1. doc.: IEEE 802.11-12/0961r0 Submission July 2012 Alex Ashley, NDS LtdSlide 1 Layer 2 Service Discovery Protocols Date: 2012-07-19 Authors:

2. doc.: IEEE 802.11-12/0961r0 Submission July 2012 Alex Ashley, NDS LtdSlide 2 Abstract The question “Should ISD: develop a Layer 2 Service Discovery Protocol or transport a higher layer Service Discovery Protocol?” has been raised by the ISD chair. The presentation describes a few of the common service discovery protocols, to hopefully aid in the discussion of this question.

3. doc.: IEEE 802.11-12/0961r0 Submission July 2012 Alex Ashley, NDS LtdSlide 3 UPnP / DLNA UPnP uses a multicast protocol called SSDP to announce and discover UPnP devices Once discovered, an HTTP request for an XML device description is used to provide a detailed description of the device. –Each device description contains at least one service description –A service is a collection of actions and state variables –An action is a remote procedure call

4. doc.: IEEE 802.11-12/0961r0 Submission July 2012 Alex Ashley, NDS LtdSlide 4 SSDP When a new device is added to the network it multicasts a number of discovery messages advertising itself, its embedded devices and its services –Address 239.255.255.250 port 1900 Each message uses SSDP protocol (similar to HTTP) A control point can send search requests to the same address to probe for devices or services NOTIFY * HTTP/1.1 HOST: 239.255.255.250:1900 CACHE-CONTROL: max-age = 120 LOCATION: http://192.168.1.1:1900/description.xml NT:upnp:rootdevice NTS: ssdp:alive SERVER: UPnP/1.0 USN: uuid:cybergarageTvDevice::upnp:rootdevice

5. doc.: IEEE 802.11-12/0961r0 Submission Apple Bonjour Implementation of Zeroconf Multicast DNS (mDNS) –mDNS multicast address 224.0.0.251 port 5353 –Used to discover IP addresses without requiring DNS server DNS-SD is used for service discovery –Like Active Directory, uses SRV DNS records IANA controlled list for services –E.g. “appletv-itunes” –http://www.iana.org/assignments/service-names-port- numbers/service-names-port-numbers.xml July 2012 Alex Ashley, NDS LtdSlide 5

6. doc.: IEEE 802.11-12/0961r0 Submission Microsoft Windows NetBIOS –Maps names to IPv4 addressed –name - A 16-byte name for an application Actually 15 bytes, last byte used for describing service type –NetBIOS over TCP/IP RFC1001 and RFC1002 Broadcast and unicast UDP, ports 137 and 138 –Windows Internet Name Service (WINS) implements NetBIOS over TCP/IP Now replaced with Active directory –Uses DNS and LDAP –DNS SRV records to discover services (e.g. domain controller) July 2012 Alex Ashley, NDS LtdSlide 6

7. doc.: IEEE 802.11-12/0961r0 Submission Conclusions Allowing a STA to perform any of the described protocols prior to association would required sending and receiving UDP and TCP frames –This would require an IP address for the unassociated STA or the AP to proxy these frames Could be a link local address –To avoid huge security whole, AP would need to act as an application level firewall to inspect these exchanges All seem to be based upon the concept of well known names –Maybe we just need to be able to advertise the presence of these names? July 2012 Alex Ashley, NDS LtdSlide 7

8. doc.: IEEE 802.11-12/0961r0 Submission July 2012 Alex Ashley, NDS LtdSlide 8 References