De Microsoft Technet :
a Service Set Identifier (SSID), also known as the wireless network name, identifies the wireless network. The SSID is a name configured on the wireless AP (for infrastructure mode) or an initial wireless client (for ad hoc mode) that identifies the wireless network. The SSID is periodically advertised by the wireless AP or the initial wireless client using a special 802.11 MAC management frame known as a beacon frame
Parece que o SSID está na camada 2 (do modelo OSI), que é a camada de enlace de dados.
EDITAR : A camada 2 do OSI se enquadra na camada de link do conjunto de IPs.
Portanto, a resposta para a sua pergunta é: Sim, o SSID para roteadores sem fio faz parte da camada de link no conjunto de protocolos da Internet.