Why we put /H/ in front and end while adding router string in SAP GUI.

A route string describes the stations of a connection required between two hosts. A route string has the syntax (/H/host/S/service/W/pass)*
It consists of any number of substrings in the form /H/host/S/service/W/pass . H, S, and W must be uppercase! Structure A route string contains a substring for each SAProuter and for the target server. Each substring contains the information required by SAProuter to set up a connection in the route: the host name, the port name, and the password, if one was given. Syntax for substrings:  /H / indicates the host name‑{}‑ Note that the host name must be at least two characters long.  /S/ is used for specifying the service (port); it is an optional entry, the default value is 3299. /W/ indicates the password for the connection between the predecessor and successor on the route and is also optional (default is "", no password)