Transport

Last Updated : Jun 01, 2015 |
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Resource Id: Sip_Transport:61100

Behavior during Service unavailable

A proxy server is considered Active once the system has received a response to an INVITE, REGISTER or OPTIONS.
In the case of the proxy server responding with 503 - Service Unavailable, it should be considered Active - In Maintenance. In this case, the following should occur:
  • If the response 503 - Service Unavailable was in response to an INVITE request:
    • If calls are tied to registrations (Calls Route via Registrar enabled) and there are other proxies available, the tied registrations should issue an Un-REGISTER and try to REGISTER with a different proxy. The call should fail with cause = Temporary Fail.
    • If calls are not tied, the INVITE should be immediately tried to a different proxy.
  • If the response 503 - Service Unavailable was in response to a REGISTER request:
    • If there are other proxies available, this registration only should issue an Un-REGISTER and try to REGISTER with a different proxy.
    • If Explicit DNS Server(s) are configured, a DNS request should be sent out to see whether the proxy server has disappeared from those being offered.
An Active-InMaintenance proxy server should not be used for a new transactions (INVITE or REGISTER) until:
  • There is a change in DNS responses indicating the proxy has become active.
  • The configuration does not leave any better option available. In this case, there should be a throttle so that no more than 5 failures (without successes) in 1 minute should be allowed.
  • A configuration merge has occurred where the ITSP Proxy Address has been changed.
  • 10 minutes has expired.

Behavior during Not Responding

A proxy server that is not-responding (UDP) is indicated when 3 requests are sent and no replies are received. This would normally occur during a single INVITE transaction.
Consideration should be given whether this is caused by a local network fault or is caused by the Proxy being out of service. Since it is likely to be local, no action should be taken unless traffic is received from an alternative proxy while this proxy is actually not responding. The state should be "Possibly non responding".
If explicit DNS servers are configured, a DNS request should be sent out to see whether this Proxy server has disappeared from those being offered.
If possible, an alternative proxy should be stimulated simultaneously with stimulating the suspect server.
The server should be considered non-responding if it is persistently non-responding while other proxies are responding or if it is non-responding and has disappeared from the DNS advertisement.
While in the "possibly not responding" state, it would be better to send an INVITE to an alternative proxy while simultaneously sending any appropriate message to this proxy. This will help to resolve whether it is really not responding rather than there being local network problems. However, there is no requirement to blacklist the proxy.
Once in the "definitely not responding" state:
  • If there are other proxies available: this registration only issues an Un-REGISTER, and try to REGISTER with a different proxy. Calls do not automatically clear.
  • If a SIP message is received from it, the state should immediately go"Active".
  • This proxy should be blacklisted unless there are no better options available. While blacklisted, only one transaction per 10 minutes is allowed.
  • Even if not blacklisted, there should be a throttle so that no more than 5 failures (without successes) in 1 minute should be allowed.

Configuration settings

The ITSP Proxy Address and Calls Route via Registrar settings are mergeable. Changing the remaining settings requires a “merge with service disruption”. When the configuration file is sent to the system, the SIP trunk is restarted and all calls on the line are dropped.
Field
Description
ITSP Proxy Address
Default = Blank
This is the SIP Proxy address used for outgoing SIP calls. The address can be specified in the following ways:
  • If left blank, the ITSP Domain Name is used and is resolved by DNS resolution in the same way as if a DNS address had been specified as below.
  • An IP address.
  • A list of up to 4 IP addresses, with each address separated by a comma or space.
    • The addresses can include an indication of the relative call weighting of each address compared to the others. This is done by adding a w N suffix to the address where N is the weighting value. For example, in the list 213.74.81.102w3 213.74.81.100w2, the weighting values assigns 1.5 times the weight of calls to the first address. The default weight if not specified is 1. A weight of 0 can be used to disable an address. Weight is only applied to outgoing calls.
      If there is more than one proxy defined, and no weight indication, then calls are only sent to the first in the list until there is a failure at which point the next proxy is used.
    • If the Calls Route via Registrar setting below is enabled, the weighting is applied to registrations rather than calls.
  • A DNS address, for example sbc.example.com.
    • The DNS response may return multiple proxy addresses (RFC 3263). If that is the case, the system will resolve the address to use based on priority, TTL and weighting information included with each address.
    • A load balancing suffix can be added to specify that multiple proxy results should be returned if possible, for example sbc.example.com(N). where N is the required number of addresses from 1 to 4.
This field is mergeable. However, no more than 4 IP Addresses should be in use at any time. So, if the combined new and old address settings exceed 4, the new addresses are only phased into use as transactions in progress on the previous addresses are completed.
Network Configuration
Layer 4 Protocol
Default = UDP.
The options are: TCP, UDP or TLS.
  • TLS connections support the following ciphers: TLS_RSA_WITH_AES_128_CBC_SHA, TLS_RSA_WITH_AES_256_CBC_SHA, TLS_DHE_RSA_WITH_AES_128_CBC_SHA, and TLS_DHE_RSA_WITH_AES_256_CBC_SHA
Use Network Topology Info
Default = None.
  • LAN1 - Associate the line with the Network Topology and DiffServ Settings settings of IP Office LAN1.
    • If no STUN server address is set for the LAN interface, then the Binding Refresh Time is ignored when calculating the timing for periodic OPTIONS messages unless the Firewall/NAT Type is set to Open Internet.
  • LAN2 - As above but using the settings of IP Office LAN2.
  • None - If selected, the IP Office does not apply STUN lookup. The IP Office system IP routing tables determine routing for the line.
Send Port
When the Layer 4 Protocol is set to TLS, the default port is 5061. When set to TCP or UDP, the default port is 5060.
Listen Port
When the Layer 4 Protocol is set to TLS, the default port is 5061. When set to TCP or UDP, the default port is 5060.
Explicit DNS Server(s)
Default = 0.0.0.0 (Off)
If specific DNS servers should be used for SIP trunk operation rather than the general DNS server specified or obtained for the system, the server addresses can be specified here. If exported or imported as part of a trunk template.
Calls Route via Registrar
Default = On
If selected, all calls are routed via the same proxy as used for registration. If multiple ITSP proxy addresses have been specified, there is no load balancing of registrations.
Separate Registrar
Default = Blank
This field allows the SIP registrar address to be specified if it is different from that of the SIP proxy. The address can be specified as an IP address or DNS name.
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