1. Concepts
  2. Deployment Scenarios
  3. Example Scenarios

Example Scenarios

This section describes Converged Application Server deployment scenarios. In particular, it describes considerations related to SIP, load balancer, and Network Address Translation (NAT), and shows the message flows in such scenarios.

Note:

For more information about implementation-dependent issues surrounding NAT, see the Internet Engineering Task Force (IETF) document NAT Behavioral Requirements for Unicast UDP at the IETF website:

http://www.ietf.org/rfc/rfc4787.txt

When deployed with multiple SIP-aware load balancers, the Converged Application Server deployment also typically includes an IP sprayer or network-level load balancer to perform IP-level message distribution.

You can also deploy the Converged Application Server with load balancers that are not SIP-aware, meaning that they do not consider existing SIP dialogues when routing requests to servers. The following sections describe the scenario given a non-SIP aware load balancer.

Example Deployment with a Non-SIP Aware Load Balancer

Figure 5-5 shows the sample network topology described in this section. A Converged Application Server cluster, consisting of engines WLSS 1 and WLSS 2, is configured on private IP network 10.1/16 (an internal 16-bit subnet). The cluster's public IP address is 1.2.3.4, which is the virtual IP address configured on the load balancer.

The User Agent, UAC A, with IP address 2.3.4.5 never sees the internal IP addresses configured for the Converged Application Server cluster. Instead, it sends requests to, and receives responses from 1.2.3.4.

The sections that follow discuss configuring the Converged Application Server cluster and load balancer for the example system.

Figure 5-5 Example Network Topology

example of network topology

Converged Application Server Configuration

The Converged Application Server cluster configuration specifies the public address as 1.2.3.4, and the public port as 5060 for each engine. The default route on both Converged Application Server engines points to the load balancer's 10.1/16 network interface: 10.1.3.4. The Converged Application Server (servers WLSS 1 and WLSS 2) routing table is shown in Example 5-2.

Example 5-2 Converged Application Server Routing Table

$ /sbin/route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.1.0.0           *            255.255.0.0     U     0      0        0 eth0
default         10.1.3.4        0.0.0.0         UG    0      0

Load Balancer Configuration

The load balancer is configured with a virtual IP address of 1.2.3.4, and two real servers, WLSS 1 and WLSS 2, having addresses 10.1.1.1 and 10.1.1.2, respectively. The load balancer also has an internal IP address of 10.1.3.4 configured on the 10.1/16 network. The UAC address, 2.3.4.5, is reachable from the load balancer by static route configuration on the load balancer. The load balancer routing table is shown in Example 5-3.

Example 5-3 Load Balancer Routing Table

$ /sbin/route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.1.0.0           *            255.255.0.0     U     0      0        0 eth1
1.2.0.0            *            255.255.0.0     U     0      0

Because the SIP protocol specification (RFC 3261) dictates the destination IP address and UDP port numbers that user agents must use when sending requests or responses, the NAT configuration of the load balancer must be done in a way that does not violate RFC 3261 requirements. Three setup options can be used to accomplish this configuration:

The sections that follow describe each approach.

NAT-based Configuration

The default UDP NAT behavior for load balancers is to perform destination IP address translation in the public to private network direction, and source IP address translation in the private to public network direction. This means setting up destination address translation in the UAC to Converged Application Server (2.3.4.5 to 1.2.3.4) direction without source address translation, and source address translation in the Converged Application Server to UAC (10.1/16 to 2.3.4.5) direction without destination address translation.

Figure 5-6 illustrates the UDP packet flow for a SUBSCRIBE/200 OK transaction.

Figure 5-6 SUBSCRIBE Sequence

Call flow example

In the figure, the source and destination IP addresses of the UDP packets are shown under the message path arrow. In the UAC-to-Converged Application Server direction, the load balancer translates the destination IP address but not the source IP address. In the Converged Application Server-to-UAC direction, the load balancer translates the source IP address but not the destination IP address.

Example 5-4 shows the complete message trace (including IP and UDP headers, as well as the SIP payload) for the sequence from Figure 5-6.

Example 5-4 Complete SUBSCRIBE Message Trace

No.     Time        Source                Destination           Protocol Info
      1 1.425250    2.3.4.5           1.2.3.4          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 1.2.3.4 (1.2.3.4)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      2 2.426250    2.3.4.5           10.1.1.1          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 10.1.1.1 (10.1.1.1)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      3 3.430903    10.1.1.1               2.3.4.5           SIP      Status: 200 OK

Internet Protocol, Src: 10.1.1.1 (10.1.1.1), Dst: 2.3.4.5 (2.3.4.5)
User Datagram Protocol, Src Port: 42316 (42316), Dst Port: 9999 (9999)
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        To: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
        CSeq: 1 SUBSCRIBE
        Call-ID: 1-25923@2.3.4.5

Figure 5-7 shows the message sequence that results from the Converged Application Server subsequently sending a NOTIFY request to the UAC:

Figure 5-7 NOTIFY Sequence

call flow example

As in the previous sequence, the IP address translation takes place in the Converged Application Server to UAC direction for the source IP address, and UAC to Converged Application Server direction for the destination IP address.

Note that this setup does not require the load balancer to maintain session state information or to be SIP-aware. The complete message trace from is shown in Example 5-5 below.

Example 5-5 Complete NOTIFY Message Trace

No.     Time        Source                Destination           Protocol Info
      1 5.430952    10.1.1.1                2.3.4.5           SIP      Request: NOTIFY sip:sipp@2.3.4.5:9999

Internet Protocol, Src: 10.1.1.1 (10.1.1.1), Dst: 2.3.4.5 (2.3.4.5)
User Datagram Protocol, Src Port: 42316 (42316), Dst Port: 9999 (9999)
Session Initiation Protocol
    Request-Line: NOTIFY sip:sipp@2.3.4.5:9999 SIP/2.0
    Message Header
        To: sipp <sip:sipp@2.3.4.5>;tag=1
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
        CSeq: 1 NOTIFY
        Call-ID: 1-25923@2.3.4.5
        Via: SIP/2.0/UDP 1.2.3.4:5060;wlsscid=1ae4479ac6ff71;branch=z9hG4bKc5e4c3b4c22be517133ab749adeece4e
        From: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Max-Forwards: 70

No.     Time        Source                Destination           Protocol Info
      2 6.430952    1.2.3.4          2.3.4.5           SIP      Request: NOTIFY sip:sipp@2.3.4.5:9999

Internet Protocol, Src: 1.2.3.4 (1.2.3.4), Dst: 2.3.4.5 (2.3.4.5)
User Datagram Protocol, Src Port: 2222 (2222), Dst Port: 9999 (9999)
Session Initiation Protocol
    Request-Line: NOTIFY sip:sipp@2.3.4.5:9999 SIP/2.0
    Message Header
        To: sipp <sip:sipp@2.3.4.5>;tag=1
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
        CSeq: 1 NOTIFY
        Call-ID: 1-25923@2.3.4.5
        Via: SIP/2.0/UDP 1.2.3.4:5060;wlsscid=1ae4479ac6ff71;branch=z9hG4bKc5e4c3b4c22be517133ab749adeece4e
        From: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Max-Forwards: 70

No.     Time        Source                Destination           Protocol Info
      3 7.431367    2.3.4.5           1.2.3.4          SIP      Status: 200 OK

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 1.2.3.4 (1.2.3.4)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: sip (5060)
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 1.2.3.4:5060;wlsscid=1ae4479ac6ff71;branch=z9hG4bKc5e4c3b4c22be517133ab749adeece4e
        From: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        To: sipp <sip:sipp@2.3.4.5>;tag=1;tag=1
        Call-ID: 1-25923@2.3.4.5
        CSeq: 1 NOTIFY
        Contact: <sip:2.3.4.5:9999;transport=UDP>

If NAT is performed on both the source (SNAT) and destination IP addresses, the configuration does not work because the load balancer usually relies on a specific destination port number value to be sent in responses to requests. That port number value is dictated by RFC 3261, and must come from the Via header, which presents a conflict with load balancer's NAT requirements. RFC 3261 requires that responses to SIP requests be sent to the IP address used to send the request (unless maddr is present in the Via, as described in maddr-based Configuration). Consequently, in step 3 in Figure 5-8 below, Converged Application Server sends a 200 OK response to the load balancer internal IP address (10.1.3.4) and port 5060. That response is then dropped.

Figure 5-8 Source and Destination NAT

call flow example

Example 5-6 shows the complete message trace.

Example 5-6 Complete Failing SUBSCRIBE Message Trace

No.     Time        Source                Destination           Protocol Info
      1 1.425250    2.3.4.5           1.2.3.4          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 1.2.3.4 (1.2.3.4)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      2 2.426250    10.1.3.4           10.1.1.1          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 10.1.3.4 (10.1.3.4), Dst: 10.1.1.1 (10.1.1.1)
User Datagram Protocol, Src Port: 2222 (2222), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      3 3.430903    10.1.1.1               10.1.3.4           SIP      Status: 200 OK

Internet Protocol, Src: 10.1.1.1 (10.1.1.1), Dst: 10.1.3.4 (10.1.3.4)
User Datagram Protocol, Src Port: 42316 (42316), Dst Port: 9999 (9999)
Session Initiation Protocol
maddr-based Configuration

When the maddr parameter is present in the Via header, the response is sent to the IP address specified in the maddr rather than to the received IP address (even when SNAT is enabled).

In the example below, the UAC specifies a maddr set to 2.3.4.5 in the Via header. Consequently, the response from the SIP server makes it to the UAC.

Figure 5-9 maddr Sequence

Call flow example

Example 5-7 shows the complete message trace represented by Figure 5-9.

Example 5-7 Complete maddr Message Trace

No.     Time        Source                Destination           Protocol Info
      1 1.425250    2.3.4.5           1.2.3.4          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 1.2.3.4 (1.2.3.4)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;maddr=2.3.4.5;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      2 2.426250    10.1.3.4           10.1.1.1          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 10.1.3.4 (10.1.3.4), Dst: 10.1.1.1 (10.1.1.1)
User Datagram Protocol, Src Port: 2222 (2222), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;maddr=2.3.4.5;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      3 3.430903    10.1.1.1               2.3.4.5           SIP      Status: 200 OK

Internet Protocol, Src: 10.1.1.1 (10.1.1.1), Dst: 2.3.4.5 (2.3.4.5)
User Datagram Protocol, Src Port: 42316 (42316), Dst Port: 9999 (9999)
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        To: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
rport-based Configuration

RFC 3581 improves SIP and NAT interactions by allowing the client to request that the server send responses to a UDP port number from the request rather than from the Via. In order for both SUBSCRIBE and NOTIFY to work correctly, both the UAC as well as Converged Application Server must support RFC 3581.

Figure 5-10 illustrates the SUBSCRIBE flow.

Figure 5-10 rport SUBSCRIBE Sequence

call flow example

The complete message trace from the figure is shown in Example 5-8 below.

Example 5-8 Complete Message Trace for rport SUBSCRIBE

No.     Time        Source                Destination           Protocol Info
      1 1.425250    2.3.4.5           1.2.3.4          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 1.2.3.4 (1.2.3.4)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;rport;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      2 2.426250    10.1.3.4           10.1.1.1          SIP      Request: SUBSCRIBE sip:subscribe@1.2.3.4:5060

Internet Protocol, Src: 10.1.3.4 (10.1.3.4), Dst: 10.1.1.1 (10.1.1.1)
User Datagram Protocol, Src Port: 2222 (2222), Dst Port: sip (5060)
Session Initiation Protocol
    Request-Line: SUBSCRIBE sip:subscribe@1.2.3.4:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 2.3.4.5:9999;rport;branch=1
        From: sipp <sip:sipp@2.3.4.5>;tag=1
        To: sut <sip:subscribe@1.2.3.4:5060>
        Call-ID: 1-25923@2.3.4.5
        Cseq: 1 SUBSCRIBE
        Contact: sip:sipp@2.3.4.5:9999
        Max-Forwards: 70
        Event: ua-profile
        Expires: 10
        Content-Length: 0

No.     Time        Source                Destination           Protocol Info
      3 3.430903    10.1.1.1               10.1.3.4           SIP      Status: 200 OK

Internet Protocol, Src: 10.1.1.1 (10.1.1.1), Dst: 10.1.3.4 (10.1.3.4)
User Datagram Protocol, Src Port: 42316 (42316), Dst Port: 2222 (2222)
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        To: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
        CSeq: 1 SUBSCRIBE
        Call-ID: 1-25923@2.3.4.5

Figure 5-11 shows the NOTIFY message flow.

Note that while source address NAT is enabled for both directions (UAS to Converged Application Server and Converged Application Server to UA), the load balancer can correctly identify the destination address in Step 3 by relying on receiving responses on the same port number as the one used to send requests. This implies that the load balancer maintains state.

Figure 5-11 rport NOTIFY Sequence

call flow example

Example 5-9 shows the complete message trace from the figure.

Example 5-9 Complete Message Trace for rport NOTIFY

No.     Time        Source                Destination           Protocol Info
      1 5.430952    10.1.1.1                2.3.4.5           SIP      Request: NOTIFY sip:sipp@2.3.4.5:9999

Internet Protocol, Src: 10.1.1.1 (10.1.1.1), Dst: 2.3.4.5 (2.3.4.5)
User Datagram Protocol, Src Port: 42316 (42316), Dst Port: 9999 (9999)
Session Initiation Protocol
    Request-Line: NOTIFY sip:sipp@2.3.4.5:9999 SIP/2.0
    Message Header
        To: sipp <sip:sipp@2.3.4.5>;tag=1
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
        CSeq: 1 NOTIFY
        Call-ID: 1-25923@2.3.4.5
        Via: SIP/2.0/UDP 1.2.3.4:5060;wlsscid=1ae4479ac6ff71;branch=z9hG4bKc5e4c3b4c22be517133ab749adeece4e;rport
        From: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Max-Forwards: 70

No.     Time        Source                Destination           Protocol Info
      2 6.430952    1.2.3.4          2.3.4.5           SIP      Request: NOTIFY sip:sipp@2.3.4.5:9999

Internet Protocol, Src: 1.2.3.4 (1.2.3.4), Dst: 2.3.4.5 (2.3.4.5)
User Datagram Protocol, Src Port: 2222 (2222), Dst Port: 9999 (9999)
Session Initiation Protocol
    Request-Line: NOTIFY sip:sipp@2.3.4.5:9999 SIP/2.0
    Message Header
        To: sipp <sip:sipp@2.3.4.5>;tag=1
        Content-Length: 0
        Contact: <sip:app-12eomtm5h5f77@1.2.3.4:5060;transport=udp;wlsscid=1ae4479ac6ff71>
        CSeq: 1 NOTIFY
        Call-ID: 1-25923@2.3.4.5
        Via: SIP/2.0/UDP 1.2.3.4:5060;wlsscid=1ae4479ac6ff71;branch=z9hG4bKc5e4c3b4c22be517133ab749adeece4e;rport
        From: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        Max-Forwards: 70


No.     Time        Source                Destination           Protocol Info
      3 7.431367    2.3.4.5           1.2.3.4          SIP      Status: 200 OK

Internet Protocol, Src: 2.3.4.5 (2.3.4.5), Dst: 1.2.3.4 (1.2.3.4)
User Datagram Protocol, Src Port: 9999 (9999), Dst Port: (2222)
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 1.2.3.4:5060;wlsscid=1ae4479ac6ff71;branch=z9hG4bKc5e4c3b4c22be517133ab749adeece4e;rport
        From: sut <sip:subscribe@1.2.3.4:5060>;tag=82722c03
        To: sipp <sip:sipp@2.3.4.5>;tag=1;tag=1
        Call-ID: 1-25923@2.3.4.5
        CSeq: 1 NOTIFY
        Contact: <sip:2.3.4.5:9999;transport=UDP