deployed a VTN Coordinator, a OpenDaylight Controller, and Mininet in my test environment
1.started controller with of13 option
./run.sh -of13
2.created topology using mininet
mininet@mininet-vm:~$ sudo mn --controller=remote,ip=10.106.138.253 --topo tree,2

• • • Creating network
    • Adding controller
    • Adding hosts:
      h1 h2 h3 h4
    • Adding switches:
      s1 s2 s3
    • Adding links:
      (h1, s2) (h2, s2) (h3, s3) (h4, s3) (s1, s2) (s1, s3)
    • Configuring hosts
      h1 h2 h3 h4
    • Starting controller
    • Starting 3 switches
      s1 s2 s3
    • Starting CLI:
      3.register the controller to the VTN Coordinator.

curl -v -X POST -H 'content-type: application/json' -H 'username: admin' -H 'password: adminpass' -H 'ipaddr:127.0.0.1' -d '{"controller": {"controller_id": "odc1", "ipaddr":"10.106.138.253", "type": "odc", "version": "1.0", "auditstatus":"enable"}}' http://127.0.0.1:8083/vtn-webapi/controllers.json

4.Now I tried to list the physical link information
curl -v -X GET -H 'content-type: application/json' -H 'username: admin' -H 'password: adminpass' http://127.0.0.1:8083/vtn-webapi/controllers/odc1/links.json

• About to connect() to 127.0.0.1 port 8080 (#0)
• Trying 127.0.0.1... connected
• Connected to 127.0.0.1 (127.0.0.1) port 8080 (#0)
  > GET /vtn-webapi/controllers/odc1/links.json HTTP/1.1
  > User-Agent: curl/7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.12.9.0 zlib/1.2.3 libidn/1.18 libssh2/1.2.2
  > Host: 127.0.0.1:8080
  > Accept: /
  > content-type: application/json
  > username: admin
  > password: adminpass
  >
  < HTTP/1.1 200 OK
  < Server: Apache-Coyote/1.1
  < Content-Type: application/json;charset=UTF-8
  < Content-Length: 12
  < Date: Thu, 20 Feb 2014 04:48:50 GMT
  <
• Connection #0 to host 127.0.0.1 left intact
• Closing connection #0 {"links":[]}

link response is empty.