Asynchronous to X.25 to IP
• X.25 saw the introduction of error detection
and correction.
• The advantages of TCP/IP include cost,
simplicity and the ability to use a range of
high level (application) protocols.
– http (web) Remote machine logins (telnet,
rlogin, remsh) FTP (File Transfer Protocol)
Smtp (e-mail) remote database access
TCP/IP procedures and application for the GTS
7, Office
V
V
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w
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netwall
Cabinet-1
Network Topology
GTS
Private or Public Addresses
Firewall
Regional
Offices
Internet
Head Office
Public Addresses
WEB FTP
Message Switch
TCP/IP procedures and application for the GTS
IP Address format
TCP/IP procedures and application for the GTS
.
IP Address format (cont.)
Class A
Class B
Class C
Class D
Class E
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
--+-------------+-----------------------------------------------|0|
NET_ID |
HOST_ID
|
|-+-+-----------+---------------+-------------------------------|
|1|0|
NET_ID
|
HOST_ID
|
|-+-+-+-------------------------+---------------+---------------|
|1|1|0|
NET_ID
|
HOST_ID
|
|-+-+-+-+---------------------------------------+---------------|
|1|1|1|0|
MULTICAST_ID
|
|-+-+-+-+-------------------------------------------------------|
|1|1|1|1|
EXPERIMENTAL_ID
|
--+-+-+-+--------------------------------------------------------
FIGURE 5. IP Address Format.
TCP/IP procedures and application for the GTS
IP Addresses
• Must have public addresses for inter-agency
communications.
• Private addresses may be used within your
organisation.
• Network Address Translation (NAT) is used
to convert between private and public
addresses
• WMO allocates public addresses for GTS:
possible allocation for hosts, but cannot be
used for Internet connection.
TCP/IP procedures and application for the GTS
IP addresses (cont.)
• GTS Allocation: 193.105.177.0 to
193.105.184.0
• Private address allocations:
– 10.0.0.0 to 10.255.255.255
– 172.16.0.0 to 172.16.255.255
– 192.168.0.0 to 192.168.255.255
• Subnet Mask: 2 ways to refer top this
– 192.168.1.1 255.255.255.0
– 192.168.1.1/24
• /24 = 11111111 11111111 11111111 00000000
TCP/IP procedures and application for the GTS
IP addresses (cont.)
• Get IP address from ISP
• Possibly get IP address from WMO
TCP/IP procedures and application for the GTS
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Cabinet-1
GTS Connection with NAT
NAT
BGP Routing
193.105.180.129
193.105.180.130
NAT Table:
Firewall
134.178.6.5
202.203.190.1 = 10.1.1.1
Firewall
10.1.1.1
7, Office
V
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Cabinet-1
TCP/IP procedures and application for the GTS
How do you know which way to
send ip packets – routing protocol
GTS
Private or Public Addresses
Firewall
Regional
Offices
Internet
Head Office
Public Addresses
WEB FTP
Message Switch
TCP/IP procedures and application for the GTS
Routing
• Two types of routing: Static and Dynamic
• An internal routing protocol is used within
your network.
• The GTS uses BGP for routing (static routes
can sometimes be used for stub networks)
• ATTACHMENT II-15
Use of TCP/IP on the GTS give examples of
setting up BGP Routing on a Cisco router –
does not cover use of NAT.
TCP/IP procedures and application for the GTS
Example of routing table
gatekeeper-gw#sh ip route
S
139.163.28.254/32 [1/0] via 139.163.79.1
B
202.245.39.0/24 [20/0] via 193.105.178.22, 2d23h
S
157.128.0.0/16 [1/0] via 202.12.61.9
B
203.10.243.192/27 [20/1] via 203.10.243.13, 05:46:25
TCP/IP procedures and application for the GTS
BGP
• Used by WMO on GTS
• Uses a tcp connection on port 179 between
to routers to send updates.
• Each Network is given an Autonomous
System (AS) number.
• WMO have allocated AS numbers out of the
private AS address range for the GTS
TCP/IP procedures and application for the GTS
GTS AS Numbers
• Private range: 64512 through 65535
• MTN Centres and reserve: 64512 to
64639
• RA I: 64640 to 64767
• RA II: 64768 to 64895
• RA III: 64896 to 65023
• RA IV: 65024 to 65151
• RA V: 65152 to 65279
• RA VI: 65280 to 65407
• Antarctic and reserve: 65408 to 65535
TCP/IP procedures and application for the GTS
Local BGP links
• Allocate AS numbers for private links out of
range: 65472 to 65535
• All GTS should not route this range.
TCP/IP procedures and application for the GTS
Example of BGP routing
gatekeeper-gw#sh ip bgp neigh 193.105.178.22 route
BGP table version is 205, local router ID is 134.178.31.9
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network
Next Hop
Metric LocPrf Weight Path
*> 140.90.88.0/24
193.105.178.22
0 64520 64513 i
*> 202.245.36.0
193.105.178.22
0 64520 ?
*> 202.245.39.0
193.105.178.22
*> 205.156.51.96/27 193.105.178.22
Total number of prefixes 4
gatekeeper-gw#
0
0 64520 i
0 64520 64513 i
TCP/IP procedures and application for the GTS
BGP Conifiguration
router bgp 64512
no synchronization
network 134.178.0.0
redistribute ospf 101 metric 20 match internal
neighbor 193.105.178.22 remote-as 64520
neighbor 193.105.178.22 distribute-list 10 out
neighbor 193.105.178.22 filter-list 4 in
neighbor 193.105.178.22 filter-list 1 out
!
ip as-path access-list 1 permit ^$
ip as-path access-list 4 permit ^64520$
ip as-path access-list 4 permit _64520$
ip as-path access-list 4 permit _64513$
!
access-list 10 permit 134.178.6.0 0.0.0.255
access-list 10 deny any
TCP/IP procedures and application for the GTS
Useful cisco BGP commands
•
•
•
•
Sh tcp
Sh ip route
Sh ip bgp neighbor 1.1.1.1 route
Sh ip bgp neighbor 1.1.1.1 advert
TCP/IP procedures and application for the GTS
NAT
• Static and Dynamic
• Static needed for GTS so that hosts inside
the network can be contacted and for
security.
• NAT addresses must appear in BGP routing
table.
TCP/IP procedures and application for the GTS
TCP overview
• Connection oriented and reliable.
• TCP uses a port number to define
connections
• Connection defined by source IP
address/source port and destination IP
address and destination port
• Can have multiple connections to the same
TCP port number
TCP/IP procedures and application for the GTS
TCP Packet format
TCP/IP procedures and application for the GTS
Common TCP ports
• ftp-data 20/tcp # File Transfer Protocol (Data)
• ftp
21/tcp # File Transfer Protocol
(Control)
• telnet 23/tcp # Virtual Terminal Protocol
• smtp
25/tcp # Simple Mail Transfer Protocol
• http
80/tcp # World Wide Web HTTP
• pop3
110/tcp # Post Office Protocol - V 3
• GTS ports >10000
TCP/IP procedures and application for the GTS
UDP
• Connectionless not reliable
• Not used for GTS transfers
• Examples: used for network management
(SNMP), voice data
TCP/IP procedures and application for the GTS
FTP
• Uses 2 TCP connections: Control (port 21)
and data (port 20)
• Two modes: normal and passive.
• Used for transferring files.
TCP/IP procedures and application for the GTS
FTP Operation
Normal
Client  host - connects to port 21
Client  host “give me file on port 2345
Client/2345  host/20 –connects to port 2345
Passive
Client  host - connects to port 21
Client  host “give me file on port 2345
Client  host/2345 –connects to port 2345
TCP/IP procedures and application for the GTS
FTP Commands
get
Retrieve a file
put
send a file
binary
send or retrieve a file in raw binary
format (no processing)
cd
Change directories on the remote
system
rename
Rename a file on the remote system
Hash
display a ‘hash’ symbol which
indicates how much data has been sent.
Ls
List the directory on the remote
system.
TCP/IP procedures and application for the GTS
FTP Example
C:\>ftp gorgon.ho.bom.gov.au
Connected to gorgon.ho.bom.gov.au.
220 gorgon FTP server (Version 1.7.212.5 Wed May 30 12:19:42 GMT 2001) ready.
User (gorgon.ho.bom.gov.au:(none)): anonymous
331 Password required for anonymous.
Password:
230 User gvm logged in.
ftp> cd temp
250 CWD command successful.
ftp> binary
200 Type set to I.
ftp> put info.txt
200 PORT command successful.
150 Opening BINARY mode data connection for INFO.TXT.
226 Transfer complete.
ftp: 833 bytes sent in 0.01Seconds 83.30Kbytes/sec.
ftp> rename info.txt to final.txt
550 info.txt: No such file or directory.
ftp> rename INFO.TXT final.txt
350 File exists, ready for destination name.
250 RNTO command successful.
ftp> ls
200 PORT command successful.
150 Opening ASCII mode data connection for file list.
test.zip
final.txt
226 Transfer complete.
ftp: 62 bytes received in 0.00Seconds 62000.00Kbytes/sec.
ftp>
TCP/IP procedures and application for the GTS
WMO Standards
• FTP transfer
• Socket Connections
TCP/IP procedures and application for the GTS
WMO Socket Connections
• WMO Use TCP ports > 10000
– Suggest that use ports > 30000
• Use separate sockets for ASCII and Binary
data and separate sockets for transmit and
receive.
• Maintain socket connection
• Old sockets should be closed when a new
connection to the same port from the same
host occurs – avoids problems with
connection loss.
TCP/IP procedures and application for the GTS
WMO Sockets Continued
• Use CSN (channel sequence numbers)
manditory – recommend 5 character CSN
• Each message is preceded by a message
length field of eight ASCII characters and a
message type field of two ASCII characters.
– BI for binary, AN for alphanumeric or FX for
facsimile
TCP/IP procedures and application for the GTS
Socket Data Format
Message
length
Message
nnn
type
SOH CR CR LF or CR CR LF Heading
(8 characters) (2 characters)
nnnnn
Message length
Message length : Length from SOH to ETX (e.g. 00001826 = 1826bytes)
Message type AN: Alphanumeric, BI: Binary, FX: facsimile
CR CR LF ETX
TCP/IP procedures and application for the GTS
Socket Programming
• See ATTACHMENT II-15
Use of TCP/IP on the GTS
TCP/IP procedures and application for the GTS
WMO FTP Procedures
• Procedures for accumulating messages into files
so as to minimise FTP overheads with short
messages (applies only to existing message types);
• file naming conventions for existing message
types (existing AHL);
• file renaming;
• use of directories;
• account names and passwords;
• FTP sessions;
• Local FTP requirements
TCP/IP procedures and application for the GTS
Accumulating messages into files
• Multiple messages in the one file
• Messages should be accumulated in files
thus:
–
–
–
–
–
–
–
length indicator, message 1 (8 characters);
format identifier (2 characters);
message 1;
length indicator, message 2 (8 characters);
format identifier (2 characters);
message 2;
and so on, until the last message;
TCP/IP procedures and application for the GTS
FTP message format
Message 1 Format
nnn
length
IdentifierSOH CR CR LF or CRCR LF Heading Text
(8 characters)
00
nnnnn
Message 2
CR CRLF ETX length
(8 chacs)
Message length
Option 1. Starting Line and End of Message present
Message length : Length from SOH to ETX (e.g. 00001826 = 1826bytes)
Format
Message 1
Identifier CR CR LF Heading
length
01
(8 characters)
Text
Message 2 Format
Identifier
length
(8 characters) 01
Message length
Option 2. Starting Line and End of Message absent
Message length : Length from first CR to end of Text (e.g. 00001826 = 1826bytes)
TCP/IP procedures and application for the GTS
File naming conventions
• CCCCNNNNNNNN.ext where:
– CCCC is the international four letter location identifier
of the sending Centre, as defined in WMO publication
No. 9, Volume C;
– NNNNNNNN is a sequential number from 0 to
99999999 generated by the sending Centre;
– ext is
– ‘ua’ for urgent alpha numeric information
– ‘ub’ for urgent binary information
– ‘a’ for normal alpha numeric information
– ‘b’ for normal binary information
– ‘f’ for facsimile information
TCP/IP procedures and application for the GTS
File renaming
• most centres detect the presence of a new file by
scanning a directory.
• To avoid problems with the receiving centre
processing a file before it has completely arrived,
all sending centres must be able to remotely
rename the files they send
• The file shall be sent with the extent ‘.tmp’ and
then renamed
• Recommended that a separate directory be used
for each host system which is initiating FTP
sessions to avoid the possibility of filename
duplication
TCP/IP procedures and application for the GTS
General FTP “Rules”
• Anonymous FTP may be used, but not on
servers accessible from the Internet
• To Limit load, only one ftp session per
centre per file type
• receiving Centres to delete files after they
have been processed
• Do not use compression of files.
TCP/IP procedures and application for the GTS
FTP suggestions
• Use format identifier “00”
– This allows the WMO request/repeat service to recover
missing data.
• Use filename of *.b to exchange alphanumeric or
binary messages
– CCCCNNNNNNNN.b - for alpha numeric and binary
– CCCCNNNNNNNN.f - for facsimile (FAX T.4)
• Send one T4 chart in each file
• Send up to 100 messages in a file but do not delay
sending a message for more than 60 seconds.
• Read incoming files at least every minute.
TCP/IP procedures and application for the GTS
Socket/FTP Comparison
• Sockets:
– Quick, low overhead
– Requires programming
– Request/Repeat system can be slow
• FTP
– More Delays
– Standard clients (less programming)
– Easy to see failures and repeat transmission.
TCP/IP procedures and application for the GTS
Checklist for GTS link
• Link requirements:
– 1.
Get link addresses and private AS
numbers from WMO
– 2.
Agree whether to use BGP or not
– 3.
Establish connectivity between routers.
TCP/IP procedures and application for the GTS
Checklist for GTS link cont.
• Use only official IP addresses
• Exchange details on host names.
• Declare which IP addresses in your Centre are
eligible to use the GTS.
• Establish an IP connection with one or more
Centres.
• Configure dynamic routing with BGP (or static
routing)
• Obtain an autonomous-system number
• Check the barrier between Internet and the GTS
• Filter incoming and outgoing traffic in accordance
with the requirements described above
TCP/IP procedures and application for the GTS
Checklist for GTS link cont.
• WMO socket requirements:
– Define socket/port numbers to receive on
– Agree on 3 or 5 digit sequence numbers
• FTP requirements:
– Exchange user-id and password of receive accounts
– Exchange directory names
– Agree on format identifier – preferably “00” (include
WMO header/trailer)
– Agree on filenames. Suggest:
– Exchange information on maximum messages to be in a
file and delays before sending a file and delays before
reading a file (not essential but is useful information)
– Agree on 3 or 5 digit sequence numbers
TCP/IP procedures and application for the GTS
Email Standard
• Proposed standard in documentation.
TCP/IP procedures and application for the GTS
END